SISP 7 - Manual for the Baltic International Trawl Surveys (BITS)

This manual describes the coordinated survey design for Baltic international trawl surveys. Randomly stratified fishing-stations location is based on ICES subdivisions and their depth layers as strata to reflect the variability of the Baltic target species temporal-spatial distribution pattern. Besides the traditional Baltic International Trawl Survey (BITS-Q1) in February-March additional coordinated, routine survey (BITS-Q4) has been conducted in November, since 2001. The above-mentioned demersal trawl surveys are coordinated by the ICES WGBIFS. The surveys aimed to the monitoring of the spatial distribution and year-classes abundance of the demersal species, i.e. cod (Gadus morhua), flounder (Platichthys flesus) and other flatfish (plaice - Pleuronectes platessa, turbot - Scophthalmus maximus, dab - Limanda limanda, brill - Scophthalmus rhombus) and to some extent to clupeids (sprat - Sprattus sprattus and herring - Clupea harengus) in the Baltic Sea. WGBIFS agreed in 2009, that data of all analysed fish are uploaded to the ICES Data-base of Trawl Surveys (DATRAS) to support the Baltic ecosystem analyses, taking into consideration ICES subdivisions and rectangles codes.