Plattform Platform	Reise-Nr. Cruise-No.	Zeitraum Period	Projekt Project	Arbeitsgebiet Working area
Alkor	AL556	14.05.2021 - 28.05.2021	DFG - TRANSLATIONAL EVOLUTIONARY RESEARC	Arkona Basin Mecklenburg Bight Gdansk Bight Bornholm Basin Baltic Sea Kiel Bight

Fahrtleiter Chief Scientist	Institut Institute	Auslaufhafen Port of departure	Einlaufhafen Port of return	Stationskarte Station map	Schiffsroute Trackchart
Reusch Thorsten	Helmholtz Centre for Ocean Research Kiel (GEOMAR)	Kiel	Kiel

Ziel der Reise / Objectives of Cruise:

The cruise AL556 "Baltic Cod" focused on the status of the Eastern Baltic cod stock, along with its prey field (zooplankton and pelagic fish prey) and hydrographic boundary conditions. The cruise extended a 35yr long-term data series on (eco-)system composition and functioning of the Baltic Sea, with a focus on the deeper basins. The resulting data- and sample sets supported ongoing projects in the Research Unit Marine Evolutionary Ecology at GEOMAR, in particular research within the DFG funded research training group (RTG) Translational Evolutionary Research /subproject "fisheries induced evolution", and several international collaborations. The spatial focus lay on the Bornholm Basin as most important spawning area of Baltic cod, but also covered parts of the pronounced salinity gradient of the Baltic Sea and included the Western Baltic Sea, Arkona Basin, Gdansk Deep, and Stolpe Trench. Specific investigations included a detailed hydrological survey (oxygen, salinity, temperature) of the cruise area, plankton surveys (zoo- and ichthyoplankton including jellyfish) to determine the composition and the abundance and vertical and horizontal distribution of species, and pelagic fishery hauls. The latter served to determine stock structure, gonadal maturation, stomach contents, and egg production of sprat and cod, and to sample tissue and otolith samples for individual-level genomic and ecological analyses of cod (Gadus morhua). The abundance and distribution of fishes in the cruise area was also assessed with hydroacoustic methods. Additional cruise components were: (i) cod gonad and liver sampling for fecundity and parasite studies (in collaboration with DTU Aqua, Kopenhagen, Denmark), (ii) sampling of blue green algae (genus Ostreococcus) and their viruses (collaboration with Dr. Luisa Listmann /University Hamburg). Due to the Covid 19-situation, AL556 could only run with 7 scientists berth which required us to substantially scale down the scientific program that was originally planned in the cruise application. All deployments of the Underwater Fish Observatory were cancelled. The cruise track was also shortened and the Gotland Basin was omitted. Preliminary results were that (i) cod nutritional condition is not significantly improving, while (ii) the size structure of the stock is still very critical, with most individuals (>98%) smaller than 50 cm in length and (iii) there is still no genetic mixing occurring among Eastern and Western Baltic cod gene pools which make the former an ideal test case to study genomic changes imposed by overharvesting.

Messungen / Measurements