EFFECTS OF TETHERING ON PREDATORY ESCAPE BY JUVENILE BLUE CRABS

Effects of tethering on predatory escape by juvenile blue crabs Callinectes sapidus Rathbun were examined. Trials were conducted in a large flume to simulate the natural sedimentary and hydrodynamic properties of open sand flats in low-energy estuarine environments. Behavioral interactions between juvenile (prey) and adult (predator) blue crabs were video recorded, then quantified by computer-video motion analysis. Significantly more tethered juveniles (70%) were captured by adults than non-tethered juveniles (10%). Kinematics of the prey swimming escape response changed little as a result of the tether. Mean velocity, maximum velocity, and maximum acceleration did not dif fer significantly between tethered and non-tethered juveniles. But tethered juveniles traveled shorter distances during bursts of swimming to escape predatory adults, and they could not evade persistent attackers. Whereas tethering is used to assess relative rates of predation, it increases vulnerability of prey organisms to attack. Predation rates will be most inflated for highly mobile prey that effectively evade capture when they are not restrained. Investigators are strongly encouraged to quantify the impacts of tethering on prey escape and survivorship.