Abstract
Fish stocking is a common practice to support endangered fish species or to promote local fisheries, also in South Tyrol, but current species protection and the maintenance of functioning aquatic ecosystems require sustainable management and stocking activity. While stocking measures in South Tyrol's waters have been documented for decades , cross-water and province-wide stocking dynamics and priorities or shifts in population densities of stocked fish species have not yet been examined. In analyzing stocking and fish survey data from the local Hunting and Fishing Office from the last 20 (fish surveys) and 30 (stocking) years we demonstrate a general decrease of fish stocking throughout the province and identify past and present prioritized fish species. The non-native Salmo trutta and Oncorhynchus mykiss have been and still are the most stocked fish in South Tyrol (46 ±3 % and 37 ±4 % of the total stocked biomass) with little differences between catchments, while the native Salmo marmora-tus was stocked much less (15 ±5 %) and has even been replaced by stocking eggs and juveniles within the last years. The minor stocking of Salvelinus fontinalis (4 ±1 %) was stopped. Similarly, comparisons of multiple fished populations reveal comparable patterns with strong positive trends for the most stocked Oncorhynchus mykiss (+7.1 %), while densities of sparsely stocked Salvelinus fontinalis decreased sharply (-7 %). Also, the native and protected Salmo marmoratus shows slight decreases over the last decades, which is why scientifically based conservation measures (e.g., egg stocking) and ongoing province-wide monitoring of population trends remain necessary.