Grey Seal teeth as Indicators of Climate Variability

No abstracts are to be cited without prior reference to the author.

The impacts of environmental changes on life history parameters of marine mammals are poorly understood. This may be due to the large spatial scales that must be examined to describe environmental changes and their impacts on biological aspects of most species. Annual growth layers in the teeth of marine mammals have long been used to determine age of individual animals. In some species, changes in tooth structure also provide a record of life-history changes such as age at sexual maturity, or records of major climatic events eg El Nino. In this study, growth layer development in longitudinal sections (N=400) of Northwest Atlantic grey seal (Halichoerus grypus) canine teeth were examined. Age, sex, and a large scale environmental variable, Minimum Cold Intermediate Layer Temperature (MCILT) all had a significant effect (p<0.05) on the thickness of the first Growth Layer Group (GLG1), while only sex had a significant effect on the thickness of GLG2. GLG1 of males was thicker than that of females. In both sexes, GLG1 thickness declined with age. GLG1 thickness was standardized to remove the effects of age and sex and the resulting deviations were compared to changes in MCILT. During the time series (1965-1998), standardized GLG1 thickness was positively correlated with changes in MCILT (p<0.05). Correlations were also observed between fish stock biomass and MCILT. Grey seal pups begin entering the water during February-March at which time they must also learn to feed. Changes in GLG1 thickness likely reflect the foraging success of pups during their first year of nutritional independence. Although MCILT is only one measure of environmental conditions, changes in this factor have important ecosystem effects that can also be detected at higher trophic levels.