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

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

Spatial variability in the growth of invasive European barbel Barbus barbus in the River Severn basin, revealed using anglers as citizen scientists

Life history trait analyses of non-native fishes help identify how novel populations respond to different habitat typologies. Here, using electric fishing and anglers as citizen scientists, scales were collected from the invasive barbel Barbus barbus population from four reaches of the River Severn and Teme, western England. Angler samples were biased towards larger fish, with the smallest fish captured being 410 mm, whereas electric fishing sampled fish down to 60 mm. Scale ageing revealed fish present to over 20 years old in both rivers. Juvenile growth rates were similar across all reaches. Lengths at the last annulus and Linfinity of the von Bertalanffy growth model revealed, however, that fish grew to significantly larger body sizes in a relatively deep and highly impounded reach of the River Severn. Anglers thus supplemented the scale collection and although samples remained limited in number, they provided considerable insights into the spatial demographics of this invasive B. barbus population

Factors influencing individual movements and behaviours of invasive European barbel Barbus barbus in a regulated river

© 2019, The Author(s). Riverine fish are often adversely affected by impoundments that reduce longitudinal connectivity and impede movements, while river fishery performance is often enhanced by introductions of non-indigenous fishes that diversify angling opportunities. The influence of factors (including impoundment) on the movements of European barbel Barbus barbus, a fish frequently introduced for angling, was tested in the continuous reach of the lower River Teme and Severn, western England. Following capture by electric fishing and angling, the movements of 18 fish were followed for 12 months using acoustic telemetry. Weirs at the upstream end of both river reaches impeded fish movements; only three fish traversed the Teme weir and no fish traversed the Severn weir. Net movements were mainly upstream in spring and downstream in autumn, and the daily movements of fish were asynchronous between individuals. Total (home) ranges varied considerably between individuals; those of fish initially captured by angling were significantly smaller than those captured by electric fishing. This potentially relates to fish with smaller total ranges being more vulnerable to angling via higher spatial encounters. The results reveal considerable individual variation in the movement of B. barbus and emphasises how river regulation can impact the dispersal and behaviour of river fishes

Predicting the ecological impacts of an alien invader: experimental approaches reveal the trophic consequences of competition

1. Ecological theory on the trophic impacts of invasive fauna on native competitors is equivocal. While increased inter-specific competition can result in coexisting species having constricted and diverged trophic niches, the competing species might instead increase their niche sizes to maintain energy intakes. Empirical experiments can test invasion theory on competitive interactions and niche sizes across different spatial scales and complexity. 2. The consequences of increased inter-specific competition from a model alien fish Leuciscus idus were tested on two taxonomically and trophically similar native fishes, Squalius cephalus and Barbus barbus. Competitive interactions were tested in tank aquaria using comparative functional responses (CFRs) and cohabitation trials. The consequences of these competitive interactions for the trophic niche sizes and positions of the fishes were tested in pond mesocosms. 3. CFRs revealed that compared to B. barbus, L. idus had significantly higher attack and consumption rates; cohabitation trials revealed B. barbus growth rates were depressed in sympatry with L. idus. For L. idus and S. cephalus, differences in their functional response parameters and growth rates were not significant. 4. Pond mesocosms used stable isotope metrics to quantify shifts in the trophic niche sizes of the fishes between allopatry and sympatry using a substitutive experimental design. Isotopic niches were smaller and more divergent in sympatric paired species than predicted by their allopatric treatments, suggesting trophic impacts from inter-specific competition. However, an all-species sympatric treatment revealed similar niche sizes with allopatry. This maintenance of niche sizes in the presence of all species potentially resulted from the buffering of direct competitive effects of the species-pairs by indirect effects. 5. Experimental predictions from tank aquaria assisted the interpretation of the constricted and diverged trophic niches detected in the paired-species sympatric treatments of the pond mesocosms. However, the all-species sympatric treatment of this experiment revealed greater complexity in the outcomes of the competitive interactions within and between the species. These results have important implications for understanding how alien species integrate into food webs and influence the trophic relationships between native species

Movements and habitat use of native and invasive piscivorous fishes in a temperate and channelized lowland river

Lowland temperate rivers provide important habitats for piscivorous fishes, but with their year-round spatial and temporal habitat use is often poorly understood, including their use of off-channel habitats. Here, the movements and habitat use of the piscivorous native Northern pike Esox lucius and invasive pikeperch Sander lucioperca were investigated using acoustic telemetry in the highly regulated (through impoundment) lower River Severn, Western England over a 12-month period, where off-channel habitat availability was limited to a single boat marina. The movements of both species varied with season and temperature, with both species moving greater distances in spring. Increasing water temperatures up to 15 °C resulted in a higher frequency of movements of both species, but movements then decreased at temperatures higher than this. Northern pike detections in the river increased in periods of lower river discharge and warmer temperatures, with the off-channel refuge providing an important habitat all year round (78% of detections occurred there). While 63% of pikeperch detections also occurred in the marina, 89% of these detections occurred between December and April. These results thus emphasise the importance of this limited off-channel habitat as potential spawning locations for invasive pikeperch and foraging areas for native Northern pike

Refinement of acoustic-tagging protocol for twaite shad Alosa fallax (Lacépède), a species sensitive to handling and sedation

Telemetry investigations to gather essential information about fish migrations are reliant on the behaviour, condition and survival of the animals being unaltered by the tagging procedure. Twaite shad (Alosa fallax Lacépède; 'shad’) is a threatened clupeid fish for which there is a considerable knowledge gap on their anadromous movements. They are also reported to be sensitive to handling and anaesthesia, resulting in practical difficulties in tag implantation; previous investigations externally attached tags without sedation. The aim of this study was to incrementally refine the acoustic-tagging protocol for shad via application of a previously un-tried anaesthetic (i.e. tricaine methanesulphonate (MS-222)) and by surgical implantation of the tag in the peritoneal cavity. All captured shad (n = 25) survived handling, anaesthesia and tagging, and were detected moving upstream after release. Surgically implantation (n = 5) was significantly faster than externally mounting the tag (n = 20) and time to recover was similar. Total upstream movement, total movement, residence time in receiver array and speed of upstream movement were statistically similar for externally and internally tagged fish. Post-spawning, a large proportion (68%) of tagged fish returned to the estuary, downstream of the receiver array. Internal tagging under anaesthesia is recommended for studying anadromous movements of shad, given welfare benefits during surgery and once at liberty, thus increasing the likelihood of tagged fish performing natural behaviours. Further, implantation of tags programmed to last many years enables multiple spawning migrations by the same individuals to be studied, which would lead to substantial advances in ecological knowledge and potentially reduce the number of fish tagged

Variability in the summer movements, habitat use and thermal biology of two fish species in a temperate river

The ability of fish to cope with warm water temperatures in summer depends on factors including their thermal traits and the ability of individuals to access cool-water refugia. Knowledge is highly limited on the in situ responses of many fishes to elevated summer temperatures, including whether they express behavioural thermoregulation. The responses of two riverine species to summer water temperatures were tested here using the movement metrics, spatial habitat use and body temperatures of individual European barbel Barbus barbus (‘barbel’) and common bream Abramis brama (‘bream’) versus river temperatures. Acoustic biotelemetry was applied in the lower River Severn basin, western Britain, in summer 2021 (barbel) and 2022 (bream), where individuals could move across > 150 km of river, including a tributary of cooler water. Across all individuals, bream occupied 37 km of river length (mainstem only), with low inter-individual variability in their spatial habitat use, movements and body temperatures. In contrast, barbel occupied 62 km of river (main river/tributary), with relatively high inter-individual variability in spatial habitat use, movements and body temperatures, with higher variation in body temperatures as river temperatures increased (maximum mean daily temperature difference between individuals on the same day: 4.2 °C). Although warmer individuals generally moved more, their activity was greatest at relatively low temperatures and higher flows, and neither species revealed any evidence of behavioural thermoregulation during elevated temperatures. Enabling phenotypically diverse fish populations to express their natural behaviours and thermal preferences in summer water temperatures thus requires maintaining their free-ranging in thermally heterogenous habitats

Influences of angler subsidies on the trophic ecology of European barbel Barbus barbus

European barbel Barbus barbus is a recreationally important riverine fish that is widely introduced outside of its natural range. Contemporary angling practices for B. barbus involve the use of baits based on marine fishmeal (MF). MF is isotopically distinct from freshwater prey via highly enriched δ13C and thus its dietary influence on B. barbus can be tested via differences in fractionation factors (Δ13C). Correspondingly, stable isotope data from 11 riverine B. barbus populations tested how their trophic ecology varied across populations according to MF from angling. Δ13C of fish with macroinvertebrate prey resources varied within and between populations (range 0.90 to 10.13 ‰) and indicated that, within populations, up to 71 % of B. barbus had relatively high dietary contributions of MF. These contributions were significantly and positively related to fish length, with MF influences increasingly apparent as fish length increased. Population isotopic niche sizes increased as the dietary influence of MF in that population increased. These results indicated that whilst MF from angling can act as a strong trophic subsidy, its influence varies spatially and with fish length, with its use as a food resource by B. barbus generally involving dietary specializations of larger-bodied individuals