Winter distribution, ontogenetic migration, and rates of egg production of Calanus finmarchicus southwest of Iceland

The winter distribution. seasonal vertical migration, and reproduction of Calanus finmarchicus in relation to water masses and chlorophyll tr were investigated southwest of Iceland between Nov ember 1996 and June 1997 as part of the TASC programme. During winter (November/December. January/February) overwintering C. finmarchicus were generally located beyond the shelf (5000-30000 individuals m(-2)); by contrast, overwintering animals were usually scarce on the banks (<800-2000 individuals m(-2)). In the Iceland Basin, overwintering C. finmarchicus resided mainly from <similar to>400 m depth to the bottom (>2000 m) at temperatures of similar to3-8 degreesC, whereas in the Irminger Basin the distribution was mainly similar to 200-1800 m in waters of similar to3-6 degreesC. During winter, most of the stock Ras present as C5 (84-86%), with a smaller proportion as C4 (12-14%) and females (1-2%). Overwintering animals resided mainly in water of Atlantic origin, but some animals were found in Labrador Sea Water and Iceland-Scotland Ridge Overflow Water. Ascent to upper layers probably took place mainly during March and April, and continued until May. On the basis of the horizontal and vertical distribution of overwintering animals and the general surface current pattern, the banks seem to be repopulated mainly from the south. By April the spring growth of the phytoplankton was about to begin on the banks, and C. finmarchicus had started to lay eggs (0-7 eggs female(-1) d(-1). Maximum individual rates of egg production (2-46 eggs female(-1) d(-1)) were observed in June. at the time of maximum phytoplankton biomass accumulation. During April, the population's average rate of egg production on the banks ( similar to 1000 eggs m(-2) d(-1)) was rather similar to that in the open ocean (similar to 600 eggs m(-2) d(-1)), whereas during June it was significantly higher in the oceanic region ( similar to 16 000 eggs m(-2) d(-1)) than in shelf waters (similar to 900 eggs m(-2) d(-1)), mainly because of the greater number of spawning females in the oceanic environment. (C) 2000 International Council For the Exploration of the Sea.