THE AGE, GROWTH and MORTALITY of THE, •LEMON SOLE (Paropnrys Vetulua Girard) on the (BRITISH COLUMBIA

THE AGE, GROWTH AND MORTALITY OF THE, •LEMON SOLE (Paropnrys vetulua Girard) ON THE (BRITISH COLUMBIA. FISHING GROUNDS

Keith S. Ketchen

A Thesis submitted in Partial Fulfilment of

(The Requirements for the Degree of

MASTER OF ARTS

in the Department of ZOOLOGY

THE UNIVERSITY OF BRITISH COLUMBIA

April, 1947. ABSTRACT

Part of the general investigation "being conducted by the Fisheries Research Board of Canada into the condition of the Pacific coast otter trawl fishery deals with the length and age analysis of the species of fish caught. The age of one of these species, the lemon sole, Parophrys vetulus GIrard has been determined through a study of the otoliths or ear- stones.

In general the older fisheries and those closest to large Canadian and American markets produce the youngest and the smallest fish. Soles of four and five years of age pre• dominate in the catches from the Strait of Georgia and from the west coast of Vancouver Island, The comparatively recent fisheries of Queen Charlotte Sound and Hecate Strait show a predominance of six and seven year old fish.

The male lemon sole reaches an age of ten years and a length of 400mm., while the female reaches twelve or thirteen years of age and grows to a length of over 500mm.

The female sole, between four and eight years of age grows approximately 11 mm. more per year than the male.

The fish in the Strait of Georgia and in northern

Hecate Strait have a slightly greater growth rate than those on the west coast of Vancouver Island and in Queen Charlotte

Sound.

Marked differences in total annual mortality rates have been shown. In the Strait of Georgia and on the west coast of Vancouver Island the rate is between (>0% and 70f. . In Queen Charlotte Sound the rate is 52%, and in northern

Hecate Strait it is between 30% and 40f».

The relative recency of the northern Hecate Strait fishery has raised the suggestion that the total mortality rates of 30?« in female fish and 39% in male fish approach the natural mortality rate.

Dominance of the 1939 year class has been observed in the s study of fish taken during ,1944, 1945 and 1946 in northern

Hecate Strait. In the last year another strong year class, that of 1942, made its appearance. The relative lack of success in the brood years of 1940 and 1941 was the factor responsible for the absence of small fish in the catches during the fishing seasons of 1944 and 1945. TABLE OF CONTENTS . .Page INTRODUCTION 1

MATERIALS AND METHODS . 7

LIFE HISTORY 13

THE ANALYSIS OF THE COMMERCIAL CATCHES

OF LEMON SOLES 18

Strait of Georgia 18

West coast of Vancouver Island.... 23

Q,ueen Charlotte Sound 26

Hecate Strait...... 27

GROWTH RATES ...... 34

MORTALITY RATES 39

DISCUSSION 44

Growth 44 Mortality. 47

The relationships of mortality and fluctuations in strengths of .year .classes to .age ~' composition. •• 52

SUMMARY AND CONCLUSIONS 56

ACKNOWLEDGMENTS 60

REFERENCES 61

APPENDIX 63 - 1 -

I. INTRODUCTION

On the Pacific coast of Canada during the past six or seven years there has "been witnessed an extensive development of the trawl fishery. This expansion has arisen mainly as a result of the need for fish products, both here and abroad, to alleviate the shortages in meat supplies brought about by war• time conditions. The Fisheries Research Board of Canada, fore• seeing the possibility of over-exploitation of this new in• dustry and of its possible conflict with other marine fishing methods, in 1943 began an investigation designed to accumulate information which could be employed in a sound program of con• servation and management.

One of the first objectives in studying the condition of the trawl fishery has been to determine the nature and abun• dance of the species of fish captured, and to determine the factors which limit this abundance.

The Problem

One of the principal species of flatfish landed by ottarr trawlers is the lemon sole (Parophrys vetulus Girard), a fish of considerable market importance because of its abundance and the high quality of its flesh. As part of the general invest• igation being conducted on this species, primary consideration is given in this work to the study of the size and age compos• ition of catches landed at important British Columbia ports during 1945 and 1946. Analysis of this sort is an essential requirement in revealing the condition of the fishery in that it shows in what way production is influenced 1. by the general age distribution in the various populations, 2. by the growth rate, 3. by the mortality rate, and 4. by fluctuations in the strength of year classes brought about by varying successes of brood years.

These aspects will be considered in detail, along with important related subjects on size and age at maturity, reproductive ca• pacities, and the growth and habits of young, post-larval fish. Afie Determination,

The age of the lemon sole has been determined through ex• amination of the otolith, a small hard, calcareous body situated in the saccular portion of the ear. The method has long been employed by European investigators of the North and Baltic Sea fisheries. Such men as Graham (1928) and Van Oosten (1941) however have emphasised that too often the reliability of age determination in one species of fish is used as justification of the reliability in another, a practice which could undoubtedly lead to substantial error in results. With this in mind the study of the lemon sole otolith has been approached with con• siderable caution. In a preliminary investigation of this sub• ject by the writer (1945 a) measurements of the otolith showed a fairly constant ratio to the length of the fish. Further studies of the alternating light and dark rings appearing on the otolith have been found to form reasonably consistent pat• terns related to annual temperature changes. On the basis of these correlations, the otolith of the lemon sole is believed to give a fairly accurate picture of age, especially for the lower and middle age groups. - 3 -

History Qt Afte pe^rgina^gn, Graham (1928) in his review of the literature states that Reibisch investigating the North Sea plaice in 1899 was one of the first to suggest that the differential structure of the otolith Is related to temperature. However Cunningham (1905) was the first to show that the opaque or white ring represents the summer growth and that the transparent or dark ring repre• sents that of the winter. Wallace (1905) also investigating the plaice fishery gave statistical evidence supporting the findings of Cunningham. In 1916 Storrow extended age determina• tion by this means to other species of flatfish. Since that time the method has spread to the study of other types of ground fish, the hake by Hickling (1933)» and cod and haddock by many- workers seeking correlations with scale readings. On the Pacific coast of North America most noteworthy advances in this field have been made by the International Fisheries Commission with respect to the study of the age of the halibut. Apparently the only published work on flatfish other than halibut from this coast has been by Smith (1936) in which he gives a general sur• vey of the ages of several species taken in Puget Sound waters.

HlSfrffY off *fre ?ra.wl Pigftgyy The trawl fishery for flatfish and lingcod on the Pacific

coast of Canada began about 1912 and was confined mainly to English Bay and the waters adjacent to Point Atkinson and Point Grey, regions all within sight of Vancouver. According to the older fishermen the fish were very plentiful in those days, but because of a very limited market the occupation was pursued by only one or two boats. However, during the first World War an increased demand saw the fishing grounds extended around Point Grey and south along the Sand Heads of the Fraser River estu• ary. In the same period three old country-type steam trawlers began operating out of Prince Rupert in northern Hecate Strait. By 1921 however these boats had been converted to other employ• ment as a result of a collapse of the market to its pre-war level. On the southern part of the coast fishing was continued by a few boats from Vancouver, and by 1923 the grounds had been extended from the Fraser estuary to the waters among the adja• cent islands in the lower portion of the Strait of Georgia.

The Baynes Sound trawling grounds, along the east coast of Vancouver Island and about forty miles north of the Gulf Islands were not discovered until 1930 and did not receive much attention until 1938 or 1939. In 1937, with the improvement of boat designs and engines, one or two boats began operating in the summer season off the southern part of the west coast of Vancouver Island near Port San Juan. By 1939 the number of boats had increased to eleven and the grounds were extended northward to Barkley Sound.

With the discovery of the high vitamin A content in dog• fish liver oil, large American boats which had previously been centered on the Swiftsure Banks off Cape Flattery moved north• ward ln 1940 to the La Perouse Bank off the west coast of Van• couver Island. By 1942 these boats far outnumbered the smaller Canadian boats, and within a few years had made their appearance on the Queen Charlotte Sound and Hecate Strait grounds.

The Goose Island grounds in Queen Charlotte Sound were opened up in the early years of the second World War, but Fig. 1

Parophrys vetulus Girard because of the long distance from port and the severe weather

conditions prevailing year-round in these waters, only large

trawlers have been able to fish with any degree of success.

The grounds of northern Hecate Strait, following the with•

drawal of the steam trawlers in 1921 have been fished only

slightly. Until 1944 only three or four boats were engaged in

the industry* Since that time the number of Canadian boats in

this region has increased to about sixteen.

PescriptloR and, PJstrjbu.UQn of 1foe Lemon, Sole

The lemon sole (Fig. 1) is a member of the flounder family,

the Pleuronectidae. The name "sole" is actually an erroneous

one, for there are no true soles (Soleidae) on the Pacific

coast of North America. The name "lemon sole" is apparently a

carry-over from the lemon sole of the coast of north-western

Europe, ffliffrofftppius k^tt. In the state of Washington to the

south, Paroohrys vetulus is generally called the English sole,

and in California, the Point sole because of its character•

istically pointed head.

The species was first described by Girard in 1854, and,

according to Clemens and Wilby (1946) was first recorded in

British Columbia waters in 1862.

Norman (1934) states that the species is the only member

of the genus Parophrys and that it is distributed along the

Pacific coast of North America from Santa Barbara, California

to Sitka, Alaska. In British Columbia waters the lemon sole occurs in considerable abundance ln the Strait of Georgia, ln

Queen Charlotte Sound and in northern Hecate Strait. On the west coast of Vancouver Island this fish reaches significant - 6 - proportion in catches only in the region of Port San Juan. Progressing northward along the coast from that point there is a decreasing frequency of occurrence. H, MATEfilMS AND METHODS The material for this work has been collected almost en• tirely from trawl landings at the two important British Columbia ^centres, Vancouver and Prince Rupert. The year round landings at the latter port are from the fishing grounds of northern Hecate Strait (Fig. 2), principally Butterworth Rocks and nearby regions. The fish landed at Vancouver, during the late spring and summer months, are in greater part from the west coast of Vancouver Island and the Goose Island grounds in Queen Charlotte Sound. In the fall and winter however, the samples are obtained almost exclusively from the Strait of Georgia. This seasonal fluctuation in the locus of fishing effort is the result of

1. severe winter weather conditions on the west coast which force the boats to seek the compara• tively sheltered waters of the Strait of Georgia, and

2. an attractive fishery produced by the concentration of fish on spawning grounds and migration routes

in the Strait during the winter months.

Primary attention will be given to samples collected dur• ing the years 1945 and 194-6. A relatively small number taken during 1944 will be referred to periodically, but because of the small sizes of the samples comparisons with the succeeding years are somewhat difficult. The data on length and age were acquired from the lemon sole in the fish filleting sheds. Sex determination which - Fig. 2

A map showing the general lemon sole fishing. grounds of the coast. (1) Strait of Georgia/ (2) West coast of Vancouver Island, (3) The Goose Island grounds, (4) northern Hecate Strait. - 8 -

ordinarily requires incision of the body wall was greatly facilitated through sampling in this manner.

Two methods of otolith collection have been employed. The first method, practiced during 1944 and 1945 involved the ex• traction of both otoliths and the recording, and filing of each pair in a shell vial under separate paper dividers. This prac• tice was found to be too slow to meet the requirements for ade• quate sampling and was subsequently discarded in favor of a more efficient technique, whereby only one otolith, the left hand one, was removed. For this method an "otolith board" was set up containing vials for each centimetre length group and for each sex. At the completion of the sampling all otoliths from fish of the same length and sex are counted, recorded under a single serial number and stored in a vial along with other such samples, separated by paper dividers. A fifty percent solution of glycerine which helps to clear the otoliths, is added to each vial. The speed with which this method of sampling can be carried out enables the handling of large samples in a very short period (approximately 200 fish per hour).

The otolith samples for 1945 and 1946 which have been ex• amined for this work amount to a little over 18,000. Collections during 1945 were composed of 1842: samples from the Strait of Georgia, 760 from the west coast of Vancouver Island, 265 from Queen Charlotte Sound and 2530 from Hecate Strait. For the fishing season, of 1946 examination was made of 12,670 samples, of which 3500 were from the Strait of Georgia, 2065 from the west coast, 860 from the Goose Islands area and 6250 were from Hecate Strait. - 9 -

lire itefitiiLflfi of tire Otoliths A common criticism of otolith reading is that much depends upon the interpretation by the investigator of what constitutes a winter check and what does not. Unless the methods and cri• teria for these determinations are definitely stated the work is of little value to other investigators in the same field.

Age determination of the lemon sole has been restricted to the left hand (blind side) otolith, and restricted still further to the posterior half of the clear surface (Fig,. 3). The effect of accessory checks in the reading of the otolith is minimal in this region.

The otolith is first placed against a black background in a small dish and examined under water with a binocular micro• scope (mag.. - 9 diam.) using.a bright illumination directed from above. Where a transparent ring shows up with equal in• tensity along several angles on the posterior half of the otolith it is considered to be a winter check. With reference to older fish in particular the results may or may not be entirely relia• ble because of the difficulty in distinguishing the rings near the margin of the otolith. However, a determined effort has i been made throughout the analysis to keep the readinp consistent. <* The determinations have been made independent of data on length and sex. Data on time of capture have of necessity been employed because of the high degree of variability as to the period during which the new growth begins in the spring. In order to keep a consistency of appraisal of this spring growth a numerical system was followed, whereby the amount of opaque growth outside the Fig. 3

An otolith of a lemon sole in its sixth year of growth. Note the five transparent (dark) winter checks. 10 -

preceding transparent ring was estimated in terms of the opaque growth during that preceding year. That is to say, an otolith with no apparent transparent (dark) ring on the margin, but with opaque (white) growth equal to about 8/10 of the growth of the previous year would be designated, if just completing its fifth year, as age 4.8. Whereas other might be 5.0 or 5.2, de• pending on the amount of white growth present on the margin. The decimal fraction then would indicate whether the new growth had begun or not. That is, 4.8 would mean that the dark (winter) check was not present, 5*0 would mean that the winter check was on the margin, and 5*2 would indicate that the spring growth had begun. Checking back through large series of such determinations it is possible to gain some idea of the approximate time when spring growth begins. The method is admittedly an approximation and subject to error, but it is more accurate than any estimate by casual observation. As otoliths may show the white growth beginning as early as January and as late as June, errors in year class determination would be considerable without some such evaluation.

The uncertainty of age determination has been mentioned with respect to higher age group fish. This is particularly so in the case of male fish. Beyond five or six years of age much of the annual deposition of calcareous material on the otolith goes to increasing the thickness of the otolith. This therefore gives the rings a cramped appearance beyond four or five years of age which makes age determination difficult. The increase in size of the female otolith is more in length and width than in depth, hence it usually appears larger and flatter than the 11

otolith of the male fish. The uncertainty of age determination is not confined en• tirely to fish in the higher age groups. Frequently samples of fish are obtained where all otoliths of both sexes are very opaque and contain many accessory checks. Outstanding in this respect are samples from the vicinity, of the Fraser River estu• ary. Whether this phenomenon is related to low salinity, type of food or some other factor, has yet to be determined. Sampling Pifflgwltipg One of the major analytical problems in the investigation of the fishery has been the question of to what degree sampling must be carried before it can be considered representative of any particular population. During the latter part of 1945 arid throughout 1946 a criterion was arbitrarily established whereby sampling was considered sufficient when thirty individuals were present in the best represented centimetre length group. Such a sample is no doubt representative of a catch, but is it rep• resentative of the population? Many factors such as tides, depth, light, temperature and food supply either dependent on or independent of one another are at all times undoubtedly in• fluencing the distribution of fish. A trawl net may capture a representative sample for one particular depth or series of depths for one particular time-interval, but to assume complete representation of the population would no doubt lead to erroneous conclusions. Another important factor which Influences the distribution of the sizes of fish in a catch is that of selec• tion. Not only does the trawl net select the larger members of the population, but the fisherman further calls out all fish < - 12 - below commercial size. Neither of these selective agents is all together constant.

These points have been mentioned in the hope that some appreciation may be gained of the limitations of the data. In an attempt to remedy these difficulties large numbers of samples have been aggregated, and until such times when specially equipped research boats can be employed, only broad general• izations can be expected. , 13 -

III. LIFE HISTORY

As an understanding of the results of the present inves• tigation depends to some extent upon a knowledge of the general

life history of the lemon sole a brief account of this is given

at this point, information on the life history is restricted in

greater part to the Strait of Georgia, and is still incomplete for some of the early phases. Spawning takes place from Jan• uary to March in well defined localities, usually in waters of 30 to 40 fathoms in depth where the ocean floor is somewhat muddy.

The eggs are pelagic, and hatching takes place in approx• imately 100 to 130 hours after fertilization, depending on the temperature of the water. The larvae are distributed over a wide area by the action of tides and wind blown watersi A certain proportion of these are swept into sandy inshore regions of the coast. Whether they reach these localities in a passive or active state, before or after metamorphosis takes place has not as yet been determined. Metamorphosis, that ls the as• suming of the side swimming behavior, is believed to take place when the larva reaches about one (Centimetre in length. Beach x seining operations have shown that the young fish remain in the inter-tidal zone during the summer months, growfing to a length of 10 cm. by August. With increase in size and the ad• vance of autumn, there is a progressive migration into deeper and deeper water. This movement away from the inter-tidal zone is apparently complete by at least the beginning of November.

Details on the life history of the lemon sole between the beach - 14

period of its existence and when it first appears in the com•

mercial catch are lacking. The size at which the fish becomes

fully available to the standard four-inch mesh of the trawl is

about 27 or 28 cm., but no quantitative data can be obtained

until experimental nets of various sizes of mesh are employed.

Maturity

Again the information on this subject is restricted to the

fish of the Strait of Georgia and is not necessarily applicable to other regions of the coast. From the examination of 1425 trawl caught fish taken during or near the spawning season it was found that approximately 50% of all female fish were mature at a length of 295 mm. The arrival at sexual maturity is shown

graphically in figure 4. Fish of 260 mm. in length were 100%

Immature, while those at 360 mm. were 100% mature. Similar information with regard to male fish is lacking, for the reason that no reliable criterion of maturity was available which oould be employed rapidly enough to cover a large number of fish.

It would appear, however, that males mature at a smaller size than do females. Fifty percent may possibly be mature at a length of 270 mm.

The relationship of age to size at maturity is not dealt with in great detail. However,data on age distribution of fish taken in the Strait of Georgia during the spawning season show that approximately 85 to 100% of the two-year-old females are immature, 40 to 50% of the three-year-olds, and 10% of the four-year-olds. Beyond that age all fish oan be considered mature. Spawning is presumed to take place each year after maturity is reached, and is apparently continued until death. 4" I

IOO R

ixi 50-

300 350 400 LENGTH - MM •

A graph showing the relationship of sexual maturity to the size of female fish. - 15 -

Fecundity

Essential to all fishery investigations is an estimation

of the reproductive capacities of the species concerned.

Quantitative data with respect to this subject have been ob•

tained from the female lemon sole. The ripe ovaries of 32

fish were collected just prior to the time of spawning, and were preserved in a formalin solution for approximately six weeks. For the sake of consistency in the measurements, the

eggs were-first freed of the membrane material and then tho• roughly dried.

The relationship of the weight of eggs produced to the length of the fish is shown graphically in figure 5. Although time has not permitted a detailed analysis of the rate of in• crease, a general trend is apparent.

As the mature lemon sole egg measures only one millimeter in diameter, and approximately 0.5 mm. when dried, it can perhaps be appreciated that great difficulty experienced in obtaining accurate determinations of the actual numbers of eggs produced. However from a number of small counted and weighed samples it was found that fish of 290 mm. produce approximately

240,000 eggs, and at the other extreme of the available data, a fish of 430 mm. produces approximately 2,100,000 eggs.

The relationship of fish length to weight of eggs produced is better-understoodyby considering that between 280 and

320 mm. the weight of eggs is tripled, between 280 and

360mm., it is multiplied by five, between 280 mm. and 400mm., by eight and between 280 and 440mm. by fourteen. Similar re• sults are shown by Raitt (1936) in his study of the haddock in 50 -

300 550 400 H50 FISH LENfrTH - MM,

Fig. 5

A graph showing the relationship of the size of female fish to the weight and number of eggs produced. -16 - the North Sea.

The Post-Larval Growth of the Lemon Sole As mentioned in the section of life history, quantitative growth data for the early part of the life of the lemon sole are available only for the period of their stay in inter-tidal waters. Samples of these fish were taken at monthly "O-Tide" intervals with a small meshed seine (£"•) in Departure Bay, Vancouver Island. The sizes of fish captured have been grouped to the nearest half centimetre and are presented graphically in figure 6. The average size of fish caught in May was 40.4 mm., and in June 63.7. This represents an increase of 23.3 mm. However fish caught in July showed an increase of only 15.3 mm. This was found by experimentation to be the result of the employment in July of two nets of the same mesh but of different depth, one 1 fathom and the other 2 fathoms. The same nets were used again in August, but the results were kept separate. The large net captured.fish averaging 107 mm., while the average for the small net was 86 mm. The results in figure 6 are for May, June and August from the large seine. The July sample was produced by both nets. Comparing the catches of the large net,then,the average increase in size was approx• imately 43.3 mm. which would represent a monthly increase of 21.1 mm. This compares with the 23.2 mm increase shown for May and June.

These results are demonstrative of a very rapid growth during the first summer. The average increase in size between May and June amounts to 55%, and between June and August about 32%. The relationship of this rate of growth to that of the adult fish will be discussed in a later section. LENGTH - r*\*.

: • —-J

Fig. 6

Graphs showing the size frequency distributions of young lemon soles captured in beach seines at month ly intervals;during the summer of 1946, at Depart• ure Bay, B.C. - 17 -

The differential selectivity of the two seine nets implies a migration into deeper water as the fish increase in size. By

November of the same year this migration had proceeded to such a point that even with the large net weighted to fish at a depth of four or five fathoms below the low tide mark only two fish were captured.

The great range of sizes present in each haul as shown by the graphs is in all probability the result of the pro• longed spawning season. Furthermore the size distribution and numbers of fish taken in beach seine samples will depend upon the success of the spawning, the height of the tide and on the depth of net employed. Carefully controlled seining operations performed over a period of years in a number of localities, oould no doubt be employed in predicting the strength of a brood year, two or three years before its entry into the fishery. Fig. 7

A map showing some of the more important lemon sole trawling grounds (shaded areas) off the Fraser River estuary and in the Gulf Islands. - 18 - i

IV. THE ANALYSIS OF THE COMMERCIAL CATCHES OF LEMON SOLES

A. THE STRAIT OF GEORGIA.

1. The Fishery of the Fraser River Estuary and Vicinity.

Hauls of marketable fish are made off Point Grey and south•

wards to the Fraser River lightship (Fig. 7) in shallow water

(5-20 fathoms) in the summer months and in deeper waters (30-45

fathoms) in the winter months. South of the lightship fishing

is conducted in waters of depths down to 75 fathoms, Small

fishing areas. English Bay to the east of Point Grey, and a

winter spawning ground near Point Atkinson are now closed to all

but one small boat. Samples from the whole region cover a period

extending from the spring of 1945 to the fall of 1946.

(a) Length Frequency Distributions.

Figure 8 shows distribution graphs of fish sampled during four periods in. 194-5 and 1946. A fifth sample from Point

Atkinson has been kept separate from the main winter sample because it represents spawning fish. In general, the lemon soles

captured from the Fraser River region are small. Male fish

average from 290 to 310 mm. in length, while female fish with the

exception of those from the Point Atkinson grounds, average be•

tween 310 and 340 mm. The fish from the spawning ground averaged

about 36O mm.

The sharp drop in the frequency curves below 290 or 300 mm.

is due to net selection and to the culling of unmarketable fish.

No male fish larger than 36O mm. were encountered: the upper I FRRSCR RIVER HHP VICINITN

MqtE — —- FEMALE.

300 350 300 3S0 LENGTH - *r*V LENGTH - K\K\.

V01MT ATKINSON

MOLE

300 350

Fig. 8

Graphs showing the length frequency distributions of lemon soles captured in the vicinity of the> Fraser River during 1945 and 1946. FRRSER RIVER »N» VICINITY

1945

HO a S to & 10 • III- 1 iw nil iiti 1110 mi nw iqm wt IIII wo WM 113?

POINT ftTKlNSOW

ISHH Wl lltJ Wl II* 1131 113* 1W IH3 IW HMI WO MM 11V) VEBR CUM Nffit CLASS

T>ec-p'Rii-

IW 111} Ml All 1110 N31 1118 nu iw mi m« iw ii3? NEAR CLASS >(E

FEMALE. .

Nil R1J i*iii Hi' 'ii? '^"i 1113 1111 1111 IH10 1131 M3?

Fig. 9

Graphs showing the year class distributions of lemon soles captured in the vicinity of the Fraser River during 1945 and 1946. - 19 -

size limit of females however was much greater, varying from

450 to 510 mm.

(b) Sex Ratio.

For the two periods in the summer and fall of1945

male fish comprised 30 and 37 % of the total number sampled. The

winter sample contained 18% males. At Point Atkinson however

where spawning was taking place 44% of the fish taken were males.

Considering the shape of the frequency curve for these fish it

is probable that this percentage was much higher in the actual

unselected population. In the summer sample for 1946 only 15%

of the fish taken were males.

The distributions of the year classes are presented

graphically in figure 9« During the summer and fall of 1945

the 1941 year class predominated in both sexes. Gn the Point

Atkinson ground male fish of the 1941 and 1942 year classes ap• peared most frequently. However the female soles were best re• presented by the 1941 and 1940 year classes. The main winter sample and the succeeding summer sample contained fish in which

the dominating male year class was 1941 and for females the 1942

class. The oldest male fish encountered were members of the

1938 year class—and the oldest females were of the 1936 year

class.

2. The Fishery of the Gulf Island Grounds. The waters of the Gulf Islands (Fig. 7) together with those

of Bayne Sound 40 miles to the north are the focal points of an

intensive fishery during the winter months of the year. Starting GULF ISLANDS

Fig. 10

Graphs showing the length frequency distributions of lemon soles captured in the vicinity of the Gulf Islands during 1945 and 1946. QULF ISLRMDS

put,.-DEC

Jh,. ns> m; iqqi i

•|H FEMALE. LiLL .IH. nn ni» mi nio nn w» mi iiiv, Neon CLASS I1H I'm Wfi PWO iw nw •I mo,

lib - JII.: nit nn is«o in ii» ISJI I

Fig. 11

Graphs showing the year class distributions of lemon soles captured in the vicinity of the Gulf Islands during 1945 and 1946. - 20 - i as early as September the winter spawning migration of the

lemon sole is heralded by sizeable catches in the regions of

Porlier Pass and Active Pass. During January, February and

March most of the fish are caught on what is known as the Boat

Harbour ground, an area at the northern end of Stuart Channel.

The samples taken, were for the greater part representative of these migrating and spawning fish.

(a) Length Frequency Distributions.

The samples from the Gulf Islands (Fig. 10) coyer a period from the fall of 1945 to the fall of 1946, In general the fish are larger than those encountered off the Fraser River estuary. The fall of 1945 sample representing fish in the process of migrating contained male fish averaging 320 mm. and females averaging 370 mm. The spawning ground sample from Boat

Harbour in the early part of 1946 contained small males avera• ging 310 mm. However the average length of female fish was

36O mm. During the summer of 1946 the average lengths of males and females were 330 and 36O mm. respectively.

The largest male fish reached a length of 390 mm,, and the upper limit for females appeared to be about 500 mm.

(b) Sex Ratio.

During the fall of 1945 and during the summer of 1946 male fish comprised 21% and 27% respectively of the total numbers of fish sampled. However, as can be seen from the graph representing the spawning season only a very small percentage

(17%) of the fish taken on the Boat Harbour grounds were male fish. Assuming that the sexes are present in equal numbers at - 21 - ( the time of spawning, the occurrence of such a ratio might

arise from two causes—

1. differential movement of the sexes on the spawning

ground,

2. the presence of a large proportion of males below

commercial size and below net selection size*

Considering the shape of the male distribution curve and its relationship to a maximium cull size of 290 mm. the latter explanation would seem the more reasonable.

As shown in figure ll^the 194-5 fall sample of male fish the 1941 year class appears most frequently and the females are best represented by both the 1940 and 1941 year classes.

The spawning ground sample taken during January and February of

1946 shows the 1941 year class predominating in both sexes.

Similar results are shown for the fish taken during the summer of the same year.

3. The Fishery of Baynes Sound.

The Baynes Sound fishing grounds are situated between

Denman Island and Vancouver Island, approximately 40 miles north• west of the Gulf Islands (Fig. 12). As in the southern waters the most intensive fishing is carried on during the winter months. During the early months of the year the important dragging area for soles lies outside of Baynes Sound in the waters just south of Cape Lazo. It is in this region that the major spawning has been found to take place. JE1&. 12

A map showing the general trawling grounds (shaded areas) in Baynes Sound and to the south of Cape Lazo. BRYMES SOUND

Fig. 13

Graphs showing length frequency distributions of lemon soles captured in the vicinity of Baynes Sound during 1945 and 1946. BflVNES SOUND

SEPT.- Dee.

F6IMAUE

1111 IW IW WO IW lilt 1931 list t

TOM.-FEB-

FEMALE.

FEB. (CAPE LMO)

MAL£ FEMftLE

1115 lilt IW mo f)3S ITO IW 111} IW 1111 l

Fig. 14

Graphs showing the year class distribution of lemon soles captured during the fall of 1945 and during the spawning season in 1946.

v - 22 - •I Samples presented are for the fall of 19-45 and for the early months of 1946, Because of the scarcity of fish during the other periods of the year satisfactory samples were not obtained. (a) Length Frequency Distributions. The distributions of the sizes of fish captured are shown in figure 13. The male fish captured were small, averag• ing from 310 to 320 mm. in the various samples. Female fish in the fall sample averaged 350 mm. and between 370 and 38O mm. in the spawning season. The marked decrease in frequency below lengths of 280 and •r*\-. 290 mm. is due to culling and net selection. Male fish up to lengths of 390 or 400 mm. were encountered. Females in the other hand reached lengths up to 490 mm. (b) Sex Ratio.

During the fall period 24% of the fish landed were males. The first samples from Bayne Sound, taken during the spawning season^contained only 14% male fish. The precise locality from which these fish were captured is not certain.

However a later sample taken in the waters outside Baynes Sound just south of Cape Lazo contained fish of which 56% were males.

The shape of the frequency curve would indicate that the actual percentage of male fish present on the grounds at that time was much higher, but that many had been culled out of the catch or selected out by the net.

The graphs in figure 14 show the male fish best rep- - 23 - resented by the 1941 year class. The same year class pre• dominated with respect to female fish in the full period. How• ever, the graph of fish taken during the early part of the spawning season shows three year classes occurring with about equal frequency, the 1942, 1941 and 1940 classes. Female fish from the Cape Lazo sample were best represented by the 1940 year class.

The oldest male fish present were from the 1937 year class and the oldest females were from the 1935 year class.

Reviewing the age distribution of fish caught in the Strait of Georgia, it can be seen that during the periods of the 1945 and 1946 fishing seasons described, the 1941 year class,generally speaking,predominated in the catches.

B. THE WEST COAST OF VANCOUVER ISLAND

Fishing on the west coast of Vancouver Island is restricted in greater part to the summer months of the year. The grounds extend from Port San Juan northward to Kyuguot Sound (see map,

Fig. 15). The lemon sole does not occur in great abundance in the waters of this part of the coast and as a result consider• able difficulty has been experienced in the collection of ade• quate samples, and much of the data have been combined. For the purposes of this work two regions are recognized, the waters be• tween Port San Juan and Tofino on the lower coast, and between

Esteban Point and Kyuquot Sound along the upper coast. Fig. 15

A map showing lemon sole trawling grounds (shaded areas) situated off the west coast of Vancouver Island. - 24 -

1. Port San Juan to Toflno.

Lemon soles are taken most frequently from a narrow strip

of trawling ground off Port San Juan between 30 and 40 fathoms

in depth; and along the inner part of the La Perouse Bank be-,

tween Long Beach and Tofino. The samples represent two periods

during the summers of 1945 and 1946,

(a) Length Frequency Distributions.

The graphs for the length distributions are shown in

figure 16. During the two periods in 1945, April to July and

August to November the average lengths of male lemon soles were

330 mm. and 320 mm. respectively. The average lengths of female

fish were 380 mm. and 370 mm. For the same general periods in

1946 the average length of male fish in the early summer was

320 mm. and of female fish, 350 mm. In the later part of the

season males averaged 330 mm. and females 370 mm.

No male fish larger than 390 mm..were recorded during 1945

and 1946, and the upper limit for female fish appears to be in

the vicinity of 500 mm.

(b) Sex Ratio.

The samples from the west coast of Vancouver Island

are characteristic in that very few male fish: appear, in the

catches. In 1945, during the early part of the summer only 8% of the fish caught were males* and in the later part of the

summer and fall, only 13%* In 1946 for the same periods the

percentages of males was 4% and 5%» The analysis of 1944 catch

data by the writer (1945 b) showed only 8% male fish. This was

at first thought to be the result of the culling of small fish* SflKI JUflM ro TCFINO

ESTcBRN TOKVUQuo r

Fig. 16

Graphs showing the length frequency distributions of lemon soles captured in two regions off the west coast of Vancouver Island during the summers of 1945 and 1946. SfiN lUfiM TO TOFlNQ N45 "

MALE 30 H PEMBLE

l: ISIl Wl IHHO iMit 1118 Lilli|

W45 Rufc<- Nov-

|,1AL£ K3o- JO" — FEMALE.

I W•••J i

MRN-TULY

MBit

W IW IfO l

RL>^.- SEPT.

' yo • B FEMALE

1913 Wl )SVI| iSHO 113") 1*)3* wm iw Nn iqni Wo iw isi» veil! c :.«•>•;

Fig. 17

Graphs showing the year class distributions of fish captured during the summers of 1945 and 1946 between San Juan.and Tof ino, on the west coast of Vancouver Island. - 25 -

However field observations by Mr* J. Manzer have shown that

there is no appreciable increase in the percentage of males in

unculled catches* Male lemon soles are apparently not present

in any numbers on the commonly trawled grounds of the west coast.

Samples taken during the two 1945 periods show the

females to be best represented by the 1940 year class (Fig. 17).

Male fish were too few to warrant consideration in this respect.

The 1942 year class predominates in both sexes in the 1946

samples, with the exception that in the first part of the year

the females are strongly represented by the 1943 year class in

addition to the 1942 year class. Between 1945 and 1946 then,

there has been a striking change in year class dominance. This matter will be dealt with in detail in a later section. Suffice it to say that this change could result from either an increase

in mortality rate brought about by an intensive fishery, or from

the influx of a new year class.

2. Esteban Point to Kvu^uot Sound.

Fishing in this region is confined to localities off Esteban

Point, Nootka Sound, Esperanzo Inlet and Kyu^uot Sound. Most of

the species of fish captured (lingcod, rockfish, rock sole, etc.)

are inhabitants of rough and broken ground, a fact which probably

accounts for the relative infrequency of appearance of lemon

soles in the catches. Because of the limited sampling oppor•

tunities and material the data have been combined and cover the

period from May to August in 1945 and in 1946. ESTEBRN TO KXUQUOT - FEMALES -

nu mi mi wo iw mt PHI n»t> lea*, CLASS

I1U 1112 IfHI 1110 1131 113? Neat CLASS

Fig. 18

Graphs shewing the year class dis• tribution of fish captured during the summers of 1945 and 1946 between Esteban Point and Kyuquot Sound on the west coast of Vancouver Island. - 26 -

(a) Length Frequency Distribution,

The distribution graphs are shown in figure 16. Male fish were too few for consideration. Females, however, averaged

approximately 38O mm, in the 1945 samples while in 1946 the

average length was slightly over 36O mm. The upper size limit in both years appears to have been around 450 or 460 mm,

(b) Sex Ratio,

The percentage of male fish in the samples for this region was-even lower than in the region to the south. In 1945

only 3% of the fish examined were males, and in 1946 out of a

total of 370 fish only 6 or 1,6% were male,

As in the lower region of the coast, the predominating year class in 1945 was the 1940 class (Fig. 18), In 1946 the dominance had changed to the 1942 year class.

C. THE GOOSE ISLAND GROUNDS.

To the north of Vancouver Island, lying in the middle of

Queen Charlotte Sound are the Goose Island grounds. This region

is one of the important halibut grounds of the coast, and the

operation of the trawlers in the area has been objected to by

the halibut fishermen on the basis of alleged serious interfer•

ence with set-lining. Little information is available on the

exact regions in which dragging is carried out, but the general

area is indicated in the maps (Fig. 2). Large trawlers operate

on these grounds during May and June. Data have been collected

during 1945 and 1946 for these periods. I

GOOSE I5LRND 3o r

300 350 HOO 150 500

BRIMKS ISLAND

LENGTH - MM .

Fig. 19

Graphs showing the length frequency distributions of fish taken during the summers of 1945 and 1946 on the Goose Island grounds in Queen Charlotte Sound, and in the summer of 1946 off Banks Island in Hecate Strait. GOOSE ISLAND

I VEHR. CLASS ^IEAK CLASS I

BRNKS ISLRND

mi MHI nm nvo IWI mk NII mi mi mo iut

I i

Fig. EC- Graphs showing the ygar class distribution of fish captured on the Goose Island grounds in 1945 and 1946, and on the Banks Island ground in Hecate Strait in 1946. - 87 - (a.) Length Frequency Distribution*

The graphs of 1945 and 1946 samples are shown in

figure 19* Male fish in 1945 averaged 320 mm. in length and

330 mm. in 1946. Female fish on the other hand averaged 360 mm.

in length in 1945 and 390 mm. in 1946. No male fish larger than

38O mm. were encountered. The upper size limit of female soles

at the time of sampling in 1945 was 450 mm. However in 1946

fish as large as 510 mm. were encountered.

(b) Sex Ratio.

In 1945 samples 12% of the fish examined were males,

and in 1946, 16.5% were males.

Male soles in 1945 were not in, sufficient numbers to warrant consideration. Female soles were represented most fre• quently by members of the 1940 and 1939 year classes (Fig. 20).

Because of the smallness of the samples in that year much sig• nificance cannot be attached to this result* However in 1946, with much more adequate sampling, these year classes again pre• dominated* Male fish showed the same situation, dominance of the 1940 and 1939 year classes. Although detailed considera• tion of this occurrence will be made later, it may be said that there is an indication here of truly dominant year classes.

That is, year classes which anethe result of successful brood years remain outstanding over a number of years. t

D. THE FISHERY OF HECATE STRAIT

The greater part of the fishing in Hecate Strait is carried Fig. 21

A map showing the approximate location of the lemon sole grounds in northern Hecate Strait - Banks Is• land, Butterworth Rocks, Triple Island, Two Peaks, and Rose Spit. 28

on in the northern part between Prince Rupert on the mainland

and Rose Spit on the Queen Charlotte Islands (see map, Fig. 21).

Four dragging grounds are generally recognized by the fisher• men, Butterworth Rocks, Two Peaks, Triple Island and Rose Spit.

Their exact limits have not as yet been determined. Future

tagging experiments:may possibly show that they are inter- con• nected.

Another lemon sole fishing area lies approximately 40 miles south-east of Butterworth Rocks in the vicinity of Banks Island.

Samples to be considered cover the spring and summer months of 1945 and 1946.

1. The Banks Island Ground.

Satisfactory samples from this region were obtained- during the summer of 1946 only. Apparently most of the fishing takes place between the buoy at the north end of the island and Bonilla

Rock to the south-west, in waters between the depths of 15 and

45 fathoms.

(a) Length Frequency Distribution.

Small fish predominated in the sample examined,

Fig. 19. The average length of male fish was 310 mm, while the average for females was 330 mm.

The sharp decline in numbers below 300 mm, may be attri• buted to net selection and culling. The largest, male sole en• countered was 410 mm, in length and the\largest female was 510 mm.

Male fish comprised 41% of a total of 617 fish ex- - 29 -

amined from this region. (c) Age Distribution. The 1942 year class highly predominates in both sexes (Fig. 20). Thirty-nine percent of the female fish and 28% of the males were found to be from this class.

2. The Butterworth Rock Grounds.

Most of the lemon soles landed at Prince Rupert through• out the year are from this ground. Fishing takes place for the most part to the south and west of Butterworth Rocks in waters between 30 and 60 fathoms in depth, Samples were collected from this region during the spring of 1945 and the spring and summer of 1946. (a) Length Frequency Distributions. The results of sampling during 1945 and 1946 are shown graphically in figure 22, In April 1945 the average sizes of male and female soles were 350 and 38O mm*respectively. In 1946 during the same period the averages were 340 and 370 mm. The largest male fish encountered was 420 mm. in length, and the largest female was 500 mm. The summer samples taken during 1946, May to June, and August show considerable differences in the distribution. In May and June the average length of male fish caught was 340 mm. and the average length of females was 38O mm. In August,how• ever, male soles averaged 360 mm. and females 420 mm. Such dif• ferences: may be .attributed mainly to differences in depth and localities fished. Fig. 22

Graphs showing the length frequency distribution of lemon soles taken on the Butterworth Rock grounds during the spring Of 1945 and 1946," and during the summer months of 1946. BUTTED WORTH BOCKS

Wi\ tVii I9V0 WJ9 Ml? Ktj7 l

FEMALE

ill* IIHI nsi mo

MON - JUNE

-••Hi!- .llilll.. J944 Km l

VEfit CLASS >jEn^ Ci.n:i

Bu«,uvr

mi HI) iHt IIXI nvo Nil IW iiti mi. iw m» mi HII Hio mi nir nn ni. nil' IDI h«

Fig, 23

Graphs showing the year class distribution of• fish caught during the spring of 1945 and 1946, and during the summer months of 1946,on the Butterworth Rock grounds. - 30 -

The upper size limit for male fish is between 420 and

430 mm. Female fish of lengths up to 500 or 510 mm. were en•

countered in all samples.

(b) Sex Ratio.

In April of 1945, 48% of the lemon soles captured

were male fish. During the same period in the following year,

45% were males. In May and June the number amounted to 43% and

in August to 25%.

The year class distributions are given in, figure 23.

The samples of female soles taken during April 1945 show the

1939 year class best represented. The distribution for male

fish, shows three years predominating, the 1940, 1939 and 1938 year classes. In April 1946 the predominating class in male fish was the 1939 year class, and in females the 1942 year class.

May and June samples in 1946 showed the 1939 year class domin• ant in both sexes. In addition to this class,however,in the distribution for female fish,the 1942 year class also shows up prominently. In the August sample the 1939 year class predom• inates in both sexes, and the 1942 year class is represented by only 7*4% of the female fish. The alternating (and sometimes concurrent) predominance of the 1939 and 1942 year classes will be discussed in a later section.

3. The Triple Island Grounds.

This fishing area lies approximately six miles north of

Butterworth Rocks. Little is known as to its extent aside from TRIPLE. ISLftND

i I

Fig. 24

Graphs showing the length frequency distributions of fish captured during 1945 and 1946 on the Triple Island, Two Peaks and Rose Spit grounds in north• ern Hecate Strait. I :

I - i TRIPLE ISLAND IS45 FEflSVJE-

1113 1112 1111 1110 1131 H3» 1131 "31. !1W HEAR CLASS

ISM6 MALE

Si x •

llUt 1113 1111 111 I 1110 mi N3J IW 113b mi ins mi mi mo ii3i H3« un IIJL lily nil NEAR CLASS NEAR CLASS

TWO PEAKS IS45 FEMALE

g 20- * jo

1111 1110 I1J1 I1J8 1131 1131, I13S iw mi m« HOT im un ins mi NEAR CLASS NEAR CLASi

FEMALE

nil ii4j m nil mo mi n3» nn list IS11 IS1J 111! 1111 MO 1131 MS 1131 1131, 1135 NEAR. CLA>4 \E«L CLASS

JFig. 25

Graphs showing the year class distributions:- of fish captured on the Triple Island and Two Peak grounds during 1945 and 1946. - 31 -

from the fact that fish sampled in the summer of 1946 were from

shallow water near the Triple Island Light. Samples taken rep•

resent two periods, September 1945 and July 1946.

(a) Length Frequency Distribution,

The graphs of the data taken in this region are shown

in figure 24. The average length of female fish in both years

was approximately 38O mm. Male soles in 1946 averaged 340 mm.,

while the average in 1945 was 320 mm.

(b) Sex Ratio.

Male fish in the 1945 catch, amounted to only 11% of

the total number present. In 1946, approximately 39% were male

fish.

The graph for the age distribution of fish caught in

1945 (Fig, 25), shows the 1939 year class dominant with respect

to female fish. Male lemon soles were too few to warrant con•

sideration. In 1946 two year classes, the 1939 and 1942 classes were dominant in both sexes. This situation is similar to that shown by samples from Butterworth Rocks during the same period,

4. The Two Peaks Fishing Ground,

This fishing ground lies approximately 10 or 15 miles north and west of Butterworth Rocks (Fig. 21), between depths of 40 and 50 fathoms. Samples were collected during two periods:June,

1945, and in January 1946. (a) Length Frequency Distribution.

The fish taken in June of 1945 (Fig. 24) were con- 32 -

siderably larger than those taken in the following January.

The average length of male fish was 38O mm, and females aver•

aged 430 mm. In January the average lengths of male and female 0 soles were 310 and 340 mm., respectively. Culling and net

selection show their effect in the shape of the frequency curve for January. However the June sample shows no culling effect.

Apparently there were no small fish present on the ground at the time fishing took place. In January there were no large fish present,

(b) Sex Ratio,

In the June sample 22% of the fish captured were males, while in January 41% were male,

The age distributions are shown in figure 2% Male fish in June of 1945 were best represented by the 1937 year class. The 1938 year class.predominated in the distribution of female fish. The samples taken during January of 1946 show the same situation that has already been observed in the study of

Butterworth and Triple Island fish, that of bimodality In the distribution curves. The 1939 and 1942 year classes dominated in both sexes,

5, The Rose Spit Fishing Ground.

Lemon soles sampled from this region are apparently caught in relatively shallow water (10-12 fathoms) about eight miles east of Rose Spit just off the edge of the Dogfish Bank (Fig,21) .

Sampling was carried out during June of 1945 and 1946, ROSE SPIT

-lllll- i:l -Jill.-

Mil Wl I9«f0 1919 I1» lUT (931- 19JS |QW mi HW MM MW HH USfc MJ5 1111 <*tii

IS46

I llllll.- lllllla.- iw mi mi mi mi m\ its nn n» nv mi »«» ni« mi "*> «w '•""> 'i* i"* "'I vece CL«5S NEW

Fig. 26

Graphs showing the year class distributions -of lemon soles captured on the Rose Spit grounds during the summers of 1945 and 1946. - 33

(a) Length Frequency Distribution,

In Fig. 24, the graph for fish caught during 1946

shows an increase in the proportion of small-fish as compared with 1945* The average lengths of male and female fish in

1945 were 370 mm. and 41G mm, respectively. In 1946 the aver•

ages were 340 mm. and 390 mm,

(b) Sex Ratio.

Male fish in the 1945 catches amounted to 19% of the total number sampled. In 1946 this percentage was slightly higher, approximately-26%,

In 1945, the 1939 year class appeared to dominate in both sexes (Fig. 26). With respect to the male fish,however, the 1937 year class was also well represented. It will be remembered that this was the dominating year class in the age distribution of male fish from the Two Peak grounds during the same period. In the 1946 graph for female fish, two year classes predominate, the 1939 and 1942 classes. Dominance is not as distinct in the samples of male fish, but there is some indica• tion of similarity to the females* - 34 -

is V. RATES OF GROWTH

The rate of growth of the lemon sole in the different lo• calities of the coast has been determined on the basis of the average lengths of fish encountered in the various year classes. Suoh determinations can be made accurately only where sampling has been partioularly intense and where it has been carried out in a fairly short period of time.

Dependence upon samples from the commercial catoh creates several difficulties in the estimation of growth rate. In the first place, data on the growth during early life are lacking entirely. Furthermore the average sizes of fish in the lower age groups whioh first enter the fishery are actually .greater than the true averages, as the net and the fishermen select out the larger members of these age groups. Henoe, as shown by Rioker (1940) the differences between age groups which are affected by selection and those which are not will be less than in the natural state.

With respeot to fish in the older age groups the possi• bility of sampling error increases as the number of fish in each suooeeding age group decreases. Also to be oonsidered is the possibility of age selection by the net. That is to say, are older fish more likely to get caught than young ones? In an effort to discount the possible effects of the above men• tioned factors, the actual determinations of growth rate have been confined to a period between four and eight years of age .

Two graph!o methods of presenting growth rate have been 500 wo FRASER RIVER Ql/LF ISLANDS

t t 1 too

v vi vn vm v VI VII Aft. -HEARS 500 BRYNES SOUND• 5AN TURN TO TOFINO

H00 •

•soo. 300

V VI VII VIII v vi vu vm

500 ESTEBRN TO KYUQUOT SNP-

I 100

'v v vi vn vui IX x RCit - \«RAS

Fig. 27

Graphs showing the growth of the lemon sole in the Strait of Georgia and on the west coast of Vancouver Island. (MALE. JFEI^AUL 500 GOOSE ISLRNP BUTTERWORTH ROCKS

I HOO

300

III IV V VI VII VIII IX X XI III IV V VI VII vm R<1£ - NGCWS SCiOr TRIPLE ISLHND 500 ROSE SPIT

I 100

-300

MI iv v vi «H vm ix < III IV V VI VII VIII

Fig. 28

Graphs showing the growth of the lemon sole on the Goose Island ground and in three regions in northern Hecate Strait. (^MAU=_ .PEr^A^e. -35- employed. The first of these deals with absolute growth, a straight plotting of age against length. Graphs of this type, .shown ln figures 27 and 28, give a picture of the general trend in growth and serve well for rough comparisons. Most striking are the consistent differences in the rates of growth between the sexes. In general the female soles show an increase of approximately 11 mm. more per year than do the males. In table I are determinations of growth rate in the various regions, shown as averages in millimetres per year from the fourth to the eighth year.

From these results it is apparent that the growth rate is greater in the strait of Georgia and in northern Hecate strait than on the west coast of Vancouver island, Queen

Charlotte sound and in the middle of Hecate strait. This is most readily seen with respect to female fish. These values represent a general growth rate and do not take into consi• deration the fact that growth is steadily decreasing during the five year period.

In an attempt to represent this changing growth rate a second method of determination has been employed. The growth rates during three time-intervals, four to six years, five to seven years, and six to eight years, have been obtained by

&t using the generalized formula for the groxtfth curve S = Pe , where t, is the time interval, P the initial size, S the size at the end of time t, and G the growth rate. The value so obtained is a natural logarithmic expression, referred to by

Ricker (19^5) as an "instantaneous growth rate," that is, -36-

TABLE I

The average growth rate between the

fourth and eighth year.

Growth Rate (mm. per year)

Male Female

Fraser River 10 23

Gulf Islands 9 22 Baynes Sound 13 23 San Juan to Tofino 11 19 Esteban to Kyuquot - 19 Goose Islands 10 19

Banks Island 11 18

Butterworth Rbcks 13 20 Triple Island 12 23 Two Peaks Ik 20

Rose Spit 13 21 W-VI V-VII VI-VIM TWO "YERR TIME-INTERVALS I

Fig. 29

Graphs showing the change in the in• stantaneous growth rate "intfemale fish between four and eight years of age. -37-

the growth rate at any one Instant during a fishing season.

The results obtained for female fish are shown in figure 29.

Similar treatment of the data for male fish proved unsatis-

" factory probably because of the inadequacy of sampling.

However, the rates as determined are given in the appendix.

The growth rate between the fourth and sixth year appears

to be greatest in female fish from the Butterworth rocks

region. Baynes sound and the Fraser river samples show a

slightly lower growth rate for the same period. The rates

are about equal in the Gulf islands, on the lower west coast

of Vancouver island, and on the Two Peak grounds. The lowest

growth rates between four and six years of age are shown by

samples from the upper west coast of Vancouver island, and

from the Goose island grounds.

In general the greatest decrease in growth rate is

shown by the samples from the northern part of the coast.

This is evident from the slopes of the lines between the

first two time-intervals. Between the second and third

time-intervals trends are Indefinite, probably because of

sampling deficiencies.

The general results from the various localities show

that differences in the growth rate of the lemon sole, after

it reaches commercial size, are not striking. More pronounced

differences may occur during the period prior to when the

fish enters the fishery, but because of the limitations

in sampling methods, nothing can be said in this respect -38- at present. The employment of small meshed nets In the future, in all probability will reveal local differences which are not detectable in the samples from the commercial

oatch. - 39 -

VI. MORTALITY RATES

One of the important factors which affect the abundanoe of fish is that of mortality. This may be of two kinds—

1. Death due to natural causes and 2. Death due to fishing.

Together they represent the total annual mortality.

The determination of total annual mortality is made either through tagging experiments or by the examination of the age composition of the stock. The latter method has been employed for this work. According to Baranor (1918), in a stable population, where the number of recruits added each year is constant /the per• centage reduction of a year class from any given season to the following season should represent the total mortality rate. However as has been indioated already in the section on age analysis recruitment does not occur with such regularity. In a fishery that is only relatively stable other methods must be sought which are less subject to error. The percentage de• crease from year to year may be obtained by plotting the lo• garithms of the numbers of fish in all age groups and deter• mining the slope of the line. This value, when converted to a natural logarithmic expression becomes what Ricker (1944) call the "instantaneous mortality rate," a figure whioh is proportional to the number of fish killed during any one short interval in the fishing season. The instantaneous mortality rate "i" may then be converted to the total seasonal mortal ity - 40 -

rate "a" by applying the formula a s l-e""* derived by Rieker

(1944).

In the utilization of this method for the calculation of mortality rates in populations of lemon soles, only those age

groups were used which were believed to be entirely free from

such factors as net selection and incomplete recruitment.

Furthermore the analysis has not been applied where sampling has been inadequate. In figures 30 and 31 are the graphs of the numbers of fish in the various age groups, plotted loga• rithm! cal ly and fitted by least squares. The instantaneous mortality rate values together with their corresponding total annual mortality rate values are shown in table II.

1. Strait of -Georgia

Female lemon soles from the Fraser River area show a straight line relationship, from which the mortality was cal• culated to be 63%. Somewhat less conclusively, the result for male fish was approximately 65% between six and seven years of age. The smallness of the samples or possibly fluctuations in recruitment may have been responsible for the irregularity of the relationship.

The Gulf Islands show a somewhat similar situation^ With a total annual mortality rate of 56% for female fish and 69% for males. Once again the dispersion of the points on the graph for male fish makes the accuracy of the result somewhat doubtful.

In Bayne Sound the mortality rate was found to be 52% for males, and 59% for female soles. m the whole Strait of Georgia then, the total annual mortality rate appears to be between 50 and 70%-averaging Fig. 30

Graphs showing the regression lines of age group frequencies in the Strait of Georgia and on the west coast- of Van• couver Island. The regression coeff• icients (converted to nat. log.) are given as instantaneous mortality rates in Table II, page 41. Fig. 31

Graphs showing the regression lines of age group frequencies on the Goose Island grounds and in Northern Hecate Strait. The regression coefficients (converted to nat. log.) are given as instantaneous mortality rates in table II, page 41. - 41 -

TABLE II ~ The total mortality rates in the various regions of the coast, J

TOTAL TOTAL INSTANTANEOUS ANNUAL MORTALITY RATE MORTAL ITT RATE

Male Female Male Female Fraser River 1,06 • 99 • 65 • 63 Gulf Islands 1.18 • 83 .69 • 56

Baynes Sound .74 •89 • 52 • 59

West Coast • 55 1,11 • 41 .67 Goose Islands .81 — .73 .56 • 52

Butterworth Rocks ,48 • 34 .38 • 29

Triple Island .48 • 32 .38 .27

Rose Spit .51 .42 .40 • 34 - 42 -

approximately 60%. 2. West Coast of Vancouver•Island For the purposes of this study the samples from the two regions of the coast have been combined. The graph for female fish shows a striking change in mortality rate after seven years of age. Two regression lines have been plotted to demon• strate the differences. During the early period the percent• age mortality rate was found to be 35% and in the latter period, 67%. Assuming that net selection and culling are not respon• sible for this inflection of the curve between the ages of four and six years, it would appear to be the result of decreased recruitment. This oould be brought about by natural conditions or by an Intensive fishery which removed a large proportion of adult fish several years previously. The value of 67% mortality is perhaps closer to the actual rate. The graph for male fish has been based on the lower age groups. The rate determined from this is perhaps, for the same reason as stated above, lower than the actual condition existing in the population.

3. Goose Island Grounds

The total annual mortality rates calculated for this area show a 56% mortality for male soles and 52% for females. The slope of the female regression line has been determined for age groups VTI to H neglecting the older ages because of a notice• able downward inflection in the lower part of the line.

4. Morth Hecate Strait

Characteristic of the three graphs presented for this area is the manner in which the rate of decline in numbers of in• dividuals in the older age groups increases sharply after nine - 43 -

years of age in the male and after ten years in the female*

The possibilities as to the cause of this inflection are given

detailed cosideration under the topic of Differential Mortalities

Rates in the Discussion section.

The annual mortality rates have been determined from the sections of the graphs exhibiting a straight line relationship, between seven and nine years in the case of the males and be• tween seven and ten years in females. Butterworth Rock sen pies show a 38% mortality rate in male fish and 29% in females. The results from Triple Island are quite similar, 38% for males and 27% for females. The mortality rates for male and female soles from the Rose Spit region are 40% and 34% respectively.

The total annual mortalities as calculated for the various regions of the coast show marked differences, the significance of which will be dealt with in the discussion. - 44 -

VII. DISCUSSION

1. Growth Rate. The growth of animals follows a pattern whioh is frequently referred to as the logistic curve. During the early stages the curve is concave upward, beginning, almost horizontally and rising very steeply. Along this steep part of the curve an inflection occurs wherein the concavity changes from upward to downward and the slope of the line steadily decreases towards the horizontal.

With regard to the lemon sole, sampling methods together with the nature of the life history have permitted the analysis of only certain sections of this growth curve. However, the results obtained from beach seizing and from examination of commercial sized fish supply sufficient information to show the general trend. In the graph in figure 32 the heavy lines re• present the known growth rate and the dotted lines that which has stilled to be determined. Plotted on this same graph is the arithmetic growth rate. From this it can be seen that the great• est rate of increase (min. per year) takes place in the first year, when there is an estimated growth of 120 to 140 min. Upon entry into the fishery the growth rate has dropped to approxi• mately 30 min- per year and continues to decrease as age increases.

What are some of the environmental factors which influence growth rate? Temperature for one, has a profound effect on the ftevelopment of fish during their early stages especially prior to the absorption of the yolk sac. According to Eudd (1940) 'Fig. 32

A graph showing a total growth curve for the lemon sole as drawn from Departure Bay and Gulf Island data. The broken line part of the curve represents that part of the growth which is yet to he determined. - 45 -

hatching of the lemon sole egg takes place about 90 hours after fertilization at a temperature of 13° C. However Mr. F. Taylor

has found that at temperatures of 5° c" hatching does not take place before 130 hours. Both food and temperature play an important role during the post-larval period. The eulittoral zone of the sea, and in particular the inter-tidal area, presents a great diversity of conditions which influence the growth rate. Through the in• fluence of the Fraser River the surface temperatures of the strait of Georgia during the summer months are much higher than in the other regions of the coast. As these waters would show a correspondingly higher productivity it is reasonable to believe that the growth rate of the lemon sole during the summer months would be higher in the strait of Georgia than in the other regions.

Migration into'8*&eeper waters brings the fish into zones of more constant conditions. Hence variations in growth rates between areas would not be as great as in the inshore regions. This may serve to^ explain why no striking differences in growth have been shown between wide-spread areas of the coast.

Another factor which should be considered,however, is-that of competition for food. In European waters it has been found that the growth rate in a heavily populated region is lower than in a sparsely populated one. Such conditions have not a been observed in the study of the lemon sale. In Hecate Strait where fishing operations have begun only recently and where supposedly there siae an abundance of fish the growth rate is apparently as high as in regions which have been fished - 46 -

for a good many years. This perhaps would indicate that there is an abundant food supply, and that competition or over• crowding is not a determining factor.

To this point no mention has been made of the differences in growth rate between the sexes. The analyses of unculled samples of small fish by the writer (1945 a) have shown little or no difference in rate of growth between the sexes to the end of the second year. Beyond that point however the growth rate of the male becomes much slower than that of the female. This change of the growth rate may be correlated with tie advent of sexual maturity, and has been attributed by various authors primarily to the differential requirements for the generation of sex products. Hickling (1933) in his studies of the hake, and Wallace (1904) investigating the North Sea plaice have suggested that as the male fish matures at a smaller size than does the female, it must detail a certain amount of energy to the production of spermatozoa which might otherwise have been employed in increasing body size. Thus there results an initial difference in growth rate between the sexes. In each

succeeding year the male devotes more and more energy to re• production at a considerably greater rate than does the female, with the result that the difference in growth rate steadily increases.

Another explanation might be that male fish are more vigorous or more aggressive than females. The conversion in the male of a considerably greater amount of metabolic energy into activity rather than into growth would result in a lower growth rate. - 47 -

Somewhat less likely is the possibility that the differences in growth rates are due not to inherent factors but to some factor in the environment. The low percentage of male fish in the catches during the summer months suggests differences in migratory habits between the sexes. Such differences in the grounds inhabited might result in differences in type or quantity of food consumed, which would produce differences in the growth rates. 2. Mortality. If, in a population of lemon soles where female fish pro• duce an average of 1,000,000 eggs each per year, only two fertilized eggs from each fish survive to develop into mature fish, the population will show no decrease. In a region * supporting a fishery the occurrence of even such an infinitely small survival as this would be considered optimal. What then are the factors which contribute to the tremendous mortality? In the first place, fertilization will to a certain extent be incomplete. A certain number of individuals will die during the incubation period or shortly after hatching. However the greatest mortality is generally assumed to take place during the short period when the yolk sac becomes absorbed anfi the larva turns to food material in the environ• ment. If this required food (presumably phytoplankton) is not present, then a vast mortality ensues.

Another important factor, as described by Sette (1943) in his work on the Atlantic Mackerel, Walford (1938) on the haddock, and HIckling (1933) on the hake, is that of the - 46 -

direction of ocean currents. Unusual wind conditions at the

time of spawning haver been found to cause the eggs and larvae

to drift into regions unfavourable to their development and

thereby produce a heavy mortality. These two factors, food

supply and direction of drift either together or separately i may be considered of prime importance in determining the success or failure of a brood year. Beyond the larval stages the percentage mortality steadily decreases. The predation factor undoubtedly takes on increas• ing importance. Another physical condition, however, which has been observed to have considerable effect on the survival of young soles during the early period of their stay in the inter-tidal zone is that of stranding. Because of the nature of the regions inhabited (sandy beaches of gradual slope), the receding tide leaves large numbers of the very small fish stranded on the sandbars or trapped in tide-pools which soon heat up to a lethal temperature. This effect will, of course, be most pronounced at the very low tide periods of each month, and will influence the survival of only the smaller fish. As the fish grow larger they inhabit deeper and deeper waters and therefore become less and less susceptible to stranding. Beyond the inshore period the young lemon soles become subject to predation by such species of fish as dogfish, lingcod and other flatfish (brill and halibut), and to some extent by hair seals and sea lions. To a certain indeterminate extent injury in escaping from trawl nets may account for some mortality. Death due to fishing does not, however, become a prominent factor until the third or fourth year. - 49 -

The results of the mortality study in fish of commercial size have shown considerable differences among^st the various regions of the coast. Assuming that the natural death rate is fairly similar in all areas these differences can be considered reflections of the intensity of fishing which the respective grounds have experienced. In a virgin fishery the mortality rate as determined from the age composition of the stock will represent the natural mortality rate. In a fishery such as that of northern Hecate Strait, which has been in progress for only a few years—the mortality rate, determined from the older age groups will be a rough approximation of the natural mor• tality. The results have shown an average mortality rate of

38% for male fish and 30$ for females. These values may be possibly higher than the actual natural mortality. Thompson and Herrington (1930) by means of tagging experiments have estimated the natural mortality of the Pacific halibut to be approximately 36%. H. Thompson, (1929) has shown"a 32% natural mortality in haddock, calculated from studies of virgin fishing grounds in European waters.

Differential Mortality Rates.

The analysis of the Hecate Strait samples has uncovered differences in total mortality rates which give rise to con• siderable speculation. In the later years of life, after nine years of age in the male and after ten or eleven years in the femal?/ there is a sharp downward inflection of the regression line. Assuming that sampling has been adequate, there are two possibilities as to the cause of this apparent change in mortality rate. - 50 - i

(1) . If older fish are more easily caught than young ones there would be a preponderance of the former in the catches when the fishery is first begun. After a period of time the proportion of these more catchable fish to the others would be so reduced that the regression line would be inflected downwards in a manner similar to that shown in the Hecate

Strait mortality graphs. It is however, doubtful that such a situation could arise in the short period in which the fishery in this region has been operating. Furthermore, the change in the slope of the graphs is too abrupt. If a fish becomes more easy to catch with increasing age the graph would show a more gradual inflection.

(2) . If older fish are not more easily caught than young ones the change of slope could be attributed to an increase in the natural mortality rate. If this suggestion Is true, what is the explanation of its occurrence? It will be noticed that the inflection in the slope of the line occurs in both sexes, but not at the same ages. Mention has been made in previous sections that males following the onset of sexual maturity grow at a greatly reduced rate in comparison to the females, and it has been suggested that the differences might be due to differences in reproductive requirements. Furthermore, length data have shown that female fish grow to a much larger size than do male fish. Few females are encountered over 500 min. and few males are found larger than 400 m:tai. It would appear then that nearing these sizes, some factor enters the picture w hich greatly increases, the mortality rate. The inference is, that towards the upper size ranges of both sexes and possibly - 51 - at the point of inflection in the mortality curve a lethal ratio is reached, between body weight and testis or ovary weight.

Considering now the occurrence of differential mortality rates between the sexes, it may be seen that prior to the sudden change in rate in the older age groups, the males generally speaking have a higher mortality rate than the fe• males. This has been found to be the case for several species of fish in the North Sea. Wallace (1925) and Atkinson (1907)

(quoted by Wallace) in their studies of the plaice could find no evidence of unequal incidence in the two sexes of extrinsic factors tending to the longer survival of one sex. Studies of the plaice in the Barents Sea, a virgin fishing ground showed a higher mortality rate in male fish than in females. The lesser viability of the male fish would then be the only explanation. * The dominance of female lemon soles in the catches during periods of the year other than the spawning season could be regarded as a factor which would produce differences in the mortality rates. If male fish are not present on the traveling grounds in their true proportions it is reasonable to believe that the total seasonal mortality • rate would be lower in that sex than in the other. This, however, is not the case, as samples from most of the regions show a higher mortality rate in the male. Increased death, then,from natural causes appears to be the reason for differences in mortality, and the most likely cause of this is the differen• tial effect produced by the processes involved in sexual reproduction. - 52 - I

(^). The Relationship^ of Mortality and Fluctuations in

Strenfths of Year Clastes to Age Composition.

In areas which have experienced a fairly intensive fishery

over a long period of time, the proportion of old fish to young fish is much lower than in areas where fishing has been relatively light. In the Strait of Georgia where the total

annual mortality rate has been estimated from 1946 samples to be

60%, between 70 and 80% of the fish entering the commercial

catch are less than six years of age. On the west coast of

Vancouver Island 80 to 85% of the fish captured were within

this range, and the mortality rate for the population as a whole amounted to approximately 67%. On the Goose Island grounds in the same year the total mortality rate was found to be about 54%, and 28% of the fish caught were less than six years of age. In northern Hecate Strait the average mortality rate was 34%, and fish of less than six years comprised 38% of the total catch. The proportions of younger fish in the catches from the various areas do show a general trend related to the history of the fishery, but there are indications of another factor which is also influencing the relative proportions of the age groups, namely,fluctuations in the strengths of year classes.

On the west coast of Vancouver Island in 1945, 65% of the fish captured were less than six years of age,approximately 15% more than in 1946. This difference may be correlated with the marked change in dominating year class which took place in this area between 1945 and 1946. In 1945, the 1940 year class pre• dominated in the catches, but in the following year the 1942 - 53 - year (class was best represented. This shifting of dominance may have been due either to the intensity of the fishery or to the advent of a new year class. On the Goose Island grounds in 194-5, 53% of the fish taken were under six years of age. However, in the following year, as mentioned above, the proportion of these fish went down to 28%. Age group analysis has shown that in both years the 1939 and 1940 year classes predominated. On the North Hecate Strait grounds in the summer of 1945 less than 20% of the total number of fish taken were under six years of age. In 1946, however, the number of fish in this range had increased to 3&%» This increase may be explained by the fact that in 1945 the 1939 year class predominated, and in the following year the 1939 and 1942 year classes predominated. The question now arises as to how all these fluctuations have arisen and to what degree they are related. In the first place, samples of fish collected from Hecate Strait and Queen Charlotte Sound have displayed an interesting characteristic in that the frequency graphs for length and age show no striking skewness which can be attributed to net selection and culling. That is to say, the decrease in numbers of fish to the left of the mode is apparently independent of these selective factors. This might at first suggest that the smaller fish are not available to the fishery. However, examination of data which cover a period of years shows that the absence of smaller fish is actual. In a preliminary study by the writer (1945 a) of the age composition of Hecate Strait fish during 1944, it was found that female fish of five years of age (1939 year class) occurred most frequently. Both the 1939 and 194-0 year classes- could be considered unaffected by selection. Yet the 1940 year class was poorly represented. This 1944 graph is shown in figure 33» 311(3 compared with Butterworth Rock samples taken during the summers of 1945 and 1946. In the 1945 samples the

1939 year class again predominated. The relative infrequency of the members of the 1940 and 1941 year classes could not be attributed to the net selection or culling factor. In 1946 two year classes were strongly represented, the 1939 and 1942 year classes. The obvious conclusion is then that the years

1940 and 1941 in the vicinity of Butterworth Rocks were poor brood years and thus accounted during 1944 and 1945 for the relative paucity of younger fish in the catches. In 1946 with the advent of the strong 1942 year class the proportion of smaller fish increased.

How far-reaching and how constant was this effect?

Samples from other regions of Hecate Strait in 1945 with the exception of those from the Two Peak grounds, showed the 1939 year class dominating in the age distribution of female fish.

In 1946 all samples showed either the 1939 year class or the

1942 year class, or both, dominating. Fish from Banks Island were predominantly 1942 year class, while those from Two Peaks,

Triple Island and Rose Spit were well represented by both the

1939 and 1942 year classes. The fluctuations in dominance of these two year classes within short periods have been shown in the Butterworth Rock samples. This in all probability is the result I

YEflft CLHSS DOMINRNCE.

fcUTTERwOBTH ROCKS - FEMBl.ES -

I'm I'm \

NEAR CLASS

Fig. 33

Graphs showing the dominance of the 1939 year class in female lemon soles from Butter• worth Rocks during 1944, 1945 and 1946. In the latter year there is an appearance of another strong year class, that of 1942. - 55 - of differences in the depths at which fishing was carried out. The over-all picture, however, for the summer months from this area (Figure 33) shows the dominance of both year classes. Throughout Hecate Strait then it is apparent that 1940 and 1941 were not as successful spawning years as those immediately preceding and following. On the Goose Island grounds there is an indication of dominance by the 1939 and 1940 year classes in both 1945 and 1946. The decrease in the relative proportions of small fish between these two years can be attributed to the poor represen• tation of the 1941 and 1942 year classes. Although further sampling is necessary before a definite statement can be made, there is an indication that 1941 and 1942 were poor brood years in this region. Sampling from the west coast of Vancouver Island during 1945 and 1946 has shown a change in dominance from the 1940 to the 1942 year class. It is difficult to say at present whether this is due to the intensity of the fishery or to the advent of a new year class. 56

VIII. SUMMARY AND CONCLUSIONS

The analysis of the length and age composition of catches of lemon soles landed at the principal British Columbia ports during 194-5 and 1946 has revealed interesting, features which

are indicative of some of the conditions prevailing in the fishery.

In general the older fisheries and those closest to large

Canadian and American market centers show the lowest age dis•

tribution in the populations. In the Strait of Georgia where the fishery has been in progress for a^.good many years, soles of four or five years of age predominate in the catches. On the west coast of Vancouver Island where a very intensive fishery has been carried on for no more than six years the age distribution is similar to that in the Gulf of Georgia. The comparatively recent fisheries of Queen Charlotte Sould and "2"

Hecate Strait, however, show a predominance of large fish averaging six or seven years of age.

Striking differences in the total annual mortality rates are also evident. Considering female fish only, the mortality rate is approximately 60% in the Gulf of Georgia, 67% on the west coast of Vancouver Island, 52% in Queen Charlotte Sound and 30% in Northern Hecate Strait. . In general the mortality rate of male fish is somewhat higher than that of females, being 62% in the Gulf of Georgia, 50% in Queen Charlotte Sound, and 39% in Hecate Strait. Results from the west coast are inconclusive because of inadequate sampling. The relative recency of the Northern Hecate Strait fishery has raised the suggestion that the total annual mortality rates

30% in the female and 39% in the male, calculated as they are

from the older age groups, present a rough estimation of the natural mortality rate. '

In the Hecate Strait samples where the older age groups are well represented it has been found that there is a sharp

increase in the mortality rate beyond nine years of«ge in the male, and beyond ten or eleven years in the female. This incr

increase has been attributed to an increase in the death rate due to natural causes, but there is the possibility that it is the result of a greater catchability of older fish.

In all areas of the coast the female lemon sole has been found to grow at a considerably greater rate than the male.

Between four and eight years of age the growth in the female averages 11 mm. per year more than in the male.

Comparisons of the growth rates in various areas show slight differences. With respect to female fish the average rate between four and eight years of age is highest in the

Strait of Georgia, being approximately 23 mm. per year. In

Northern Hecate Strait the rate during the same period is 21 mm per year. The lowest rate of growth, 19 mm. per year takes place on the west coast, in Queen Charlotte Sound and in the middle of Hecate Strait. In the male fish the growth rate appears to be greatest in Northern Hecate Strait, but dif• ferences in the various regions are not as distinct as in the case of the females. - 58 -

A study of the changes in rates of growth in female fish shows a tendency toward a sharper drop in the rate between five and six years of age in northern Hecate Strait than in the other regions.

Through beach seizing operations some information has been obtained on the growth of the lemon sole during its first year of life. The growth rate in Departu«?«Bay during the

summer of 194-6 was approximately 23 mm. per month. By late

August the average length was about 107 nun.

Information collected on the maturity of the female lemon sole in the Strait of Georgia has shown that 50% of the fish are mature at a length of 295 mm.

Studies of the fecundity of female'fish from the Strait of Georgia show that production of eggs rises rapidly from

280,000 in fish of 290 mm. in length, to 2,100,000 in fish of

430 mm.

This information on maturity and fecundity, if correct for all regions of the coast would indicate that the reproduc• tive potential of Hecate Strait and Queen Charlotte Sound populations is very much greater than in the populations in the

Southern part of the coast. That is to say, in the latter region where the average size of female fish is 355 mm. the average production of eggs per fish is 650,000, while in the northern region where the average size is 390 mm. the average production is possibly as high as 1,100,000 eggs.

The fact that lemon sole populations are subject to fluctuations in the strength of year classes has been shown in the study of the Hecate Strait fishery. The 1939 year class has predominated in the catches during 1944, 1945 and 1946.

In the latter year another strong year class, that of 1942, made its appearance. The relative lack of success in the brood years of 1940 and 1941 was the factor responsible for the absence of small fish in the catches during 1944 and 1945* - 60 -

IX. ACKNOWLEDGMENTS .

The author wishes to express his sincere appreciation and thanks to Dr. R. E. Foerster, director of the Pacific

Biological Station, and to Dr. J. L. Hart, in charge of the otter trawl investigation, for granting the use of facilities and materials necessary for this work.

The author is indebted to Dr. W. A. Clemens and Dr.

W. S. Hoar of the Department of Zoology for their helpful suggestions and criticisms.

Grateful appreciation is extended to fellow field workers, W. E. Barraclough, J*. I. Manzer and F. H. C. Taylor for their cooperation in the collection of commercial catch data, for their assistance in the beach seining operations, and for information and advice supplied with regard to aspects of the trawl investigation unfamiliar to the author. - 61 -

X. REFERENCES

Baranov, F. I. 1918. On the question of the biological basis of fisheries. U.S.S.R. Bull. Dept. Fish, and Scientific-Industrial Invest. 1/1/ 1918.

Budd/ P. L. 1940. The development of the eggs and early. larvae of six California fishes. Calif.„ Div. Fish and game. Fish Bull. 56, 1940.

Clemens, W. A. and G. V. Wilby. 1946.' Fishes of the Pacific coast of Canada, Fish. Res. Bd. Can. Bull. 68, 1946.

Graham, M. 1929. Studies.of age determination in: fish/ Part II. A survey;of the literature. Min. Agric. &,Fish.; Fishery Investigations. Series U, 11/ 3^ 1928.

Hickling/ C. F.; 1933. The natural history of the hake. Part IV. „ Age determination and rate of growth.; Min. Agric. & Fish."1 Fishery Investigations. Series II,' 13? 2,' 1933.'

Jordan,' D. S. and B. W. F^ermann. 1898. Fishes of North and Middle America.' Washington^ Govt. Print Off.

Ketchen/ K.' S. 1945a.1 Age determination and rate of growth of the lemon sole in British Columbia;waters. Essay manuscript,- Deptj? of Zoo!.' Univ. Brit.f Col.^ 1945.

1945b. Preliminary report on age and growth of lemon soles from British Columbia fishing grounds.. Fish. Res. Bd. Can. Prog.' Rep. Pac./ 63/ 1945.

Norman, J. R. 1934. A systematic monograph of the flatfishes (Heterosomata). Brit. Mus. Nat. Hist., 1, 1934.

Raitt/ D. S. 1936. Stock replenishment and fishing intensity in the haddock of.the North Sea. Jour.; Cons.,' Cons.1' Perm. Internat. Explor. mer. 11, 1936.

Ricker, W. E. 1942, The rate of growth of blue gill sunfish in lakes of northern Indiana. Invest, of Indiana Lakes and Streams, _2/ 1942. - 62 -

1944. Further notes on fishing mortality and effort. Copeia, 1944/ 1.

1945. A method of estimating minimum size limits for obtaining maximum yield. Copeia,' 1945, 2.

Sette, 0. E. 1943. Biology of the Atlantic mackerel of North America. Part I. Early life history. U. S. Dept. Int. Fish and wildlife service. Fish Bull. 38, 1943.

Smith, R. T. 1936. Report on the Puget.Sound otter.trawl. investigations. Wash. State Dept. Fish. Biol. Rep.,! 36B,1 1936.

Thompson/H. 1929. Haddock biology_(North Sea). Rapp. et. Proces-verb.Cons,' Perm. Internat. Explor. Mer, 54,1 1929.

Thompson, W. F. and W. C. Herrington. 1930. Life history of the,Pacific halibut. (1) Marking experiments. Rep. of Internat. Fish. Comm., 1930

Van Oosten, J. 1941. The age and growth of freshwater fishes. A Symposium of.Hydrobiology. Univ. Wise. Press,' Madison,5 Wise.

Walford,' L. A. 1938. The effect of currents on the distrib• ution and survival of eggs and larvae of the. haddock on Georges Bank. U.S. Dept. of Int. Fish and wildlife service. Fish. Bull. 29, 1938.

Wallace, W. 1904. Report on the' age and growth rate of the plaice in the southern North Sea as deter• mined by the investigation of otoliths. Jour. Mar. Biol. Assoc. Internat,'.Invest. Second Rept. Southern Area,' 1904-5.

1925. Mortality in plaice. Nature, 115. no. 2888 1925. - 63 -

XI. APPENDIX Table 1

Length Frequency Distribution of Young Lemon Soles Caught in Departure Bay, between may and August 1946.

Length May June July Aug. (mm.) 20 1 - 25 4 30 11. 1 35 21 5 40 11 4 45 11 14 1 50 15 5 .55 5 14 5 60 1 13 9 65 1 17 16 70 10 13 1 75 9 11 1 80 15 14 4 85 7 9 3 90 4 4 12 95 7 9 100 7 10 105 1 8 9 110 1 3 10 115 12 120 1 "8 125 5 130 4 135 • 3 140 145 3 Table 2

Length Frequency Distributions of Fish Captured in the Vicinity of the Fraser River during 1945 and 1946. (See fig. 8)

1945 1945 1945-46 1946 * 1946 Length May-July .-Oct. Dec. -Apr. Jan. -Mar. May-Aug. (mm.) M F M F M F M F M F 240 1 3 250 6 6 4 4 260 27 12 32 22 270 53 33 89 62 7 15 1 280 81 76 127 89 10 42 19 1 3 2 290 54 91 144 124 15 '54 47 9 12 7 300 65 126 76 125 29 61 45 19 9 45 310 44 121 49 151 20 68 49 20 12 36 320 23 95 20 117 18 53 25 23 13 30 330 14 91 13 88 12 49 15 17 8 44 340 4 63 4 56 2 44 7 23 4 44 350 1 50 1 43 3 45 5 27 2 44 360 1 45 3 25 33 3 24 31 370 20 20 20 25 21 380 14 15 13 19 18 390 14 10 13 21 14 400 8 5 13 16 8 410 13 7 3 8 5 420 2 3 1 8 1 430 2 5 7 4 440 1 1 2 2 1 450 1 2 3 1 460 2 1 470 1 480 1 490 500 1 510 1

* Point Atkinson. Table 3

Length Frequency Distributions of Fish Captured in the Gulf Islands and in Baynes Sound During 1945 and 1946. (See Fig. 10 and 13)

qr ulf Islands Elayne s Sound 1945 1946 1946 1945 1946 * 1946 Length Sep. -Dec. Jan.--Feb. Jun. -Sep. Aug .-Dec. Jan. -Feb. Fjsb. (mm.) M" F M F M F M F M F M F 260 1 1 2 4 1 270 1 3 1 22 14 1 280 11 4 7 2 29 36 2 13 290 12 4 3 7 64 39 2 5 24 1 300 25 13 19 16 2 2 77 95 11 ' 11 30 2 310 41 37 19 12 14 4 93 129 15 26 11 5 320 36 36 11 19 23 13 90 165 12 24 15 4 330 37 56 7 33 35 13 53 166 14 31 14 5 340 17 60 4 33 14 17 32 145 5 31 7 2 350 8 59 32 10 34 ' 21 138 3 49 4 3 360 8 72 43 3 35 8 142 1 39 2 7' 370 7 84 1 39 4 29 6 113 2 35 1 4 380 3 81 26 2 29 103 25 10 390 2 59 21 17 1 67 29 11 400 53 20 24 55 21 1 13 410 47 7 19 50 24 11 420 32 11 22 28 14 7 430 19 3 11 18 16 4 440 23 4 8 7 9 6 450 14 3 7 16 15 2 460 22 2 2 9 5 1 470 4 3 5 1 480 5 2 3 2 490 1 4 1 500 1

^ Cape Lazo. Table 4

Length Frequency Distributions of Fish Captured in the Waters off the West Coast of Vancouver Island during 1945 and 1946. (Fig.* 16)

Port San Juan to Tofino Esteban 1i o Kyuquot 1945 1945 1946 1946 1945 1946 Length Ap:p.-Jul y Aug. -Nov. May- July Aug.-Sep. May-Aug. May-Aug. (mm.) M F M F M F M F M F" M F 250 1 1 260 1 3 ' 1 1 1 270 1 1 2 1 1 280 4 8 8 1 7 1 290 8 7 15 5 18 2 6 1 2 300 6 17 16 29 7 54 5 14 3 8 310 3 19 6 35 4 117 2 23 3 9 15 320 11 15 16 55 7 126 7 31 2 12 1 19 330 10 39 28 42 4 124 5 52 1 20 2 25 340 5 29 9 44 5 101 6 65 1 20 1 39 350 8 52 11 70 4 82 2 55 2 31 46 360 5 53 6 62 1 • 86 3 57 1 27 2 46 370 1 53 5 65 1 81 1 59 38 61 380 60 2 77 2 57 54 42 35 390 57 66 1 47 50 39 23 400 57 65 27 27 41 23 410 36 61 28 33 30 8 420 32 30 28 24 30 14 430 25 26 13 20 10 7 440 17 15 8 11 8 450 10 6 8 4 2 460 6 4 3 6 470 2 3 6 480 1 1 1 490 1 3 500 1 Table 5

Length Frequency Distributions of fish Captured in Queen Charlotte Sound and Hecate Strait During 1945 and 1946. (Fig.'s 19 and 22)

Goose Island Banks Is. Butterworth Rocks 1945 1946 1946 1945 1946 1946 1946 Length May-June May-June April April May-June August (mm.) M F M F- M DM F M F M F M F 250 3 1 260 7 7 3 1 o 1 270 14 8 1 1 4 5 4 280 4 1 26 10 1 1 3 7 8 1 290 3 1 3 1 29 25 3 4 8 10 15 11 300 2 4 7 4 53 42 11 5 26 30 20 15 1 310 8 13 12 6 37 41 11 6 31 31 23 17 2 320 7 22 25 18 26 48 16 10 45 35 35 24 1 330 3 16 22 27 18 35 13 7 41 25 29 18 4 340 .13 25 33 15 43 34 11 34 27 38 19 8 350 24 4 20 56 10 24 19 15 34 29 46 34 11 360 19 1 13 68 7 22 22 9 30 27 34 38 18 10 370 25 8 60 1 15 22 25 32 25 23 34 18 11 380 19 1 59 4 9 21 20 16 35 27 35 21 10 390 21 61 1 10 13 17 11 21 13 38 14 16 400 15 84 5 12 31 11 31 12 30 6 15 410 11 66 6 8 12 4 24 6 "30 5 28 420 4 67 1 2 16 1 12 1 30 2 430 3 37 1 8 10 3 14 1 440 2 20 4 10 7 16 1 450 4 19 2 4 13 15 460 8 1 10 11 9 470 5 1 5 8 480 4 2 1 1 3 490 1 4 500 2 1 1 510 2

9 Table 6

'Length Frequency Distributions of Fish captured in Hecate Strait During the years 1945 and 1946.

Triple Island Two Peaks Rose Spit Length 1945 1946 1945 1946 1945 1946 (mm.) M F M F M F M F M F M F 250 2 2 1 4 • 260 1 2 8 2 3 1 270 4 5 7 3 3 4 280 7 6 6 5 8 9 . 290 2 1 7 6 17 9 9 18 300 3 4 12 11 24 20 2 31 27 310 3 5 15 10 1 22 13 3 39 36 320 3 9 23 18 2 17 24 2 55 77 330 5 8 37 28 3 17 23 8 4 52 69 340 2 16 35 25 5 15 24 8 3 46 71 350 12 41 47 11 1 11 24 15 13 47 76 360 2 14 50 37 11 7 5 18 16 14 43 52 370 2 16 32 38 17 13 2 17 20 19 43 67 380 14 20 29 27 9 4 22 12 34 22 87 390 16 16 23 18 19 10 11 47 17 78 400 19 7 30 :;8 38 1 8 7 51 13' 94 410 18 2 22 5 35 1 3 4 59 4 89 420 16 27 2 43 2 2 51 2 88 430 8 30 40 45 2 73 440 7 19 24 33 68 450 3 23 45 34 61 460 3 25 34 15 35 470 1 10 21 11 26 480 9 15 14 16 490 5 5 4 9 500 4 4 3 7 510 1 520 p 530 1 540 1 Table 7

Percentage Age Composition of Fish Caught in the Vicinity of. the Fraser River During 1945 and 1946. (Fig. 9)

May-Oct. 1944 194? 1942 1941 1940 1939 1938 1937 I936 1^35 1945 MALE No. 1 34 52 27 5 1 .8 28.5 43.7 22.6 4.1 FEMALE 3 58 162 87 26 7 No. .9 16.9 47.2 25.3 7.6 2.0 Dec.-Apr. i :1945-46 MALE No. 1 15 39 54 24 6 1 . .7 10.8 28.1 38.8 17.3 4.3 FEMALE 1 122 201 106 36 19 7 3 2 No. .2 24.5 40.4 21.3 7.2 3.8 1.4 .6 .4 Jan.-Mar. i 1946 MALE NO. 2 13 68 67 42 17 3 % .9 6.1 32.7 31.1 19..8 8.0 1.4 FEMALE No. 13 61 89 80 24 8 3 1 4.7 21.9 31.9 28.7 8.6 2.9 1.1 .4 May-Aug. 7. 1946 MALE No. 1 4 19 26 9 "3 1 i 1.6 6.3 30.2 41.3 14.3 4.8 1.6 FEMALE No. 33 145 114 37 11 3 1 9.6 42.2 33.1 10.8 3.2 .9 .3 i Table 8

Percentage Age Composition of Fish Captured in the Vicinity of the Gulf^Islands During 1945 and 1946. (Fig. 11)

Aug.-Dec. 1944 194? 1942 1941 1940 1939 1938 1937 1936 1935 1945 MALE No. 6 17 13 9 7 2 2 10.6 30.6 23.2 16.1 12.5 3.6 3.6 % FEMALE 1 9 57 64 36 20 9 7 No. ' .5 4.4 28.1 31.5 17.7 9.9 4.4 3.4 Jan.-Feb. i 1946 MALE „ No. 6 22 25 It) 12 1 i 7.9 28.9 32.9 13.2 15.8 1.3 FEMALE No. 20 93 136 50 25 8 3 3 1 1 5.9 27.4 40.1 14.7 7.4 2.4 .9 .9 .3 Jun.-Sep. 1946 MALE No. 13 26 50 25 1 1 1 i 2.8 24.3 46.7 23.4 .9 .9 .9 FEMALE No. 14 74 115 56 18 7 7 1 % 4.8 25.3 39.3 19.2 6.2 2.4 2.4 .3 Table 9

Percentage Age Composition of Fish Captured in the Vicinity of Baynes Sound During 1945 and 1946. (Fig. 14) Year Class Aug.-Dec. 1944 1943 1942 • 1941 1940 1939 1938 1937 1936 1935 1945 MALE No. 2 •4l 86 72 22 17 1 1 % •8 16.9 33.5 29.8 9.1 7.0 •4 .4 FEMALE ... No. 13 163 22$ 116 44 33 8 7 3 % 2,0 25.4 39.7 18.1 6.9 5.1 1.2 1.1 .5 Jan.-Feb. 1946 MALE No. 1 13 22 18 4 3 1 1.6 21.0 35.5 29.0 6.5 4.8 1.6 FEMALE — No. 8 130 126 112 22 8 5 1 * 1.9 31.6 30.6 27.2 5.3 1.9 1.2 .2 February 1946 MALE (Cape No. 4 32 46 23 10 4 3 Lazo) 3.3 26.2 37.7 18.9 8.2 3.3 2.5 FEMALE No. 2 16 26 35 12 6 3 1 2.0 13.8 25.7 34.7 11.9 5.9 3.0 1.0 Table 10

Percentage Age Composition of Fish Captured Off the West Coast of Vancouver Island, Between Port San Juan and Tofino,. During the Summers of 1945 and 1946. (See fig. 17)

Year Class Apr.-July I944 1943 1942 1941 1940 1939 1938 1937 1936 1935 1945 MALE No. 2 11 5 5 2 8.0 44.0 20.0 20.0 8.0 % FEMALE 3 45 86 101 51 22 6 2 1 No. .9 14.2 27.1 31.9 16.1 6.9 1.9 .6 .3 Aug.-Nov. i 1945 MALE No. 4 14 5 6 - 1 % 13.3 46.7 16.7 20.0 3.3 FEMALE 3 27 28 42 17 15 6 1 No. 2.2 19.4 20.1 30.2 12.2 10.8 4.3 .7 May-July 1 1946 MALE No. 1 5 15 11 62 f. 2.5 12.5 37.5 27.5 15.0 5.0 FEMALE No. 1 360 309 161 92 46 20 2 4 1 .1 36.1 31.0 16.2 9.2 4.6 2.0 .2 .4 .1 Aug.-Sep. i 1946 MALE No. 7 10 4 6 3 6 % 19.4 27.8 11.1 16.7 8.3 16.7 FEMALE No. 8 150 189 109 91 31 17 6 1 f. 1.3 24.9 31.4 18.1 15.1 5.1 2.8 1.0 .2 o

Table 11 Percentage Age Composition of Fish Caught between Esteban Point end Kyuquot Sound on the West Coast of Vancouver Island, and in Queen Charlotte Sound During 1945 and 1946. (Fig. 18 and 20)

o Year Class • - - Summer 1944 1945 1942 1941 1940 1939 1938 1937 1936 1935 1934' ESTEBAN 1945 to MALENo. - - 2 1 - - - KYUQUOT '* FEMALE 0 No. 1 7 42 67 38 19 8 1 i .6 3.8 23.0 36.6 20.8 10.4 4.4 .6 Summer 1946 ' MALE No. 1 - 1 3 1 h FEMALE No. 64 158 80 34 17 2 - % 18.0 44.5 22.5 9.6 4.8 .6 0

Summer 1945 MALE No. 3 8 4 6 1 1 GOOSE % 13.0 34.8 17.4 26.1 4.3 4.3 ISLAND FEMALE No. 9 36 49 43 23 9 2 1 i 5.2 20.9 28.5 25.0 13.4 5.2 1.2 .6 Summer 1946 MALE No. 1 2 11 28 35 36 18 '• 7 5 % .7 1.4 7.8 19.9 24.8 25.5 12.8 5.0 2.1 FEMALE No. •1 13 61. 123 178 186 81. 39 21 8 2 i .1 1.8 • 8.6 17.3 25.0 26.I 11.4 5.5 2.9 1.1 .3 3 , Table 12 Percentage Age Composition of Fish Caught in the Vicinity of Banks Island and Triple Island in Northern Hecate Strait During 1945 and 1946. (See Fig. 20 and 25)

Year Class .... Summer 1944 1943 1942 1941 1940 1939 1938 1937 1936 1935 1934 1946 MALE BANKS NO. 25 72 51 41 44 13 7 1 ISLAND % 9.8 28.3 20.1 16.1 17.3 5.1 2.8 .4 FEMALE No. 1 56 142 70 36 31 11 8 8 2 % .3 15.3 38.9 19.2 9.9 8.5 3.0 2.2 2.2 .5

Sept. 1945 MALE No. 1 7 7 6 1 1 TRIPLE % ISLAND FEMALE No. 1 26 25 35 53 26 15 8 1 . i .5 13.7 13.2 -18.4 27.9 13.7 7.9 4.2 .5 July 1946 MALE No. 3 23 61 52 56 61 37 12 5 i 1.0 7.5 19.7 16.8 18.1 19.7 11.9 3.9 1.6 FEMALE 7 38 114 68 66 73 55 38- 28 2 > 1.4 7.6 22.8 13.6 13.2 14.6 11.0 7.6 5.6 2.0 .8 Table 13 Percentage Age Composition of Fish Caught in the Vicinity of Butterworth Rocks In Northern Hecate Strait During 1945 and 1946. (Fig. 23)

Year Class April 1944 1943 1942 1941 1940 1939 1938 1937 1936 1935 1934 1933 1945 MALE No. 1 9 13 53 46 48 25 14 1 i .5 4.3 6.2 25.2 21.9 22.9 11.9 6.7 .5 FEMALE No. 1 11 33 38 59 40 18 15 11 % .4 4.9 14.6 16.8 26.1 17.7 7.9 6.6 4.9 April 1946 MALE No. 5 25 53 73 79 56 30 8- 2 1.5 7.6 16.0 22.1 23.9 16.9 9.1 2.4 .6 FEMALE ••- No. 6 26 111 83 54 59 46 15 22 2 t 1.4 6.1 26.2.19.6 12.7 13.9 10.8 3.5 3.2 ,8 May-June MALE - - • No. 4 16 27 47 66 84 46 36 12 1 1 % 1.2 4.7 7.9 13.8 19.5 24.7 13.5 10.6 3.5 .3 .3 FEMALE No. 7 19 80 55 50 100 61 45 26 12 2 1.5 4.2 17.5 12.0 10.9 21.9 13.3 9.8 5.7 2.7 .4 August MALE - No. 2 5 13 17 21, 29 15 9 4 % 1.7 4.3 11.3 14.8 18.3 25.2 13.0 7.8 3.5 FEMALE No. 2 12 26 43 54 63 51 46 33 11 7 1 %' .6 3.4 7.4 12.3 15.5 18.1 14.6 13.2 9.5 3.2 2.0 .3 Table 14

Percentage Age Composition of Fish Caught in the Vicinity of Two Peaks and Rose Spit in Northern Hecate Strait During 1945 and 1946. (Fig. 25 and 26)

Year Class ... . June L944 1943 1942 1941 1940 1939 1938 1937 1936 1935 1934 1933 1945 MALE No 9 4 12 20 23 30 15 4 TWO % 3.7 11.1 18.5 21.3 27.8 13.9 3.7 PEAKS FEMALE No 1 1 11 22 71 78 63 63 39 11 .3 3.1 6.1 19.8 21.7 17.5 17.5 10.9 3.1 Jan. t 1946 MALE Cl No . 6 4 30 10 38 53 21 9 2 1 % 3.4 2.3 17.2 5.7 21.8 30.5 12.1 5,2 1.1 .6 FEMALE No 3 11 52 38 28 45 26 15 9 5 •1 t 1.3 4.7 22.3 16.3 12.0 19.3 • 11.2 6.4 3.9 2.1 .4 June 1945 MALE No 1 6 14 27 18 25 - 11 4 - 2 25.0 10.2 — SPIT % .9 5.6 13.0 16.7 23.1 3.7 1.9 -FEMALE No » 4 13 40 120 89 82 58 34 13 2 .9 2.9 8.8 26.4 19.6 18.1 12.7 7.5 2.9 .4 June i 1946 MALE * No • 6 46 76 66 84 77 50 28 7 1 1 % 1.4 10.4 17.2 14.9 19.0 17.4 11.3 6.3 1.6 .2 .2 FEMALE • - . -•• No .4 127 238 163 164 202 158 93 59 31- 8 % .3 10.2 19.1 13.1 13.2 16.2 12.7 7.6 4.7 2.5 .6 Table 15

Instantaneous Growth Rates During Three Time- Intervals as Calculated from the 1946 Data. (See Fig. 29)

Time-Intervals (Years) Locality 1Y-VI V--VII VI-VIII M F M F M F Fraser River .039 .073 .044 .062 .006 .052

Gulf Islands .030 ;069 .026 .061 .036 .045

Baynes Sound .035 .080 .036 .066 .026 .036

San Juan to Tofino .043 .071 .031 .052 .037 .032

Esteban to Kyuquot - .058 - .051 mm .032

Goose Island .029 -.057 .019 .040 .029 .035

Banks Island .033 .044 .022 .048 .035 .056

Rose Spit .049 .066 .030 .045 .026 .043

Butterworth Rocks .037 .086 .034 .061 .040 .036

Triple Island .050 .066 .033 .048 .035 .051

Two Peaks .060 .070 .023 .053 .024 .030 Table 16

Percentage Age Composition of Female Fish Captured in the Vicinity of Butterworth Rocks During 1944, 1945 and 1946. (See Fig. 53)

1944 1944 1943 1942 1941 1940 1939 1938 1937 1936 1935 1934 1933

FEMALE No. 5 9 11 40 28 21 12 7 i 3.7 6.7 8.2 30.0 21.0 15.7 9.0 5.2 1945 FEMALE No. 1 11 33 38 59 40 18 15 11 i .4 4.9 14.6 16.8 26.1 17.7 7.9 6.6 4.9 1946 FEMALE No. 15 57 217 171 158 222 158 106 81 25 9 1 % 1.2 4.7 17.8 14.0 12.9 18.2 12.9 8.6 6.6 2.0 .7 .08