Icelandic groundfish survey data used to improve precision in stock assessments

The main objective was to improve the precision of stock assessments of demersal fish in Icelandic waters, with particular emphasis on cod. Sampling was carried out on approximately 600 stations in the Icelandic shelf area in March 1985 and again in March 1986. Stations were distributed in the survey area through a semi-randomly stratified process. A standardized bottom trawl was designed for the sampling and the data collected included length measurements, otolith samples and sex determination, as well as information on the environment and fishing gear. Results are presented for cod, haddock, saithe, redfish, catfish and long rough dab. The distributions of the different species indicate common nursery grounds in the northern part of the survey area. Age disaggregated stock indices of the gadoid species are well correlated with virtual population analysis (VPA) values. However, the total stock indices differ in their proportion of the VPA stock size. In comparison with previous surveys, the precision of stock indices has been increased markedly through this survey for all species except saithe. Skipper-selected stations (non-random) generally gave higher aggregated indices than random ones, although statistically significant differences are exceptional. -from Authors