During the northbound migration, a small number of individually identified gray whales (n=14) divert from the migratory path to enter the Strait of Juan de Fuca, travelling >100 miles to northern Puget Sound (NPS), where they feed on dense patches of ghost shrimp. Efforts to photographically identify these whales began in 1990, and most of these whales (71%) have been sighted in NPS in at least ten of the past 24 years. These whales arrive in NPS in the spring and feed for 2-3 months. While most of these whales are presumed to subsequently migrate to feeding grounds further north, one individual is known to have spent multiple summers feeding in the area between northern California and southeastern Alaska and is considered part of the Pacific Coast Feeding Group of gray whales. Although matrilineal fidelity of gray whales to summer feeding areas is known to occur, no calves have been identified with NPS whales, suggesting that fidelity to this area has arisen through exploratory movements that resulted in the identification of a highly productive feeding ground. To further test this hypothesis, genetic analysis of biopsy samples collected from eight of these whales is being conducted. Thus far, results include: 1) five of the eight whales for which sex has been genetically determined are males, 2) six mitochondrial DNA haplotypes have been identified among seven sampled individuals, and 3) all six haplotypes are also found among whales feeding in the northern Bering/southern Chukchi Seas. These results are generally consistent with expectations under a scenario where exploratory movements of random individuals result in the identification of a rich prey resource and the subsequent return of the whales in later years. Microsatellite genotyping of these samples is currently underway and will allow additional analysis of potential relatedness patterns among individuals to be conducted.
Pease, VL, A Perez, M Lauf, A Lang, J Calambokidis. 2015. The road less taken: Why do a small number of gray whales demonstrate inter-annual fidelity to springtime feeding areas in northern Puget Sound?. Abstract (Proceedings) 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, California, December 14-18, 2015.