Water diversions worldwide may entrain or impinge fish and have population‐level impacts, but barriers like fish screens can reduce such threats. Traditional barriers are ineffective in the San Juan River, USA, due to high sediment and debris loads, so the Hogback Diversion Canal, NM, employs a novel weir wall design to reduce entrainment of sub‐adult and adult fishes. We evaluated the effectiveness of the weir wall in reducing the entrainment of larval fish using a combination of experimental and overnight trials. Larval fish densities were compared between the irrigation canal that delivers water to irrigators and subsequently entrains fish and the bypass canal that conveys water and fish back to the river. The density of hatchery‐produced larval fish collected in the irrigation canal during the experimental trial (0.74 fish/m3) was 52% of their density in the bypass canal (1.43 fish/m3), suggesting entrainment reduction. The density of wild‐produced larvae during overnight trials indicated some minor, mostly nonsignificant, differences between catch rates in irrigation and bypass canals, ontogenetic phases, and sampling dates. Though entrainment rates of wild‐produced larvae were not significantly reduced, density differences among postflexion mesolarvae and metalarvae suggest possible entrainment reduction of more developed ontogenetic phases. More intensive research is necessary to better elucidate the efficacy of the novel weir wall for reducing the entrainment of larval fish. However, our larval fish results and the results from prior large‐bodied entrainment studies suggest the novel weir wall may reduce fish entrainment in water diversions and benefit fluvial ecosystems in which traditional screens are unfeasible.

中文翻译：

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评估圣胡安河 Hogback 导流运河中幼鱼的夹带情况

世界范围内的水改道可能会夹带或撞击鱼类，并对人口产生影响，但防鱼网等屏障可以减少此类威胁。由于沉积物和碎片含量高，传统屏障在美国圣胡安河中无效，因此新墨西哥州霍格巴克导流运河采用了新颖的堰墙设计，以减少亚成鱼和成鱼的夹带。我们通过实验和过夜试验相结合的方式评估了堰壁在减少幼鱼夹带方面的有效性。比较了向灌溉机输送水并随后夹带鱼的灌溉渠和将水和鱼输送回河流的旁路渠之间的幼鱼密度。试验期间在灌溉渠中收集的孵化场生产的幼鱼密度（0.74 条/m3）是旁路运河中密度的 52%（1.43 条鱼/米）3），建议减少夹带。隔夜试验中野生幼虫的密度表明，灌溉和旁路运河的捕获率、个体发育阶段和采样日期之间存在一些微小的、大多不显着的差异。尽管野生幼虫的夹带率没有显着降低，但屈曲后中幼虫和后幼虫之间的密度差异表明，更发达的个体发育阶段的夹带可能会减少。需要进行更深入的研究，以更好地阐明新型堰壁在减少幼鱼夹带方面的功效。然而，我们的幼鱼结果和之前的大型夹带研究的结果表明，新型堰墙可能会减少引水中的鱼类夹带，并有利于传统屏障无法实现的河流生态系统。