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

The winter distribution. seasonal vertical migration, and reproduction of C alanus finmarchicus in relation to water masses and chlorophyll tr were inv estigated 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 (500 0-30000 individuals m(-2)); by contrast, overwintering animals were usually scarce on the banks (<800-2000 individuals m(-2)). In the Iceland Basin, o verwintering 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 wa ters of similar to3-6 degreesC. During winter, most of the stock Ras presen t 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 s ome animals were found in Labrador Sea Water and Iceland-Scotland Ridge Ove rflow Water. Ascent to upper layers probably took place mainly during March and April, and continued until May. On the basis of the horizontal and ver tical 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). Maximu m individual rates of egg production (2-46 eggs female(-1) d(-1)) were obse rved in June. at the time of maximum phytoplankton biomass accumulation. Du ring 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 oc ean (similar to 600 eggs m(-2) d(-1)), whereas during June it was significa ntly higher in the oceanic region ( similar to 16 000 eggs m(-2) d(-1)) tha n 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 Int ernational Council For the Exploration of the Sea.