Patterns in the variations of copepod spring and summer abundance in the northeastern Norwegian Sea and the Barents Sea in cold and warm years during the 1980s and 1990s

Abstract

Abundance estimates of copepodite and adult Calanus finmarchicus, Pseudocalanus spp., Oithona atlantica, O. similis, and Oncea borealis have been obtained twice a year by PINRO for the northeastern Norwegian Sea and the Barents Sea for the 30-year period 1964–1994. The data cover the upper 50 m of the water column during spring or early summer (i.e. April–July) along five inshore–offshore transects at 67°30′N, 71°10′N, 72°50′N, from North Cape to Bear Island, and at Kola (33°30′E). Along the Kola transect, data are also available for three depth strata covering the entire water column. For this study, information is extracted from these data sets for eight years, three cold (1979, 1980, and 1981) and several intermediate and warm years (1983, 1984, 1989, 1991, 1992). Spatial distribution patterns and the demography of C. finmarchicus, the target species, are described for the study area. In the time window studied, changes in abundance of C. finmarchicus between years appear to be a large-scale phenomenon throughout the entire study area. Unlike the results of previous studies, no clear interannual relationship between water temperature and copepod abundance was found. A correspondence analysis including the smaller copepod forms, as well as temperature and salinity data, revealed a consistent regional difference in the demography of Calanus, with stages from CIV to adult more common in the southwest of the study area. Other copepod taxa dominated over the shelf in the northeast of the study area, perhaps related to differences in the physical environment and in habitat preference.