This paper not to be cited without prior reference %o the authors.
Minisymposium
On the geographical distribution of Arctic Cod in relation to the distribution of bottom temperatures in the Barents Sea, 1977-1984.
Odd Nakken and Askjell Raknes Institute of Marine Research
P.O.Box 1870 5011 Nordnes-Bergen
Norway
ABSTRACT
The results from acoustic-trawl surveys in January-March were analysed tagether with observations of bottom temperatures at the same cruises. Distributions of fish abundance for each age group of csd on temperature were established. The analysis
showed that the older age groups, fish aged 6 and 7 years, were consistently found in warmer waters, i.e. further to the west, than the younger fish, aged 1-3 years, The variations from year to year in bottom temperatures of the distributian areas appear- ed to be largest for the youngest fish, the l year olds, and
considerably larger than the carresponding temperature variations in tws fixed reference areas. The mean lengths at age 4, 5 and 6 years were observed to increase significantly for the year- classes 1975-1980 and this increased growth coincided with an increase in mean temperature of the distribution areas of the fish.
The stock of Arctic esd is the most important comereiaP fish stock in the Barents Sea. The speeimens reach maturity at an age of 6-9 yeass and the mature psstlon of the stsck undertakes yearly spawning migratisns southward a%sng the Norwegian coast in February-April, The bmature es9 I s feeding %n the Barents Sea and %n the Bear Esland-Svalbard area thrsughout the year and makes seasonal east-west and north-south migrations (Fig, b), I n addåtion to the seasonal displacements of the concentrations
I a k s temperature related dåsplacehents have been reported both
l
on a small and large time and space scale (Eggvin 6938, Lee
l 1 9 5 2 , Hylen et al.
- -
1961, Konstantinov 1967, 1969 and Mukkin 7-1979). The main conclusion arrived at from the studie~ referred to is: When temperatures are %ow in the Barents Sea the eoncen- tratfsns of young csd are %ound lurther west and south tkan i n periods wfth high sea temperatures.
1
In most of $he $nves$igatisns referred to absve, the vslumes of the comersia% catehes were used as a measure of cod csncen-
tratåons and abundance, and the displacements sf the main
~
fishing areas were related to variations in temperature.
I Midttun et al. 1981 made a different apprsach. They studied the l geographfeal dåstribution of eack age group as observed by
combined aeoustie-trawllng surveys and related the displaee- ments a% khe distribution areas of the fish to variations in
sea temperature for the period 1977-1981. The main results of their investigations appear from Fig. 2. The Barents Sea was diirided into three sectors
-
West of 30%, between%oo
and3 4 ' ~ and east of 3 4 " ~
"
and Fiq. 2 shows how the varisus age groups were distributed wåth respect to these sectors.Tws prsnounced features åre clearly ådentified in the
figure: A systematfe westward displaeement of fish as it grows older and
a
displacement of all aqe groups which follows the variation of the annua1 mean temperature in the Kola section.Midttun
- -
et al. (19811 als0 attexupted to quantify the apparent relation between cod distribution and sea temperatures and showed that a drop in annual mean temperature in the Kola section from~ O C to %C' coincided with a transfer of fish from the middle and
eastern sectors to the western one of about 30% of the 3-5 year olds. The authors conclusion of the study was: "The results show a wsstward displacernent of cod with increasing age of the fish and with decreasing water temperature in the Barents Sea.
Consequently, an extrerne westerly distribution of the biornass of young cod occurs when both the sea temperatures are low and
v . -
the age of the predominant yearclass (es) of immature cod is -.',. :. % ,
:
relatively hlgh, which is the situation experieneed during the period 1979-1981".
In the Rarewts Sea the temperature decreases from west towards east. Thus, the punger age groups which are
situated in the eastern garts inhabit waters o% bower ternpera-?L tures than the older ones. In order to be able to throw some more light on the possible cod-temperature relationship one
should therefore know the ternperature conditions within the actual distribution area of the various age groups, In the present paper we have computed the average temperatures in the distribution areas of each age group in February and compared these with similar values in two fixed reference localities for the period 1977-1984. FTe have also studied the developnent of the mean lengths of the fish throughout the same period.
MATERIAL AND METHODS
The material has been coflected on yearly research vessel cruises lasting from late January to the beginning of March
(Dalen
- -
et al. 1983). Courselines and station netwark (Fig. 31 have been approximately the same every year, 19.77-1984, Each year since 1981 two commercial trawlers have been hirsd to cooperate with the research vescel in order to increase the number of fish samples (Fig. 3 1.The acoustkc and hiolsgical data
A
A comprehensive description of the sampling and processing procedures is given by Dalen and Nakken 1983, The results of the cruisec are given in reports to the annual meetings of
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~ U T T A & ? I & * 3 9 ~ 3 q s d r q s ayq buoqe aauqxmq9 oysa syg A ~ s n o n u % q n s s axnsesm smeqeAs aoqsnoap ayaThe calculatisn of the mean temperature for each age group were made in the following way, For squares falling within the same one degree fnterval of temperature the number of fish were added together to give a total number of fish of a given age. This was done for all the temperature intervals, resulting in a distribution of fish numbers on temperature for each age group. Finally, the mean values and standard deviations of these distributions were calculated using the number of fish as weights in the calculation.
The-:geogtaphical distribution of temperature and fish The series of distribution maps of bottom temperatures in Fig. 4 demonstrate the large temperature variations which occurred in the area throughout the period of investigation.
An extreme westward displacement of the isotherms took place from 1977 t~ 1979, and the bottom temperatures in the entire area to the east of 34'-35'~ dropped to below 0 . ~ O C in 1979.
From 1979 to 1980 the isotherms were displaced slightly eastward again and this distribution was more or less main- tained throughout the period 1980-1982, but in 1983 a pro- nounced eastwcard c3ispLacemen.t had taken place,:hhe~.~bbserved distribution being similar to that in 1977. In 1984 the
bottom temperatures were considerably lower than in 1983 but higher than those experienced throughout the period
1979-1982.
The geographical distributions of young cod as recorded by the acoustic integration systems are shown in Fig. 5. From 1978 to 1979 the distribution area of the fish. decreased considerably, Xn 1977 and 1978 quite large amounts of fish were recorded to the east of 3 5 O ~ and to the north of 7 2 O ~ while in 1979, and particularlv in 1980, the distributions were limited to a rather narrow area off the Norwegian coast.
In the entire period 1979-1983 fish was scarce in the
eastern parts of the sea and more offshore north of Norway
bu$ $n 1984 the distribution was more similar %o the distri- butionc exgerienced in P947 and 1978. Vfien camparing the two
s e t s of maps (Figs 4 and 5) it seems that the dfsplacernents
of the two distråbutfons, bottom temperature and fish coincided, b u t with a time lag. The coldest years were 1979 and 198%
while the most westerly fåsh distributions wese observed in b980 and 1983, Mukhån ( 1 9 7 5 ) e x m i n e d how the catek rates in various areas of the Barents Sea varied wikh the mean tempera- tures in the Kola sectian, He abserved a rather high eorre- lation betwsen temperatures in the secsnd half of the year and the catch rates in the eastern areas during the following spring. Midttun - - et a$. (1981) using the same data on fish as we have used, indisated a similar time lag (Fig. % ] * Since eomplete maps of fisk distribution are avaibable only for the winter season (February) it is impossible to deseribe the apparent time lag more accura%e%y.
It shouåd be noted that the distribution maps in Fig, 5 include a l l age gretaps of youraeg eod
-
and haddsck as w e b % - In order to study the distributhon of the varLous age groups in relation to bottorn temperatures the procedure deseribed in the preceeding chapter was adopted. The results of the computations are skown in Table b.Table L. shsws hsw the fish in eaeh age grsup was distri- buted in percent in relation to the bottsm temperatures. The mean values and standard deviations of the distributions are afso presented as we%a as the acoustic estimates. {The
estimates for 1980 are tos Isw due to a calibration error of the integration system, bu% tkis error wi11 not affect
the relative dbstributions of fisk in rebation to temperaturel, By exarnination of table 1, it ås seen that the older fiches inhabited w a m e r waters than the young ones (Midttun
- -
e% a%.198%). It a l s ~ appears %hat the bsttom temperatures in the waters inhabited by each of the age groups varied considerably throughout the investigation period, the variations behng larqer for the younger fish than for the older, In Fig.6 these varia- tisns can be compared witk the bottom temperature variationa
in twa fixed reference areas. The two sets of data seem to vary in the same way for the older fish, age group 4 and older ones, with exception of the 1978 observations which seem to low.
In 1978 the western areas of the fish distribution were not covered satisfactorily (Fig.4) and consequently the calculated mean values for the older age groups, 4
-
8+, should be expected to be too IOW. The temperatures representing the areas inhabited by the yaunger fish, age groups 1-
3, in 1978, are believed to be representative, as these age groups were distributed in the eastern parts of the sea.From Fåg.6 it appeass that the two years showing the eastern- most dåstribution of the younger age groups, were 1978 and
i-
1984. In 1978 all the three young fish age groups, 1-3 were inhabiting waters of low bottom temperatures in the eastern Barents Sea whereas in 1984 only the one year olds showed an extreme eastern and low temperature distribution. In the period in between, 3979-1983, the youngest fish, age group 1, were observed in areas further mest with temperatures closer to those experienced for the older fish. In this
connection it shsuld be remembered that the winter distribution of the 1 year old fish probably to a large extent depends on the drift patterns of the larvae and O-group stages when
the fish is distributed in the upper 75 m of.the water column The O-grsup fish migrates to the bottom layer in late~autumn
i and hence the distribution of the l-group in February might reflect the areas of bottom settling of the O-group.
Growth and temperature
In Fig. 7 the mean lengths of the various agegroups are given, A significant and steady increase of mean lengths seem to have taken place during the observation period for all yearclasses after the 1975 yearclass.This is clearly seen in Fig. 8 where
the mean lengtl~s are plotted against the mean winter temperatures- The 1976 yearclass which during its second, third and fourth
year of Iife inhabited rather cold waters had a mean length as 4 year olds of about 42 cm while the 1980 yearclass inhabiting warmer watermasses were 49 cm as 4 year olds. The tendency of
increased mean lengths wåth increasing water temperature
seems quåte elear a%ss f o r the 5 and 6 year old fish. Wowever, it also appears %som Fig. 8 that the lengths varied with
the strenqths of the yearclasses, the grow%h increasing with decreasing abundanee, the $975-yeare%asc being the most
abundant a%so shawfng the cmallest growth, while the weak
%98Q yearelass grew faster.
The increesed grawth of the cod m i g h t kave lead to maturation of the fish a$ a younger age, Hylen and Nakken (1982, 1983 and 1984) have shswn %hat the percentage of 5-8 year old fish in the s p a m i n g staek in later years, have increased significantly as sompared to previous periods (Psnsmarenko et al. %988). Fige 6 shows that the yearclasses for whieh
- -
this earlier maturatfon has oecured, 1975-1996-1977-1978, kave inhabiked gradually wamer waters and have shown a consistently increasing growth and a decreasing abundance.
The coupliag between the l a r g e enviramental ehanges and
%Re variaue pspu%a%ion parameters (dictribytidn area, abuwdance, growth and ma%urity) for the Arctic Cod % a pro- bably far more complex khan the simple length-temperature relationahig indicated in Fig'. 8, wltabek was experieasceil during the inves%%gatfan peråad, The develapment of the
abundant 1983-yearcåass w i l l in t K s cantext be an tmportant sub-ject of observation during the eombng years.
Ref erences
Dalen, J., Hylen, A., Nakken, O., Randa, K, and Smedstad, O.M, 1983. Preliminary report of the Norwegian investi- gatisns on yourig eod and hcaCld~ck. in the Barents S e s i during the winter %983., -Coun. Meet, %n$, Ceun- _ _ - _ m _ Explsr. Sea. v -1983 (G:lEiE: 1-22 ( M i g ~ i e a . 1
Dalen, J. and Nakken, O. 19-83., On the application of the echs integration method. Coura. Meet, Prat, Coun.
Explor, Sea. 1983 (B:191: 1-30 (Mirneo-1
Eggvin, Trekk f r a Mord-Norges o c e a n o g r a f i s e t t i sammenheng med t o r s k e f i s k e t , F i s k . Dir. S k r . S e r . HavUnders.,
-
5 ( 7 ) : 33-46.Hylen, A . , M i d t t u n , L. og S æ t e r s d a l , G . 1961, Torskeunder- s d k e l s e n e i L o f o t e n og i B a r e n t s h a v e t 1960.
F i s k e t s Gang
-
4 7 ( 5 ) : 1 0 1 - 1 1 4 , 16 f i g .Hylen, A. and Nakken, 0. 1982. S t o c k s i z e o f North-East A r c t i c cod. E s t i m a t e d from A c o u s t i c s u r v e y d a t a 1982. Coun
P
Meet. En%. Coua. E x p l o r . S e a , 1982
- -
/G 61: 1-12.Hylen, A . and Nakken, 0. 1983. S t o c k s i z e o f North-East A r c t i c c o d , e s t i m a t e s from s u r v e y d a t a 1982/1983,
- -
Coun, Meet, I n t . Coun. E x p l o r .E,
1983/G 57: 1 - 1 4 . ( M i m e ~ , )- -
Hylen, A. and Nakken, O. 1983. S t o c k s i z e o f North-East A r c t i c cod, e s t i m a t e s from s u r v e y d a t a 1983/1984.
Coun. Meet. I n t . Coun, E x p l o r , S e a 1984/G 45:l-13.
- - - r -
( M i m e o
.
)K o n s t a n t i n o v , K.G. 1967. F o r e c a s t i n g o f t h e d i s t r i b u t i o n a f fish c o n c e n t r a t i o n s in. t h e B a r e n t s Sea a c c o r d i n q t o t h e t e m p e r a t u r e f a c t o r , F i s h ,
- - - -
R e s , B d , Can., T r a n s l a t i o n S e r i e s NO. b132- -
: 1-28.K o n s t a n t i n o v , K.G. 1969, E E f e c t o f n a t u r a l E a c t a r s and f i s h i n g on t h e abundance o f g r o u n d f i s h i n N o r t h e r n S e a s ,
Fish. R e s . Bd. Can., T r a n s l a t i o n S e r i e s No. 1559: 1-12.
- - - p
- -
- Lee, A . J . 1952, The i n f l u e n c e o f hydrography on t h e Bear I s l a n d cod f i s h e r y . Rapp. P.-v. - -Reun. Cons. E x p l o r . p
g.
3.31: 74-102.
--
Midttun, L., Makken, O. og Raknes, W. 1981, VarLasjsner i u%- bredelsen av torsk i B a r e n t s h a v e t i p e r i o d e n 1997-1981,
[Varieeåons %n %he geographisal distributian of cod in the B a r e n t s Sea in the perisd 1977-l983.1. Fisken Hav,, 1981 (4): 1-16.
Mukhfn, A.I. 1979. D$s$sbbution o f the dernessal fishes in the Csutkern B a r e n t s Sea depending on t h e h e a t csntent of water masses. Csun. bfeet. Int. Coun. E-plar. PSea, 1999 -
(G %$)-: %-$, 2 figs.
Psnomarenko, V.P., Pancsmarenko,I.Ya, and Yaraguåa, N,A. 1980, G r a w t h and maturation of the Lofaten-Barente; Sea b o d , Coun. Meet. Int. Coun. Explor,
E,
%988[~ 2 5 : 1-28,- - p -
(Mimeg. %
Table 1. The abundance of cod i n r e l a t i o n t o temperature. The t a b l e shows t h e frequency d i s t r i b u t i o n ( p e r c e n t of numbers) of f i s h on bottom
temperatures f o r each age group. Mean v a l u e s ( t O C ) , s t a n d a r d d e v i a t i o n a
( 9 ) and a c o u s t i c e s t i m a t e s a r e given.
Temperature O C
-1.5 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 Number
( m i l l i o n ) Year Age
In the Barents Sea and the seasonal movements of the stock.
A and B a r e used a s reference l o c a l i t i e s f o r temperature.
- - - p
18" 20' 22O %Le 2ee 28O 380 32' 3L0 36' 38'
Fig. 2. The d l s t r i b u t i o n (per cent of numbers) of various age groups of cod in the Barents Sea i n February
-
March 197'7-
1951. Right:annua1 means of temperature i n O
-
200 m depth in the Kola cection, f o r the ealendar year prior t o the biological ~ b s e r v a t i o n s .te* 8 m. zr a' 16. zc iff u i o i s . w L@ r2' uo '6'
" "
" ' " ' I
Fig. 3. Course l i n e s and s t a t i o n s i n t h e Barents Sea i n February
-
March1984. Upper: STD-sonde s t a t i o n s
,
Midd1 e: Trawl s t a t i o n s worked by t h e research v e s s e l , O-
bottom t r a w l , A-
pelagic t r a w l ,Lower: Bottom trawl s t a t i o n s worked by two t r a w l e r s .
F i g * 4 * The temperature ( t % ] d i ' s t r i b u t i o n s a t t h e battom i n the Barents Sea i n February
-
March, 1977-
1984Fig. 5. The d i s t r i b u t i o n s o f echo abundance ( r e l a t i v e u n i t s ) o f cod and haddock i n t h e Barents Sea i n February
-
Yarch, 1977-
1984.Y E A R
F i g . 61 F4ean bottom temperatures i n February i n the d i s t r i b u t i o n areas of the various age groupa of cod compared with the bottom temperatures In the tv^^ reference areas A and B. Figures show
I age i n years.
2 0 I I I l
78 7 9 O O 81 8 2 83 8 b
Y E A R
F i g . 7. Mean lengths ( t o t a l length) of cod in the Barents Sea i n February. Ful l l i nes i n d i c a t e yearcl acses, dashed l i nes i ndi cate agegroups
.
5 YEARS
6,'
99 79
6 0 -1 I 1 I I I I I I I I I I 1
2 3 4
M E A N W I N T E R T E M P E R A T U R € C'( l
Fig. 8. Mean lengths at 4, 5 and 6 years of age plotted against the mean bottom temperatures in winter for the intervals 2-4, 3-5 and 4-6 years of age respectively. The figures below the points show yearclasses while those above the points show total number of fish in the yearclasses.
