Estimation of biological characteristics of adult sea trout (Salmo trutta) in the upper Rhine.
Résumé
An analysis of the total length and scales of a sample of 120 adult sea trout caught for the most part by electrofishing in the upper Rhine (700 km from the North Sea) from 1989 to 1996 lent information to characterize this population under restoration. The calculation of the Catch Per Unit of Effort (CPUE) with data from 1994 to 1996 allowed to study the migration pattern and to improve the estimation of the general population characteristics. In this part of the Rhine, anadromous migration of sea trout occurs with two successive peaks from June to December, the older fish arriving first. The population is characterized by a predominance of fish aged 1+ (49,2%) and 2+ (45,8%) years at sea, that is to say an average sea age (AMM) of 1.54 year. The average smelting age (AMS) and sea age at maturity (AMR) are respectively estimated at 1.30 and 1.39 year. Moreover, in this population, sea age at maturity increases when smelt age decreases, The results are discussed according to the methods and are compared with results obtained from other French or more northern rivers populations. Thus, the characteristics of the Rhine sea trout population correspond to what could be expected from its latitudinal situation and its great river status.