Life history and population biology of the white-clawed crayfish, Austropotamobius pallipes pallipes, in a brook from the Poitou-Charentes region (France)

Abstract

A protected population of the white-clawed crayfish, Austropotamobius pallipes pallipes (Lereboullet), has been studied between 1995 and 1996. 1,511 crayfish were collected over the period of study including trap and hand catches. 356 animals exceeded the minimum legal size -90 mm TL (Total Length)-, representing 23.6% of the total catches. Catch Per Unit Effort (C.P.U.E.) ranged from 1.2 in February to 8.6 in October. The sex ratio of total catch was biased in favour of females (1:l.g). Males are only dominant during the cold period where water temperature is less than 10°C. Thelohania seems to be cyclic in this population with high levels of infected crayfish during both summers. No infected crayfish were found between January and March. Estimated densities ranged from 4.4 to 2.2 adults.m2 of brook area. Mating activity started in mid to end November as day-length shortened and water temperature fell below 10°C. Berried females ranged from 58.5 to 100.4 mm in TL. Mean pleopodal egg number declined over the duration of the incubation period (mean = 55 eggs per female in December to 30 eggs per female in May). The maximum number of eggs was 85 for a female (85 mm TL) captured in November. In the beginning of May, 40% of females sampled had no eggs. All the results seem to show an over-density of crayfish in this population and recommendations to regulate it are discussed.