Strategies for the Management of Grayling Thymallus thymallus in the Alpine Rivers of Tyrol (Austria) and South Tyrol (Italy)

Alpine freshwater fish fauna has entered a crisis phase. In fact, numerous taxa face a multitude of anthropogenic disturbances, exhibit restricted distribution areas and are ranked in red-list categories. Major threats derive from hydro-morphological alterations (disrupted continuum, flow modification, river regulation) leading to fragmented and often genetically isolated subpopulations, in many cases in conjunction with small population sizes and therefore reduced resilience.

We analysed the river network of the Austrian province of Tyrol and the neighbouring province of South Tyrol (Italy) concerning the habitat quality for the grayling which used to be a key fish species. In total 1,152 stream kilometres provide natural grayling habitat. We developed a “habitat pressure index” (HPI) and found clear correlations between the HPI and the current status of grayling populations. Based on the analyses we developed strategies to sustain, protect and/or restore vital grayling populations: (1) by detecting and/or defining management units based on genetics as well as (2) developing mitigation/restoration measures to re-establish migration routes and to improve habitat quality. Finally, (3) ecologically sound restocking measures are taken into account, although up to now extensive stocking of grayling in the province of Tyrol show no or even negative effects on the local stocks.