The spatial relationship between pelagic fish species in the Barents Sea

Abstract

Capelin (Mallotus villosus) is a pelagic fish species with large interannual stock variations in the Barents Sea ecosystem. Together with polar cod (Boreogadus saida) and juvenile herring (Clupea harengus), it functions as an intermediate link that transfers energy from zooplankton to higher trophic levels. Capelin is a key prey and important as a food resource both to sea birds, sea mammals and other fish species. In late summer capelin perform a feeding migration from the central part of the Barents Sea and into Arctic water masses in the north and east. Earlier studies have shown that this migration is strongly density dependent. In years of high abundance, capelin has a more aggregated spatial distribution and migrate further compared to years of low abundance. In this study I investigate how this density dependent migration might affect the distribution and habitat selection of two competing species; polar cod and herring. I compare two years with contrasting abundance in capelin and investigate the spatial distribution of the three competing species with respect to oceanographic habitat. As predicted, capelin showed a shift in distribution into colder water masses in the year with high abundance. One of my hypotheses, which suggested increased spatial overlap with polar cod in years with high capelin abundance, was supported. On the other hand, no increase in overlap with herring was detected. Neither did I find any significant displacement of polar cod or herring that could be connected to capelin abundance. I suggest that the overlap between polar cod and capelin would increase the opportunity of ecological interactions, as they probably utilize many of the same resources. Possible interactions between capelin and its neighbouring pelagic species were connected to the competitive exclusion principle and ecological niche theories.