Changes in the reproductive parameters of female harp seals (Pagophilus groenlandicus) in the Northwest Atlantic

• Published in: ICES Journal of Marine Science
• Main Authors: Sjare, Becky, Stenson, Garry B.
• Format: Text
• Language: English
• Published: Oxford University Press 2010
• Subjects: Articles; Harp Seal; Northwest Atlantic; Pagophilus groenlandicus
• Online Access: http://icesjms.oxfordjournals.org/cgi/content/short/67/2/304; https://doi.org/10.1093/icesjms/fsp267

<qd> Sjare, B., and Stenson, G. B. 2010. Changes in the reproductive parameters of female harp seals ( Pagophilus groenlandicus ) in the Northwest Atlantic. – ICES Journal of Marine Science, 67: 304–315. </qd>Changes in female harp seal ( Pagophilus groenlandicus ) reproductive parameters from 1980 to 2004, and long-term trends since the early 1950s, are evaluated. Estimates of the total number of seals in the Northwest Atlantic declined from ∼3.0 million in the 1950s to 1.8 million in the early 1970s, then increased steadily to 5.5 million in 1996, at which relatively stable level it has remained since. Pregnancy rates increased from ∼86% in the 1950s to a high of 98% in the mid-1960s, then declined to ∼65–70% by the early 1990s; the rate then varied between 45 and 70% from 2000 to 2004. Concurrently, the mean age at sexual maturity decreased from 5.8 (s.e = 0.02) years in the mid-1950s to 4.1 (s.e. = 0.02) in the late 1970s, increased to 5.5 (s.e. = 0.03) years by the early 1990s, and peaked at 5.7 (s.e. = 0.01) in 1995. From 2000 to 2004, mean age varied from 4.9 (s.e. = 0.01) to 6.0 (s.e. = 0.01) years. Although the direction of change in each of the parameters was consistent with a density-dependent response, changes in population size explained relatively little of the variability observed, suggesting that other ecological or environmental factors were influential.