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

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Abstract
Previous methods of estimating population size and natural mortality rate in P. groenlandica are reviewed. Excepting the method of Beddington and Williams (1980) all previous methods rely heavily upon the survival index method of estimating pup production. The mathematical rationale underlying this method and potential sources of bias are described. 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. The method may not be able to estimate these parameters accurately. This conclusion is supported by several unpublished analyses. An alternative method of analysis is presented that is based on the concept of maximum likelihood. The rate of natural mortality and trend in 1 + population size from 1967-1980 is estimated, using mark-recapture estimates of pup production in the late 1970s and the obseved ratio of the survival of adjacent cohorts in the late 1960s and early 1970s to constrain population trajectories from a simulation model. The population is probably increasing and the present total catch may be substantially smaller than the replacement yield.

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