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

Abstract

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 °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 °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.