Following the migration of glass eel and three-spined stickleback passing Europe’s largest pumping station and world’s largest sluice

In order to quantify abundance, to study migration behaviour and to evaluate different fish passages along a 26 km long canal (North Sea Canal) in the Netherlands, a mark recapture experiment was carried out by tagging 6750 glass eel (Anguilla anguilla), 625 three-spined stickleback (Gasterosteus aculeatus) caught in marine environment and 625 three-spined stickleback caught in brackish environment in spring 2018. To reach the canal, migratory fish must pass a large complex of four large sea sluices, spill gates and Europe’s largest pumping station. Twenty five groups could be distinguished using different combinations of fluorescent colours of Visible Implant Elastomer Tags. The majority of the marked fish were released at the sea side and just behind a large tidal barrier (each group: 2000 glass eel and 500 stickleback). In addition, different groups of both species were caught and released locally at different sites along the canal to evaluate fish passage efficiency. Fish were recaptured in an extensive netting program of volunteers along the canal, twelve especially designed glass eel monitoring devices and professional fisherman who monitored fish passages along pumping stations or sluices. Stickleback originally caught in brackish environment showed higher recapture rate (7.6%) compared to stickleback caught in the marine environment (2.8%). Also, fastest average migration speed was estimated on 0.09 m/s and migratory delay at the tidal barrier was limited since difference groups were recaptured in comparable ratio’s and migration speeds. Glass eel were recaptured along almost all monitoring locations along the canal. Fastest, average migration speed was estimated at 0.02 m/s and the furthermost recapture was 28 km from release site after 26 days (average speed 0.01 m/s). Migratory delay at the tidal barrier seemed limited, however some individuals were caught after 23 days at the sea side and others were flushed out by the spill gates