Paternity of Western Gray Whales Feeding Off Sakhalin Island, Russia

Abstract

While understanding mating systems can provide critical insight into a population's long‐term persistence and resilience, such information remains limited for most baleen whales. However, extensive research on the western gray whales that feed off Sakhalin Island, Russia, led to the collection of biopsy samples from 75% of the 207 whales photo‐identified between 1994 and 2011, providing a rare opportunity to learn about this small population's mating system and to identify factors potentially influencing its recovery. Using 22 microsatellite loci, we conducted a paternity analysis to identify males contributing to reproduction in this population. We identified 22 putative fathers among sampled males, accounting for paternity of 50% of the calves with sampled mothers ( n = 70). While the assignment of putative fathers for half of the calves provides evidence of interbreeding among Sakhalin whales, the lack of sampled fathers for the remaining calves suggests some males contributing to reproduction may feed in other areas. Additional findings suggest that the number of individuals contributing to reproduction is small, with an estimated contemporary effective size of 59.8 whales (95% CI [46.0, 81.1]), the identification of four putative full‐sibling pairs, and higher than expected relatedness coefficients in some putative breeding pairs.

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