Global distribution

All known Sebastes species are found in the marine environment. About 96 per cent of all Sebastes species are found in the North Pacific, inhabiting cold shelf or deeper waters. There is at least one species known to occur south of the Equator (S. capensis; Eschmeyer and Hureau, 1971; Andrew and Hecht, 1996). Distribution maps of the Sebastes species in the Northeast Atlantic are given in Whitehead, 1986. S. marinus and S. mentella are mainly found along the Norwegian coast up to Spitsbergen and in the western Barents Sea, in the northern North Sea, around Iceland and in the Irminger Sea, along the Greenland coast and along the North American coast southward to the Flemish Cape, the Grand Banks and the Gulf of St. Lawrence (e.g. Tåning, 1949; Templeman, 1959; Anon., 1992). S. mentella also forms an oceanic (pelagic) stock in the Irminger Sea with high concentrations along the Reykjanes Ridge (Magnússon, 1977; Pavlov et al., 1989b; Gerber, 1990; Magnússon and Magnússon, 1995). S. fasciatus is very localised in an area southwest of Iceland, off western Greenland, from the south-eastern coast of Labrador southward to the latitude of Long Island (S. fasciatus fasciatus) and in shallow water at Eastport, Maine (S. fasciatus kellyi)(Whitehead, 1986). S. viviparus is very common along the Norwegian and in the northern North Sea, west of Scotland and Ireland, in the Irish Sea, around Iceland and the Faroes, and sporadic off East Greenland (Whitehead, 1986).

The stock identification of S. mentella still remains difficult and complicates the management measures of these stocks (Anon., 1992). Besides the mentioned biochemical and morphometric studies, a further stock identification study uses the Cs-137 content in the fish due to the advection of the Sellafield reprocessing plant sea water (Reinert et al., 1992). Stock identification, especially the separation of the oceanic S. mentella stock in the Irminger Sea from other stocks, is also possible using parasite infestation frequency patterns.

Migration

Population studies on S. marinus and S. fasciatus in the Gulf of Maine-Georges Bank region have shown that there is probably a southerly migration of adults from the Baffin Island region to areas southwest of Newfoundland (Mayo, 1980 and 1993). In the Northeast Atlantic, adults of the oceanic and deep-water stock of S. mentella have different migration patterns, related to their life cycles.

Depth distribution

In the Northeast Pacific, smaller rockfishes of the genus Sebastes are found in shallower waters (30-150 m) and the proportion of bigger fish increases with depth (Westrheim, 1970; Lenarz, 1980; Wilkins, 1980; Richards, 1986). In the Northwest Atlantic, the bigger redfish (S. fasciatus, S. mentella) have a larger depth range (250-400 m) than smaller fish of the same species (Templeman, 1959). It is well documented that these fish exhibit considerable diel vertical migrations, moving up from the bottom at night probably in pursuit of their prey (Beamish, 1966; Sandeman, 1969; Parsons and Parsons, 1976; Pálsson et al., 1985). There are also seasonal variations in the depth distribution of redfish. Steele (1957) reported that the largest bottom trawl catches of S. marinus in the Gulf of St. Lawrence were made in autumn in depths of 400 metres. The depth distribution of redfish in this area ranges from 20 to 730 metres, with peaks at 400 to 500 metres (Steele, 1957). In the Northeast Atlantic, different trends in the vertical distribution of redfish were reported. Bel’skiy et al. (1987) report a decrease in the mean length of the oceanic S. mentella with increasing depth, whereas Rikhter (1996) found the inverse trend. These differences could mainly explained by feeding behaviour and preferences of female redfish during the period of the extrusion of larvae (Magnússon and Magnússon, 1995). The oceanic redfish stock in the Irminger Sea is distributed in depths from 50 to 400 metres with the highest concentrations in 100 to 200 metres depth, whereas the deep-sea stock is most abundant in depths from 400 to 600 metres (Magnússon and Magnússon, 1995). The diel and seasonal variations in availability and size distribution of redfish have important implications for commercial fisheries and scientific stock estimates (Atkinson, 1989).

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