Unscreened Water-Diversion Pipes Pose an Entrainment Risk to the Threatened Green Sturgeon, Acipenser medirostris

Over 3,300 unscreened agricultural water diversion pipes line the levees and riverbanks of the Sacramento River (California) watershed, where the threatened Southern Distinct Population Segment of green sturgeon, Acipenser medirostris, spawn. The number of sturgeon drawn into (entrained) and killed by these pipes is greatly unknown. We examined avoidance behaviors and entrainment susceptibility of juvenile green sturgeon (35±0.6 cm mean fork length) to entrainment in a large (>500-kl) outdoor flume with a 0.46-m-diameter water-diversion pipe. Fish entrainment was generally high (range: 26–61%), likely due to a lack of avoidance behavior prior to entering inescapable inflow conditions. We estimated that up to 52% of green sturgeon could be entrained after passing within 1.5 m of an active water-diversion pipe three times. These data suggest that green sturgeon are vulnerable to unscreened water-diversion pipes, and that additional research is needed to determine the potential impacts of entrainment mortality on declining sturgeon populations. Data under various hydraulic conditions also suggest that entrainment-related mortality could be decreased by extracting water at lower diversion rates over longer periods of time, balancing agricultural needs with green sturgeon conservation.萨克拉门托河（加利福尼亚州）流域的堤防与河岸沿线，布设了超过3300根未加装防护网的农业引水管道，该区域为受威胁的绿鲟（Acipenser medirostris）南部独特种群（Southern Distinct Population Segment）的产卵栖息地。被这些管道卷吸（entrained）并致死的鲟鱼数量目前仍极不明确。本研究在一座容积大于500千升的室外实验水槽中，针对平均叉长为35±0.6厘米的幼龄绿鲟，探究了其对直径0.46米引水管道卷吸的逃避行为与卷吸易感性。实验结果显示，幼鲟的卷吸率普遍较高（区间为26%至61%），这大概率源于幼鲟在进入无法逃脱的水流环境前未表现出逃避行为。本研究估算，若幼鲟三次途经活跃引水管道周边1.5米范围内，其卷吸率最高可达52%。上述数据表明，绿鲟极易受到未加装防护网的引水管道的威胁，且需开展进一步研究以明确卷吸致死对鲟鱼种群衰退的潜在影响。不同水力条件下的实验数据同时显示，通过采用更低的引水速率、延长取水时长的方式，可降低卷吸相关致死率，从而兼顾农业用水需求与绿鲟物种保护。