Linking habitat to density-dependent population regulation: How spawning gravel availability affects abundance of juvenile salmonids ( Salmo trutta and Salmo salar ) in small streams

摘要: Rivers with abundant spawning gravel may produce more fry of anadromous brown trout (Salmo trutta) and Atlantic salmon salar); however, does not provide suitable shelter to parr, suggesting an optimization problem for habitat in streams. This hypothesis was tested on 40 small streams western Norway. Juvenile salmonid densities were estimated from samples counted during backpack electrofishing surveys the available visually surveyed while walking upstream through rivers. Consistent predictions, positively related availability gravel. However, a second-order polynomial determined improved fit (ΔAIC = |8.02|), relationship between amount parr. Our results demonstrate that abundance parr strongly depend on avilability and seems be maximized at 20% 40% coverage. Beyond ca. 40%, mortality becomes density dependent, likely owing predation competition shelter, below density-dependent will limit numbers. These should considered when enhancing or restoring productivity salmonids.