Distribution of Capelin (Mallotus villosus) in Relation to Coastal Upwelling in the Avalon Channel

Abstract

Three hypotheses were developed from a series of studies of capelin (Mallotus villosus) distribution in the southern Labrador Current. The hypotheses were that: (1) water mass replacement due to coastal upwelling occurs at the spatial scale predicted by the balance between buoyant and Coriolis forces; (2) upwelling generates a cross-shore gradient in capelin abundance; and (3) this gradient decays after an episode of upwelling favorable winds. An initial experiment, reported elsewhere, confirmed these predictions for a single strong episode of upwelling favorable winds ending 2 July 1987. To determine whether these predictions hold for typical upwelling events, closer to the average strength, the experiment was repeated during the period of high capelin abundance (mid-June to mid-July) over a 3 year period. The first hypothesis, of wind driven water mass replacement, was confirmed in 29 out of 30 cases where a test was possible. The average lateral extent of cold water near the coast was 5 km as predicted. A gradient in capelin abundance (higher abundance near the coast) was observed at this scale in 13 out of 15 instances, confirming the second hypothesis. The gradient changed in response to upwelling during the strong event in early July of 1987, and in another event during mid-July of 1988. On average, however, the gradient changed in the expected direction in only 2 out of 7 instances where a test was possible. Repeated observational experiments showed that capelin respond to strong upwelling events (sea surface temperature less than 2°C) but do not respond to more typical events.