Abstract

In 1970-1972, the isolated population of Astacus astacus L. in the little lake (1.2 ha) Beržiukas Lithuanian SRR was under investigation. The quantity of crayfish was determined by marking adults, setting them free, and by the recapture of young. The population (Table 1) was on the average, more than 18,000 and in the course of investigation, it remained stable. The sexual structure had a predominance of females. The quantity of adult groups was stable (Table 1). The spatial structure of the population was bounded with the feeding base; the migration was due to the search of food. The most migrative were the males of adult group 4 +, who were under spawn, less migrative were the males and the females of post reproductive age (Tables 4, 5, 6). The productivity of population P (Table 7) was on the average about 42 kg/ha per year. The most productive was the adult group 2 +. The biomass B (Table 8) was on the average 60kg/ha in October. P/B in the average is equal to 0.79.

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