Research Document - 2009/113

Reproductive rates of Northwest Atlantic harp seals, 1954-2007

By G.B. Stenson, M.O. Hammill and B. Healey

Abstract

Obtaining accurate estimates of fecundity are critical for estimating the population dynamics of a species. Data on pregnancy rates of Northwest Atlantic harp seals have been collected since the 1950s. However, sample sizes were highly variable with little or no reproductive data for many year-age combinations. To obtain the data required to estimate total abundance, we used a non-parametric regression estimator to estimate the expected annual age-specific pregnancy rates using data collected up to 2007. Pregnancy rates among 4 year olds remained low (<10 %) throughout the time period. Seals aged 5 and 6 showed a similar pattern; age-specific pregnancy rates initially increasing during the 1970s, but declined by the mid 1980s to levels similar to, or lower than, those seen in the 1960s. Seals 7 years of age and older remained high until the mid 1980s when they declined to their current low levels. Estimates of recent reproductive rates are slightly lower than those used previously to estimate total population size of Northwest Atlantic harp seals.

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