A study of the population biology of the British fresh water crayfish austropotamoblus pallipes (lereboullet)

Abstract

The general biology and population dynamics of the fresh water crayfish, Austropotamobius pallipes, were studied in a man- made aqueduct in Northumbrla. The paucity of ecological knowledge of this species; the threat of the pathogenic crayfish 'plague' fungus, which has destroyed many European crayfish stocks; and several features of this aqueduct which made it particularly suitable for a population study inspired this investigation. The latter features were: the population was delimited to a known area (ca. 0.25 ha.); immigration was unlikely and the water level could be artificially manipulated allowing the collection of many crayfish by hand. Two sampling methods, hand-collection and funnel traps, and two marking schemes, one date-specific and one individual-specific were used to monitor the population. Over 4,500 crayfish were numbered and over 6,000 given a date- specific mark between March 1974 and June 1977. Moulting and growth were followed and found to occur only between late June and mid-September; this was limited by higher summer water temperatures. A potential life span of I0-I3 years was projected. Fecundity was estimated for individuals and the whole population. No recognizable 'home range' was observed. An attempt was made to describe crayfish diel activity patterns and trophic interrelationships. The effects of a protozoan parasite were observed under natural conditions. It was demonstrated that hand- collection provided relatively unbiased mark-recapture estimates of population size; trap samples seriously underestimated this parameter. The density of crayfish of body length ≥ 26 mm. was estimated as 8+/m(^2) in the summiers of 1974 and 1975 and to have varied between 10.4/m(^2) and 3.8/m(^2) from June 1976 to May 1977. Annual production (ca. 170.5 Kg./ha.) and mean annual biomass (ca. 409.7 Kg./ha.) were estimated in 1976.