Changes in the vertical distribution of capelin (Mallotus villosus) off Newfoundland

Vertical distribution patterns of capelin were examined using data from spring and autumn acoustic surveys off northeastern Newfoundland in the years 1988–2000. Until 1991, capelin typically underwent diel vertical migrations from 50 to 150 m. Since 1991, vertical migrations have been reduced or have become erratic, with capelin commonly located deeper in the water column (200+m) and closer to the seabed. Changes in vertical distribution initially coincided with the onset of a severe cold period, but distributions failed to return to normal as waters warmed. Vertical distribution was examined with regard to potential habitat-selection factors, including capelin density, water temperature, fish size, maturity stage, and proximity of predators. Of these, only fish density and predator (Atlantic cod) presence were significant. Capelin occupied more of the water column when their density was high than when it was low, and they were found farther from the seabed in areas with cod than without. Results indicate that, during the 1990s, capelin should have been able to optimize vertical distribution and feeding. This is not consistent with reports of poorer capelin condition and size-at-age in the 1990s, suggesting that vertical distributions are likely a result of changes in other factors, such as prey availability.