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.
Trends in capelin (Mallotus villosus) biomass in NAFO Div. 3L during 1982-89 projected from Canadian acoustic surveys were compared to trends in indices of inshore abundance from aerial surveys and trap catch rates. Trends in the two inshore indices of abundance were significantly correlated with each other but were not significantly correlated with the Canadian series. The major differences occurred during 1986 and 1987. Age-compositions in the inshore mature stock were similar to the age-compositions predicted from the acoustic surveys although the latter tended to underestimate the proportions of older fish. The time series was short and the relationships tested were not always statistically significant, however, the general agreement in trends of all indices engendered confidence in the approach and especially in the acoustic surveys which provide absolute abundance indices which can be used directly for management advice.
A method of calculating age-specific maturation rates for capelin (Mal/otus villosus) off southern Labrador and northeastern Newfoundland from catch-per-unit-effort data is presented. The data indicate that most of the capelin have matured at age 4. Underestimates of the instantaneous rates of either natural mortality or spawning mortality result in overestimation of the proportions of mature capelin by age-group, and overesti mates of these mortality rates result in underestimation of the proportions of mature fish. In all cases, the percent error in proportions of mature capelin by age-group is considerably less than the percent error in the natural mortality or spawning mortality rate. from Div. 2J to Div. 3K during the autumn. This conclusion was based mainly on the temporal and spatial distributions of catches by fishing vessels, complemented by research vessel data. Because there are no offshore spawning areas in Div. 3K, it may be inferred
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