van Leeuwen Casper H A, Museth Jon, Sandlund Odd T, Qvenild Tore, Vøllestad L Asbjørn
Department of Biosciences Centre for Ecological and Evolutionary Synthesis (CEES) University of Oslo Post Office Box 1066 Blindern 0316 Oslo Norway.
Norwegian Institute for Nature Research (NINA) Fakkelgården 2624 Lillehammer Norway.
Ecol Evol. 2016 Mar 10;6(8):2414-25. doi: 10.1002/ece3.1937. eCollection 2016 Apr.
Habitat fragmentation is a growing problem worldwide. Particularly in river systems, numerous dams and weirs hamper the movement of a wide variety of species. With the aim to preserve connectivity for fish, many barriers in river systems are equipped with fishways (also called fish passages or fish ladders). However, few fishways provide full connectivity. Here we hypothesized that restricted seasonal opening times of fishways can importantly reduce their effectiveness by interfering with the timing of fish migration, for both spring- and autumn-spawning species. We empirically tested our hypothesis, and discuss the possible eco-evolutionary consequences of affected migration timing. We analyzed movements of two salmonid fishes, spring-spawning European grayling (Thymallus thymallus) and autumn-spawning brown trout (Salmo trutta), in Norway's two largest river systems. We compared their timing of upstream passage through four fishways collected over 28 years with the timing of fish movements in unfragmented river sections as monitored by radiotelemetry. Confirming our hypothesis, late opening of fishways delayed the migration of European grayling in spring, and early closure of fishways blocked migration for brown trout on their way to spawning locations during late autumn. We show in a theoretical framework how restricted opening times of fishways can induce shifts from migratory to resident behavior in potamodromous partial migration systems, and propose that this can induce density-dependent effects among fish accumulating in lower regions of rivers. Hence, fragmentation may not only directly affect the migratory individuals in the population, but may also have effects that cascade downstream and alter circumstances for resident fish. Fishway functionality is inadequate if there is a mismatch between natural fish movements and fishway opening times in the same river system, with ecological and possibly evolutionary consequences for fish populations.
栖息地破碎化是一个在全球范围内日益严重的问题。特别是在河流系统中，众多的水坝和堰闸阻碍了各种各样物种的移动。为了保护鱼类的连通性，许多河流系统中的障碍物都配备了鱼道（也称为鱼类通道或鱼梯）。然而，很少有鱼道能提供完全的连通性。在此，我们假设鱼道有限的季节性开放时间会通过干扰鱼类洄游的时间，对春季和秋季产卵的物种产生重要影响，从而显著降低其有效性。我们通过实证检验了这一假设，并讨论了受影响的洄游时间可能产生的生态进化后果。我们分析了挪威两大河流系统中两种鲑科鱼类的移动情况，即春季产卵的欧洲茴鱼（Thymallus thymallus）和秋季产卵的褐鳟（Salmo trutta）。我们将它们通过四条在28年期间收集数据的鱼道向上游洄游的时间，与通过无线电遥测监测的未破碎河段中鱼类移动的时间进行了比较。正如我们的假设，鱼道开放时间延迟导致欧洲茴鱼春季洄游推迟，而鱼道提前关闭则在深秋阻止了褐鳟前往产卵地点的洄游。我们在一个理论框架中展示了鱼道有限的开放时间如何在河川性部分洄游系统中促使鱼类从洄游行为转变为定居行为，并提出这可能会在河流下游区域聚集的鱼类中引发密度依赖效应。因此，破碎化不仅可能直接影响种群中的洄游个体，还可能产生级联效应，改变下游的环境以及定居鱼类的生存条件。如果同一河流系统中自然鱼类移动与鱼道开放时间不匹配，鱼道功能就不完善，这会对鱼类种群产生生态甚至可能的进化影响。
