Zooplankton biomass in the reproductive area of the southern blue whiting (Micromesistius australis).

Abstract

Total and size-fractioned zooplankton biomass (larger and smaller than 5 mm) were analyzed over two cruises conducted in the late austral winter (September 1994 and 1995) in the area surrounding Malvinas Islands at the time that massive spawning of southern blue whiting was expected to take place. Biomass was rather uniformly distributed in the area and dominated by the fraction larger than 5 mm in which euphausiids and secondarily chaetognaths were dominating in terms of both weight and number. The smaller fraction was mostly made up of copepods. From the high occurrence of euphausiids and seasonal abundance of the several species of copepods normally present within the area it was hypothesised that the feeding requirements of juvenile and adult blue whiting as well as those of larvae and postlarvae may be met during the winter spawning season. The data were also examined in conjunction with the general pattern of zooplankton biomass occurring in autumn and spring in the Southern Patagonian shelf.