THC EFFECT OF OCEANOGRAPIIIC CONDITIONS ON DISTRIBITIOII AND POPULATION DYNAMICS OF COKMERCIAL FISH STOCKS IN TtlE BARENTS SEA
Proceedings a t tiie third Soviet-Norwegian Symposium, klurmansk, 26-26 May 1986 E d i i r d by li. Loeiig. Iiiscituti of .\!srine Researih, Berge-, 1987.
DISTRIBUTION OF DEEP S E A SHRlMP (Pandalus borealis K r ~ y e r ) I N RELATION T 0 TEMPERATURE
!N
THE BARENTS S E AKjell Nedseaas and Per Bynes Institute of Marine Researeh
P,O,Box L870 - Nordnes P024 Bergen
Norway
In the years 1980 to P985 stratided raildom bottom trawl surveys were carried out on the shrimp fields in the Svalbard and Barents Sea regions. The objeetives of the cruises were to study the s t r u c t u r e of the shrimp stock and to estimate the abundance of shrimp. On each trawl station t h e bottom temperature was measured. Only the results from the surveys in the Barents Sea have throroughly been analysed with regard to temperature. In the investigated area the deep sea shrimp was abundant in areas with temperature between -l°C and 7 ' ~ . The deep sea shrimp appear to avoid cold water fronts of bottom water. The highest shrimp densities were found on the warm water side of the front.
INTRODUCTION
The deep sea shrimp (Pandalus borealis, KrØyer) is widely distributed in the boreal waters
.
The distribution is discontinuous circumboreal. Factors influeneing the distribution patterns are depth, temperature, salinity and sObstratumb The most common temperature range for P. borealis i s between 0 C alad 5 6 ( e . g , HJORT and RUUD 1938, B R Y A Z G ~ N 1967, RASMUSSEN 196'9). The deep sea shrimp has been reported found in waters with ternpteratures of -1. G O C (GORBUNOW 1934, INGRAKAM 1981) and upwards to 1 2 ' ~ (BJ0RK 1913). It has been reported that extended exposure to temperatures below-loe
is deleterious and may cause mass mortalities (IIORSTED and SMIDT 1956, and INGRAKAM 1981). SMIDT (1978) observed that ehanges in the distribution of age classes in Disko Bay, West Greenland,o o were likely caused by intrusion of warm bottom water ( 7 -8 C ) . ABERCROMBIE and JOHNSON ( l 9 4 1 ) describe the effects of temperature shock on shrimps, They (op.eit.) observed that termal death at low temperatures was a slow process, At low lethal temperatures the period of depression may last for hours or days, The aetivity of shrimps increases as the temperature increases. A t high lethal temperatures, between 10°6 and 1 5 ~ 6 , there may be no period of depression, and the shrimps may be subjeet to a sudden death.
MATERIAL A N D METHODS
A seralifled random sampllng scheme was uced on bottom trawl surveys with R I V '>Michael Sass" In the years P980 to E985 In the Barents Sea, The main objeetive w a s to estimate the abundanee and s t r u e t u r e of the deep sea shr-lmg
populations. Similar investigations were eondueted in the Spitsbergen waters in the years 1982 to 1985. The results from both these investigations are published as reports to the ICES Shellfish Committee (TAVARES and ØYNES 1980, TEIGSMARK and 0YNES 1981, TEIGSMARK and ØYNES 1982, TEIGSMARK and @YNES 1983, HYLEN, TVERANGER and OY'NES 1984, TVERANGER and
@YESES 1985). In this instance, only the results from the Barents Sea are presented,
The bottom temperature was measured at each trawP statisn in this psogram.
Hswever, during 1983 very few temperatures were measured because of some administrative and technleal problems. Also from 1984 there are few temperature re-lstrations avallable in time for this meeting because 0% an error in the computer system,
In the Basents Sea there are bottom temperatures from 93 trawl stations In 1981, 106 In 1982 and 116 in 1985, During 1984 the bottom temperature was measured, but only 1 4 can be h u n d in the gomputer system. However, we know tkat the bottom temperature was above O G at eaeh station (Loeng pers.
eomm
. 1 .
The investigations took plaee in the same area and during the same period of the year each year, namely AprilIMay.
RESULTS AND DISCUSSION
Table 1 shows the number of trawl stations in each half degree temperature interval and the mean amount by weig-ht of shrimps per 3 nautical miles (1 hour trawled). In 1981 the highes; density ofo deep sea shrimps were in waters of temperature between -0.9 C and -0.5 C (233 k g per 3 nautieal miles). In 1982 there were small differenees in eateh per hour in the different temperature intervals, and the maximumo catch (19g0kg per hour) were taken in an area with temperature between 2 - 1 G and 2 . 5 C . In the years 1984 and 1985 the bottom water was warmer on the shrimp fields than the years before.
T a b l e 1. Number of t r a w l s t a t i o n s i n d i f f e r e n t t e m p e r a t u r e regimes, and t h e mean amount by w e i g h t o f shrimp i n e a c h hau1 o f one h o u r d u r a t i o n ( k g / h ) .
YEAR
Temperature 1981 1982 1984 1985
NO. kg/h NO. kg/h NO. kg/h NO. kg/h
(D u> Ti- m N F O r
. r. r. r. P- P- r.
During these two years there were no temperatures below OOC on the shrimp fields. The hie;hest density of shrimps were found i n the coldest water between 0 and l C. Figs 1 and 2 show the position of trawl stations and the eatch per 3 nautieal miles on each station. The bottom isotherms are indicated based on the temperature measurements taken at each station. In 1981 the eastern part of the shrimp fields was overflown by cold water (Fig.
11,
The highest density of shrimps was at the border between the cold and warm bottom water. The same situagon occurreg during 198% on the Orimp field at the Tiddly Bank between N 7 2 00' to N73 00' and E32 00' to 36 00' LFig. 1).During the years 1984 and 1985 there were no temperatures below 0 6 . But for 1984 and 1985 the cold front was elose to the eastern shrimp fields (Fig, 2 )
I t looks lik% the shrimp do not prefer m y cpecific temperature interval between -0.5 C and 4 ' ~ but the deep sea shrimg seem to avoid fronts of cold bottom water. A t temperatures below -0 , t ) C, the catehes of shrimps decreased sharply. Other faetors like depth, c u r r e n t s , and predation from fish a r e probably more decisive factors for the density of shrimps.
REFERENCES
ABERCROMBIE ,M. and JOHNSON ,M. L . 1 9 4 1 . The effect of temperature on the respiratory movements and viability of a cold-water prawn, Pandalus borealis. Proc
.
Zool. Soc, Lond,
Ser. A . 111 : 87-99.B JØRK ,W. 1913. Bidrag til kannedomen om nordhafsrakans ( Pandalus borealis K r . ) utbredning och biologi i Kattegat oeh Skagerak. Svenska hydrogr. - biol. Komma Skr. No. 4 : 1-11.
BRYAZGIN,V.F. 1 9 6 7 . On the biology and distribution of Pandalus borealis in the offshore waters of the Barents Sea. Ann. Biol. 2 4 : 204.
GORBUNOW,G, 1934. Die Decapoden Crustaceen der nordischen Halfe des Karischen Meeres. Trans. Arctic. Inst. Vol IX. 1934.
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Shrimp ( Pandalus borealis) In the Barents Sea in April-May 1983 and In the Spitsbergen area in July 1983, Goun. Meet. i n t . Coun.
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shrimps (Pandalus borealis) i n the Barents Sea in May and in t h e Svalbard region in July-August 1985. Coun. Meet. int. Goun.
Explor, Sea, 1985 (K:56) r 1-25.
