Population ecology and behaviour of European barbel Barbus barbus, a recreationally important, translocated fish.

Abstract

The intentional introduction of fish species into new environments for enhancing recreational angling is common. The intentional translocation of European barbel Barbus barbus into the middle River Severn in 1956 resulted in their establishment and dispersal throughout the catchment, including its tributary, the River Teme, where they supported high catch rates until the mid-2000s. Anecdotal evidence suggests that since then, there have been large declines in catch rates in the Teme and thus in the size of the adult population. However, data to evidence this were lacking, with minimal ecological data available. The aim of this research was to thus generate new knowledge on the ecology of this invasive B. barbus population in the River Teme to provide baseline information that could be used as a basis for fishery and river management. The focus of the research was initially on understanding the reproduction of B. barbus in the river, with focus on the quality of the spawning substrate and the temporal and spatial production of 0+ fish in the river via their reproduction. This was followed by investigating the B. barbus trophic relationships with other cyprinid species, and in relation to angling. In addition, the tracking of B. barbus in the lower river provided insights into the behaviours of individual fish. The majority of the spawning gravels analysed in the River Teme had generally low fine sediment content and organic matter compared to other lowland rivers, with this potentially important for B. barbus larval emergence and survival. The spawning of B. barbus involves construction of a nest (‘redd’) that results in large volumes of sediments being moved and thus they can have a zoo-geomorphic impact on sediments. Spawning in the Teme B. barbus population utilised a protracted spawning strategy, as per their native range, with this strategy also utilised by chub Squalius cephalus and minnow Phoxinus phoxinus. These results suggest some consistency with the pre-adaptation hypothesis, whereby the non-indigenous B. barbus utilised traits in the new range that it utilises in their indigenous range, providing considerable advantages for invasion success. Investigations into the trophic interactions of the B. barbus with other fishes revealed that, in general, there were consistent patterns of partitioning in their trophic and isotopic niches, with little evidence to suggest high inter-specific competitive interactions. Stomach contents analyses revealed that whilst the 0+ fishes were all primarily generalist in their diet, B. barbus was the most specialist out of the four analysed fishes, with the trophic niche of invasive B. barbus being highly dissimilar to S. cephalus and dace Leuciscus leuciscus. Stable isotope studies then suggested these patterns of inter-specific niche partitioning remained through the life of these fishes, but with some dietary convergence when larger fishes (generally > 400 mm) had diets composed of high proportions of angler bait based on marine fishmeal. Acoustic tagging of B. barbus in the lower river tracked their movements over a 12 month period and revealed that two weirs provided substantial impediments to their movements. There were also considerable differences between the size of the home ranges of individuals, but with this explained more by their method of capture (angling versus electric fishing) than any other variable, suggesting inherent differences in the behaviour of individuals that affect their vulnerability to angler capture. These results thus provide considerable new knowledge on this invasive B. barbus population that can be utilised to better manage populations both in the River Teme and elsewhere in their range. They revealed considerable differences in the behavioural ecology of individuals, but with their invasive population generally having minimal impact on other fishes in the river.