Model of Monthly Marine Growth and Natural Mortality for Babine Lake Sockeye Salmon (Oncorhynchus nerka)

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Abstract
Monthly marine growth and natural mortality rates were calculated for each major life history type of Babine Lake sockeye salmon (Oncorhynchus nerka) and compared with estimates by other methods. Growth rates were based on sizes at the beginning and end of each marine year and adjusted according to seasonal changes in environmental temperature. Temperature effects were derived from information on growth responses of cultured fish. Mortality estimates were based on a model which equates mortality rate to an inverse function of weight. Monthly sizes determined from the growth model were substituted into the mortality model, together with estimates of smolt and adult runs (catch plus escapement), to examine the population dynamics of an average Babine Lake smolt cohort. Using these predictions we suggest that 90% of natural mortality occurred during the first 4 mo at sea.