Greenland Shark in the Barents Sea: Biology, Distribution and Bycatch

ICES CM 2010/E:26

Greenland shark in the Barents Sea: biology, distribution and bycatch

by Rusyaev S.M., Sokolov K.M. and Drevetnyak K.V. E-mail:[email protected]

Knipovich Polar Research Institute of Marine Fisheries and Oceanography (PINRO) 6 Knipovich Street, Murmansk, 183038 Russia

Introduction

Russian fishery for the Greenland shark (Somniosus microcephalus) was commenced in the Barents Sea in the late 19th century (Danilevskiy, 1862) and it was developed there in the early 20th century (Zhilinsky, 1923). Due to the diminishing of the demand for the liver fat of sharks that was caused by the commencement of the synthetic vitamin A production as well as since the coastal fishery was replaced by the oceanic one, the target fishery of the Greenland shark had been virtually ceased by 1961. In the absence of shark fishery, the research on distribution and abundance dynamics of a large predator may be important and urgent in the scope of ecosystem approach which is being developed in fishery science. The research on the Pacific Sleeper shark (Somniosus pacificus) showed that the abundance of representatives from that genus could significantly increase for a short time (Courtney, Sigler, 2002) and pose a threat for fisheries of the main commercial species (Orlov, 2003).

Materials and methods

Since there are no purposeful researches, the information on shark captures is limited and occasional, as a rule. The material for paper was the data on bycatches of Greenland shark by bottom and midwater gear in the Barents Sea obtained by research and fishing vessels: 233 captures from1981 to the present and 964 captures from January 1968 to August 2009, respectively. The relationship of temperature and distribution of the Greenland shark was analyzed on the basis of data on shark bycatches in bottom trawls of fishing and research vessels in 1981-2010 grouped by 5-year periods and the mean annual temperature in 150-200 m layer at Stations 3-7 of the Kola Section (Karsakov, 2007) for the chosen periods. To analyze the shark bycatches with the dynamics of the fishing fleet effort in the cod fishery (in fishing days) the data from the reports of the fishing

1 vessels in 1981-1992 (to the North of 73ºN; the greatest data array) were grouped by two months. During with 1979 for 2009 the measurement, identification of sex and the analysis of a feed of 75 fishes is executed.

Results In accordance with the data from the trawl survey in the Barents Sea, the Greenland shark occurs more often in the central and eastern sea areas where in the second half of a year the water temperature in the bottom layer usually varies from -1ºC to +3ºC. The importance of temperature in the distribution of the Greenland shark is also corroborated by the long-term data on bycatches of sharks in bottom trawls. When the temperature in the Barents Sea increased the bycatch of sharks decreased and on the contrary (Fig.1).

79°

60 n, sp 4,4 T, ºC 50 4,2 4 40 3,8 30 3,6 76° 20 3,4 10 3,2 0 3 81-85 86-90 91-95 96-00 01-05 06-10 Warm years Years 1991-1995 73° 2000-2010

Cold years 1981-1990 1996-2000 Kola section 70°

10° 15° 20° 25° 30° 35° 40° 45° 50° 55°

Fig.1 Total bycatch of the Greenland shark in the all TAS of the Barents Sea and mean annual water temperature (for five-year periods)in the 150-200 m layer at Station 3-7 of the Kola Section in 1981-2010

The occurrence of sharks (fishing vessels) correlates with the dynamics of fleet fishing effort in the cod fishery (Fig. 2). The time lag of the fishing effort peak and the bycatch of sharks may be explained by the reaction of sharks to the increase of discards and fishery waste.

2 effort, fishing days 20000 bycatch, sp. 200 18000 180 16000 160 14000 140 12000 120 10000 100 8000 80 6000 60 4000 40 2000 20 0 0 I-II III-IV V-VI VII-VIII IX-X XI-XII Months

Fig.2 Dynamics of fleet fishing effort in the cod fishery and bycatch of sharks (in specimens) in 1981-1992

In the specific composition of catches by bottom trawls, the portion of cod caught together with the Greenland shark accounts for, on the average, 78 % . In the shark diet cod (61%) and haddock (20 %) occurred most often (by the frequency of occurrence from the number of food detection cases). Significant relationships between the number of sharks in trawls (1-14 individuals) and the catch size (from 700 to 2500 kg), duration (30-220 min.), the haul rate (3.5±1.1 knots) have not been found. Fish size in catches by trawls varied from 104 to 480 cm (Fig. 3).

79°

16 14 12 10

p 8 s ,

n 6 4 76° 2 0 51-100 101-150 151-200 201-250 251-300 301-350 351-400 Length, ñm

73°

70°

10° 15° 20° 25° 30° 35° 40° 45° 50° 55°

Fig.3. Length composition from the trawl catches in the Barents Sea in 1981-2010 (red-to the north of 73º N; blue-to the south of 73º N)

3 The average size of fish was 220 cm with the mean weight of 140 kg. Among the fish caught by trawls the sex ratio was close to 1:1. The portion of mature fish (males from 300 cm, females from 420 cm; Yano, Stevens, Compagno, 2007) accounted for 35 %. Adult individuals (400-480 cm) were taken in the northwestern sea, at the Spitsbergen coast. The specimens with the least body length (less than 130 cm) were registered in the southwestern part of the sea. In our view, the occurrence of adult and young fish in the western sea shows that there is a reproductive area in the deep-water part of the Northeast Atlantic. This is also corroborated by the newborns found in the Jan-Mayen area (Kondyurin, Myagkov, 1983). Evidently, that the migrations of the Greenland shark group occurring in the Barents Sea are transboundary and the group is recruited from the adjacent areas. Diurnal dynamics of shark bycatch, obviously, depends on lighting or indicates vertical migrations of the species following fish aggregations. The analysis of data on catches (research vessels) showed that the bulk of sharks (62 %) were taken by bottom trawl in the time period from 6 a.m. to 6 p.m. (Fig. 4). The ratio of the day and night hauls was 1:1.1. The researches in the Canadian Arctic, where the telemetry depth sensors were used, indicated bottom way of life of the Greenland sharks in the daytime and migrations of the fish to surface at night (Stokesbury et al., 2005).

62 %

38 %

Fig.4. Distribution sharks of the diurnal bycatch in the bottom trawls (research vessel)

According to the data from hauling by the research vessels to the south of 73ºN in the Barents Sea, the Greenland shark catch by trawls is, on the average, 0.01 fish per a haul, to the north of 73ºN, it is 0.02 fish per a haul. With the current catch rate of the russian trawl fishery (taking into account the fishing effort by areas) it is assumed that about 1.2 thousand sharks with the total weight of not less than 140-150 t may are caught in the Barents Sea annually. The obtained calculated value of bycatch exceeds the annual catch of the Greenland shark, 50-75 t (Glebov, 1950), by the vessels of the Soviet trawl fleet in 1930-1941. It should be noticed that, in 1981-2000, the fishing effort was three-four times more than in the 1930-1940s .

Conclusion

Water temperature in the Barents Sea is an important factor for the increase in the shark abundance in the Barents Sea. Adult fish occur more often to the north of 73º N. The catches of young individuals are typical for the south-western sea. The vertical migrations of the Greenland shark are more pronounced in the night time. The bycatches of shark to some extent depend on the fishing effort (cold years). Possible bycatch of the Greenland shark by the Russian fleet in 1981-1990 was not less than 140-150 t .

References

Danilevskiy N.Y. Research on the state of fisheries in Russia. T.6. Sant- Petersburg. 1862.p.115. Zhilinskiy A.A. Fishery of shark in Murman. Petrozavodsk, 1925, p.14 . Courtney D.L., Sigler M.F. Trends in Area-Weighted CPUE of Pacific Sleeper Sharks Somniosus pacificus in the Northeast Pacific Ocean Determined from Sablefish Longline Surveys // Alaska Fishery Research Bulletin 12(2):292316 Orlov, A.M. 1999. The capture of especially large Pacific Greenland shark Somniosus pacificus (Squalidae) and some comments regarding its ecology in the northwestern part of the Pacific Ocean . Voprosy ikhtiologii, 1999, Volume 39, No.4, pp.558-563 (in Russian) Karsakov, A.L. 2007. Some results of summarizing hydrographic observations on the secular Kola Section for 1900-2005. Voprosy promyslovoj okeanologii. 2007, Issue 4, No.4, pp.136-158 (in Russian) Yano K., Stevens J.D., Compagno L.J.V. Distribution, reproduction and feeding of the Greenland shark Somniosus (Somniosus) microcephalus, with notes on

5 two other sleeper sharks, Somniosus (Somniosus) pacificus and Somniosus (Somniosus) antarcticus // Journal of Fish Biology. Volume 70, Issue 2, February 2007 p. 374. Kondyurin, V.V. And N.A.Myagkov. 1983. On the capture of a newborn Atlantic Greenland shark Somniosus microcephalus. Voprosy ikhtiologii. 1983. Vol.23, Issue 6, pp.1027-1028 (in Russian) Stokesbury M.J.W., Harvey-Clark C., Gallant J., Block B.A., Myers R.A. Movement and environmental preferences of Greenland sharks (Somniosus microcephalus) electronically tagged in the St. Lawrence Estuary, Canada // Marine Biology (2005) 148:159-165. Glebov, T.I. 1950. Annual reviews of coastal fishery in 1940, 1945-1949. PINRO. 1950. Murmansk (in Russian)