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Use of naturally occurring mercury to determine the importance of cutthroat trout to Yellowstone grizzly bears

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Abstract:

Spawning cutthroat trout (Oncorhynchus clarki (Richardson, 1836)) are a potentially important food resource for grizzly bears (Ursus arctos horribilis Ord, 1815) in the Greater Yellowstone Ecosystem. We developed a method to estimate the amount of cutthroat trout ingested by grizzly bears living in the Yellowstone Lake area. The method utilized (i) the relatively high, naturally occurring concentration of mercury in Yellowstone Lake cutthroat trout (508 ± 93 ppb) and its virtual absence in all other bear foods (≤6 ppb), (ii) hair snares to remotely collect hair from bears visiting spawning cutthroat trout streams between 1997 and 2000, (iii) DNA analyses to identify the individual and sex of grizzly bears leaving a hair sample, (iv) feeding trials with captive bears to develop relationships between fish and mercury intake and hair mercury concentrations, and (v) mercury analyses of hair collected from wild bears to estimate the amount of trout consumed by each bear. Male grizzly bears consumed an average of 5 times more trout/kg bear than did female grizzly bears. Estimated cutthroat trout intake per year by the grizzly bear population was only a small fraction of that estimated by previous investigators, and males consumed 92% of all trout ingested by grizzly bears.

Les truites fardées (Oncorhynchus clarki (Richardson, 1836)) en fraye constituent une ressource alimentaire potentiellement importante pour les grizzlis (Ursus arctos horribilis Ord, 1815) dans l'écosystème du Grand Yellowstone. Nous avons mis au point une méthode pour estimer la quantité de truites fardées ingérées par les grizzlis vivant dans la région du lac Yellowstone. La méthode utilise (i) la concentration naturelle et relativement élevée de mercure chez les truites fardées du lac Yellowstone (508 ± 93 ppb) et son absence virtuelle (≤6 ppb) dans les autres aliments des ours, (ii) des dispositifs pour récolter à distance des touffes de poils des ours qui visitent les cours d'eau de fraye de la truite fardée (utilisés de 1997 à 2000), (iii) des analyses d'ADN pour déterminer l'identité et le sexe des grizzlis qui ont laissé ces touffes de poils, (iv) des essais alimentaires chez des ours en captivité afin d'établir la relation qui existe entre l'ingestion de poissons et de mercure, d'une part, et la concentration de mercure dans le poil, d'autre part, et (v) le dosage du mercure dans le poil d'ours sauvages afin d'estimer la quantité de chair de truite consommée par chaque ours. Les grizzlis mâles consomment en moyenne 5 fois plus de chair de truite par kg d'ours que les femelles. L'ingestion annuelle estimée de chair de truite par la population d'ours n'est qu'une petite fraction de celle obtenue par des chercheurs antérieurs; de plus, les mâles consomment 92 % de toute la chair de truite ingérée par les grizzlis.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2004

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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