Temporal variations in Hudson Bay ringed seal (Phoca hispida) life-history parameters in relation to environment

Abstract

We related temporal variation in the environment to demographic parameters and body condition of ringed seals (Phoca hispida) in Hudson Bay, near the southern limit of the species' geographic range. Ringed seals harvested by Inuit hunters for subsistence purposes in Arviat, Nunavut, Canada, from 1991 to 2006 were measured and sampled. Ringed seal ovulation rate did not change over time, but pregnancy rate and percent pups in the fall harvest increased in the 2000s, compared to the 1990s. Ringed seals grew faster and attained sexual maturity earlier in life, and the population age structure shifted to younger age classes in the 2000s compared to the 1990s. Ringed seal demographic parameters were characteristic of a population in decline in the 1990s and a growing population in the 2000s. A quadratic polynomial regression best described the relationship between percent pups in the harvest and snow depth, and between pup and adult female body condition index and date of spring breakup, suggesting that ringed seals have evolved to do best within a relatively limited range of environmental conditions. We propose that the decline of ringed seal reproductive parameters and pup survival in the 1990s could have been triggered by unusually cold winters and heavy ice conditions that prevailed in Hudson Bay in the early 1990s, through nutritional stress and increased predation pressure. The recovery in the 2000s may have been augmented by immigration of pups, juveniles, and young adult ringed seals into the study area. We discuss the possibility of a decadal-scale biological cycle that reflects fluctuations in climatic variables, and particularly in the sea ice regime. © 2012 American Society of Mammalogists.