Research Document - 2004/107

Changes in the Reproductive Parameters of Female Harp Seals (Pagophilus groenlandicus) in the Northwest Atlantic

By Sjare, B., G.B. Stenson, B. Healy

Abstract

Reliable data on harp seal (Phoca groenlandicus) fertility rate, age specific pregnancy rates and mean age of sexual maturity are required to understand the population dynamics of this species and to provide a sound scientific base for the development of a sustainable management plan. The objectives of this manuscript are to examine changes in female reproductive parameters from 1980 – 2001 as well as long-term trends since the early 1950s. 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 1996 where it has since stabilized. During this period, annual fertility rates increased from approximately 86% in the 1950s to a high of 98% in the mid 1960s and then declined steadily to approximately 65-70% by the early 1990s where it has stabilized. Concurrently, the mean age of sexual maturity decreased from 5.8 years in the mid 1950s to 4.1 in the early 1980s, then increased to 5.3 years by the early 1990s and peaked at 5.7 years by 1995. In 2001 the mean age was approximately 5.3 years. Although the direction of change in each of the reproductive parameters examined was consistent with a density dependent response, changes in population size explained very little of the variability observed in ovulation rates and mean age of sexual maturity. Given the current formulation of the harp seal population model, pregnancy rates were not independent from population size and could not be tested statistically, but there was a significant year effect. These data suggest other ecological or environmental factors may be important; possible implications of changing oceanographic conditions in the Northwest Atlantic are discussed.

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