Relative influence of local and landscape-scale features on the density and habitat preferences of longfin and shortfin eels

The relative structural influence of local-scale versus landscape-scale habitat features on size-class matrices of both longfin (Anguilla dieffenbachia) and shortfin (Anguilla australis) eels collected along six different New Zealand rivers (10 river-year combinations) are quantified using variance decomposition. The total explained variation of these species and size-class matrices was related to both local-scale and landscape-scale variables, and some proportion was shared between these two scales. When compared with landscape-scale variables, local-scale physical habitat variables such as water velocity and fish cover explained more about patterns in the size-distribution of longfin eels. The opposite situation was true for shortfin eels whose size-distribution was more strongly related to landscape-scale variables such as distance from sea and channel slope. These findings suggest that management of river flows is required to ensure flow regimes that maintain availability of suitable local-scale hydraulic conditions, and that biodiversity conservation efforts need to be targeted at protecting a gradient of rivers across New Zealand's river landscape.