Scientia Marina, Vol 67, No S1 (2003)

Capelin and herring as key species for the yield of north-east Arctic cod. Results from multispecies model runs


https://doi.org/10.3989/scimar.2003.67s1315

Johannes Hamre
Institute of Marine Research, Norway

Abstract


A conceptual temperature dependent multispecies model for stock interactions and harvesting of herring, capelin and cod in the Norwegian Sea-Barents Sea region has been developed. The concept presupposes that good recruitment of herring and cod is linked to warm ocean climate, which may occur with a frequency of 8 to 10 years. Strong herring year classes overlap the distribution of capelin larvae in 3-4 years causing mass mortality of the capelin fry, and depletion of the capelin stock. At the same time the herring is about to leave the Barents Sea, and lack of food in subsequent years reduces the potential yield of cod. Immature cod is the main predator on mature capelin and cannibalism is an important factor in reducing the abundance of juvenile cod when the capelin stock is rebuilding. The model is used in a study of the effects of different fishery management strategies on stocks and yield. Results show that optimum yield of cod is obtained by high fishing mortality on immature cod from the end of a warm period until the spawning stock of capelin is rebuilt. This fishing strategy will result in large fluctuation in the yearly cod catches but yield an optimum average biomass production of capelin and an optimum potential catch of cod. These results are in accordance with the catch history of cod. Prior to the 1970s, the effort of the fishery in the Barents Sea followed to a large extent the abundance of immature cod, resulting in large catches when the stock was abundant. The yearly catches varied from 0.4 to 1.3 million tonnes, but the average catch obtained in the two periods 1950-1958 and 1959-1969 are the highest on record. Moreover, the trawlers fished with small meshes in the cod end, discarding considerable quantities of the smallest fish. It is concluded that the interaction between climate and fish stocks, and fish stock interactions in the north east Atlantic region, are of fundamental importance to the dynamic of the processes which govern the fish production of the region.

Keywords


multispecies model; ecosystem; management; yield

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