Stable Isotope Models Predict Foraging Habitat of Northern Fur Seals (Callorhinus ursinus) in Alaska

Abstract

We developed models to predict foraging habitat of adult female northern fur seals (Callorhinus ursinus) using stable carbon (δ13C) and nitrogen (δ15N) isotope values from plasma and red blood cells. Binomial generalized linear mixed models were developed using blood isotope samples collected from 35 adult female fur seals on three breeding colonies in Alaska during July-October 2006. Satellite location and dive data were used to define habitat use in terms of the proportion of time spent or dives made in different oceanographic/bathymetric domains. For both plasma and red blood cells, the models accurately predicted habitat use for animals that foraged exclusively off or on the continental shelf. The models did not perform as well in predicting habitat use for animals that foraged in both on- and off-shelf habitat; however, sample sizes for these animals were small. Concurrently collected scat, fatty acid, and dive data confirmed that the foraging differences predicted by isotopes were associated with diet differences. Stable isotope samples, dive data, and GPS location data collected from an additional 15 females during August-October 2008 validated the effective use of the models across years. Little within year variation in habitat use was indicated from the comparison between stable isotope values from plasma (representing 1-2 weeks) and red blood cells (representing the prior few months). Constructing predictive models using stable isotopes provides an effective means to assess habitat use at the population level, is inexpensive, and can be applied to other marine predators.

Motive for Killing: What Drives Prey Choice in Wild Predators?

“…The integration of the multidimensional nutritional framework NG and data collecting abilities offered by biologging and, in particular, AVEDs could thus significantly advance the science of nutritional ecology and its applications, by helping insights derived from laboratory studies to be interpreted and extended in the context of the wild. Biologging technology has been successfully integrated with traditional methods of diet estimation in predators, such as scats, stable isotopes and fatty acid analyses (Iverson et al 2004;Zeppelin et al 2015) and recently NG (Machovsky-Capuska et al 2016b). AVEDS clearly offer the advantage of providing an animal's perspective on dietary intake by directly recording what is selected and consumed.…”

Should fatty acid signature proportions sum to 1 for diet estimation?

“…Consequently, the development of methods to estimate diets has long been a focus of research in quantitative ecology and several methods remain in common use (e.g., Bowles et al 2011;Chambellant et al 2013;Haynes et al 2015;Roberts and Lalas 2015;Zeppelin et al 2015). Consequently, the development of methods to estimate diets has long been a focus of research in quantitative ecology and several methods remain in common use (e.g., Bowles et al 2011;Chambellant et al 2013;Haynes et al 2015;Roberts and Lalas 2015;Zeppelin et al 2015).…”

“…Knowledge of animal diets, and how diets differ among individuals or age and sex classes, provides essential insights into ecological processes. Consequently, the development of methods to estimate diets has long been a focus of research in quantitative ecology and several methods remain in common use (e.g., Bowles et al 2011;Chambellant et al 2013;Haynes et al 2015;Roberts and Lalas 2015;Zeppelin et al 2015). Quantitative fatty acid signature analysis (QFASA; Iverson et al 2004) is one such method, being implemented most widely for diet estimation of marine species (e.g., Bowen and Iverson 2013).…”

Variability in trophic level and habitat use in response to environmental forcing: isotopic niche dynamics of breeding seabirds in the southeastern Bering Sea

“…In the southeastern Bering Sea, there is a δ 13 C gradient in seabird prey: prey from the continental shelf have higher δ 13 C values compared to alternative prey from the continental slope or ocean basin (Zeppelin et al 2015), which is also reflected in the stable isotope ratios of bird blood tissues (Dorresteijn et al 2012). In cold conditions, when juvenile pollock are relatively scarce on the shelf, we predicted that the isotopic niche of birds with access primarily to shelf foraging habitat (St. Paul Island) would expand as species separate themselves by prey type and geographic location.…”

“…In contrast, we predicted that the isotopic niche used by seabirds on colonies closer to the shelf break would contract during cold years. On St. George Island, all species have access to more heterogeneous foraging habitat, so during cold ocean conditions when prey availability is low on the shelf, we expected seabirds to concentrate their foraging efforts on prey inhabiting the continental slope region (Pomerleau et al 2014, Zeppelin et al 2015, Suryan et al 2016.…”