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

January 1, 2004

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 Information

Publication Year 2004
Title Use of naturally occurring mercury to determine the importance of cutthroat trout to Yellowstone grizzly bears
DOI 10.1139/z04-013
Authors L.A. Felicetti, C.C. Schwartz, R. O. Rye, K.A. Gunther, J. G. Crock, M.A. Haroldson, L. Waits, C.T. Robbins
Publication Type Article
Publication Subtype Journal Article
Series Title Canadian Journal of Zoology
Series Number
Index ID 70027529
Record Source USGS Publications Warehouse
USGS Organization Northern Rocky Mountain Science Center