Norwegian combined acoustic and bottom trawl surveys for demersal fish in the Barents Sea during winter

A combined acoustic and bottom trawl survey for demersal fish in the Barents Sea has been conducted annually since 1981. The main aim is to map the spatia1 distribution and obtain indices of abundance (numbers at age) of cod, haddock, redfish and Greenland halibut. In 1 addition other biological information and CTD-data are collected. The survey covers an area of about 150,000 square nautical miles, and is carried out with 3 vessels and about 25 scientific staff for a period of 25-30 days. The abundance indices and weight at age data are used directly in the stock assessments in ICES. Stomach data of cod are together with other information used to estimate the Northeast Arctic cod stock's consumption of important prey species, e.g. capelin, cod and haddock. This information is further used in the assessment of these species. The tuning diagnostics indicate that the indices from the survey are the most reliable among the tuning data, and the assessments of Northeast Arctic cod and haddock are thus heavily dependent on the results of the survey. Since the management relies heavily on the assessments, the surveys can have a direct effect on the TAC7s. Several changes in survey methodology aiming at increased reliability of the results have been introduced. Some of these changes had large effects on the index level. The time series have therefore been adjusted in order to maintain and improve comparability. However, it is suggested that also in the adjusted series, most recent years indedstock ratios for cod are higher than those from the first 10 years period; a matter that should be taken into account in the stock assessments. l. CURRENT OBJECTIVES A combined acoustic and bottom trawl survey for demersal fish in the Barents Sea is conducted annually in January March by the Institute of Marine Research, Bergen (IMR). The main aim of the survey is to map the spatia1 distribution and obtain indices of abundance (numbers at age) for the most important commercially exploited derrnersal fish species in the Barents Sea. The target species are cod (Gadus morhua), haddock (Melanogrammus aeglefinus), golden redfish (Sebastes marinus), deep-sea redfish (S. mentella) and Greenland halibut (Reinhardtius hippoglossoides). The main objectives are: to obtain indices of abundance of the target species by length and age groups to estimate mean length and weight at age for cod and haddock to collect stomach samples of cod for studies of growth processes in cod and cod predation on important prey species, itself included (cannibalism) Data and results are used in the stock assessments in ICES and in several projects at M R , especially multispecies research and development of survey methodology.

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