Research Document - 2000/077

Recent estimates of reproductive rates for harp seals in the Northwest Atlantic.

By B. Sjare and G.B. Stenson

Abstract

The pregnancy rate and mean age of sexual maturity of harp seals (Phoca groenlandicus) are two important reproductive parameters with respect to the management of this species in the Northwest Atlantic. They may be useful indices of population change, and in addition, pregnancy rate data are incorporated into the current harp seal population model. This research document provides new data on these parameters and describes our general reproductive sampling protocol. Estimates of the total number of harp seals in the Northwest Atlantic declined from approximately 3.0 million in the 1950s to 1.8 million in the early 1970s and then increased steadily to 5.2 million in 1998. During this period, overall pregnancy rates increased from approximately 85% in the 1950s to a high of 95.7% in the mid 1960s and then declined steadily to approximately 64.3% by the mid 1980s and early and 1990s. Pregnancy rates for the period from 1995-1997 have increased to 70.6%. Concurrently, the mean age of sexual maturity decreased from 5.8 years in the mid 1950s to 4.6 in the early 1980s and then increased to 5.6 years of age by the late 1990s. Given the population dynamics of the harp seals, these changes in pregnancy rates and mean age of sexual maturity are consistent with a density dependent response. However, coinciding with the increase in seal abundance in recent years there have also been significant changes in oceanographic conditions in the Northwest Atlantic that may have influenced the availability of prey species.

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