Abundance, maturity and growth of the krill species Thysanoessa inermis and T. longicaudata the Barents Sea

Abstract

Thysanoessa inermis and T. longicaudata were the dominant krill species observed in the western and central Barents Sea between 1984 and 1992. Both species are typically boreal and subarctic, and were found in very low abundances in the Arctic water masses in the northern Barents Sea. High abundances (up to 100 to 200 ind. m(-2)) of T, inermis and T. longicaudata were found in the slope and adjoining deep waters south and south east of the Svalbard Bank. The main spawning times of T. inermis and T. longicaudata occurred in May-June and coincided with the spring phytoplankton bloom. T, inermis has a life span of 3 to 4 yr, while T. longicaudata can live up to 2 yr. Growth took place from late winter to autumn; a marked negative growth occurred during the late autumn and winter periods. The seasonally oscillating von Bertalanffy growth function gave a reasonably good fit to the growth curves. Coinciding with a strong reduction in the older capelin stock between 1984 and 1987, there was a subsequent increase in the abundance and biomass of T. inermis and T. longicaudata. A decrease in krill abundance and biomass was observed to correspond with the rapid recovery and growth of capelin stock up to 1991. This indicates a clear predator-prey interrelationship between planktivorous capelin and krill in the Barents Sea and suggests that the krill populations are to a large extent controlled by predation.