Feeding patterns of dominating small pelagic fish in the Gulf of Riga, Baltic Sea

Abstract

We investigated the feeding of the dominant small pelagic fish—herring Clupea harengus membras and three-spined stickleback Gasterosteus aculeatus—in the Gulf of Riga (Baltic Sea) in the summers of 1999–2014. The share of empty stomachs, stomach fullness and taxonomic composition of fish diet was analysed. On average, large herring had the highest (19%) and small herring the lowest (6%) share of empty stomachs. Small (<1 mm) cladoceran Bosmina spp. was the most important prey for three-spined stickleback; preying on small (<1.5 mm) copepod Eurytemora affinis was the most efficient for small herring, while Bosmina spp. and E. affinis were equally important for the large herring, followed by the large (mean body length <2.0 mm) non-indigenous cladoceran Cercopagis pengoi. The number of prey taxa per stomach exhibited significant differences between the fish groups studied; the highest mean value was recorded for small herring and the lowest for three-spined stickleback (2.1 and 1.4 taxa, respectively). Although present, the fish group-specific spatial dynamics in feeding parameters (share of empty stomachs and feeding intensity) were weak compared to the observed interannual variation.