Figure 9.

Directionality as a function of reaction distance. Theoretical considerations [20] suggest that copepods should be less able to detect the direction of the predator's approach and thus will be less able to orient escapes consistently away from it: (a) when the distance between fish and copepod relative to the fish size ([d + a]/a) is large; and (b) when copepods have shorter antennules, because when antennules are long relative to the distance to the fish (A1/[d + a]), it is easier for copepods to detect the secondary flows that signal the direction of approach. There was no support for these predictions in the data. A1 is the length of antennule based on average, stage-specific prosome lengths from McKinnon et al. [59] for B. similis: CII–CIII (early copepodite) mean = 0.318 mm; CV (late copepodite) mean = 0.455 mm; and CVI (adult) mean = 0.538 mm. (Online version in colour.)