Occurrence and distribution of twaite shad (Alosa fallax Lacépède) in the lower Elbe River, Germany

Abstract

Stow net and ring net catches from 1989 to 1994 were analysed and compared to previous catch data in order to evaluate the current status of the twaite shad (Alosa fallax) Elbe population. No significant differences were found between mean total abundances of twaite shad from 1989 to 1990 compared to 1984 to 1986. From 1991 to 1994 lower mean total abundances were estimated and found to be influenced by lower abundances of age group 0 super(+). No significant spawning stock decrease of twaite shad was found during the last 10 years. An upstream displacement of about 20 km of the main spawning grounds was observed. Currently, twaite shad mainly spawns between stream-km 645 and 660. In June, after a short period of larval retention, age 0 super(+) group fish migrate downstream. Length of age 0 super(+) twaite shad reaches up to 10 cm at the end of the first year of life. Highest abundance and biomass occurred from May to September. Adults and age 1 super(+) group were less abundant in marginal areas than in the main channel. Low fishing mortality and high spawning success are probably the most important factors determining the relative stability of the twaite shad Elbe population