Passage facilities for Diadromous freshwater shrimps (Decapoda: Caridea) in the Bananier River, Guadeloupe, West Indies

The relative selectivity of two fast-flowing concrete channels acting as passage facilities for shrimps was investigated at two low-head dams by comparing shrimps migrating through the channels to shrimps captured by experimental (trapping) passes offering splash zones. Complementary visual observations of shrimp behaviour were also carried out. At both dams (150 and 320 m above sea level (a.s.l.)), the upstream migration was mainly undertaken by small (subjuvenile) individuals but some larger ones, notably Atya innocous adults, were also captured. Strong water currents (1.5 m s−1) in the concrete channels compelled most shrimps to climb over the vertical walls but only the smallest individuals were able to do this. Thus, lower proportions of larger individuals were captured in the passage facilities than in the experimental passes. In the same way, the lightly built Macrobrachium spp. was found in lower proportions in the passage facilities than in the experimental passes. Furthermore, because of submerged orifices and whirling currents, the continuous-flow tanks which supplied the channels with water trapped numerous climbing shrimps. Hence, because they do not take biological criteria into account, the passage facilities investigated here were not only selective but also inefficient for shrimps. Finally, the benefits of such installations for shrimps are doubtful and simple waterfalls flowing over spillways would be at least as efficient, if not more so. Copyright © 2000 John Wiley & Sons, Ltd.