MEPS 553:185-202 (2016)  -  DOI: https://doi.org/10.3354/meps11761

ABSTRACT: Major groundfish populations in the western Atlantic north of Georges Bank/Western Scotian Shelf experienced near-total population collapses beginning in the late 1980s-early 1990s. Explosive increases in the abundance of their pelagic fish and invertebrate prey (notably capelin, sand lance, herring, shrimp and snow crab) generally followed. However, several investigators have concluded, based on the results of annual acoustic surveys, that the lightly exploited capelin stock in the Newfoundland/Labrador (NL) region experienced a sudden 6.8 Mt (98%) decline in biomass from 1990 to 1991 coincident with the groundfish collapse. Given the enormity, duration and unexpected nature of this decline, it was characterized as a collapse. The contrasting response of this capelin stock to the groundfish collapse relative to other North Atlantic (NA) ecosystems prompted us to undertake systematic analyses of the NL ecosystem. The reported capelin collapse in NL should have induced significant responses of trophically linked species, as have been reported in other NA ecosystems. We found little evidence of changes in the population abundance, diet and condition of marine mammals, cod, seabirds and zooplankton, in indexes of the areal occupancy and spawning biomass of capelin, or of environmental effects. These results strongly support the hypothesis that the reported collapse did not occur. Profound seasonal distribution changes, a fixed in time and space acoustic survey in a restricted portion of the distributional range of capelin, and the possibility that NL capelin stock has become less migratory provide a more robust and consistent explanation of the observations.

KEY WORDS: Forage fish · Stock collapse · Ecosystem response · North Atlantic · Acoustic surveys · Migration