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Probable Discards of Cod in the Barents Sea and Ajacent Waters During Russian Bottom Trawl

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unuftp.is Final Project 2002 PROBABLE DISCARDS OF COD IN THE BARENTS SEA AND AJACENT WATERS DURING RUSSIAN BOTTOM TRAWL Konstantin Sokolov Knipovich Polar Research Institute of Marine Fisheries and Oceanography (PINRO) Murmansk, Russia [email protected] Supervisor Dr. Palsson, O.K. Marine Research Institute Reykjavik, Iceland ABSTRACT Unaccounted discarding of small-sized fish is an important and acute problem in many fisheries because it affects the condition of stocks and reduces the reliability of fishery statistics. Such discards are regarded as a threat to intensively exploited species, such as the North-East Arctic cod (Gadus morhua morhua L.) which inhabits the Barents Sea and adjacent waters. In the present study an attempt is made to estimate of the quantity of small-sized cod discarded in the Russian bottom trawl fishery in 1996-2001. This work is based on cod length measurements onboard Russian commercial vessels in the period 1996-2001 and distributional features, such as density and size composition inferred from catch statistics. The calculated annual discards of small cod were estimated to be in the range of 3-80 million individuals. Discards appeared to be highest in 1998 and lowest in 1996 and 2001. This was found to be related to the abundance of cod recruits and the portion of total catch taken in the Eastern-Central part of the Barents Sea. The features of spatial and seasonal distribution of small-sized cod, the depth and duration of trawling and catch of cod influence the catch of small cod per unit of effort and, as a consequence, discards of such fish. Keywords: North-East Arctic cod, Barents Sea, bottom trawl fishery, small fish, Sokolov TABLE OF CONTENTS 1 INTRODUCTION ................................................................................................. 4 2 LITERATURE REVIEW ...................................................................................... 6 2.1 Methods to estimate discard ............................................................................ 6 3 MATERIAL AND METHODS ............................................................................. 8 4 RESULTS ............................................................................................................ 11 4.1 Spatial distribution of the Russian trawl catch 1999-2000 ........................... 11 4.2 Spatial distribution of small cod CPUE in 1999-2000 .................................. 12 4.3 Length distribution of cod in 1996-2001 ....................................................... 13 4.4 Changes in the total cod CPUE in 1996-2001............................................... 14 4.5 Changes in the small cod CPUE in 1996-2001 ............................................. 15 4.6 Relationship between CPUE of small cod and other factors ........................ 15 4.6.1 Relationship between CPUE of small cod and total CPUE ................... 15 4.6.2 Relationship between mean length and proportion of small cod ........... 15 4.6.3 Interrelationship between small cod CPUE and depth of hauling ......... 16 4.6.4 Interrelationship between small cod CPUE and duration of hauls ........ 16 4.7 Calculation of discards of small cod ............................................................. 17 5 DISCUSSION ...................................................................................................... 18 6 CONCLUSION .................................................................................................... 23 AKNOWLEDGEMENTS ............................................................................................ 24 LIST OF REFERENCES ............................................................................................. 25 APPENDIX .................................................................................................................. 28 UNU – Fisheries Training Programme 2 Sokolov LIST OF TABLES Table 1: Present bottom trawl fishery regulations in different areas of the Barents Sea. ........................................................................................................................................ 5 Table 2: Number of cod length measurements (thousands of fish) in 1996-2001 divided by national and international zones. .................................................................. 8 Table 3: Number of analysed bottom trawlings in 1999-2000, in different quarters of the year. .......................................................................................................................... 9 Table 4: Mean length of cod from commercial trawl catches in the different parts of the Barents Sea, divided by quarters, cm ..................................................................... 14 Table 5: Values of standard deviation of the mean length of cod from commercial trawl catches in the different parts of the Barents Sea, divided by quarters ................ 14 Table 6: Calculated number of discarded small cod in the Barents Sea and adjacent waters in 1996-2001 separated by areas (values of DL50 40 cm and 50 cm are used), thou. spec. .................................................................................................................... 17 Table 7: Calculated weight of discarded small cod in the Barents Sea and adjacent waters in 1996-2001 separated by areas (values of DL50 40 cm and 50 cm are used), thou. tonnes .................................................................................................................. 18 Table 8: Proportions of total catch and calculated total discards taken in Eastern- Central (EC) and Northern (N) parts of the Barents Sea in 1996-2001, % ................. 20 Table 9: Number of small cod discarded during Russian bottom trawl cod fishery in Barents Sea and adjacent waters in 1996-2001 according to different sources, mill. sp. ...................................................................................................................................... 21 Table 10: Number of discarded small cod in the Barents Sea and adjacent waters in 1996-2001 separated by areas (A. - Values for 1996-2000 are borrowed from Sokolov (2002), 2001 are calculated by old method; B. - Discards corresponds DL50=42 cm), thou. spec. .................................................................................................................... 22 UNU – Fisheries Training Programme 3 Sokolov 1 INTRODUCTION The cod (Gadus morhua L.) in the Barents Sea and its adjacent waters (partly including also the Norwegian, Greenland and White Seas) is managed as a separate stock, the North-East Arctic cod, here after referred to as cod. This fish is one of the dominant species in the fisheries of Norway and Russia. The bulk of the catch comes from the Barents Sea. At the turn of this century the stock of cod stood at about 1.1 million tonnes. Each year Russia and Norway agree on a quota for the following year. Annual total landings during the last decade totalled more than 400,000 tonnes. The stock is considered heavily exploited. According to the Arctic Fishery Working Group of the International Council for the Exploration of the Sea (ICES AFWG) “fishing mortality exceeded upper limit of the reference point of the fishing mortality throughout the 8 latest years” (1993-2001) (Anon. 2002). This may be interpreted as a sign of the stock being at a risk of collapse. The main regulatory tool, the cod quota, is given in tonnes and does not take into consideration the size of the fish. But there are also some accessory regulations aimed at protecting small-sized fish. There are regulations on minimum mesh size, minimum landing size as well as maximum allowable by-catch of undersized fish (Table 1). A specified area is temporarily closed to trawl fishing if the amount of undersized (less than minimum landing size) fish in the catches exceeds 15% by number. The minimum closure time is no less than one week. At present, no agreement exists between Russia and Norway for the reciprocal enforcement of these fishery regulations within any section of the Exclusive Economic Zones (EEZ) in the Barents Sea. There are two permissible mesh sizes and minimum landing sizes for cod used in different fishing areas (Table 1). From the 1950s until the early 1980s the minimum mesh size was increased several times to reduce catches of small fish. At the same time the minimum landing size was also increased. It was not until 1982 that unified rules for the cod fishery in the Barents Sea and adjacent waters for all countries were adopted (125 mm mesh size for bottom trawl and 42 cm minimum landing size). Since then Norway has unilaterally increased these limits for the Norwegian Economic Zone (NEZ) up to 135 mm and 47 cm respectively. Such existing differences make additional difficulties for protecting young fish. The main gear in the cod fishery are bottom trawl, long line, gill nets and hooks. The main gear in the Russian fishery is bottom trawl with a mesh size of 125 mm, equipped with a sorting grid device with an inter-bar distance of about 55 mm. Use of the sorting grid has been obligatory since 1998. About 90% of the annual Russian catch of cod is taken in bottom trawl. UNU – Fisheries Training Programme 4 Sokolov Table 1: Present bottom trawl fishery regulations in different areas of the Barents Sea. Area Regulations Bottom trawl minimum Minimum landing Allowable by-catch of mesh size, mm size for cod, cm undersized cod, % by number in catch* EEZ of RF 125* 42* 15 NEZ 135* 47* 15 Spitsbergen area 125** 42** 15 135*** 47***
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