Production and standing stock of copepod nauplii, food items for larvae of the walleye pollock Theragra chalcogramma in the southeastern Bering Sea

Abstract

In late May 1981, during a 48 h study in the southeat Bering sea, each Pseudocalanus spp. female produced an average of 5.1 nauplii d-1 [day-1], resulting in a production of 25,757 nauplii m-2 d-1 by the Pseudocalanus spp. population. Similar calculations showed that the only other abundant copepod female at this station, Oithona spp., produced 1337 nauplii m-2 d -1. From these rates, it is calculated that a standing stock of 721,034 nauplii m-2 would result if there were no mortality. However, lower temperatures and lower concentrations of females were found prior to the study and a more realistic estimate of the potential stock is 495,328 nauplii m-2. The average observed stock of nauplii was 463,173 m-2, suggesting a mortality rate of 7-36% of the daily production with values in the lower part of this range being more probable. Pollock larvae, found at an average concentration of 6.3 m-2, ingested an average of 115 nauplii m-2 d-1 and therefore ingested only a small fraction of the daily naupliar production. Pollock larvae are insignificant as predators on copepod nauplii and overall naupliar mortality is low during the springtime in this area.