“水力-集群”交互作用对鲢幼鱼上溯行为的影响

Effects of hydrodynamic-schooling interaction on upstream migration behaviour of juvenile Hypophthalmichthys molitrix

摘要:

目的 厘清鱼群上溯过程中的“鱼-水”运动响应关系是水电工程过鱼设施设计的重要基础。为量化鱼类在水力驱动与集群效应共同影响下的上溯行为规律。方法 以我国重要经济鱼种鲢为对象，测定个体与10尾群体鲢幼鱼在非疲劳、不同湍动水平流场中的溯流运动特征。结果 ①在低湍动流场中，单尾鲢幼鱼上溯成功率为100%，平均耗时 (40±27) s，运动分布均匀，对流速无明显偏好。②在局部高湍动流场中，单尾鲢幼鱼倾向在低流速与低湍动区驻留，利用卡门涡街降低瞬时能耗，上溯耗时显著增加 (84±54) s。③ 10尾鲢幼鱼群体上溯轨迹分布相对集中，集群吸引和引导作用促使鱼类成队列沿主流上溯。④在局部高湍动流场中，10尾鲢幼鱼群体受集群排斥作用影响，未能有效避开高速高湍动水流，其上溯过程受阻，上溯成功率显著降低至54%，上溯耗时延长至 (88±12) s。结论 鲢幼鱼在上溯过程中的运动分布主要受流速和湍动能的综合影响，且表现出对高湍动水流的规避趋势。集群游动时，个体间的吸引和引导作用有助于优化上溯路径节约能耗，而排斥作用则可能降低其上溯效率，不利于个体鱼对水流条件的充分利用。本研究可在集群规模调控与特征流场营造两方面为过鱼设施的优化设计与高效运行提供理论依据和数据支持。

Abstract:

Elucidating the hydrodynamic-fish motion response relationship during the upstream migration of schooling fish is fundamental for designing fish passage in hydropower infrastructure. The current study quantified the upstream movement patterns of individual and group (ten individuals) juvenile Hypophthalmichthys molitrix, an economically significant fish species in China, under the combined hydrodynamic-schooling influence in non-fatigued flow fields with varying turbulence levels. We concluded that: ① In the low-turbulence flow field, individual juvenile H. molitrix achieved a 100% passing rate with an average time expenditure of (40±27) s, exhibiting uniform movement distribution without a clear velocity preference. ② Within the locally high-turbulence flow field, individual juvenile H. molitrix tended to linger in areas of lower velocity and turbulence, utilising the Kármán vortex street to minimise instantaneous energy cost, leading to a significantly increased time expenditure [(84±54) s, P<0.001)]. ③ The swimming trajectories of juvenile H. molitrix in school were relatively concentrated, with the attraction and guidance effects between neighbour fish promoting their linear formations along the primary flow. ④ In locally high-turbulence flow field, the inter-individual repulsion effect of juvenile H. molitrix in school hindered their effective avoidance of high-speed, high-turbulence flowing areas, causing impeded upstream movement, with passing rate dropping significantly to 54% (P<0.05) and time expenditure extending to (88±12) s. The study indicates that the movement distribution of juvenile H. molitrix during upstream migration is primarily influenced by the combined effects of flow velocity and turbulence intensity, with a tendency to avoid high-turbulence areas. During schooling, the attraction and guidance between individuals help optimize the upstream path and reduce energy expenditure, while the repulsion effect may decrease migration efficiency and hinder the full utilization of favorable water flow conditions by individual fish. The findings offer theoretical foundations and data support for optimising the design and enhancing the operational efficiency of fish passage by regulating fish school size and developing characteristic flow fields.