Recruitment abundance estimation:: Role of glass eel (Anguilla anguilla L.) response to light

Most fish populations are declining worldwide and their management would benefit from a better estimation of recruitment. In glass eels, field studies suggest that estuarine migratory glass eels are sensitive enough to light to change their vertical location according to factors such as water turbidity and/or moon brightness. The response of glass eel (Anguilla anguilla L.) to light was tested in the laboratory using boxes where fish could choose between a lit and an unlit side. Responses were quantified as the proportion of glass eels remaining in the unlit chamber. Decreasing light levels were used and tested on different age glass eels (age in days since capture). In addition, measures of light at different depths of the water column were carried out in the Adour estuary (43 degrees 30' N, 1 degrees 30' W). The glass eel light avoidance level was lower in non-pigmented glass eel (less than 10(-10) W cm(-2)), than in pigmented ones (10(-9)-10(-8) W cm(-2)). These results and field data on the measurement of light energy in the water column of Adour estuary are compared with previously published data on the estuarine migration of glass eel. (c) 2005 Elsevier B.V. All rights reserved.