Norwegian investigations on Gonatus fabricii (Lichtenstein)

Abstract

By far the majority of the investigated Gonatus fabricii were caught as bycatch by pelagic trawls fishing in the upper 60 m. Sampling took place in April/May, June/July and August/September in the period 1978- 1991. The distribution of gonatus along the Norwegian coast south of 71 °N is clearly connected with Atlantic water with salinities above 35‰ . The highest concentrations are found in the area between Jan Mayen and Spitsbergen, i.e. in the Polar front area. The biomass of young gonatus in the Norwegian Sea constituted at least 1,5 mill tonnes in July 1994. Young gonatus begin to occur in the surface layers in May, and they seem to descend from the upper 60 m at a length of 50-60 mm. They might then live near the bottom or pelagically at depths of 200-600 m. Age and growth based on counts of primary growth rings should be treated with caution. At least in the eastem part of the Norwegian Sea prey items for gonatus are, in decreasing order of impoerance, amphipods, mainly Parathemisto spp., copepods, chaetognaths and euphausiids. Larger gonatus consume fry of Sebastes sp., Maurolicus miilleri, and small gonatus. Based on catch statistics are four spawning areas for gonatus suggested: West of Spitsbergen, off Vesterålen, off Møre and between Iceland and Jan Mayen. Hatching seems to take place throughout the year while the main spawning takes place from December to April. The growth rate of the statoliths decreases strongly in gonatus with DML 70-250 mm. The correlation between the rostral length of the gonatus beak and dorsal mantle length was calculated. Gonatus are important as food for the bottlenose whale. It has been recorded in stomachs of hooded seals, salmon, blue ling and Greenland halibut.