Mountain whitefish (Prosopium williamsoni) are among the most abundant native fishes in western North America, yet their role in ecosystems is largely unknown. We investigated their ecology in Big Creek, a 7th-order wilderness watershed in central Idaho. Based on underwater visual counts and hook and line surveys conducted during summer months, as well as tissue analysis, we estimated mountain whitefish distribution and abundance, total biomass, production, and energy and nutrient contributions along a 60 km segment of Big Creek. We observed that abundance decreased with distance upstream, and 93% of mountain whitefish surveyed in Big Creek were greater than 200 mm (≥ 3 years); few juveniles were observed, suggesting that rearing occurs in habitats downstream. Mountain whitefish were the dominant fish in Big Creek, in terms of both abundance (33% of fish observed) and biomass (57% of salmonid biomass). We estimated their production averaged across the study segment as 0.51 g m-2 yr-1, though it ranged up to 6.8 g m-2 yr-1 in downstream reaches. Mountain whitefish tissue energy content was 5.3 Kcal g-1 and its composition was 10.5% N, 3.0% Ca, 2.3% P, 1.2% K, 0.7% S, 0.3% Na, and 0.1% Mg. The ratio of N:P(4.5:1) was slightly lower than those observed in other salmonids and considerably higher than more bony taxa. Our results suggest mountain whitefish constitute an important pool of energy and nutrients in the Big Creek ecosystem, and seem likely to play important roles that have not yet been investigated in this and other rivers throughout their range.
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1 August 2011
Abundance, Production, and Tissue Composition of Mountain Whitefish (Prosopium williamsoni) in a Central Idaho Wilderness Stream
Michael J. Lance,
Colden V. Baxter
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Northwest Science
Vol. 85 • No. 3
August 2011
Vol. 85 • No. 3
August 2011