Shelter use of the red-swamp crayfish (Procambarus clarkii) in dry-season stream pools.

Patterns of shelter use of the red-swamp crayfish, Procambarus clarkii, were studied in a temporary stream of the south of the Iberian Peninsula during the summer of 1999. By shelters, we mean both excavated burrows and natural refuges, such as crevices under rocks, boulders, and stones. Both crayfish shelter use and faithfulness, and the relationship between the use of shelters and some abiotic parameters of the habitat were analysed. Five main issues were raised. (1) Crayfish did not hide exclusively inside excavated burrows, but regularly used natural refuges. The low burrowing activity recorded might be related to the large particles of the sediment and to the scarce presence of free water. (2) Burrows were mostly found either empty or occupied by a single individual, while refuges had a higher rate of occupancy. Shelters were often used by both females and smaller individuals. (3) A role played by burrows and refuges was to help crayfish to withstand high environmental temperatures; in fact, the number of specimens inhabiting the same shelter increased with the air temperature. Shelters also provided protection against predation and cannibalism. Burrows seemed more efficient shelters, since crayfish more often moved from a refuge to a burrow than vice versa. (4) Crayfish were found outside the shelters mainly at night and dawn, while they were mostly hidden in burrows during the day. (5) Procambarus clarkii seemed not to be faithful to a unique shelter; thus this species seems to have “ephemeral home ranges” with a shelter as the core. Although refined orienting capabilities have been reported in several decapods, in this case, crayfish did not exhibit a “homing behaviour”, which may be related to the fact that burrows were used mostly for protection purposes.