The behavioural response of the invasive signal crayfish Pacifastacus leniusculus to experimental dewatering of burrows and its implications for eradication treatment and management of ponds with crayfish

Abstract

Invasive non-indigenous crayfish threaten indigenous crayfish and aquatic communities. Biocide treatment to eradicate unwanted populations has been tried on small water bodies in the UK and a few other countries. It needs to be applied to the whole water body occupied by crayfish, so partial dewatering may reduce the cost of biocide. The whole population must be in the submerged dosed area, because if some individuals remain in exposed areas they may avoid treatment and hence eradication will not be achieved. This study looks at the response of signal crayfish Pacifastacus leniusculus to exposure of occupied burrows, in tanks and in the banks of a dewatered pond. Some crayfish emerged from exposed burrows by day (34% in tanks, 9% in field); the rest remained in burrows until after dark. In tanks, 96% of crayfish vacated exposed burrows on the first night when submerged burrows were available, but when all burrows were exposed, poorer-quality submerged refuges (open-ended tubes) and competition between crayfish kept subordinate individuals in the damp exposed burrows (32.5%). Subordinates did not vacate exposed burrows until dominant crayfish were removed. In the field, most crayfish emerged in 1–2 nights, but 0.5% remained alive in burrows six nights after exposure. In tank and field, about half of the crayfish climbed up onto dry exposed areas. In light of these findings, we recommend that if dewatering is a precursor to biocide treatment, exposed areas should be tested for presence of crayfish. If dewatering is for other management the potential for terrestrial roaming to other sites should be considered.