BURROWING BEHAVIOR OF THE INTRODUCED RED SWAMP CRAYFISH PROCAMBARUS-CLARKII (DECAPODA, CAMBARIDAE) IN PORTUGAL

Burrowing behavior of Procambarus clarkii in Portugal was investigated at 6 sites (3 rice fields, 2 reservoirs, and 1 marsh) from February 1991 to February 1993. Average burrow density (number of burrows/m(2)), relation between burrow density and substrate type, burrowing activity, burrow occupation (sex, size, and maturation of the animals), burrow morphology (burrow complexity, mean tunnel depth), and burrow distribution in relation to the water level were studied. Average burrow (b) density ranged from 0.013 b/m(2) to 6.28 b/m(2), the highest density being in a rice-field drainage channel. A burrowing activity index was estimated, indicating that burrowing is mostly a seasonal activity, being most intense from May-October. Burrowing activity occurred only when the ratio of fine particles over coarser particles was higher than 0.1-0.2. Mean carapace length of burrowing animals varied from 35.3-43.8 mm. Most of the individuals in burrows were mature. Immature and juvenile animals occupied burrows in late fall, winter, and early spring, while mature crayfish were found in late spring, summer, and early fall. The burrow morphology was generally simple, but more complex burrows were also observed. Mean tunnel depth ranged from 0.28-0.58 m. The longer burrows measured approximately 4.20 m long. The burrows were generally located at the water level in rice-held sites and above the water level in marsh and reservoir sites. Burrows were observed only in a zone of Myriophillum sp. in marsh and reservoir sites.