Populations of long-clawed crayfish Pontastacus leptodactylus: Effect of commercial fishing on the size and age structure

Abstract

Fishing affects the population of crayfish, while it changes the size and age characteristics. The size and age parameters of two populations of the narrow-clawed crayfish Pontastacus leptodactylus in the Loktyshi (Brest Region) and Krasnoslobodskoe (Minsk Region) reservoirs in Belarus have been compared. The Krasnoslobodskoye reservoir is intensively exploited with an annual catch of 3–4 tons of crayfish. There is no commercial fishing in the Loktyshi reservoir. Studies show that the average size of individuals in an intensively exploited population is smaller in comparison with a population where there is no commercial fishing for crayfish. Since crayfish fishing is regulated by a commercial measure (10.5 cm of total length) in intensively exploited populations, the average sizes of individuals are close to these limiting values. The life expectancy of crayfish is somewhat higher in the Loktyshi reservoir, where only amateur crayfish fishing is noted. Intensive fishing increases the mortality of females, whose annual survival rate is 37 %, while in the absence of fishing, the survival of females increases up to 57 %. The annual survival rate of males is 41–49 %. The fishing pressure leads to decrease in the survival rate of individuals and disappearance of crayfish aged 9–10 years from the population.