Ecological and recreational interactions of the native pike Esox lucius and the invasive pikeperch Sander lucioperca in England.

Abstract

In England, freshwater angling is an important recreational pastime with substantial socio-economic benefits, but is also a major introduction pathway for non-native fishes. As recreational anglers often prefer targeting large-bodied fishes, introductions of non- native species have become an integral part of fisheries management practices to diversify angler opportunities and increase satisfaction. However, these introductions were often completed without full understanding of their ecological consequences, including their potential to develop invasive populations. To ensure management and policy measures improve the angling experience without resulting in negative ecological consequences, it is important to understand the ecological role of introduced non-native fishes and their interactions with native species. Of equal importance, however, is understanding angler motivations and behaviours in their choice of angling for non-native fishes, and their perceptions of the consequences of their activities, particularly when catch-and-release practices are widespread. Pikeperch Sander lucioperca were introduced into open waters in England in the 1960s and subsequently established populations that dispersed through many river catchments. Due to their piscivory and correspondingly high trophic positions, their ecological impacts on prey fish populations are often considered, but their interactions with and potential impact upon native large-bodied piscivorous fish remain relatively poorly understood. Here, the ecological interactions of the native pike Esox lucius and the invasive pikeperch in England were quantified, including their life history traits, size- structured feeding relationships, and their trophic and spatial interactions. For anglers who exploit these species, their recreational interactions were assessed, including their behaviours in relation to their catch-and-release activity, and their motivations and perceptions in relation to their angling experience. The results demonstrated that the expression of pikeperch life history traits vary spatially, and may be explained partially by latitude. Stable isotope analysis (SIA) revealed that tissues collected non-destructively can be reliably applied to diet assessments in piscivorous fish and are a useful tool in providing assessments of size structured feeding relationships between native and invasive piscivorous fishes. Assessments of ontogenetic dietary shifts on the trophic position and niche size of pike and pikeperch revealed a switch to piscivory at smaller body sizes in pikeperch and a partitioning of resources across both insectivorous and piscivorous life stages in both species. Additionally, the presence of marine resource pathways from angling baits and anadromous fishes to the diet of pike were revealed to be as a function of their spatial availability, pike body size, and individual trophic specialisations. A telemetry study revealed movement variability within species and that increased movement was associated with spawning for both pike and pikeperch, and highlighted the potential importance of limited off-channel habitat in a channelized lowland river which was important to pike all year and to pikeperch in winter and spring. Qualitative interview and quantitative survey methods found that the invasive pikeperch is a valued fishery target species, with the experiences of anglers targeting non- native species influencing their perceptions on the ecological impact of introductions, such that they were seen as not causing adverse ecological impact. Additionally, angler conservation values towards native fishes were also reflected in their behavioural safeguarding of pikeperch populations, especially catch-and-release practices that are contrary to current regulations on pikeperch, such that 94% of surveyed predator anglers reported to always adopting catch-and-release practices for pikeperch despite it being illegal in England to release the species back into open waters after capture. In conclusion, these results suggest that there remains a considerable disjuncture between the views of many recreational anglers and the underlying legislation governing the introduction and keeping of non-native fishes and that for species such as pikeperch, their integration into native fish communities and widespread dispersal requires management measures that consider their ecology, ecological impacts and angling value.