Shoal behaviour and maturity relations of spawning capelin (Mallotus villosus) off Newfoundland:: demersal spawning and diel vertical movement patterns

We investigated shoals of capelin (Mallotus villosus), the focal forage fish species in the Northwest Atlantic, in nearshore Newfoundland during spawning (2000-2003). Large shoals of maturing capelin were observed in warm (> 0 degrees C), deep (> 240 m) water. Smaller shoals of maturing fish were located in two specific areas closer to shore in shallower water (100-150 m). Shoals persisted in these staging areas in all years and moved into warm surface water during dark but remained in cold (< 0 degrees C) deep water during daylight. These diel vertical movement patterns may reflect a trade-off between growth and survival, whereby cold, deep water allows reduced predation risk from visual, air-breathing predators while warm, surface water allows increased gonadal development. Shoals of spent capelin, mainly females, were also found in these areas. Sex-specific shoals were observed between staging areas and the coast. Closer to shore, mature, mixed-sex shoals revealed two previously undocumented demersal spawning sites (28-33 m). Suitable habitat for spawning and staging areas resulted in persistent aggregations of capelin shoals, reflecting key foraging areas for top predators and critical areas for conservation.