Habitat use of age - 0 twaite shad (alosa fallax lacépède, 1803) in the tidal freshwater region of the Elbe River, Germany

Abstract

Between April and August 1997 the distribution of twaite shad larvae in the lower Elbe River downstream the city of Hamburg was examined by ring net, lift net and pop net sampling. During each haul six environmental parameters - water depth, water temperature, conductivity, oxygen concentration, distance from shore line and distance from river channel - were estimated. Twaite shad larvae were found from 26 May to 10 July. Yolk sac larvae were present from 26 May to 25 June. High abundances of twaite shad larvae were found in the side channels and main channels. A canonical correspondence analysis was calculated to evaluate the importance of measured environmental parameters for the distribution of age - 0 fishes. Water depth, distance from shore line and distance from river channel were identified as main parameters for the distribution of species. Twaite shad larvae preferred maximum water depth and distance from shore line and short distances to the river channel. An upstream displacement of the spawning grounds of twaite shad was observed, following a trend first noticed in the early 90th. Nowadays, the location of spawning grounds corresponds to the situation at the beginning of the 19th century. Reduced water pollution is believed to be the main reason for this phenomenon.