This study investigates the effect of large woody debris (LWD) on the abundance of juvenile Atlantic salmon (Salmo salar, L.) and anadromous brown trout (Salmo trutta, L.) in semi-alluvial side channels of the river Aurlandselva (Norway) using point electrofishing and microhabitat mapping. Not the presence of LWD, but stream bed shelter availability and the distance to spawning grounds affected the fish abundance (fish/point), independent of other habitat components. LWD showed only an effect on fish abundance when in interaction with other habitat components. This discrepancy can be explained by the availability of cavities in the shelter-rich coarse substrate which provide sufficient cover and territory for juvenile fish at the given carrying capacity of river Aurlandselva. Whilst LWD may be most effective to provide shelter in lowland streams (bed slope <0.005), maintaining or restoring shelter-rich coarse substrates should be considered a key priority in steeper salmonid rivers and associated semi-fluvial streams.

中文翻译：

---

挪威一条混积半河流中幼鱼的丰度——河床庇护是否能打败大型木质残骸？

本研究调查了大型木质碎片 (LWD) 对奥兰塞尔瓦河（挪威）半冲积侧河道中幼年大西洋鲑鱼 ( Salmo salar , L.) 和溯河产卵褐鳟 ( Salmo trutta , L.)丰度的影响使用点电捕鱼和微生境测绘。不是 LWD 的存在，而是河床庇护所的可用性和到产卵场的距离影响了鱼类丰度（鱼/点），与其他栖息地组成部分无关。LWD 仅在与其他栖息地成分相互作用时对鱼类丰度产生影响。这种差异可以通过富含庇护所的粗基质中存在的空腔来解释，这些空腔在奥兰塞尔瓦河的给定承载能力下为幼鱼提供了足够的覆盖和领地。虽然 LWD 可能最有效地在低地溪流（河床坡度 <0.005）中提供庇护，但在陡峭的鲑鱼河流和相关的半河流中，维护或恢复富含庇护的粗基质应被视为首要任务。