Aquatic Sciences Meeting, Albuquerque 2001

SS35 Biological and Ecological Responses to Low Oxygen in Constant and Fluctuating Environments (Spatial and Temporal Connections)

Date: Thursday, February 15, 2001, Time: 11:45:00 AM

Location: La Cienega

Tomkiewicz, J, , Institute of Marine Sciences , Kiel, Germany, jtomkiewicz@ifm.uni-kiel.de

Köster, F, W, Institute of Marine Sciences, Kiel, Germany, fkoester@ifm.uni-kiel.de

Neuenfeldt, S, , Danish Institute for Fisheries Research, Charlottenlund, Denmark, stn@dfu.min.dk

St. John, M, A, Danish Institute for Fisheries Research, Charlottenlund, Denmark, msj@dfu.min.dk

Hinrichsen, H, H, Institute of Marine Sciences, Kiel, Germany, hhinrichsen@ifm.uni-kiel.de

INFLUENCE OF OXYGEN CONDITIONS ON BALTIC COD SPATIAL DISTRIBUTION, SPAWNING HABITAT QUALITY AND EGG SURVIAL

Cod in the Baltic Sea exists in what is effectively a large stratified estuary. A permanent halocline forms an effective barrier to thermal convection. The oxygen condition in deeper waters mainly depends on frequency and intensity of inflows from the North Sea. Larger immature and adult cod forage in near bottom layers of the basin’s slopes, with the upper habitat limit defined by the halocline and the lower by oxygen saturation. Prior to spawning adult cod migrate into deeper areas of the basins, where they aggregate pelagically in saline water just below the halocline, but avoiding the oxygen depleted deep water. Their eggs reach neutral buoyancy at salinities of 11-15 PSU, i.e. they float within and below the halocline. These characteristics of Baltic cod are interpreted as an adaptation to the ambient low salinity and decreasing oxygen concentration with increasing depths. Utilizing research survey results, we demonstrate that the temporal variability of the volumes suitable as habitats and their hydrographic quality defines adult distribution patterns as well as egg survival and thus reproductive success of Baltic cod.

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Aquatic Sciences Meeting, Albuquerque 2001

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