Investigations on the distribution, occurrence and population structure of the roundnose grenadier (Coryphaenoides rupestris Gunnerus) in the coastal waters off Trøndelag, Norway

Roundnose grenadier (Coryphaenoides rupestris Gunnerus) were found in reasonable concentrations in four areas in Trøndelag, Norway. Inside the Trondheimsfjord, within a 400 to 500 m deep basin, about 340 kg was taken per half-hour-tow using a bottom prawn trawl. Around 500 kg per half-hour was taken in a 400-530 m deep basin in the Flatanger-Folla area, while catches above 3060 kg per half-hour were taken in a 350 m deep basin in the inner part of Foldenfjorden. Only few specimens were taken by use of pelagic trawl. In the deeper basins outside the near coastal areas, the catch rates were found too small for commercial fishing. The age of maturity was found to be about 8 and 10 years for males and females, respectively. Natural mortality rate was estimated to 0.1. The biomass in the four major areas was calculated to about 15 000 tonnes using echo-integrations combined with pelagic and bottom trawl sampling, and a sustainable yield of 2000 per year was suggested. The roundnose grenadier was only found in waters with temperatures above 7.0°C. The roundnose grenadier and the greater silver smelt (argentine), Argentina silus, were the two dominant fishes caught; the former accounted for 70% to 95% and the latter for 3% to 25% of the total catch