ICES C.M.
1998!M:18
Paper ft>rt~ 1998 lCI'S Annulil Science Conference in Casmis. Portugal
Session Name: Impact of Cephalopods in the Food Chain and t.heir
Interaction with t.he Enviromnent(M). (No.313)
"Not to be cited without prior reference to the author"
Changes in inferred spawning sites of Todarodes pacificus (Cephalopoda:
Ommastrephidae) due to changing environmental conditions
Yasunorl Sakurai, ,John R. Bower, Hidetosbi
Kiyofuji, Sei-i~ Saitoh, Tsuneo Goto, Yoshiald
Hiyama, Ken Morland Yoshikazu Nakamum
Yasrmori Sakurai, JOM R Bower. Hideloshi Kiyofilji
ond Sei-ichi Saifoh: Faculty af Fisheries, Hokkaida
University, Hakodafe, Hokkaido 041-8611, Japan.
Tsuneo Gola, Yoshiaki Hiyama: Japan Sea Nalional
Fisheries Research Inslilufe, Niigata 951-8121,
Japan. Ken Mori and Yoshikazu Nakamura:
Hokkaido National Fisheries Research Inslilule.
Kushiro,
Hokkaido
085-0802,
Japan.
Correspondence 10 Y. Sakurai: lel: +81 138 40
8863; fax:
+81 138 40 8860; e-mail:
sakurai@popjishhokudai.acJp
Abstract
Annual catches of Todarrxles pacificus in Japan have
gmduaIly in=sed, since the late 1980s despite the
lack ·of catch. regulations Paralarval abundances
have also been higher since the late 1980s th;m
during the late 1970sand mid-I 980s. We propose a
possible scenario for this recent stock increase based
on changing environmental conditions. First, we
reviewlrends, in the annual variations of ~ and
1arval' catches, and infer, possible spawning sites
aroll!ld Japan, assuming that egg masses and
. batchlingsoccur at.temperarures between IS and
23°C, and above the ~tinental shel£ We then infer
possiblecbanges in the spawning sites of T. pacificus
during 1984-95 based on GIS data We conclude that
as stock size has in=sed since the. late 1980s, the
full and winter spawrung sites have overlapped in the
Tsushima Strait and near the Goto !sands, and that
winter spawning sites have expanded above the
continental shelf and slope in the East China Sea
Introduction
Most commercially exploited squids live for a year or
less. Reproductive success will depend on the
physical and biological environments~~~~pawning
and nursery grounds. POS5ible causes of the "failures"
of Todarodespacifir:us (Steenstrup, (880) and I1lex
illecebrosus (Lesueur, 1821) fisheries in the 1980s
includechangingenvironmo;ntal conditions and
heavy fishing pressure (Lipinski ef al., in press).
Todarodes pacificus migrates seasonally near
Japan and Korea and spawns at the southern end of
its distribution (Murata, 1989; 1990). Three
spawning groups (winter, full and summer) occur
with overlapping spawning grounds. Catches have
fluctuated during the 20" century (Fig. 1); during
1986 -%, annual catches near Japan have in=sed
from 99,000 to 444,000 tons.
Keywords: GIS, stock fluctuations, paralarvae,
spawning sites, Todarodes pacificus, regime shifl.
70
......
60
.s
50
I!
-~
40
...,
30
~
10
~
.r:
Total
20
0
Year
Fig. 1 Annual fluctuations in Todarodes J10cificus catches in Japan during the 20·' Century.
Catches before 1951 include other squid species (modified ITom Murata, 1989).
1
,4nnilal varitldon in stock and larval densities
Annual variations in stock density of 1'. pacificus
Iurl<e been estimated IlSing average catch weight per
EpisOdic "regime shift" involving entire biological
corrurumity structures occur worldwide (Lluch-Belda
et 01., 1992). In the Western NOrth Pacific,
interdecadaI regime shifts in water tempernture
haveoCcUITOOfrom Ii' warm'regime begirmingin
the late 194Os, to a cool regime in the late 19708, and
hack to a warm regime in the late 1980s (e.g.
Kodama et 01., 1995). Theseregimeshiftsappear
to affeetthe Catches of TodarOdes jJacificus,
particularly the earIYj980s catch decrease and
the late '19808 catch itlcrease. Hill paralarval
abWK1ances since the late 1980s have been higher
than during the late I 970s to the mid-1980s. This
increase correspondsto the increase in adult squid
catches .tllRt IlllS occurred since the late 1980s (Goto
and KidOkoro, peIS. corrun.). These stock tlllctuations
may be related to the effects of regime' shifts oil
spawning and paralarvalsuivival.
.
In this paper, wereviewthe recenttrendlwfaimual
variation in stock size and larval density of
Todarodes pacifiC/Is. We then propose II possible
scenario for the. stock fluctuations re1ated to the
effects of phanging envirOruriental' fegimes ' based
on Iw<? ";;sun;ptions: . 1) stock size in the w~stem
North PaCific increases with a shift t6 a warm
regime; and 2)a
regimecriiates mvorable
enwOnrtten\a1 conditioiJs 'fot repioductionand
reCnllllllertt' Fina1l)', we' estimate the 'relatiOnship
betWeen the • recentseasonaland annual' changes in
the inferiedoptimwn SpaWning giouridS and water
terhpci-atures,ar<iund Ja~an:
fishing boat per day (CPUE) throughollt the fishing
season (MlU'IIta, 1989; 1990). AnnIlaI variations, in
CllUE can reveal trends in the stock index of the fiill '
and winter spawning groups better than annuaI catch
variations (Okulani and Watanabe, 1983; MlU'IIta,
1989; 1990). Para1arval abwdancehaS aisoooen
used to aSsess the stock,recruilm.entre1atiOnship'(e.g. :.'
Murata, 1989; 1990). The Japan Sea Natiriruil '
Research Institute has conducted paraIarva1
collections of the fall-spawning group in the' If '
southwestemSea of Japanimd the northim part of '
the East Chiria Sea since 1973, and theHokkIiiclo "
National Fisheries ReSearch Institute has '00ndUCted
simil3r surveYs of the winter-spawning group off the
pacifiC coast of southemJapan and in the East Ehina "
Sea Since 1995.
To anaJyz.\ recent trends in the stock-recruitmeirt "
relatioriship,we eXlIlllinOO paraIarvai density index'
(PDI) 'Vafues i in the northern part of the East ChiruI' '
Sea and the SouthweStern Sea of Japan during fa1l,'
and •tile amrual CPUE values of the full-spawrriDg
group in the Sea of Japan. PDIwas calcu1atedas'the
numberofparalarvaeper 1,000 m3 0fwater filtered in .,
obliqoe tows of a 8O-cm plankton net (0:508 mm
mesh) rrom 75-ni &pthtothesmface. CPUEis'the
mean catch (ton) per fishing day by 7()'IOO iron'
vesseIstising 8!ltomatic jigging machines in' oflShote
ofthe Sea ofJapan each AtJgust.
warm
Matl!rials and Methods
Fig.2 Working hypothesis on reproduction of Todarodes pacificu,," in nature, based on
the results of experimental studies.
2
Determining ~~ spawning sites
We estimated the possible spawning sites of using
infonnation collected from Iaboratory and, field
slUdies. l'odarodes pac!ficlIs produces gelatinous,
nearly neutrally bUQyant egg rnasses(BPwen!nd.
Sakurai, 1996). The temperature range for rtorinal.
embryonic development is 15-23°C (Sakurai et aI.,
1996). Most hatchlingscollectedoffsouthetnJapan
where sea surface temperiIIures range 17 to '23°C
'(Bower, 1997) In the present SU¥Jy,we used
temperatures at 50-m·. depthtoestimatespawning
of . the mean monthly temperature at 5O-m depth
during \90(')-72 (JODC,1978), and the. position
of, me corit.iriemaI. shelf near the Japanese
ArchiPe)!ig~.
Recent changes in possible spawning site,Y IHlYl!li.on· .
GISdata
. .
sires,sincemost~ occurat,~50mdepth
(Watilnabe,I965). We: asswned that spawning .
above theci>ntintirttal·sbelf. andslope .
around Japan (Fig. 2) because captive females
regularly sit on the tank .bottom just before spawning
(Bower and Sakwai; 1996), and bottom trawls on the
continental shelf and slope at 100-500 m depth often
collect exhausted speot females (Hmnabe I and
Shimizu, 1966; YamiIda, 19988, 1998b). To estimate .
the possible spawning areas, we used data·
occurs
'D:
:.cco'
2.5
2,
.l,~
.......
C. . 1
!
~
0..
o
0.5
0._.,
~ ~'_~"e-e
_
500m
,
!-: S\I :: ! :: i·I::'.': :t'! ::.: :-::.:-,
- -- - - - - - - - - - - - - - - - -yiar,
Results!lnd ~DSSion
Fig. 3 Annual i:hanges 'in CPUEof . the Todarodes
pacijiclls fall spawning group in the Sea of Japan during
1976-96. .Cf'UE:Catch in' (ton) per fishing, day. by
automatic jigging ofluOOium-sizedvessels(70-IOO tons) in
offsllOre waters of the Soodf Japan in August.
100
'0
......
80'
E
B,O"
f'J
... C
10
110
.a
0
1
eo,
E::::, 50';'
:d
0..
Japap,
Sea of
lIIUIual POI vall!eli were relatively high
in 1975, low. . during 19~O:S8,and
remarl<ablyafter 1989, whichCOIreSWl1ds to ,annual
changes QfCPUE val~ (Figs. 3,4). Pa,.darvae ~
more .widely dis~ during 199+96 than during
the late 1970s .;my 1980s (Fig, 5), ';"'iten annual .,
POI values were low (Goto and.l(;lsahm1l, i991).
'.
Oufing I'!13-84, positive relationShips
bernteen both adult catCh.and tit<: POI of tht,ir'
oftSpring and ~ the POI and adult catCh oflhe
same generation for the full-spawning group (MWlIta, .
1989). We examined the relationship l:letween POI .
and CPUE in the Sea of J!IPBIl using datafrom 1975- '.
96 (fig. 6). The.. CPUE. .in. ~ffshore.·
. '. . wateJ:s... .of. the.
ofJapan and the P~ in\V8lersfrom the northern East
China.Sea to the. ~\I1I:twestem~ ofJapaninfiill
were strpngly =re~, (R2=O.91). A positi~
2
relationship (R =O.77)also occurred between POI
increased
occurred
3.
20
i ':
--l
AnnuaIChanges.qfPDI andCPUE .
In the~. East.ChinaSe!i and the southwestem
to
1\
I,
S ~= ..
C -
Geographical Infonnation System (GIS) was
developed foruse in terrestrial fields, but is now
increasinglyiJsed fdr oceanograp1ric and fisheries
slUdies (Sin)pson, 1994; Kiyofuji e/ al., 1998). We
examinedihe retationship.· between .the monthly
and amruaIcitanges of spawning grounds and water
temperatures af21-53° N and 121"153~ E .during
1984-95..
To determine possible spawning sites, we collected
three data sets: monthly GMCSST (global mu)tiChannel sea surfuce tempeJ:;jture), Levitus,
cIimatological. oceanographic .and topography data. i
NOAAINESDIS .(Natioual Environmental Satellite!
Data and Infonnation) and the NODC (National
Oceanogr3jJhic Data Center) produced the GMCSST
and Levitus 'data sets.' We detennined. a linear
equatiorndatingtemperaturesat O-m and 5O-m depth
.foreiU:h .. grid and 11)1en estimated the 50-m dt:pth
temperat;ure for ~ll month during 198+95 using .
this equation and GMCSST data. We then estimated'
the surface area where the 50-m depth temperature' . .
ranged 15-23°C above the bottom depths of 100-
··~~-~-·~~~:~i~~~·~~~~
e e,;,!
'! !,~ i!!:!.!!.! =. ~,~ . ; -E,~,!i !;,!
. .....
.... ' . . .
.
Year.
Fig. 4 Amlual c!wtges of the Todt1rodes jJacificllS
paralarval density index (POl)during 'faUin 1975"1996 in
the notthem East China' S~. and the SOtilliwestem' Sea of
Japan. PDt: nwnber of paralarvae'per l;OOOml of wafer;
from the results of paralarval collections by oblique tows
of a 80-cm plankton net (0.508 mm mesh size) from 75 m
depth to the surface.
~ :~
Sea.'.
3
y
90
= 58.921. - 42.488
R 2.:= '0.9073'
80
I
1"
,Q.
.- ,.
•
••
, 00
, 050
'.I
1,·1 .
.
4"
30
_,i"
.'
,:2~ i
10
0+.__~~S-~__~__~__.,~
~~~
o
' o.S
1.5
-·2
CPUE
Fig,'6 Relationship between CPUEandPIDI
, 'in the sameyear,in t1ul'Sea ofJapan,usingthe
. 'Same dritafrom Figs. 3 and 4 during 1975,96.
3
= 0.0139. + 017704
R' =.0.7719 '
y
.••
'"
'I; .
•
fp~arva1 distributions (POll of T.jxtc!ticus '(left)
and temperntun:s at 50-m depth (right) diliirig fall of 1994-
Fig.
-':::'
"","
::
,-
':':.',
'
1996.. , .."
"-', I
.
warensoff ShikokU(J:iig 8). During. spring,tO
summer, the estimated spawning areas gradUaJly
shifted northW!lfds along. the .,continen!1d shel,,'fl.
Of'the JapanSea and. Pacific Ocean. In. 'fiill;'
the areas occurred arolIDcl., the, Tsushima. Strait
andNoro 'Peninsll1a; limited . spaWtJing could. al!lO
haVe occurred along the coast of northern JajJ!ll,.'
These results suggest that the main spa\\IDng,
gt'O\!l1ds occurred in the Tsushirna Strait in fiiIJ,
and the East China Sea in winrer,asreported
by Murata (1989; 1990). Spawning sites ofthe three
grDupSJ1la}'seasonaIly shift and overlap in
soutliwesteni 'Japan Sea to the East China Sea,
However, possible. spawning sites along Central :i.hd
northerrl Japan are ,n;stricted due to the ~'Y
corttiJ:)eI)talshelf
and low ~,tbat
occurduring Winter to spring. The seasona1 shifJs in
infened spawning sites based on •tCinpetalures
cpanges at 5Q mdepthand therangeof~tali'
Shelf aro1Jl1d Japan are similar to the chariges I iIi I, •
~arvaldistri1;nrtion
(Mufam, 1989).
,
.':
I
and
.
,'
,the:
,
zone
li,ll:
posril,re"~,
".'~"
POI
Fig.7 Relationship between POI and CPUE 'inthe
next year in the Sea of Japan using the same
data from Figs. 3 and 4 during 1975-96.
.
and CPUE in the next year (Fig. 7).
These results suggests thatthecailih 'increases
since the late 1980s may reflect a favorable stockrecruitment relationship Stock siieOfthe Wintet"
spa\VIlibg gtoUp was the largest Of the three groups'
throUg1i' the l~ie 1960s, bLitthe'fiill-spaWriing group
has bclt!ri theJargest sfuee'ilie I 970s(Murat:\, 1989).
ThePiilserit .re'sllltS suggeSt that the recent stock
incre'asehlts6ccun'edin both ofthe'wfurer-andthe
fal1-~' !!roup~and 'thatspaWJ1;ngsites have
expariiled
'oVerlapped from offshOre' Of the
sout):lweStein Sea ofJapanin fal1to'the'EilSt China
Sea" U\.' ~er. 'Thus "i/e' deci£! 'to d8riJy the '
~. c!kJg~~ pC' ;paWnilig I'sites I tlifutighout the
yeaf,.. . .
O+-~-r~--~~-r~--~~~
o
10 20 30 40 50 80 70 80 9'0 faD
' I , ".
."
The ~~rmiifd "spawrung rireriSfot 'tlfe Wiritei-'
spa~1ing: ~occUn-edMdelyl .'. wOng ··tJW
contin~" shelf.8Hd sloPe ofthti'Elist' China
Sea fibir; Kytilibu,to Taiwan,arili Srmill i!pam,mg
areas'&cUireQ in the 'weirtem· and the 'soUthliVesterit
~dt KYrishu'lIrui pacific" 'toils\aJ .
'
coasiill'
'
"
"
4:
j;j
i-October
I
'n'
-'OG"
'December;
Fig. 8 EstilIll!li:d .moothlyspawninti· sites· of Todarodes
pacificus armmd
based on meiin telllpellilure lit 50-m
J#an
depth duringJ900~j912 (JODC, .1978). StiPPled areas
indicate sites. 0(. optimum 'temperature fdr embtyonic
development (IH3°q above tlleCorttinentaFsbelf·and
slope surrounded by) OO~5(jO In isobathS:
Fig. 9 Comparison 'of seasonal shifts. of infemxl !'Jlliwning
silesbelween.Octobel1 to April in 1985/86 (cold years) and
1990191 (wann yIllirs), ,based on GIS data.
,.t
Recent changes in t/le possible;SpllWPling sites ~
011 GIS d o t a ,
We Used GIS dam I to examine, the reIatioDShip
between the recent ~and armual changtis of .
the optimum spawning grounds and the shift fuxn
a ooldregimeto a warm regitnc,that~iO. the
latel980s by .rompl!fing1l1e sea;;qna1 and ~ual
shiflS ofestimatedSjll}wning grounds during 1984 to
1995. Kiyofuji .Il( a! (1998) oon:Ciude<i
tilepossible spawning mounds,~ year-wUruI ,in
TsushimaStraitandn!llll'the Goto ~limds inJ989-91,
which was the, beginning of the warm ~"~
fallparalarval~andarmua,l~h irl~.
From OctobertoDfC\lIJlber, the WSSible spawning
grounds did not vary geographically between
!hiii:
5
1985186 sod 1990191 '(Fig. 9). During J,!!lUary sod
April in 1991, infurred spawning sitesoccmred in
waters ftom the Tsushima Strait to the East China
Sea along the oontiJ1ental shelf; but not in Tsushima
Strait in 1986. We !hen compared the interannual
variability of possible spawning . sites in .February
during 1984-94 (Fig. 10), which is the peak of
spawnirig month 'of thewinter"Sp8W1l.inggroup
(Murata, 1989).Jn February ofl989, 1990, 1991 and
1994, the inferred spawning sites occmred widely
ftom the Tsushima Strait to the East China Sea
Spawning sites'in Februaryofl984, 1986; 1988 and
in 1992 occmred above the continental shelf in the
East China Sea sod southweSt ofKyushu.
These results suggest that winter spawning
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·
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Seas from bottom trawl surveys in winter of 1991
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Japanese]
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