Prey Capture and the Fast-Start Performance of Northern Pike Esox Lucius

Abstract

Fast-start performance of northern pike Esox lucius (mean length, 0.38m) during prey capture was measured with subcutaneously implanted accelerometers. Acceleration-time plots and simultaneous high-speed ciné films reveal four behaviours with characteristic kinematics and mechanics. The fast-start types are identified by the number of large peaks that appear in the acceleration-time and velocity-time data. Comparisons of mean performance were made between each type of feeding fast-start. Type I fast-starts were of significantly shorter duration (0.084 s) and displacement (0.132 m) than type III (0.148 s and 0.235 m) and type IV (0.189 s and 0.306 m) behaviours, and higher mean and maximum acceleration (38.6 and 130.3 ms−2, respectively) than type II (26.6 and 95.8 ms−2), type III (22.0 and 91.2 ms−2) and type IV (18.0 and 66.6 m s−2) behaviours. The type II behaviours were of shorter duration (0.115 s) and displacement (0.173 m) and of higher mean acceleration than type IV fast-starts, and were also of significantly shorter duration than type III behaviours. Prey-capture performance was compared to escapes by the same individuals. When data are combined, regardless of mechanical type, mean acceleration (37.6 vs25.5ms−2), maximum acceleration (120.2 vs 95.9ms−2), mean velocity (1.90 vs 1.57 ms−1) and maximum velocity (3.97 vs 3.09 ms−1) were found to be larger and duration shorter (0.108 vs 0.133 s) during escapes than during prey capture. No differences were found through independent comparisons of the performance of feeding and escape types II and III, but type I escapes had significantly higher mean velocity (2.27 vs 1.58 ms−1), maximum velocity (4.70 vs 3.12 ms−1) and mean acceleration (54.7 vs 38.6 ms−2) than type II feeding behaviours. Prey-capture performance was also related to prey size, apparent prey size (defined as the angular size of the prey on the pike's retina) and strike distance (the distance from the pike to the prey at the onset of the fast-start). Mean and maximum acceleration increased with apparent size and decreased with strike distance, while the duration of the event increased with strike distance and decreased with apparent size. No relationship was found between the actual prey size and any performance parameter. Strike distance ranged from 0.087 to 0.439 m and decreased as the apparent size increased from 2.6 to 9.9° (r2=0.75). The type I behaviour was usually employed when the strike distance was small and the prey appeared large. As strike distance increased and apparent size decreased, there was a progressive selection of type II, then III and then IV behaviours.