Duration of cruise:  2. bis 28. May 2024

Cruise area:  Baltic Sea

Purpose of the cruise:  Hydroacoustic survey of Baltic Sea sprat (BASS)

The main objective of this hydroacoustic survey is the annual assessment of small pelagic fish stocks, especially sprat, in the Baltic Sea. This survey is part of the international "Baltic Acoustic Spring Survey (BASS)". In addition to Germany, which covers the biggest part of the investigation area, Sweden, Estonia, Latvia, Lithuania and Poland are involved. The survey is coordinated by the International Council for the Exploration of the Sea (ICES) working group on Baltic International Fish Surveys (WGBIFS) and has been conducted annually since 2001. The survey delivers the most important fisheries-independent abundance index for the annual ICES stock assessment of Baltic sprat. The main tasks are:

• Hydroacoustic investigation of sprat, herring and cod in the Arkona Sea to Gotland Sea (ICES subdivisions 24 to 29).
• Fishing with pelagic trawl according to hydroacoustic requirements
• Biological measurement of catches (species, length composition, sex, maturity and age)
• Sampling of herring, sprat and cod (whole fish, otoliths, stomachs and gonads) for further laboratory studies at the Thünen Institute of Baltic Sea Fisheries.
• Hydrographic measurements with a CTD probe on predetermined stations and after each fishing station. In case of time constraints, only part of the hydrographic stations will be realized.
• Sampling of Ichthyoplankton (and mesozooplankton) in the Bornholm Basin (with a main focus on cod early life stages