Seasonal activity and depth distribution of resident yellow-phase American eels (<i>Anguilla rostrata</i>) in a large fluvial ecosystem

Abstract The American eel (Anguilla rostrata) is a catadromous species occupying diverse habitats, but little known about the specific activities of this elusive nocturnal fish. Mobile radio and acoustic telemetry were used to locate 33 transmitter-implanted resident yellow eels (729 ± 22 mm TL), acquiring 1613 locations from 2014 2017 in 21-km2 slow-flowing section upper St. Lawrence River. Measurements distance moved, water depth, temperature study activity, homing, site fidelity. Movement was greatest spring, late April (422 m, median semi-monthly), after emergence winter dormancy, their deepest habitat (3.71 0.06 m) shallowest (1.74 0.17 m). Activity low early summer fall (69 As reached maximum during midsummer (24.3 0.29°C), most became more active (106 moved deeper (2.46 0.28 m), probably following prey increased mid-to-late (277 decreased considerably at ≲8°C when settling into habitat, ceased ≲4°C. Temperatures ≃10°C (8.1–11.1°C) corresponded with seasonal activity spring/fall commercial hoop-net catches. These spatial temporal insights can help focus sampling assessment procedures, as well suitability modelling.