Smallmouth bass (Micropterus dolomieu) predation on subyearling fall Chinook salmon (Oncorhynchus tshawytscha) was examined in the Snake River (USA) to identify seasonal and habitat-related changes in bass diets, and associated subyearling consumption and loss in various riverine and impounded reaches. Smallmouth bass diets reflected opportunistic foraging that at times showed predation on subyearlings is influenced by the consumption of other prey such as crayfish, sand roller (Percopsis transmontana), and smaller invertebrates. Estimated loss of subyearlings was influenced by bass abundance and consumption rates. The highest bass abundances (> 1,000 bass/river kilometer) were observed in the upper reach of Hells Canyon early in April and May, and in Lower Granite Reservoir. Peak consumption rates of subyearlings (≥ 0.12 subyearlings/bass/day) occurred in the upper reach of Hells Canyon during May and in most reservoir reaches in June. Predation losses accumulated evenly along the river continuum from riverine to reservoir habitats. We estimated that 869,371 subyearlings could be lost to smallmouth bass predation between riverine production areas and Lower Granite Dam in a given year. To provide a context for this estimated loss, we provide an illustration of its potential effect on the adult population. Assuming no juvenile mortality occurred downstream of the dam and depending on smolt-to-adult return rates, this represented up to 3.9–16.0% of the potential adult run that could have returned to Lower Granite Dam had no subyearling predation by smallmouth bass occurred upstream of the dam. Although this study was limited by a number of assumptions and constraints, it does provide an illustration of how predation affects juvenile and adult salmon loss over a broad, changing river landscape.

中文翻译：

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捕食小嘴鲈鱼对宽阔河流连续体上的亚一岁秋季奇努克鲑鱼的影响

在美国斯内克河对小嘴鲈 (Micropterus dolomieu) 捕食亚一岁秋季奇努克鲑鱼 (Oncorhynchus tshawytscha) 进行了研究，以确定鲈鱼饮食的季节性和栖息地相关变化，以及各种河流和蓄水河段中相关的亚一岁鱼消费和损失。小嘴鲈鱼的饮食反映了机会主义觅食，有时显示对亚一岁幼体的捕食受到其他猎物的影响，如小龙虾、沙辊（Percopsis transmontana）和较小的无脊椎动物。估计的亚龄幼体损失受鲈鱼丰度和消费率的影响。4 月初和 5 月初，在地狱峡谷的上游和下花岗岩水库中观察到了最高的鲈鱼丰度（> 1,000 鲈鱼/河流公里）。亚岁幼仔的峰值消费率（≥ 0. 5 月在地狱峡谷的上游和 6 月的大部分水库河段发生了 12 只幼仔/巴斯/天。捕食损失沿着从河流到水库栖息地的河流连续体均匀累积。我们估计，在特定年份，河流产区和下花岗岩大坝之间的小嘴鲈鱼捕食可能会导致 869,371 头亚一岁的幼崽丧生。为了提供这种估计损失的背景，我们提供了它对成年人口的潜在影响的说明。假设大坝下游没有发生幼鱼死亡，并且取决于小鱼到成年的回归率，这代表了高达 3.9-16.0% 的可能返回下花岗岩大坝的潜在成年奔跑，上游没有发生小嘴鲈的亚岁捕食大坝的。