MEPS 557:277-288 (2016)  -  DOI: https://doi.org/10.3354/meps11832

ABSTRACT: Harbor seals Phoca vitulina in Alaska have experienced large fluctuations in abundance in recent decades. Changes in environmental conditions can significantly influence growth and reproductive characteristics of individuals, potentially leading to changes in population size. This study assesses pre- and postnatal growth and sexual maturity of harbor seals in the Gulf of Alaska using samples collected by subsistence hunters as part of the Alaska Native Harbor Seal Commission’s Biosampling Program from 1998 through 2005. Female harbor seals matured at a minimum age of 3 yr, standard length of 122 cm, and mass of 48 kg. The average age of sexual maturity was 4.2 ± 0.7 yr (95% CI). Female seals attained an asymptotic standard length of 147.7 ± 2.6 cm and body mass of 82.2 ± 4.8 kg. Fetuses increased 0.33 cm d^–1 standard length and 0.09 g^1/3 d^-1 mass. Implantation date ranged from 22 September to 17 October, with a mean ± SD date of 30 September ± 8 d. Age at onset of reproduction portends improvements in reproductive rates and possibly environmental conditions since the population crash in the late 1970s. Harbor seals in the present study are smaller in length and have later implantation dates with lower pregnancy rates than in the 1960s. These indices may reflect that environmental conditions are not currently at optimal levels and are limiting growth and maturation.

KEY WORDS: Harbor seal · Sexual maturity · Fetal growth · Alaska · Subsistence