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The unimpeded downstream movement patterns and migration success of small female and male Anguilla anguilla through a catchment in north-west Europe were studied using an acoustic hydrophone array along the River Finn and into the Foyle Estuary in Ireland. Twenty silver-stage A. anguilla (total length, LT, range: 332-520 mm) were trapped 152 km upstream from a coastal marine sea-lough outlet and internally tagged with acoustic transmitters of which 19 initiated downstream migration. Migration speed was highly influenced by river flow within the freshwater ( FW) compartment. Anguilla anguilla activity patterns were correlated with environmental influences; light, tidal direction and lunar phase all influenced the initiation of migration of tagged individuals. Migration speed varied significantly between upstream and lower river compartments. Individuals migrated at a slower speed in transitional water and sea-lough compartments compared with the FW compartment. While 88·5% survival was recorded during migration through the upper 121 km of the river and estuary, only 26% of A. anguilla which initiated downstream migration were detected at the outermost end of the acoustic array. Telemetry equipment functioned efficiently, including in the sea-lough, so this suggests high levels of mortality during sea-lough migration, or less likely, long-term sea-lough residence by silver A. anguilla emigrants. This has important implications for eel management plans. [ABSTRACT FROM AUTHOR]

The body attack angle of common breamAbramis bramavaried with swimming speed and was best described byθ = −3·32(±0·24) − 9·23(±0·54)e− u( r2 = 0·56,P < 0·0001;±1s.e. given in parentheses), whereθ is the body attack angle anduis swimming speed. The hypothesis that neutrally buoyant fishes may swim with body attack angles deviating increasingly from 0° as the swimming speed decreases is supported. [ABSTRACT FROM AUTHOR]