Staged spawning migration in Icelandic capelin (Mallotus villosus): effects of temperature, stock size and maturity

Abstract

AbstractCapelin (Mallotus villosus) is the largest commercial fish stock in Icelandic waters and also an important forage fish. Every winter pre‐spawning capelin migrate 500–1000 km from their offshore (>200 m bottom depth) northern feeding areas (67–71°N) to inshore (<200 m bottom depth) southern spawning areas (63–65°N). The major migration route is east of Iceland. The route consists of both offshore and inshore phases. The migration begins offshore as capelin skirt the shelf edge north of 65°N, then abruptly veer inshore between latitudes 64° and 65°N. Hydro‐acoustic data from 1992–2007 demonstrated that the timing of the offshore phase migration varied by as much as 1 month, from 22 December to 21 January. A combination of larger spawning stock and colder feeding ground temperatures (August–December) resulted in earlier offshore migration. The timing of the inshore migration phase was not dependent on the offshore migration timing, and never began prior to the first week of February. Many cohorts arrived at latitudes 64–65°N in early January but staged offshore at latitudes 63.8–65.8°N until early February. The longest observed delay in the staging area was 5 weeks. Timing of the inshore migration was controlled by gonad maturity, with migration beginning when roe content attained 12–14%. Staging limited the time capelin spent on the continental shelf before spawning to 3 weeks. We suggest that offshore staging evolved to minimize temporal overlap with predatory gadoids, especially Atlantic cod (Gadus morhua).