Proportion of higher trophic-level prey in the diet of Pacific walruses (Odobenus rosmarus divergens)

Seymour, J.; Horstmann-Dehn, Larissa; Wooller, Matthew J.

doi:10.1007/s00300-014-1492-z

Cited by 20 publications

(22 citation statements)

References 57 publications

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“…In this study, chemical lipid extractions significantly increased the δ 13 C values of walrus liver and skin, indicating that lipids affected δ 13 C in these tissues. Muscle δ 13 C remained unchanged, likely because marine mammal muscle is typically comprised of lean protein with little lipid content 47–49 . Lipids are stored primarily in the blubber layer in these animals, rather than interspersed among the muscles.…”

Section: Discussionmentioning

confidence: 99%

“…A rough estimate of diet-muscle discrimination can be made for walruses using published prey stable isotope values. Average reported δ 13 C and δ 15 N of bivalve species common in walrus diet ( Serripes groenlandicus and Macoma calcarea ) are ~−18.8‰ and ~9.2‰, respectively 48,49,78,79 . Using these values to estimate diet-muscle discrimination estimates for walruses in this study results in a value of +1.8‰ (Δ 13 C) and +3.3‰ (Δ 15 N).…”

Section: Discussionmentioning

confidence: 99%

“…Using these values to estimate diet-muscle discrimination estimates for walruses in this study results in a value of +1.8‰ (Δ 13 C) and +3.3‰ (Δ 15 N). Though bivalves comprise a large portion of their diet, walruses consume a wide variety of prey items, including higher trophic level prey such as predatory snails, seabirds, and seals 49,59,80 . The estimate for Δ 15 N muscle-diet may thus be high, as inclusion of these higher trophic level prey items would increase the estimated average δ 15 N of walrus prey.…”

Section: Discussionmentioning

confidence: 99%

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Lipid normalization and stable isotope discrimination in Pacific walrus tissues

Clark

Horstmann

Misarti

2019

Sci Rep

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Analysis of stable carbon and nitrogen isotope values (δ 13 C and δ 15 N) of animal tissues can provide important information about diet, physiology, and movements. Interpretation of δ 13 C and δ 15 N values, however, is influenced by factors such as sample lipid content, tissue-specific isotope discrimination, and tissue turnover rates, which are typically species- and tissue-specific. In this study, we generated lipid normalization models for δ 13 C and investigated the effects of chemical lipid extractions on δ 13 C and δ 15 N in Pacific walrus ( Odobenus rosmarus divergens ) muscle, liver, and skin. We also evaluated tissue-specific isotope discrimination in walrus muscle, liver, skin, and bone collagen. Mean δ 13 C lipid-free of skin and bone collagen were similar, as were mean δ 15 N of muscle and liver. All other tissues differed significantly for both isotopes. Differences in δ 13 C lipid-free and δ 15 N among tissues agreed with published estimates of marine mammal tissue-specific isotope discrimination factors, with the exception of skin. The results of this work will allow researchers to gain a clearer understanding of walrus diet and the structure of Arctic food webs, while also making it possible to directly compare the results of contemporary walrus isotope research with those of historic and paleoecological studies.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Lipid normalization and stable isotope discrimination in Pacific walrus tissues

Clark

Horstmann

Misarti

2019

Sci Rep

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“…The Pacific walrus population is currently a candidate species under the ESA due to concern regarding the species' response to changes in summer sea ice habitat (Robards and Garlich-Miller, 2013;USFWS, 2011). Walruses feed primarily on benthic invertebrates including marine worms (e.g., polychaetes, sipunculids, echiurids priapulids), mollusks (e.g., bivalves and gastropods), and crustaceans (e.g., amphipods, shrimp, crabs) (Born et al, 2003;Bowen and Siniffand, 1999;Dehn et al, 2007;Fay, 1982;Sheffield et al, 2001;Sheffield and Grebmeier, 2009) although fish and other vertebrates (including seals) are also occasionally reported (Fay, 1982;Seymour et al, 2014;Sheffield et al, 2001;Sheffield and Grebmeier, 2009). Walruses are not physiologically adapted for deep diving and concentrate foraging efforts in shallower waters, typically using the sea ice as a resting platform between feeding trips (Fay, 1982).…”

Section: Pacific Walrusmentioning

confidence: 99%

Prevalence of algal toxins in Alaskan marine mammals foraging in a changing arctic and subarctic environment

et al. 2016

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Current climate trends resulting in rapid declines in sea ice and increasing water temperatures are likely to expand the northern geographic range and duration of favorable conditions for harmful algal blooms (HABs), making algal toxins a growing concern in Alaskan marine food webs. Two of the most common HAB toxins along the west coast of North America are the neurotoxins domoic acid (DA) and saxitoxin (STX). Over the last 20 years, DA toxicosis has caused significant illness and mortality in marine mammals along the west coast of the USA, but has not been reported to impact marine mammals foraging in Alaskan waters. Saxitoxin, the most potent of the paralytic shellfish poisoning toxins, has been well-documented in shellfish in the Aleutians and Gulf of Alaska for decades and associated with human illnesses and deaths due to consumption of toxic clams. There is little information regarding exposure of Alaskan marine mammals. Here, the spatial patterns and prevalence of DA and STX exposure in Alaskan marine mammals are documented in order to assess health risks to northern populations including those species that are important to the nutritional, cultural, and economic well-being of Alaskan coastal communities. In this study, 905 marine mammals from 13 species were sampled including; humpback whales, bowhead whales, beluga whales, harbor porpoises, northern fur seals, Steller sea lions, harbor seals, ringed seals, bearded seals, spotted seals, ribbon seals, Pacific walruses, and northern sea otters. Domoic acid was detected in all 13 species examined and had the greatest prevalence in bowhead whales (68%) and harbor seals (67%). Saxitoxin was detected in 10 of the 13 species, with the highest prevalence in humpback whales (50%) and bowhead whales (32%). Pacific walruses contained the highest concentrations of both STX and DA, with DA concentrations similar to those detected in California sea lions exhibiting clinical signs of DA toxicosis (seizures) off the coast of Central California, USA. Forty-six individual marine mammals contained detectable concentrations of both toxins emphasizing the potential for combined exposure risks. Additionally, fetuses from a beluga whale, a harbor porpoise and a Steller sea lion contained detectable concentrations of DA documenting maternal toxin transfer in these species. These results provide evidence that HAB toxins are present throughout Alaska waters at levels high enough to be detected in marine mammals and have the potential to impact marine mammal health in the Arctic marine environment.

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“…Seals constitute the staple diet of polar bears across the Arctic, but their T. nativa prevalence (0–1.9% in bearded and ringed seal surveys; Seymour et al 2014a) is generally an order of magnitude lower than that of polar bears. Walrus may also be occasionally hunted or scavenged in some areas but are an unlikely suspect for maintaining high T. nativa prevalences in polar bears throughout the Arctic, given that they are not regularly consumed in every polar bear subpopulation (Thiemann et al 2008); that they are generally only hunted by large males (Thiemann et al 2008); and that their T. nativa prevalence only reaches high levels in areas where the walrus also consume seals (Fay 1960, Seymour et al 2014b). Other potential carrion items, such as bowhead whales Balaena mysticetus , have not been reported to carry T. nativa at all (Rausch et al 1956).…”

Section: Introductionmentioning

confidence: 99%

Mechanistic models can reveal infection pathways from prevalence data: the mysterious case of polar bears Ursus maritimus and Trichinella nativa

Penk

Bodner

Soto

et al. 2020

Oikos

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Parasites exhibit a diverse range of life history strategies. Transmission to a host is a key component of each life cycle but the difficulty of observing host–parasite contacts has often led to confusion surrounding transmission pathways. Given limited data on most host–parasite systems, flexible approaches are needed for disentangling the obscure transmission dynamics of these systems. Here, we develop a modelling framework for formally testing long‐standing hypotheses regarding how the parasitic nematode Trichinella nativa is maintained at high prevalences in polar bear populations. We evaluated transmission from marine prey, from scavenging terrestrial carrion, from cannibalism and from scavenging on dead infected bears as possible pathways, and assessed their respective importance by comparing model‐projected prevalences for each mechanism against observed total and age‐specific population prevalences in the Southern Beaufort Sea polar bear subpopulation. Cannibalism and the scavenging on conspecifics have previously been assumed to be critical transmission pathways, but despite data scarcity, our model exposes these mechanisms as ineffective across a wide range of plausible parameter values. Instead, our analyses suggest that transmission from the consumption of infected marine prey, and in particular seals, can explain observed prevalence levels by itself, with other transmission pathways likely playing varying small contributing roles. Furthermore, our model suggests that transmission declines with bear age, perhaps due to age‐dependent changes in diet or immunity. By formalising multiple transmission mechanisms in a unified, mathematical framework, we distilled several hypotheses to a likely main mode of T. nativa transmission to polar bears. The specifics of our model are tailored towards the T. nativa‐polar bear system, but the approach is easily generalized; it provides a powerful, quantitative means for ecologists to explore competing hypothesis for parasite transmission and other difficult‐to‐observe animal interactions even in data‐poor systems.

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Proportion of higher trophic-level prey in the diet of Pacific walruses (Odobenus rosmarus divergens)

Cited by 20 publications

References 57 publications

Lipid normalization and stable isotope discrimination in Pacific walrus tissues

Lipid normalization and stable isotope discrimination in Pacific walrus tissues

Prevalence of algal toxins in Alaskan marine mammals foraging in a changing arctic and subarctic environment

Mechanistic models can reveal infection pathways from prevalence data: the mysterious case of polar bears Ursus maritimus and Trichinella nativa

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