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The correlation between temperature and salinity and the catch of coho salmon (Onchorhyncus kisutch)… Taylor, Vincent Reginald 1952

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THE CORRELATION BETWEEN TEMPERATURE AND SALINITY AND THE CATCH OF COHO SALMON (ONCORHYNCHUS KISUTCH) IN THE KAINS ISLAND FISHING AREA  by VINCENT REGINALD TAYLOR  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF .. THE REQUIREMENTS FOR THE DEGREE OF . MASTER OF ARTS  i n the Department of ZOOLOGY  We accept t h i s t h e s i s as conforming t o the standard required from candidates f o r the degree of MASTER OF ARTS  Members of the Department' of Zoology  UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1952  ABSTRACT  The r e l a t i v e abundance of coho salmon (Oncorhmchus kisutch) i n the Kains i s l a n d t r o l l f i s h i n g area was computed, f o r the years 1943 to 1951 i n c l u s i v e , on the basis of the average catch per boat per day each year.  The r e s u l t i n g f i g u r e s varied from a minimum  of 75, pounds per boat per day i n 1946 to a maximum of 231 pounds per boat per day i n 1951. These y i e l d per u n i t e f f o r t f i g u r e s were then s t a t i s t i c a l l y compared with the average surface s a l i n i t y , or average surface temperature, f o r various periods i n the l i f e h i s t o r y of the coho taken by the f i s h e r y i n these years. I t was found that a very high correlation ( r = 0.85, p = 0.01 - ©.001) existed between the average "summer" s a l i n i t y (June to September i n c l u s i v e ) and the poundage y i e l d per u n i t e f f o r t during that same year. I t i s suggested that t h i s c o r r e l a t i o n i s explainable i n terms of varying growth rates i n d i f f e r e n t years, and by variations i n the numbers of f i s h taken i n these years, both of these factors being governed by the a v a i l a b i l i t y of food, as evidenced by surface s a l i n i t y .  (i) TABLE OF CONTENTS Page LIST OF TABLES  i i i  LIST OF FIGURES  i i i  INTRODUCTION Statement of Problem  1 .  L i m i t a t i o n s of the Study  1 . .  1  Species L i m i t a t i o n s  2  Area L i m i t a t i o n s  2  L i f e H i s t o r y of the Coho Salmon Fresh-water Phase  3 4  ......  5  Salt-water Phase The Ocean T r o l l F i s h e r y f o r Coho  5  Data from Tagging Experiments  6  • Coastal Oceanography  '  7  The Off-shore Currents  7  The In-shore Currents  .  9  L a t e r a l In-shore System V e r t i c a l In-shore.System  8  ....  Local Features of the Kains" I s l a n d F i s h i n g Area  9 11  MATERIALS F i s h i n g Records  11  S a l i n i t y and Temperature Records  13  METHODS Treatment of F i s h i n g Records  ......  13  (ii) C r i t e r i o n of R e l a t i v e Abundance . .'  14  The Boat-day, a Basic Unit of E f f o r t  16  Average Catch per Boat per Day each Year  ...»  Treatment of S a l i n i t y and Temperature Data  . .  16 17 17  S t a t i s t i c a l .Treatment C o e f f i c i e n t of C o r r e l a t i o n  ......  Test of S i g n i f i c a n c e  .  17  •  Regression C o e f f i c i e n t  . . . . . . .  RESULTS  17  . .  Average S a l i n i t y and Y i e l d  18 18  20  '.  The C o r r e l a t i o n between Y i e l d and Average S a l i n i t y the same year  23  Average S a l i n i t y F i r s t Year i n the Sea, and Y i e l d 24  f o l l o w i n g year  25  Average Temperature and Y i e l d  27  DISCUSSION Nutrient S a l t s and Phytoplankton  28'  Phytoplankton and Zooplankton  . . . . . . .  29 29  Zooplankton and Nekton F i s h Populations and Hydrographic Factors  . . . . . . . . . . .  30 32  S a l i n i t y Correlation Direct Influence of S a l i n i t y  32  I n d i r e c t Influence of S a l i n i t y  33  M o r t a l i t y during Second Year i n the Sea Growth Rate during Second Year i n the Sea Temperature Non-correlation  . .  . 34 34 37  . SUMMARY  38  "  ACKNOWLEDGEMENT  (page)  . .  39 40  LITERATURE CITED LIST OF TABLES I. II. III.  15  The f i s h i n g record compiled on a'yearly basis . . . . . . . .  19  Average s a l i n i t y f o r periods i n marine l i f e o f coho  IV. V. VI.  Number of boat-days f i s h e d  caught i n any year  21  Correlation'between average s a l i n i t y and y i e l d  22  Average temperature f o r periods i n marine l i f e of coho caught i n any year ....... C o r r e l a t i o n between average temperature and y i e l d . . . . . .  26 27  LIST OF FIGURES ( f o l l o w i n g page) 1.  Map showing l o c a t i o n o f Kains i s l a n d f i s h i n g area  2.  Average "summer" s a l i n i t y and y i e l d per u n i t e f f o r t same year plotted' as.percentage deviations from mean ( s a l i n i t y deviation x20)  23  S c a t t e r diagram of average "summer" s a l i n i t y and y i e l d per u n i t e f f o r t same year, 1943 t o 1 9 5 1  23  Y i e l d per u n i t e f f o r t and average "summer" s a l i n i t y preceding year p l o t t e d as deviations from the mean. ( S a l i n i t y deviation x20)  24  3. 4.  2  INTRODUCTION The relationship between animals l i v i n g i n the sea and their environment i s a very intimate one, and small changes i n environmental conditions are quickly brought to bear upon the forms living there. This i s as true of the nektonic animals, especially f i s h , as i t i s of the numerous other types of l i f e found i n the sea. Workers i n fisheries research have always appreciated that such a relationship existed, but i t i s only within relatively recent years that any concerted effort has been made to interpret variations i n f i s h populations with the aid of oceanographic data. The main drawback i n using oceanographic data i n fisheries research has been—and s t i l l i s — a lack of fundamental knowledge about the marine areas concerned.  In particular, there i s a lack of longterm knowledge.  Records over considerable numbers of years are necessary-so that the "norms" of the various hydrographical components may be calculated. I t i s necessary that these "norms" be known i f the changes i n hydrographical conditions from year to year are to be properly assessed. This present study i s an attempt to interpret the yield of one commercially important species of f i s h i n terms of some of the more obvious features of i t s marine habitat. Statement of Problem The study i s an attempt to determine statistically, for a limited area, whether or not a correlation exists between the commercial catch of coho salmon (Oncorhynchus kisutch) i n their marine habitat, and the environmental factors of salinity and temperature. Limitations of the Study There are two primary limitations affecting this study.  These are:  (2)  ( l ) the number of species t h a t are i n v e s t i g a t e d , and (2) the l i m i t e d area f o r which f i s h i n g records were obtained.  I t was considered that a s m a l l  scale study such as t h i s would l e n d i t s e l f b e t t e r to an accurate assessment of the v a r i a b l e s i n v o l v e d . Species L i m i t a t i o n s The coho salmon has been the only species i n c l u d e d i n the i n v e s t igation.  I t i s one of the two species of P a c i f i c salmon t h a t i s i n t e n s -  i v e l y f i s h e d i n the marine h a b i t a t by ocean t r o l l fishermen. species thus f i s h e d i s the s p r i n g salmon (0. tshawytscha).  The other The coho was  chosen i n preference t o the s p r i n g , p r i m a r i l y because of the r e g u l a r i t y of i t s l i f e c y c l e , both i n the r i v e r and i n the sea, as compared w i t h the i r r e g u l a r i t i e s of the l i f e c y c l e of the spring. Area L i m i t a t i o n s I t would have been d e s i r a b l e , had the necessary information been a v a i l a b l e , to have considered the complete marine catch of coho salmon i n B r i t i s h Columbia.  The needed records were however, not a v a i l a b l e , and i t  was not p o s s i b l e to c a r r y out such a comprehensive study*  Instead i t has  been confined to only one of the major f i s h i n g areas of the coast of Vancouver i s l a n d . The area chosen from which to o b t a i n the necessary records was the Kains i s l a n d f i s h i n g area.  This area i s s i t u a t e d o f f the mouth of Quat-  sino sound, on the northwest coast of Vancouver i s l a n d .  The s i z e of the  area and i t s l o c a t i o n are shown approximately i n Figure 1.  The area  o u t l i n e d w i t h i n the q u a d r i l a t e r a l i n d i c a t e s the area t h a t i s most c o n s i s t e n t l y , and most i n t e n s i v e l y f i s h e d .  The f i s h i n g f l e e t may, s p o r a d i c a l l y ,  range s e v e r a l miles i n v a r i o u s d i r e c t i o n s from t h i s area.  Figure 1. Map showing l o c a t i o n of the Kains i s l a n d f i s h i n g area. The dotted l i n e o f f the coast represents the IOO-fathom l i n e .  (3)  As mentioned, there are several major fishing areas for coho on the British Columbia coast. Of these, the Kains island area i s about the only one that has a l l of the following advantageous characteristics. These are: (1) Kains island i t s e l f , which i s situated on the.edge of the actual fishing grounds, i s a recording station for temperature and salinity data of the coastal waters. ( 2 ) I t i s a well delimited area, and i s intensively fished. (3) A l l of the fish caught i n the Kains island fishing area are landed at the same place, namely at Winter Harbour. (4) I t i s a "day-fishing" area, which means that a l l fish caught are landed that same day. ( 5 ) L i t t l e or no fish from other areas are landed at the Winter Harbour fishing camp. The exceptions w i l l be noted later. (6} Detailed records of the Kains island catch were available over a period of several years. (7) The writer i s personally familiar with the fishing area, and with the operations there. A l l of the factors listed above contribute to the f a c i l i t y with which the fish population of the area may be interpreted i n terms of the variables i n their environment. Life History of the Coho Salmon The coho, like the other four species of Pacific salmons i n British:. Columbia, i s an anadromous fish. I t i s thus subjected to two completely different environments during i t s l i f e history, one during the period that i s spent i n the sea, and the other during the time spent i n the river.  (4) - In either of these two environments i t exhibits a behaviour that i s different from that i n the other—each being a distinct part of i t s l i f e cycle. Fresh-water Phase The maturing coho enter the British Columbia coastal streams between the months of September.and November each year. The peak of the upstream migration usually occurs i n October. They travel varying distances upstream, some spawning only a short distance from the sea, others going upriver for many miles until they reach the tributaries of the larger rivers. When a suitable location i s found i n the river bed the eggs and ^aperm are deposited and covered with gravel. The adults, their l i f e over, then drift downstream and shortly die. The fry begin to emerge from"the spawning beds during March and April of the following year and, i n the smaller tributaries, immediately begin a migration downstream to the larger rivers.  This migration con-  tinues throughout the spring of that year (43). The majority of the young coho spend about one f u l l year i n the . river system. A few migrate to the sea i n their f i r s t and third years. According to the scale studies of Pritchard (4S, 49) these f i r s t and third;, year coho make up less than two percent of the total migrants i n any one year. The peak of the downstream migration occurs between April and June of the coho's second year. They are now between, four and seven inches In length, the average being about five inches (20). Some few of them may spend a period i n estuarial waters, vacillating between the river and the sea, but for the bulk of them the sea w i l l be their home for almost two years.  (5) Salt-water Phase Little or nothing i s known about the young coho during their f i r s t year i n the sea. They seem to disappear, and are not seen again u n t i l they become available to the ocean t r o l l fishery i n the spring of the next year. At this time they may be up to five hundred miles from the streams that they left the previous year. They have, also grown considerably and usually weigh between two and four pounds. The coho's second year i n the sea i s better known, and a large number of tagging experiments have been carried out on them during this period. Pritchard and Tester (51) have studied their food habits i n British Columbia waters during the second year. They found the main items of the coho diet during this time to be herring, sandlance, and other small fishes chiefly; but also including certain members of the zooplankton, especially euphausiids. The relative importance of the different species i n the diet varied from year to year. I t .also varied i n the different areas (22, 57)o The growth rate of the coho during their last year i s a very rapid one.  Their weight increases rapidly from about three or four pounds i n  May to six or eight pounds, or more, by the end of September (17, 18, 38, 67). In general, when the coho appear i n the open ocean t r o l l fishery they seem to have reached the end of their seaward migration, and to have begun a movement toward the rivers. I t i s during this movement back to the streams that they are particularly available to the fishery. The Ocean Troll Fishery for Coho The fishery i s mainly confined to the area over the continental shelf. I t i s an intensive fishery i n British Columbia, and several hundred boats engage i n i t every year. Most of the catch i s taken between  (6) the months of May and September, with July and August generally being the most productive. A survey of the coho t r o l l fishery of the Pacific states of the United States, where the fishery i s similar to that i n British Columbia, i s given,by various authors, i n bulletin number two of the Pacific Marine Fisheries Commission (19, 31, 6 7 ) .  A detailed description of the boats  and gear used i n the t r o l l fishery may be found i n Western Fisheries magazine (2, 69). During the fishery, and usually, in conjunction with i t , many coho have been tagged or otherwise identified, and released into the sea. Much information about their movements i n the sea during this last year, and other data as well, has been obtained i n this manner. Data from Tagging Experiments The early tagging operations on coho, conducted i n 1925 and 1926 in Canadian waters, seemed to indicate a general southeasterly movement of maturing fish from the feeding grounds to the coastal rivers.  The  results of more recent experiments tend to modify this conception somewhat. Milne (39), summarizing the tagging operations up to 1950, showed that the coho tend to wander a good deal during this return period, and also that they radiate 'in many directions from their feeding areas. In British Columbia though the southeasterly movement is s t i l l predominant. A l l of the evidence to date, both from tagging and from the f i s h ery i t s e l f , indicates that while i t i s a spawning migration i t i s a more or less leisurely movement during which very active feeding occurs. By the middle or late f a l l of each year, depending on the area, most of the coho have l e f t the truly oceanic areas for the inlets and  (7) rivers.  By the end of November the m a j o r i t y have entered the r i v e r s  where, when a s u i t a b l e l o c a t i o n i s found, they w i l l deposit t h e i r spawn. The adults die when spawning has been completed, but the cycle w i l l be repeated by t h e i r progency which emerge from the gravel, the f o l l o w i n g spring. Coastal Oceanography The b i o l o g i c a l p r o d u c t i v i t y of an area i s l a r g e l y determined by the c u r r e n t s , both l a t e r a l and v e r t i c a l , t h a t are operative w i t h i n i t . These currents are r e s p o n s i b l e , not only f o r water temperatures w i t h i n the area, but a l s o f o r the amounts of b a s i c n u t r i e n t m a t e r i a l s that are a v a i l a b l e - f o r the support of b i o l o g i c a l organisms. The ocean currents o f f the coast of B r i t i s h Columbia may, venience, be d i v i d e d i n t o two c a t e g o r i e s .  f o r con-  These are: the off-shore  currents, whose primary i n f l u e n c e i s exerted some distance from the coast, and the in-shore currents which are operative between the coast and the i n s i d e edge of the off-shore water movements.  The two systems are not  independent, and the c o n f i g u r a t i o n of the inshore system i s , . t o a l a r g e extent, determined by the vagaries of the off-shore currents. The Off-shore  Currents  The surface current of primary importance i n the North P a c i f i c ocean i s that commonly known as the Japanese current, or the West Wind Drift.  I t i s a mixture of the warm waters of the Kuroshio current t h a t -  flows i n a n o r t h e a s t e r l y d i r e c t i o n along the coast of Japan, and of the cold waters of the Oyashio current f l o w i n g south along the northeast Japanese coast.  The two meet and mix t h e i r waters:at about 35° N l a t i t u d e  o f f the coast of Japan.  The mixed water then flows i n an e a s t e r l y  (8) d i r e c t i o n across the' North P a c i f i c .  The f l o w becomes l e s s w e l l defined as  i t t r a v e l s f a r t h e r east, but i s perpetuated and d r i v e n on by the p r e v a i l i n g westerly winds.  This f l o w , u s u a l l y c a l l e d the Japanese c u r r e n t , i s more  c o r r e c t l y r e f e r r e d t o as the A l e u t i a n , o r S u b a r c t i c current (59, pp. 712). Before the A l e u t i a n current reaches the west coast o f North America i t d i v i d e s i n t o two main branches, one o f which flows south t o become the C a l i f o r n i a current, and one going north as the Alaskan current.  According  to "The Oceans" (59, pp. 724) t h i s d i v i s i o n takes place a t about 35° N latitude.  The d r i f t b o t t l e experiments o f the I n t e r n a t i o n a l F i s h e r i e s Com-  m i s s i o n , however, i n d i c a t e that the d i v i s i o n may occur a t l e a s t two degrees f a r t h e r north than t h i s .  Thompson and Van Cleve (64, pp. 50-57) show t h i s ,  and t h e i r r e s u l t s a l s o show t h a t there i s probably considerable v a r i a t i o n from year to year, as w e l l as w i t h i n the same year. The main flows o f the C a l i f o r n i a and Alaskan c u r r e n t s , e s p e c i a l l y the C a l i f o r n i a , do not u s u a l l y extend t o the Immediate c o a s t l i n e .  I n the  case 'of the Alaskan current i t has been shown (64, pp. 59) that i n i t s n o r t h e r l y f l o w i t i s d e f l e c t e d towards the coast and reaches i n t o the passages o f B r i t i s h Columbia and southeastern Alaska. The c o n f i g u r a t i o n of these major currents determine t o a l a r g e extent the c o n f i g u r a t i o n of the more l o c a l ones i n any year. The In-shore Currents Over the area of the c o n t i n e n t a l s h e l f , which has been c a l l e d the "in-shore" area, there are both l a t e r a l and v e r t i c a l c u r r e n t s , the v e r t i c a l currents being mostly operative i n the summer.  These are i n t i m a t e l y  .connected w i t h the p r e v a i l i n g winds, and w i t h the o f f s h o r e systems.  (9) L a t e r a l In-shore System.  I n t h i s more shallow water area, one, hun-  dred fathoms or l e s s , which has been taken as the l i m i t s of the c o n t i n e n t a l s h e l f , there are numerous eddies from the shore side of the main currents off-shore.  These eddies are r e i n f o r c e d or dampened by the shape of the  c o a s t l i n e and-by l o c a l t i d a l i n f l u e n c e , which i s of great importance i n the mixing of water immediate to the coast. Besides these l a t e r a l water movements i n the c o n t i n e n t a l s h e l f area there i s also a v e r t i c a l movement of water upwards.  The v e r t i c a l movements  are of f i r s t importance i n terms of the l i f e that the area supports. V e r t i c a l In-shore System.  I n summer, the net e f f e c t of the p r e v a i l -  i n g winds along the B r i t i s h Columbia c o a s t l i n e i s to produce a movement of the warmer and l i g h t e r surface water off-shore.  To replace t h i s , water  comes up from the deeper l a y e r s . This coming to the surface of deeper water i s known as "upwelling", a w e l l e s t a b l i s h e d phenomenon. A. d e t a i l e d a n a l y s i s of the upwelling process o f f C a l i f o r n i a has been given by Sverdrup  (5&).  Some i n d i c a t i o n of the amount of water that i s coming to the surface i n an area may be gained by an examination of the surface temperature and s a l i n i t y .  However, McLeod (37) i n 1951  showed t h a t the surface s a l -  i n i t i e s of c e r t a i n areas i n B r i t i s h Columbia also c o r r e l a t e d w e l l w i t h the r i v e r runoff during the summer season.  T h i s , of i t s e l f , does not  negate the existence of upwelling, since such a c o r r e l a t i o n would be ex- . pected due to the change i n p r e c i p i t a t i o n that i s concomitant w i t h a change from predominantly  southeasterly ^^dnds during most of the year to predom-  i n a n t l y northwesterly during the summer.  Thus the same f a c t o r responsible  f o r upwelling i s a l s o responsible f o r the amount of runoff.  Because of  (10)  t h i s i t would be expected that u p w e l l i n g , as evidenced by s u r f a c e , s a l i n i t y , would show some c o r r e l a t i o n w i t h the amount of r u n o f f . The depth from which the r i s i n g waters o r i g i n a t e i s not e n t i r e l y agreed upon.  Sverdrup ( 5 9 , pp. 7 2 5 ) , says that i t r i s e s from moderate  depths of probably not greater than two hundred meters o f f the C a l i f o r n i a I g e l s r u d ( 2 6 ) , working on the d i s t r i b u t i o n of phosphates o f f south-  coast.  ern Vancouver i s l a n d , found that i t may come from as deep as f i v e hundred meters, or more. results.  Temperature and s a l i n i t y data i n the area gave the same  I t i s probable t h a t t h i s a l s o v a r i e s i n d i f f e r e n t years, depending  on the mean v e l o c i t y of the summer \»dnds. The b i o l o g i c a l importance of these water movements l i e s i n the f a c t t h a t deep waters are r i c h i n n u t r i e n t s a l t s which are e s s e n t i a l f o r phytoplankton growth.  Because these p l a n t s , the phytoplankton, grow only i n  the euphotic zone, i t i s necessary t h a t the s a l t s , which.they are u s i n g up, be constantly replenished to insure an abundant crop. coming to the surface accomplishes t h i s ireplenishment.  The deep water Because phyto-  plankton i s at the base of the marine food chain, the f i s h production a l s o i n such an area, i s i n d i r e c t l y r e l a t e d to the amount of upwelling that occurs. I n summary, i t may be s a i d that the area over the c o n t i n e n t a l s h e l f o f B r i t i s h Columbia i s an area of diverse water movements, both l a t e r a l and v e r t i c a l , and that due to t h i s the waters are w e l l mixed and the nutr i e n t s brought to the zone where they can be u t i l i z e d by phytoplankton. To a l a r g e extent these things determine i t s b i o l o g i c a l p o t e n t i a l .  Itis  probable that w i t h i n t h i s area there e x i s t l o c a l areas, the geographic and hydrographic f e a t u r e s of which are such t h a t they tend t o be major centers of food production f o r the f i s h populations.  (11)  Local Features of the Kains Island Fishing Area The limit of the continental shelf (the 100-fathom line) i s close to the coast i n this area, usually being between ten and fifteen miles offshore. The-bottom configuration, as deduced from hydrographic charts, i s f a i r l y even and contains no major prominences or submarine canyons.  The  position of Brooks peninsula, jutting out into the sea about twelve miles to the south, probably contributes to eddy formation i n the general area. The fishermen operating i n the area suggest—and this was also the writer's experience—that there i s a general northwestward current proximate to the coast from the vicinity of the mouth of Quatsino Sound. This probably represents a net outflow of water from the Sound, which i s deflected to the right parallel to the coast due to the influence,of the earth's rotation. There are numerous tiderips and eddies very close to the shore, and these contribute to mixing of the waters of the area. MATERIALS  The records on which a l l of the calculations herein are based were obtained from two main sources.  These were, the Fishermen's Cooperative  Association, and the Pacific Oceanographic Group. The f i r s t named organization supplied the fishing records, while the published and unpublished records of the second were the source of salinity and temperature data (46). Fishing Records The records that have been used, those for the years 1943 to 1951, were compiled i n the originals on a basis of the daily landings. For each fishing day during the coho seasons the poundage of coho salmon was given, and also the number of boats contributing to each day's landing, each of  (12) the boats being i d e n t i f i e d by the owner's name. T o t a l catch records were a v a i l a b l e from the year 1936,  but these were not used since these e a r l y  years were a p e r i o d of expansion f o r the company concerned i n t h a t area. W i t h i n the l a s t decade the number of boats f i s h i n g the area has  remained  reasonably constant. No adjustments were made to the records f o r the years 1943 For the years 1950  "to 1949.  and 1951 i t was necessary to make some adjustments.  This was due to the i n t r o d u c t i o n of a new f a c t o r i n t h e landings at the Winter Harbour camp, and stemmed from the opening of an i c e - p l a n t a t t h a t place i n  1950.  Up u n t i l 1950  a l l , or p r a c t i c a l l y a l l , of the f i s h landed at Winter  Harbour had been f i s h taken i n the Kains i s l a n d f i s h i n g area. a l s o f i s h t h a t had been caught on the same day as landed.  They were  With the i n t r o -  duction of i c e making operations a t t h a t p l a c e , i t became an important l a n d i n g place f o r the s o - c a l l e d "ice-boats".  These "ice-boats" are l a r g e r  salmon t r o l l e r s , operated by a two man crew, which f i s h the more d i s t a n t t r o l l i n g grounds.  These boats do not l a n d t h e i r catch every day but about  every f i v e to ten days i n s t e a d .  I t was necessary then because: ( l ) they  were not l a n d i n g f i s h caught i n the Kains i s l a n d area, and (II) they were confusing the d a i l y record by l a n d i n g several days' catch at once, to eliminate t h e i r i n f l u e n c e from the d a i l y record. The records d i d not i d e n t i f y the ice-boats as such, but i t was not d i f f i c u l t t o remove the greater part of t h e i r i n f l u e n c e from the catch. This was accomplished i n two ways.  The f i r s t was the w r i t e r ' s f a m i l i a r i t y  with the f i s h i n g f l e e t (the boats were i d e n t i f i e d by the.owner's name i n the r e c o r d ) , which i n many cases enabled him to exclude c e r t a i n catches  (13)  immediately.  Secondly, and t h i s was the important means, there i s u s u a l l y  a very wide discrepancy between the poundage landed a t any one time by a day-boat and t h a t landed by an i c e - b o a t . Day-boat landings u s u a l l y run between one hundred pounds and twelve hundred pounds. they exceed the highest f i g u r e .  I t i s rarely that  The i c e - b o a t s , however, may l a n d i n one  day (representing s e v e r a l days' f i s h i n g ) between two thousand and f i v e thousand pounds, o r more. Except i n a few instances then, i t was easy t o d i s t i n g u i s h between the landings of the tvro types of boats. S a l i n i t y and Temperature Records These were a v a i l a b l e f o r the area concerned from the records o f the P a c i f i c Oceanographic Group. records.  Only one minor adjustment was made t o these  I t consisted of excluding from the mean s a l i n i t y f o r the month  of J u l y , 1 9 4 7 , the reading given f o r the fourteenth day.  I t v a r i e d by  about 5 $ ° - ( p a r t s per thousand) from the readings of the days immediately preceding i t and f o l l o w i n g i t .  I t \vas concluded t h a t the reading was i n -  fluenced by some, unknown f a c t o r since t h i s was a greater v a r i a t i o n than i s u s u a l l y found over the course of a year i n t h i s area. METHODS The time periods that have been used as a b a s i s on which t o compile the records are calendar periods.  The monthly and y e a r l y f i g u r e s that are  given are the average of the d a i l y f i g u r e s over these periods. Treatment of F i s h i n g Records The t r o l l f i s h i n g season f o r coho salmon i n the Kains i s l a n d area begins i n May.  This period c o n s t i t u t e s the f i s h i n g season o r , as i t i s  sometimes c a l l e d h e r e i n , a " f i s h i n g year". From the o r i g i n a l records the f i s h i n g data were arranged on a monthly h a s i s i n terms o f : ( l ) the t o t a l poundage landed, and (2) the  (14) number of landings each month.  Because the boats l a n d t h e i r catch each  day, the number of landings each month i s equivalent to the number of "boat-days" f i s h e d each month.  This lends i t s e l f r e a d i l y to a c r i t e r i o n  of e f f o r t based on the u n i t of a "boat-day".  Thus, i f twenty boats make  a' landing of coho i n one day the t o t a l f i s h i n g e f f o r t expended t h a t day i s equal to tvrenty boat-days. C r i t e r i o n of R e l a t i v e Abundance Some index was necessary whereby the catch of coho from year t o year might be compared.  The y a r d s t i c k of " y i e l d per u n i t of e f f o r t " was  s e l e c t e d to accomplish t h i s .  I t i s a measure that has been widely used i n  the past, and i s probably the best such measure a v a i l a b l e .  Ricker (53)  gives a mathematical discussion of t h i s index i n terras of i t s r e l a t i o n t o r e l a t i v e abundance and the rate of  exploitation.  Various workers have used d i f f e r e n t u n i t s as t h e i r c r i t e r i o n of f i s h i n g e f f o r t ; i n every case the u n i t used i s dependent on the.type of f i s h e r y , and on the manner i n which i t i s prosecuted (8, 9, 10, 6 l , 63). The c r i t e r i o n of r e l a t i v e abundance used i n t h i s study has been the average catch per boat per day each year.  Except f o r the d a i l y time  u n i t , t h i s i s s t r i c t l y comparable to the method used by C l a r k (8) i n h i s study of the C a l i f o r n i a h a l i b u t (Paralichthyes c a l i f o r n i c u s ) . has been used here without any adjustments.  This index  This means that two main  assumptions have been made; they are: ( l ) t h a t the t o t a l amount of gear used i n the f i s h e r y has remained constant over the p e r i o d of years considered, and (2) t h a t the e f f i c i e n c y of the gear has remained unchanged. Some i d e a of the t o t a l amount of gear used i n the f i s h i n g area over these years may be gained from an examination of the number of  (15) boat-days fished each year. (The amount of gear fished by any one boat has been the same since several years earlier than the years studied.) TABLE I Year  Boat-days  Year  Boat-days  1943  2,515  1948  1,908  1944  2,778  . 1949  2,179  1945  2,181  1950  2,102  1946  2,066  1951  2,282  1947  1,544  Table I shows that the amounts of gear used i n each year, as measured by the number of boat-days fished, has been f a i r l y constant. Such variations as do occur may probably be attributed to the influence of weather conditions, since this w i l l limit or increase the number of days that the boats are able to fish; and, to the time of arrival i n the different years of the main body of fish.  The year 1947 may be an exception to  this, the number of boat-days fished that year being considerably less than that for any other year, and i t may be that fewer boats—that i s , a lesser amount of gear—fished the area during that year. In any case, i t i s felt that the differences between the various years are not sufficient to invalidate the results obtained. I t i s worth noting that this same year, 1947, i s the year that w i l l later be shown to exhibit the greatest discrepancy i n terms of correlation with yield of any of the years studied. The second assumption made was that the efficiency of the gear remained unchanged. This i s a valid assumption for the years considered. The actual fishing gear used by the t r o l l fishermen has undergone no major changes within these years. There has, i n recent years, been the intro-  (16)  duction of such e l e c t r o n i c aids as echo-sounders, d i r e c t i o n f i n d e r s , radio-telephone, e t c . .However, a m a j o r i t y of the day-boats (day-boats are the boats that land t h e i r catch every day, as opposed to ice-boats which may l a n d only once a week or so) f i s h i n g the Kains i s l a n d area s t i l l do not carry such a i d s ; of those boats that may have one or more of these aids they b e n e f i t mostly by the e x t r a safety f a c t o r that these b r i n g , r a t h e r than by increased catches.  I n the case of the ice-boats these  aids assume a greater importance but need not be considered here since t h e i r landings have been excluded from the records used. The Boat-day, a B a s i c Unit of E f f o r t The boat-day, f o r the purposes of t h i s study, i s defined as ".the amount of f i s h i n g e f f o r t expended by one boat f i s h i n g f o r one day or a part thereof." I t has been necessary to i n c l u d e the i d e a of. a part of a day because there was no d i s t i n c t i o n made i n the records between those boats that f i s h e d a f u l l day, and those that f i s h e d f o r only p a r t of a day.  We have assumed, i n computing the r e l a t i v e abundance each year,  that such e r r o r s as t h i s may introduce balance each other out from year to year. Average Catch per Boat per Day each Year This i s the index that has been used to compare the r e l a t i v e abundance of coho from year to year.  I t was c a l c u l a t e d by adding up the  t o t a l poundange of coho landed each f i s h i n g year, and d i v i d i n g the f i g u r e obtained by the number of boat-days f i s h e d i n the same period. 200,000  Thus, i f  pounds of coho were landed i n year X, and i t represented an ex- ,  penditure of f i s h i n g e f f o r t equal to 2 , 0 0 0 boat days, then the average catch per boat per day f o r year X was 1 0 0 pounds.  (17) Treatment of S a l i n i t y and Temperature Data Average s a l i n i t y and temperature figures were calculated f o r d i f f e r e n t periods i n the marine l i f e h i s t o r y of the coho salmon; the £ f i g u r e s used i n the calculations are the means of the monthly means within those periods. S t a t i s t i c a l Treatment The s t a t i s t i c a l treatment of the data throughout has been of a simple nature. Four common s t a t i s t i c s have been, used to measure the c o r r e l a t i o n , or lack of c o r r e l a t i o n , between the variables of s a l i n i t y (or temperature) and the y i e l d to the commercial f i s h e r y of coho salmon. The s t a t i s t i c s used i n the calculations are outlined below: (1) The C o e f f i c i e n t of Correlation,r. This s t a t i s t i c i s used to measure the degree of c o r r e l a t i o n between the v a r i a b l e s ; the formula used to compute the value of r i s that of Johnson (29,pp. 54), where:  X( r  X - X ) ( Y - Y )  ^/[r(X-rX) l 2  [I(Y - Y ) ] 2  In t h i s equation X i s the average s a l i n i t y i n parts per thousand (  ),  and Y i s the average y i e l d per boat per day each year i n pounds. X and Y are the means of X and Y. (2) Test of S i g n i f i c a n c e , t and p.  This a t e s t applied to r by c a l c u l -  ating the value of t and using i t i n certain tables (the t t a b l e s ) . The formula used to compute t was: .  n,, i n t h i s formula, i s the number of p a i r s , while n - 2 i s the number of degrees of freedom.  (18)  The value of p was found from the t a b l e s of the d i s t r i b u t i o n of t ( 3 0 , pp. 3 6 0 ) .  I t may be i n t e r p r e t e d as f o l l o w s : l e t us suppose t h a t f o r  a c e r t a i n value of r , the value of p i s found to be 0 . 0 2 .  "...  This i s  i n t e r p r e t e d as meaning t h a t i f the population c o e f f i c i e n t , P, i s equal to zero, that i s to say i f there i s no c o r r e l a t i o n between the v a r i a b l e s sampled, we would expect to get an r value as l a r g e as t h a t obtained o n l y twice i n a hundred times on the b a s i s of random sampling ..." ( 2 9 , pp. 6 3 ) . ( 3 ) Regression C o e f f i c i e n t , by^-.  This s t a t i s t i c was c a l c u l a t e d to enable  the path of the Regression Line between any two sets of v a r i a t e s to be p l o t t e d more p r e c i s e l y .  The formula used was:  :a  x  - x  " a  h  )  x  ( Y  - x  - Y  )  )2  The value f o r b , thus obtained was then s u b s t i t u t e d i n the equation: yx Y  I n the above equation X  = Y  + byx  ( X  - X  )  and Y are the regression values of X and Y.  These s t a t i s t i c s were taken i n v a r y i n g degrees from e i t h e r A r k i n and Colton  (3),  Johnson, L . P . V .  (29),  or Johnson, P.  0.  (30).  RESULTS The r e l a t i v e abundance of coho salmon in" the Kains i s l a n d f i s h i n g area, f o r each of the years s t u d i e d , was c a l c u l a t e d on the b a s i s of y i e l d per u n i t of e f f o r t .  This index, y i e l d per u n i t of e f f o r t , i s expressed  f o r each year from 1943 to 1951 i n terms of the average catch per boat per day.  The f i g u r e s are given i n Table I I , along w i t h the t o t a l catch  and the number of boat days f i s h e d i n e^ach year.  These y i e l d per u n i t  e f f o r t f i g u r e s are the f i g u r e s t h a t are used i n . a l l the c a l c u l a t i o n s w i t h which to compare the average s a l i n i t y or temperature during the d i f f e r e n t  (19) periods i n the l i f e h i s t o r y of the coho caught i n any year. TABLE I I The F i s h i n g Record, Compiled on a Yearly  Basis  Year  T o t a l catch lbs.  No. o f boat-days  1943  281,980  2,515  112  1944  404,700  2,778  182  1945  345,490  2,181  • 158  1946  155,830  2,066  75  1947  225,400  1,544  146  1948  170,700  1,908  89  1949  263,260  1950 1951  •  l b s . per unit effort  2,179.  121  216,130  2,102  103  527,130  2,282  231  I t has been shown by previous workers that the y i e l d o f c e r t a i n marine f i s h e s , i n s o f a r as hydrographic f l u c t u a t i o n s are concerned, i s determined by only a r e l a t i v e l y small p o r t i o n of t h e i r l i f e h i s t o r y i n the sea ( 2 8 , 6 8 ) .  Consequently, f o r t h i s study, the marine h i s t o r y of the  coho was d i v i d e d i n t o several periods.  The average s a l i n i t y , o r temper-  ature, o f each of these periods was c a l c u l a t e d f o r each population o f t h i r d year coho, and the f i g u r e s obtained compared s t a t i s t i c a l l y w i t h the y i e l d per u n i t o f e f f o r t f o r these years. On t h i s b a s i s , the l i f e h i s t o r y o f the coho i n the sea was d i v i d e d i n t o the following;:; periods: A.  During i t s f i r s t year i n the sea: ( l ) June t o September; t h i s i s the period o f upwelling  during i t s  (20)  f i r s t year.  I f m o r t a l i t y i n t h i s year i s dominant, due to  hydrographic f a c t o r s , i t should be operative during t h i s p e r i o d . B.  During i t s second year i n the sea; (2) A p r i l to September; t h i s covers the p e r i o d during which the coho are a v a i l a b l e to the f i s h e r y . (3) June to September; t h i s i s the p e r i o d during which most upw e l l i n g occurs during the l a s t year.  I t I s a l s o a p e r i o d of  very r a p i d growth f o r the coho. C.  During both years i n the sea. (4) This i s the average of one and two above, and covers the p e r i o d of u p w e l l i n g during both years i n the sea. (5) A p r i l of the f i r s t year to September of the second year; t h i s eighteen-month  p e r i o d covers, approximately, the e n t i r e time  that the coho spends i n the sea. Average S a l i n i t y and Y i e l d The average s a l i n i t i e s c a l c u l a t e d f o r these periods are given i n Table I I I .  I n t h i s table the y i e l d years, given i n the l e f t hand column,  are the years that the coho were taken i n the commercial f i s h e r y . numbers at the top of the columns r e f e r to the numbers given i n the preceding c l a s s i f i c a t i o n .  The  (21) TABLE I I I Average Salinities for Periods i n the Marine Life of Coho Caught i n any Year Yield year  1  June to .Sept. CD •foo  Period of Average Salinity June, to April to .Sept. Sept. (2) (3), °L  °/oo  June to Sept. (4) foo  April to Sept. (5) • °/oo  -•  1943  32.05  31.43  32.01  32.03  30.95  1944  32.01  32.08  32.28  32.14  31.31  1945  32.28  31.58  32.05  32.16  31.08  1946  32.05  30.97  31.55  31.80  30.67  1947  31.55  31.25  31.63  31.59  30.70  1948  31.63  31.07  31.31  31.47  30.66  1949  31.31  31.04'  31.67  31.49  • 30.67  1950  31.67  3Q^.70  31.35  31.51  30.63  1951  31.35  31.99  32.37  31.86  30.65  From the data given i n Tables I I and I I I , the correlation between the average salinities of each period and the yield per unit effort over the years studied was determined. This correlation, or i n many cases lack of correlation, has been expressed i n terms of the correlation coefficient, r. That i s to say, that the yield per unit of effort over the period of years from 1943 to 1951, has been separately compared with the average salinity during each of these periods of the coho's l i f e i n the sea. Table IV gives the values of the correlation coefficients found to exist between the average salinities for the different periods, and the yield per unit effort. I t also gives the values of the statistics t and p  (22) which are used to show the r e l a t i v e s t a t i s t i c a l significance of r . A value of unity f o r r indicates a perfect c o r r e l a t i o n between the variables examined. The value of p i s the p r o b a b i l i t y that such a value f o r r as shown would occur s o l e l y due to chance. TABLE IV The Correlation between Average S a l i n i t i e s and Y i e l d Value of r  Value of t  (I) June - Sept. . ( f i r s t year)  -0.22  0.60  (2) A p r i l - Sept. ... , ( y i e l d year)  -K5.86  5.18  0.01 -  0.001  (3) June - Sept. . „ ( y i e l d year) r  +0.85  5.02  0.01 -  0.001  (4) June - Sept. „ ,. (both years)  -K3.53  1.65  0.10  (5) A p r i l - Sept. , (IS months)  -KD.39  I.I2  0.30  Salinity period  Value of P  0.2 - 0.3  Table IV shows, that f o r most of the periods i n which average s a l i n i t y was calculated, there was no s i g n i f i c a n t correlation with y i e l d . The periods that do show a s i g n i f i c a n t c o r r e l a t i o n are those that were calculated f o r some period within the y i e l d year i t s e l f , - namely, ( i ) A p r i l to September, and (II) June to September. These two  correlations  w i l l be presented i n some d e t a i l . The lack of c o r r e l a t i o n between the average s a l i n i t y from June to September of the f i r s t year i n the sea, and the y i e l d of coho one year l a t e r , w i l l also receive further consideration  (23) The Correlation between Y i e l d and Average S a l i n i t y the Same Year. The values of the c o r r e l a t i o n c o e f f i c i e n t , r , obtained between y i e l d and the average s a l i n i t i e s of the periods from A p r i l to September, and June to September, were 0.86 and 0.85  respectively, the periods being c a l c u l -  ated within the y i e l d year. S t a t i s t i c a l l y , these two correlations do not s i g n i f i c a n t l y d i f f e r one from the other. I t i s known, from the oceanography of the coast, that intense upwelling i s present each year during the months of June to September. I t i s probable that some upwelling occurs i n May. The influence of t h i s colder water during May may account i n some degree f o r the s i m i l a r i t y between the correlations of the two periods. I t i s l i k e l y that the i n f l uence of the upwelling from June to September i s s u f f i c i e n t to influence the figures f o r the A p r i l to September period to the extent that the average of the two periods i s very s i m i l a r , thus showing a s i m i l a r corre l a t i o n with y i e l d . Therefore only the c o r r e l a t i o n shown to e x i s t between y i e l d and average s a l i n i t y from June to September w i l l be presented i n d e t a i l . The c o r r e l a t i o n between the "summer" s a l i n i t y ("summer" salinity.' i s the June to September s a l i n i t y ) of the y i e l d year, and the y i e l d that year, are graphically shown In Figures 2 and 3. In Figure 2, the data are p l o t t e d as percentage deviations from t h e i r respective means. I t i s obvious from t h i s graph that the trends of the two variables p a r a l l e l each other very closely. The greatest d i s c r e p ancy i s f o r the year 1947. I t was e a r l i e r pointed out that i n t h i s year the f i s h i n g i n t e n s i t y — a s measured by the number of boat-days— was much lower than that f o r any other year. The e f f e c t of t h i s lowered  Figure 2. Average "summer" s a l i n i t y and y i e l d per u n i t - e f f o r t same year, p l o t t e d as percentage d e v i a t i o n s from the mean ( S a l i n i t y d e v i a t i o n x20)  .20 .40 .60 .80 32.00 .20 .40 AVER. SUMMER SALINITY - %o Figure 3. S c a t t e r diagram of average "summer" s a l i n i t y and y i e l d per u n i t e f f o r t same year, 1943 t o 1951, i n c l u s i v e . The two hollow c i r c l e s represent the two points XY and XY.  (24) f i s h i n g i n t e n s i t y on the c r i t e r i o n of y i e l d per u n i t e f f o r t may be part of the cause of t h i s discrepancy. In Figure 3 the y i e l d per u n i t e f f o r t data are p l o t t e d d i r e c t l y against the average "summer" s a l i n i t i e s , t h i s time i n the form of a scatter diagram. The l i n e running diagonally across, the figure i s the l i n e of regression. The proximity of the p l o t t e d points to t h i s l i n e indicates the degree of c o r r e l a t i o n between the variables measured. The value of the c o r r e l a t i o n c o e f f i c i e n t between the average "summer" s a l i n i t y and the y i e l d per unit e f f o r t the same year ( r = 0.85) i s , s t a t i s t i c a l l y , a very s i g n i f i c a n t c o r r e l a t i o n . Average S a l i n i t y F i r s t Year i n the Sea, and Y i e l d Following Year. I t was mentioned that e a r l i e r workers had found good correlations to e x i s t between s a l i n i t i e s during the brood years and y i e l d several years l a t e r , f o r f i s h . o t h e r than salmon. I n 1946, Walford (66), found that, almost a perfect correlation existed between the average summer s a l i n i t y during the brood year of the C a l i f o r n i a sardine (Sardinops eaerulea)and the y i e l d three years l a t e r . I t was thought that something comparable might be operative i n the coho population, and a s i m i l a r comparison was made. Although the coho salmon are not spawned i n the sea, they are very small during t h e i r f i r s t year i n the ocean. I t might be expected that during t h i s year they would be more sensitive to environmental changes than i n the f o l l o w i n g year. I n Figure 4, the average  salinities  during t h i s f i r s t year i n the sea are plotted against the y i e l d the f o l l owing year, as percentage deviations from the mean. The f i g u r e shows that there i s no obvious c o r r e l a t i o n exhibited between the two v a r i a b l e s . The value of the c o r r e l a t i o n c o e f f i c i e n t , r , was calculated as being equal to -0.22. This value has no s t a t i s t i c a l s i g n i f i c a n c e .  ro  10  to  o  oo CD  CD  lO  CD  lO CD  YIELO YEAR Figure 4 . Y i e l d per u n i t e f f o r t and "summer" s a l i n i t y of preceding year, p l o t t e d as percentage deviations from the mean. (Years on scale are the y i e l d years. S a l i n i t y d e v i a t i o n x 2 0 . )  (25)  The l a c k of c o r r e l a t i o n shown i n Figure 4 may mean that during t h i s period of the coho's sea l i f e , of which almost nothing i s known, i t f r e quents an area that i s not p r i m a r i l y dependent on upwelling f o r i t s supply of n u t r i e n t s a l t s . island.  Such an area might be the " i n s i d e waters" of Vancouver  Another explanation, assuming t h a t m o r t a l i t y during t h i s year i s  not dependent on the amount of upwelling, may be that v a r i a t i o n s i n the r e l a t i v e l y slow growth r a t e during t h i s period are of i n s u f f i c i e n t  magni-  tude to be r e f l e c t e d i n the poundage y i e l d the f o l l o w i n g year. Average Temperature and Y i e l d The same time periods have been used to compare average temperature w i t h y i e l d as were used to compare s a l i n i t y w i t h y i e l d .  They are:  (1) June to September of f i r s t year I n the sea. (2) A p r i l to September of second year i n the sea. (3) June to September of second year i n the sea. (4) June to September during both years i n the sea. ( 5 ) A p r i l of f i r s t year i n sea to September of the second, a period of eighteen months. The average temperatures f o r these periods i n the l i f e h i s t o r y of the  coho caught i n any year are given I n Table V.  year that the coho were caught.  The y i e l d year i s the  The number at the top of the columns  r e f e r to the numbers of the periods as given above.  (26)  TABLE V Average Temperatures f o r Periods i n the Marine L i f e . of Coho caught i n any Year.  Period of Average Temperature Yield year  June t o .Sept.  A p r i l to Sept. (2)  (1)  1943  55.4  1944  54.7  1945  .  54.7  June to Sept. (3)  i June t o Sept. (4) po  A p r i l to Sept. (5) po  52.8 52.9  54.7  55.0  51.2  54.7  54.7  51.4  51.3  52.7  53.7  51.3  1946  54.7  52.7  54.8  53.7  50.1  1947  54.8  53.2  55.2  55.0  50.5  1948  55.2  52.3  54.2  54.77  51.0  1949  54.2  52.3  54.3  54.2  50.1  1950  54.3  54.1  54.2  50.1  1951  54.1  53.7  53.9  50.4  .  51.6  52.1  . .  From the average temperature f i g u r e s of Table V, and the y i e l d per u n i t e f f o r t f i g u r e s given i n Table I I , the degree of c o r r e l a t i o n between the temperatures of the d i f f e r e n t periods and the y i e l d per u n i t of e f f o r t was c a l c u l a t e d .  The values f o r the c o r r e l a t i o n c o e f f i c i e n t , r ,  that were found are presented i n Table V I .  (27) TABLE VI The C o r r e l a t i o n between Average Temperatures and Y i e l d Value of r  Temperature period  Value . of t  Value of P  ( l ) June to Sept. ( f i r s t year)  •K).13  XX  XX  (2) A p r i l - S e p t . , ( y i e l d year)  -0.07  XX  XX  (3) June - Sept. . ( y i e l d year)  -0.33  (4) June-Sept. . (both years)  -0.09  XX  XX  (5) A p r i l to Sept. (18 months)  -0.13  XX  XX  xx  0.924'  0.3 - 0.4  Values not c a l c u l a t e d .  The values of the s t a t i s t i c s given i n Table VI show that there i s no obvious c o r r e l a t i o n e x i s t i n g between the temperature of the various periods and the y i e l d i n pounds over the years studied.  The highest  value found f o r the c o r r e l a t i o n c o e f f i c i e n t , r , was equal to -0.33. This value has no s t a t i s t i c a l s i g n i f i c a n c e . DISCUSSION The marine l i f e of the coho salmon includes the period from about Hay of i t s second year to the' f a l 1 of the f o l l o w i n g year,, a period of approximately eighteen months.  During t h i s time i t i s subject to the  i n f l u e n c e of p r e v a i l i n g environmental c o n d i t i o n s , the state of which a t any time i s determined by the current systems, both l a t e r a l and v e r t i c a l , that are operative w i t h i n the area.  (28)  A major f a c t o r t h a t i n f l u e n c e s coho during t h e i r sea l i f e i s the a v a i l a b i l i t y of food.' I n t h i s regard, the population of any marine animal i s u l t i m a t e l y dependent on the annual crop of phytoplankton; the phytoplankton i n t u r n are dependent on s e v e r a l other f a c t o r s , one of the most important ones being the amount of n u t r i e n t s a l t s a v a i l a b l e .  These s a l t s  the phytoplankters must have f o r growth and reproduction, so that i n the long run the salmon, and other f i s h , are a l s o dependent on the amounts o f nutrient salts. Between the two v a r i a b l e s o f n u t r i e n t s a l t s and f i s h populations, there i s a l o n g s e r i e s of r e l a t i o n s and i n t e r r e l a t i o n s , a l l of which t o gether c o n s t i t u t e the "chain of l i f e " i n the sea. The component l i n k s o f t h i s chain are: n u t r i e n t s a l t s , phytoplankton, zooplankton, and nekton (which i n c l u d e s a l l of the f r e e swimming animals).. The r e l a t i o n s h i p s e x i s t i n g between these have been determined, i n t h e i r e s s e n t i a l s , by numerous workers i n many countries. Nutrient S a l t s and Phytoplankton The dependency of the phytoplankton population on the n u t r i e n t s a l t s (phosphates, n i t r a t e s , etc.) a v a i l a b l e has been w e l l e s t a b l i s h e d by many i n v e s t i g a t o r s ( 1 1 , 1 6 , 2 1 , 5 2 , 54, 5 5 ) .  Their r e l a t i o n s h i p i s such t h a t  i n areas where the waters of the euphotic zone (the l i g h t e d zone) cons t a n t l y have t h e i r supply of n u t r i e n t s a l t s replenished, due to l a t e r a l or v e r t i c a l turbulence, the phytoplankton crop i s very dense.  Conversely,  where the s a l t s removed by the phytoplankton are not being replenished, as i n areas of converging c u r r e n t s , the phytoplankton population i s sparse. The r e l a t i o n s h i p has a l s o been shown experimentally.  Raymont (52)  showed that when n i t r a t e and phosphate s a l t s were added t o the waters of  (29)  c e r t a i n S c o t t i s h sea lochs the d e n s i t y of the phytoplankton was g r e a t l y increased.  The same experiment a l s o showed t h a t such f e r t i l i z e d areas  were able to support a higher zooplankton population. Other f a c t o r s besides the concentrations of n u t r i e n t s a l t s a f f e c t the phytoplankton, a p a r t i c u l a r l y important one being the amount of l i g h t a v a i l a b l e f o r photosynthesis.  Johnson i n "The Oceans" has summed i t up'  thus "... many f a c t o r s are s t i l l unknown but i t i s c l e a r that w i t h suff i c i e n t s u n l i g h t the combination of n u t r i e n t cycles and the v e r t i c a l c i r c u l a t i o n of the water are dominant causes..." ( 5 9 , pp. 7 8 4 ) . Phytoplankton and  '  Zooplankton  Phytoplankton c o n s t i t u t e s the food supply of the members of the zooplankton, which feed on them by f i l t e r i n g them from the water.  The  r e l a t i o n s h i p between the two i s , however, l e s s obvious than t h a t shown to e x i s t between phytoplankton and n u t r i e n t s a l t s . Riley, and Bumpus ( 5 6 ) have shown that between the p h y t o p l a n k t o n — zooplankton populations of George's Bank an i n v e r s e c o r r e l a t i o n e x i s t s . This i s a t t r i b u t e d to the grazing e f f e c t of the zooplankters on the phytoplankton, such t h a t i n an area where the zooplankters are dense they r a p i d l y reduce the phytoplankton by t h e i r feeding a c t i v i t y . Zooplankton and Nekton  :  Many marine animals feed d i r e c t l y on zooplankton.  Prominent among  these are the Baleen whales ( M y s t a c o c e t i ) , and c e r t a i n f i s h e s of. major commercial importance, i n c l u d i n g some members of the mackerel f a m i l y (Scomb r i d a e ) , and the h e r r i n g f a m i l y (Clupeidae). The d i s t r i b u t i o n of Baleen inhales has been c o r r e l a t e d with the d i s t r i b u t i o n of the zooplankton on which they e x i s t  (59,  pp.  904-907)  9  (30)  e s p e c i a l l y i n c e r t a i n parts of the a n t a r c t i c .  The abundance of mackerels  has also been correlated w i t h the abundance of zooplankters.  Bullen  (4)  showed that the abundance of mackerel i n the E n g l i s h f i s h e r y p a r a l l e l e d the greater or l e s s abundance of zooplankton during the same period. F i s h Populations and Hydrographic Factors Many workers have analysed the oceanographic environment, when studying f i s h populations, i n terms of temperature and s a l i n i t y (hydrographic f a c t o r s ) , rather than i n terms of the. abundance of the forms themselves that constitute the food supply.  Such f a c t o r s as s a l i n i t y  and  temperature are e a s i e r to measure, q u a n t i t a t i v e l y , than i s the abundance of phytoplankton or zooplankton. I n 1927,  Johansen (28)  showed that there was  a significant correl-  a t i o n between the f l u c t u a t i o n s i n the q u a n t i t i e s of p l a i c e f r y and surface s a l i n i t i e s f o r January and February of the same years.  the'  The  correl-  a t i o n he calculated to be equal to 0.57j and the mean e r r o r (or) to be. 0.15.  He concluded from t h i s that the c o r r e l a t i o n exhibited "...must be  regarded as an established f a c t . . . " ( r = 0.31)  He found a somewhat lower c o r r e l a t i o n  between surface temperature and p l a i c e f r y , but s a i d that  " . . . i t seems to be a r e a l i t y . . . "  He then i n t e r p r e t e d these c o r r e l a t i o n s  i n terms of the a v a i l a b i l i t y of plankton organisms to the young p l a i c e , as governed by the water movements i n t o and out of the area. Oaarruthers and Hodgson (6) showed, i n 1937,  that the percentage  of a c e r t a i n year class of h e r r i n g i n the East Anglian autumn f i s h e r y c l o s e l y p a r a l l e l e d the atmospheric pressure gradients c o n t r o l l i n g the winds of the area during the spawning years; the winds being a major c o n t r o l l i n g f a c t o r i n the surface water movements.  I t has also been  (31) shown (32) that the decline i n the Plymouth h e r r i n g f i s h e r y was coincident with a s i m i l a r decline i n the phosphate content of the waters of the area concerned. I n 1946, Walford (68), showed that there was almost a p e r f e c t c o r r e l a t i o n ( r = 0.96) between the average summer s a l i n i t i e s during the brood years of the C a l i f o r n i a sardine (Sardinops  caerulea) and the y i e l d  of f o u r t h year f i s h f o r the year classes of 1934 t o 1941 i n c l u s i v e .  He  concluded from h i s c o r r e l a t i o n that "... the s a l i n i t y r e f l e c t s the i n t e n s i t y of upwelling which brings up m a t e r i a l nourishing the plankton; and i t i s suggested that the summer, when the a f o r e s a i d r e l a t i o n s h i p i s best demonstrable, i s the most c r i t i c a l period i n the l i f e of the young .sardine, when an abundant supply of food i s most e s s e n t i a l . " An unsuccessful attempt t o c o r r e l a t e the deviations from the catch trend of coho salmon i n the S i l e t z r i v e r i n Oregon w i t h the surface s a l i n i t i e s at-Cape S t . James,-British Columbia, was reported i n 1950 by McKernan, e t a l (36).  Perhaps the f a c t that the two areas are some s i x  hundred miles apart may be an important f a c t o r i n determining the l a c k o f c o r r e l a t i o n that these workers found.  Their assumption that changes i n  surface s a l i n i t y i n the Cape S t . James area r e f l e c t s i m i l a r changes o f f the coast of Oregon i s - o f doubtful v a l i d i t y . The c o r r e l a t i o n s t h a t have been shown by these workers t o e x i s t between adult f i s h o r , i n the case of Johansen the numbers of f r y , and various hydrographic f a c t o r s have, i n each case been i n t e r p r e t e d i n terms of l a r v a l m o r t a l i t y .  Thus, Johansen (28) r e l a t e s the numbers of young  p l a i c e f r y i n any year t o the s a l i n i t y and temperature during January and February of the same year; Carruthers and Hodgson (6) r e l a t e abundance of  (32) herring to factors influencing surface water movements during t h e i r spawning years; and, Walford (68), correlates the abundance of  sardines  with the s a l i n i t y during t h e i r brood years. In the f i n a l analysis they have a l l attributed the correlations shown to greater or l e s s l a r v a l mortality i n the brood years, due to the paucity or abundance of food, as f i n a l l y evidenced by temperature and  salinity.  S a l i n i t y Correlation In the r e s u l t s presented i t was f i s h i n g area that, (I) there was  shown f o r the Kains i s l a n d  a very high c o r r e l a t i o n between the  "summer" s a l i n i t y and the y i e l d i n pounds .the same year; and.  (II)  that no obvious c o r r e l a t i o n existed between the "summer" s a l i n i t y duri n g the coho's f i r s t year i n the sea and the y i e l d the following year; (III(J> no s i g n i f i c a n t c o r r e l a t i o n was temperatures of any period and The  shown between the average surface  yield.  c o r r e l a t i o n shown to e x i s t between average "summer" s a l i n i t y  and the y i e l d the same year, i s of such magnitude that i t must be accepted as being a r e a l i t y , and not a t t r i b u t a b l e to a chance ar nonsense correlate i o n . This c o r r e l a t i o n must be due to the v a r i a t i o n s i n s a l i n i t y being r e f l e c t e d i n some manner on the coho population. Generally speaking, t h i s influence of s a l i n i t y on the population of f i s h may  be e i t h e r d i r e c t or  indirect. Direct Influence  of S a l i n i t y  D i r e c t l y , s a l i n i t y may  influence the salmon e i t h e r through phy-  s i c a l changes i n the environment, or, by the p h y s i o l o g i c a l e f f e c t s on the f i s h i t s e l f . The physical changes i n the environment that are concomitantv¥i*h a change i n s a l i n i t y are p r i m a r i l y e i t h e r a change i n s p e c i f i c gravity,  (33)  i n osmotic pressure, or i n v i s c o s i t y .  Because the salmon i s a completely  t o l e r a n t form, spending part of i t s l i f e i n f r e s h water, and p a r t i n s a l t water, i t i s d i f f i c u l t to imagine that:—due to the comparatively narrow range of the s a l i n i t i e s of the years s t u d i e d — a n y of these f a c t o r s are of more than minor importance i n determining the s i z e of the f i s h popula t i o n , or of the s i z e of the animals making up that population.  Were the  salmon spawned i n the sea, and the c o r r e l a t i o n found to e x i s t between the s a l i n i t y of the brood years and the y i e l d a t some l a t e r date, the f a c t o r of s p e c i f i c g r a v i t y might assume considerable, importance; however, at the beginning of t h e i r second year the coho are r e l a t i v e l y l a r g e f i s h and not, as i n the case of eggs or l a r v a e , dependent to some degree on the r e l a t i o n between t h e i r s p e c i f i c g r a v i t y and that of t h e i r environment. For the same reasons i t i s not probable t h a t the p h y s i o l o g i c a l e f f e c t s of the changes i n average s a l i n i t y observed are of s u f f i c i e n t magnitude t o be.of more than minor importance. I t i s concluded, t h e r e f o r e , that the c o r r e l a t i o n shown i s not explainable i n terms of these d i r e c t i n f l u e n c e s . I n d i r e c t Influence o f . S a l i n i t y The average summer s a l i n i t i e s t h a t have been used are, as shown, •a c r i t e r i o n of the amount of upwelling that has occurred i n the area over the year considered, the u p w e l l i n g i n t u r n being an index of the amount of n u t r i e n t s a l t s a v a i l a b l e f o r the production of plankton and, through the food chain, the amount of food a v a i l a b l e f o r salmon production. Thus, i n a year when s a l i n i t y i s low there i s l e s s food a v a i l a b l e to the salmon. I n d i r e c t l y , the greater or l e s s abundance of food may a f f e c t the coho dviring t h i s period i n one or both of two ways, namely through t h e i r m o r t a l i t y r a t e , or through the i n d i v i d u a l growth r a t e s .  (34) M o r t a l i t y during Second Year i n the Sea.  I n s o f a r as n a t u r a l  m o r t a l i t y i n the sea i s concerned, due to fluctuation's i n food supply, t h e i r f i r s t year i n the sea must be the most c r i t i c a l one. -  During t h e i r  second year, when they are l a r g e r , they should be l e s s subject to such changes i n t h e i r immediate environment as v a r i a t i o n s i n food supply. They are a l s o l a r g e r and stronger f i s h and consequently b e t t e r able to range a f i e l d s u f f i c i e n t l y to avoid o u t r i g h t s t a r v a t i o n , except i n v e r y extreme cases.  I t i s d i f f i c u l t , t h e r e f o r e , to postulate t h a t n a t u r a l  m o r t a l i t y during the second year i n the sea, due to f l u c t u a t i n g food supply, i s s u f f i c i e n t to account f o r the c o r r e l a t i o n shown. Growth Rate during Second Year i n the Sea.  The coho salmon has  a very r a p i d growth'rate during i t s second year i n the sea.  Fraser  (17)  says "... there i s a greater v a r i a t i o n i n the growth of coho i n the t h i r d year i n proportion to the s i z e of the f i s h at the beginning of the year than i s the case i n any other species i n any year."  ( T h i r d year coho are  coho i n t h e i r second year i n the sea.) Milne (3S) has shown that during the p e r i o d from May to September i n I95O the average weight of coho landed at U c l u e l e t , B. C , increased from three and one-half pounds i n May to about eight pounds i n September. He a l s o shows that a t Nanaimo,. B. C ,  the increase was from about two  and one-half pounds to almost s i x pounds during the same p e r i o d . A simi l a r l y r a p i d increase i n weight was shown by Van Hyning (67) f o r . t r o l l coho landed i n Oregon.  I n t h i s area there was an increase from about  f o u r and one-half pounds i n May to about nine pounds i n November. The a c t u a l rate of growth during t h i s second year v a r i e s i n d i f f e r e n t year classes.  Milne (3&) shows t h a t the average s i z e of coho  (35)  landed at Nanaimo i n May 1950 was considerably l e s s than t h a t i n the corresponding month i n 1 9 2 8 , i n d i c a t i n g t h a t i n 1950 the growth r a t e was slower.  Van Hyning ( 6 7 ) shows t h a t the growth rates of coho i n t h e i r  second year i n the sea i n Oregon was d i f f e r e n t i n each of the years of 1946,- 1 9 4 7 ,  1948  and 1949.  I t i s probable t h a t the major f a c t o r c o n t r o l l i n  the r a t e of growth of these f i s h i n any year i s ' t h e a v a i l a b i l i t y of food, the rate being f a s t e r when there -is an abundance of food and slower when i t i s scarce.  I t must be emphasized at t h i s p o i n t that the index-of  r e l a t i v e abundance has been compiled i n terms of the number of pounds of coho landed, since no f i g u r e s were a v a i l a b l e on the numbers of f i s h landed i n these years.  • .  Of the f a c t o r s considered to account f o r the c o r r e l a t i o n shown to e x i s t between average summer s a l i n i t y and the y i e l d per u n i t e f f o r t the same year, only the l a s t named, growth r a t e , i s of s u f f i c i e n t importance to be dominant.  The e f f e c t of the r a t e of growth, which i t i s suggested  i s more r a p i d i n years when food i s abundant (high s a l i n i t y ) , and slower when there i s a s c a r c i t y of food (low s a l i n i t y ) , would be to cause the weights of the i n d i v i d u a l coho to be greater i n years of high s a l i n i t y and l e s s i n years of low s a l i n i t y .  The y i e l d per u n i t of e f f o r t , i n  terms of pounds of coho landed, would a l s o f l u c t u a t e i n the same manner. V a r i a t i o n s i n growth r a t e , however, are not s u f f i c i e n t to account completely f o r the wide r n g e of y i e l d per u n i t e f f o r t values between the a  lovrest f i g u r e and the highest one.  To i l l u s t r a t e t h i s , l e t us assume  that the f i g u r e s i n the two extreme years were the a c t u a l weights of coho caught.  They were a minimum f i g u r e of 75 pounds i n 1 9 4 7 , and.a maximum  of 230 pounds i n 1 9 5 1 , and l e t us s i m p l i f y them to 100 pounds i n 1947 and 250 pounds i n 1 9 5 1 .  I f g r o i ^ h r a t e alone w i l l account f o r these v a r i a t i o n s  (36)  we assume that a t o t a l of twenty f i s h were caught i n 1947, then the average weight of coho i n that year was 5 pounds. • I f the v a r i a t i o n between that year and 1951 i s completely explainable i n terms of growth rates then the average weight of the f i s h caught i n 1951 must be pounds.  12.5  I t has not been shown that such a wide v a r i a t i o n i n average  weights from year to year e x i s t s i n the area under study.  I t i s known  that there i s a wide v a r i a t i o n from year to year, but probably not as wide as the above f i g u r e s would suggest.  I t i s probable then that some  other f a c t o r i s operating concurrently w i t h the speeded up growth rate i n the years of high y i e l d .  The o n l y f a c t o r that t h i s could be i s an  increase i n the numbers of f i s h landed i n these years. An examination of the t r o l l f i s h i n g areas o f f the West coast of Vancouver i s l a n d shows that the great m a j o r i t y of the coho landed come from a few r e l a t i v e l y small areas.  Kains i s l a n d f i s h i n g area, where  approximately n i n e t y square m i l e s are i n t e n s i v e l y f i s h e d , i s one of these; another i s the "Steamer Grounds", which i s a l a r g e r area o f f the S c o t t i s l a n d group.  Between these two areas i s a distance of about  f i f t y sea miles where, except f o r one small area, Sea Otter Cover, l i t t l e or no f i s h i n g f o r coho i s c a r r i e d out. are  These " f i s h i n g areas"  areas that c o n s i s t e n t l y give good y i e l d s of salmon, while the r e - •  mainder of the area over the c o n t i n e n t a l s h e l f does not.  There must be-  some difference between the l o c a l i z e d f i s h i n g areas and the general area off the coast that cause the salmon to be a v a i l a b l e i n greater numbers there.  This f a c t o r i s probably the greater a v a i l a b i l i t y of food i n  these areas. Due to changes i n oceanographic conditions the food supply i n these areas v a r i e s from year to year.  I t i s probable a l s o that the amount of  food a v a i l a b l e v a r i e s between d i f f e r e n t areas i n the same year, due t o l o c a l f a c t o r s , and to v a r i a t i o n s i n the offshore current systems as they  (37) a f f e c t the f i s h i n g areas. I t i s suggested that two major f a c t o r s determine the p o s i t i v e c o r r e l a t i o n shown to e x i s t between average "summer" s a l i n i t y and the poundage y i e l d per u n i t e f f o r t the same year, they are: ( i ) Changes i n growth r a t e , due to a greater or l e s s abundance of food. This causes the average weight of the coho to vary up or down i n d i f f e r e n t years i n the same manner as the average s a l i n i t y , and t h i s i s r e f l e c t e d i n the number of pounds of f i s h landed. (II)  V a r i a t i o n s i n the number of f i s h landed i n the area i n d i f f e r e n t  years, due t o the l e n g t h of time that the f i s h remain i n the area, and thus the period during which they are a v a i l a b l e to the f i s h e r y .  It is  suggested that when food i s abundant the coho stay i n the area f o r a longer time and thus are a v a i l a b l e t o the f i s h e r y f o r a greater p e r i o d . I t i s postulated then, that i n a year when there i s a great abundance of food i n an area, not only are the f i s h landed there of a greater average weight, but a l s o more of them are landed; and, that the v a r i a t i o n s i n these two f a c t o r s i n d i f f e r e n t years accounts f o r the c o r r e l a t i o n that has been shown to e x i s t between y i e l d and average salinity. Temperature Non-correlation No c o r r e l a t i o n of s t a t i s t i c a l s i g n i f i c a n c e was shown to e x i s t between average temperature during any period i n the coho's marine l i f e and the y i e l d of t h i r d year coho to the t r o l l f i s h e r y .  I t i s thought  such i n f l u e n c e as temperature might be expected to show would be p r i m a r i l y an i n d i r e c t one, and f u n c t i o n a l only i n s o f a r as i t i s a c r i t e r i o n of the amount of upwelling that occurs.  (38) Surface s a l i n i t y i s a good c r i t e r i o n of the i n t e n s i t y of upwelling i n d i f f e r e n t years because i t i s not r e a d i l y susceptible to change due to atmospheric  conditions above the sea surface. Surface tempereture,  however,  r e a d i l y changes with changes with changes i n atmospheric temperature,  con-  sequently i t i s not a good measure of the amount of upwelling that occurs. I t i s suggested that i t i s because of t h i s that surface temperature does not show as s i g n i f i c a n t a negative c o r r e l a t i o n with y i e l d as s a l i n i t y does a p o s i t i v e one (negative because high temperature should indicate l e s s upw e l l i n g , and vice v e r s a ) . SUMMARY 1. The r e l a t i v e abundance of coho salmon i n the Kains i s l a n d f i s h i n g area during the years 1943 to 1951 was  calculated on the basis of the  average catch per boat per day each year. 2. The r e s u l t i n g figures were compared with average surface s a l i n i t y , or average surface temperature,  f o r d i f f e r e n t periods during the l i f e  h i s t o r y of the coho taken i n any year. 3. No c o r r e l a t i o n was shown to e x i s t between average surface temperature and y i e l d per u n i t e f f o r t . No c o r r e l a t i o n was  shown between  y i e l d and the average s a l i n i t y of the preceding year. 4. A very high c o r r e l a t i o n (r=0.85, p =6.001 - 0.01) was shown to e x i s t between the average "summer" s a l i n i t y (average s a l i n i t y from June to September) and the y i e l d that same year, i n pounds. 5. This correlation i s explained as being due to the f a c t that surface s a l i n i t y may be used as a measure of the abundance of food i n the d i f f e r e n t years. 6. I t was  suggested that the abundance of food i n the f i s h i n g area  (39) i n f l u e n c e d the coho during t h e i r l a s t year i n the sea by, ( l )  controlling  the growth r a t e , and thus the average s i z e o f the f i s h caught, and ( I I ) , r e s t r i c t i n g o r lengthening the p e r i o d during which the coho i n a f i s h i n g area are a v a i l a b l e to the f i s h e r y . 7. I t was postulated that i n a year such as 1951, which gave the highest catch on record f o r the Kains i s l a n d area, that not only were the f i s h caught o f a greater average weight, but a l s o they were a v a i l a b l e t o the f i s h e r y f o r a longer p e r i o d of time, consequently more o f them were a l s o taken. ACKNOWLEDGEMENT The w r i t e r i s g r e a t l y indebted to the Fishermen's Cooperative Associ a t i o n f o r the use o f t h e i r f i s h i n g records, and i n p a r t i c u l a r t o Mr. G. T. Greenwell, General Manager, and Mr. A. E. Carr, Manager a t V i c t o r i a .  Their  help has been i n v a l u a b l e , not only i n l o c a t i n g the necessary records, but also i n t h e i r subsequent advice and h e l p f u l information. Numerous other i n d i v i d u a l s have given much assistance throughout the course of the work.  The w r i t e r p a r t i c u l a r l y wishes t o thank Dr.  W i l l i a m Cameron of the I n s t i t u t e of Oceanography, U n i v e r s i t y of E. C , f o r h i s very valuable help and advice-, and. Dr. D. J . Milne of the P a c i f i c B i o l o g i c a l S t a t i o n who provided c e r t a i n necessary information.. The w r i t e r ' s thanks are a l s o due t o Dr. W. S. Hoar, and Dr. W. A. 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