Use of naturally occurring mercury to determine the importance of cutthroat trout to Yellowstone grizzly bears
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Resource 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.
Citation
Title Use of naturally occurring mercury to determine the importance of cutthroat trout to Yellowstone grizzly bears