COSEWIC assessment and status report on the Atlantic wolffish Anarhichas lupus in Canada
Spawning in the Atlantic wolffish appears to vary greatly in time and place. Off the east coast of Newfoundland some Atlantic wolffish migrate to shallow inshore waters in spring, spawning in September with hatching occurring by mid-December (Keats et al., 1985). In both the Gulf of Maine (Nelson and Ross, 1992) and eastern Newfoundland (Keats et al., 1986), it is thought that only fish over 50 cm and sexually mature move inshore, while smaller, juvenile fish remain in deep water. In Greenland the maximum number of spawners was observed by Beese and Kandler (1969) in September and October. In Iceland the situation is quite different from that in Newfoundland; Jónsson (1982) reports that the Atlantic wolffish moves from shallow into deeper waters to spawn from September to December or January, subsequently returning to shallow waters to feed. Similarly, spawning and feeding are exclusive events in the White Sea, with spawning occurring in the deep waters between 70 m and 300 m from August through September (Pavlov and Novikov, 1993). Keats et al. (1985: 2567) point out that the literature “suggests geographical and depth-related variability in the reproductive season of Atlantic wolffish”. As such, discrete geographical populations of Atlantic wolffish on the large-scale may have distinct and different life histories, a possibility that requires further study.
Wolffish lay some of the largest eggs of any fish known – up to 6.0 mm in diameter. The eggs are deposited in a large mass on the bottom and are guarded by the male. Larvae remain mostly close to the bottom, rarely swimming to the surface and tending to remain close to the site of hatching.
Compounded, limited adult migrations and the restricted dispersal of larvae from their hatching site are potential risk factors for the survival of Atlantic wolffish populations on the smaller scale. If the population of a given region is decimated through environmental or anthropogenic causes, it is unlikely to be replenished by populations from elsewhere. The broad range of temperature and depth to which the Atlantic wolffish appears to be adapted may be indicative of the unique depth and temperature regimes of discrete and separate, rather than confluent, populations.
Growth rates of the Atlantic wolffish in Canadian Atlantic waters are unknown and there are little data available for other areas. In Europe, it takes three years to reach 25 cm (Wheeler, 1969), and Scott and Scott (1988) report that growth rates in Atlantic Canada are slow after the first summer. It is known that growth slows even further at five to six years of age when energy is diverted to gonadal development (Nelson and Ross, 1992). Off eastern Newfoundland the Atlantic wolffish reaches maturity between 43 and 67 cm (weights of 0.56 and 2.39 kg); fifty percent of individuals between 52 and 60 cm (1.02 and 1.57 kg) are mature (Templeman, 1986). Fish of this size are 8 to 10 years old. Atlantic wolffish are known to reach 152 cm in length and specimens aged to twenty years have been taken off Iceland (Scott and Scott, 1988).
Nutrition and Interspecific Interactions
The Atlantic wolffish feeds primarily on hard-shelled benthic invertebrates such as echinoderms, molluscs, and crustaceans. It is thought to be a key player in the ecosystem, known to control the density and spatial distribution of species such as green sea urchins (Hagen and Mann, 1992), crabs (Witman and Sebens, 1992) and giant scallops (Stokesbury and Himmelmann, 1995). The Atlantic wolffish also consumes small amounts of fish, particularly redfish. Young wolffish eat echinoderms almost exclusively but this food source becomes less important as the fish grows. While mature males reduce feeding close to spawning time and until their egg-guarding duties have ceased, females reduce feeding as gonads mature, but resume feeding immediately following spawning (Keats et al., 1985). Little is known about what preys on the Atlantic wolffish itself, but juvenile specimens have been reported in the stomach contents of cod (Scott and Scott, 1988).
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