MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12319

Diel vertical interactions between Atlantic cod Gadus morhua and sprat Sprattus sprattus in a stratified water column

Niels G. Andersen*, Bo Lundgren, Stefan Neuenfeldt, Jan E. Beyer

*Email: nga@aqua.dtu.dk

ABSTRACT: Information about species interactions at a spatial scale comparable to the perceptive abilities of the involved species is crucial for establishment of predictive, food consumption models at the population level. Nevertheless, such information is sparse due to methodological constraints. We studied the diel, vertical dynamics of species interactions between Atlantic cod Gadus morhua and its major clupeid prey sprat Sprattus sprattus at a location in the Bornholm Basin of the central Baltic Sea during late winter. This was accomplished by combining acoustic information on diel vertical fish distribution, time of ingestion of individual sprat estimated from cod stomach content data and observed vertical profiles of salinity, temperature and oxygen content. Cod predation took place primarily at dusk and dawn during ascent and descent of sprat associated with school dissolution and formation. Cod resided close to the bottom outside these temporal predation windows. Sprat schools were located at the same depth as cod in the light hours, whereas dispersed sprat at night were situated higher in the water column. These vertical dynamics could be explained by fitness optimization using bioenergetics and trade-offs between temperature, oxygen saturation of the water, and predation risk. The study thus forms a first step towards providing a mechanistic background for the predatory impact of cod at basin scale and beyond.