Stable carbon and nitrogen isotope ratios in muscle and epidermis of arctic whales

Collection of minimally invasive biopsy samples has become an important method to establish normal stable isotopes reference ranges in various wildlife species. Baseline data enhance the understanding of feeding ecology, habitat use, and potential food limitation in apparently healthy, free-ranging cetaceans. Epidermis and muscle were collected from subsistence-hunted northern Alaskan bowhead (n= 133 epidermis/134 muscle) and beluga whales (n= 42/49) and subsistence-hunted Russian gray whales (n= 25/17). Additional samples were obtained from gray whales stranded in California (n= 18/11) during mortality events (1999, 2000). Both d15N and d13C are trophic position and benthic/pelagic feeding indicators, respectively, in muscle and epidermis. Epidermis is generally enriched in 15N over muscle, while epidermal 13C is more depleted. Lipid extraction does not alter d15N in either tissue, but affects epidermal d13C. Nitrogen-15 is enriched in muscle, but not epidermis of stranded compared to subsistence-hunted gray whales, indicating probable protein catabolism and nutritional stress in stranded whales. Similarly, epidermal d13C of harvested whales is lower than in stranded whales, suggesting depleted lipid stores and/or food limitation in stranded animals. Epidermal isotope signatures are similar in both present-day bowheads and in an ancient sample from the Northern Bering Sea region. Although only one specimen, this suggests trophic level of the ancient whale compares to modern bowheads after a millennium.