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Growth and reproduction of the lake sturgeon (Acipenser fulvescens rafinesque) of the Nelson River in… Sunde, Leif Axel 1961

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GROWTH AND REPRODUCTION OF THE IAKE STURGEON (ACIPENSER FULVESCENS RAFINESQUE)OF THE NELSON RIVER IN MANITOBA by LED? AXEL SUNDE B. A., University of British Columbia, 1955 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Science in the Department of Zoology We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1961 In presenting this thesis i n p a r t i a l fulfilment of the re-quirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It i s understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Zoology The University of British Columbia, Vancouver 8, Canada. Date October 2, 1961. Magnified Image of a Cross - l e c t i o n of the Marginal "seine" of a Lake tur-eon. i ABSTRACT Depletion of Nelson River sturgeon through over-exploitation by the commercial fishery forced two closures of this fishery between 1921 and 1946. These failures prompted a program of biological research to determine rates of growth, reproduction and increments to stocks to provide a basis for the scientific management of this economically important species of fish. From 1953 to 1956 and 1959> 791 sturgeon were sampled from the commercial catch in the Sipiwesk Lake area of the Nelson River. Preliminary studies were conducted to determine the best method of age determination and back-calculation of growth. It was concluded that the best cross-sections of pectoral "spines", for purposes of age determin-ation and back-calculation of growth, were located at the proximal end of the spine at the base of the swelling which forms the "knuckle"of the spine. The easiest and best measurement on this cross-section for back-calculation of growth was along the radius of the spine from the centre of ossification to the posterior edge of the spine, along the acute angles formed by the annuli in this area. The relationship between fork length (x) and the average radius of the pectoral spine (y) as determined by the method of least squares wass x " .14y + 2.2. In the calculation of size at any previous age, best results were obtained by back-calculating along a line which converged with the intercept. The best representation of growth in Nelson River sturgeon was obtained by cumulatively totalling the average annual calculated increments of growth for a number of specimens. It i s readily apparent that female lake sturgeon of the Nelson River grows faster and lives much longer than the male. The average annual i i increment in size to age 20 years in both sexes i s about 0.9 pounds, round weight, and 1.9 inches, fork length. From age 20 to 50 years, males average 0.4 pounds and 0.4 inches per year and females average 0.7 pounds and 0.5 inches per year. Beyond age 50 years, the average annual increment in round weight of females increases to about 1.0 pounds. A very noticeable change in growth at age 20 to 25 years in both sexes correlates very closely with reproductive maturity of these fish. There i s no indication of any asymptotic size in Nelson River sturgeon. The length-weight relationship of male Nelson River sturgeon i s : log W = -3.55 + 3.002 log L. That for the female i s : log W - -3.84 + 3.204 log L. (W is round weight in pounds and L is fork length in inches). There is a straight-line relationship between dressed weight and round weight. A simple rule of thumb for this relationship i s : dressed weight * 2/3 round weight. Nelson River sturgeon spawn in the spring in late May and early June. The average female matures and spawns the first time at age 25 to 30 years. This corresponds to a round weight of 24 to 29 pounds and a fork length of 42 to 45 inches. A l l or most males are mature by age 20 years which corresponds to a round weight of about 18 pounds and a fork length of about 38 inches. Nelson River sturgeon do not spawn every year. The best inform-ation available suggests that the female spawns every three to six years. Older fish appear to spawn more frequently than young ones. The frequency of spawning of Nelson River male sturgeon is unknown but i t is very unlikely that they spawn every year. Several lines of evidence indicate that the failure of recent Nelson River sturgeon fisheries is the result, of over-exploitation. This species is particularly vulnerable to depletion because of several atypical aspects of its l i f e history, habits and high market value. i i i Recommendations for the management of future fisheries on the Nelson River and other areas are given. These pertain to production limits, fishing seasons and the minimum legal size of fish and fishing gear. ACKNOWLEDGEMENTS Material for this thesis was obtained while the writer was em-ployed by the Fisheries Branch, Department of Mines and Natural Resources, Manitoba. Thanks are due to Mr. B. Kooyman, Director of Fisheries, for permission to use this material and for his direction, encouragement and criticism during the course of the study. Thanks are also due to Dr. K. Doan, Chief Fisheries Biologist, Manitoba Fisheries Branch, for his criticism of the manuscript. Gratitude i s expressed to Dr. P. A. Larkin, Director, Institute of Fisheries, University of British Columbia, for his valuable assistance and criticism i n the analysis of material and i n the preparation of the manuscript. Acknowledgement i s made to the office and f i e l d staff personnel of the Game and Fisheries Branches i n Northern Manitoba for their assist-ance and advice during the course of this study and to Mr. B. Kooyman and Mr. W. B. McTavish who collected a l l data i n 1953 and 1954 respectively. Special thanks are due to my parents for their help and encouragement throughout the years that I spent i n the University and to my wife for her help and encouragement during the preparation of the f i n a l draft. i v CONTENTS PAGE ABSTRACT i TABLE OF CONTENTS i v TABLES v i ILLUSTRATIONS v i i ACKNOWIEDGMENTS . i x I. INTRODUCTION 1 A. AREA OF RESEARCH 1 B. MATERIAL COLLECTED 1 C. NATURE AND HISTORY OF THE FISHERY 3 II . LITERATURE REVIEW 5 A. THE EFFECT ON STURGEON OF COMMERCIAL FISHERIES 5 B. ARTIFICIAL PROPOGATION 6 C. AGE DETERMINATION OF STURGEON 6 D. GROWTH 6 E. REPRODUCTION 7 III . AGE DETERMINATION OF NELSON RIVER STURGEON 8 A. AGING TECHNIQUE 8 B. THE CHARACTERISTICS OF CROSS-SECTIONS FROM DIFFERENT POINTS ALONG THE MARGINAL "SPINE" OF THE PECTORAL FIN 9 (a) Methods 9 (b) Results and Discussion 10 IV. GROWTH OF NELSON RIVER STURGEON 13 A. BACK-CALCUIATION OF GROWTH 13 (a) Methods Used to Determine the Relationship Between Growth i n Length of the Sturgeon and Growth of the Pectoral Spine. 13 (b) Measurements Used i n Back-Calculation of Growth 19 B. METHOD OF BACK-CALCULATION 20 C. RESULTS AND DISCUSSION 22 (a) Growth i n Length of Nelson River Sturgeon 22 (b) Growth i n Length by Sexes 33 (c) Growth of Nelson River Sturgeon i n Various Calendar Years 35 (d) Growth i n Weight of Nelson River Sturgeon 38 (e) The Length-Weight Relationship 40 (f) The Relationship of Dressed Weight to Round Weight 43 (g) Comparison of the Growth of Nelson River Sturgeon with that of Sturgeon from Other Areas 44 V PAGE V. REPRODUCTION OF NELSON RIVER STURGEON 49 A. METHODS AND MATERIALS 49 B. DEVELOPMENT OF THE GONAD 50 G. THE TIME AND PLACE OF SPAWNING 52 D. THE AGE OR SIZE OF REPRODUCTIVE MATURITY 54 E. THE FREQUENCY OF SPAWNING IN STURGEON 56 VI. THE EFFECT OF THE COMMERCIAL FISHERIES ON NELSON RIVER STURGEON 61 A. THE EFFECT OF THE PRESENT FISHERY ON STOCKS OF NELSON RIVER STURGEON 64 (a) Changes in the Age Structure of Nelson River Sturgeon from 1953 to 1959 64 (b) Changes in the Size Structure of Nelson River Sturgeon from 1953 to 1959 67 (c) The Catch Per Unit of Effort 70 (d) Year Class Strength 72 B. DISCUSSION 74 VII. FUTURE MANAGEMENT OF THE NELSON RIVER STURGEON FISHERY 76 A. PRODUCTION LIMITS 76 B. THE MINIMUM LEGAL SIZE OF STURGEON 79 C. FISHING GEAR 81 D. FISHING SEASONS 82 VIII. THE MANAGEMENT OF OTHER STURGEON FISHERIES IN MANITOBA 83 A. PRODUCTION LIMITS 83 B. THE MINIMUM LEGAL SIZE OF STURGEON AND OF FISHING GEAR 83 C. FISHING SEASONS 84 IX. FUTURE RESEARCH ON LAKE STURGEON 85 SUMMARY 86 LITERATURE CITED 91 vi TABLES I. Analysis of The Loss of Annuli in Cross-Sections Taken at Regular Intervals Along the Length of the Pectoral Fin "Spine". II. Age Composition and Range in Size of Sturgeon Specimens Chosen for Back-Calculation of Length. III. The Average Size (Empirical Fork Lengths) by Age Groups of Nelson River Sturgeon. IV. The Average Size (Calculated Fork Length) by Age Groups of Nelson River Sturgeon. V. The Average Size (Round Weight in Pounds) by Age Groups of Nelson River Sturgeon. VI. Length-Weight Relationship of Nelson River Sturgeon. VII. The Relationship of Dressed Weight to Round Weight of Nelson River Sturgeon. VTII. The Age of Reproductive Maturity of Various Species of Sturgeon. IX. The Frequency, by Age Groups, of Nelson River Female Sturgeon at each Stage of Reproductive Maturity. X. The Age and Size at Reproductive Maturity of Lake Sturgeon of Various Regions. XI. The Frequency and Ratio of Female Sturgeon, by Age Groups, at Each Stage of Gonad Development. XII. The Age Composition of Sturgeon Sampled from the Nelson River Commercial Fishery from 1953 to 1956 and 1959. XIII. The Size Composition (Round or Live Weight) of Sturgeon Sampled from the Nelson River Commercial Fishery from 1953 to 1956 and 1959. XIV. The Size Composition (Dressed Weight) of Sturgeon Sampled from the Nelson River Commercial Fishery between 1953 and 1959. XV. The Average Catch Per Unit of Effort in the Nelson River Sturgeon Fisheries of 1937 to 1946 and 1953 to I960. • v i i ILLUSTRATIONS PAGE Fig. 1. Nelson River Sturgeon Production Statistics. 4 Fig. 2. The Enlarged Image of a Cross-Section of the Marginal "Spine" of the Pectoral Fin Illustrating the Loci of the Radial Axes Along Which Measurements for Back-Calculation of Growth Were Made. 15 Fig. 3 . The Relationship Between Fork Length and the Radial Length of the Pectoral Spine Cross-Sections in Nelson River Sturgeon. 16 Fig. 4 . Relationship Between Fork Length and the Average Radius of Pectoral Spine Cross-Sections in Nelson River Sturgeon. 18 Fig. 5» Nomograph Used in Back-Calculation of Length of Nelson River Sturgeon. 22 Fig. 6. Growth in Length of Nelson River Sturgeon (Average Empirical Fork Lengths by Age Groups). 24 Fig. 7. Growth in Length of Nelson River Sturgeon (Average Back-Calculated Fork Length by Age Groups). 27 Fig. 8. Growth in Length of Nelson River Sturgeon (Cumulative Average Back-Calculated Increments of Fork Length by Age Groups). 28 Fig. 9 . Comparison of Growth Curves Representing Three Methods By Which Growth in Fork Length of Nelson River Female Sturgeon was Determined. 29 Fig. 10. Waiford Transformation of Calculated Lengths of Nelson River Female Sturgeon. 32 Fig. 11. The Relationship Between Fork Length at any Age and the Following Year's Increment in Fork Length. Nelson River Female Sturgeon. 34 Fig. 12. Average Relative Growth in Fork Length by Calendar Years of Two Samples of Nelson River Female Sturgeon. 37 Fig. 13. Growth in Weight of Nelson River Sturgeon. 39 Fig. 14. Length-Weight Relationship of Nelson River Sturgeon. 42 Fig. 15. The Relationship of Dressed Weight to Round Weight in Nelson River Sturgeon. 45 v i i i PAGE Fig. 16. Comparison of Growth in Length of Lake Sturgeon from Several Regions. 46 Fig. 17. Male Lake Sturgeon (Testes Illustrated). 51 Fig. 18. Female Lake Sturgeon (Ovaries Illustrated). 5L Fig. 19. The Age Composition of Sturgeon Sampled from the Nelson River Commercial Fishery from 1953 to 1956 and 1959. 66 Fig. 20. Year Class Representation of Sturgeon Sampled From the Nelson River Commercial Fishery from 1953 to 1956 and 1959. 73 1 I. INTRODUCTION Wherever sturgeon have been commercially exploited, marked depletion of stocks has resulted. In many cases this has progressed to the point of commercial extinction of these economically important fishes. To properly manage and protect any stock of fishes f o r purposes of insuring a sustained yield, biological research i s required to establish rates of increment to such stocks. The pertinent aspects of such research are knowledge of growth, reproduction, natural mortality and qualitative and quantitative ecology. The research reported herein mainly concerns the study of growth and reproduction of lake sturgeon of the Nelson River, Manitoba. These data are applied to a preliminary assessment of stocks as a tentative basis for provincial legislations. A. ARM OF RESEARCH Research on sturgeon has been conducted on several lakes and rivers of Northern Manitoba but sufficient data for adequate appraisal of stocks were obtained only on the Nelson and Churchill Rivers. Data present-ed here are from f i s h taken i n the v i c i n i t y of Sipiwesk Lake (55°00' N, 97°30' W), an enlargement of the Nelson River. B. MATERIAL COLLECTED From 1953 to 1956 and i n 1959, data were obtained on 791 sturgeon. A l l specimens were sampled randomly from the commercial catch by biologists of the Provincial Fisheries Branch. Mr. B. Kooyman and Mr. W. B. McTavish obtained a l l data i n 1953 and 1954 respectively and the writer obtained a l l data i n 1955, 1956 and 1959. The following measurements and observations were made on each f i s h : 1. LENGTH: Fork length to the nearest quarter inch was recorded i n a l l years. Total length was recorded i n 1955 and 1956. Two additional body length measurements were made i n 1955 for the purpose of establishing a new minimum legal size l i m i t . These were: (i) the distance from the most posterior limit of the g i l l c l eft to the junction of the posterior edge of the dorsal f i n with the body, ( i i ) the distance from the most posterior limit of the cleithrum to the junction of the posterior edge of the dorsal f i n with the body. 2. WEIGHT: Round or l i v e weights to the nearest half pound were recorded i n a l l years. Dressed weights (the carcass minus head and pectoral girdle, viscera, and fins) were recorded i n 1953 and 1954. 3. SEX: The sex and the stage of development of the gonad was recorded i n a l l years. 4. STOMACH CONTENT: This was recorded only from a small number of stur-geon. Other particulars such as the date and the l o c a l i t y of k i l l i n g of each specimen were also noted. The marginal "spine" of one of the pectoral fins of each specimen was retained for the purpose of age determination. These were attached to plastic data tags by means of a thin wire which was threaded through a prominent blood vessel i n the cartilage at the base of the ray. C. NATURE AND HISTORY OF THE FISHERY Available records indicate that the first sturgeon fishery on the Nelson River began in 1907. Since then there have been several periods.of fishing alternating with periods of closure, each of several years duration. The last fishery (1953 to I960) followed a six-year closure. The annual production in pounds is presented graphically in Figure 1. The Nelson River sturgeon fishery is closely regulated. Only local residents are eligible to hold licenses and the number of licenses is limited, the only legal fishing gear is g i l l nets and each licensee i s allowed not more than 500 yards of net, the minimum legal size of which is 12 inches extension measure. The size of fish to be retained is also restricted by a minimum legal size of ten pounds dressed weight or eighteen pounds round (live) weight. There i s also an annual production limit on that part of the river which was opened to fishing. This limit was 25,000 pounds per year from 1953 to 1957 and 50,000 pounds from 1958 to I960. 160 140 Q Z o CL 120 100 to Q z < to Z) o I so 60 u Z) Q O or CL 40 20 1900 1910 1920 1930 Y E A R 1940 1950 I960 Figure I. Nelson River Sturgeon Production Stat is t ics (dressed weight) 5 I I . LITERATURE REVIEW Several authors have contributed to our knowledge of the biology of various sturgeon. In Canada, the most extensive studies are by Cuerrier (1949), Roussow (1955), and Harkness (1923). Classen (1944) discusses research done i n Spain. Derjavin (1922) and others who are referred to by Roussow (1955), report on research conducted i n Russia and Eastern Europe. The following subjects, which are pertinent to this paper, are discussed and reviewed by a number of authors. A. THE EFFECT ON STURGEON OF COMMERCIAL FISHERIES The effect of commercial exploitation on populations of sturgeon i n North America i s considered by several authors. Rodd (1926), i n a literature review, ill u s t r a t e s the drastic depletion of sturgeon i n the St. John River, the Fraser River and i n Lake Winnipeg. The over-exploitation of sturgeon and the decline of the fishery on the Great Lakes i s described by Van Oosten (1936), and Williams (1951). Depletion of sturgeon i n Lake of the Woods i s reported by Carlander (1947) and Evermann and Latimer (1910). Wirth and Cline (no date), Pycha (1956) and McCrimmon (1956) report respectively on the depletion i n Wisconsin lakes, California rivers and i n Lake Simcoe, Ontario. Various other authors present further reasons for the depletion of sturgeon i n different parts of the world. Dams, pollution, shipping and canalization as well as inadequate protection and management of stocks are a l l blamed. Cuerrier and Roussow (1951), Roussow (1955), Cuerrier (1949) and Harkness (1923, 1936) discuss the situation i n Eastern Canada. Roussow (1955) presents the case i n Russia and Eastern Europe i n a literature review 6 while Ehrenbaum (1926) and Meyr (1950) comment on the situation in Germany and Classen (1947) describes the situation in Spain. B. ARTIFICIAL FR0P0GATI0N Literature on the a r t i f i c i a l propogation of sturgeon in Russia, Eastern Europe and in North America Is reviewed by Roussow (1955). The success of sturgeon culture in North America i s summarized by Rodd (1926). Ryder (1890) and Dean (1884) outline many of the problems encountered in the first experiments in sturgeon culture in North America. C. AGE DETERMINATION OF STURGEON Literature on age determination of sturgeon is reviewed by Cuerrier (1951), Roussow (1955), Chugunov (1925) and Classen (1944). In these papers the procedure for aging sturgeon by means of thin cross sections of the marginal "spine" of the pectoral fin is described. These authors also present evidence substantiating the validity of this method. Probst and Cooper (1954) provide further evidence to support this method. D. GROWTH Reviews of literature on the growth of various species of sturgeon are provided by Roussow (1955) and Cuerrier (1949). Roussow refers to studies done on sturgeon in Asia, Europe and North America. Cuerrier refers mainly to North American studies. Aspects of growth of the lake sturgeon in North America are pres-ented by Roussow(l955 and 1957), Cuerrier (1949), Cuerrier and Roussow (1951), Vladykov (no date), Kooyman (1955), Harkness (1923), Schneberger and Woodbury (1944) and Probst and Cooper (1954). 7 Roussow (1955) and Classen (1944) discuss methods of back calculation of growth i n sturgeon and review the pertinent literature. E. REPRODUCTION An extensive literature survey and a thorough discussion of the general aspects of reproduction i n sturgeon are presented by Roussow (1955, 1957) and Cuerrier (1949)• Roussow refers extensively to research conducted i n Europe and North America while Cuerrier refers mainly to North American publications. Notes on the age of maturity and the periodicity of spawning of sturgeon i n Spain and Russia are presented by Classen (1944, 1947) and Derjavin (1922). The periodicity of spawning and the age of maturity of the lake sturgeon i n North America i s discussed by Harkness (1923, 1936), Kooyman (1955) and Vladykov (no date). Further data on the time and place of spawn-ing of the lake sturgeon are presented by Bajkov (1930) and Williams (1951). 8 I I I . AGE DETERMINATION OF NELSON RIVER STURGEON The sturgeon i s aged by means of i t s bony parts. Seasonal changes i n the metabolism of the f i s h produce seasonal difference i n the amount and kinds of calcium added to the bony parts. These difference are distinguish-able as concentric bands which are interpreted as annuli. Bones commonly used i n the aging of sturgeon are: otoliths, cleithra, clavicles, scutes and the marginal "spine" of the pectoral fins (Cuerrier, 1951)* Cross sections of the marginal "spine" of the pectoral f i n have proved to be most satisfactory, especially for the lake sturgeon (Cuerrier, 1951 and Roussow, 1955)* The d i f f i c u l t i e s encountered and the reservations which must be made i n the use of this method are discussed by Classen (1944), Cuerrier (1951) and Roussow (1955). The v a l i d i t y of this method for aging of sturgeons i s s t i l l i n -conclusive. There i s , however, considerable evidence to support this method. Chugunov (1925) reports on an experiment by H. Holzmayer i n which sterlets (A. ruthenus). kept i n captivity for as long as ten years from the period of incubation, exhibited a number of "annuli" i n the cross section of the marginal "spine" of the pectoral f i n which corresponded exactly to the age of the f i s h . Chugunov also states that the number of annuli present i n different bones of the same f i s h i s constant. Probst and Cooper (1954) offer further indirect proof for this method. Both age and length-frequency distributions of lake sturgeon from the Lake Winnebago region of Wisconsin were bimodal. These modes i n age and length both corresponded closely with points on the growth curve. A. AGING TECHNIQUE 9 Cross-sections of the marginal spine of the pectoral fin were obtained by the method outlined by Cuerrier (1951). These sections, 0.3 to 0.5 millimeters in thickness, were cut by means of a jewellers saw using size 2/0 or 3/0 blades. Good sections were obtained either by the use of a single blade or by two closely aligned blades. The sections were obtained from the proximal end of the spine, roughly at the base of the thickened portion of the spine which articulates with the basal elements. Thus, depending on the size of the fish, the sectioning would be made at a point which is roughly one quarter of an inch to one inch from the proximal end of the spine. Most sections were read under a low power binocular miscroscope using transmitted light. Some were also aged by means of a micro projector. Each section was placed in a medium of absolute alcohol to increase the differentiation in transparency of the winter and summer rings. As no perm-anent mounts were made, finished sections were dried and stored in vials. The microscope image of a fin spine section is illustrated in the frontispiece. The narrow, light-colored rings represent winter growth and the wider, more opaque zones represent summer growth. The closest narrow ring to the centre of ossification is interpreted as the f i r s t winter ring. Since a l l samples were obtained in June and July, the time of year that sturgeon are born, the number of winter rings should correspond to the exact age of the fish. B. THE CHARACTERISTICS OF CROSS-SECTIONS FROM DIFFERENT POINTS ALONG THE MARGINAL "SPINE" OF THE PECTORAL FIN (a) Methods Cuerrier (1951) suggests that the cross-section of the pectoral spine be obtained about one-quarter of an inch from the proximal end of the 1 0 spine. Classen ( 1 9 4 4 ) suggests that i t be obtained one to one and one-half centimeters from the end of the spine. They do not discuss the relative merits of sectioning elsewhere along the spine. The writer found that better sections were obtained at a point half an inch to one inch from the proximal end of the spine of large sturgeon. The location on the pectoral spine of the clearest and best cross-sections for purposes of aging and back calculation of growth i n Nelson River sturgeon was determined by the following study. A series of sections were cut from pectoral f i n spines of sixteen sturgeon of various sizes and ages. These sections were taken at quarter inch intervals along a two and one-half inch portion of the proximal end of the spine. Annuli counts were then made on a l l cross-sections of each series. In series where aging was d i f f i c u l t , counts were terminated at some well defined reference point which was easily recognizable throughout the series ( i . e . a closely packed band of annuli). The results are presented i n Table I as "loss" of annuli along the f i n spine beginning at the proximal end. Note that counts of annuli were possible on few of the sections obtained a quarter of an inch from the proximal end of the spine. (Annuli here were often too closely packed i n the periphery of the spine to be differentiated). Counts of annuli along each series was terminated when the reference point was lost or when the annuli became obscure. (b) Results and Discussion It i s evident from Table I that, for age determination, cross-sections of the pectoral spine of Nelson River sturgeon should be obtained within half an inch of the proximal end of the spine. Beyond this point a rapidly increasing number of annuli are lo s t . At three-quarters of an inch, roughly half of the cross-sections had lost one annulus and by one inch most cross-sections had lost at least one annulus. 11 TABLE I. Analysis of the Loss of Annuli in Cross-Sections Taken at Regular Intervals Along the Length of the Pectoral Fin "Spine". Specimen Fork Length Ace of Location of Cross-Section*  Number of Fish Fish \ % 1 l i 1* 2 2\ N 58 50.8 ins. 34 0 0 0 0 1 1 i 2 m • N 70 50.0 ins. 32 • 0 0 2 3 4 4 5 6 6 N 2 48.8 ins. 35 0 1 1 N 84 48.5 ins. 45 0 0 1 1 2 2 • • . • • • W 30 47.5 ins. 32 . 0 0 0 1 1 2 • • • N 38 46.5 ins. 39 0 0 1 1 2 2 3 • » N 72 44.5 ins. 45 0 0 1 i 2 3 4 • N 99 43.8 ins. 25 • 0 0 0 l 1 2 2 • a N 50 42.2 ins. 31 • 0 0 0 0 1 2 • • H 21 41.0 ins. 31 0 1 2 2 3 3 5 6 0 N.,4 40.5 ins. 21 0 1 1 2 2 3 • • o H 23 40.0 ins. 23 0 1 1 1 2 2 3 3 0 H 27 40.0 ins. 21 0 1 1 1 1 2 3 3. 4 N 93 38.5 ins. 19 . 0 0 1 1 2 2 3 • © H 22 34.0 ins. 20 0 0 0 0 1 1 1 2 • • SF 1 24.2 ins. 11 0 0 1 1 1 2 2 3 • © Average Loss 0.0 0.1 0.4 0.8 1.3 1.8 2.2 3.2 4.5 5.0 * The distance in inches from the proximal end of the spine. This factor, however, is not the only important consideration. Before accurate aging is possible, the cross-section must exhibit clearly discernible annuli. From the series of spine sections studied, i t was found that those obtained between half an inch and one inch from the proximal end of the spine were most easily read. (It should be noted that most of these specimens were large fish). Sections obtained within half an inch of the proximal end of the pectoral spine of larger fish were wedge shaped, the bony part being quite narrow. Annuli in this section were so closely packed that aging was very difficult, i f not impossible. Sections obtained between half an inch and two inches from the proximal end of the spine generally were quite easily differentiated. The winter rings were narrow and well defined. Those obtained over an inch from the proximal end of the spine lacked one or more annuli, however. 1 2 Sections obtained further out along the pectoral spine had not only lost annuli, but were d i f f i c u l t to interpret for several other reasons. Annuli i n this area were more closely packed as the cross sectional area of the spine decreased and the spine was often damaged or eroded. The spine also became deformed as more recent annuli of the marginal spine encircled and became fused with the second and even the third f i n rays. It is therefore evident that i n aging of sturgeon weighing twenty pounds or more, i t i s best to obtain the marginal spine cross-section at a point roughly half to three-quarters of an inch from the proximal end of the spine (roughly at the base of the swelling formed at the "knuckle"). In this area the annuli are most distinct, the spine i s generally undamaged or worn away and the loss of annuli i s not great. I f the f i r s t annulus of a section obtained i n this area i s f a i r l y closely aligned with the second annulus (i . e . leaving a large central area devoid of annuli), i t i s l i k e l y that this cross-section i s missing the f i r s t winter ring. 13 IV. GROWTH OF NELSON RIVER STURGEON Growth i n length of Nelson River sturgeon was determined by back calculation and by the age-length relationship. Results are presented i n the following sections. Growth by sexes, growth i n various calendar years, growth i n weight, the length-weight relationship, the relationship of dressed weight to round weight and a comparison of growth i n widely sep-arated stocks of lake sturgeon i s also discussed. A. BACK-GALCUIATION OF GROWTH (a) Methods Used to Determine the Relationship Between Growth i n Length of the Sturgeon and Growth of the Pectoral Spine  Back calculation of growth In fishes i s possible only when one has determined the relationship between the rate of growth i n length of the f i s h and that of a body part on which annual growth increments can be measured. The only structure which has been used for back calculation of growth i n sturgeon i s the cross-section of the marginal spine of the pectoral f i n i n which the annuli are readily discernible (Roussow, 1955 and Classen, 1944). Two series of observations were made to determine the relationship between growth i n length of Nelson River sturgeon and the growth of the pectoral spine. Series 1 In the f i r s t series, cross-sections of the pectoral spine were prepared from a sample of 74 f i s h selected i n such a way that the greatest possible range i n size was represented ( s t r a t i f i e d random sample). The sections were obtained at a point roughly one-third of the distance from the proximal end of the spine. This position was chosen for the following reasons: the spine i n this area i s only sli g h t l y tapered, cross-sections from various specimens are relatively uniform i n shape and the cross-sections are only sli g h t l y bifurcated compared to those obtained at the proximal end of the spine. The prepared sections were mounted on a concave glass slide i n a medium of absolute alcohol. A l l measurements were made on an image of the cross-section (roughly 40x) produced by a microprojector. Three measurements were made on the image. The area delimited by the outer annulus was measured by means of a polar planimeter. The perimeter of the outer annulus was measured by means of a map measure. A map measure was also used to determine the t o t a l length of two radial measurements, the l o c i of which are illu s t r a t e d i n Figure 2. The common origin of these lines i s the centre of ossification of the pectoral spine. They are traced along the acute angles formed by the annuli i n the posterior portion of the spine and terminate at the outer annulus at the periphery of the section. These three measurements were each plotted against fork length on log-log and on arithmetic.graph paper. From these graphs i t was evident that there was a linear relationship between the length of the f i s h and the measurements made on the cross-section of the marginal spine of the pectoral f i n . This relationship, however, was poor i n a l l cases. Averaging of the pectoral spine measurements by one inch intervals of fork length did not significantly improve the linear relationship. The relationship between fork length and the radial length of the pectoral spine sections i s illustrated graphically i n Figure 3» This series indicated that measurements for back calculation of growth i n sturgeon cannot be made on cross-sections obtained from central or dis t a l portions of the marginal spine of the pectoral f i n . Despite several 15 Figure 2. The enlarged image of a cross-section of the marginal "spine" of the pectoral fin illustrating the loci of the radial axes along which measurements for back-calculation of growth were made. advantages of selecting cross-sections from this area, a few important dis-advantages were also apparent. Many of the spines in this area were badly abbraded along the leading edge and more recent annuli often encircled the second or even third fin ray. Cross-sections from this portion of the spine may also lack the first few annuli. This series also indicated that the only possible measurement on the pectoral spine section for purposes of back calculation of growth is the radial measurement. The perimeter of each annulus or the area delimited by 8.0 7.0 6.0 O LU CO CL CO 5.0 - 4.0 16 o o o o o o o> • o o oo o oo • oo o o CO 2 3.0 Q < or UJ O < 2.0 or LU • MALES o FEMALES 1.0 0 -/ A L. 20 30 40 50 FORK LENGTH IN INCHES 60 70 Figure 3. The Relationship Between Fork Length and the Radial Length of the Pectoral Spine Cross - Sections in Nelson River Sturgeon . each annulus cannot be measured i n larger f i s h because few annuli can be traced throughout the circumference of the pectoral spine due to crowding of annuli or abrasion along the leading edge of the spine. Series 2 The second series of observations made to determine the relation-ship between growth In length of the sturgeon and growth of the pectoral spine was made on 97 specimens. These were again selected to insure that the greatest possible range i n size of specimens was represented and that each size group (one inch intervals of fork length) was represented by a minimum of three specimens where possible. Cross-sections that were damaged, deformed or d i f f i c u l t to age were discarded. In this series, pectoral spine sections were obtained at the proximal end of the spine where sections for aging of specimens were ob— tained. Gross-sections were temporarily mounted on a concave glass slide i n a medium of absolute alcohol. An image of each section (roughly 50x) was projected upon a sheet of paper by means of a 35 mm. slide projector equipped with an attachment for microscope slides. A pencil tracing was then made on the image from the centre of ossification of the spine, posteriorly along the acute angles formed by the annuli, to the outermost annulus at the posterior edge of the spine. (See Figure 2 for i l l u s t r a t i o n ) These two radial axes were then measured and the average "radial length" of the cross-section was calculated. Results are presented i n Figure 4, where the average radial length of the pectoral spine of each specimen i s plotted against the fork length. The regression line (x = 0.14y + 2.2) calculated from these data also appears i n this figure. I t i s evident from the scatter of points that the linear relationship between these two variables i s somewhat poor. This may be Figure 4. Relationship Between Fork Length and the Average Radius of Pectoral Spine Cross -Sections in Nelson River Sturgeon. 19 attributed mainly to the d i f f i c u l t y of obtaining a cross-section from the same relative area of the tapered pectoral spine i n each specimen. This i s akin to neglecting to use a "key scale" i n other species of f i s h . Since these data are the best available, this regression line was used i n back calculation of growth of Nelson River sturgeon. This was con-sidered better than the only other alternative which was to assume a direct relationship between growth i n length of sturgeon and growth of the pectoral spine. It i s to be noted that the data presented i n this series are not treated separately according to sex. The po s s i b i l i t y of a -difference between males and females concerning the relationship between growth i n length of sturgeon and growth of the pectoral spine was tested by an analysis of covariance i n the f i r s t series. This test confirmed the supposition that no significant difference i n this relationship exists between male and female sturgeon. (b) Measurements Used i n Back-Calculation of Growth For purposes of back-calculation of growth of Nelson River sturgeon a sample of 2 3 males and 25 females was again selected so that the greatest possible range i n size (or age) of f i s h was represented. The age distribu-tion and the range i n size of specimens chosen i s presented i n Table I I . A l l cross-sections of pectoral spines taken for back calculation of growth were obtained at the proximal end of the spine i n the same area where sections for age determination were obtained. These sections were temporarily mounted on a glass slide i n a medium of absolute alcohol and a magnified image (approximately 50x) was projected upon a sheet of paper by means of a microprojector. The radial axes were then traced on the paper (as i n Figure 2) and the intersection of each annulus along these axes was marked off. The distance between each annulus was then measured with a scale graduated i n thirtieths of inches. These measurements were added cumulatively to provide the distance between the centre of ossification and each annulus. TABLE I I . Age Composition and Range i n Size of Sturgeon Specimens Chosen for Back-Calculation of Length Age Group Males Females Frequency Size Range* Frequency Size Range* 3 1 11.0 • . 4 , • • 1 14.3 8 1 22.3 • • 9 1 27.3 • • 16 1 38.7 • • 18 1 37.5 1 33.5 19 1 41.0 1 34.0 21 2 39.7 - 42.0 • 22 3 36.0 - 39.5 2 40.3 - 45.5 23 4 34.0 - 40.7 3 38.5 - 49.0 24 1 46.3 2 42.7 - 45.0 25 1 44.7 . o 26 • • 1 41.0 27 1 44.5 • © 28 1 43.3 • 0 31 2 42.7 - 47.5 • • 32 . 2 38.7 - 46.7 34 2 51.0 - 51.5 35 1 44.5 37 . • - 2 37.7 - 48.7 39 1 56.0 40 2 48.7 - 49.5 43 47.7 • • 49 1 52.0 50 1 56.0 53 1 55.0 55 1 42.7 • • 62 • 1 55.5 * Fork length i n inches. B. METHOD OF BACK-CALCULATION It i s evident that few of the data plotted i n Figure 4 l i e directly on the regression l i n e . Thus, to determine size at a previous age 21 for any individual i t i s necessary to back calculate along a line parallel to the regression line or along a line that converges to the same intercept as the regression l i n e . In the parallel method i t i s assumed that the slope of the regression line of pectoral spine radius measurement against fork length i s a constant for a l l individuals. In this case, back-calculation of length at a previous age involves the implication that at the theoretical fork length of zero, the size of the pectoral spine was not necessarily the same i n a l l individuals. In the convergent method i t i s assumed that the slope of the regression li n e of f i n radius measurement against fork length i s not the same i n a l l individuals. In this case i t i s implied that at the theoretical fork length of zero, the pectoral f i n was the same size for a l l f i s h and that the relation between f i n radius measurement and fork length could be different i n each individual. Back-calculations of growth of Nelson River sturgeon were done by both the convergent and parallel methods. Only the results obtained by the convergent method are presented however, since i t i s unlikely that a large difference i n f i n size i s possible among small sturgeon. I t was also ev-ident that the convergent method produced results that were more similar to growth rates determined from actual measurements on sturgeon of different age groups. Furthermore, i t was found that the calculated size of many sturgeon of age group one was less than zero when determined by the parallel method. A nomograph (Figure 5) was designed for the purpose of speeding up the back-calculation of lengths which involved roughly 1300 calculations on the 48 specimens. The two scales represent the x and y axes. The short scale, which represents fork length, has been rotated to a ver t i c a l position so that the moveable thread may intersect both scales. 22 FIGURE 5. Nomograph Used in Back-Calculation of Length of Nelson River Sturgeon In the operation of the machine by the convergent method of back-calculation the pectoral spine radius scale was fixed and the fork length scale was set at the average intercept determined from the regression line. The latter was then moved laterally to left or right to provide the different theoretical slope for each fish. This is comparable to joining the point for a particular fish to the intercept for the average regression line and back-calculating along this line. C. RESULTS AND DISCUSSION (a) Growth in Length of Nelson River Sturgeon Growth in length of Nelson River sturgeon was determined by three methods: (l) by averaging empirical lengths of age groups, (2) by averaging 23 calculated lengths by age groups, (3) by cumulatively totaling average calculated increments of length between successive age groups. Determin-ations by method ( 1 ) are presented i n Table III and i n Figure 6 . Those for methods (2) and (3) are presented i n Table I? and i n Figures 7 and 8 . A comparison of growth curves determined by a l l three methods for female sturgeon i s presented i n Figure 9 . TABLE III. The Average Size (Empirical Fork Lengths) by Age Groups of Nelson River Sturgeon. 1 9 5 3 to 1 9 5 6 Data. Males Females Males Females Age Freq. Ave.* Freq. Ave.* Age Freq. Ave.* Freq. Ave.* Group Length Length Group Length Length 1 - 3 1 1 1 . 0 • • 49 -51 6 4 9 . 5 2 2 50 .5 4 - 6 • • 1 1 4 . 3 5 2 - 5 4 7 4 7 . 7 8 52 .0 7 - 9 2 2 4 . 9 • • 5 5 - 5 7 1 4 8 . 0 7 4 9 . 9 1 0 - 1 2 • • « • 5 8 - 6 0 . • • 13 -15 • • 1 2 7 . 2 6 1 - 6 3 5 5 5 . 6 1 6 - 1 8 6 4 0 . 0 3 3 5 . 5 6 4 - 6 6 5 2 . 5 7 5 6 . 7 1 9 - 2 1 2 8 3 9 . 2 7 3 7 . 8 6 7 - 6 9 • 3 52 .7 22-24 4 3 4 1 . 1 2 4 4 2 . 5 7 0 - 7 2 • 2 5 6 . 0 2 5 - 2 7 3 4 4 3 . 3 25 4 3 . 7 7 3 - 7 5 • 2 5 5 . 5 2 8 - 3 0 3 4 4 2 . 2 2 2 4 3 . 8 8 4 only • 4 6 3 . 0 3 1 - 3 3 3 4 4 3 . 5 3 5 4 5 . 9 8 6 only • 1 6 0 . 5 3 4 - 3 6 4 6 4 4 . 8 3 8 4 7 . 1 8 8 only 1 6 5 . 0 3 7 - 3 9 3 4 4 4 . 9 3 8 4 6 . 8 9 8 only • 1 5 9 . 0 4 0 - 4 2 2 7 4 5 . 1 3 4 4 8 . 6 1 0 2 only • 1 6 9 . 0 4 3 - 4 5 4 2 4 6 . 0 4 2 4 8 . 4 1 0 5 only 1 6 7 . 0 4 6 - 4 8 1 6 4 6 . 3 3 7 5 0 . 3 1 1 0 only • • 1 6 3 . 0 Totals 3 6 2 3 7 2 * Average fork length i n inches. 24 80 I r- i 1 1 r 70 h 60 h 0 I I i 1 1 1 1 1 0 10 20 30 40 50 60 70 A G E IN Y E A R S Figure 6. Growth in Length of Nelson River Sturgeon (Average Empirical Fork Lengths by Age Groups.) 25 TABLE IV. The Average Size (Calculated Fork Lengths)by Age Groups of Nelson River Sturgeon Males Females Ave.* * Ave.* * * Age Calc. Ave. Cumul. Calc. Ave. Cumul. Group Freq. Size Incr. Incr. Freq. Size Incr. Incr. 1 23 6.6 6.6 6.6 25 7.1 7.1 7.1 2 23 11.5 4.9 11.5 25 12.3 5.2 12.3 3 23 15.5 4.1 15.6 25 16.4 4.1 16.4 4 22 19.0 3.2 18 .8 25 19.6 3.2 19.6 5 22 21.7 2.7 21.5 24 22.3 2.5 22.1 6 22 23.8 2.2 23.7 24 24.3 2.0 24.1 7 22 25.6 1.8 25.5 24 26.2 1.8 25.9 8 22 27.1 1.5 27.0 24 27.6 1.5 27.4 9 21 28.9 1.6 28.6 24 29.0 1.3 28.7 10 20 30.5 1.5 30.1 24 30.1 1.2 29.9 11 20 31.8 1.3 31.4 24 31.2 1.1 31.0 12 20 33.0 1.2 32.6 24 32.2 1.0 32.0 13 20 33.9 .9 33.5 24 33.1 .9 32.9 14 20 34.8 .9 34.4 24 33.8 .9 33.8 15 20 35.2 .7 35.1 24 34.9 .9 34.7 16 20 36.4 .7 35.8 24 35.2 .8 35.5 17 19 36.9 .7 36.5 24 36.5 .8 36.3 18 19 37.6 .7 37.2 24 37.2 .7 37.0 19 18 38.2 .5 37.7 23 38.1 .7 37.7 20 17 38.5 .5 38.2 22 38.9 .6 38.3 21 17 39.0 .5 38.7 22 39.6 .7 39.0 22 15 39.1 . .4 39.1 22 40.3 .7 39.7 23 12 , 39.7 .4 39.5 20 40.7 .6 40.3 24 8 41.6 .4 39.9 17 41.1 .7 41.0 25 7 41.4 .5 40.4 15 41.4 .7 41.7 26 6 41.1 .3 40.7 15 42.1 .7 42.4 27 6 41.6 .5 41.2 14 42.8 .7 43.1 28 5 41.5 .5 41.7 14 43.6 .7 43.8 29 4. 41.4 .3 42.0 14 44.2 .7 44.5 30 4 41.8 .3 42.3 14 44.7 .5 45.0 31 4 42.1 .4 42.7 14 45.2 .5 45.5 32 2 39.7 .6 43.3 14 45.8 .6 46.1 33 2 40.2 .6 43.9 12 46.8 .4 46.5 34 2 40.5 .2 44.1 12 47.1 .4 46.9 35 2 40.9 .4 44.5 10 46.8 .5 47.4 36 2 41.3 .4 44.9 9 47.5 .5 47.9 37 2 41.6 .4 45.3 9 48.1 .6 48.5 38 2 42.2 .5 45.8 7 50.1 .5 49.0 39 2 42.4 .2 46.0 7 50.6 .5 49.5 40 2 42.6 .2 46.2 6 50.2 .4 49.9 u 2 43.0 .4 46.6 4 51.0 .2 50.1 42 2 43.2 .2 46.8 4 51.3 .2 50.3 43 2 43.4 .2 47.0 4 51.6 .4 50.7 44 1 39.5 .3 47.3 4 51.8 .2 50.9 45 1 40.0 .5 47.8 4 52.4 .5 51.4 46 1 40.2 .2 48.0 4 52.6 .3 51.7 47 1 40.5 .3 48.3 4 53.0 .3 52.0 26 TABLE IV continued Males Females Ave.* * Ave.* Age Calc. Ave. Cumul. Calc. Ave. Cumul. Group Freq. Size Incr. Incr. Freq. Size Incr. Incr. 44 1 40.7 .2 48.5 4 53.2 .3 52.3 49 1 41.2- .5 49.0 4 53.6 .3 52.6 50 1 41.5 .3 49.3 3 54.4 .3 52.9 51 1 41.7 .2 49.5 2 53.8 .2 53.1 52 1 42.0 .3 49.8 2 54.0 .3 53.4 53 1 42.2 .2 50.0 2 54.4 .3 53.7 54 . 1 42.5 .3 50.3 1 54.0 .3 54.0 55 1 42.7 , .2 50.5 . 1 54.2 .2 54.2 56 . • . . • 1 54.5 .3 54.5 57 • • 1 54.7 .2 54.7 58 • • 1 55.0 .3 55.0 59 • • 1 55.1 .1 55.1 60 • . • 1 55.2 .1 55.2 61 • 1 55.3 .1 55.3 62 • • 1 55.5 .2 55.5 * Fork length in inches. Ave. Gale. Size » Average Calculated Size. Ave. Incr. - Average Increment. Cumul. Incr. - Cumulative Increment. Significant differences are evident in some of these growth curves. This is particularly so of the curves for male sturgeon that were determined by both methods of back-calculation. These curves are very similar to age 30 but thereafter the curve determined by method (2) i s erratic and falls off rapidly. This can hardly be considered significant, however, as calc-ulations beyond age 30 are unreliable because of scanty data. This erratic curve serves only to illustrate the principle that' slower growing fish appear to live longer. The curves determined by empirical measurements also differ significantly from those determined by the two methods of back-calculation. The lower portion of the curve representing empirical lengths, however, is also unreliable because of scanty data. The discrepancies in the curves representing empirical and calculated sizes beyond age 20 may be due to several factors. This fishery 27 0 10 20 30 40 A G E IN Y E A R S 50 60 Figure 7. Growth in Length of Nelson River Sturgeon (Average Back - Calculated Fork Lengths by Age Groups) 28 40 YEARS Figure 8. Growth in Length of Nelson River Sturgeon (Cumulative Average Back - Calculated Increments of Fork Length by Age Groups.) 7 0 6 0 29 5 0 _ n o , 6 ° ° CO UJ I o Z 4 0 z CC o 3 0 2 0 r* 5 4° ^ 6 ° * ° / 6 / 0 / a / 0 / / • / / 6 / EMPIRICAL LENGTH CALCULATED LENGTH O O O O O CUMULATIVE CALCULATED INCREMENTS 10 10 2 0 3 0 A G E IN 4 0 Y E A R S 5 0 6 0 7 0 Figure 9. Comparison of Growth Curves Representing Three Methods by Which Growth in Fork Length of Nelson River Female Sturgeon was Determined. 3 0 would tend to select for f i s h of a particular size range. Fish of age 20 to 25 which grow fast would be disproportionately taken i n the commercial catch. The average actual size would therefore be greater than the average calculated size for f i s h age 20 to 25 years. , Fish of age 3 0 and over which grow slowly would also be disproportionately taken i n the commercial catch. The average actual size beyond age 30 would therefore be less then the average calculated size. Growth rates for older sturgeon that were determined by the two methods of back-calculation may have been overestimated too. Of the large, old specimens, only those with easily differentiated annuli were chosen for back-calculation to insure accuracy. It i s very possible that these were the healthiest and fastest growing individuals. Each of the methods presented has i t s limitations. Method (l) i s the fastest and simplest procedure for determining growth but i t s accuracy i s greatly reduced by selective sampling and insufficient representation of a l l age groups. The main disadvantage inherent i n back-calculation i s the frequent occurence of Lee's phenomenon where successively older year classes appear to have been smaller at early ages than the younger year classes. There i s also the tendency to select easily aged, faster growing specimens for back-calculation. There are several important advantages i n growth determinations by back-calculation. It i s possible to determine the size of a f i s h of any age even though specimens of each age group are not represented, i t i s possible to explore the peculiarities of growth of single year classes or individuals, and i t i s possible to determine the growth of a l l age groups i n any year. This method may also l i m i t some of the effects of selective sampling and i n -sure that the growth potential i s not underestimated (Ricker 1 9 5 8 ) . 31 The following discussion of growth i n length of Nelson River sturgeon w i l l be based mainly on calculations made by method (3) where the average back-calculated increments of growth are cumulatively totalled. This method appears to provide the best representation of growth over the greatest range of age groups i n Nelson River sturgeon. The growth curves for Nelson River sturgeon determined by method (3) are more or less typical of long l i v i n g fishes of cool-temperate or subarctic waters. Note i n Figure 8 that although the rate of growth decreases with age, neither asymptotic length nor an inflection i n growth at early ages i s apparent. From these data i t i s impossible to determine the age at which the f i r s t inflection i n growth may occur because accurate back-calculation of growth i n the f i r s t few years of l i f e i s d i f f i c u l t . The annuli v i s i b l e i n a cross-section of the pectoral spine are actually cross-sectional views of concentric cones of growth, much l i k e those i n trees. In obtaining the cross-section i t i s d i f f i c u l t to section the cone representing annulus "one" at the same point on each f i s h . This results i n a variation i n the relative diameters of the f i r s t few annuli which cannot be corrected. The Walford transformation for female sturgeon (Figure 10) produces two relatively straight lines which suggests that these f i s h have two growth stanzas. The lower segment appears to intersect the 45° diagonal at an 1^, of about 34 inches. This corresponds approximately to age 15. The upper segment l i e s close to the 45° diagonal but does not intersect i t . The Wal-r ford plot for male sturgeon i s almost identical to that of the female sturgeon except that the lower segment of the curve appears to intersect the 45° diagonal at ah L^ . of about 32 inches. Further evidence that no maximum size i s attained by sturgeon i s indicated i n Figure 6 where the empirical length of specimens i s plotted 0 10 20 30 40 50 60 L E N G T H AT A G E " T " Figure 10. Walford Transformation of Calculated Lengths of Nelson River Female Sturgeon. 33 against age. It i s seen here that after age 60, growth of female sturgeon appears to accelerate again rather than level off towards an asymptotic length. Various other studies on lake sturgeon have yielded similar results. Cuerrier (1949) and Roussow (1955) present growth curves for lake sturgeon, of Quebec that show no tendency to level out towards an asymtotic length. The maximum age of specimens i n each case was 50 and 55 years respectively. On the other hand, the curve for Wisconsin sturgeon presented by Probst and Cooper (1954) illu s t r a t e s a marked leveling towards an asymptotic length at age 80 or more. The shape of the curve at ages beyon^f 50 years, however, was determined by only one specimen. A plot of the length at any age against the following year's i n -crement i n length ( l ^ x L ^ - \ ) should produce a straight l i n e i f Nelson River sturgeon grow according to Von Bertalanffy's equation: I»t = { l - e " " K ^ t ~ t o ^ . Such a plot of back-calculated data for female sturgeon appears i n Figure 11. Again two stanzas of growth are indicated by the two straight lines which were f i t t e d by eye. The asymptotic length of the f i r s t stanza again i s about 34 inches. The second stanza also indicates an asymptotic length that appears to be between 60 and 65 inches. (b) Growth i n Length by Sexes It i s apparent from Tables III to V and Figures 6 to 8 and 13 that female sturgeon grow faster and larger and l i v e longer than male sturgeon. From back-calculated data, the growth rate of males and females to age 20 i s about the same, averaging 1.91 inches per year. Beyong age 20, however, the growth rate of the female i s greater. Between age 20 and 50, the average growth i n length of the female i s 0.49 inches per year while that of the male i s 0.37 inches per year. The growth rate of the female again accelerates beyond age 60. 34 Figure II. The Relationship Between Fork Length at any age and the Following Year's Increment in Fork Length. Nelson River Female Sturgeon. 35 Similar results for lake sturgeon were obtained by Cuerrier (1949) and Schneberger and Woodbury (1944) • Both found that the female sturgeon of Quebec and Wisconsin grew faster than the male. Probst and Cooper (1954) however found no significant difference in growth of the male and female sturgeon in four lakes in Wisconsin. Studies of other species of sturgeon have also produced varying results concerning the growth of sexes. Classen (1944), Derjavin (1922) and Roussow (1955) a l l report that the female stur-geon grows faster than the male. Classen was referring to Acipenser sturio of Spain while Derjavin and Roussow were referring to Acipenser stellatus of Europe. Probst and Cooper (1954) stated that certain Russian authors found no difference in the growth rates in males and females of the Russian sturgeon, Acipenser stellatus and Acipenser guldenstadti. It is noticeable that the growth rate in both sexes of Nelson River sturgeon decelerates at approximately age 20. It is at this point that the growth curves of the two sexes diverge. This corresponds very closely to the age of maturity of these sturgeon. (c) Growth of Nelson River Sturgeon in Various Calendar Years It i s very interesting and informative to examine the back-calc-ulated growth of fish in various calendar years. Sturgeon are admirably suited to such a study because of their extraordinarily long l i f e span. It is well known that both extrinsic and intrinsic factors have a very strong influence on the annual growth of an organism. The effect on growth of extrinsic factors alone can be determined by averaging growth in each calendar year for a number of specimens, preferably of different ages. This was done for the ten largest specimens of Nelson River female sturgeon on which back-calculated data were available. These speci-mens were representatives of year classes: 1893, 1903, 1905, 1906, 1915, 36 1916, 1919 and 1921. Year classes 1916 and 1919 are represented by two specimens. The relative growth in each calendar year was calculated for each specimen. The fi r s t ten years of l i f e were excluded from calculations on each specimen, however, because l i t t l e annual variation was evident in the first few years of back-calculated growth in a l l large sturgeon. The average relative growth in length per calendar year was then determined for the representatives of year classes 1893 to 1906 and 1915 to 1921. The sample was divided to provide some test of the consistency of the data. These data are presented graphically in Figure 12. The upper curve represents year classes 1915 to 1921 and the lower curve represents year classes 1893 to 1906. •* It is evident that these curves are relatively consistent. The factors that produce a noticeable peak in the annual growth of one group produces a similar peak in the curve representing the other. The general "straight line" trend of these curves indicates a diminishing rate of relative growth between 1915 and 1950. This may be th e actual case but i t is more likely that this trend is due to bias in the nature of the data. In calculations of the relative growth of the specimens since 1935 or 1940, a l l specimens were relatively old, large fish. On the other hand, most of the calculations prior to 1935 were based on young, small fish. These curves therefore serve to illustrate that relative growth de-creases with size and/or age rather than with calendar years. These curves suggest that growth was abnormally high during the period 1929 to 1931• Relative growth also appears to have been high in the years 1919, 1937, 1942 and 1947. These fluctuations in the relative growth of Nelson River sturgeon may be due to one or more of a number of extrinsic factors such as abundance 37 Figure 12. Average Relative Growth in Fork Length by Calendar Years of Two Samples of Nelson River Female Sturgeon . 3 8 or a v a i l a b i l i t y of food, annual difference i n water temperature or levels, etc. These data on relative growth were correlated with mean water discharges (in cubic feet per second) at a station located on the Nelson River about twenty-five miles from Sipiwesk Lake. They were also correlated with Nelson River sturgeon production s t a t i s t i c s . Although i t appears that growth may have been sl i g h t l y greater i n years of low water and/or years when population density would have been low; the correlation of these data is not sufficiently consistent to be significant. (d) Growth i n Weight of Nelson River Sturgeon The growth i n weight of Nelson River sturgeon i s presented i n Table V where the average size has been calculated for age groups of three-year intervals. These data are also presented graphically i n Figure 1 3 . Data are based on 7 3 3 specimens sampled from 1 9 5 3 to 1 9 5 6 . TABLE V. The Average Size (Round Weight i n Pounds) by Age Groups of Nelson River Sturgeon. 1 9 5 3 to 1 9 5 6 Data. Males Females Males Females Age Ave. Ave. Age Ave. Ave. Group Freq. Weight Freq. Weight Group Freq. Weight Freq. Weight 7-9 2 4.2 • • 52-54 7 32.4 8 44.7 1 0 - 1 2 * • • • 55-57 1 3 3 . 0 7 41.3 13 - 1 5 • • 1 5.5 58-60 . . • • 16-18 6 17 . 1 3 1 0 . 8 61-63 5 56.6 1 9 - 2 1 28 17.5 7 16.9 64-66 44 . 0 7 64.4 22-2 4 4 3 1 9 . 8 2 4 22.6 6 7 - 6 9 3 4 5 . 3 25-27 3 4 20.8 2 5 24.9 70-72 2 56.0 28-30 3 4 20.6 2 2 26.5 7 3 - 7 5 2 5 7 . 8 3 1 - 3 3 3 4 23.0 3 5 31.4 8 4 only 4 7 9 . 2 3 4 - 3 6 46 25.2 3 8 3 2 . 0 8 6 only • 1 7 7 . 0 3 7 - 3 9 3 4 24.7 3 8 3 1 . 4 8 8 only • 1 1 0 0 . 0 40-42 27 24.8 3 4 35.4 9 8 only 1 52.0 4 3 - 4 5 4 2 27.0 4 2 3 4 . 2 1 0 2 only 1 1 1 0 . 0 46-48 1 6 28.1 37 3 8 . 2 1 0 5 only 1 122.0 4 9 - 5 1 6 34. 3 2 2 38.7 1 1 0 only • • 1 1 0 1 . 0 Totals 3 6 1 3 7 2 39 0 20 40 60 80 100 A G E IN YEARS . Figure 13. Growth in Weight of Nelson River Sturgeon. 40 The scatter of points in Figure 13 is quite wide despite the fact that most age groups are well represented by specimens. This illustrates the variability of growth in weight of the individual. It is evident from these curves that female sturgeon grow much faster than the male sturgeon and attain a much larger size. Of 361 males and 372 females sampled from 1953 to 1956, only 5 male sturgeon exceeded 40 pounds and none exceeded 50 pounds while 97 female sturgeon exceeded 40 pounds, 40 females exceeded 50 pounds and 11 females exceeded 70 pounds. The growth curves in Figure 13 suggest that the female sturgeon grows slower than the male to age 20. This portion of the growth curve, how-ever, is not likely representative of the average growth of Nelson River sturgeon since only eight males and four females under 19 years of age are represented. It is more reasonable to assume that the rate of growth in weight of males and females is similar at these ages as in the case of growth in length determined by back-calculation. From the growth curves (fitted by eye) in Figure 13, i t is evident that the average annual increment in weight to age 20 is 0.90 pounds in both sexes. Beyond age 20 the female grows much faster than the male. From age 20 to 50, the average annual increment in weight of the male i s 0.44 pounds while that of the female is 0.68 pounds. Beyond age 50, the average increase in weight per year of the female sturgeon is about 1.0 pounds. Note that there is no indication whatsoever of an asymptotic weight in either sex. (e) The Length-Weight Relationship The length-weight relationship of male and female Nelson River sturgeon is presented in Table VI. 41 TABLE VI, Length-Weight Relationship of Nelson River Sturgeon. 1953 to 1956 and 1959 Data. Fork Males Females Length* Frequency Ave. Weight* Frequency Ave. Weight* 20.1-22.0 1 3.3 • • -22.1-24.0 1 3.0 1 3.5 24.1-26.0 . • • • 26.1-28.0 1 5.0 1 28.1-30.0 • • • • • 30.1-32.0 1 8.5 • • 32.1-34.0 2 9.1 3 14.6 34.1-36.0 4 13.8 2 11.3 36.1-38.0 17 15.0 6 19.8 38.1-40.0 28 18.4 13 19.2 40.1-42.0 54 19.7 30 20.8 42.1-44.0 76 21.8 41 26.0 44.1-46.0 60 24.7 53 28.6 46.1-48.0 55 28.4 44 32.7 48.1-50.0 24 31.2 56 36.1 50.1-52.0 4 35.0 45 39.9 52.1-54.0 2 41.5 18 47.5 54.1-56.0 1 54.5 15 50.7 56.1-58.0 . 3 59.7 58.1-60.0 7 56.6 60.1-62.0 7 70.3 62.1-64.0 . • • 3 86.7 64.1-66.0 3 96.3 66.1-68.0 2 106.0 68.1-70.0 • 1 111.0 Total 331 354 * Fork Length in inches and round weight in pounds. A logarithmic plot of these data appears in Figure 14. The regression lines were determined by the least-squares method. For males and females respectively, these regression lines are; Log W - - 3.55 + 3.002 log L Log W - - 3.84+ 3.204 log L These regression lines indicate that growth of Nelson River stur-geon i s very nearly "isometric" since the slope of these lines i s close to 3. This would more aptly apply to larger sturgeon as few specimens under 35 inches in length are represented. 42 43 These data indicate that female sturgeon are more rotund than males. This may be accounted for by the large volume of eggs carried by mature females, or the large body of fat that i s associated with the developing ovary i n immature females. No data are available on the ratio of gonad weight to body weight for Nelson River sturgeon but Cuerrier (1949) found that the weight of the gonad of Quebec Lake sturgeon accounted for as much as 12.7% and 28.8$ of the body weight of males and females respectively. Probst and Cooper (1954) found no appreciable difference i n the length-weight relationship of male and female sturgeon from Lakes Poygan, Winneconne and Butte des Morts i n Wisconsin. (f) The Relationship of Dressed Weight to Round Weight The relationship of dressed weight to round weight of Nelson River male and female sturgeon sampled i n 1953 and 1954 from the commercial fishery i s presented i n Table VII. TABLE VII. The Relationship of Dressed Weight to Round Weight of Nelson River Sturgeon Round Weight Dressed Weight Round Weight Dressed Weight Freq. Average Range Freq. Average Range 9.2-10.8 1 6.0 41.2-42.8 11 28.0 24-32 11.2-12.8 1 8.0 43.2-44.8 3 29.7 28-32 13.2-14.8 1 10.0 . 45.2-46.8 5 31.0 24-35 15.2-16.8 9 10.3 10-11 47.2-48.8 5 33.0 30-36 17.2-18.8 14 10.9 10-12 49.2-50.8 3 33.7 32-37 19.2-20.8 37 12.5 11-16 51.2-52.8 3 36.0 34-39 21.2-22.8 31 13.4 11-16 53.2-54.8 2 34.5 34-35 23.2-24.8 31 15.2 12-19 55.2-56.8 3 35.7 31-43 25.2-26.8 28 16.7 13-18 60 only 1 48.0 27.2-28.8 24 18.4 15-21 65 only 1 51.0 29.2-30.8 22 19.4 15-23 72 only 1 47.0 31.2-32.8 22 21.2 17-25 77 only 1 63.0 33.2-34.8 23 21.8 19-27 90 only 1 67.0 35.2-36.8 19 24.2 22-30 97 only 1 52.0 37.2-38.8 8 23.1 16-27 100 only 1 62.0 39.2-40.8 7 26.6 25-30 122 only 1 76.0 Total 321 Note: A l l weights are i n pounds 44 These data are presented graphically i n Figure 15» The dots represent average dressed weights and the vertical bars represent the range i n dressed weights for each two inch interval of round weight. The range i n dressed weight that i s recorded for each interval of round weight below 15 pounds and above 42 pounds cannot be considered too reliable because of the scanty data. The data presented here indicates that the relationship between round and dressed weights of Nelson River sturgeon i s very variable. Much of this v a r i a b i l i t y can be attributed to the fact that these data represent both males and females. The v a r i a b i l i t y within each sex, however, would also be f a i r l y great due to differences i n the general "condition" or the stage of reproductive maturity of the individual. Differences i n the method of dressing by various fishermen may also introduce some v a r i a b i l i t y i n the round to dressed weight relationship. The curve i n Figure 15, which was f i t t e d by eye, indicates a f a i r l y straight l i n e relationship-between. round and dressed weights. This line suggests a simple "rule of thumb" for determining dressed weights from round weights of average sturgeon: Dressed weight = 2/3 round weight (g) Comparison of the Growth of Nelson River Sturgeon with that of Sturgeon from Other Areas Curves representing growth i n length of lake sturgeon of several regions are presented i n Figure 16. These data were obtained from the following sources: Lake Nipigon, Ontario; Harkness, 1923 Lake St. Francis, Quebec; Cuerrier and Roussow, 1951 Lake St. Peter, Quebec; Cuerrier, 1949 Lake Winnebago Region, Wisconsin; Probst and Cooper, 1954 46 B O i 1 1 f 1 1 1 1 1 1 1 I ol I • ' I I I 1 1 1 1 1 1 0 5 10 15 20 25 30 35 40 45 50 55 60 A G E Figure 16. Comparison of Growth in Length of Lake Sturgeon from Several Regions. 47 These curves represent average empirical lengths. Males and females are considered together i n a l l cases. A l l age determinations were made from cross-sections of the marginal spine of the pectoral f i n with the exception of those of Lake Nipigon which were aged by means of otoliths. The curve for growth i n length of Lake Winnebago sturgeon cannot be compared directly with those for sturgeon of the other areas since i t i s based on t o t a l length while the others are based on fork length. Some comparisons of these curves could be made, however, i f to t a l lengths for each age group of %nnebago sturgeon were reduced by three to four inches. This assumption i s based on data presented by Cuerrier and Roussow (1951) who used the factor 0.9166 to calculate fork lengths from t o t a l lengths for Lake St. Peter sturgeon. This agrees with measurements made on Nelson River sturgeon. The average difference between t o t a l and fork lengths of 100 Nelson River sturgeon of various sizes that were sampled i n 1956 was 4.05 inches. Even i f the curve for Winnebago sturgeon was lowered by reducing each point on the curve, the curve for these sturgeon would s t i l l remain above the others. The curves i n Figure 16 show that Nelson River sturgeon grow slower than those from other regions with the exception of Lake Nipigon. This may be explained by the difference i n latitude of these waters. Although the Nelson River i s relatively productive, the growing season i s quite short. The growth rate of sturgeon i s highest i n Lake Winnebago which i s the most southerly lake considered. The curves for growth i n weight of lake sturgeon of these areas i s similar to those for length except that a greater difference i n the rates of growth i s apparent, ^he curves for Lake St. Francis and Lake St. 48 Peter are also interchanged, indicating that the sturgeon of Lake St. Francis grow faster in weight but slower in length than sturgeon of Lake St. Peter. The curves for growth in length and weight of Nelson River sturgeon both exhibit a marked change in slope between age twenty to twenty-) five. This correlates closely to the age of maturity of these sturgeon. The sturgeon of Lake St. Francis, Lake St. Peter and Lake Nipigon mature at a similar age to those of the Nelson River (Roussow, 1955; Cuerrier, 1949 and Harkness, 1923) but reproductive maturity is not reflected in the growth curves of these fishes. 4 9 V. REPRODUCTION OF NELSON RIVER STURGEON Without some knowledge of the age of reproductive maturity, the time and place of spawning and the reproductive capacity of a species of fi s h , i t i s impossible to properly manage and regulate a commercial fishery on a sustained yi e l d basis. These factors are of prime importance i n the establishment of regulations pertaining to the type and size of fishing gear, minimum legal sizes of f i s h , fishing areas and seasons, and production limits. Relatively l i t t l e i s known about reproduction i n sturgeon, particularly the duration of each stage i n the development of the gonad and the frequency of spawning. The investigations on Nelson River sturgeon that pertained to reproduction were designed mainly to determine the age and size at which these f i s h attain reproductive maturity. Some data were also obtained on the time and frequency of spawning. A. METHODS AND MATERIALS Each sturgeon sampled on the Nelson River was sexed and classified according to an arbitrary classification which described macroscopically the various stages i n the development and maturation of the gonad. These classifications were as follows: MALE STURGEON 1. IMMATURE: Testes small i n comparison to fat body, gray and hard. 2. MATURE: Testes white or cream i n color, lobed, much larger than fat body (see Figure 17). Subscript "S" after Stage 2 indicates that the sturgeon had spawned earlier that year ( i . e . milt easily expressed from gonad). 50 FEMALE STURGEON 1. IMMATURE: Ovary very small i n comparison to the fat body. Eggs minute and visible on the surface of the ovary only along a narrow longitudinal groove on the dorsal surface of the fat body. 2, 3 , and 4 . Gonad comprised mostly of ovary. Eggs evident on at least 1/3 to 1/2 of the surface of the gonad. Eggs pinhead or larger i n size; white, pale yellow or darkening. 5. CAVIAR TOO FAT: Eggs are present throughout the gonad and are im-bedded i n a matrix of f a t . They are grey or olive i n color and are f u l l or almost f u l l size (2 mm. to 3 mm. i n diameter) (See Figure IS). 6. CAVIAR: Eggs are f u l l size and dark olive to black i n color. They are no longer firmly attached to the ovary. L i t t l e or no fat i s evident on the surface of the ovary. Subscript "Sw after stages 2, 3 and 4 indicates that the sturgeon has spawned out (i. e . a few unspawned eggs are l e f t on the ovary or i n the body cavity. B. DEVELOPMENT OF THE GONAD In the development of the sturgeon gonad, adipose tissue appears f i r s t as large paired bodies which run the length of the coelomic cavity. As the f i s h matures, testicular or ovarian tissue, which f i r s t appears as a narrow fold on the dorsal surface of the adipose body, invades and replaces the fat which almost disappears at reproductive maturity. The gonad of a sturgeon (particularly the female) matures very slowly and the period between spawnings i s of much longer duration than i n most other fishes. This i s suggested by the many stages of gonad development 51 Figure 18. Female Lake Sturgeon. The Enlarged Ovaries are Typical of Stage 5 (Caviar Too Fat). 52 that are evident at any season of the year. Cuerrier (1949) describes six stages i n the development of both testis and ovary of lake sturgeon of Lake St. Peter i n Quebec. He also refers to other workers who described from four to seven stages i n the development of the gonad of various species of sturgeon. The f i r s t stage described i s usually the immature state where the gonad is just beginning to develop. The last stage usually describes the spawned out state. It was hoped that an analysis of data concerning these stages of development would provide some clue to the age of maturity and the frequency of spawning of Nelson River sturgeon. C. THE TIME AND PLACE OF SPAWNING The lake sturgeon spawns i n fast water near rapids and f a l l s i n the spring. Bajkov (1930) states that Manitoba sturgeon usually spawn below rapids i n ten feet of water while Cuerrier (1949) and Harkness (1936) say that eastern lake sturgeon spawn near rapids i n shallow water. Bajkov (1933) adds? "the actual spawning takes place usually very close to rapids or waterfalls and very often under waterfalls i n the white-boiling water." The eggs are swept downstream and usually come to rest on mud or clay (Harkness, 1936 and Cuerrier, 1949). Bajkov (1930), Harkness (1936) and Williams (1951) claim that lake sturgeon sometimes spawn i n lakes on shallow beaches. The date of spawning of lake sturgeon i n Canada i s usually i n May and/or June. Manitoba sturgeon usually spawn during the l a t t e r half of May and the f i r s t week of June. Rodd (1926) found some ripe females between June 10 and 20 at the north end of Lake Winnipeg but he saw no ripe males after June 15. Bajkov (1930) says that Lake Winnipeg sturgeon spawn from mid-May to the beginning of June. 53 Nelson River sturgeon appear to spawn sl i g h t l y later than Lake Winnipeg sturgeon since an occasional ripe male has been taken i n the Nelson River commercial fishery after June 10 i n several years. Of speci-mens examined i n 1955, 1956 and 1959, 7 out of 77 male sturgeon were ripe (milt present) on or before June 16. By June 21, however, only 5 of 83 males examined were ripe and of 30 males examined after June 21, none were ripe. Very few females sampled after June 10 i n any year were i n spawning condition. It i s of interest that the Indians of southern Manitoba claim that the sturgeon spawns when the oak trees begin to leaf out. Northern Manitoba Indians believe that the budding of the poplar heralds the spawn-ing of sturgeon. Harkness (1923 and 1936) states that lake sturgeon of Lake Nipigon spawn about June 1 at water temperatures of about 56°F. Cuerrier (1949) says that lake sturgeon of Lake St. Peter i n Quebec spawn from mid-May to mid-June with the peak at the end of May (54° to 60° F). He adds that lake sturgeon of the Upper Ottawa River spawned between June 15 and 20 i n 1947 (53° to 58° F). Vladykov (no date) says that Quebec sturgeon spawn from the end of May to the beginning of July (65° F) and Roussow (1957) says that they spawn i n late May and the f i r s t three weeks of June at water temperatures of 9° to 18° C (about 48° to 64° F). Wirth (1959) reports that most sturgeon of the Wolf River i n Wisconsin spawned i n the f i r s t week of May i n 1959. Williams (1951) claims that lake sturgeon of Michigan spawn at water temper-atures of 60° to 70° F. Although most sturgeon are spring spawners, i t is apparent that some species also spawn i n the f a l l . Barannikova (1954) suggests that cer-tain races of Acipenser guldenstadti i n Russia spawn i n the f a l l and Derjavin (1922) refers to f a l l spawning races of Acipenser stellatus. 54 D. THE AGE OR SIZE OF REPRODUCTIVE MATURITY The sturgeon matures at a very late age compared to most other species of fish. Although one Eurasian sturgeon is reputed to mature at three to five years of age (Roussow, 1957), most species of sturgeon do not mature before age ten to fifteen years. The age of maturity of various species of sturgeon is summarized in Table VIII. TABLE VIII. The Age of Reproductive Maturity of Various Species of Sturgeon Species of Age of Maturity Sturgeon Males Females Region Reference A. fulvescens 22-28 22-28 Ontario Harkness, 1953 A. fulvescens 14 23 Quebec Cuerrier, 1949 A. fulvescens 12-19 14-23 Quebec Roussow, 1957 A. fulvescens 15 22 Wisconsin Probst, 1954 A. transmontanu6 11-12 California Pycha, 1956 A. sturio 7-9 8-14 • Roussow, 1957 A. sturio 10-11 14-15 Spain Classen, 1944 A. guldenstadti 9 • Russia Kuzmin, 1954 A. guldenstadti 8-14 13-20 • Roussow, 1957 A. schrencki 8-10 • Roussow, 1957 A. stellatus 12-15 14-18 Russia Derjavin, 1922 A. baeri 10-12 12-14 • Roussow, 1957 A. ruthenus 3-7 5-12 • Roussow, 1957 Huso huso 12-14 16-18 • Roussow, 1957 Huso dauricus • 18-20 • Roussow, 1955 Nelson River lake sturgeon mature at slightly greater ages than those in Eastern Canada. This is suggested in Table IX where the number, by age groups, of Nelson River female sturgeon at each stage of reproductive maturity is summarized. These data are from samples obtained on the Nelson River in 1955 and 1956. These data suggest that most Nelson River female sturgeon mature and begin to spawn between 25 and 30 years of age. Only two females under age 25 were spawned out and few "ripening" females were under 28 years of age. No immature females were over 30 years of age. 55 TABLE IX. The Frequency, by Age Groups, of Nelson River Female Sturgeon at Each Stage of Reproductive Maturity Age Group 1 Immature 2, 3, 4 Developing 5, 6 Ripening* S Spawned Out Totals 17-19 2 • 2 20-22 7 . 1 . 8 23-25 22 5 • ' 2 29 26-28 7 3 3 2 15 29-31 2 6 3 • 11 32-34 . 8 6 3 17 35-37 8 6 2 16 38-40 2 5 2 9 41-43 5 7 • 12 44-46 6 9 1 16 47-49 5 10 2 17 50 & over • 5 17 7 29 Totals 40 53 67 21 181 * It is assumed that females at Stages 5 and 6 would have spawned in one to two years. These observations agree closely to those made by Kooyman (1955) who made a similar analysis of data obtained on the Nelson River in 1953 and 1954. He found that female sturgeon mature between the ages of 20 and 30 years, with the majority of fish s t i l l being immature at age 25. The age at which Nelson River female sturgeon mature and spawn (25 to 30 years) corresponds to a round weight of about 24 to 29 pounds and a fork length of about 42 to 45 inches. The male Nelson River sturgeon appears to spawn at an earlier age than the female. The exact age of maturity was very difficult to determine by macroscopic examination of specimens, however, because most of them were obtained well after the spawning period and few definit ely mature males (those wiih milt) were sampled. The youngest of fourteen "ripe" males sampled in 1955, 1956 and 1959 was 20 years of age. Three of them were 22 to 23 years of age and the rest were 30 to 40 years of age. Of the other 181 males sampled in these three years, most of the individuals over 20 years 56 of age appeared to be fully developed and mature. This suggests that most Nelson River males first spawn at about 20 years of age. This corresponds to a round weight of about 18 pounds and a fork length of about 38 inches. It is significant that these estimates of the age and size of reproductive maturity of Nelson River sturgeon correspond very closely to the inflections that appear in the curves for growth in length and weight of these sturgeon (Figures 6 and 13). A comparison of the age and the size of reproductive maturity of lake sturgeon of several regions is presented in Table X. TABUS X. The Age and Size at Reproductive Maturity of Lake Sturgeon of Various Regions MALES Age Weight Fork Length Reference Region (years) (lbs.) (ins.) Nelson River 20 18 38 This paper St. Lawrence River 14 8-10 30 Cuerrier, 1949 Ontario 22-28 • 35 Harkness, 1953 Quebec • 11•5(youngest) . Vladykov, no date Wisconsin 15 7-8 • Probst, 1954 FEMALES Age Weight Fork Length Region (years) (lbs.) (ins.) Reference Nelson River 25-30 24-29 42-45 This paper St. Lawrence River 23 25-30 40 Cuerrier, 1949 Ontario 22-28 • 40 Harkness, 1953 Quebec • 17(youngest) • Vladykov, no date Wisconsin 22 30 * Probst, 1954 E. THE FREQUENCY OF SPAWNING IN STURGEON It is generally conceded that no species of sturgeon regularly spawns each year but the interval between spawnings is not definitely known for any species. Several authors have voiced opinions on the periodicity of spawning in various species of sturgeon but few have presented conclusive 57 evidence. Classen (1944 and 1947) states that male Acipenser sturio of Spain spawn each year while females spawn every two years. Cuerrier (1949) quotes Borodin as saying that there is a two year interval between spawn-ings in Acipenser oxvrhynchus and Acipenser guldenstadti. Cuerrier also quotes Menshikov who believes there is a two year cycle of spawning in Acipenser ruthenus. Most biologists who have studied aspects of reproduction in the lake sturgeon conclude that the interval between spawnings varies from two to five years. Vladykov (no date) states that lake sturgeon spawn every two to three years and Harkness (1953) believes that there is a two to four year interval between spawnings. Wirth and Cline (no date) provide definite proof that at least some male lake sturgeon in Wisconsin spawn every year, - two marked males were observed on the spawning grounds in "ripe" condition in two successive years. Probst (1954) states that male lake sturgeon of Wisconsin spawn every second year and females spawn every fifth or sixth year. Kooyman (1955) believes that the interval between spawnings of Nelson River female sturgeon is three to four years since less than 30$ of mature specimens sampled in 1953 and 1954 were ripe or spawned out. He also suggested that older mature female sturgeon spawn more frequently than young ones. Cuerrier (1949) is of the opinion that the male lake sturgeon of the St. Lawrence River spawns twice as often as the female. He bases this assumption on the fact that he observed twice as many males as females on the spawning grounds. He concludes that the male spawns every two to three years and the female spawns every three to five years. Roussow (1957) states that there is a four to seven year spawning cycle in the female lake sturgeon of Quebec. He bases these observations on a study of growth stanzas in sturgeon. In the magnified image of a 58 cross-section of the marginal "spine" of the pectoral fin, closely packed bands of annuli are often seen to alternate with widely spaced bands of annuli. Roussow assumed that the maturation of the gonad was enough of a strain on the physiology of the sturgeon that i t was responsible for a decrease in growth rate. He therefore interpreted these growth stanzas as an indication of first and subsequent spawnings; i.e. he suggested that the end of each closely packed bank of annuli corresponded to the end of each spawning cycle and that the widely spaced band of annuli following, corresponded to the resting period prior to the next development and maturation of the gonads. In his analyses, Roussow did not consider the possible effect of extrinsic and other intrinsic factors which doubtlessly have a considerable effect on growth of sturgeon. It is not possible to determine precisely the interval between spawnings of Nelson River sturgeon from the type of data obtained there in 1955, 1956 and 1959. Some of these data however can be used to make a reasonable estimate. In Section V-A, five definite stages in the development and matur-ation of the ovary were described. Experienced sturgeon fishermen claim that these stages are recognizable at any season of the year but that spawning occurs only in the spring. It is therefore likely that the duration of each stage is relatively uniform, i.e. about one year. Females at Stage 6 (Caviar) in the late spring or early summer would therefore spawn the following spring. Those at Stage 5 (Caviar Too Fat) would spawn in about two years and those at Stages 1 to 4 would spawn in three to five years. This suggests that the average interval between spawnings of Nelson River female sturgeon i s about four years. A higher ratio of spawned out and caviar bearing females in the older age groups suggested that older sturgeon spawn more frequently than 59 younger ones. (Those at Stages 5 and 6 also carry a batch of eggs at Stages 2 or 3.) The spawning frequency of various age groups of Nelson River female sturgeon i s indicated i n Table XI. These data were obtained on the Nelson River i n 1955 and 1956. TABLE XI. The Frequency and Ratio of Female Sturgeon, by Age Groups, at Each Stage of Gonad Development Age Group 1 2, 3 & 4 5 6 Spawned out (s) Average 5, 6 & S 24 & under 25-34 35-39 50 & over 25 (.81) 16 (.31) • • 3 (.10) 19 (.37) 26 (.37) 5 (.17) 1 (.03) 9 (.17) 29 (.41) 9 (.31) 3 (!o6) 8 (.11) 8 (.28) 2 (.06) 5 (.10) 7 (.10) 7 (.24) .03 .11 .21 .28 Since relatively few specimens are represented i n each category, the average ratio of spawning or near-spawning females was calculated i n the last column. From these data i t appears that about 28$ of female sturgeon of age 50 and over w i l l spawn i n any year. This suggests that older female sturgeon spawn every three to four years. By the same reason-ing i t would appear that 35 to 49 year old females spawn every five years. This method cannot be used to determine the frequency of spawning of younger sturgeon because a relatively high ratio are immature. It can be approx-imated however by excluding immature fish from the calculations. Thus, of 36 mature females of age 25 to 34, an average of about 6 were represented i n each of Stages 5, 6 and S. This suggests that these sturgeon spawn every six years. In attempting to determine the frequency of spawning of Nelson River female sturgeon by these methods i t must be assumed that the sample obtained i s representative of the population as a whole rather than either the spawning group or the non-spawning segment of the population. Since these specimens were captured at various depths and currents of water and 60 i n many different locations, i t i s reasonable to assume that they were representative of the population as a whole. The fact that a l l stages of development of the gonad were well represented provides further confidence that the whole population was adequately sampled. No attempt was made to determine the spawning frequency of male sturgeon because few were s t i l l ripe at the time of sampling. It was there-fore impossible to calculate the proportion of mature males that had spawned i n any year. 61 VI. THE EFFECT GF THE COMMERCIAL FISHERIES ON NELSON RIVER STURGEON Sturgeon were, at one time, found in great abundance in most of the waters of the Northern Hemisphere. Over-exploitations, dams, canals and pollution, however, are responsible for a very great reduction in numbers of a l l species of sturgeon. Only in small isolated bodies of water far from civilization, where a fishery is unprofitable, are sturgeon present in numbers which anywhere resemble their past abundance. The important sturgeon fisheries of Russia and Eastern Europe are declining despite intensive research, fish culture and strict legislation (Roussow, 1955). The once important sturgeon fisheries of Western Europe no longer exist. Meyr (1950) says that there was formerly a sturgeon run in a l l large German rivers but that they are now becoming extinct in those waters. Ehrenbaum (1926) suggests that pollution and shipping are important factors in the disappearance of German sturgeon and warns that the protection of sturgeon should not be relaxed. Classen (1947) says that sturgeon were once abundant in Spain but that they are now found only in the Guadalquivir River. He claims that dams are primarily responsible for their disappear-ance. Nowhere have sturgeon been more depleted than in North America. Early explorers and settlers describe our waters as teeming with sturgeon. The rate of exploitation was low prior to 1800 but large numbers were killed during the latter half of the last century and the early part of this century (Roussow, 1955). The depletion of sturgeon in the Great Lakes in the last century has been tremendous. Over 7,000,000 pounds were produced in 1880. By 1917, 62 however, the annual production had fallen to 100,000 pounds (Roussow, 1955)* Van Oosten (1936) stated that sturgeon are now merely "museum curiosities" in the Great Lakes. Production in the St. Lawrence River i s also decreasing rapidly (Roussow, 1955)* Evermann and Latimer (1910) said the Lake of the Woods was once considered the greatest sturgeon pond in the world. Over 7,500,000 pounds of sturgeon were taken from 1690 to 1900. Between 1900 and 1925, however, less than 1,000,000 pounds were produced and only 25,000 pounds were taken from 1925 to 1947 (Oarlander, 1947). Evermann and Latimer (1910) and Carlander (1947) blame over-exploitation for the disappearance of these sturgeon. The sturgeon of Lake Simcoe were reduced to the point of extinction by fishing (McCrimmon, 1956). From 1881 to 1898 a total of 136,500 pounds of sturgeon were produced. Since then, however, only one sturgeon has been reported and i t was believed to have escaped from an impoundment during a flood. Other reports of serious depletion of sturgeon by over-fishing concern the St. John River, the Fraser River and certain rivers in California. Rodd (1926) reports a 97$ reduction in production on the St. John River between 1880 and 1886 and a 98.3$ reduction in production on the Fraser River between 1897 and 1905. Pycha (1956) comments on the serious depletion of sturgeon in California waters. The history of the sturgeon fishery in Manitoba is l i t t l e different from that in other parts of North America. Few sturgeon were taken in Lake Winnipeg, Manitoba's principal sturgeon producer, before com-pletion of a railroad in 1887 which linked Manitoba to the Eastern markets. Thereafter, production rose gradually as prices and markets expanded. By 63 1896 the annual production was approximately 175,000 pounds and by 1900 production had reached a peak of 981,500 pounds. This high rate of exploitation resulted in depletion of sturgeon stocks and production be-gan to decrease despite good prices. This prompted closure of the fishery in 1910 when only 30,000 pounds were taken (Harkness, 1936). The fishery was recommended in 1916 due to the war need. Produc-tion in that year amounted to 118,600 pounds but f e l l to 7,500 pounds by 1920. Rising prices from 1922 to 1928 resulted in another production increase to 1924 after which i t decreased drastically (Harkness, 1936). Lake Winnipeg sturgeon stocks never recovered from the over-exploitation of these early fisheries. More recent fisheries a l l failed after a relatively short period and production was very low in comparison to that at the turn of the century. The Nelson River was first fished for sturgeon in 1907 but i t wasn't until 1917 that they were fully exploited (see Figure l ) . The second major sturgeon fishery persisted for most of the 1920's; a period during which sturgeon prices rose steadily. Production, however, followed the trend of rising prices only to 1924 and f e l l drastically there-after due to depletion of stocks. This resulted in the closure of this fishery in 1929. The Nelson River was again opened for sturgeon fishing in 1937. Despite a steady rise in prices, production began to f a l l after 1941. Depletion of stocks prompted the closure of this fishery in 1946. The most recent fishery commenced in 1953 and terminated in I960. Production remained relatively steady to 1957 but decreased markedly in each of the last three years. Since sturgeon prices and fishing effort was high throughout this period, the failure of the fishery is also attributed to depletion of sturgeon stocks. 64 It is evident from the low production totals of the last two fisheries that Nelson River sturgeon stocks never fully recovered from the serious depletion of the 1920's. A l l other major sturgeon fisheries in Manitoba; the most important of which are the Winnipeg, Saskatchewan and Churchill River fisheries, also failed after relatively short periods of time. In each case, the production totals of the more recent fisheries f e l l far short of the amounts taken in the first major fishery when virgin stocks were exploited. A. THE EFFECT OF THE PRESENT FISHERY ON STOCKS OF NELSON RIVER STURGEON The failure of each sturgeon fishery on the Nelson River i s obviously the result of depletion of stocks. Annual recruitment and growth increment has been insufficient to sustain these fisheries at the rate of exploitation that prevailed. If this hypothesis is valid, i t is to be expected that the fishery has had a profound effect on the age and size structure of the population, the catch per unit of effort of the commercial fishery, and the year class strength. These are discussed in the following sections. (a) Changes in the Age Structure of Nelson River Sturgeon from 1953 to 1959. ; ; The age composition of the Nelson River sturgeon sampled from the commercial fishery from 1953 to 1956 and 1959 i s presented in Table XII and Figure 19. The curves in Figure 19 which represent the percent -frequency of specimens by age groups have been smoothed by means of a moving average involving five mid-points of age groups. 65 TABLE XII. The Age Composition of Sturgeon Sampled from the Nelson River Commercial Fishery from 1953 to 1956 and 1959. Males Females Age A l l A l l Groups 1953 1954 1955 1956 1959 Years 1953 1954 1955 1956 1959 Years Combined 15 & under • 1 1 • 2 • • 1 • • 1 3 16-18 2 1 1 1 1 6 1 • • 1 • 2 8 19-21 2 4 5 13 4 28 2 • 5 1 2 10 38 22-24 2 6 9 19 7 43 • 3 13 8 3 27 70 25-27 4 6 7 12 1 30 2 4 13 5 4 28 58 28-30 6 8 5 8 1 28 6 1 13 1 2 23 51 31-33 5 13 9 4 1 32 12 8 9 4 4 37 69 34-36 5 13 13 9 3 43 7 10 H 1 2 34 77 37-39 4 13 5 8 1 31 6 20 7 2 • 35 66 40-42 2 14 6 5 4 31 9 7 10 3 1 30 61 43-45 8 20 6 7 1 42 7 16 11 4 1 39 81 46-48 8 3 5 1 17 2 15 16 4 • 37 54 49-51 4 1 5 1 9 7 5 2 24 29 52-54 3 2 5 • 2 5 1 • 8 13 55-57 • 1 1 1 3 1 2 • 7 8 58-60 61-63 • • • • 2 2 1 • 5 5 64 & over 1 • • 1 3 10 2 5 • 20 21 Totals 40 114 74 92 25 345 59 110 129 48 21 367 712 Summary of Data Presented in Table XII 1953 1954 mi 1956 mi A l l Years Modal Age of Males 44 44 35 23 23 23 & 35 Mean Age of Males 35.0 37.2 33.2 30.1 29.7 33.7 Modal Age of Females 32 38 47 23 26 & 32 44 Mean Age of Females 40.8 44.3 37.2 40.9 31.1 40.0 Mean Age of Both Sexes 38.5 40.7 35.8 33.8 30.6 37.0 Note: Mean ages were calculated on the basis of grouped data. These data indicate that the age of sturgeon sampled from the Nelson River commercial fishery has decreased noticeably from 1953 to 1959. This is most apparent in the case of the males where the trend to younger fish is more regular and pronounced. The general trend is well illustrated in Figure 19 . The shape of the curves indicates a pronounced increase in the number of young fish taken from year to year. The depression that develops near the peak of the 6 6 A G E G R O U P S Figure 19. The Age Composition of Sturgeon Sampled from the Nelson River Commercial Fishery from 1953 to 1,956 and 1959. 67 curve in 1955 and continues through 1956 and 1959 illustrates the effect of the fishery on fish of age thirty to forty. These are the age groups which were most vulnerable to the twelve inch g i l l nets which were used in this fishery. The seriousness of this depletion is emphasized by the fact that a change in age composition can be demonstrated in as short a period as six years. This is especially so in the case of this particular species where the number of fish in the fishable population is always large in relation to the number of recruits. (b) Changes in the Size Structure of Nelson River Sturgeon from 1953 to 1959.  The size composition (round and dressed weights) of Nelson River sturgeon sampled from the commercial fishery from 1953 to 1959 is presented in Table XIII and XIV. TABLE XIII. The Size Composition (Round or Live Weight) of Sturgeon Sampled from the Nelson River Commercial Fishery from 1953 to 1956 and 1959. Weight Males Females  Group A l l A l l (Lbs.) 1953 1954 1955 1956 1959 Years 1953 1954 1955 1956 1959 Years Combined 8 only • • 1 1 • • • * 1 9 only * 1 • 1 • • • • o 1 10-12 • 3 2 1 6 1 • • 1 2 8 13-15 • 2 6 5 2 15 1 1 4 • 6 21 16-18 3 15 11 19 6 54 • 4 8 3 15 69 19-21 7 32 13 15 4 71 3 9 10 3 3 28 99 22-24 12 24 14 19 6 75 2 8 13 4 6 33 108 25-27 6 17 6 11 4 44 3 7 10 4 3 27 71 28-30 5 12 5 11 2 35 9 16 15 4 3 47 82 31-33 3 10 5 3 • 21 7 15 12 3 2 39 60 34-36 2 3 • 2 1 8 9 17 12 8 1 47 55 37-39 1 . 1 1 3 5 7 7 1 1 21 24 40-42 1 1 1 3 7 7 14 4 2 34 37 43-45 . . • 1 2 4 5 3 1 15 16 46-48 1 1. 3 4 2 2 • 11 12 49-51 • 2 1 • 1 1 5 5 52-54 1 2 4 4 2 1 13 14 55-57 • 1 3 3 • • ' 7 7 58-60 • 1 1 • 1 • 3 3 61-63 • • • • 1 1 • 2 2 68 TABLE XIII continued Weight Males Females  Group A l l A l l (Lbs.) 1953 1954 1955 1956 1959 Years 1953 1954 1955 1956 1959 Years Combined 64-66 72 only . 74 only . 77 only . 84 only . 86 only . 90 only . 97 only . 100 only . 101 only . 122 only . Totals 40 116 65 91 28 340 1 • • 1 1 1 • 2 3 3 • 1 2 2 1 • 1 1 • 1 1 1 • - 1 1 1 1 • 1 1 • • 1 1 1 • 1 1 • 1 • 1 1 1 • • • 1 1 114 122 48 26 369 709 Summary of Data Presented in Table XUI 1953 1954 mi 1256 1959 A l l Years Modal Wt. of Males 23 20 23 17 & 23 17 & 23 23 Mean Wt. of Males 25.3 23.6 21.9 22.6 22.0 23.1 Modal Wt. of Females 29 & 35 35 29 35 23 29 & 35 Mean Wt. of Females 36.0 35.9 32.6 36.6 33.6 34.7 Mean Wt. of Both Sexes 31.7 29.7 28.8 27.4 27.6 29.2 Note: Mean round weights are calculated on a basis of grouped data. 69 TABLE XIV. The Size Composition (Dressed Weight) of Sturgeon Sampled From The Nelson River Commercial Fishery Between 1953 and 1959. Weight Group In Pounds 1953 1954 1957 1958 1959 10-12 4 40 154 169 40 13-15 21 19 124 118 41 16-18 20 23 96 99 13 19-21 12 19 53 48 7 22-24 16 18 27 42 8 25-27 8 13 26 26 1 28-30 4 4 12 17 2 31-33 4 3 8 8 2 34-36 2 5 3 7 1 37-39 • 2 • 1 1 40-42 * 1 4 1 43-45 1 2 6 1 46-48 2 • 1 1 49-51 • 1 • 1 • 52-54 • • 1 1 55-57 2 58-60 2 • 63 only 1 1 • 64 only • • 1 67 only 1 • • 76 only • • 1 • 79 only • • 1 • • Total No. 92 152 510 552 120 Total Weight (lbs.) 1861 3010 8517 9655 1965 Mean Weight (lbs.) 20.2 18.1* 16.7 17.5 16.4 * This figure includes data on 625 other sturgeon whose individual weights were not available. Note: Mean dressed weights were calculated on the basis of grouped data. It is readily apparent from these data that the average size of Nelson River sturgeon has decreased between 1953 and 1959. This trend is most evident in the dressed weight statistics which include by far the great-est number of samples. The seriousness of this depletion is again emphasized by the fact that a change in size composition can also be demonstrated in as short a period as six years. 70 (c) The Catch Per Unit of Effort The catch per unit of effort; the production i n pounds (dressed weight) of sturgeon per fisherman per year, i n the past two periods of commercial fishing on the Nelson River i s summarized i n Table XV. TABLE XV. The Average Catch Per Unit of Effort i n the Nelson River Sturgeon Fisheries of 1937 to 1946 and 1953 to I960 Production No. of Ave. Catch Year (Pounds) Fishermen Per Man (Pounds) 1937 15,000 17 880 1938 30,000 19 1580 1939 26,000 20 1300 1940 26,400 24 1100 1941 25,200 21 1210 1942 15,400 25 620 1943 10,600 30 350 1944 9,200 27 340 1945 13,400 29 460 1946 5,800 44 130  1953 27,000 33 820 , 1954 30,900 39 790 1955 24,400 46 530 1956 27,600 50 550 1957 26,100 59 440 1958 16,600 53 310 1959 9,500 41 230 1960 3,500 49 70 Note: Production figures are rounded off to the nearest 100 pounds and average catches are rounded off to the nearest 10 pounds. It i s readily apparent from these data that the catch per unit of effort i n both periods of fishing decreased steadily and substantially. It i s also apparent that fishing success i n the 1937 to 1946 fishery was almost twice that of the 1953 to I960 fishery. Statistics regarding f i s h -ing effort i n the fishery of 1921 to 1927 are not available. Nevertheless, the very high production figures of this period suggest that fishing success was much higher than either of the two last fisheries. It i s very unlikely that this decline i n the annual catch per 71 fisherman is the result of changes in fishing intensity. An eightfold rise in the price paid to fishermen for sturgeon from 1937 to 1946 and a slight increase from 1953 to I960 should have increased the incentive to fish during these periods. The average proficiency of the fishermen should also have increased during each period of fishing because the majority of the fishermen were local residents who took out licenses every year. Neither should government restrictions have influenced the fishing intensity. The length of the fishing season was reduced only once during the course of either fishery (a 15$ decrease in 1946). The production limit was also decreased only once during the course of either fishery (1946) and this had no effect because; production was lower than the limit that year too. No changes were made in regulations regarding mesh size of gear or the number of nets allowed per license. It is also very unlikely that the steady decline in fishing success was due to changes in the catchability of the sturgeon. It is true that variations in water levels or in the date of spawning can effect the dispersal or concentration of the sturgeon and hence, their vulnerability to capture. Certain combinations of water levels, temperature and currents can also influence the amount of floating and semibuoyant debris and drifting filamentous green algae which can very greatly reduce the efficiency of the fishing gear. These factors however should be expected to produce only random variations in the catch per unit of effort. The very noticeable and orderly decrease in catch per unit of effort within each fishery and even between fisheries along with the f a i l -ure of the last three fisheries suggests that the sturgeon of the Nelson River have been over-exploited and serious depletion of stocks has resulted. This depletion was so great in each of the last three fisheries that the effect i s evident from one fishery to the next despite the fact that they were separated by six or seven year closures. 72 (d) Year Class Strength Year class representation by sturgeon sampled from the Nelson River sturgeon fishery from 1953 to 1956 and 1959 is illustrated in Figure 20. The few representatives of year classes prior to 1&90 and after 1940 have been omitted. The time and duration of each commercial fishery to 1940 is indicated by the horizontal bars above the histogram. The poor representation of year classes prior to 1910 and after 1935 can be attributed to high natural mortality among older sturgeon and to the low selectivity of the fishing gear for very old or very young sturgeon. If annual recruitment of young sturgeon from 1910 to 1935 had been equal, one would expect the representation of these year classes in recent samples to be in proportion to the length of time they had been exposed to a uniform mortality. The 1910 to 1935 year classes were vulnerable only to the last two fisheries. A l l of these year classes were vulnerable to the 1953 to I960 fishery but only those up to about 1924 were vulnerable to the 1937 to 1946 fishery. One would therefore expect the year class distribution of recent samples (as in Figure 20) to be at a peak in the early 1920's, f a l l off uniformly but rather abruptly on the left for older year classes and uniformly but more gradually on the right for more recent year classes. Since this is only partly so, i t is evident that changes in the fishery account only in part for the relative representation of year classes. The differences that are apparent in the strength of year classes from 1910 to 1935 are therefore most likely due to changes in annual recruitment of young sturgeon. There is also some evidence that recruitment was low during periods of intense fishing which suggests that recruitment of young sturgeon 73 36 -33 " 30 -O or 24 21 O 1 8 • or U J CO 15 -9 -6 -3 -YEAR CLASSES Figure 20. Year Class Representation of Sturgeon Sampled from the Nelson River Commercial Fishery from 1953 to 1956 and 1959. 74 i s directly related to the size of the adult population. These apparent changes i n the age and size structure of the Nelson River sturgeon population, fishing success and strength of year classes could possibly be due to bias or random variations i n the sample or to changes i n regulations or fishing methods and intensity. This i s very unlikely the case, however, because samples were obtained i n roughly the same manner and areas each year and the fishery i t s e l f never changed markedly. Some of these data also relate to the fishery as a whole rather than to samples only. Furthermore, this trend to sturgeon of smaller size and age and to poorer catches i s quite orderly and consistent and i s established by several lines of numerous data. It i s therefore concluded that the changes that are apparent i n the samples are true reflections of changes that have occurred i n the stur-geon population and that they are the result of depletion of stocks by the commercial fishery. B. DISCUSSION It i s quite obvious that Nelson River sturgeon have been very seriously depleted i n numbers over the past forty years and that over-exploitation by the commercial fishery i s responsible. Several aspects of the l i f e history, the habits and the value of this atypical species of f i s h renders i t highly susceptible to depletion. The lake sturgeon i s a relatively slow growing fish with an exceptionally long l i f e span. Though they can become very numerous, natural population turnover i s very slow. An abnormally low rate of recruitment i s apparently compensated for by an abnormally low rate of natural mortality. The reproductive capacity of this species i s f a i r l y low despite 75 the large numbers of eggs laid by the average female. (Cuerrier, 1949> determined that each female produced an average of 5831 eggs per pound of body weight.) They mature at a very late age and subsequent spawnings are at intervals of several years. The high market value of sturgeon (about one dollar per pound for their flesh and several dollars per pound for caviar) provides a very strong incentive to employ maximum fishing effort. A fisherman can realize a good profit at daily catches as low as two or three sturgeon. Sturgeon are also very vulnerable to capture at certain times of the year. They congregate at falls and in river channels in the spring, shallow bays in the summer and deep holes in the winter. 76 VII. FUTURE MANAGEMENT OF THE NELSON RIVER STURGEON FISHERY The Nelson River can be expected to produce a sustained yi e l d of sturgeon i n the future only i f this species i s offered much more protection and i f the fishery i s very carefully and s t r i c t l y managed. Present stocks of Nelson River sturgeon are obviously much too low to support a profitable commercial fishery. Further depletion may also reduce the population to a level where natural reproduction i s i n -sufficient to increase or even sustain the population at i t s present size. These sturgeon should therefore be completely protected for a period of at least ten years to allow stocks to increase to a size that w i l l support a profitable commercial fishery on a sustained y i e l d basis. A. PRODUCTION LIMITS Even though Nelson River sturgeon are protected for a period of years, future production limits w i l l have to he greatly reduced i f a sus-tained yield i s to be realized. The failure of the last two fisheries reveals that this river i s incapable to yielding even 25,000 pounds of sturgeon (dressed weight) per year. The best evidence available suggests that the average annual re-cruitment to the Nelson River sturgeon fishery i n the past thir t y years was about 10,000 pounds. It i s evident from Table XV that the catch per unit of effort was quite similar i n the last few years of the fisheries of 1937 to 1946 and 1953 to I960. I f the catch per unit of effort i n both fisheries i s comparable, i t is reasonable to assume that the sturgeon population was equal or similar i n size i n 1946 and I960; the years that each of these 77 fisheries collapsed. It would then follow that the production from 1953 to I960 would be equal or similar to the recruitment to the fishery from 1947 to I960. Since the total catch from 1953 to I960 was 165,600 pounds, the average annual recruitment to the fishery in the fourteen year period from 1947 to I960 must have been about 12,000 pounds. This figure would be, at best, the maximum annual recruitment to the fishery. The catch per unit of effort in the last year of the 1953 to I960 fishery was considerably lower than that of the 1937 to 1946 fishery. The average catch per unit of effort in the 1953 to I960 fishery (450 pounds per licensee per year) was also 65.2$ lower than that for the 1937 to 1946 fishery (690 pounds per licensee per year). This would suggest that the sturgeon population was smaller at the end of the 1953 to I960 fishery than at the end of the 1937 to 1946 fishery and that recruitment to the fishery was considerably less than 12,000 pounds per year from 1947 to I960. The fishing effort expended during the 1921 to 1929 fishery is un-known. The value of sturgeon during this fishery was quite high however, so it i s very likely that fishing effort was as great as that from 1937 to 1946 and that the sturgeon were reduced to as low a level of abundance in 1929 as in 1946. The total catch from 1937 to 1946 should therefore be equal or similar to the recruitment to the fishery in the seventeen year period from 1930 to 1946. As the total catch from 1937 to 1946 was 177,000 pounds, the average annual increment to the fishery should have been about 10,000 pounds. It is very likely that the average annual recruitment to the fishery in the past thirty years would be closer to the 10,000 pound estimate than the 12,000 pound estimate. This figure may have been the maximum possible recruitment to the fishery at the low level of abundance at which the sturgeon population has been held during this period. 78 It i s therefore recommended that future sturgeon production limits on the Nelson River be limited to 10,000 pounds (dressed weight) per year. It should be pointed out that this limit would apply only to that portion of the Nelson River which was fished during the course of the last fishery. From 1953 to I960, fishing was permitted on a 280 mile stretch of the Nelson River and the lakes through which i t flows; from Whitemud Falls (54° 45' N, 97° 53' W) to the junction of the Nelson and Weir Rivers (56° 55' N, 93° 22• W). It i s estimated that about 75$ of the production from 1953 to I960 was taken from a 75 mile portion of the river which included Sipiwesk Lake; a 12 mile stretch of river above and a 25 mile stretch of river below. The annual harvest may possibly be increased i n ten to twenty years i f a ten year closure allows stock to build up to a much higher l e v e l . This i s based on the assumption that the rate of reproduction and recruit-ment would be greater at higher population densities. It i s doubtful that a profitable commercial fishery would be feasible at an annual production limit as low as 10,000 pounds. If such i s the case, i t would be permissible to take substantially larger annual limits for a period of years i f each period of fishing was interrupted by a period of closure so designed that the average long term annual production was no greater than 10,000 pounds. The cumulative catch during each of these periods of fishing should not exceed 100,000 pounds nor should the annual catch exceed 35,000 pounds. Thus, i f present stocks were allowed to increase for ten years by completely protecting the sturgeon, future annual limits of 20,000 pounds for five year periods would be permissible i f each five year period of fishing was interrupted by a five year period of closure. Similarly, annual limits of 25,000 pounds for four year periods would be permissible 79 i f each period of fishing was interrupted by a six year period of closure and annual limits of 30,000 to 35,000 pounds for three year periods would permissible i f each period of fishing was interrupted by a seven year period of closure. B. THE MINIMUM LEGAL SIZE OF STURGEON A re s t r i c t i o n governing the minimum legal size of sturgeon has been i n effect i n past fisheries to protect immature sturgeon and to dis-courage the capture of small sturgeon which are low i n market value. The minimum legal size of sturgeon i n the 1953 to I960 Nelson River fishery was 18 pounds round weight and 10 pounds headless dressed weight. From data presented i n Tables IX and XIII i t i s evident that this regulation offered l i t t l e , i f any, protection to immature sturgeon. It i s common practice i n fisheries management to impose restrictions regarding fishing gear specifications and/or the minimum legal size of f i s h that protect immature fish and insure that a large proportion of the adult population i s allowed to spawn at least once before being selected for by the fishery. Since there i s evidence that the rate of recruitment to stocks of Nelson River sturgeon i s related to the size of the adult population, i t would seem that protection of immature sturgeon i s very important. If a l l Nelson River sturgeon are to be allowed to spawn at least once, the minimum legal size would have to be raised to about 29 pounds round weight. Such a regulation would impose considerable hardship upon the fishermen since 53.3$ of 709 sturgeon sampled from the fishery from 1953 to 1959 were below 28 pounds round weight. It i s therefore recommended that the minimum legal size of Nelson River sturgeon be set at 25 pounds round weight. This would correspond to a headless dressed weight of about 80 15 pounds. This figure would afford complete protection to a l l immature male sturgeon and to a much larger proportion of the immature female sturgeon. Even this limit may impose some hardship upon the fishermen. The 655 sturgeon sampled from the fishery from 1953 to 1956 indicated that 42$ of the total number of fish taken in this period were under 25 pounds round weight. These sturgeon, however, accounted for only 28$ of the total catch by weight. Once the fishery is stabilized, a 25 pound minimum legal size should no longer effect the fishery. Recruitment to a 25 pound size group should be l i t t l e less than recruitment to an 18 or 20 pound size group in such a large and long lived species of fish. It would be advantageous i f future restrictions regarding the minimum legal size of sturgeon were based on a measurement of length rather than weight. Past experience has revealed that the relationship between round and dressed weights is very variable because of differences in the "condition" and/or the stage of reproductive maturity of individual sturgeon. In the last fishery, for instance, the minimum legal size of sturgeon was 18 pounds round weight and 10 pounds headless dressed weight. Data collected on the Nelson River in 1953 and 1954 revealed that one 18 pound sturgeon dressed out to 12 pounds and four dressed out to 11 pounds. Of twenty-four 20 pound sturgeon sampled; one dressed out to 11 pounds, twelve dressed out to 12 pounds, eight dressed out to 13 pounds, two dressed out to 14 pounds and one dressed out to 15 pounds. Of fifteen 25 pound sturgeon sampled; <-one dressed out to 13 pounds, three dressed out to 15 pounds, three dressed out to 16 pounds, seven dressed out to 17 pounds and one dressed out to 18 pounds. Such variability in round and dressed weight makes enforcement of 81 the minimum legal size limits very difficult. The end result is that many "borderline" sturgeon are killed and dressed as a final test to determine whether or not they are legal fish. A length measurement that is applicable to both live and headless dressed sturgeon would be most satisfactory as a criterion for the minimum legal size of sturgeon. One such measurement that is applicable to live sturgeon i s : from an easily defined point on the dorsal fin or the fork of the caudal fin to the most posterior limit of the pectoral girdle (the most posterior edge of the cleithrum, which lies beneath the skin in a mid-lateral position, is easily located by touch). A corresponding measurement applicable to headless dressed sturgeon i s : from the dorsal or caudal fin to the mid-lateral point of the anterior cut edge of the skin. These measurements would be identical on any fish because the cut that is made to remove the head and pectoral girdle is made as close to the pectoral girdle as possible. C. FISHING GEAR In the course of the past two Nelson River sturgeon fisheries, small and immature sturgeon have been protected by a restriction governing the mesh size of fishing gear as well as the minimum legal size of fish. This restriction specified twelve inch (extension measure) g i l l nets. It is evident from data presented in Tables IX and XIII that the twelve inch g i l l net afforded l i t t l e protection to immature female sturgeon in the last fishery. Although the average size of sturgeon caught from 1953 to 1956 was 28.9 pounds, this mesh size efficiently captured sturgeon as small as 16 pounds round weight. Over 40$ of the total number of sturgeon taken during this period were under 25 pounds round weight. 82 I f the reproductive capacity and recruitment of Nelson River sturgeon i s to be increased; the legal size of g i l l nets should be increased regardless of whether the minimum legal size of sturgeon i s increased. Many sub legal sturgeon are retained by the fishermen for food or for l o c a l sale. The optimum mesh size for future sturgeon fisheries can only be estimated because no information on the size selectivity of g i l l nets greater than twelve inches i s available. It i s the writer's opinion that either thirteen or fourteen inch mesh would allow an adequate escapement of immature females. The advantages to the sturgeon population and the dis-advantages to the fishery of these mesh sizes would be tested most easily and conclusively by applying one of these mesh sizes to the next fishery. It i s therefore recommended that fishing gear i n the next Nelson River stur-geon fishery be restricted to thirteen inch (extension measure) g i l l nets. D. FISHING SEASONS Data presented i n Section V-C indicate that Nelson River sturgeon have not wholly completed their spawning ac t i v i t i e s by June 10, the date at which the Nelson River sturgeon fishery usually commences. This would suggest that some sturgeon at least, are caught before they have spawned; perhaps for the f i r s t time. I t i s therefore recommended that the opening of future sturgeon fisheries be postponed to at least June 15 to allow a greater percentage of fi s h to spawn. 83 VIII. THE MANAGEMENT OF OTHER STURGEON FISHERIES IN MANITOBA Since a l l other sturgeon fisheries i n Manitoba, both past and recent, have failed and as very l i t t l e i s known of the biology of these sturgeon, i t would seem wise as a f i r s t step to apply the conclusions and recommendations of this study to other sturgeon fisheries i n Manitoba. A. PRODUCTION LIMITS The Sipiwesk Lake area of the Nelson River, which i s the main sturgeon producing portion of that river, can be expected to produce a sus-tained yield of about 7,500 pounds of sturgeon per year. Since the area of this portion of the river i s about 190 square miles, i t can be expected to yield about 40 pounds of sturgeon per square mile per year. Other Manitoba waters at the same latitude and of comparable f e r t i l i t y can there-fore be expected to produce a similar annual yie l d . More northerly waters with shorter open water seasons may be expected to produce sl i g h t l y less and southern Manitoba waters may be expected to produce considerably more (possibly 50 to 75 pounds per square mile per year). B. THE MINIMUM LEGAL SIZE OF STURGEON AND OF FISHING GEAR tt was concluded from Nelson River studies that recruitment of sturgeon may be increased by raising the minimum legal size of round (live) sturgeon from 1 8 to 25 pounds and the legal size of g i l l nets from 12 inches to 13 or 14 inches (extension measure). It i s l i k e l y that sturgeon of more northerly waters mature at a greater age and that those of southern Manitoba mature at an earlier age. 84 The size at which they mature, however, i s very l i k e l y similar throughout Manitoba. It i s therefore recommended that the legal size of sturgeon and of fishing gear i n other sturgeon fisheries i n Manitoba be raised to comply with that suggested for the Nelson River fishery. C. FISHING- SEASONS It was recommended that the opening date of future Nelson River sturgeon fisheries be changed from June 10 to at least June 15 to allow a greater percentage of sturgeon to fin i s h spawning. Since sturgeon of more northerly waters spawn at a later date, the opening date of sturgeon fisher-ies on these waters should be delayed according to the best information available on prevailing temperatures and the time of spring breakup. Southern Manitoba sturgeon fisheries could safely be opened five to ten days earlier than the Nelson River fishery. 85 IX. FUTURE RESEARCH ON LAKE STURGEON It is quite evident that relatively l i t t l e is known about the l i f e history, the biology and the habits of the lake sturgeon. Much more knowledge will be required before a game or commercial fishery for this species can be managed properly to insure a sustained yield. Some of the more important questions to be answered concern the reproductive capacity and the rate of recruitment to stocks at various levels of population density. The practicality of ar t i f i c i a l propogation of this species may also be considered. Further studies regarding the spawning of lake sturgeon is warranted. These should include the time and place of spawning, the age of maturity and, most important of a l l , the periodicity of spawning. Spawning and nursery ground investigations should also be under-taken to assess the amount of predation on eggs and fry and the effect upon juvenile sturgeon of other g i l l net fisheries which use much smaller mesh sizes. 86 SUMMARY Lake sturgeon of the Nelson River i n Northern Manitoba have been exploited by the commercial fishery intermittently since 1907. The failure of two fisheries between 1921 and 1946 indicated the need for a program of biological research which would provide a basis for the future management of this economically important species. A resumption of the Nelson River sturgeon fishery i n 1953 which followed a six year closure afforded an opportunity to study this species. From 1953 to 1956 and 1959, 791 sturgeon were sampled from the commercial catch i n the Sipiwesk Lake area of the Nelson River by biologists of the Provincial Fisheries Branch. Each specimen was weighed, measured and sexed and the marginal "spine" of the pectoral f i n was retained for the purpose of age determination. Preliminary studies were conducted to determine the.location on the pectoral "spine" of the best cross-sections for purposes of aging and back-calculation of growth. It was concluded that annuli were most easily differentiated i n cross-sections obtained about half to three-quarters of an inch from the proximal end of the spine. The easiest and best measurement on this cross-section for back-calculation of growth was the radius of the spine from the centre of ossification to the posterior edge of the spine, along the acute angles formed by the annuli i n this area. For purposes of back-calculation of growth i n length of Nelson River sturgeon, the relationship between growth i n length of the pectoral "spine" to growth i n length of the fish was determined by the method of least squares. The equation for this relationship i s x B L4y + 2.2 where x i s the fork length i n inches and y i s the average radius of the pectoral spine. 87 In the determination of size at any previous age, best results were obtained by back-calculating along a l i n e which converged with the intercept. Growth i n length of Nelson River sturgeon was determined by av-eraging empirical lengths by age groups, by averaging back-calculated lengths by age groups and by cumulatively totalling average annual calculated increments of growth for a number of specimens. The l a s t method appeared to provide the best representation of growth i n Nelson River sturgeon. It i s readily apparent that the Nelson River female sturgeon grows faster and lives longer than the male. The average annual increment i n size to age 20 i n both sexes i s about 0.9 pounds, round weight, and 1.9 inches, fork length. From age 20 to 50 years, the average annual growth increment i n males i s 0.4 pounds and 0.4 inches while that for females i s 0.7 pounds and 0.5 inches. Beyond age 50 years, the average annual increment i n round weight of females increases to about 1.0 pounds. A very noticeable change i n the rate of growth i n weight and length at age 20 to 25 years i n both sexes correlates very closely with re-productive maturity of these f i s h . There i s no indication of any asymptotic size i n Nelson River sturgeon. The relative growth of Nelson River sturgeon for the years 1915 to 1950 was determined from back-calculated data. Noticeable fluctuations i n relative growth were apparent. Although i t appears that growth may have been slightly greater i n years of low water and/or years when population density was low; the correlation of these data i s not sufficiently consistent to be significant. The length-weight relationship of male Nelson River sturgeon i s : log W « -3.55 + 3.002 log L. That for the female i s : log W- -3.84 + 3.204 log L. (W i s round weight i n pounds and L i s fork length i n inches). 88 There i s a straight-line relationship between dressed weight and round weight. A simple rule of thumb for this relationship i s : dressed weight - 2 / 3 round weight. The rate of growth of Nelson River sturgeon was compared to that of lake sturgeon from Ontario, Quebec and Wisconsin. Nelson River sturgeon grow slower than lake sturgeon of Lakes St. Peter and St. Frances i n Ontario and Lake Winnebago i n Wisconsin but grow faster than those of Lake Nipigon i n Ontario. The growth curves for lake sturgeon of these other waters do not exhibit the noticeable change i n slope that i s typical of Nelson River lake sturgeon. Nelson River sturgeon spawn i n late May to early June. The average female matures and spawns for the f i r s t time at age 25 to 30 years. This corresponds to a round weight of 24 to 29 pounds and a fork length of 42 to 45 inches. A l l or most males are mature by age 20 years which corres-ponds to a round weight of about 16 pounds and a fork length of about 38 inches. Nelson River sturgeon do not spawn every year. The best inform-ation available suggests that the female sturgeon spawns every three to six years. Older f i s h appear to spawn more frequently than young ones. The frequency of spawning of Nelson River male sturgeon i s unknown but i t i s very unlikely that they spawn every year. Over-exploitation, dams, and pollution have greatly reduced or eliminated sturgeon throughout the world. A l l major sturgeon fisheries i n Manitoba, including the Nelson River fishery, failed after a relatively short period and the production i n more recent fisheries has always fallen far short of the amounts taken i n i n i t i a l fisheries when virgin stocks were exploited. The depletion of Manitoba sturgeon i s attributed solely to over-exploitation by the commercial fishery. The failure of the last three 89 commercial fisheries on the Nelson River, variations i n strength of year classes from 1910 to 1935, an orderly decrease i n the catch per unit of effort i n the last two fisheries and changes i n the age and size structure of the sturgeon population during the most recent fishery i s ample evidence that depletion of stocks has occurred and that i t i s a result of over-exploitation by the commercial fishery. Lake sturgeon are vulnerable to depletion for several reasons. They are r e l a t i v e l y slow growing f i s h and the rate of recruitment i s low. They have a very high market value and are easily caught during certain seasons when they congregate i n well defined areas. For these reasons i t i s readily evident that the Nelson River sturgeon fishery can be managed on a sustained yield basis only i f sturgeon stocks are afforded much more pro-tection than i n the past. It i s recommended that regulations i n any future fishery on the Nelson River be changed to afford such protection. These regulations pertain to production limits, fishing seasons, and the minimum legal size of f i s h and fishing gear. This fishery i s closed at present and should remain closed for at least ten years to allow sturgeon stocks to increase to a level which w i l l insure a higher rate of recruitment and an economical rate of yield to the commercial fishery. PRODUCTION LIMITS. It i s recommended that future production limits on the Nelson River be reduced to no more than 10,000 pounds (dressed weight) per year. This limit could be increased substantially for short periods as long as the cumulative production for each ten-year period does not exceed 100,000 pounds. FISHING SEASONS. It i s recommended that future fishing seasons be postponed u n t i l at least June 15 to allow a larger number of adult sturgeon to finish spawning. THE MINIMUM LEGAL SIZE OF STURGEON. It i s recommended that the minimum legal size of sturgeon i n the future be increased to at least 25 pounds round weight (or i t s equivalent i f a measurement of length i s adopted as a size criterion). FISHING GEAR. It i s recommended that the minimum legal size of g i l l nets i n the future be increased to at least 13 inches, extension measure. It i s also recommended that regulations i n future sturgeon fisheries i n other parts of Manitoba be revised to conform to those suggested for the Nelson River. Minor changes i n production limits and fishing seasons would be i n order for areas that d i f f e r markedly i n basic productivity and climate from that of the Nelson River. 91 LITERATURE CITED Bajkov, A. D. 1930. Fishing industry and fisheries investigations in the Prairie Provinces. Trans. Amer. Fish. Soc. 60: 215-237* Bajkov, A. D. 1933* Report on.Fisheries Investigations in Manitoba. (Manuscript Report) Manitoba Department of Mines and Natural Resources, Fisheries Branch, Winnipeg. Barannikova, I. A. 1954. (Completion of the process of change to the spawn-ing condition by female and male winter sturgeon) Doklady Akademii Nauk, SSSR. New Series 99(4): 641-644.(Russian Text). Carlander, K. D. 1947. Some trends in the Commercial Fisheries on the Lake of the Woods; Minnesota. Trans. Amer. Fish. Soc. 2Z: 13-25• Chugunov, N. L. 1925. On the Methods of Age Determination in Sturgeon. Bulletin of Fisheries Economy, Number 11: 33-34. Moscow. Classen, T. E. A. 1944. Estudio Bio-Estadistico del Esturion 0 Sollo del Guadalguivir (Acipenser sturio Linne). Instituto Espanol de Oceanografia, Madrid. Trabajo numero 19: 52-70. (Translated by-John Greenbank; Wisconsin Conservation Department, 1949). Classen, T. E. A. 1947. Notas sobre el Sollo 0 Estarion del Guadalquivir. . Montes (Madrid) 3(15): 256-262. Cuerrier, J. P. 1945. Les stades de maturite chez l'esturgeon du Lac Saint-Pierre. Bibl. de l'off. prov. de Biol., Minestere de la Chasse et des Pecheries, Quebec, MS 2212. (Manuscript). Cuerrier, J. P. 1949. Observations sur l'esturgeon de lac (Acipenser fulvescens Raf.) dans la region duelac Saint-Pierre au cours de la periode du fr a i . These Manuscrit. Universite' de Montreal, Montreal. Cuerrier, J. P. 1951. The Use of Pectoral Fin Rays for Determining Age of Sturgeon and Other Species of Fish. Canadian Fish Culturist. ( l l ) : 10-18. Cuerrier, J. P. and G. Roussow. 1951. Age and Growth of Lake Sturgeon from Lake St. Francis, St. Lawrence River. Report on material collected in 1947. Canadian Fish Culturist. (10): 17-29. Dean, B. 1884. Recent Experiments in Sturgeon Hatching on the Delaware River. Bull. U.S. Fish. Comm. VIII: 335-339. Derjavin, A. N. 1922. The Stellated Sturgeon (Acipenser stellatus Pallas), A Biological Sketch. Bulletin of the Ichthyological Laboratory of Baku. I: 1-393. Ehrenbaum, E. 1926. Die Eider als stbrfluss and die shonung des stbrs. Naturforscher 2(10): 510-515. 92 Evermann, B. W. and H. B. Latimer. 1910. Fishes of the Lake of the Woods and Connecting Waters. Proc. U.S. Nat. Mus. 2£: 121-136. Harkness, W. J. K. 1923. The Rate of Growth and the Food of the Lake Sturgeon (Acipenser rubicundus LeSueur). Univ. Toronto Studies. Publ. Ont. Fish. Res. Lab. (18): 13-42. Harkness, W. J. K. 1936. Report on the Sturgeon situation i n Manitoba. Manuscript Report, pp 1-12. Manitoba Department of Mines and Natural Resources; Fisheries Branch, Winnipeg. Harkness, W. J. K. 1953. Letter to the Fisheries Branch, Manitoba Department of Mines and Natural Resources. Winnipeg, Manitoba. Kooyman, B. 1955. An analysis of data collected i n 1953 and 1954 from the Sturgeon Fisheries on the Nelson and Churchill Rivers. Manuscript Report. Manitoba Department of Mines and Natural Resources; Fisheries Branch. Winnipeg. Kuzmin, A. N. 1954. Structural and developmental changes i n the testes and ovaries of Juvenile Sturgeon (Acipenser guldenstadti Brandt). Doklady Akademii Nauk. SSSR. New Series 99(4): 645-647. McCrimmon, H.R. 1956. Fishing i n Lake Simcoe. Ontario Dept. of Lands and Forests. McTavish, W. B. 1954. Investigation of Sturgeon on the Nelson River. -June, 1954. Manuscript Report. Manitoba Department of Mines and Natural Resources; Fisheries Branch. Winnipeg. Meyr, A. 1950. Der Stor, ein aussterbender Fisch i n Deutschen Gewassern. Allgem. Fischerei. Zeit (75(5): 114-115. Probst, R. T. 1954. Why Study Sturgeon. Wise. Cons. B u l l . 19(3): Probst, R. T. and E. L. Cooper. 1954. Age. Growth and Production of the Lake Sturgeon (Acipenser fulvescens; i n the Lake Winnebago Region, Wisconsin. Trans. Amer. Fish. Soc. 84.: 207-22?. Pycha, R. L. 1956. Progress Report on White Sturgeon Studies. C a l i f . Fish and Game 42(l): 31-35. Ricker, W. E. 1958. Handbook of Computations for Biological Statistics of Fish Populations. Fisheries Research Board of Canada. Bulletin No. 119. 300 pp. Rodd, J. A. 1926. Propagation of Sturgeon. Manuscript Report. Manitoba Dept. of Mines and Natural Resources; Fisheries Branch. Winnipeg. Roussow, G. 1955. Les Esturgeons du fleuve Saint Laurent en Comparaison avec les autres Especes d'Acipenserides. Office de Biologie, Ministere de l a Chasse et des Pecheries, Province de Quebec. Montreal. 124 pp. 93 Roussow, G. 1957. Some consideration concerning sturgeon spawning periodicity. Jour. Fish. Res. Bd. Can. 14(4): 553-572. Ryder, J. A. 1890. The Sturgeons and Sturgeon Industries of the Eastern Coast of the United States, with an account of experiments bearing upon Sturgeon Culture. Bull. U.S. Fish Comm. VIII: 231-328. Schneberger, E. and L. A. Woodbury. • 1944. The Lake Sturgeon (Acipenser  fulvescens Rafinesque) in Lake Winnebago, Wisconsin. Trans. Wise. Acad. Sci., Arts and Letters. ^6: 131-140. Van Oosten, J. 1936. The Great Lakes Fisheries; Their proper management for sustained yields. Trans. Amer. Fish. Soc. 66: 131-138. Vladykov, V. D. The Fishes of Quebec. Album #5, Sturgeon. Dept. of Fisheries of Quebec. Williams, J. P. 1951. The Lake Sturgeon. Michigan Conservation 20(6): 15-18. " Wirth, T. L. 1959. Sturgeon Tagging Operations on Wolf River, Wisconsin. (Wisconsin Conservation Department, Interdepartmental Memorandum, June 16, 1959). Wirth, T. L. and C. Cline (no date). The Harvest of Lake Sturgeon (Acipenser fulvescens) by Spearers in Lake Winnebago and Connecting Waters, Wisconsin. CManuscript Report). 

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