Understanding recreational targets and ecological consequences: increased northern pike stocking reflected in top avian predator diet

Abstract

Fish stocking is commonly used to enhance recreational fisheries; however, the side effects of stocking at the ecosystem scale have rarely been tested. Avian predators, because of their high position in food webs, can serve as indicators of environmental change, including prey-species abundance. The scope of this study was to understand whether recent changes in northern pike (Esox lucius) stocking on a national scale could cascade through food webs and significantly shape the diet of a predator––the white-tailed eagle (Haliaeetus albicilla). The stocking of pike in state-owned waters in Lithuania has increased two- to threefold since 2005. A significant increase in the proportion of pike in the breeding-season diet of the white-tailed eagle has also been observed. We explain the increase in pike in the predator’s diet as being a causal consequence of pike stocking. We encourage consideration of the entire food web when launching/terminating recreational fish stocking programmes.