NEXT PAGE

Page 6

Unable to compete for nonexistent shelter on sand habitat, age-0 cod school for protection (Tupper and Boutilier 1995a); however, the population density in these areas reached zero by late June (Tupper and Boutilier 1995b). Predation by three Cottids - sea raven (Hemitripterus americanus), grubby (Myoxocephalus aeneus) , and longhorn sculpin (Myoxocephalus octodecemspinosus) - was most successful on sand and least successful on cobble and rock reef. Age-0 cod schooling over sand bottoms have low site fidelity which is disadvantageous to survival (Grant and Brown 1998a).

Young-of-the-year appear to lose site fidelity and disperse into deeper water during the December-January period (Tupper and Boutilier 1995a; Gregory and Anderson 1997) adopting winter behavior of reduced activity and food consumption (Brown et al. 1989). Still, some marked demersal juveniles remained localized in the shallowest (<1.2 m) sampling site in Trinity Bay, Newfoundland, throughout the winter even when ice was present (Grant and Brown 1998b). Age-0 and older juveniles are more adapted than adult cod to survive icy subzero water due to elevated plasma antifreeze levels in their blood (Goddard et al. 1992).

Age-1 and Older Juvenile Habitat and Movements
Age-1 juveniles are found during day and night in shallow inshore waters, including locations with moderate to high wave exposure (Keats 1990). Older juveniles are generally distributed farther away from shore than 0-group and 1-group cod and at depths >25 m. Age-1 associate to a greater degree with rocky substrate and fleshy macroalgae or bottom dominated by sea urchins and coralline algae (Keats et al. 1987; Keats 1990; Gotceitas et al. 1997). The association with a macroalgal canopy seems to be more one of refuge from predators than feeding purposes (Keats et al. 1987; Gotceitas et al. 1995; Gotceitas et al. 1997). They congregate in small groups near boulders and in large crevices. In Newfoundland bays, age-1 cod have been collected within a slightly narrower temperature range, 1-16°C, than demersal0-group fish (-1.7-17°C) (Methven and Bajdik 1994).

At dusk during summer and autumn seasons, age-1 and older juveniles move shoreward into warmer water feeding areas where the young-of-the-year cod are concentrated. The attracting stimulus appears to be the periodic influxes of early settled cod (Keats 1990; Clark and Green 1990; Methven and Bajkik 1994). Age-1 cod have usually been found feeding until dawn ' primarily on mysids and gammarid amphipods; however, when they become about three times larger than settled age-0 juveniles, they begin cannibalizing the demersal0-group cod (Grant and Brown 1998a). By late fall, the earliest age-0 settlers may be large enough to begin intracohort cannibalism on the late settlers, as has been noted in waters of Iceland (Bogstad et al. 1994).

When abundance of older juveniles is high, mortality may increase on young-of-the-year because of competition and predation from conspecifics (Grant and Brown 1998a).

Age-1 cod have also been observed feeding on plankton after moving inshore in spring (Keats et al. 1987) as well as resting near bottom in shallow water at night (Keats and Steele 1992). In the latter situation, age-1 were not feeding and analysis of stomach contents indicated daytime foraging on planktonic crustaceans leading the authors to speculate that post-transitional feeding on benthic invertebrates might be patchy in space and time. Where, when, and to some extent what yearlings eat is likely related to trade-offs between predation risk and food availability.

.