Ling, blue ling and tusk of the North-East Atlantic

The longline fisheries for ling (Molva molva) and tusk (Brosme brosme) have long traditions in Norway. Blue ling (Molva dipterygia) was always a by-catch in Norwegian slope waters but about 15 years ago this species became the target of a deep-water gill-net fishery. In recent years 5-10% of the firsthand value of Norwegian landings was attributed to these species. This report provides an overview of the fisheries and population biology of the three species, with emphasis on aspects of relevance to future stock assessments, based on results from Norwegian investigations in 1993-95 and literature reviews. The Norwegian fleets which target ling, tusk and blue ling are the high-seas autoline vessels which operate in waters to the west and north of the British Isles, in the North Sea and at the Faroes and Iceland, and longline and gill-net vessels of various sizes fishing in home waters along the Norwegian slope. Exploitation occurs in all parts of the distribution area of the species. It is still unclear whether separate stocks occur in different sub-areas. Spawning areas are wide-spread, also the distribution of eggs and larvae. Very little is known about migrations. The age and size structure of the catches in various fishing areas show only minor variation. New studies by electrophoresis of tissue enzymes and hemoglobins indicate that tusk from all areas sampled in the northeastern Atlantic belong to the same gene pool, where the results for ling and blue ling are inconclusive. Estimates of mortality show that exploitation rates are high, and catch per unit of effort (CPUE) analyses of ling and tusk based on both private and official logbooks from the longliners indicate a considerable decline in the population sizes since the 1970s. The catch per unit of effort may have declined by about 70%. Strategies and requirements for future monitoring by improved CPUE measures and age-based assessement models are discussed. NORSK SAMMENDRAG:Linefisket etter lange og brosme har lange tradisjoner i Norge. Blålange har alltid vært tatt som bifangst i fisket på Eggakanten, men for rundt 15 år siden startet et direkte garnfiske etter denne arten på dypt vann. De sener år har disse artene gitt 5-10% av førstehåndsverdien i norske landinger. Denne rapporten gir en oversikt over fisket og bestandsbiologien til disse tre artene med spesiell vekt på ting som er relevante for framtidige bestandsberegninger basert på resultat fra norske undersøkelser fra 1993-95 og relevant litteratur. Lange, brosme og blålange fiskes av den havgående autolineflåten i områdene vest og nord av de Britiske øyer, i Nordsjøen og ved Færøyane og Island. Dessuten av line- og garnbåter av forskjellig størrelse i hjemlige farvann langs Eggakanten.