2012 population estimate for the harbor seal (Phoca vitulina concolor) in New England waters

This survey was conducted to obtain an abundance estimate for the New England harbor seal (Phoca vitulina concolor) population, as the previous estimate (2001) was outdated for stock assessment purposes. Aerial photographic surveys and radio tracking of harbor seals on ledges along the Maine coast were conducted during the pupping period in late May 2012. Twenty-nine harbor seals (20 adults and 9 juveniles) were captured and radio-tagged prior to the aerial survey. Of these, 18 animals (6 adult males, 6 adult females, 2 juvenile males and 4 juvenile females) were available during the survey to develop a correction factor for the fraction of seals not observed. The estimate of harbor seal abundance in 2012 was 75,834 (11,625 standard deviation [sd]; 0.153 coefficient of variation [CV]). Nmin, the lower 20% confidence limit, was 66,884. The 2012 point estimate is 24% lower than the 99,340 reported for 2001. Possible reasons for the lower estimate include changes in survey design, differences in the age/sex ratio of radio-tagged seals available for obtaining a correction factor, differences in harbor seal distribution between 2001 and 2012, and/or that the population has actually declined.