Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The availability , exploitation, abundance and movement of the butter sole (Isopsetta isolepis Lockington)… Manzer, James I. 1949

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata


831-UBC_1949_A8 M27 A8.pdf [ 2.94MB ]
JSON: 831-1.0106954.json
JSON-LD: 831-1.0106954-ld.json
RDF/XML (Pretty): 831-1.0106954-rdf.xml
RDF/JSON: 831-1.0106954-rdf.json
Turtle: 831-1.0106954-turtle.txt
N-Triples: 831-1.0106954-rdf-ntriples.txt
Original Record: 831-1.0106954-source.json
Full Text

Full Text

THE AVAILABILITY, EXPLOITATION, ABUNDANCE AND MOVEMENT OF THE BUTTER SOLE (Isonsetta isolenis. Lockington) IN SKI DE GATE INLET, QUEEN CHARLOTTE ISLANDS, DURING 1946.. BY James I. Manzer A Thesis submitted i n Partial Fulfilment of The Requirements for the Degree of MASTER OF ARTS in the Department of ZOOLOGY a, THE UNIVERSITY OF BRITISH COLUMBIA Apr i l , 1949 ABSTRACT The accumulation of butter sole within Skidegate inlet .pro-vides an* important winter trawl fishery for northern B r i t i s h Columbia. The availability, prior to spawning, has been deter-mined from catch statistics offered willingly by fishermen and industry. The ava i l a b i l i t y fluctuates during the season but the real peak period, after the accumulated stock has been re-moved, occurs during the last week that fishing was permitted. Distortions which could have been produced by boats of different fishing efficiencies and, also, by boats which fished for only part of the season are compensated for. The minimum estimate of fishing intensity, as determined from tagging experiments, i s 30.8%. The abundance of the stock, calculated from the fishing intensity, sex ratios, and length-weight data, i s appro-ximately 3,130,000 f i s h . The differential appearance of the sexes upon the grounds has been determined. The male f i s h ap-pear upon the grounds f i r s t and are later followed by the fe-males. Tag returns provide information concerning movement be-tween the various grounds within the inlet and also dispersion from the inlet into Hecate strait after spawning has occurred. TABLE OF CONTENTS Page I. INTRODUCTION ± I I . MATERIALS AND METHOD 8 III. ANALYSIS OF THE DATA .• 13 A. , Catch Statistics 13 B. Fishing Intensity 17 C. Abundance 26 D. Movement 28 IV. DISCUSSION 34 V. SUMMARY AND CONCLUSIONS 37 VI. ACKNOWLEDGEMEHTS 3? VII. REFERENCES 40 VIII. APPENDIX 41 I. INTRODUCTION One of the primary functions of a commercial fishery i n -vestigation i s to obtain pertinent information necessary for adequate regulation or management of that fishery in order to provide an optimum sustained yield. With this in mind, the Fisheries Research Board of Canada in 194-3 began investigation of the increasingly important trawl fishery i n Br i t i s h Colum-bia, placing special emphasis on the species which supported major fisheries. The butter sole (Isonsetta isolenis Locking-ton) which congregates in Skidegate in l e t , Q,ueen Charlotte islands, during the early part of each year was regarded as one of these and, accordingly, in 1946 a study of this population was undertaken. The Problem Sound regulatory measures for any species of f i s h are those which permit stabilization of the stock at a level at which the optimum growth potential of that species i s taken f u l l advantage of. It i s not good management i f a portion of the stock, due to under-exploitation, i s allowed to die natural-l y when i t could otherwise be u t i l i z e d . It i s equally unwise to allow exploitation to an extent where a continued success-f u l fishery i s not assured. Management, therefore, i s the balancing of the removal of the stock with the numbers neces-sary to guarantee a maximum sustained yi e l d . However, before management can be accomplished i t i s important to know, amongst other things: 1. the a v a i l a b i l i t y and abundance of the stock being ex-ploited i 2. the extent of the removal of the stock by the fisheryi 3. the behaviour of the f i s h upon the grounds on which i t i s found,.and whether 4. the stock i s fished in more than one general area. The purpose of the present study i s to obtain pertinent information on the above four mentioned aspects concerning,the Skidegate inlet butter sole. An account of the methods used and the results obtained are presented In the succeeding sec-tions. •History of the Fishery Prior to 1943 fishing for butter soles i n Skidegate . inlet was carried on only by the white and indian residents i n that vic i n i t y to supply their own limited demands. In 1943, however, while prospecting for dogfish (Squalus suckleyi Girard), Captain C. B. Shannon of Vancou'ver.. accidently came upon the stock which assembles each winter in the inlet to spawn. The size of the stock at that time was reflected i n the length of time which the trawl was allowed to remain out. During seven minutes of dragging time 8,000 pounds of f i s h were caught. The discovery of the butter sole fishery i n an area sheltered from strong prevailing south-easterly winter winds and a war time demand for f i s h products encouraged trawl fishermen to exploit this stock. Most of the fleet was comprised of vessels from the port of Prince Rupert but one or two vessels -3-from Vancouver engaged i n the fishery each year, but for the most part discharged their fares i n the northern fishing port. The depletory trend of the fishery since 1944 has been continuous and i s indicated in the available catch s t a t i s t i c s which are presented along with the duration of the fishing season from 1943 to 1946 and the number of vessels fishing during each season (Table I ) . In 1943 only two boats were engaged in the butter sole fishery which lasted 5 weeks. The quantity of f i s h removed from the stock was at that time re-gulated by the i n a b i l i t y of shore plants interested in the butter sole to process more than 100,000 pounds of f i s h per week. The, return-per-unit of fishing effort approximated 1,000 pounds per minute. In 1944, with a waiting market for f i l l e t t e d -products, the number of boats fishing for butter soles and plants increased. In 1945 the season was longer and the i n -terest remained, but the continuous increase in the fishing intensity reduced the return-per-unit-effort u n t i l , i n 1946, the average return for the 6 weeks period was approximately 800 pounds per fishing hour. The future of the fishery i s dependent upon the a b i l i t y of the butter sole to compete with other species of. f l a t f i s h as a marketable product. Due to i t s thinness and, consequently, the low percentage recovery of the flesh as a . f i l l e t , the f i l -letting houses are reluctant to u t i l i z e this species i f other f l a t f i s h with a greater percentage recovery of flesh as f i l l e t s can be had or caught. Also, the fishermen themselves favour fishing for other species which are more suitable for f i l l e t t -ing and for which they receive a higher monetary return. How*-Table I Total landings for the Skidegate inlet butter sole fishery for the years 1943 to 1946, inclusive, and the number of units fishing during .each season. YEAR LANDINGS (pounds) DURATION (weeks) FISHING UNITS (boats) 1943 300,000 5 2 1944 1,750,000 3 6 1943 1,028,700 6 6 1946 831,600 6 8 -4-ever, the fishery, in a l l probability, does not face extinction. During periods of inclement weather or when fishing for other species i s poor, i t does not appear unreasonable to anticipate some fishing for butter soles i n Skidegate i n l e t . Description and Distribution of the Butter Sole The butter sole was f i r s t recognized and described by Lockington in 1880. It i s a member of the Family Pleuronec-tidae and represents the only member of the genus Isopsetta (Norman 1934). The species i s dextral, that i s , both eyes are on the right hand side of the fish as i t takes up i t s nor-mal position on the bottom. Compared to most other species of f l a t f i s h on the British Columbia coast i t i s thin, and this feature i s of valuable assistance in sex determination as the sexes possess no apparent differences in their external mor-phology. If a f i s h should be held between a source of lig h t , ther observer can readily determine the sex, even in^immature f i s h . In females the ovaries are identified as posterior ex-tensions from the peritoneal cavity into the body musculature. In males the testes do not extend beyond the margin of the peri-toneal cavity. To the casual observer, the butter sole may be confused •with vcertain other members of the plueronectid. family found on this coast. However, and according to Clemens and Wilby (1946), i t may be recognized by the presence of rough scales on the ocular side of the body, including the head, and the lemon yellow colour on the tips of the anal and dorsal f i n s . -5-Norman (1934) states that the butter sole inhabit waters from southern California to Puget sound. Clemens and Wilby (1946) extend this distribution northward u n t i l now the species i s known to range from southern California to north-western Alaska. In British Columbia, waters the species i s found in the strait of Georgia and off the west coast of Vancouver i s -land, but hot as abundantly as in Hecate st r a i t and certain waters adjacent to i t . Butter soles are found on f l a t , mud bottom ranging in depths up to 33 fathoms. The butter sole has been known by a variety of names. Scaly-finned flounder, Bellingham sole, Skidegate sole, and occasionally lemon sole have added confusion to the common terminology of the species. In 1943, however, the term butter sole was adopted when fishery biologists, fishermen, and repre-sentatives..from the. fishing industry on this coast met and de-cided upon a standardized l i s t of common names for a l l f l a t -f i s h found in northern Pacific coast waters. Description of the Gear Commercial fishing for butter soles in Skidegate inlet i s carried out exclusively by trawls. This i s a large conical shaped net which has on each side extensions which form "wings". Attached to each end of a wing by lines i s an otter board which serves to keep the mouth of the net open and, also, possibly to assist in directing the fish into the net. On the anterior bottom margin of the net is a heavy "sole" or "ground" rope which keeps the net close to the fishing floor and i s thus capable of raising f i s h which might otherwise escape being caught i f allowed to remain p a r t i a l l y buried in the mud. Op-posite but above the ground rope i s the "head" rope. To i t glass floats are attached and these serve to keep the top of the net up and thus increase the effective catching area of the net. The.captured f i s h are removed from the net by pulling a draw rope which, during actual fishing procedure, acts as the posterior end of the trawl. According to regulations, a mini-mum mesh stretch of 4 1/2 inches i s allowed. Attachment of the trawl to the fishing vessel i s by means of a wire rope, the length of which can be regulated by deck winches, depending upon the depth of the fishing grounds. By this means the net i s towed over the grounds by the fishing craft. The size of the crews and boats engaged in the Skidegate inlet butter sole fishery i s relatively constant, the former usually being four men, including the captain, and the latter averaging 55-60 feet in total length. Discussion of the Fishing Grounds in Skidegate Inlet Skidegate inlet is that body of water, adjacent to Hecate strait,which forms the eastern portion of the channel separat-ing the Q,ueen Charlotte island- group Into Graham island to the north and Moresby island to the south- (('Inset,; Fig. 1). Fishing for butter soles i n Skidegate inlet i s limited to four grounds. For the purpose of differentiation these have been arbitrarily called the Beach, the Buoy,- the Village, and Grassy island grounds. The depths of each are 15, 30, and 33 Fig. 1 A map showing the relative positions of the butter sole fishing grounds in Skidegate in l e t . (1) Grassy island, (2) Village, (3) Beach, (4) Buoy fathoms respectively. The relative position of each i s shown in figure.!. Prior to 1946 only the village and Grassy island grounds were known. In that year, however, the scarcity of fish on those grounds prompted fishermen to seek new trawlahle grounds. This resulted in the discovery of the Buoy and Beach areas. Of the four areas the Buoy, Beach, and Village grounds were most important in 1946. The Grassy island ground, he-cause of the smaller sized fish and the abundance of the com-mercially undesirable yellow-fin sole (Limanda aspera Pallus), was turned to only when the south-east winds were too severe to permit fishing on the north-western side of the i n l e t . The Beach ground, because of i t s irregular submarine• topography and snags, was fished only by those boats willing to risk net damage or even net loss. -8-I I . MATERIALS AND METHODS The methods employed in the investigation of the butter sole in Skidegate inlet during the 194-6 fishing season were three in number. Tagging studies were used to determine the fishing effort"1'which the species was subjected"; In addition, recovered tags made i t possible to determine the movement of the fis h within and from the i n l e t . Sampling for sex at the port of Prince Rupert, where almost a l l landings were made, supplied information concerning the arrival of the sexes upon the grounds. The collection of catch statistics provided data which were useful in determining . fluctuations in the availa-b i l i t y during the course of the regular fishing season. The period of observation at Prince Rupert commenced on January 10 and ceased on February 13. Operations in Skidegate inlet began on January 18 and continued u n t i l February 16, both dates inclusive. In order to f a c i l i t a t e comparison of one portion of the fishing season with another, and thereby detect trends i n availab i l i t y , the entire fishing period, January 3 to February 17, was divided up into nine periods of five fishing days each. The days which each period includes i s found in table I I . Tagging Study. The tagging of butter sole was conducted from one of the vessels engaged in commercial fishing operations during the entire fishing season. The objective was to release 100 tags 0 Table II The Total Landings of Butter Sole for the Different Fishing Periods and the Time Required to make these. Period Date Total Landings (pounds) Time (hours) I Jan. 5- 9 52,200 37 II Jan. 10-14 83,300 104 III Jan. 15-20 60,000 82 IV Jan. 21-25 109,200 145 V Jan. 26-30 88,000 106 VI Jan. 31-Feb. 4 149,700 172 VII Feb. 5- 9 80,900 123 VIII Feb. 10-14 126,300 148 IX Feb. 15-17 81,650 94 - 9 -pn the f i r s t day and 50 on each day thereafter. Except for inclement weather or "harbour days" the intention was appro-ximated (Table 3 ) . In a l l 1,175 f i s h were tagged; Fish for tagging were obtained from the grounds which the captain of the vessel upon which the tagger was stationed)had selected to fi s h . Selection of the ground was usually deter-mined by the ease of capture, quantity,and sizes of the f i s h caught there. A l l f i s h were caught by means of a trawl, the length of a "drag" usually being of one hour* duration. Tagging took place immediately upon landing the f i s h on deck. Only those fish which were selected at random and which were apparently uninjured were used for this study. To reduce the chances of mortality due to handling after capture, only a few fi s h were tagged from each drag. These were placed i n a 1 1/2' x 21 x 3 l / 2 T live tank through which passed a con-stant supply of fresh sea water. The tags used in this study consisted of two celluloid disks, each 12 millimetres i n diameter and approximately l/2 millimetre thick. One disk of each pair was white and on i t was visible a serial number and the legend "Pac. B i o l . Sta.". The other disk was yellow and carried the name and address of the Pacific Biological Station and the request that both disks be returned to the investigating organization. To f a c i l i t a t e recognition of the tag the white portion of the tag was placed on the dark ocular side of the fish while the yellow portion was placed on the white blind side. Attachment of the tag to the fish was made possible by passing a sharp corrosion-resistant nickel pin through the -10-white portion of the tag, then through the flesh of the f i s h just below the dorsal f i n but at a distance equal to approxi-mately one half of the length of the f i s h , and then f i n a l l y through the whaftfe portion of the tag. Usually the pin was longer than necessary and when such was the case the unneces-sary portion of the pin was cut off with long-nosed pl i e r s , and the remaining protruding portion of the pin was rolled into a loop which held the baffles secure to each side of the f i s h . A record of the number on the tag, the tagging location, the tagging date, the total length to the nearest centimetre and the sex of each f i s h was maintained. Each individual f i s h could then be later identified upon recovery and the i n -formation obtainable at the time of tagging and recovery could then be outlined. To insure maximum effectiveness of the tagging operations considerable effort was exercised, both on the fishing grounds and on shore, in order that a l l possible recovered tags would be received. To encourage receipt of a l l tags and to increase the usefulness of each, tag envelopes, upon the back of which was found a questionnaire requesting desirable recovery infor-mation, were made available to a l l fishermen. A reward of f i f t y cents was also paid for each recovered tag received. Sampling Study Sampling was carried out on shore for sex and total length. Measurement of the fi s h was made to the nearest centimetre. The fis h used were selected at random from landings made throughout the fishing season. Six samples totaling 2,244 f i s h were used -11-in this study. Identification of the sexes was by inspection. The fe-males could readily be recognized by the ovary which bore eggs and which showed up as a tapering longitudinal extension from the body cavity. In males this feature was lacking. Collection of Catch Statistics Complete and accurate information on the t o t a l amount of f i s h caught by a fishery i s essential when employing catch statistics to the study of that fishery. For the butter sole fishery catch data were obtained throughout the fishing season from each participating vessel and these were used i n the total catch and a v a i l a b i l i t y studies. The type of information sought from each vessel was the days upon which i t was engaged in fishing, the quantity of fis h in pounds which were caught, and the time required to make the catch. For certain vessels the exact fishing time was not ob-tainable and when such was the case the number of sets made per day was used as the daily fishing time, a set generally being of one hour's durat ion. Two methods were used to acquire reliable catch s t a t i s -t i c s . After each t r i p the captain of each vessel was personal-ly interviewed and the desirable information was obtained from him. When this was not possible, due to d i f f i c u l t y of contact, the total landings could be secured from the landing record sheets kept by fishing companies accepting the catch. Except for mechanical breakdown or net damage, the time required for these vessels to make the catch can be assumed to be the same -12-as for those fishing during that period and for which the fishing time was known. The latter method was applied to those fishing crafts which remained continuously on the fishing ground and which were attended to by packers. -13-III. ANALYSIS OF THE DATA A. CATCH STATISTICS •1* -Total Catch.,' The fishing season for butter sole, January 5 to Feb-ruary 17,.has been divided up into nine periods, each being in duration five days on which fishing occurred. This unit of time was selected as a period because i t represented the average time necessary for a l l boats to make a tr i p (Table 1). With the exception of Period III and Period IX a l l periods consist of five days. Period III includes six days but i n -clement weather prohibited fishing on one of these days. Period IX i s only three days long, fishing having terminated before completion of that period. Fluctuations in the total catch occur throughout the fishing season and these are shown i n table II and graphically i n figure 2 together with explanations for their causes. 2* Availability Total catch figures, when not supported by other data which show the fishing effort expended, do not necessarily i n -dicate true fluctuations in the availability of a species of f i s h . Changing conditions in a fishery such as the number and size of boats, differences in their fishing efficiencies, and the period of the fishing season during which they each operated may significantly affect the total catch. Such changes can be accounted for and the true ava i l a b i l i t y of a species can be shown by determining the yield of fish per unit of fishing effort. Fig. 2 A graph showing the fluctuation in the total catch of butter sole per period and the reasons for these. -14-For the butter sole fishery the yield per unit of effort has been calculated and this index has been used to indicate the success of fishing as the average number of pounds of f i s h caught per hour per period of five fishing days. This index of fishing reward i s comparable from period to period and con-sequently can be used to show the trend of the ava i l a b i l i t y of butter sole throughout the fishing season. • The data used in the avai l a b i l i t y study of the butter sole were obtained, as discussed previously, by personal i n -terview with the captains of each fishing vessel or from f i s h house records. The information used in this study was the amount of fi s h caught and the effort expended in catching that amount. Since complete co-operation of a l l agencies was en-, joyed the data are considered reliable. Two factors appeared worthy of consideration when deter-mining the availability of butter soles. In order to eliminate the influence of these, certain adjustments were necessary. F i r s t , fishing units operating during just part of the fishing season w i l l not show the fluctuations in the av a i l a b i l i t y throughout the entire season but only for the period during which i t fished. Therefore, i f a l l vessels are considered as having operated throughout the entire fishing season i t i s pos-sible to eliminate the influence of vessels operating when the availability was either high or low. Second, fishing units of different fishing efficiencies influence the av a i l a b i l i t y trend each in i t s own way, disproportions being a reflection of the degree of efficiency of the vessels operating during each period. -15-The adjustment for these two factors i s similar to that used by Hart (1933) and in other availability studies carried out by the Fisheries Research Board 1s Pacific coast trawl i n -vestigation when distortions i n ava i l a b i l i t y which were pro-duced by different fishing efficiencies and by boats operating for only part of a fishing season were n u l l i f i e d . Arrival at the availability trend for the entire fishing season with a l l boats considered i s as follows. The data are f i r s t weighted so as to compensate for boats fishing during part of a season. To do this i t was necessary to calculate the seasonal average catch per hour for a l l boats fishing throughout the fishing season. Next,the average catch per hour per period was deter-mined and this was done by dividing the total amount of- f i s h caught during each period by the total number of hours fished in that period. To determine the factor for each period the seasonal average catch per hour was divided by the average catch per hour for that period. To adjust for boats fishing for only part of the season the daily catches of a l l boats fishing in one period were multiplied by the factor for that period. Next, the data are treated so as to eliminate fluctuations in the ava i l a b i l i t y which are due to differences in fishing efficiencies of the vessels. To do this the weighted seasonal average catch per hour i s determined by dividing the total adjusted boat catches of a l l periods by the number of hours fished in, a l l periods. Then the weighted seasonal average catch per hour for each boat was determined by summaiing the adjusted daily catches of each boat in a l l periods and dividing -16-this by the total number of hours fished by that boat during the entire season* To determine the boat factor of each boat the weighted seasonal average catch per hour was divided by the weighted seasonal average catch per hour for that boat. Next, the unweighted daily catches of each boat were multiplied by the factor of that boat. The daily weighted catches for each period were then summed and the tot a l for each period i s divided by the number of hours fished in that period. The re-sulting value i s the availability or the average number of pounds of butter, sole caught for each period of the fishing season after variations due to fishing efficiencies have been eliminated. The results are presented in table III and graphi-cally in figure 3. It w i l l be observed that the maximum return per unit of effort occurred during Period I. This high rate of return may be attributed to accumulation of the stock upon the spawning ground prior to the appearance of the f i r s t fishing craft early in January. During Period II and III an apparent de-cline i s evidenced and i t i s during Period HI that the avail-a b i l i t y i s lowest for the entire fishing season. The avail-a b i l i t y increases i n Period IV and remains relatively constant at this new level throughout the following three periods. It may be that immigration into the inlet during this time balances natural and fishing mortality. In Period VII a further increase in a v a i l a b i l i t y i s shown but the value decreases slightly by the time commercial operations cease. Table III The Availability of Butter Sole i n Skidegate Inlet during the Fishing Season. Period Av a i l a b i l i t y (pounds per hour) I 1,403.0 II 807.5 III 658.4 IV 727.8 V 721.3 VI 728.3 VII 710.5 v n i 864.4 IX ' 850.7 Fig-. ? A graph showing the ava i l a b i l i t y of butter sole for the different periods throughout the fishing season* -17-B. FISHING INTENSITY Several workers (Russell 1931, Thompson and B e l l 1934, Graham 1933) have shown that a fishery can be stabilized at different levels of fishing intensity, but that there i s an optimum rate for each species of f i s h . Whether the optimum rate of exploitation for butter soles prevailed during the 1946 season .: is.' • not known. However, an estimate of the fishing rate during that year i s possible. The returns from the tagg-ing experiments have greatly facilitated the determination of this rate. In tagging experiments extending over a period of several days or weeks many factors tend to influence the rate of re-capture of the tagged fi s h . The most important of these must be recognized and wherever possible values should be assessed for them. Ricker (1942, 1948) in his discussion on estimating fish populations by means of recaptured tagged or marked f i s h has brought attention to several sources of systematic errors. Some of these are worthy of consideration and application in the determinations of fishing intensity and are discussed be-low. Others specific to this particular study are also discuss-ed and accounted for. These are: (1) An important source of error arises i f application of the tag causes mortality additional to the natural mortality rate. In this experiment no mortality rate due to' tagging could be assessed in view of the short period during which the actual study was conducted, but i t i s f e l t that the care taken in selecting only the apparently uninjured fis h for tagging -18-would minimize the number of deaths which might be caused directly by application of the tag or i t s subsequent presence on the f i s h after release. In the event, however, that a tagging mortality rate should exist the number of effective tags available to the fishery would be less than the number released, and consequently the estimate of the fishing inten-sity would be too low. (2) Knowledge of the behaviour of tagged individuals as compared with untagged individuals i s lacking. If random dis-tribution of tagged f i s h throughout the entire population i s achieved we might assume that the tagged f i s h form an integral part of the population, and that recoveries from a l l parts of the fishing grounds would be in proportion to the number of butter soles present there. In such a case a reliable estimate of the fishing intensity should be possible. I f , however, tagged f i s h behaved in a manner peculiar to themselves and possibly not form a part of the general population, i t is not unlikely that -an estimate of the fishing intensity would be low. (3) Also, continuous immigration of f i s h onto the fishing grounds w i l l affect the number of tags available to the fishery in relation to the number of f i s h . The effect w i l l be a dilution of the number of tagged f i s h throughout the ; population, the influence of which w i l l result in an estimate of the fishing intensity which w i l l be lower than what i s actually occurring. (4) Emigration of tagged and untagged f i s h from the fishing grounds presumably occurs at the same rate, provided - 1 9 -that tagged and untagged individuals behave alike. If emigra-tion exceeded immigration, a decrease in the population would occur along with a proportionate decrease i n the number of available tags. Important as this consideration may be in a study of a moving population, i t s effect here i s not f e l t since spawning had not taken place and, therefore, movement from the inlet had s t i l l to occur when the investigation terminated. (5) As another source of error the loss of tags may be mentioned. Two possibilities are realized. F i r s t , tags may be caught and torn from f i s h as they take up positions on the bottom. The numbers of tags lost in a manner such as this would appear, at present, to be negligible. Tags may also become lost to the investigator i f they should be misplaced or lost by the recoverer after recovery. To minimize the loss of tags due to failure of reporting the recovery of each an energetic programme was instituted and was coincident with the attempt to personally interview each trawl captain when he unloaded his catch. Owing to the favourable circumstances under which this part of the programme was carried out and, also, that a l l f i s h which were landed were f i l l e t t e d and, therefore, tags could not have been overlooked. I t i s believed that not more than three tags from landed f i s h could have been missed. (6) Another source.of error for which a value i s immeT-diately indeterminate i s the number of tagged f i s h which die naturally and not as a result of being tagged. The effect i s a further reduction in the number of tags available to the fishery and this would result in an estimated fishing rate 20 lower than that which was occurring. (7) The unequal vulnerability of f i s h of different sizes to the fishing gear i s an additional source of systema-t i c error to be considered. The smallest f i s h are possibly not only the most liable to be injured in the act of hauling .the gear, but they are also more'liable than the larger f i s h to pass through the meshes of the trawl, as well as escape notice of the fishermen when actually recaptured. On this account the tagged f i s h were divided into two groups, f i s h which are smaller than the minimum commercial size of 300 millimetres and f i s h which are larger. A graph i l l u s t r a t i n g the number of tagged and recovered tagged f i s h in each of the two size groups i s shown in figure 4. To. eliminate any erroneous conclusions, the chi-square test of significance was used. The nul hypothesis established was that tagged f i s h , whether of commercial size or not, were ". equally liable to recapture. The reason for this assumption was that these f i s h had already failed to escape catching and therefore were capable of being caught again, provided that they do not die from.other causes. The formula used was = S(x-m)2 , where x i s the observed value of an event hap-m pening and m the expected. The number of degrees of freedom for this 2 x 2 contingency classification can be determined from the formula n = ( r - l ) ( c - l ) given by Simpson and Roe (1939) where n i s the number of degrees of freedom, r the number of rows in the contingency tableland c, the number of columns. The calculated value for chi-square was found to be 0.108. NON COMMERCIAL SIZE COMMERCIAL SIZE 100 1 MALES \ TAOSED — ad - \ REOOVERED — >• _ z b l 3 o*° -IT U . 1 0 ' i v.,V, i- , • 0 0 9 0 9 0 0 L E N G 6 0 4 0 0 9 0 ' 9 0 0 T N (MM.) 1(0 ~NON COMMERCIAL SIZE COMMERCIAL SIZE 100 -FEMALES / \ TAGGED ' \ RECOVERED • 0 > o f 0 z Ul 3 ° 4 0 Ul a: '* \ / 7 ' l \ \ t \ \ ' ""*•* \ i \ \ \ » \ * \ i N V i i 1 0 0 9 0 3 0 0 L E N 0 SO « 0 0 SO SOO T H (MM.) Fig. 4 graph showing the frequency distribution of tagged and recovered male and female f i s h ; -21-When examining the prohahility tables which give the d i s t r i -bution of chi-square a value of 3.84 was found for one degree of freedom at the 5% level of probability. From this, there-fore, i t may be concluded that the data do not disagree signi-ficantly from the hypothesis that a l l tagged f i s h , whether of commercial or non-commercial size, are equally susceptible to catch and detection, and therefore usable i n the estimation of the fishing intensity. The rate of exploitation or fishing intensity has been simply defined (Ricker 1945b) as the ratio of the number of recaptured tagged f i s h to the number tagged. This obviously holds good only for the simplest of cases where a l l tags are released just before fishing commences and where systematic errors due to natural and tagging mortality and fluctuations i n abundance do not exist. In the present problem u t i l i z a t i o n of this ratio as an estimate would at best only afford a mini-mum unadjusted value for the .true fishing intensity. This minimum unadjusted value i s 256, the number of tagged f i s h re-covered since commencement of the tagging programme, divided by 1,175, the total number of tagged f i s h released. Expressing this fraction in per cent the fishing rate becomes 21.8. Affecting this minimum unadjusted value, i n addition to the systematic errors already mentioned, i s the fact that the presence of the tagger on board one of the vessels which was actively engaged in commercial operations has influenced the number of recoveries made by that vessel. During tagging, which was carried out concurrently with commercial fishing, i t was observed that occasionally tagged fis h which were just released were landed in the haul which was.being made while tagging was in progress at that time. The explanation offerred for this i s that these f i s h , after having been returned to the water, did not have sufficient time to disperse during their descent and as a result swam into the path of the oncoming net as they attempted to take up their position on the bottom. During the seven consecutive tagging days during which obser-vations were made, eight tagged fish were recovered in this manner. This overabundance of tags recovered by the tagging ves-sel i s corroborated when the total landings of the entire fleet and that of the tagging vessel are compared with the total num-ber of recoveries made by each. ' During the period of observa-tion, 162,250 pounds of butter sole and 69 tagged f i s h were caught by the entire f l e e t . During this same period the tag-ging vessel caught 51»500 pounds of fish and 32 tagged f i s h . Assuming a random distribution of the tagged fis h throughout the population and therefore the chances of a tagged f i s h being caught equal, the tagging vessel should have recovered 51.500 x 69 or 21.9 tagged f i s h . Instead, the tagging vessel 1,622 recovered 32 tags. If this condition of recovering "extra" tags should exist for part of the tagging season there i s no reason why i t should not be operative throughout. To correct for these "extra" tags only the tagging days upon which the tagging vessel recovered tagged f i s h could be used. A factor for "extra" tags was -23-obtained as a result of the observations carried out over seven tagging days and the- "extra" tags per tagging day was corrected for throughout the whole season. The correction would mean •that actually less tags were available to the fishery than what were released, and consequently, there could only be fewer tags from which to compute the correct fishing intensity. The method of correcting for this error i n the number of tagged f i s h re-covered i s shown below. No. of tagging days during which /-'observations were carried, out..- 7 No. of "extra" tags recovered during the period under observa-tion = 8 Correction by observation = 8- or 1.14 per tagging day. 7 No. of tagging days upon which tagging vessel recovered tags = 22.5 "Extra" tags per season = 22.5 x 1.14 = 25.65 or 26 Legitimate recovered tags = 256 - 26 = 230 Before continuing with the explanation of the method of calculating the adjusted fishing intensity two other factors and the correction for these should be considered. One con-cerns the date of recapture of those tags for which the exact date of recapture i s not knowA, and the other i s that a l l f i s h were not out the same length of time, and consequently a l l could not be considered as equally liable to be caught. Those f i s h tagged earlier i n the season were subjected to greater chances of being caught than those released later. To adjust for the former, the known period during which a tag could have been -24-recovered i s halved and the half period i s added to the time when i t i s known that the tagged f i s h could have been recovered. By doing this the error introduced by not knowing the exact date of recapture i s minimized. For the la t t e r , the complement of the total seasonal catch for each period of the season was used. The method, suggested by Dr. J. L. Hart, only considers the tags which were recovered during the period in which i t was released or thereafter as one of the f i s h s t i l l to be caught during the period which transpired between tagging of the f i s h and when fishing i n the inlet ceased. The method of calculating the adjusted fishing intensity using the corrected number of tags available and recovered by the fishery for the different periods throughout the season follows. The complement of the total seasonal catch for each period i s tabulated in column 6. To determine the suscep-t i b i l i t y of a tag to recapture both column 3 and 7 were summed and the former divided into the latter. A further division of this quotient into the product of the sum of column 5 and total catch for the periods III-IX, inclusive, gives the total number of effective tags which would have been recovered had a l l f i s h been released at the beginning of the fishing season. - 2 5 -• 1 2 3 4 5 6 7 Period Tags used Actual Tags Tags used Recov. Legitimate Actual Tags Recov. Legitimate Complement Column 3 Total Seas. x Catch Column 6 (lbs.) I 0 II 0 III 2 0 0 1 9 5 . 4 4 44 39.44 669,450 1 3 0 , 8 3 7 , 3 0 8 17 2 2 5 2 2 1 . 0 1 5 5 5 1 . 0 1 5 8 5 , 9 5 0 1 2 9 , 5 0 0 , 8 0 0 V 2 0 0 195.44 4 7 42.44 5 0 2 , 7 5 0 9 8 , 2 5 7,460 VI 1 0 0 2 9 7 - 7 2 2 2 1 9 . 7 2 3 7 0 , 2 5 0 3 . 6 , 1 8 0 , 8 3 0 VII 2 0 0 1 9 5 . 4 4 2 9 24.44 244 , 7 5 0 4 7 , 8 3 3,940 VIII 1 5 0 146 .58 41 3 7 . 6 8 149 , 8 5 0 2 1 , 9 6 5 , 0 1 3 IX 1 0 0 9 7 . 7 2 1 8 1 5 . 7 2 49,450 4 8 , 3 2 2,540 Total 1 , 1 7 5 1,149-35 2 5 6 2 3 0 . 3 5 2,572,450 5 1 2 , 8 9 7 , 9 0 1 Total"Column 7 Total Column 3 - 512.897.901 = 446 ,250.4 (Recovery Susceptibility 1,149.35 Factor) Total Column 5 x Total Catch (III-IX) . 230.35 x 686.250 = 3 5 4 . 2 Recovery Susceptibility Factor 446 ,250.4 Adjusted Fishing Intensity = 354.2 « 3 0 . 8 % 1,149.35 The rate of fishing arrived at by the above method i s con-sidered the most accurate obtainable from the data on hand. It is impossible at this time to say whether this rate i s the optimum level of exploitation for the butter sole. -26-C. ABUNDANCE Many studies of the abundance of various animal popula-tions (Peterson 1896, Lincoln 1930, Jackson 193&) have been carried out by liberating a known number of marked or muti-lated individuals. .At a later date the population i s resampled using the same methods as previously and the proportion of mutilated or marked individuals to unmarked ones i s noted. This proportion of marked to unmarked individuals should be the same in the sample of the*"population as in the population at large. Therefore, Total marked - Number of recovered marked individuals Tdtai popiaiiation." Total number of individuals in sample Transposing, the total population can be determined. It- i s obvious, however, that the above formula i s useful only in the simplest of cases, that i s , when marking takes place at the beginning of the experiment, and where fluctuations in 1 abundance due to recruitment,, migration and mortality are not extensive enough between the periods of sampling to cause any significant variations in the abundance of the population. These conditions do not prevail in the present study, and in addition the release of marked fish was coincident., .with \.. the removal of marked and unmarked f i s h . As an alternative for the above method the following pro-cedure was used to estimate the abundance of the butter sole population. Instead of u t i l i z i n g the method of proportions the estimated rate of fishing, the average seasonal sex ratio, the average seasonal length and average seasonal weight of both sexes, and the total catch were used. This method i s consider-ed to give at best only an approximate value for the absolute -27-numbers of f i s l i in the population but at the present time know-ledge of this sort i s desirable. In the section on fishing intensity the rate of exploita-tion as assessed from tag returns was found to be 30.8 per cent. At this level of exploitation 830,000 pounds of butter sole were removed from the total stock. The escapement, therefore, can be the quantity of f i s h not caught. The quan-t i t y of fish i n the escapement determined in this manner would represent the absolute escapement only i f there were an equal number of male and female f i s h and only i f each were one pound in weight. However, sampling for length-frequency and sex ratio indicated that this was not the case, but instead that there were many f i s h of different size groups, and therefore of different weights, comprising the catch. To compensate for the differences i n length and disparity of the sexes which occurred during the season and also to mini-mize the error which would result i f the data for just part of the season were used, the seasonal average for length and weight of both sexes and sex proportions were used. The average length for males and females which was obtained from length measurements taken on a l l grounds and throughout the fishing period was 323.4 millimetres and 353.4 millimetres, respectively. The average weights were obtained from length weight curves (unpublished data) and the weights of average male and female f i s h were determined from the respective curves. The average weight was found to be 12 ounces for males .and 16 ounces for females. The average seasonal sex ratio as determined from shore samplings was 48.8 per cent males. -28-The abundance of butter soles i s regarded as the number of f i s h on the grounds during the season, that i s , the f i s h which contributed to the total catch and the escapement. The abundance was computed in the following manner. Number of fi s h in total catch of 830,000 pounds. Weight of males in tot a l catch '•- j^-- * 830,000 = 405,040 pounds. Weight of females in total catch - 830,000 - 405,040 -424,960 pounds. Number of males in total catch at 12 ounces per male = 16 x 405,040 = 540,040 f i s h . 12 Number of females in total catch at 16 ounces per female = 424,960 f i s h . •Number of f i s h i n escapement = 69.2 x 830,000 = 1,864,805 pounds. 307F Weight of males in escapement =. 48.8 x 1,864,805 = 100 910,025 pounds. Weight of females i n escapement = 1,864,805 - 910,025 -954,780 pounds. Number of males at 12 ounces per male = 16 x 910,025 = 12 1,213,366 f i s h . Number of females at 16 ounces per female J» 954,780 f i s h . o Abundance (summation of total catch and escapement) = 3,131,146 f i s h or approximately .3,130,000 butter soles. D. MOVEMENT 1. Differential Appearance of the Sexes upon the Fishing Grounds. Examination of the landings made at the port of Prince Rupert throughout the fishing season for sex ratios provides - 2 9 -information which i s useful in determining the diffe r e n t i a l appearance of the sexes in Skidegate i n l e t . Shore samples were used in this study because i t was thought that these would best represent the general population since boats usually fished more than one ground while catching a sufficient quantity of fi s h which would permit making a profitable t r i p to port. Also, during handling on board and on shore the f i s h would become reasonably mixed and this would further alleviate the possi-b i l i t y that the sample would be representative of an area which at the. time of fishing one sex, due to some cause, might be more abundant than the other but s t i l l not represent the popu-lation at large. Samples were obtained for a l l periods except Periods-I and VII. Where a boat fished during portions of two succes-sive periods the sample was considered as an average for those periods concerned. The sample size in numbers of individuals ranged from 230 to 696. A tabulation of the percentage of females for each sample according to the periods of the fishery i s presented in table IV. It w i l l be observed from table IV. that there i s a pre-ponderance of males u n t i l Period III. This disparity decreases to approximate equality by the latter portion of Period V and by the beginning of Period VI, and i s then followed by a pre-ponderance of females. When fishing ceased 60 per cent of the fish landed were females. Since no extensive spawning had occurred at the time of closure of the area and,'therefore, the males would not have Table IV The Proportion of Females Comprising the Catch during the Different Periods of the Fishery. Period Female s (per cent) II 41.4 III 48.6 III-IV 51.1 V-VI 52.6 VI 55-6 VIII 59-1 -30-withdrawn from the area before this time, i t would appear that the male f i s h enter the inlet f i r s t to be later followed by the female s. 2. Movement within Skidegate Inlet. A study of the movement of the butter, sole within Skide-gate inlet was made possible by tagging f i s h on the four f i s h -ing grounds, and then noting where each recovery was subsequent^ ly made. The distribution of the 1,175 f i s h tagged on the various grounds i s as follows. JTlve hundred and.fifty-three were put out 0 1 1 the Village ground, 130 on the Grassy island ground, 342 on the Buoy ground, and 150 on the Beach ground. Only tags which were out one day or more were used. The re-covery information of only two fishing crafts were considered sufficiently reliable to warrant their use. These two vessels accounted for 56 of the 256 recoveries made prior to cessation of fishing in the in l e t . In order to eliminate any indications of a preferred move-ment between areas which might be suggested i f only the abso-lute number of recoveries were considered, the number of re-coveries were weighted up as i f 1,000 tags had been released in a l l areas. This procedure provides a method whereby i t i s possible to compare the number of recoveries made in one area with those made in another on the basis that the same number of tags were released in each. Further, realizing that a concen-tration of fishing effort on any one ground might also tend to influence the number of recoveries made on that ground, the number of fishing days which the two boats spent on each ground during the entire season was determined. Once knowing the- num-ber of recoveries made on each ground and the effort expended in obtaining these, the number of tags recovered per fishing day on each ground can be computed. Using this as an index of tag recovery and expressing i t as a per cent of the total of "the indices for any one area in which tagging was carried out, i t i s possible to determine the extent of movement between the different grounds. The.percentages are presented in table 37y. the columns representing the recovery areas, the rows the tagging areas. No usable recoveries from the Beach taggings are avail-able for inclusion in table Y. Two reasons may be offered for this. F i r s t , the taggings which were carried out there were done so during the last three days of the fishery, and there-fore the chance of recovering these was not very great. Second, only one reliable vessel fished in Skidegate inlet during this period and i t s efforts were not confined to the Beach ground alone. Table V shows that: 1. The dispersion of butter sole from the Village ground to other grounds i s approximately equal. Most of the recoveries (28.2%), however, occurred in the area where tagging was carried out. 2. The greatest dispersion of fish_tagged on the Grassy island ground occurred towards the Beach ground. From this tagging approximately three times as many f i s h were recovered on this ground than on any other. Table V Number of Tags (weighted and. expressed in per cent) Recovered, According to Area of Tagging and Area of Recovery, during January and February. Tagging Area RECOVERY AREA Village Grassy Island Buoy Beach Village 28.2 22.8 26.5 22.5 Grassy Island 20.4 14.6 6.8 58.3 Buoy 6.3 — 38.7 55.0 Beach — — — — -32-3. The interchange of tags from the Village ground to the Grassy island ground and vise versa is approximately equal, 22.8% and 20.4% respectively. 4. Relatively l i t t l e movement (6.8%) from the Grassy i s -land ground to the Buoy ground is evidenced. 5. Over half (35»0%) of the recaptured tagged fish which were released on the Buoy ground were recovered on the Beach ground. There were no recoveries from this tagging made on the Grassy island ground. Only 6.3% were reported to have taken place on the Village ground. 3- Dispersion of Butter Sole from Skidegate Inlet. Information pertaining to the dispersion of butter sole from Skidegate inlet is a product of the commercial interest shown in this species after spawning has been completed and the withdrawal from the area has been affected. Recoveries, how-ever, can only be made where fishing occurs. Knowledge concerning the movement of this fish from the spawning ground has been obtained from 12 recovered tagged f ish . Eleven of these were recovered during 1946 while the twelfth was recovered during 1947. A tabulation of the re-coveries according to location and date appears in table VI. A chart illustrating position of the recoveries in Hecate strait is presented in figure 5« Movement towards Fife Point is shown by a group of 9 recoveries. One of these was recovered 12 miles north-east of Cape Ball during the latter part of May. The remainder were'* recovered off Fife point, approximately 33 miles north of Table "VI Movement of Butter Sole, tagged i n Skidegate Inlet, into Hecate Strait, with Reference to Date and Locality of Recapture. Location Date Number 12 miles N.E. Cape B a l l 24/5/46 1 Off Fife Point 25/5A6-3/8/46 8 South of Butterworth Rocks 28/5/46 1 35 miles E.X.N.E. of Kunghit Island 28/6/46 1 Off White Rocks -/10/47 1 -33-Skidegate inlet during the period from the latter part of May to August. Other recoveries were made south of the Butterworth rocks, off White rocks and 35 miles east~by north-east-' 6f Kuhghit island. A l l recoveries except the one made off White rocks were made during 1946. The recovery off White rocks occurred during October, 1947. Interpreting the recoveries on a seasonal basis i t appears that after spawning in Skidegate inlet the butter sole move out into Hecate strait during March, Apr i l and. May.and remain there u n t i l October at least. The most extensive movement, as shown by tag returns, appears to be towards the ground situated off Fife point, where the occurrence of this species there affords a summer time fishery which lasts from June to August. The remaining recoveries suggest that there i s some dispersion throughout Hecate strait with no evidence of concentration in numbers similar to that shown by the tags recovered off Cape Fife. IV. DISCUSSION The investigation of the butter sole i n Skidegate inlet during January and February has employed a v a i l a b i l i t y , tagging, and sampling studies. of the a v a i l a b i l i t y of the species has shown that fluctuations exist during the regular fishing season. During the f i r s t week of the fishery the avail-a b i l i t y i s maximal (1403.0 pounds per hour). It i s believed that an accumulation of early migrants i n the inlet and compet-i t i o n for these by relatively few boats i s responsible for this i n i t i a l high return for the effort expended. Following this period of maximum availabilty an addition of boats to those already fishing occurs. Accompanying this increase in the number of boats i s the simultaneous drop in the availablity u n t i l January 15-20, <:'. when: i t i s the lowest. Following this period of low availablity a recovery i s made and the availabilty commences to increase, then remains relatively stable u n t i l February 5-9, and then further increases u n t i l the end of the season. At no time, however, does the availabilty approximate the level which prevailed during the early part of the season. What are the factors influencing the a v a i l a b i l i t y of the butter sole in the inlet? It has been pointed out above that competition between boats appears to be responsible for the < decline during the very early portion of the season. This reason, however valid for this period, does not hold for the remainder of the season when there i s an increase i n the availability as well as i n the number of boats. Examination of -35-shore samples for sex proportions indicate that the retardation of the drop and the eventual increase i s concurrent with the differential appearance of the male and female f i s h into the inlet where spawning w i l l later take place. When the availab-i l i t y commences to increase ( January 15-20) the smaller male fi s h are prevalent. As their dominance i s gradually replaced by the larger female' f i s h an increase i n the availablity occurs, continuing u n t i l the end of the season. It i s possible, also, that weather, temperature, and hydrographic conditions may cause fluctuations in the av a i l a b i l i t y but i t i s thought that the influence of these i s not important here. It has been mentioned earlier that there i s an optimum rate of fishing for each species of f i s h . This rate i s one which takes f u l l advantage of the maximum growth rate of the population. For the butter sole the fishing rate has been determined but i t i s impossible to say at this time whether the rate of 30.8 per cent i s most suitable for maintenance of maximum yield. An attempt of this would require information on the growth, mortality, and recruitment of the population. Knowledge of these v i t a l s t a t i s t i c s are necessary for i n t e l l -igent fishery management but the study of these does not come within the scope of the present investigation. During the period of study movement of the butter sole has been determined. The appearance of the f i s h i n the inlet i s undoubtedly the result of a spawning migration of maturing and mature individuals. Within the inlet the f i s h move about but movement towards the Beach ground i s most common. It may -36-be that this i s the region where most of the spawning takes place. After spawning the Spent f i s h disperse into Hecate s t r a i t . The dispersion i s most extensive towards.the grounds off the north-east corner of Graham island. The movement in that direction may have been caused by a search for food which ultimately resulted i n a -feeding migration. Suggestions for Improvement i n the Method of Study. Based on the d i f f i c u l t y of obtaining adequate data for certain aspects of this study, the author offers suggestions which i t i s hoped w i l l assist the planning of any similar fut-ure study. Since much of the results depend upon tag returns, i t i s recommended that the tagging be controlled and the i n t -ensity much greater oh a l l grounds than that employed i n the present study, and that the periods of tagging should be app-roximately one week apart instead of daily. The tags recovered from ah intensified programme should also provide;, adequate and accurate data concerning the movement of vthe f i s h between the various grounds. To determine whether this movement can be correlated with the development of the spawning condition of the f i s h samples for gonadal and egg development should be taken on these grounds. To give accurate results the observat-ions should be approximately simultaneous since i t i s useless to combine observations taken at different periods as the phenomena dealt with are continually changing. To effectively carry out such a programme a chartered vessel or one which can be used f u l l time i n the study should be made available to the investigator. -37-V. SUMMARY AND CONCLUSIONS 1. The fishery for butter soles i n Skidegate inlet i s one of the important winter trawl fisheries i n northern Br i t i s h .Columbia waters. During 1946 approximately 830,000 pounds of fi s h were caught and landed during the 6 week fishing period. 2. The species migrates into the inlet to spawn and in so doing affords an accumulating population which can be easily exploited. 3. The analysis of catch .statistics reveals that the avail-a b i l i t y i s not constant throughout the entire season but that i the highest return per unit of effort i s indicated during the very early portion of the season when the accumulated stock i s f i r s t fished. 4. The minimum fishing intensity in Skidegate inlet was found to be 30.8%. 5. The abundance of butter soles, during the 1946 fishing season was estimated to be approximately 3»130,000 f i s h . 6. A differential appearance of the sexes upon the grounds in the inlet i s indicated. During the early part of the season the males are most abundant. Their dominance i s gradually overcome by the female f i s h by mid-season. Following this time there i s a greater proportion of females. 7. After removal of the accumulated stock of butter soles the availability increases and the increase i s simultaneous with the increase in the proportionate number of female f i s h appearing on the grounds. 8. Movement of "butter sole throughout Skidegate inlet is shown. There i s a greater movement from the south-eastern shore towards the north-western shore than in the reverse direc-tion. Of the grounds situated towards the north-western shore most movement is shown to occur towards the Beach ground. 9. Dispersion of butter sole froituSkidegate inlet into Hecate strait i s evidenced. The most extensive dispersion i s towards cape Ball and Fife point, east coast of Graham island, where a summer fishery for this species prevails. -39-VI. ACKNOWIEDGEMENTS The author wishes to express his thanks to Dr. R. E. Foerster, Director of the Pacific Biological Station, for permitting the use of the material for this work. The. author extends his sincere appreciation to Dr. J. L. Hart, in charge of the trawl investigation, for helpful sugges-tions and criticisms. The writer acknowledges appreciation to Dr. W. A. Clemens and Dr. W. S. Hoar of the Department of Zoology for suggestions and. assistance rendered during the preparation of this manu-script. The author i s indebted to Mr. P. Haan, owner of the vessel from which the investigation was conducted. Sincere thanks are also extended to Miss P. V. Collins for typing this report and to Mr. C. R. Forrester for assist-ing in the preparation of the figures. \ -40-VII. REFERENCES Clemens, W. A. and G. V. Wilby. 1946. Fishes of the Pacific coast of Canada. Fish. Res. Bd. Can. B u l l . 68, 1946. Graham, M. 1935. Modern theory of exploiting a fishery, and application to North Sea trawling. J. Con-s e i l . , 10, 264-274, 1935. Hart, J". L. 1933. Catch statistics of the B r i t i s h Columbia pilchards. B u l l . B i o l . Bd. Can., No. XXXVIII, 1-12, 1933. Jackson, C. H. N. 1939« The analysis of an animal population. J. Anim. Ecol., 8, 238-246, 1939. Lincoln, F. C. Norman, J. R. Ricker, W.-E, Russell, E. S Thompson, W 1930. Calculating waterfowl abundance on the basis of banding returns. U.S. Dept. Agric. Circ. 118, May, 1930. 1934. A systematic monograph of the flatfishes (Heterosomata). B r i t . Mus. Nat. Hist,, 1, 1934. 1942. Creel ^gensus, population estimates and rate of exploitation of game fi s h i n Shoe Lake, Indiana. Invest. Ind. Lakes and Streams, 2, (12), 215-253; 1942. I945. Abundance, exploitation and mortality of the fishes in two lakes. Invest. Ind. Lakes and Streams, 2,- (17), 345-448, 1945. 1948. Methods of estimating v i t a l s t a t i s t i c s of f i s h populations. Ind. Univ. Publ., Sci. Ser. No. 15, I-94, 1948. 1942. The overfishing problem. Cambridge Univ. Press, London, 1-127, 1942. F. and F. H. B e l l . 1934. Biological s t a t i s t i c s of the Pacific halibut fishery: (2) Effect of changes in intensity on total yield and eld per unit of gear. Rept. Int. Fish. Comm., gieia 49, 1934. Simpson, GV G. and A. Roe. 1939. Quantative Zoology. McGraw-H i l l Book Co. Inc., New York, 1939. -41-VIII. APPENDIX Table 1 Number of Trips Made by Fishing Vessels and the Average Duration of Each. Vessel Number of Trips Average Time Per Trip (days) A . 3 3 B 4 C 2 3 D 3 4 E 1 F * 4 G 4 7 H 1 3 •i .-1 Mean 4.88 1 -y * Fishing craft which remained continuously on the fishing grounds and discharged their fares by packer. Table 2 Daily Catches of Butter Sole Made by Each Boat Operating i n Skidegate I n l e t . ..' Date P 0 u N D S A B c D E F G H Jan. 5 4,000, 6 5,000 7 5,000 8,ooo 8 10,000 11,000 3,200 9 6,000 10 6,000 8,000 5,000 10,000 n 6,000 7,500 7,000 12 6,700 2,500 5,000 13 2,629 5,000 14 3,000 9,000 ii 4,000 6,000 _ L O 17 300 6,500 18 5,000 5,000 19 3,000 500 3,000 7,000 20 6,000 3,000 6,000 5,000 21 2,000 2,000 1,000 4,000 4,000 22 6,000 8. ,000 5,000 7,000 5,000 6,000 23 4,000 2,000 4,000 5,500 6,000 24 7,000 7,000 3,400 6,000 25 3,000 5,300 4,000 26 5,000 5,000 6,000 27 4,000 4,000 28 5,000 4,200 29 12,000 3,000 6,300 30 12,000 12,000 4,500 8,000 5,000 31 6,000 7,000 5,6oo 5,000 Feb. 1 7,000 13,000 5,900 6,000 5,000 2 8,000 9,000 5,500 5,000 5,000 3 8,000 6,000 8,000 7,000 4,000 4,700 4 6,000 2,000 2,000 1,000 5 6,500 5,000 5,000 4,000 6 6,000 9,000 4,800 4,000 7 6,500 5,000 8 6,000 5,000 9 8,500 5,600 t 10 8,000 6,000 13,000 11 6,500 10,000 5,800 9,000 12 5,000 4,000 6,500 4,000 13 14,000 6,000 14 6,000 . 9,000 5,500 8,000 15 14,000 7,500 5,900 5,000 16 9,500 7,000 6,750 6,000 17 14,000 6,000 18 I T a b l e 3 Tags R e l e a s e d ( D a i l y ) on the V a r i o u s Grounds and the Numbers S u b s e q u e n t l y R e c o v e r e d . DATES OF RECOVERIES DATE TAGGING NO. TAGS NO. OF J a n u a r y F e b r u a r y 8 16 TAGGING LOCALITY USED RECOVERIES 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7 9 10 11 12 13 14 15 1 J a n . 18 1 100 18 1 2 5 2 1 2 19 2 50 15 1 1 1 2 2 - — — - - - - 1 - 1 1 - 1 - - - - - - 1 2 - 1 - -20 1 50 11 2 2 - 2 1 2 1 1 21 1 25 5 2 1 1 1 - - -22 1 50 12 5 — 1 1 — — 1 - - - 1 — — — - - — - - - - 1 - 1 - - 1 23 1 50 12 3 3 1 3 1 1 24 1 50 10 2 2 — - - 2 — - - — 1 2 - — — - - - — - 1 - - — — 23 1 50 16 6 — 1 — 1 — 1 — _ 4 — — — 1 — — 1 — - — — - — 1 26 1 20 3 2 — _ — — - — — _ — — — — — — — _ 1 — — — — 26 2 30 10 3 — — - — 1 - 1 - 1 - — - — - - — 1 1 2 — - — 27 2 50 4 1 1 2. 29 1 50 17 6 3 - — 1 — - 1 - - 3 — - - - 2 1 — — -30 3 50 13 6 2 — 2 2 — — — — - — - - - — 1 — _ — Feb., 1 3 50 15 6 4 4 - 1 3 3 50 7 3 1 1 — — - 1 - - - 1 — - - -5 3-1 50 8 4 1 1 — — - 2 — — — — — 6 1-3 50 4 2 — - — - 1 — — 1 - — — 7 3 50 8 2 1 1 2 1 — — 1 — — — 9 3 . 50 9 4 - - — 2 2 1 — — 10 1 50 19 4 7 1 - 6 - - 1 12 1 50 8 5 - 3 - - -14 4 50 14 9 2 3 -15 4 50 12 7 4 1 16 4 50 6 4 2 TOTAL 1,175 256 1 3 8 5 10 9 6 10 5 2 1 9 12 5 8 1117 6 8 85 4 6 9 11 9 11 29 11 11 6 T a g g i n g A r e a s - 1. O f f S k i d e g a t e V i l l a g e 2. O f f G r a s s y I s l a n d 3. S k i d e g a t e V i l l a g e n e a r Buoy 4. S k i d e g a t e V i l l a g e n e a r Shore Table 4 Length Distribution of Male and "Female Butter Soles Landed at the Port of Prince Rupert, Jan. 10 - Feb. 13. PERIOD Length II III III--IV V-•VI VI VII (cm.) 6* <S ? d 9 0" 9- • c? 0* "9 20 ; i 21 1 22 ' 3 l 23 1 2 4 3 2 ^ 7 1 26 10 4 1 27 26 I . 7 28 18 2 7 2 9 3 2 5 1 6 29 25 4 9 1 6 2 7 1 2 4 1 30 35 5 19 3 13 3 17 5 8 1 12 1 31 . 5 19 2 20 6 22 5 10 1 15 4 32 46 9 25 6 16 13 26 10 23 10 1 4 9 33 59 19 27 22 2 4 19 5 £ 21 23 15 21 9 34 58 35 34 21 1 4 18 28 23 19 26 4 1 4 35 52 53 29 51 16 29 26 4 0 20 2 4 12 22 36 2? 4 1 11 30 8 20 1 4 33 13 26 5 26 37 6 4 2 1 22 1 13 5 31 6 22 1 17 38 1 35 1 12 2 10 22 1 18 19 39 1 20 2 5 11 12 9 4 0 9 2 1 3 4 4 1 2 2 1 1 4 2 1 43 Total 4 1 5 281 185 175 . 1 4 0 1 4 6 180 206 129 159 94 136 Table 5 The Number of Tagged Fish Recovered on the Various Grounds with Relation to the Area in which they were Tagged. Recovery Area Tagging Area Village Grassy island Buoy Beach Village 16 • 6 15 3 Grassy island 3 1 1 2 Buoy 1 - 6 2 Beach - - -


Citation Scheme:


Citations by CSL (citeproc-js)

Usage Statistics



Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            async >
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:


Related Items