TAIL-FLIP MECHANISM AND SIZE-DEPENDENT KINEMATICS OF ESCAPE SWIMMING IN THE BROWN SHRIMP CRANGON-CRANGON

Tail-flip escape swimming by the brown shrimp Crangon crangon has been investigated across a range of body lengths (11-69mm) using high-spee d video analysis. This has revealed several novel aspects of the tail- flip mechanism when compared with that of other decapod crustaceans th at have been studied. (i) The pattern of body flexion in C. crangon pr oduces movement of the cephalothorax as well as the abdomen about the centre of mass. (ii) Shrimps form a 'head-fan' with their antennal sca les, in addition to the tail-fan formed by their uropods, apparently f or generating thrust during tail-flips. (iii) Shrimps typically swim o n their side rather than in an upright body position. It is suggested that these features may be interlinked and derive from habitat special isation. The kinematic properties of tail-flips were found to vary wit h shrimp size. As shrimp body length increased, the rate of body flexi on and re-extension decreased whilst the duration of tail-flips increa sed. Mean (and maximum) velocity estimates ranged between 0.4 m s(-1) (0.7 m s(-1)) and 1.1 m s(-1) (1.8 m s(-1)) for shrimps of different s izes. The combined effects of escape behaviour and size-dependent vari ability in tail-flip kinematics will have important implications with regard to predation risk.