Habitat suitability indices development in Denmark: are international indices applicable under small lowland stream conditions?

The transferability of habitat suitability indices (HSIs) remains a controversial issue within physical habitat-based modelling. This issue is often exacerbated when the indices are obtained from international sources without adequate transferability tests being conducted. The aim of this paper was to assess the applicability of seven sets of HSIs (three local and four international) to small lowland Danish streams applied to large parr brown trout (Salmo trutta), an important ecological indicator in these systems. Using a simple hierarchical literature review, the applied indices were ranked firstly for their biological and physical similarities to the local Danish small lowland stream conditions, secondly on the methods used to devise the HSIs and collect the field data, and thirdly if they were locally or internationally sourced. The review ranked background information hierarchically (from most important to least) provided with the HSIs literature: (1) size class of species, (2) season, (3) river type...