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

Abstract

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 ␦ 15 N and ␦ 13 C are trophic position and benthic/pelagic feeding indicators, respectively, in muscle and epidermis. Epidermis is generally enriched in 15 N over muscle, while epidermal 13 C is more depleted. Lipid extraction does not alter ␦ 15 N in either tissue, but affects epidermal ␦ 13 C. Nitrogen-15 is enriched in muscle, but not epidermis of stranded compared to subsistence-hunted gray whales, E173 E174 MARINE MAMMAL SCIENCE, VOL. 28, NO. 2, 2012 indicating probable protein catabolism and nutritional stress in stranded whales. Similarly, epidermal ␦ 13 C 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.

Regional diving behavior of Pacific Arctic beluga whales Delphinapterus leucas and possible associations with prey

“…3). Stable isotope values from BS and ECS belugas suggest reliance on both benthic and pelagic prey (Dehn et al 2006, Horstmann-Dehn et al 2012, which fits the mixed pattern of benthic and pelagic diving among regions in our results. Benthic invertebrates (e.g.…”

Trophic niche partitioning and diet composition of sympatric fin (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) in the Gulf of Alaska revealed through stable isotope analysis

“…studies thus recommend analyzing d 13 C from lipid extracted samples and d 15 N from nonextraced samples (Lesage et al 2010, Ryan et al 2012, in this study lipids were extracted from all prey and whale samples to maintain a consistent processing protocol within the GAP program. Isotope values from other baleen whale were not influenced by lipid extraction (Horstmann-Dehn et al 2012, Ryan et al 2012.…”

“…Isotope values from other baleen whale were not influenced by lipid extraction (Horstmann‐Dehn et al . , Ryan et al . ).…”

Assessing δ13C, δ15N and Total Mercury Measures in Epidermal Biopsies From Gray Whales

“…Hg concentrations have increased in Arctic environments during the past 150 years, leading to more than 92% of Hg body burden in higher trophic level species possibly originating from anthropogenic activities (Dietz et al, 2009). The relative longevity of gray whales sets the stage for bioaccumulation, but gray whales primarily feed on lower trophic levels of benthic invertebrates (Dehn et al, 2006a,b;Horstmann-Dehn et al, 2012) as compared to piscivorous cetaceans well known to have much higher Hg tissue concentrations. It is challenging to measure adverse effects from Hg in free-ranging species, but reports from pinnipeds ( Van-Hoomissen et al, 2015;Kennedy et al, 2019) suggests an increase in abnormal behavior and a decrease in haptoglobin levels, associated with increased Hg concentrations.…”

“…Assessments of feeding ecology are also important in longlived cetaceans. Ratios of stable isotopes of carbon-13 and nitrogen-15 have been used extensively to trace pathways of organic matter and complexity of trophic levels (Rounick and Winterbourn, 1986;Caraveo-Patino and Soto, 2005;Dehn et al, 2006b;Horstmann-Dehn et al, 2012) as well as movement (migration) between regions with varying isotopic signatures (Hoekstra et al, 2002). The eastern gray whale population migrates from their summer feeding grounds in Alaska to their winter grounds in Baja California Sur, Mexico.…”