Capelin (Mallotus villosus) Spawning on the Southeast Shoal: Influence of Physical Factors Past and Present

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Abstract
Co-occurrence of beach- and offshore bottom-spawning populations of capelin (Mallotus villosus) in the Northwest Atlantic appears to be unusual. To explain the evolution of bottom-spawning in the offshore spawning population on the Southeast Shoal, we examined relevant substrate, water temperature, and biological data. Published data indicate that the Southeast Shoal was not glaciated during the Wisconsin glaciation (about 20 000 yr ago) and was above sea level. As the glaciers melted, this area was a surf zone before it became inundated. This suggests that this stock was once a beach-spawning stock and supports our hypothesis that substrate is the ultimate factor affecting spawning location. Analysis of 7 yr of distribution, maturity, and bottom temperature data showed that the variation in the final spawning location was not large and spawning occurred where bottom temperatures exceeded approximately 2 °C. We conclude that bottom temperature is a proximate factor influencing the final spawning location. Physical data for other areas of the Grand Banks indicate that only the Southeast Shoal has favourable substrate, bottom temperatures and environmental factors subsequent to spawning to allow the long-term survival of a capelin population.

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