Special scientific report

/(^

THREE PAPERS ON THE STOCKS
OF TUNA IN JAPANESE WATERS

Marine Biolopi'-.il I ••- :
MAY I8i35n

WOODS HOLE, MA:.S.

SPECIAL SCIENTIFIC REI'ORT: FISHERIES No. 16

v

UNITED SUr.S DEPARTMENT OF THE INTERIOR
FISH ANO WILDLIFE SERVICE

JL-

THREE PAPERS ON THE STOCKS
OF TUNA IN JAPANESE WATERS

Marine Biological L

X. I £i K A. II i'

MAY 18 1950

WOODS HOLE, MAoS.

V

SPECIAL SCIENTIFIC REPORT: FISHERIES No. 16

UNITED STATIS DEPARTMENT OF THE INTERIOR
FISH AND WILDLIFE SERVICE

Explanatory Note

The series embodies results of investigations, usually of
restricted scope, intended to aid or direct management or
utilization practices and as guides for admini strati to or
legislative action* It is issued in limited quantities for the
official use of Federal, State or cooperating agenoies and in
processed fonn for economy and to avoid delay in publication.

Washington, D. C*
April 1950

.J

TJiiited States Deparianent of the Interior
Oscar L* Chapman, Secretary
Fish and Wildlife Service
Albert M. Day, Director

Special Scientific Report - Fisheries
No. 16

THREE PAPERS ON THE STOCKS OF TUNA.S IN JAPANESE WATERS

By
Morisaburo Tauohi l/

Translated from the Japanese Language by

1I« G. Van Cam pen

Pacific Oceanic Fishery Investigations

CONTENTS

Preface Page

On the stock of Thunnus orientalis (Temminck it Schlegel). • 1
On the stock of the Yellowfin Tuna Neothunnus macropterus
(Temminok & Sohlegel) «•••••••••••••••••• 6

On the stock of the Albaoore, Germo germo (Laoepede). • • e 10

L/ From the Bulletin of the Japanese Society of Scientific
Fisheries [Nippon Suisan Gakkai Shi], Vol. 9, No. 4*

Cn the Stock of Thiiiigus i3liej?t£iig (Temminck & Schlegei)
Synopsis in English

A study on the stock of Th'.:^nnu5 orientalja (Termiinck 4 Schlegei), in which
the catch records for each boc'y-waight class were utilized as bases, showed that
survival rate is ,30 for young fish, Tiie.ii. but .75 for the adults, r/hile fishing
rate is ,55 for the youngs bat «10 foi* the adults, {end of English synopsisj

According to Kimura^-^' on the fishing grounds of Shigedera in the north-
f^astern corner of Suruga Bay juvenile black tuna are first taken in the large
set nsts aroimd July and August. At the end of that yoar and the beginning of
the next year they are 2 - 4 kg in weight, and dui-ing the peak season in April,
May, and June they weigh about 5 kg. In the spring of their third year they a t-
tain a weight of about 10 kg, and around March and April they leave the fishing
grtmcdfl. Consequently fish in their third year and older may be regarded as en-
gaged in the great migratiors of the species,

Aikawa end f'ato have determined the ages of the black tuna from the ver-
tebrae and have established thn ages for each length-weight class. As they have
pointed out, their results disagrfje to soTie extent with those obtained by
Kimurad)* One point which is difficult to explain is their fl'^ding that sixth-
year fish were not taken on the Shigedera gro'inds during the five years from 192^1,
to 1928. Nevertheless, in the present paper the discussion of th© stock of the
black tuna will be based tentatively on the findings of Aikawa and Kato.

The number of fish of each year class tai'en on the Shigedera grounds during
the nine years from 192^ to 1932 has been calculated according to the findings
of Kimura and Ishii(3). (Table 1), If we seek the survival rate from these
figures, we get ,7A,*IP, on the basis of KawRna'sC-^) data (Table 2), we calculate
the survival rate for the periods 1922-1925 and 1926-1932, we get .70 and .66
respectively.**

According to Aika^ta and Kato'^\ In the landings at Numazu large fish pre-
dominate in the spring i*ile fish of the year and second-year fish predominate
in the autumn. Fish of the year, which are taken daring roughly half of the year,
comprise A9% of the catch, and second-year fish, which ere taken the year round,
make up 4.736, The third-year fish, which appear for only a short time in the
spring, form only 4.% of the catch. If we calctilate the survival rates for young
fish from these data/ we get ,23 for fish of the year and ,3A for second-year
fish. A similar calculation made l>y substituting age groups for length-weight
groups in Aikawa and Kato's data on the landings of black tuna at AburatBu in the
spring of 1937 (Table 3) gives a survival rate of .57,

The Fisheries Experiment Station^ 5) reports by weight classes the number of
black tuna taken by yellowtcil nets and tuna nets along the coast and by pole
fishing, long lines, trolling, drift nets, and harpooning in the offshore waters,
A study of this data for the three years 1937, 1938, and 1939 (Table U) gives
the survival rates^^"of ,90 for small and medium tuna and , '8 for medium and
large tuna. If we assijme further that the natural mortality rate is the same
for all fish of the second year and older, we deduce from the ratio of adult to
young fish that the fishing rate for the young is .57 and that for the adults is
J)60, This leaves us Tdth a nat^iral mortality rate of .20. Of 50 small black
tuna released on the Japan Sea side of Hokkaid? in August and September, 1932,

6,
only 6 were recaptured giving a fishing rats of 50 or ,12. However, „06 is the
proportion of the tn.na belonging to the stock which is taken ia one year \7hile
.12 is the proportion of the tuna which come in to the Japan Sea side vfhich is
taken in one year, and therefore it is hard to malco any cloc6i comparison, but it
is thought that both of these valueo are not too fer off.

Because vrL th species like the black tuna, #iich have a Tjide rangf^ of migra-
tion, the course and time of migration probably differ with age, it may happen
that older fish are comparatively plentiful or ecarce over a r&ther long period
of time, ?.nd it may be difficult to Ljarn the composition of tho stock by study-
ing the catch from a limited area. Furthermore a short" term study of the catch
frora a rather broad area can hardly ©scape being affected by year-to-year varia-
tions in oceanographical conditions. Kevertheless, since there is differmce
betT?een the survival rates obtained frora data from various sourcsa, it is prob-
ably permissible to make general deductions concerning the stock on the basis of
these data. It is therefore probably not too far wronjj to consider that the
rates of survival are on the order of .30 for young fish and .75 for aduJLt fieh,
and that the catch rate is on the order of .55 for young fish and .10 for adult
fieh„

Qnotes]

(l)Kinsure, Kinosuke : Growth Rates of Black Tuna and Yellowfin Tuna as Revealed
in the Catch from the Shigedera Fishing Grounds. Bull. Jap, Soc. Sci, Fiah.,
1 (1). Hay 1932.

^2)Aika?mj, Hiroaki and Kasuo Kato : Ag® Determination of Piehoa (Preliminary Re-
port Ko.l). Bull. Jap. Soc. Sci. Fish., 7 (2). July 1938«

(3)Ki!5ura, Kinosuke and Kazurai lohii : Fishing Conditions in the Northeastern
Part of Suruga Bay (Part 1), On tho Black Tuna and its Young. Bull. Jap, Soc.
Sci. Fioh., 1 (5). January 1933.

{4.)Kawana, Takeshi : On the Relationship Between the Tuna Fishery and Oceano-
graphical Conditions. Report of Fisheries Investigations (31) , Warch 1934-,

(5) Fisheries Kxperiment Station : Appendix to Oceanographic Charts, Fixed
Fisfieriee; Pelagic Fisheries,

^^Accarding to Aikarsa and Kato's data, fish in the 4.0-100 kg group include
f}''^ " ^"^ * .05 of th© fourth-year class, all of the fifth-year class, and
V?n '° ^i " •''^ °^ *^® sixth-year class. The fish weighing over 100 kg include
1 - ,73 a .27 of the sixth-year class and all fish of th© seventh-year and older
classes. Therefore if p is the rate of survival, the ratio between large and

medium fish is 1-p This gives |±^ s ,91 and therefore p s ,655.

.05^-p+,73p'• ^^°

If we assume that there are no third=year young tuna included among the small

adult tuna wsighlng less than 40 kg, since these fish include 1 - .05 s .95 ef

Teble 1
Landings of Young and Adult Black Tuna from the Shigodera Grounds in Shizuoka

Prefecture

Total For Seven Years 1924.°32

(fish of the year 1A»000 fish

first-year fish 150,000

second-year fish 2,600

Asraall (under UO kg) 235

adults< rocdiuTi (40-100 kg) 3/+0

l^larga (over 100 kg) 310

Table 2
Black Tuna Catch at Kushiro in Hokkaido

Average 1922-25
small (under 10 kan) i4..29 thousand fish
medium (10--15 kftn) 1.72
large (over 15 kan) 6,72

Average 1926-32

sssall (under 10 kan) 52.80 thousand fish

medlura (10-20 kan) 21, A9

large (over 20 kan) 31.89

[TH: 1 kan 3 8,27 lbs.]

Table 3
Tuna Landed at Aburatsu Between the Latter Part of January and the

End of May, 1937

Year Class

Height

Number of Fish

Fifth

11.0 - 19 5 kar>

2*

Sixth

19=5 - 29,3

367i

Seventh

29.3 - 38.6

2g06l

Eighth

38.6 - A9.A

2,380

Ninth

U9.U ^ 61.3

2,129

Tenth

6le3 - 80.0

9^8

Eleventh

80.0 -

2

survival rate - g. jLg9 ^- 948 4 ^

2,380+2,129 + 948

5,457
: .565

Table U
Catch of Black Tuna in Japanese Coastal and Offshore /Taters
(Average of 1937, 1938, 1939)

Japan Sea (including Yellow Sea)

Pacific Coastal

Pacific Offshore

young (under 3 kan) 373,163 fish

586,259 flah

885,978 fish

Tsmall (3-10 kan) 5,470

adult s< niediiAm (10«-A0 kan) 10,7il9

(large (over UO kan) 5,781

1,7U

737

4,232

> 89,188

(

the fouvth-year class, the ratio between sniall and medium fish 18 * qc^ =.

This ^iveo 2^s 1.4.5 so p s .83» Averaging these figures p s ,74.
235

''*In the same way the ratio between large (over 15 kan) and medium (15-10 kan)

.53p^-^
fish is 1-p . This gives 3.9 which means that p r .70. The ratio be-

,19+.47p .95p*t_Ei

tween larj;^ (over 20 kan) and medium ^20-10 kan) fish is 1-p or I.48

.19+P+-.05P*'
which gives the value p r .655.

^ Fish taken in their first year are represented by f© , those which become
second-year fish by po, those taken in their second year by f; , those which sur-
vive into the third year by pi , and those taken in their third year by fx. If
the proportion of each of these year classes rtiich is captured is related to the
length of time during which the fish are present on the fishing grounds, we get
fotfi :fa.« ^:1::^. Therefore the proportions of fish of the year, second-year fish,
and third-year fish which are taken are ^:pc:^oPi. This gives 49:47:4 so

n - 42 X i s .48 and p s ^ x 4. s .34.» Therefore the percentage iriiich live an
4-9 2 » **i

additional year, that is the survival rate, is (.48) z .23 for fish of the year
and .34 for second-year fish,

■'^Since small adult tuna weigh 3-10 kan they include l*'^lZ^''2 = '78 of the
third-year fish, and J;9'q'§^Z| s .81 of the fourth-year fish. Medium fish weigh
10-40 kan and include 1-.81 r,19 of the fourth-year class, all of the fifth-^
sixth-, and esventh-year classes, and /q^/^^|^| = •13 of the eighth-year class.
Large fish weigh over 40 kan and include 1 - .13 z "S? of the eighth-year class
and all fish of the ninth-year class and older. Accordingly if p represents the
survival rate thon small: medium: large s .78f,Slp:.19pfp''+p^+p'*"+.13p'' : .87p-f ^^ ,
In both the Japan Sea and the Pacific the ratio between medium and small fish is
1,61 so p s ,90, and the ratio of large and medium is .87 so p x .78.

If the catch rate for young tuna is represented by f and the catch rate of

adult tuna by .f , and the young tuna include fish cf the year, all of the second-
year class, and. 1 - .78 s ,22 of the third-year class ^lle the adult tuna group
includea .78 of the third-year class and all of tho older year classes, then the
ratio between adult tuna and young tuna is

f X .73x.4.8x.3^f.4-8x.3/^l-.75 • .»62 f s .61 f
Since^ this gives .064 for the ^ole area, J'. 9.5. If we use 6 to represent an
identical natural mortality rate for all fish above the second-year class, then
(l-i)(l-fO=3A,(l-s)(l-f)=.75. Accordingly f=.060,f' «.57, and5s.20.

On the Stock of the Yellowfin Tuna Weothunnus macropterus

(Temmlnck & Schlegel)

Slynopsis [ixi English^

Based on the catch records given for each body- length and body-weight
classes, the stock of Meothunnas macropterus (Temmlnck et Schlegel) was studied.
If the natural mortality rate is assumed to be .20, the survival rate is known
to be .75 for young fish but .57 for the adults irtille the fishing rate to be
,06 for the youngs but .29 for the adults, [end of English synopsis)

The ages deduced by Kimura^^' frora.the length distribution in the catch
and those determined by Aikawa and Kato^^) on the basis of the circuli appear-
ing on the vertebrae are not in agreement. In this paper I have followed the
conclusions of the latter, and have studied the stock by deducing the ages of
the fish from their length and weight.

According to Kimura and Ishii^^' among approximately 2,980 small yellowfin
tuna and about 630 large yellowfin tuna taken on the Shigedera fishing grounds
during the nine-year period from 192A to 1932 fourth-year fish predominated
among those weighing 12 kg or more followed by seventh and eighth-year fish in
that order, (Table 1, calculated from Kimura' s^^) graph of weight distribution).
According to Aikawa and Kato'av2) table of the weights of yellowfin landed at
the Nuimzu market in 1937, which includes 1,214 fish under 12 kg and 1,292 fish
over 12 kg, fourth-year fish predominated among those weighing more than 12
kg (Table 2). However, among fish taken east of FormosaU) on longllnes sixth-
year fish were most numerous follo77ed by seventh-year fish (Table 3). Wear
the South Sea islands quite a few small yellowfin are taken nixed in with skip-
jack (5) (6) (7)^ but among those taken farther off shore sixth-year fish pre-
dominate (Table 4), In both cases the number of young yellowfin taken is small.

Collating these facts it appears that third-year fish leave the islands
and bays and take up a migratory life, that fourth-year fish are comparatively

Table 1
lellovTfin Tuna Taken on the Saigedera Grouuds (Juveniles Omitted)

Age

''-Jeight

Number of Fish

3

5
6
7
8
_ 9

8.6 - UiO kg
U.O - 21.it
2\.U - 30.0
30.0 - U.O
U.O - 57.5
57.5 - 75.C
75.0 -

6.0
68.7
17.3
U.O
23.0
20.5

1.5

total 151.0

Table 2

Yellowfin Tuna landed at the Numazu Market in 1937

Age

iteight

Number of Fish

0

= .itO kan

124.5

1

.40 - 1.15

825.5

2

1.15 - 2.30

163.0

3

2.30 - 3.70

231.0

Note: 130 of the third

k

3.7 - %7

931.0

year fish were

5

5.7 - 8.0

70.5

over 12 kg.

6

8.0 -11.7

it3.5

7

11.7 -15.3

50.0

8

15.3 -20.5.

17„0

1 total

2, 506.0

Table 3

YeJlowfin Tuna Taken East of Taiwan

Age

Length

Number of Fish

Tfeight

Number of Fish

0

- 38 cm

—.

- 1.5 kg

__„

1

38 - 54

1.5 - 4.3

1

2

54 - 70

1

4.3 - 8.6

1

3

70 - 85

1

8.6 -U.O

«

A

85 - 100

1

U.O -21.4

1

5

100 - 115

3

21.4 -30,0

3

6

115 - 130

39.5

30.0 -U.O

40o5

7

130 - 145

26

U.O -57.5

24

8

145 - 160

1.5

57.5 -75.0

2.5

total 73.0

total 73.0

/

coastal in character, that sixth-year fish are corparatively pelagic, and that
in their seventh and eighth years the fish again nilgrate into the coastal waters.
Consequently a good deal of caution is necessary in deducing the composition of
the stock from the data gathered at various fishing grounds.

Since it is thought that fish in their first and second years remain close
to islands and in bays, the ratio of first-year to second-year fish will prob-
ably give the survival rate for each locality. For the waters adjacent to
Numazu this is |||*^ s.l98. Aft^r they enter their third yrar the fish enter

upon a ifiigratory existence and there is prob-
ably no great age diffeirential in the subsequent survival rates. However, there
are differences between the ages of the fish which occur in coastal waters and
those found in pelagic waters and this gives rise to differences in the ago com-
position of the catch. The survival irate for sixth-, seventh-, and eighth-year

^^^^ ^® S'sIsO^O "•'''^^ ^°^ *^® waters adjacent to Numazu, and

(?§^t'??.^ (^4"^8'^^ . = .^6 for the waters east of Taiwan, The former is a

coastal fishing ground while the latter is a pelagic ground so the average .5oo
for the two can be said to be the survival rate for ^ixth-year to eighth-year
fish. On the Shigedera fishing grounds the survival rate for fish of the fourth
year and older is ^j'l^lj^'^^fj'^^lj'^^^^^e'^i g ^ •5;29, which indicates that the

excessively small number of fifth-year fish in th^ vaters adjacent to Numazu
probably represented a condition restricted to tlje year 1937. Consequently it
will probably be satisfactory to consider the svyvival rate of the fish after
they have entered upon a migratory life as .57.

On the Pacific coast of the American continent and from Southern California
to the Lquator a considerable quantity of yeHowfin is taken along with skipjack.
On the northern grounds migratory schopls^are fished during a three-month sea-
son in August, September, and October/ but on the southern grounds the fishing
continues throughout the year. It is thought that the schools fished are mainly
migratory schools of young fish. These yellowfin of the Fastern Pacific, like
those of our '.festom Pacific waters, are probably related to the small yellow-
fin >irtiich reside permanently around the various islands which are scattered
over a wide area north and south of the Equator, but since we do not have enou^
data to pursije these questions any further tit present it is recommended that we
proceed on the assumption that the yellowfin tuna of the eastern and western
Pacific should be treated as separate stocks.

As was mentioned above, in the South Seas young yellowfin occur mixed with
skipjack, but we have no exact knowledge of their numbers. In the course of his
investigations Kimura found that in the Ogasawaras a fairly large quantity of
snail yellowfin is taken along with the larger fish, however, detailed knowledge
is lacking regarding the numbers of small and large yellowfin taken at other
places so a thorough treatment of this question will have to be left until a
later date, What we wish to postulate here is that among the stock of fish ^rtiich
come into the waters adjacent to Numazu the proportion of small and large yel-
lowfin is about equal and th^it there is no great difference in the rate of catch
for the two size groups. Assuming this to be the case, it appears from the
amount landed at the Numazu market that the survival rate of young yellowfin in
the stock as a whole is „75, If we assume that the natural mortality rate for
yellowfin is the same as for the black tuna f Thunnus orientalis"]. vte get a
fishing rate of .06 for the young fish and o29 for the mature fish.*

Tattle i^
Yellowfin T-jna Taken in the feters of tho South Sea Is].Ends

Age

Number of Fish

3

.5

U

1,0

5

U.5

6

137.0

7

9.0

8

total

16?.. 0

[footnotes]

vlvKiimira, Kinosuke : Growth Rttes of Black Tuaa and Tellowfin T^ana as Revealed
in the Catch from the Shigedera Fishing Grounds, I^ull, Jt.p. Soc. 3ci, Fish.,
1 (1). May 1932.

t2)Aikawa, Hiroaki and Masuo Kato- : Age Detenaination of Fishes ( PreliTninury Re-
port No.l). Bull. Jap. Soc. Sci. Fish., 7 (2). J-ily 1938.

(3)Kimura, Slinosuke and Kazumi Ishii : Fishing Conditions in the Northeastern
Part of Suruga Say (Part 2), On Yelloivfin Tuna, Spearfish. TellovTtail, Amber-
jack, and B3ackerel Scad, Bull. Jap. Soc, Sci. Fish., 2 (2), July 1933.

(^)Kanaimira, Masami and Kakuji Imaiz-jmi ; Fxperimontal Tuna Longline Fishing
East of Taiwan. Report of Experimental Fishing by tho Shonan F.^aru in 1936„

(5)ii{ebe, Kenzo : On the Age of lellowfin Tuna froir Palau Skaters. South Sea
Fishery News, 3 (10). December 1939.

(6)lkebo, Kienzo : Weights and Ages of Tuna from Palau ?laters. South Sea Fishery
News, A (1). February 19A0.

(''')lkebe, Kenzo ; Measurements of lellowfin Tuns from South of the Marshall
Islands. South Sea Fishery News, U (2). Bferch 19^0,

*0f the total number of fish of the year So, those which come into the \'?aters

adjacent to Numaau are represented by r, <, The rate of catch in those waters is

fo' and the rate of survival is p©', but for the stock as a whole the rate of

catch is fo and the rate of survival is p©. Of the fish in their third year and

older which have entered upon a migratory life, the part irtiich comes into Numazu

waters is represented ty r and their rate of catch in those watsrs by f ' , but

for the stock as a whole tiie rate catch la f. As shown above, se get the

values pj - .20, p ; .57, f^'r^S,, (.5fpJfPo'>-|~~p'-^) s 1,200; (the rate of catch

of if^' is given here for fish of the year because, althoufjh eecond-year and third-
year fish are both taken froni May to December, fish of the year are taken only
after August); l^r S^Po^ (l~gl+ȣ_.) . 1,300. Accordingly |JX- p^' - 1*|^ x

The young yellowfin in the waters adjacent to Sumazu come up throu^ the Ogasa-

waras together vdth the mature fish and are carried from the south by the same

ocean currents which bring the inigrt:.tory schools, and for these reasons it is

probably approximately coiTect to consider that r^s r. Since the catch in Numazu

waters is made with fixed nets, it is probably also safe to assume that f^ i f '.

Consequently if £-2 a 1 then p^j .75o The natural aortality rates for both

young and adult yellowfin do not differ greatly and are thought to be of the

same order as those for the black ttina. Therefoi'e if Ss .20, the rate of catch

for the young fish Is f^s 1 - -s^S, - ,062 and that for adult fish is

•30

i" = 1 - *S = .287,

On the Stock of the Albacore, Germo germo (Lacepbde)
S^jrnopsis jin English^

Stock of Germo gertno (Lacepede) was studied on the basis of catch records
classified according to the body-length and body-weight. Survival rate was es-
timated to be about ,66, while fishing rate as about ,18. Qend of English
synopais]

The California albacore, which had been showing a tendency to decrease in
abundance since 1916, had by 1926 fallen into e condition in which it might be
said that there was almoet no catch at all, and that condition has persisted
to the present day. (1) In the past the albacore catch on the coasts of Japan has
been very small, but under the stimulus of the demand from California positive
efforts have been made to increase the catch and the fishing grounds have been
extended farther and farther out to sea in the search for the schools. Along
with these developments, hoTrever, certain ill omens have appeared in the fish-
ing situation. The comparatively large albacore which migrate in close to the
coasts in the sumirer have gradually diminished in numbers and the fisheiy has
barely been able to keep going by increasing the catch of the medium-sized al-
bacore which migrate into the offshore waters in the winter. v2) This may per-
haps be due to a change in the course of migration of the albacore, «rtiich are
the most truly pelagic of all the tunas, but in case this decline may possibly
be due to overfishing, it is a problem which requires a great deal of attention.
The present study was undertaken because of my desire to gain some knowledge
concerning these points.

10

Uno^^' investigated the covnposition of the tuna catch taken by pole fish-
ing in the waters east of Cape Kojima and found that in f&iy and June of 1935
the catch was 6« fourth-year fish, 86% fifth-year fish, and ffi& sixth-year fish
while in June of 1936 it was 16)5 fourth-year fish, 70% fifth-year fish, and
Li./& sixth-year fish. Jilhen the weight groups of the albacore taken east of Cape
Nojima from January to Way, 1936, and the length groups of those taken on the
same grounds in the same period of 1937 by the Pumi MaruU) are converted into
age groups by the method of Aikaiva and Kat5 '^), fifth-year fish are most
numerous followed by fourth-year, third-year, and sixth-year fish in that order
(Table 1). A consideration of that part of the reports of investigations of
the Fisheries Experiment Station^?) in irtiich the catch is indicated by sizes
of fish shows that the proportion of large fish is greater in the Northeastern
Area than on the distant offshore grounds (Table 2). The proportion of small
fish was greater on both grounds in 1937 than it vsas in 1936, however, it is
thought that there still appears to be room for the development of fishing
grounds for large fish in the distant offshore areas.

Where two or nore of the size categories of small, medium, and large are
combined in the table of albe«ore catch by sizee compiled by the Japanese Tuna
Cannei'S Association, (6) they have been broken down and distributed proportionally
by numbers of fish into small, medium, and large size groups (Table 3). If we
compute the survival rate* from these data, me get ,5^ for 1934-, «8^ for 1935,
.56 for 1936, and <,6A for 1937, an average for the four years of .66. The con-
siderable variation in the survival rate value from year to -ypar is probably
due to the fact that the age composition of the fish which migrate into the
present limited fishing grounda cannot be regarded as the agR composition of
the stock. This Indicates that the above-mentioned irregularities which h^ave
recently appeared in the fishing situation cannot, be said to be necessarily due
exclusively to overfishing. This is all the more apparent when we consider that
the survival rate is proportionately large and that accordingly the fishing
rate is proportionately small. '^

[hotesj

(l)Bureau of Commarcial Fisheries: The commercial fish catch of California for
the year 1935, Fish Bjlletin (A9) f 1937.

(2)Hasegawa, K. s On the Report of the Sumnier Albacore Investigation. Collected
Lectures on the Canning of '^Jnas in Oil. February 1938.

(3)uno, Michioj The Composition of the Catch of Tuna Taken by Pole Fishing in

the Haters East of Caps Mojima. (Preliminary Report No.l)« Bull. Jap. Soc.

Sci. Fish. Vol. 4., No. 5. January 1936j (Preliminary Report No. II), Vol.5,
No, A, November 1936,

(A)Aikawa, Hiroaki and I&suo Kato: Age Determination of Fishes (Preliminary Re-
port No,l)« Bull. Jap. Soc. Sci. Fish. 7ol.7, No. 2. July 1938,

(5) Part published in Reports of Oceanographical Investigations (58) -(61), (63),

(6)japan Tuna Canners Association: Report of Activities for 1937 (Sixth Yearly
Report). 1938.

11

Table i
Albacore Catches by the Fuji Maru on Grounds East of Cape Wojlma

January to ?.'ay, 1936

Age

Weight

NuKber of Pish (Estimated)

Per Cent

0

- .27 karj

_—

1

.27- .61

7.5

2.0

2

.61-1.07

6.5

1.7

3

1.07-1.68

4.8.0 .

12.6

U

1.68-2,A5

lU.O

30.0

5

2,A5-3.52

176.0

i;6cl

6

3.52-i;.82

29.0

7.6

7

^.82-6.-4

._

8

6.^ -

-—

Total

381.0

100.0

January to May, 1937

Age

Length

Number of Fish (Estimated)

Per Cent

0

- 35 ca

43

8o0

1

35- A6

11

2.1

2

A6- 55

19

3.6

3

55« 6A

96

18.0

U

U' 73

136

25.4

5

73- 82

161

30.2

6

82- 91

5U

10.1

7

91-100

U

2.6

8

100-

—

—— -

Total

534

100 oO

12

ca

in

•

S

3

c

1^

a:

B^

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14

*The "large" categoiy comprises fish of 5 kan weight and over [1 kan ;

8,27 pounds] so according to Aikawa and Kato (^' it includes ^ ~ ^rQ „ ; .89

6.-4 - -^.82
of the seventh-year fish and all of those of the eighth year and older. The

njedium fish are from 3 to 5 kan in weight and include 1 - .39 r .11 of the

seventh-year fish, all of the sixth-year fish, and h^ ' |*^ - ,19 of the

fifth-year fish. Small fish comprise 1 - .4.9 s .51 of the fifth-year fish and

all fish in their fourth year or younger. If the survival rate is represented

,89p^4- -al

by p, the ratio between large and medium fish is l-p This formula

.49tp+.llp^
gives a figure of .57 for 1934, 3.55 for 1935, ,6A for 1936, and .97 for 1937

or an average of lo05 for the four years. The corresponding survival rates are

,5A, ,^At .56, ,6a, and 0656 respectively,

♦♦Among other tunas the natural mortality rate for the black tuna has been

calculated at ,20 (see preceding article in this journal). The albacore

probably does not differ \7idely in this respect, so if we assume a natural

66
mortality rate of .20, we get a catch rate of 1 - 1^2726" ° *^^'' '^® catch

rate for the black tuna is .10, but the catch rate for the young fish shows the

high figure of ,55. For the yellowfin tuna the catch rate for the young fish is

,06 vrtiile that for the mat'ire fish is .29. (See the two preceding articles in

this journal.)

7^837

15

MBL WHOI Libra™ " .Sf'jj

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