Abstract

Lake Divonne is a gravel-pit lake managed for recreation. Pacifastacus leniusculus was planted as a possible means of control of aquatic weeds and it proved efficient. Observations on crayfish populations gave data on the size of the crayfish according to age. The rate of growth is good and compares favourably with that of the Sacramento River. The implanted Pacifastacus scarcely suffer from disease problems, and presently do not seem to constitute a risk to natural populations of crayfish in France. Using standardised traps as the sampling device and taking into consideration catch per unit of effort revealed an increase in population since planting. The population densities were estimated at 4.2, 5.6 and 7.3 crayfish per square meter. The numbers are similar to the figures observed in California. Despite quite stringent fishing regulations, the number of crayfish anglers is increasing. People enjoy angling for crayfish even under difficult conditions. Fishing pressure is high and the annual catch can be estimated at 100,000 crayfishes or 4.5 metric tons. Lake Divonne is probably the best crayfish lake in France at this time. Pacifastacus proves to be a very appropriate species for stocking gravel­pits with crayfish.

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