Ecological and population features of the beaked redfish Sebastes mentella (Scorpaenidae) in the Norwegian Sea, as revealed by analysis of the parasite fauna

The data of the investigations carried out on the basis of the results of the complete parasitological dissection of 669 beaked redfish Sebastes mentella caught at 100–600 m depths in ten areas of the bathial waters and pelagial zone of the Norwegian and Barents Seas in April – August 1996–2009 have been used. Based on the ecogeographical analysis of the parasite fauna, the occurrence of ectolesions and sexual maturity of Sebastes mentella from ten areas of the Norwegian Sea and adjacent waters, the conclusion on the recruitment of the fish concentrations by maturing individuals from the east and north in the bathyal waters (the Kopytov area) has been confirmed. The relationship of the beaked redfish concentrations in the pelagic zone and bathyal waters of the northern Norwegian Sea under the predominance of fish migration to the pelagic zone has been revealed. The composition of the parasite fauna shows greatly weakened relationship of the pelagic beaked redfish with near-bottom biocenoses. This indicates the fish occurrence in the Norwegian Sea pelagic waters during the most of the annual life cycle. The mass return of the fish from the pelagic waters to the bathyal zone in the Norwegian Sea as opposed to the North Atlantic population assumed by some explorers has been substantiated. It has been concluded that S. mentella aggregations in the Norwegian Sea pelagic waters represent a pelagic ecological group formed by early maturing fish. The near-bottom ecological group in the bathyal waters is composed by late maturing beaked redfish. Peculiarities of the parasite fauna and patterns of two phenes indicate the independent Norwegian-Barents Sea S. mentella population. However it has been found that great amounts of the beaked redfish from the Irminger Sea pelagic waters penetrate to the Norwegian Sea and mix with those ones from the Barents Sea when migrating to the northeast.