ESCAPE MANEUVERS OF SCHOOLING CLUPEA-HARENGUS

The escape behaviour of schooling herring startled by an artificial so und stimulus was observed by means of high speed video filming. Respon se latencies showed two distinct peaks, at 30 ms and c. 100 ms. Escape responses belonging to the two latency groups showed different turnin g rates during the first stage of the response, and showed different e scape trajectories. We suggest that long latency escapes may be respon ses to startled neighbours or simply weak responses to the sound stimu lus. In addition, the different contraction rates during the C-bend fo rmation seen in the two latency groups may imply differences in the ne uronal commands. The escape responses of herring were directed away fr om the stimulus more often than towards it (88% of the total). These a way responses were more common in long latency responses, suggesting t hat the latter enable herring to be more accurate in discerning the di rection of the threat. Startled fish contracting their body towards th e stimulus (performing a towards response) appear to correct their esc ape course, since their escape trajectory distribution is non-uniforml y distributed around 360 degrees and directed away from the stimulus. We hypothesize that when herring are schooling, the ability of each fi sh to correct its trajectory following turns towards the stimulus is e nhanced.