4.2 Article

Stable carbon and nitrogen isotope values in teeth of Steller sea lions: age of weaning and the impact of the 1975-1976 regime shift in the North Pacific Ocean

Journal

CANADIAN JOURNAL OF ZOOLOGY
Volume 86, Issue 1, Pages 33-44

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CANADIAN SCIENCE PUBLISHING
DOI: 10.1139/Z07-108

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We measured delta N-15 and delta C-13 values and tooth width from the first 4 years' dentinal growth layer groups (GLGs) in the teeth of 113 female Steller sea lions (Eumetopias jubatus (Schreber, 1776)) born between 1960 and 1983, a period that included a large population decrease and a climate regime shift. A linear discriminant analysis on the 613 C and delta N-15 values estimated 60% of Steller sea lions were weaned in their 1st year, 30% in their 2nd year, and 8% in their 3rd year. GLG-1 was wider in weaned animals than those still nursing in their 2nd year, suggesting that faster growing pups weaned earlier. Except during the regime shift, the average age at weaning increased and the size of GLG-1 in weaned animals decreased. We suggest that during the regime shift a greater proportion of pups which survived (to have their teeth sampled for this study) grew faster and were weaned by the end of their 1st year. We hypothesize that the long-term weaning age increase and growth rate decrease are consistent with a change in relative mortality of weaned pups and those that continued to nurse, possibly caused by a reduction in available resources, characterized as a switch from a live-fast to a live-slow life history.

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