Ecology

Diet

Generally, Sebastes larvae have been characterised as opportunistic feeders (Moser and Boehlert, 1991). Earliest larvae of redfish typically feed on copepod nauplii and to a lesser extent on invertebrate eggs (Bainbridge and McKay, 1968; Marak, 1974). Larger larvae and juveniles also take copepodites, adult copepods and euphausids (Anderson, 1994). Adult oceanic S. mentella feed on bigger zooplankton (Magnússon and Magnússon, 1995), whereas adult S. marinus also feed on small fish like herring (Clupea harengus), capelin (Mallotus villosus) and small Greenland halibut (Reinhardtius hippoglossoides; Pedersen and Riget, 1993), epibenthic invertebrates and fish eggs (S. marinus; Steele, 1957; Magnússon et al., 1988, Muus and Dahlström, 1991). According to the distribution of their prey, redfish undertake diel vertical movements (Atkinson, 1989). This behaviour is well known among fishermen who catch larger amounts of fish in bottom trawls during day-time when most of the fish are seeking their prey within the bottom layer.

Predation

Larvae and juveniles of Sebastes are subject to predation from harp seals (Phoca groenlandica; Lawson et al., 1995) and piscivorous fish like starry rays (Raja radiata; Pedersen, 1995), Greenland halibut (Reinhardtius hippoglossoides; Pedersen and Riget, 1993) and Atlantic cod (Gadus morhua).

Competition

In the North Pacific, interspecific competition occurs among the numerous Sebastes species and other fish with similar feeding habits (Murie, 1995). Redfish in the North Atlantic have species specific distribution patterns and different feeding ecology, resulting in higher competition with other fish than among the four Sebastes species. Redfish are mostly associated with other bottom-living fish like Atlantic cod (Gadus morhua), Greenland halibut (Reinhardtius hippoglossoides) polar cod (Boreogadus saida) and starry ray (Raja radiata) (Pedersen and Kanneworff, 1995). The association of redfish off the Greenland coast with northern shrimp (Pandalus borealis) leads to a great by-catch of young redfish in the shrimp fishery (Veim et al., 1994).

Behaviour

Behavioural studies on redfishes in the laboratory are rare, due to the fact that these fish have to be brought from deep waters to the sea surface with very slow towing speed in order to avoid organ damage due to decompression. More information is available on the schooling behaviour of Sebastes. According to Breder (1959), Sebastes forms characteristic 'pods', roundshaped accumulations of hundreds to thousands of individuals.

Parasites

Sebastes marinus and S. mentella are infested by several parasites, varying in frequency from area to area. The ectoparasitic copepod Sphyrion lumpi is embedded permanently in the body of the host. Its remnants are responsible for lesions and colouration abnormalities which could be used for the identification of stocks or origin areas (Templeman and Squires, 1960; Bakay, 1988; Bogovski and Bakay, 1989; Nagel et al., 1991; Magnússon, 1992). High infestion rates do, however, lead to increased discard amounts in commercial fishing since the infested tissue and skin parts are not marketable (Rätz, pers. comm.). Sphyrion lumpi is concentrated in the Irminger Sea and characterises the oceanic stock of S. mentella (Magnússon and Magnússon, 1995). Other important parasites of redfish in the North Atlantic are the ectoparasitic copepod Chondracanthopsis nodosus, which attaches itself to the basal parts of the gills, and the systemic fungus Ichthyosporidium hoferi, which produces white nodules on and in the heart, spleen and liver (Sindermann, 1961; Williams, 1963).

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