Population Dynamics and Management of the Northwest Atlantic Harp Seal ( Phoca groenlandica )

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Roff, Derek A., Bowen, W. Don
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1983
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Harp Seal; Northwest Atlantic; Phoca groenlandica
• Online Access: http://dx.doi.org/10.1139/f83-118; http://www.nrcresearchpress.com/doi/pdf/10.1139/f83-118

Previous methods of estimating population size and natural mortality rate in harp seals (Phoca groenlandica) are reviewed. Excepting the method of Beddington and Williams (Marine Mammal Comm., Washington, DC., Rep. MMC 79-03, 1980) all previous methods rely heavily upon the survival index method of estimating pup production. We describe the mathematical rationale underlying this method and indicate potential sources of bias. Beddington and Williams' analysis produces a combination of vital rates for 1952 that would not enable a population to persist in the absence of hunting. This suggests that the method may not be able to estimate these parameters accurately. This conclusion is supported by several unpublished analyses. We present an alternative method of analysis that is based on the concept of maximum likelihood. We estimate the rate of natural mortality and trend in 1 + population size from 1967 to 1980, using mark–recapture estimates of pup production in the late 1970s and the observed ratio of the survival of adjacent cohorts in the late 1960s and early 1970s to constrain population trajectories from a simulation model. From this analysis we conclude that the population is increasing and that the present total catch may be substantially smaller than the replacement yield.