Evaluation of the North-East Arctic saithe (Pollachius virens) acoustic survey
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Since 1985 an acoustic survey specially designed for saithe has annually been conducted in October-November by the Institute of Marine Research (IMR) on the Norwegian near coastal banks. Since 1992 the survey has covered the area from the Varangerfjord close to the Russian border and southwards to 62°N. Because of the schooling behaviour of the saithe, the survey has tried to cover known saithe grounds rather than sailing regular survey tracks. This paper describes and tries to make a critical evaluation of this research survey with regards to survey design, timing, cruise tracks, stratification, fishing ground selection, and attribution of species composition to acoustic data. Including the acoustic survey in the XSA-tuning will slightly improve the statistical diagnosis of the assessment, and will lead to a small reduction in fishing mortality and a 3-10% larger juvenile biomass the four most recent years. For the prediction, however, the consequences are bigger. The input fishing pattem to the prediction and the stock size in numbers will lead to 10-12% larger total biomass, up to 40% higher SSB and up to more than 80% larger catches in the short term when the survey is included in the XSA-tuning. Out of presently three XSA tuning series, the acoustic survey is the only fishery independent one, it both improves the reliability and has a significant impact on the results. It is therefore concluded that the survey should continue to be conducted annually at more or less the same time of the year.