17. Growth and Reproduction of Spiny Dogfish off the Eastern Coast of Canada, including Inferences on Stock Structure
Steven E. Campana, Warren Joyce, and David W. Kulka
Abstract.—As part of an intensive study of spiny dogfish Squalus acanthias off the Atlantic coast of Canada, we studied the sexual maturation and growth of dogfish collected on research surveys and as part of the commercial fishery. Sexually mature and pregnant females were distributed throughout the waters of southwest Nova Scotia during the summer and fall but moved offshore to deeper waters in the winter. Juveniles were most abundant off Georges Bank and near the edge of the Scotian Shelf during the winter. The fork length at 50% maturity for males was 55.5 cm at age 10, while that for females was 72.5 cm at age 16. Free embryos were observed in 62% of all pregnant females (n = 1,491), the number of embryos increasing with the size of the female. Free embryos first became apparent in June at a fork length of 16 cm and would be expected to reach their birth size of 22–25 cm during the winter. Validated ages based on spine growth bands indicated a longevity of 31 years (n = 525). Males and females grew at similar rates until the size and age of male maturity, after which male growth rate slowed considerably. Two-parameter von Bertalanffy growth equations using a fixed size at birth gave L∞ = 78.0 and K = 0.099 for the males and L∞ = 119.5 and K = 0.042 for the females. Atlantic dogfish appear to grow more quickly and die at a younger age than do Northeast Pacific dogfish. Small amounts of offshore pupping in southern Nova Scotia waters probably represent the northern limits of an extended distribution centered in U.S. waters. Although they probably originate from the same population, dogfish living in the Gulf of St. Lawrence and off Newfoundland may be functionally isolated from dogfish found further south. Our results and published tagging studies suggest that both resident and migratory components of the Northwest Atlantic population occupy Canadian waters.