Distribution, egg production and growth of euphausiids in the vicinity of the Pribilof Islands, southeastern Bering Sea, August 2004

Spatial distribution, egg production and growth of the predominant euphausiids in the vicinity of the Pribilof Islands, Bering Sea, were studied during August 2004. Thysanoessa longipes was abundant in the oceanic water, aggregations of Thysanoessa inermis were observed both in the oceanic region and on the shelf near the Pribilofs, while Thysanoessa raschii was found near the islands. Euphausia pacifica and Thysanoessa spinifera occurred in much smaller quantities in the oceanic water. Euphausiid abundances on the middle shelf were several orders of magnitude lower than in the cold summer of 1999. The instantaneous growth rate (IGR) technique was applied to measure somatic growth. Juvenile T. inermis showed the most intensive growth (∼8% of dry body weight per day). In contrast, the somatic growth of mature specimens of both T. inermis and T. raschii was slow (<1% of dry body weight per day) suggesting the investment of resources into seasonal lipid deposition and reproduction. Egg release corresponded to an average of 1.1% of female dry body weight per day for T. raschii, indicating that enough resources were available for the animals to maintain reproductive activity. Our data suggest that the area near the Pribilofs, known for its high biological productivity, may provide a refuge for the shelf euphausiid population during warmer summers, when conditions on the shelf are unfavorable for their growth and reproduction.