Recent declines in abundance of Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in the upper Blackfoot River drainage in Idaho coincided with establishment of a nearby nesting colony and increased abundance of American white pelicans Pelecanus erythrorhynchos (hereafter, “pelicans”). Published pelican predation rates have been estimated to be as high as 70% on Yellowstone Cutthroat Trout in the Blackfoot River. Consequently, the Idaho Department of Fish and Game established management objectives for pelicans of less than 350 breeding pairs or 700 adults. However, a thorough assessment has not been conducted to evaluate if the pelican abundance objective would reduce predation to an extent that would allow Yellowstone Cutthroat Trout to recover to levels that meet minimum objectives for abundance. A Bayesian state-space model that integrated survival and abundance data was used in this study to evaluate the effects of local pelican abundance on survival, abundance, and population growth rate of Yellowstone Cutthroat Trout. Survival of both juvenile and adfluvial adult Yellowstone Cutthroat Trout decreased as pelican abundance increased, and there was a positive relationship between survival of both life stages and population growth rate. If the current management objective for abundance of 700 breeding pelicans was met, the probability of meeting or exceeding the Yellowstone Cutthroat Trout objective was 0.44 and declined substantially as simulated pelican abundance increased beyond 700. Results of this study suggest that if pelican abundance can be maintained at or below the current management objective, there is a reasonable chance of meeting the management objective for Yellowstone Cutthroat Trout.

中文翻译：

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评估美洲白鹈鹕丰度的目标水平以实现黄石鳟鱼的管理目标

最近爱达荷州黑脚河上游流域的黄石割喉鳟鱼Oncorhynchus clarkii bouvieri丰度的下降恰逢附近建立了一个筑巢群，而美国白鹈鹕Pelecanus erythrorhynchos 的丰度增加（以下简称“鹈鹕”）。已公布的鹈鹕捕食率估计高达 70% 对黑脚河黄石鳟鱼的捕食率。因此，爱达荷州渔猎局为少于 350 对繁殖对或 700 只成年鹈鹕制定了管理目标。然而，尚未进行彻底的评估来评估鹈鹕丰度目标是否会将捕食减少到一定程度，使黄石鳟鱼恢复到满足最低丰度目标的水平。本研究使用整合了生存和丰度数据的贝叶斯状态空间模型来评估当地鹈鹕丰度对黄石鳟鱼的存活、丰度和种群增长率的影响。随着鹈鹕丰度的增加，黄石鳟鱼的幼鱼和成年鱼的存活率均下降，并且两个生命阶段的存活率与种群增长率之间存在正相关关系。如果满足当前 700 只繁殖鹈鹕丰度的管理目标，达到或超过黄石割喉鳟鱼目标的概率为 0.44，并且随着模拟鹈鹕丰度增加超过 700 只大幅下降。 本研究结果表明，如果鹈鹕丰度能够保持在当前管理目标或低于当前管理目标时，有合理的机会实现 Yellowstone Cutthroat Trout 的管理目标。