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Survival and Harvest Vulnerability of Elk in the Cascade Range of Washington

Scott M. McCorquodale, Ray Wiseman and C. Les Marcum
The Journal of Wildlife Management
Vol. 67, No. 2 (Apr., 2003), pp. 248-257
Published by: Wiley on behalf of the Wildlife Society
DOI: 10.2307/3802766
Stable URL: http://www.jstor.org/stable/3802766
Page Count: 10
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Survival and Harvest Vulnerability of Elk in the Cascade Range of Washington
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Abstract

We studied survival and vulnerability to hunting mortality among adult male, subadult male, and adult female elk (Cervus elaphus; n = 78) in the Cascade Range of south-central Washington, USA, 1992-1999. Among several candidate survival models, the weight of evidence suggested that the data best supported a model wherein survival varied by sex, ($\hat{S}_{\text{MALE}}$ = 0.65 [95% CI: 0.54 to 0.75], $S_{\text{FEMALE}}$ = 0.83 [95% CI: 0.70 to 0.91]). Thirty-nine (50%) of the radiomarked elk died during the study. All deaths among subadult (≤4 yr) males and all but 1 death among females were caused by hunting. Eleven of 17 (64.7%) deaths among adult (≥5 yr) males were hunting-related, whereas 5 deaths (29.4%) were independent of hunting. We evaluated 12 candidate logistic regression models relating elk harvest risks to landscape features within summer-autumn home ranges, where most hunting mortalities occurred, using an information-theoretic approach. Akaike model weights indicated that 5 models represented a best-model subset using data from all radiomarked elk and 4 models represented a logical best-model subset when the analysis was limited to data from male elk, although collective Akaike weights differed between the 2 subsets. Several models in the best-model subsets contained road density (km/km2) as an explanatory variable, but models using road density as the only explanatory variable were not among the best-model subsets. Two additional variables appeared to be useful for modeling harvest risks. Aspect diversity, an index of topographic complexity (which influenced hunter effort), and percent of elk home ranges in managed forest were common to several models in the best-model subsets. The managed forest variable indexed the proportion of an elk's home range that was roaded. All models in the best-model subsets had either a road density or percent managed forest variable, suggesting that broadly defined road effects were important sources of harvest vulnerability. For all elk, the model with the highest Akaike weight (56%) used road density and 2 topographic variables to explain elk harvest risks. For male-only data, the best-supported model (weight = 25%) used percent managed forest and aspect diversity as explanatory variables. Our analysis supported the inference that harvest vulnerability in elk in the south-central Cascades was strongly affected by the presence and/or density of open roads, but that topographic complexity influenced the likelihood that elk were killed apart from roading effects.

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