RELATIONSHIPS BETWEEN CHANGES IN HABITAT CONDITIONS AND POPULATION DENSITY OF AN INTRODUCED POPULATION OF SIGNAL CRAYFISH (PACIFASTACUS LENIUSCULUS IN A FLUVIAL SYSTEM.

After the disappearance of the native crayfish in many rivers in Biscay, Basque Country, Spain, the signal crayfish Pacifastacus leniusculus was introduced in the main fluvial stretches and several breeding populations have established. One of the most productive zones was the Cadagua River, where the population was established from 1989 (first introduction) to 1995. Starting from that year, a marked decrease in population was recorded downstream, and this fact is studied in relation to fluctuations in physical and chemical conditions caused by human perturbations in the fluvial corridor mainly caused by the construction of a road.