Abstract

The population structure and gut contents of Astacus astacus populations were studied in August 1969 and 1970 in two Finnish rivers, Jarvenpaankoski at Keuruu and Raudanjoki at Loppi. In Jarvenpaankoski, 195 crayfish (length range 13-124 mm) and in Raudanjoki 1309 crayfish (length range 14-105 mm) were collected using electric fishing. Females comprised 52.1% and 49.9% of the population in Jarvenpaankoski and Raudanjoki, respectively. Males comprised 47.9% and 50.1%. In Raudanjoki the males are apparently at least 3 to 4-years old when they reach sexual maturity, while the females are 4 to 5-years old. At Jarvenpaankoski the females evidently do not become sexually mature until they reach 6 years or more. In Jarvenpaankoski, the mean density of crayfish aged two summers or more was 0.4/m² and in the best areas 5/m². In Raudanjoki the mean density was 4.1/m². In Jarvenpaankoski and Raudanjoki, plant food was found in 81% and 79% of the crayfish, respectively. The proportion of plant material in the individual animals averaged 33% in Jarvenpaankoski and 56% in Raudanjoki. In Jarvenpaankoski animal food was found in 67% of the examined guts while in Raudanjoki this figure was 57%. In Jarvenpaankoski and Raudanjoki animal food constituted 10% and 29% of the food, respectively. In both streams the most predominant types of animal food were insect larvae (Chironomidae, Trichoptera), bryozoans, molluscs and crayfish. As the crayfish grow, the frequency and amount of plant food seem to increase. The proportions of the various food components also change. Not one of the crayfish was observed to have eaten fish. Their major source of food seems to be plant matter, which has little importance as fish food. The food used to produce crayfish is thus largely based on material that would probably otherwise not be utilized.

Supplemental Documents

• There are no supplementary documents for this article

Cited By

Citations: