Angling bait consumption and stable isotope niche of two cyprinids in different lake fisheries

Abstract

Abstract Terrestrial subsidies are important for freshwater ecosystems and, in lakes supporting recreational fisheries, angling baits can represent an important allochthonous input. This resource can directly contribute to fish diet but its consumption may be influenced by fish body size and the type of angling baits used in different fisheries. In this study, we evaluated angling baits consumption by two common cyprinid species, Cyprinus carpio and Rutilus rutilus, in three fishery types (specialised carp, specialised roach, and put‐and‐take fisheries). We used stable isotope analyses (δ13C and δ15N) of cyprinids, their natural prey and different angling baits in 16 gravel pit lakes located in south‐western France, including four lakes without angling. Angling baits were significantly δ13C‐enriched and δ15N‐depleted compared to natural prey. Overall, angling bait consumption was highly variable between individuals. For C. carpio, angling bait consumption averaged 30.5% (±17.0 SD) and was higher in specialised carp fisheries (40.0% ± 16.7 SD) than in put‐and‐take fisheries (15.9% ± 9.0 SD) and was not related to body size. For R. rutilus, angling bait consumption averaged 41.3% (±15.7 SD), did not differ significantly among fishery types, but increased with body size. The niche width of C. carpio was six times larger in specialised carp fisheries than in lakes without angling. For R. rutilus, niche width was two times larger in specialised carp and put‐and‐take fisheries compared to lakes without angling and specialised roach fisheries. These results indicate that angling bait subsidies represent a novel and substantial resource opportunity for fishes in angling lakes, with trophic consequences for the targeted species through increase of their stable isotope niche size. These impacts are partly influenced by the type of angling baits used by anglers and the characteristics of the fisheries, suggesting the need for improved quantification of the temporal dynamics of this type of subsidy to better understand its consequences on freshwater fish and recipient ecosystems.