von Dewitz, Burkhard (2015) FS ALKOR Cruise Summary Report AL457. . GEOMAR, Kiel, Germany, 4 pp.

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Abstract

16.05.2015 - 30.05.2015
Physical, chemical, biological research and fishery oceanography

This multidisciplinary cruise extended a long-term data series on (eco-)system composition and functioning of the Baltic Sea, with a focus on the deeper basins. The series has been collected in similar form since 1986. A key characteristic of the cruise is the integration of oceanographic and biological information to enhance understanding of environmental and (fish) population fluctuations, and evolutionary processes in this system. The resulting datasets and samples are an essential component of the international EU project BONUS BIO-C3 coordinated by GEOMAR. The spatial focus lay on the Bornholm Basin (the most important spawning area of Baltic cod), but also included the Western Baltic Sea, Arkona and Gotland Basin, Gdansk Deep, and Stolpe Trench.

Specific investigations included a detailed hydrographic survey (oxygen, salinity, temperature) of the Bornholm Basin, plankton surveys (zoo- and ichthyplankton, with the goal to determine the composition and the abundance and vertical and horizontal distribution of species, and to take samples for later measurements of nutritional condition), and pelagic fishery hauls for clupeid and gadoid fish. The latter served to determine stock structure, gonadal maturation, stomach contents, and egg production of sprat and cod, and to sample tissue for later genetic analyses and otoliths for age estimatation of individual cod. The abundance and distribution of fish species in the investigated area was also assessed with hydroacoustic methods.

Additional cruise components were: (i) cod gonad and liver sampling for the determination of lipid content and histological studies; (ii) vertically resolved phytoplankton and zooplankton sampling for studies of plankton phenology.

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