ALIENFISHMIGRATIONS · Assessing the risk and understanding the processes of invasion by non-native fish species within and between river catchments

Final Activity Report Summary - ALIENFISHMIGRATIONS (Assessing the risk and understanding the processes of invasion by non-native fish species within and between river catchments)

This fellowship aimed to contribute to biodiversity and species conservation in providing information on the dispersal processes of selected non-native freshwater fishes. The specific objectives were to: 1) determine the dispersion potential, in particular the frequency and timing of salt/brackish water incursions, of pikeperch (Sander lucioperca); and 2) assess the dependence of successful establishment in river catchments by the sedentary omnivorous North American sunfish, pumpkinseed (Lepomis gibbosus), on access to adjacent still waters, with particular regard to diel and seasonal movements. These investigations included laboratory-based studies to determine the impact of tag insertion on pikeperch, pumpkinseed and topmouth gudgeon (Pseudorasbora parva). All objectives were achieved or exceeded, with the collection of telemetry data on-going. Laboratory studies of tag retention and impacts: To obtain accurate data on the natural behaviour of wild fish, the potential short and long-term effects on the fish of the tag implantation techniques were assessed using a non-invasive technique for monitoring cortisol released into the water by the fish. Tag retention was high in pumpkinseed and pikeperch for all types of tags with minimum tag-related mortality, but topmouth gudgeon demonstrated elevated post-tagging mortality and tag rejection, even when alternative tag insertion sites were used, with tag rejection increasing to unacceptable levels after about 14 days. Stress responses were greatest in topmouth gudgeon, followed by pikeperch and then pumpkinseed. Field studies of fish migrations and movement patterns of pikeperch and pumpkinseed: To assess the ability of pikeperch, which is salinity tolerant, to move through saline waters to new river catchments, we used acoustic telemetry to monitor the movement of pikeperch in the non-tidal and tidal River Thames. Initial data suggest variable seasonally and daily movement patterns, with greatest pikeperch activity in spring and at dusk, as well as multiple "intentional" movements downstream and upstream through locks. Daily movements in tidal and non-tidal parts of the Thames do not appear to differ, suggesting that salinity fluctuations do not influence pikeperch movements (i.e. between-river migration is likely). Pikeperch movements in the lower River Lee, unlike the Thames, suggest limited mobility, even site fidelity. Pumpkinseed were observed (using coded-wire tags) to move from on-line lakes into adjacent streams, and movement intensity was influenced by the type of water outlet. A high proportion of passive integrated transponder tagged pumpkinseed (43.5%) were recaptured, with maximum movements being 2.5 km downstream (app.30 m per day). Age 3+ pumpkinseed moved furthest (both up and downstream), with furthest distances in spring (when variations in home range area were greatest), and mean age of maturity in streams was 3.3 years, suggesting maturity related movements. In assessing pumpkinseed habitat use and interactions with native brown trout (Salmo trutta), radio tracking data revealed that pumpkinseed can negotiate long shallow rapids (up to 0.7 m/s) when migrating upstream. Pumpkinseed and brown trout have small home ranges, with multiple "core sites" between which they move; the core sites were distributed non-randomly, suggesting habitat-dependent selection. The home ranges (mainly pools with overhanging trees) overlap considerably but without avoidance or cohesion between the species. There was no evidence (from gut analysis) that pumpkinseed prey on native fishes, but native brown trout, perch and eel (Anguilla anguilla) were found to prey on pumpkinseed.

Data: CORDIS, © European Union