Abundance and taxa composition of copepod nauplii over southeastern Bering Sea deep water spawning grounds of walleye pollock, Theragra chalcogramma

This project examined the abundance, taxa, stage and size of copepod nauplii available as prey for walleye pollock larvae in its deep water spawning grounds of the southeastern Bering Sea. Nauplii of the genera Oithona, Eucalanus, and Metridia were the most commonly encounted types while Pseudocalanus and Microcalanus were rare. There was marked interannual variation in the taxa and abundance of copepod nauplii coexisting with the pollock larvae. Stages I-IV of Oithona were present at 0 to 8 l(-1) at different depths. Individual stages III-VI of Metridia nauplii occurred at 0 to 6 l(-1), while Eucalanus nauplii were present at 0.1 to 9 l(-1), depending on stage and depth. Nauplii III-IV of the genera Pseudocalanus and III-VI Microcalanus were usually present at less than l l(-1). In 1992, 54 to 56% of the nauplii had body lengths of 150-350 mu m which are typical of those found in stomachs of first-feeding pollock larvae. In 1993 corresponding estimates were 64 to 68%. Copepod nauplii with body lengths of 150-350 mu m were generally present at 1 to 15 l(-1) but at one station their counts exceeded 20 l(-1).