Distribution, Age and Growth of Eastern Pacific Albacore(Thunnus alalun gcl Grnelin)'

Bx J. M. Penrr.o2Pacific Biological Statiory Nanaimo, B.C.

ABSTRACTSeasonal and regional variations in the abundance of albacore during the 1949, 1950

and 1951 British Columbia ffshing seasons suggest that exploitable stocks occurred in in-

creasingly northerly areas during July and August and in more southerly areas during lat_e

August, September and early October. Catches were composed of four lengt-h-groups -withurr"iug" lengths of 54.3, 62.9, 7I.7 and 81.9 centimetres. These groups were sometimes fairly

discrete, but usually overlapped broadly, so that it was necessary to plot frequency dis-

tributions on probability paper in order to choose the best points of separation.Concentric marks on the centra of vertebrae were used as indicators o{ the age of the

ffsh. The relationship of body length to vertebral radius is rectilinear. There is good agreement

between the estimated average length and standard deviation in length of the ffsh when

grouped by length and when grouped by vertebral ring numbr, The ages indicated for the

iorr. gro.rpr are III, IV, V and VI; however the ffrst vertebral ring is somewhat less clear than

the others and if it were discounted these ages would be reduced by one year. The ffsh whosevertebrae were examined had almost completed a year's growth.

The length-weight relationship is expressed by the formula, Iog \Az - -4'912 + 3,13

log L, where W is the weight in kilograms and L is the fork length in centimetres"

INTRODUCTION

Tnu seasonal course of development of the ffshery suggests that the albacore(Tlwnnus alalunga) may migrate northward along the Pacific coast of North

America during late spring and summer. The difficulties of capturing and mark-ing this species in sufficient numbers have prevented the use of tagging to study

migration or growth.Information on related species has been obtained by methods other than

marking. Sella (1930) established the distribution of the blueffn tuna (Thunnus

thynnus) in the Mediterranean and Eastern Atlantic waters by recording com-mercial hook recoveries. In the same paper he presents the growth rate of the

species based on the examination of vertebrae. Aikar.va and Kat6 (1938) studiedthe growth of albacore of the Western Paciffc by similar methods.

This paper presents the results of an analysis of length frequency dis-tributions of the B.C. albacore catch for 1949-51, and of aqe determinationsmade from vertebrae taken in 1950.

LENGTH COMPOSITIONMarnnrar- UsBo

Data on casual samples of the British Columbia albacore catch have beencollected since 1941 by representatives of the Fisheries Research Board of

lReceived for publication April L2, 7954; as revised, July 19, 1954.2Present address: 104 Union Blvd., Kitchener, Ont.

J. Frsn. Rrs. Bo. Cewane, l2(l), 1955.Printed in Canada.

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rl t)

Canada. Recently these have included length measurements, number and weightof fish caught, location and time of capture, number of hours spent ffshing,number of lines trolled, and the names of the vessel and captain. Data collectedprior to 1949 have not been used in this analysis because measuring methodswere not standardized. The measurements used here were from the tip of thesnout to the fork of the tail, taken as the fish lay on a flat measuring board. Thework has been based on samples which together comprise about one-tenth of thetotal annual catch, the number of measurements taken being as follows: 38,418in 1949; 29,474 in 1950; and 10,524 in 1951. Most individual samples represent thetotal catch of a boat and vary in size from 20 to 1,341 fish. Those of less than 50fish make up 5.5% of the total number of samples. Port contact representativesmade the measurements and compiled trip reports recording the fishing successon various grounds.

Differences between samples representing the same area and period ofcapture did not appear to be appreciable for samples of more than fifty fish(Table I ) .

Supplementary to the length data are the voluntary records submitted byeach vessel captain in the form of log-book reports, which provide for recordso{ date, time, position, water temperature, wind velocity and direction, catch,and general information. These records duplicate a portion of those collectedby the port representatives but also provide more detailed information that hasproved valuable in estimating the availability of albacore with relation to timeand location. For the years under consideration the percentage of the total catchreported in the tuna log books and the number oJ vessels- reporting were asfollows:

Year1949r9501951

These data were also grouped according to areas of capture and time the fishwere delivered.

ANanysrs or Dare

LENGTH FREeuENCTES. The length data, when distributed according to areaand time, formed polymodal frequency distributions which were divlded intonormal frequency distributions by the method described by Harding (1949),using probability graph paper developed by Hazen (1913). The application ofthis graphical method was based on the assumption that the poiymodal fre-quency distributions were composed of natural length-groups and that thetrengths contained within each group were distributed approximately normallyabout the group mean.

Examples of the plots on probability paper are given in Figure 1. Theordinates of the original frequency distribution are expressed as cumulative per-centages and plotted at the upper limit of the class interval (solid circles in thediagram), giving a series of two or more straight lines joined by curved con-

Percentage of catch No. of aessels62.243.345.8

135107I6

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.I'esln I. Example of the distribution of samples for one area and time period: Columbia l{iver to Destruction Island-4th quarter July' 1950.

Length offish Frequency

1

i+

. ;

120I4T 7q 2

r0.7

2

J

4

a

2

I1

i .2 . .

it

4J

1

82I30t t r

D+bv3830221 1

ot 3

o

i11

i22.)

i2o

26,1JA D

O J/ a

4 lq A

q /

2321I

1512

3I

112122

267

741924o.)

29I t l

7 263

o

42

iI

2

r,i)201 a

2816655427

2

t1 a

294I4'48402525, 1

I10l21 1

D

I11

i122

3

1329314T26261 , 7

121 88

o

2

2

t

1

DA J

2328261510202446na

1049396804632I412l81013

o

1

. .224I323

10262020247

L217I2

21

.?

1

I 22 ,

4 46 5J D< 9

8 t i7 r 0

71 L420 3231 50. l O l U

36 6441 6933 5428 4820 4022 252 0 1 1I 108 1 16 2/ o2 5I D

I

2 . . 3q t

2 2 81 1 1

1 13 . . 64 7 1 08 1 6 1 95 2 4 2 0

11 45 4616 43 4l18 49 4815 42 34

4 3 2 2 013 17 17I 1 1 84 I I 97 7 0 82 3 53 6 31 6 42 5 3

l 42 1 1

I1

t10q 2

47D I

464527242315191 I

o472I

em.ooi t l

58DY6061626364656ti676869707 l72

74l i t

7677l 6

79808182838485866 /

121328

l3,n1610

+1

22J

,

88

l i )

I t

l 8L48

1 166416I22

1

13036r404221rlDi)bJD550393135 335 324410Total131101

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38

to 20 30 40 50 60 70. 80 90

Frcunr t. Examples of the probability-paper *;:tJTtr,,ing normal curves to observedfrgquencl distributions. (A) DestrucUon Island to Cape Flatiery, 3rd quarter of August,1949. (B) Destruction Island to Cape Flattery, 4th quarter of August, 1949. (C) CapeMendocino to Cape Blanco, 2nd quarter of October, lg4g.

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39

necting sections which represent the region of signiftcant overlapping of the

compo?ent distributions. 'ihe points of inflection on these connecting sections

deteimine the proportion of tire distribution that is assigned to each normal

curve. In Figurl Ib there are two well-deffned glolps, the smallest consisting

of the shorteit fish and comprising 36% of the totil; there is some evidence of a

third group at the other eid of -the

curve, but as the point of inflection lies

beyonX th; gg% point this group seemed too inconsiderable to be separated from

the others.When the component groups were separated as above, each was brought up

to terms of L0070 fr"q,r".r"i, e"iress"d in terms of cumulative percentages, and

plotted (open circles^ in Figure t). The straight lin-es joining these points de-

termine normal curves such'as are shown in Figure 2; the 507o point, (in Figure

1) gives the mean length, and half the difference betrveen the lengths atL5.87%

^n{ B4.IS7" gives the"standard deviation in length. Ordinates of the normal

curves, for cionvenient /-values (i.e., distances from the mean, divided by,the

standard deviation), were obtained. from Snedecor's Table 8'5' To put these

into terms of the original percentage scale, they were_ multiplied by n/s, where

ru is the percentage of the'total freiqoency represented by the particular nolmal

curve and s its standard deviation.It is appreciated that an albacore population would be unlikely to consrst of

completelj irormal length-group., "rr"n

if-"ach age were- sampled in a completely

representatirr" -urn"r] In"addition, the smallest and largest gtoYp-s are likely

to diverge from normality because of incomplete representation of their smaller

and larg"er members, respectively. However this method of breaking down the

multim;dal frequency distributions seems justifiable as a_ simple, interpretation

of the data avalilabte. lt ttr" soodness of fit of the combined theoretical dis-

55 60 65 70 75 80 85

L E N G T H l N c m .

Frcunr 2. Example of the effciency of fftting normal curves by the probability-PaPer method.

The histogram ripresents the obseived frequencies, and the fftted normal curves are obtained

from Figure fn. the dotted line represents the sum of the two normal curves.

de

Irro

Udl=z

TOTAL NO OF FISH= 447

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40

tributions to a whole sample is tested by the 12 test, there are small divergenceswhich appear significant when the very large samples of several thousand fishare examined, but there are no deviations which can be detected in samples ofless than 1,000 fish. one such test is shown in Table II and Figure 2. The agree-

Teellr II. I'est of goodness of lit of normal curves to the frequcncy distribution shou'n in Figure 2,based on 447 measurements. Cun'es B and C are added and extreme values grouped togive 20 class intervals. One degree of freedom is subtracted for each mean, for each standarddeviation, for all but one of the comporent populations, and for the total; this leaves14 degrees of freedom. Probability of larger 12 is P, u,here 0.95 < p > 0.90.

Calculated frequencyfrom lormal cLtrves

Length- Actualgroups frequency

Combinedexpecreo

frequency

(Difference)2

Difference Expected

%%

o. oo0 . 0 10 . 0 30 0 90 . 2 30 5 11 0 51 9 33 . 1 94 . 7 56 3 67 . 6 6L298 . 0 77 . 0 7

3 9,12 . 5 7L . 4 40 7 40 . 3 40 . 1 40 . 0 50 0 20 . 0 10 . 0 0

6 4 . 0 0

(j/

/oc1n.

DJ

4

678o

60I2a

678I

7012

4D

o

78o

8012o

4Totals

0 . 6 70 . 6 7r . 7 22 0 r, L t

4 . 7 05 1 56 . 2 66 . 7 r6 2 67 . 6 19 1 79 7 78 7 37 . 6 76 9 45 . 5 94, 03r . 7 9I . 3 40 . 6 70 6 70 . 2 20 . 2 20 . 0 0n n0 . 2 2

9 9 . 9 9

"/o

0 0 00 . 0 10 . 0 30 0 70 . 1 70 3 8U . / 51 . 3 3q 1 q

3 0 43 9 21t . oJ

4 7 04 . 3 93 6 72 7 61 8 71 . 1 40 . 6 20 3 01 , 1 30 . 0 50 . 0 20 . 0 1ool

1 . 3 42 t 5D , I O

4 7 55 . 0 45 . 7 56 . 3 26 8 67 5 18 2 38 . 8 08 . 9 18 . 3 77 2 05 . 6 23 . 9 62 . 5 r\ . 1 1

1 . 3 0

0 . 0 7

0 2 20 . 1 40 . 8 9

-0 55- 0 . 1 1- 0 . 5 1- 0 . 3 9

0 . 6 0-0 10-0 94-0 37

0 . 1 80 . 7 6o . 2 60 . 0 3

- 0 . 0 70 . 7 20 1 0

0 9 2

0.0035

0 .03610 .00910.25310.07290.00240.04520 02410.05250 .00130. 10740 . 0 1 5 60 00360.06900.00940 .00020 .00120 .20650 0069

0 . 6 5 1 1

7 . 5 7 r r36 .01 100 .01

+ + l

x 2 : 1 . 5 7 1 1 Y - . ^ . : 7 . 0 2 3IUU

d.f. : 14

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4I

I'rcuru 3. Length frequency distribution of the 1949 British Columbia albacore catcb by

geographical a.Ia aod iime.'The histograms describe the length frequencies prior to analysis.

The normal frequency curves describe the length distributions of component size-groups_as

determined by the piobability graph method of analysing polymodal length frequency dis-

tributions.

ment of observed and expected values is somewhat better than would usually

be obtained by sampling from normally distributed age-groups.

The percentage length data for the three years considered, together_ with

the fitted normal iurves, are shown in Figures 3 to 5 and further details are

given in Tables III to V.

AVArLABrLrrv. The proportions of the (component) length-grouPs in the

Iength frequency distributions for each area and time are relative and conse-

quently do not indicate actual abundance on the grounds of any group of ffsh.

To supplement the length frequency information, estimates of availability ( catch

per unit efiort) were used. Several measures of availability were calculated but

only the number of "ffsh caught per boat-hour ffshed" proved applicable. "Fish

caught per lure,hour ffshed" was examined because the number of lures trolled

varied between vessels, but no appreciable increase in the catch correspondingto an increase in the number of lures was observed within the limits of the

numbers of lures actually used (6-12). "Fish caught per boat-hour ffshed" was

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1950 British

( c v )

Columbia

60 70 ao 60 ?o 30 90

by geographical area and time.Frcunn 4. Length frequency distribution of the

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43

Frcung 5. Length frequency d,istribution of the 1951 British Columbia albacore catch bygeographical area and time.

calculated for each area and time interval by dividing the total catch in numbers

of fish by the total number of hours spent fishing

In order to compare the availability of each length-group it was assumed

that there was no siie selection by troliin g Sear; this seemed leasonable under

the conditions of the fishery. The availability for each area and time interval was

divided in the ratio of the frequencies of its component length-groups.

SBasower- axo Rncroxan VamrerroNs

The length frequency data indicate that the exploited stocks of the Eastern

Pacific albaJore ure "o*pot"d

of four natural length-groups, hereafter referred

to as A, B, C and D, with average mean lengths of 54.3, 62.9,7L.7 and 81.9 centi-

metres, respectively. These arrerage mean lengths cover the three years (1949,

1950, 1951tbutthe yearly mean lengths are relatively close (Table I). Similarly

when the mean lengths for each area and time period are comPared, only minor

difierences are found among them (Fig. 3-S;.4

sThe greatest divergence occurs in the area from Cape Cook to Cape St' James during_llgfust and second quarter of September, 1949, where the mean lengths of group C (Table III)are smaller thanlxpected (T;ble VI), being 68.7 and 68.4, respectively, as compared_ withthe average value i.1. Comparison with adjbining areas shows that in the area immediatelyto the norih (north of Cape St. James) the mean for the second quarter of September is72.5,or greater than the 71.1 oi the total catch. While it is possible that the larger fish of this groupweit farther north and the smaller ones stayed south, these contrasts are more apt to beattributable to the large chance fluctuations which are almost sure to occur in one or twoplaces in any large body of data.

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lanrB III' The percentage composition, mean lertgth, stanciard deviation, ancl availability (fish per boat-hour lished) of component length-groups (A, B, Cand D) of the 1949 British Columbia albacore catch for selected geographical areas and quarter-molth time periods. iotal availability estimates byarea and time are included.

l .ength-groups

Totalavaila- Availa- Availa-Time Area bil i ty % Mean s.D. ;i l i t; % Mean s.D.

-^bii i t i o/o Mean S.I)

Avai la-bi l i tv

A v a i l aS . D . b i l i t y

I-ytos cm. cm. cm-Jul. Columbia R. to4 t h D e s t r u c t i o n L 2 . 8 4 1 b . 0 $ 2 . 7 5 t . 2 7 0 . 4 8 7 7 . S 2 0 . 5 0 77 . 80 | . 70

84 .05 3 .05

82 .90 7 .37

82. 80 2 .38

82 .20 2 .60

83 .87 2 .90

84 . 50 2 .77

Aug. Destruction I.l s t t o C . F l a t t e r y 5 . 0 7 2 5 . O 6 8 . 5 0 2 . O E I . 2 Z Z B . 4 2 1 . 0 0

C. Flattery toC . C o o k 6 . 7 7 S . 2 6 2 . 6 0 0 . 6 5 O . A b 8 Z . B Z O . S O

Aug. Destruction I.2 n d t o C " F l a t t e r y 6 . 6 0 1 0 . 0 t i 3 . 0 0 1 . 8 0 0 . 6 6 8 6 . 4 T l . . 4 O

C. Flattery toC . C o o k 5 . 4 2 1 1 . 0 6 3 . 0 0 2 . r 0 0 . 6 0 8 5 . i 1 7 O . Z O

Aug, Destruction I.3 rd to C. F la t te ry 4 .35 lZ .O 64 .30 2 .O2 O .24 80 . 5 Z1 . 65

C. Flattery toC . C o o k 3 . 9 4 i 5 . 0 6 8 . 9 0 2 A . 1 0 0 . b 9 8 3 . 2 Z : ) . T O

Aug. Destruction I.4 t h t o C . F l a t t e r y 1 . 1 4 8 6 . 0 6 4 . 8 5 g . 0 5 0 . 4 1 6 4 . 0 2 I . 2 5

C. Flattery toC . C o o k 1 . 8 2 5 2 . O 6 8 . 0 0 L . g Z 0 . 9 5 4 6 . 9 6 9 . 1 0

North ofS t . James 7O.b0

C. F'lattery toC. Cook

C. Cook toC. St. James

C. Cook toC. St. James

North of C.St. James

Pt. Reyes toC. Mendocino

2 . 9 0

2 . 3 0

2 . 9 0

3 . 0 0

2 . 9 6

3 . 00

3 . 0 7

3 . 2 0

3 . 3 0

2 . 2 0

3 . 7 2

5 . 8 6

5 . 7 0

3 . 50

3 . 2 8

0 . 7 3

0 . 85

o . 7 7

1 . 6 3

1 . 46

7 . 5

f . i i

3 . 6

1 . 8

o . 2 1

0 . 08

0 . 50

o . 2 1

0 . 1 9

0 . 1 1

0 . 07

0 . 021 . 1 8 3 . 2 0 2 . 4 2

7 . O 8 0 . 8 5 2 . 8 5S"p.ls t

sep.2nd,

0 . 90

2 . 3 9

2 . 5 1

8 I . 0 f i 3 . 50 2 . 11 0 .73

3 2 . 0 6 3 . 1 0 1 . 6 4 0 . 7 6

4 2 . O 6 3 . 0 5 1 . 8 2 1 . 0 5

1 9 . 0 7 r . 7 0 2 . 5 0

6 8 . 0 6 8 . 7 0 3 . 0 0

58 .0 68 .40 3 .42

93 .0 72 .50 2 .a5 l Y . / a l . l r D

1 9 . 0sep3rd 2 1 . 4 6 5 9 . 3 5 1 . 5 0 4 . A i 8 r . 0 r i 0 . 7 0 t . 7 2

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Te.nrn III (contd.)

Length-groups

Totalavailabil ity

Avai la-bi l i ty 1Vl eanN{ean S.D

Avai la-S.D. bi l i ry M e a n S . D Mean S.D.

Availa-bil i ty bil i ty

c1n,i-mos.

Oct,1s t

Oct.2nd

Oct.3rd

C. Mendocinoto C. Blanco

C. Mendocinoto C. Blanco

C. Mendocinoto C. Blauco

26.42

10 .31

6 . 94

34 .0 52 .70 r . o2

4 0 . 8 5 3 . 6 5 7 . 5 7

40 .8 53 . 25 r . 47

8 . 9 8 6 6 . 0 6 2 . 1 8 2 . 1 2 L 7 . 4 4

4 . 2 7 t : 9 . 2 6 2 . 4 0 1 . 6 6 6 1 0

2 . 8 3 5 9 . 2 6 2 . , + 0 7 . 7 O 4 . 1 1

T.q.sLE IV. The percentage composition, mean length, standarcl deviation, and ar.ailability (frsh per boat-hour frshed) of conponerlt lcngth-grorrps (A' B' C

and D) of the 1950 Dritish Cohrmbia zrlbacore catch for selectecl geogrnphical areas and quarter-month time periods.'lbtal zrvailability estirnates by

area and timc are included.

Length-grou ps

Tota lavaiia- Availa- Availa Availa-

;t i i ; % Mean S D. ' ir i l i iv

% Mean S I) ' bil i tv o/o Mean s D bil i tv Nlean S.DAvaila-bilir.y

Area

!-mos-Ju l4th

Aug'1s t

cm. cm.

5 . 5 6 2 . 2 5 7 . 7 5

2 . O 6 2 . 4 0 7 . 9 2

7 . 0 6 2 . 6 8 2 . 0 0 0 . 1 8 8 5 . 5

8 .0 62 .25 1 .87 0 .2 r 85 .0

88 . 5

7 t . 5 0 2 . 5 5 2 . 2 3

7 1 . 4 0 2 . 5 5 2 . 2 7

7 1 . 5 0 2 . 2 8 2 . 1 0

7 . 5 7S . 65 2 . 29 0 . 20

7 . O 8 0 . 2 0 1 . 8 1 0 . 1 9

1 1 . 5 7 9 . 0 0 1 . 1 5 0 . 2 7

Columbia R.to Destruction I.

Destruction Lto C. Flattery

Columbia R. toDestruction L

Destruction Lto C. Flattery

C. Flattery toC. Cook

89 .0

8 7 . 0o . 0 6

77 .60

7 r . 7 5

2 . 6 3

2 . 9 0

80. 60

79 .1 ,5

0 . 1 92 . 3 05 . 53 . 003 . 3 8

3 . 1 8

2 . 6 1

2 . 6 7

2 . 3 7

2 . 7 7 1 1 . 0 0 . 3 5

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- I ' rerE IV lcontd,)

I -engtL-gr,r r ps

Time

Totalavaila-bil i ty

Availzrbil i ty

\vai labi l i tvM e a n S . D M e a n S . D o/o Mcan S.D % Meau S.D.

Avai labi l i t r .

Avai iabi l i ty

f,-ntos

2ndSouth of Pt.Rel'qg

Columbia R. toDestruction I.

Destruction I.to C. F.lattery

C. Flattery toC. Cook

Columbia R. toDestruction I.

a F l .+ r - . , , r ^C. Cook

C. Cook toC. St. James

North of C.St. James

North of C.St. James

North of C.St. James

C. Mendociuoto C. Blanco

North of C.St. James

North of C.St. James

Pt. Reyes toC. Mendocino

Pt. Reyes toC. Mendocino

Pt. Reyes toC. Mendocino

2 3 . 4 5 5 . 0 0 1 . 6 5

am.

4 7 . 6 6 1 . 2 5

3 4 . 0 6 2 . 5 0

17.O 62.40

2 4 . O 6 3 . 1 0

6 3 . 0 6 2 . 0 5

0 . 6 9 2 7 . 9

1 . 09 63 . 7

o . 4 2 7 7 . 5

0 . 6 8 7 6 . 0

0 . 5 3 3 7 . 0

0 . 6 9 7 5 . 7

0 .49 80 .2

o . 7 5 7 8 . 0

0 . 51 80 . 3

0 . 2 0 8 9 . 5

6 . 5 7 3 1 . 6

0 . 06 91 . 3

0 .04 90 .6

2 . r 7 6 5 . 9

1 . 6 8 6 6 . 0

8 . 7 8 2 0 . 0

7 r . 7 2 2 . 3 4

71 . 00 2 . 17

7 r . 3 0 2 . 7 5

7 1 . 0 0

7 0 . 1 8 2 . 8 0

7 1 . 0 0 2 . 5 2

70 .70 2 .57

77 . 25 2 .45

7 t . 25 2 .37

7 r . 40 2 .80

7 t . 70 I . 70

72 .80 2 .A7

72 .50 2 .83

7 2 . 7 5 2 . 5 2

7 3 . 6 5 2 . 6 7

74 .70 2 . 77

8 1 . 9 5 1 . 1 6 0 . O 2

80 .00 2 .47 0 .08

79 .70 1 .86 0 .13

8 0 . 0 0 2 . 7 0 0 . 0 7

8 1 . 0 0 0 . 7 0 0 . 0 4

80 .75 3 .42 0 .47

80. 90 1 .90 0. 37

8 1 . 1 0 2 . 2 5 0 . 2 a

6 2 . 8 2 1 . 8 2

6 2 . 9 0 1 . E E

6 2 . 7 0 2 . 0 0

6 2 . 9 5 2 . O 5

6 2 . 6 5 | . 6 2

6 1 . 6 0 3 . 7 4

6 2 . 9 5 2 . 0 0

6 3 . 3 0 7 . 5 2

$ 2 . 5 0 1 . 8 0

6 3 . 3 5 1 . 6 0

6 2 . 7 5 2 . 7 5

Aug.3rd

1 . 4 6

3 . 2 7

2 . 4 5

2 . 8 4

0 . 8 3

3 . 1 1

2 . 6 8

t _ 5 t

6 . 4 0

5 . 7 7

6 . 9 6

6 . 3 7

5 . 1 5

12.72

0 , 3 4 t . 7 5

1 . 9 5

1 . 9 1

1 , . 9 2

2 . O 2

0 . 4 1

2 . O +

1 . 90

2 . 3 8

0 . 1 3

2 . 3 2

2 . I 5

4 . 3 1

5 . 5 2

4 . 6 3

1 . 50

3 . t 7

2 . 8 7

4 . 2 0

3 . 40

2 . 5 1

1 . 1

D . D

2 . 1 6

2 . 1 6

1 . 5

8 . 5

5 . 8

Aug.4th

Sep.ls t

Sep.2nd

sep.3rd

Sep.4th

Oct.1s t

Oct .3rcl

22.O

1 8 . 3

1 3 . 5

8 . 0

5 . 0

78 .6

1 a

1 . 4

7 . O 8 0 . 8 5 2 . 8 5 0 . 2 4

8 . 0 8 0 . 2 5 2 . 3 5 0 . 2 6

1 . 4

r 1 . 0

3.+. 1

54 .10 L .42 0 .07 32 .6

5 4 . 6 5 7 . 7 2 1 . 4 0 6 9 . 0

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Tee,,, v. 1.he percentage composilion, mea' lcr-rgth, standard deviation, and availability (lish per boat-hour fished) of conponent length-groups (A' B' c

and D) of the jg51 British c.lumbia albaccre catch for selected geographical zrreas ancl rquarter-month time periods. Total availability estimates by

area and tine are iucluded.

Lel lgth-groups

Totalavai labi l i ty

Avai la- Avai la

bi l i ty % Mean S D. bi l i tY M e a n S . D .Avai la-

bi i i ty Mean S.I)Avai la-

bi l i tvM e a n S . D .l-ime Area ,/o

i-mosAUg.1st

Aug.2rd

C. Blanco toVaquina Hd.

Yaquina IId. toColumbia R.

Columbia R. toDestruction I{.

Yaquina Hcl. toColumbia R.

Desuuction I.to C. Flattery

Pt. Reyes toC. Mendocino

Destruction I.to C. Flattery

Yaquina Hd. toColumbia R.

Pt. Reyes toC. I\Iendocino

Pt. Reyes toC. Mendocino

Pt. Reyes toC. Mendocino

C. Mendocinoto C, Blanco

1 . 6 9 0 . 1 2

1 . 0 8 0 . 0 8

61 . 40 2 .50

61 . 70 2 . 70

62 .E0 3 .25

6 1 . 6 5 3 . 1 3

6 1 . 8 5 3 . 2 0

63 .00 2 .80

61 . 70 3 . 40

6 2 . 8 0 3 . 2 5

63 .00 2 .45

6 3 . 0 5 2 . 1 0

02 . 85 3 .O7

1 . 6 5 8 . 0

3 . 5 1 1 8 . 5

0 . 3 4 2 3 . O

1 . 3 3 2 0 - 5

3 . 7 0 7 . O

1. .O2 32.3

3 . 2 8 5 . 5

7 . 9 2 1 8 . 0

o . 7 3 1 6 . 0

4 .47 12 .8

7 . l + t 7 . 3

c1fl.

72 .O0 2 .33

70 .75 2 .70

73 .25 2 . 35

0 . 1 6 4 . 0

0 . 8 7 5 . 0

o . l 2 72 .O

cn.

8 1 . 9 5 2 . 8 8 0 . 0 8

8 1 . 7 0 1 . 8 0 0 . 2 +

8 1 . 6 5 7 . 2 5 0 . 0 6

2 . O 7

4 . 7 7

0 . 5 2

1 . 7 8

3 . 9 8

L . 7 9

2 . 5 6

0 . 9 3

5 . 3 3

8 . 8 1

0 . 5 8

6 . 0

1 . 8

82 . 0

93 . 0

5 7 . O

9 4 . 5

7 5 . O

78 . 5

83 .9

81 . 0

cm.

54. 50

53.25

3 . 5Aug.4rh

sep.lst

72 .50 2 .73 0 . 37

73 .O5 2 . 78 0 . 28

73 .30 2 .70 0 .58

7 r . 2 0 2 . 2 3 0 . 1 9

72 .75 2 .50 0 .46

7 1 . 8 0 2 . 2 0 0 . 1 5

7 2 . 2 5 2 . 7 5 0 . 6 8

7 1 . 6 0 2 . 7 8 r . 5 2

83 .00 | .72 0. 05

0 . 065 4 . 1 5 1 . 3 3

8 . 0 5 5 . 5 0 1 . 5 0

0 . 02

0 . 1 4

0 . 05

0 . 03

0 . 1 0

sep.3rd

Sep.4th

Oct.l s t

Oct .2nd,

Oct .3rd

2 . O 5 4 . 5 0 1 . 1 0

3 . 5 5 4 . 6 0 0 . 9 0

2 . O 5 4 . 9 5 | . 1 0

5 . 0

1 . 0

1 . 0

83 . 30 2 . 55 0 . 13

8 0 . 6 0 1 . 0 5 0 . 0 2

8 3 . 1 0 3 - 7 0 0 . 0 8

8 4 . 5 0 2 . 7 5 0 . 1 5

a 2 . 5 5 2 . O 5 0 . 0 17 0 . 5 6 3 . 9 0 2 . 2 3 0 . 4 1 2 8 . 5 7 1 . 8 5 2 8 0 0 . 1 6

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Trnt r , \ ' I . Percentage ccmpcsi t ion, mearr le lgth, sta lc lard der. iat ion, stanclarc l error of the mean,and ar-ailability (fish per boat-hour lishec'l) of component size-groups of the 194g, 1950and 1951 British Coluntbia albacore catchcs. Total availability estimates for each -voarr areincluded.

YearTotal Sizc-

availability grcupPcrceltage l",Ieau

composi t ion lensth S.D, S.E Avai labi l i ty

I 949 5 0 4

3 3 9

1951 2 . 1 9

ABCD

AD

CD

3 0 528 .9565 .502 . 5 0

0 4 011 9080 .707 0 0

3 . 5 081 5013 101 . 9 0

0 .0400 0200 . 0 1 80 093

0 . 1600 . 0 3 00 0170 0 5

0 .0860 029o .0740 .211

u . l c

1 4 6:t 300 1 3

0 0 10 4 0t 7 t

0 . 2 1

c nl,

53 .25 1 .356 3 3 0 2 0 77 1 1 0 2 8 28 2 9 5 2 8 7

ABCD

5 1 . 2 7 t . 7 562 35 2 .057 L . 3 5 2 6 27 9 7 0 2 3 7

5 5 2 5 1 . 6 56 2 . 9 0 2 . 7 5n o r x t n t r

8 2 9 5 3 . 0 2

0 . 0 E1 . 7 80 . 2 90 0 4

It is not possible to demonstrate that the size of the fish within a groupvaries significantly with latitude. Also, there u'as no marked increase in lengtfi,r,vith time, over the period for r,vhich samples were obtained in any y"ur. Thitrvould indicate a slow grorvth rate at this time of year, if there is any consider-able continuity in the stock available throughout the season. The lattei conditionwould of course require confirmation

Although the groups A, Il, c and D, when present, are always centred aboutapproximately the same mean lengths, their relative proportions vary within theseason, among fishing areas, and between years (Tables III-vI, Fig. s-6). Thecatch-per-unit-of-efiort data indicate how these changes in the ielative pro-portions of the length frequency distributions are rel"ated to chanqes in fishabundance on the ffshing grounds. From them it may be determinecl-whether arclatiae increase of a particular class is caused by an influx of fish belonging tothat class or merely shows that the fish belonging to other classes have l-eft"thearea. The importance of a particular class ma1 be readily assessed by comparingits availability for a particular area and time with the average for that class oveithe whole period (Table IV).

_ In general, the seasonal and regional variations of length-group abundanceindicated an increasingly northerly occurrence of exploitable stocks-during earlyperiods of

-the -fishing sellon and an increasingly southerly occurrence "during

later periods. lhe

larger fish (groups c and D) piecede the smaller ffsh (groupiA and B ) in the northern areas of the fishery, and the smaller ffsh disippeirfrom the northern areas first. However, near the end of october ot ,o.rlir"r1ffshing grounds the larger length-groups disappeared from the ffshing areassooner than the smaller length-groups (F-ig. s-5). This pattern is consistent with

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d_

oz

l

U(r

) 7 0L E N G T H ( c m . )

Frcunr 6. comparison "t Hgf j::lm;r^$ilj:'j,"J':ff:.the 1e4e, re50 and re51

a theory of along-shore migration of the stocks, northward in early_ summer and

southwld later;"but it would not preclude other possibilities, such as seasonal

movements toward the coast of sections of a stock normally present farther ofi-

shore.Albacore occurred in the area between the Columbia River and Destruction

Island during the last week of July, but were not captured in the area north of

Cape St. Jaies until the third or'fourth quarter of August. The occurrence of

the smaller length-groups in the southern areas coincided with their gradual

decrease in abuirdance in the northern areas later in the fishing season (end of

August and beginning of september). The larger size-groups were not

abrindant in areas adjacent to ea[fornia until after the cessation of fishing in

areas adacent to British Columbia, in the third and fourth periods of September'

Movement of the stocks is most strongly suggested by the availability figures

for 1950 ( Table IV ). In the area north of Cape St. James the availability of

classes B, C and D was above the year's average during the third and fourth

periods in August. The availability of groupt 9 -uld D continued 1"--b9 ligh t*ihe first three"periods in September. The availability o{ group B fell below the

average in this-area, but waJas high as 6.57 in the southern area (between Cape

Mend-ocino and Cape Blanco) in the second period of September'During 1S49 and 1950 the larger length-groups ( C and. D ) dominated the

catches in-waters adjacent to the itate of Washington until mid-August. With

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50

few exceptions, group B increased in relative numbers with the advance of theseason in all areas between the Columbia River and Cape St. James. At anygiven time, its percentage contribution decreased progressively from south toriorth. The reverse was of course observed for length-groups C and D.

In the area south of the Columbia River only length-groups A and B wererepresented during the later periods of the 1949 fishing season; of these thelarger fish (group B) decreased in relative numbers as the season advanced.Similarly in 1950, when groups B and C were the important ones south of theColumbia, the larger ffsh (group C) showed an early increase in relative num-bers after cessation of fishing north of the Columbia, but decreased in relativeabundance in areas adjacenl to California iust before the end of the season.This late increase in relative abundance of groups B and C in the southernareas, in 1949 and 1950, respectively, and the failure of groups C and D toreturn to southern ffshing areas after ffshing ceased north of the Columbia Riverin 1949, suggest that groups c and D leave the ffshing areas earlier than dogroups A and B.

The smallest length-group (group A ) was never found in the catches northof the Columbia River. Furthermore, group B gradually decreased in relativeabundance northward, and approached the northern limit of its occurrencejn the area immediately north of Cape St. James., unfortunately, inadequacies in the coverage of areas by the 1951 fishery

did not permit a comprehensive picture of albacore distribution to be obtainedin that year. There was only scattered fishing north of cape Flattery, so nousable information was obtained from the three northern areas. A peculiarity ofthe year is the fact that, contrary to observations in the two previous years, tirerewas no decrease in the abundance of the larger fish just before the terminationof the fishing season.

DrppnnnNcns BETwEEN YsARs

In 1949 and 1950 length-group C was the dominant group in the fishery butin 1951 length-group B was relatively more abundant (Table VI, Fig. 6). Sincein 1949 and 1950 the relative abundance of groups C and D in the northern areasof the fishery was greater than in more southern areas, the absence of catchesnorth of Cape Flattery in 1951 might be related to the relative scarcity of thesegroups in the totals for the year.

In addition, or alternatively, change in the environment may have been afactor contributing to the decline in availability and to the change in dis-tribution of albacore during 1951, as compared with the two previ,ous years.

frlring the 1950 fishing season the relatively warm body of water normally in-habited by albacore was confined to a narrow band parallel to the coast ofBritish columbia (waldie and Doe, tg50); it was 20 miles wide and close toshore in the region of the Queen charlotte Islands and 120 miles wide butfarther from shore near the southern extremity of British columbia. During1951, however, this body of water was found to extend at least 650 miles truEwest from the coast of southern British Columbia (Doe, 1g5t). Since the Cana-dian fishing fleet is limited in the distance it may safely operate from shore,

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it may be concluded that only a small -portion of the water favourable for alba-

"or" *u, covered. Accordingly, the observed decrease in availability and the

change in distribution of the";lbacore population may have been caused by the

disp#sal of previously exploitable stocks over a greater area than during the

two previous years.

AGE COMPOSITION

\{erBnrar- eNp Mnuroos

vertebrae from 531 fish captured during the 1950 ffshing t""-tgl_I"j"

collected at processing plants in iancouver, B.C., d}ring _the winter of 1950-51.

The ninth piehaemal"virtebra was selected for study. Selection of this thoracic

vertebra was based on its accessibility, uniformity of shape, and the legibility

of the concentric rings on its centrum. Body lengths (i.e- fork lengths) were

measured from the tiiof the snout (most anterior part of lhe upp-e1i1*.),.Y1""

the jaws were closed, to the cartilaginous median part of the caudal fork ( Marr

and Schaefer, 1g4g). Weights of BOS of the 531 albacore sampled were de-

termined. to the neatest ounce using a Chatillon spring scale'

The material was considered io be reasonably representative of the 1950

albacore population from ofishore waters adjacent to California, Oregon, Wash-

rngton and ^British

Columbia. Some size selection may, have occurred when can-

nery operators removed the fish from cold storage for proe.essing, but it was

urrrr*"i that size selection by fishing gear did not occur' No allowance was

made for possible shrinkage caused by freezing the-catch'

The length data weL segregated into normal frequency distributions as

Ior the geneial sample. Thls rias done in order that the vertebral_ring-classes

co.,ld be"compared i,ith thor" of the natural length-gloups of both the vertebral

sample and tlie larger sample of the year's catch used for the length analysis in

the nrevious section.'sectioning of vertebrae and accentuation of growth rings on the centra

facilitated verlebral examinations. Each vertebra was sectioned in the horizontal

plane into tr,vo unequal segments with the aid of a fine-toothed circular saw'

Th" lurg", segment *"s gro.rnd on a motor-driven disc sander until the centre

of the centrum *", ,"rr"u-i"d. Growth rings were accentuated by immersing the

vertebrae in 1% KOH for 36 hours, washing in tap water, and preserving in 95%

alcohol (Fig. 7-9; these show sagittal sections).

The aninhicoelus albacore vertebra, sectioned in the above manner, reveals

trvo hollow ion"s whose vertices meet at the centre of the centrum and whose

hases form the anterior and posterior margins of the vertebra, Upon the inner

surface of these cones are complete rings running parallel to the base of the cone

:rnd encircling the centrum. fh"y ate narrow translucent zones sepalated by

broad opaq.,J "on",

similar to those described by Freidenfelt (1922) Ior Lu'

ci,operca'.In^the albacore the narrorr'zones were observed not only as translucent

bancls but also as eruptions or ridges on the centrum surface. The innermost ring

difiered slightly frori the others but was nevertheless clearly marked' Ring

measurements were made to the midpoint of each ridge'

Vertebral rings were measured by the method developed b1' Freidenfelt

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52

Frcunn 7. Albacore vertebra, sagittal section, prior to treatment.

(1922) and applied to scombrids by Aikawa and Kato (tgs8). vertebrae wereexamined by refected light using a microscope having 12\ magnification. Thesectioned surface of each vertebra was placed in contact with the under surfaceof the glass stage. Measurements were made to the nearest tenth of a millimetre.with the aid of a rule graduated in O.5-millimetre intervals, which was placedbelow th." gl"tt stag_e. The distances from the centre of the centrum to eacl ringand to the outer edge of the centrum were measured along the four

"*por"Jedges of the cones. corresponding measurements were averaled. These urr-"t"g"measurements are referred to as ring radii and vertebral radii, respectively.

Frcunp 8. Albacore vertebra, sagittal section, after 36 hours in a l% KOH batl.

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Frcunr 9. Albacore vertebra, sagittal section, after ffxation in 95% alcohol' The numerals

designate annuli'

Rnr-erroNsrnp oF FoRK LnNcrrr AND VERTEBRAT RADrus

Prerequisite to growth calculations based on measurements of a skeletal

Dart is thJ establishient of a definite relationship between the growth of the

irart and the growth of the entire body, In the present :t"^dy lh" radius of the

iiinth prehaerial vertebra was "o-pu."d

with fork l_*gl! for 200 ffsh through-

out th3 range of sizes represented in the entire sample, The vertebral radii were

plotted aritimetically against the fork lengths iiq "- rectilinear regression was

ialculated by the method of least squares (Fig. l0), thus:

R : - 0 . 0 6 9 + 0 . 1 2 7 L ,

where R is the vertebral radius in millimetres and L is the fork length in centi-

metres. As the line passes very close to the origin and as the data do not give

any values for fish oJ l"tt than 50 cm. to confirm the extrapolation to the axes,

it is assumecl in subsequent calculations that vertebral radius and fork length

are directly proportional at all sizes.

Acn DnrBnurNATroNsIn order to establish that vertebral rings r,vere true year marks the data were

examined in several ways. Counts of rings were reproducible with high con-

sistency. If they are year marks, and if the natural length-groups also lepr9s9njug"-gro.rpr, there shoulcl be agreement between ( 1) the mean length of

.fishaisigied-to each vertebral ring-class and the mean length of corresponding

ienfh-groups in the sample, u"a 1Z; the lengths of young ff_sh calculated from

veri"b.il -iurrr."rn"nts of older fish, and the observed lengths of young fish'

Comparison of mean lengths of component length-groups with mean lengths

of ring-cLsses in the vertebral sample showed acceptable agreement (Fig. 11,

Tablentt;. Agreement was also observed between the mean lengths of com-

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I

E

l

6E

J ^

E@

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3

F O R K L E N G T H ( c m s . )

Frcunr 10. Relationship between fork lengtli and vertebral radius of Eastern Pacificalbacore; sampled from the 1950 British Columbia commercial catch.

ponent length-groups of the vertebral sample and those of the larger sample ofthe 1950 catch used in the previous section (Table VII).

Lengths at the time of vertebral ring formation calculated from vertebralradius measurements were compared with observed lengths of ffsh of each ring-class at time of capture, for a subsample of 98 albacore (Fig. lB, Table vIIIf.

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++I B*+

IIrttu

a

^ 7 0E3FozU' 6 0

3 4 oo. o*or3,

6

Frcunr 11. Comparison of component length-groups (A) and assigned-a-ge-classes (B) in the

vertebral ,a-pl"i The vertical iirr" ,"pr"rJots"theiength rangej the solid rectangle"l:lt1""1t:

two standard deviations, the light rectangle rePresents two standard errors on either side ot tne

mean described by the horizointal line within the light rectangle'

There was good. agreement, although of course the observed lengths were con-

sistently gr"?t", thin the caiculatedlengths because the fish were ca-ptured sorne

time after the last ring was formed. Oie discrepancy occurred in the data: the

average length at cap?ure of fish having four v-erte6ral rings tligliY :i:":d^*

the a,ierage"calculated length at the_formation of the next growth ring, but there

ur" orrty f;ve 4-ring ffsh. pYsh with three vertebral_rings were not represented in

the subsample of iertebral data used for these calculations.From the above it seems clear that the third and subsequent vertebral rings

are produced annually. It is assumed, in _the absence of contrary evidence, that

the lnner two rings 'ar"

"rrtrrul also. Subsequgnl rgielence to. ring-classes-l-€

will be expressed is "assigned age-groups I-VI." Similarly length-grouPs *_Bl9and D, deiscribed earlier Yn this"palpet, *ill be expressed as age-groups III, IV,

V and VI.

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56

TasrE VII. Comparison of the percentage composition and mean length of assigned age-groupsin the vertebral sample with component size-groups in the vertebral sample and withcomponent size-groups in the commercial catch sample (1950).

Vertebral Samole

Assignedage-groups

Percentage of totaldistribution

Meanlength

Standarddeviation

Standarderror

I I IIVVVI

1 32 9 66 1 . 6

l . a

ctn.54 .2861 227 0 . 8 37 9 . 8 5

, 9.1

1 .902 . 7 0q t r l

0 . 8 3u . 1 50 1 50 . 4 0

Vertebral Sample

Componentsize-groups

Percentage of totald ist r ibut ion

Meanlength

Standarddeviation

Standarderror

2 2 01 . 9 52 8 7, K '

ABCD

1 . 13 0 . 962.O6 . 0

cm.

53 .4061 .307 1 . 0 080 55

0.2s0 . 1 50 1 60 . 4 5

Commercial Catch

Componentsize-groups

Percentage of totald ist r ibut ion

Meanlength

Standarddeviation

Standarderror

AD

( _D

0 . 41 1 98 0 . 77 0

cln.

54.2762.35/ r . J i )

79 70

L . 7 52 . 0 52 6 2t 2 a

0 . 1 60 . 0 30 . 0 20 . 0 5

Gnow*r rN LENGTH GRowrH RATE

Once it has been established that the ring-classes are annual. the calculatedlengths for each year of life give an estimate of the growth rate. The slope of thecurve_in Figure 13 and the increments given in Table VIII show that althoughgrowth in length is almost linear there is a slight decrease with age, as woJdbe expected.

_ Th" subsample of 98 fish did not contain any Ill-year-olds but the averagelength at capture for the whole vertebral sample is available for comparison(values from Table vII are repeated in Table VIII). considering tlie twocentral well-repls5snted groups, IV and v, these observed lengths exceed theaverage calculated lengths by about three quarters of the annual increments,indicating that most of the annual growth had occurred before capture. (Slowgrowth during the ffshing season was also surmised from the stability of themeans of length-groups throughout the season. ) The large observed value forage-group III, 54.3 cm., which exceeds the calculated length for age-group

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Frcunn 12. Showing the fft of the calculated length-weight curve (solid line) to the measured

data (dots). Sample taken from 1950 Eastern Pacific albacore.

Tesln VIII. Calcr.rlatecl fork length, in centimetres, at time of vertebral attnulus formation for a

small sample of 1950 albacore whose age has been assigned by ring-class determinations.

(The calculation was made by assuming direct proportionality bet'n''een fork length and

vertebral growth for each hsh.) The average length at c:r"pture of the lvhole vertebral

sample (Table !) is included for conrparison.

Average length

. \ ge -g roup No . o f f i sh a t cap lu re Length at ages indicated

I V 5v 8 5VI 8

6 3 . 07 0 . 879 .6

I I I3 9 . 93 9 . 64 0 . 83 5 7t 2 . 4D + . ! l

(7)

I I It5 .4 26.41 5 1 2 7 . 375.7 28.7r 5 2 2 7 315 .2 12 . I

IV V \II5 2 952 0 62.85 3 . 3 6 4 . 3 7 2 . r5 2 . 2 6 2 . 9 7 2 . rr 2 . 5 r 0 . 7 L 26r.2 70 8 79 9(r57) (327) (40)

Average calculated length (r,veighted)

Average annual increment

Average length at capture, rvhole vertebral sample(Nos. of fish in brackets)

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=IF

2colrJJ

| 2 AGE , i , ro . ro

s 6

Frcunr 13. Showing agreement between the mean length of albacore each year calculatedfrom vertebral ring radius by assuming direct proportionality (solid circles), and the actualmean lengths at time of capture. Ring radii were measured on a subsample of 98 fish; actuallengths were obtained from both this subsample (triangles) and from the whole vertebralsample of 531 ffsh (open circles)

IV at time of ring formation, 52.2 cm., might be only a sampling efiect, sincethere were few III's in the total sample. However it is more likety to reflecta scarcity of the smaller ffsh of this age in the ffshery, to which may be relatedtheir limited northern occurrence (see length-group A, Table IV).

No division of the data '"vas made on the basis of sex difierences. Accordingto Brock (1943) the sex ratio of albacore closely approximates one to one, andno significant difference in length occurs between the sexes. It was assumedthat this condition holds for the- albacore population under investigation.

CoupenrsoN \Mrrrr \MESTEnN Pacrrrc Ar-reconn

- The growth estimates above are at a variance with those observed byAikawa and Kat6 (19ss) for albacore of the western Pacific. A comparison of

/

O WHOLE SAMPLE ACTUAL LENGTHA S U B _

. SUB - " CAIJULATED .

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vertebral ring radii ( Table IX ) shows that those of the eastern stocks are con-

sistently t.+J.S mm. less than those of the western stocks for each age-group

up to ihe fifth, with the exception of the first where the difference is 1.3 mm.

If'the radii for the western stocks are compared to those for ring-classes orle

ring louer in eastern albacore there is very close agreement: hence possibly

Aik-awa and Kat6 did not recognize, or did not accept as an annulus, the first

ring measured in this study, rto independent evidence is available in either

stuty to corroborate the eslimate of fiist-year growlf, _but the certainty with

which later rings are established as annual makes it likely that our ring I has a

similar origin.

LrNcrrr-Wnrcrrr Rer-arroNSHIPweights and lengths of both sexes were used to determine the weight-

length relationship:Iog W - -4SL2 + 3.I3 log L,

where W is the weight in kilograms and L is the fork length in centirnetres.

The above relatidnship is shown as a curve in Figure 12, where the average

weight of fish at each cenltimetre of length is shown for the 1950 sample' The

gea"test difierence between actual and calculated weight occurs at Jengths that

ire poorly represented in the data. The observed average weights of age groups

are;Age

IIIIVV

VI

7.5610.4I14.8323.64

Vreighttb,kg.

3.434.726.73

r0.72

SUMMARY

In ofishore waters adjacent to Canada the albacore formed the basis of a

commercial fishery during the summer months of July, August and September,

i.949-51. It was also encountered in more southerly waters later in the year.

fn general, the seasonal and regional variations of length-group abundance

sug[est a progressive northward o"".rrr"nce of available stocks until mid-

AJgust, aft"r rihich a southward progression occurs. In the northern areas the

Tir.sr-B IX. The average vertebral ring radius in millimetres at annulus formation in Eastern and

Western Pacific albacore stocks. Data for western stocks are from Aikawa and Kat6

(1938, p. 79).

Age-class I IAverage vertebral ring radius

I I I I \ - \ - \ ' I \- I I

9 . 11 1 0

1 . 9 3 . 4 5 . 0 6 5 7 . 93 . 2 4 . 9 6 - 1 7 9 9 4

EasternWestern 12.7 14 .2

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larger (older) ffsh appear in abundance before the smaller (younger) ffsh, butthe reverse situation occurs when the ffshery is falling ofi in these areas andincreasing in southern areas. Of the four length-groups which make up theexploitable population, the smallest (youngest) is not encountered north of theColumbia River. Environmental changes which occurred over the years studiedmay have contributed to the observed decline in average abundance from 5.04fish per boat-hour ftshed in 1949 to 2.19 in 1951.

Vertebral age determinations of British Columbia albacore indicate thatIour age-gronpt

-ut" involved. These are provisionally identified as 3-, 4-, 5- and

6-year-old fish, which attain respective mean lengths of 39.7, 52,2, 623 and 72.1cm. (Table VIII) at time of annulus formation, and 54.3, 61.2,70.8 and 79.9cm. (Table VII) at time of capture. The rate of growth in length decreasesslightly with increasing age, and weight increases at a rate greater than the cubeof the length.

ACKNOWLEDGMENTS

The writer is indebted to Messrs. R. M. Wilson, D. Odlum and R. ]. Karjala,who assisted in collecting samples. Catch samples were obtained through thecourtesy of Tullock Fisheries Ltd. and Canadian Fishing Company Ltd. Aid instatistical analysis by Dr. W. E. Ricker and Miss Y. M. M. Bishop, and the readyco-operation of other stafi members of the Pacific Biological Station are grate-fully acknowledged.

REFERENCES

Arxewa, H., eNn M. Ker6. 1938. Age determination of fish. 1. BuIl. lapanese Soc. Sci. Fislt.,7 (2 ) : 79-88 .

Bnocx, V. E. 1943. Contribution to the biology of the albacore (Cermn alalunga) of theOregon coast and other parts of the North Pacific. Stanford lchthyol. BuIL, 2(6):t9g-248.

Dor, L. A. E. 1951. Sea surface temperatures, 1950-51. Fish Res. Bd. Canada, Pacific Prog.Rep., No. BB, pp. 53-56.

FnemaNnrrr, Av. T. 7922. IJnder4kninger over Gosens tillvant sarskilt i Hjalmarcn. Medd.Kungl. Lantbrukslgreken, No. 235, pp. 1-75.

IlanorNc, J. P. 1949. The use of probability paper for graphical analysis of polymodal fre-quency distributions. Jour. Mar. Biol. Assoc. U.K.,28(1 ): 141-153.

Haznw, A. 1913. Storage to be provided in impounding reservoirs for municipal watersupply. Proc. Amer. Soc. Ciail Eng.,39: 1943-2044.

Mann, J. C., aNo M. B. Scnannnn. 1949. Definitions of body dimensions used in describingtunas. U.S. Fish andWildli.fe Seroice, Fish. BuIl.,5I(47): 24I-244.

Srr.r,e, M. 1930. Distribution and migration of the tuna (Thunnrc thynnus L. ) studied bythe method of hooks and other observations. Internat. Reo. Hydrobiol. u. Hydrogr.. 24:446466.

SNnor;con, G. W. 1946. Statistical methods. Iowa State Coll. Press, Ames, Iowa, 485 pp.War-orn, R. J., eNo L. A. E. Doe. 1950. Oceanographic discovery. Fish Res. Bd. Canada,

Pacific Prog. Rep., No. 84, pp. 59'63.

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