The behaviour of spawning herring in relation to a survey vessel

Vessel avoidance of spawning herring (Clupea harengus L.) was studied off the coast of southwestern Norway in April 2000. In eight repeated night-time passages a demersal layer of herring was recorded acoustically by a small stationary reference vessel (96 GRT), while a survey vessel (710 GRT) passed at short ranges (8–40 m). No avoidance attributable to the survey vessel was observed. We interpret vessel avoidance as a response to a perceived threat and herring are known to exhibit strong avoidance reactions to survey vessels during wintering and the spawning migration. At the spawning site, the high priority given to reproductive activities seems to overrule the avoidance responses to a passing survey vessel.