Growth and natural mortality rates (M) of the red sea urchin (RSU), Strongylocentrotus franciscanus, were estimated based on tetracycline tagging studies and abundance surveys in Queen Charlotte Islands (QCI), Price Island (PI), Alert Bay (AB), and Tofino, British Columbia. Growth was modeled using the Tanaka function and logistic dose-response function and was variable between locations. The growth rate of the RSU remained constant or even increased in the first few years, before declining with test diameter or age. The RSU appeared to be a slow growing and long lived species. Growth for the RSU to recruit into the fishery, at a test diameter of 90 mm, took about 10 and 14 y in QCI and AB respectively, and about 18.5 y in PI and Tofino. Growth rates seemed to be correlated with population density. RSU density was the lowest in QCI, and lower in AB than in PI or Tofino. M was estimated by comparing the survey-derived density of the RSU with the expected density calculated using the growth function and the densities in the previous survey years. The estimated mean M was about 0.08 y−1 in PI and Tofino, 0.12 y−1 in QCI, and 0.21 y−1 in AB.
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Vol. 27 • No. 5