The use of acoustic and bottom trawl surveys in the assessment of north-east arctic cod and haddock stocks [fra "a workshop on comparative biology, assessment and management of gadoids from the North Pacific and Atlantic oceans" 24-28 June, 1985 Seattle, Washington]

Abstract

In recent years survey results constitute the most important part of the material on which the stock assessments of North-east Arctic cod and haddock are based. Both acoustic surveys and bottom trawl surveys have been applied. The acoustic surveys were carried out in January-April each year, covering the young fish grounds of both species in the Barents Sea and the spawning grounds for cod along the Norwegian coast. The bottom trawl surveys covered the young fish grounds in the Barents Sea during the same period of time as the acoustic surveys. In addition the Svalbard region was surveyed by bottom trawling in September. Both the total and the spawning stocks of cod were assessed on the basis of survey data and estimates of number of fish at age were worked out. These results were further used together with catch data to select input fishing mortalities for virtual population analysis (VPA). Comparison between survey estimates in previous years and the back calculated figures from the VPA showed rather good agreement for age groups 5-7. The younger age groups were underestimated by the surveys whilc the older fish appeared to be overestimated. The underestimation of the young (small) fish is explained by lower availability, but the overestimation of the old cod is unexplained. In general, the surveys tend to give more consistent and reliable results for cod than for haddock.