Trends of Intraspecific Differentiation in the Beaked Redfish Sebastes mentella (Scorpaenidae) from the Atlantic Ocean and Adjacent Waters

Аннотация

Based on studies of the population structure of the beaked redfish Sebastes mentella in the Atlantic and Arctic oceans, a conclusion has been made about the existence of another, epigenetic, trend of its intraspecific differentiation, in addition to the population trend. Analysis of the vast array of our data and those available in literature, which were obtained by the methodological approaches accepted in population biology, made it possible to distinguish three isolated populations of beaked redfish: the North Atlantic, the Norwegian Barents Sea, and the Flemish Cap. The first two are subdivided into demersal and pelagic epigenetic groups that differ morphophysiologically and ecologically. One of the main factors of the epigenetic differentiation of beaked redfish is ontogenetic—individuals reach sexual maturity at different times. Based on the dynamics of the physiological condition of gonads, two groups of fish are identified: early maturing individuals that mainly inhabit the ocean pelagic zone and late-maturing fish that predominantly live in the near-bottom layer along the continental slope. In the first group, the mass maturation of redfish (50% of individuals) occurs at an FL of 29–33 cm and the age of 9–12 years; in the second group, it occurs at an FL of 35–43 cm and the age of 14–19 years. Another factor of epigenetic differentiation is biotopic; it is manifested as the association of discrete groups with different biotopes. Late-maturing redfish stay in the near-bottom layer of the continental and island slopes throughout the year, while early maturing individuals tend to live in the pelagic zone of open ocean areas. The biotopic epigenetic differentiation is closely related to the onset of return migrations from the nursery grounds of juveniles upon their reaching maturity. Juvenile beaked redfish stay in the nursery ground, which is located in the shelf and shallow coastal waters, up to the age 6–10 years. Early maturing individuals are the first to leave the juvenile grounds and move to the ocean pelagic waters. Late-maturing fish, as they grow during prolonged (up to 5–7 years) migration, are recruited to demersal aggregations in deep-sea areas on continental slopes. The complication of the species’ ecological structure due to the differentiation of epigenetic groups by biotopes has led to trophic specialization and weakening of the competitive interactions between them. Their habitation in different biotopes and the physiological polymorphism of redfish have not affected the unity of species populations. In the breeding season, there is no spatiotemporal isolation between the epigenetic groups, and the demersal and pelagic aggregations are replenished by common sources.