Journal Article

Baltic cod recruitment – the impact of climate variability on key processes

Friedrich W. Köster, Christian Möllmann, Hans-Harald Hinrichsen, Kai Wieland, Jonna Tomkiewicz, Gerd Kraus, Rüdiger Voss, Andrei Makarchouk, Brian R. MacKenzie, Michael A. St. John, Dietrich Schnack, Norbert Rohlf, Tomasz Linkowski and Jan E. Beyer

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 62, issue 7, pages 1408-1425
Published in print January 2005 | ISSN: 1054-3139
Published online January 2005 | e-ISSN: 1095-9289 | DOI:
Baltic cod recruitment – the impact of climate variability on key processes

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  • Environmental Science
  • Marine and Estuarine Biology


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Large-scale climatic conditions prevailing over the central Baltic Sea resulted in declining salinity and oxygen concentrations in spawning areas of the eastern Baltic cod stock. These changes in hydrography reduced the reproductive success and, combined with high fishing pressure, caused a decline of the stock to the lowest level on record in the early 1990s. The present study aims at disentangling the interactions between reproductive effort and hydrographic forcing leading to variable recruitment. Based on identified key processes, stock dynamics is explained using updated environmental and life stage-specific abundance and production time-series. Declining salinities and oxygen concentrations caused high egg mortalities and indirectly increased egg predation by clupeid fish. Low recruitment, despite enhanced hydrographic conditions for egg survival in the mid-1990s, was due to food limitation for larvae, caused by the decline in the abundance of the copepod Pseudocalanus sp. The case of the eastern Baltic cod stock exemplifies the multitude effects climatic variability may have on a fish stock and underscores the importance of knowledge of these processes for understanding stock dynamics.

Keywords: eastern Baltic cod; egg survival; hydrography; larval prey availability; predation; recruitment

Journal Article.  9815 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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