Effect of boat noise on the behaviour of bluefin tuna Thunnus thynnus in the Mediterranean Sea

摘要

The effect of boat noise on the behaviour of bluefin tuna Thunnus thynnus was investigatedudin the Egadi Islands, Sicily, during spring 2005 using a fixed tuna trap set near shipping routes.udTuna behaviour was observed when exposed to both natural ambient sound and sound generated byudhydrofoil passenger ferries, small boats and large car ferries. Acoustical and behavioural analysesudwere conducted with and without extraneous sound to define a list of behavioural categories. Eachudvessel produced different engine sounds with regard to their composition and bandwidth, and alludwere distinctly different from ambient sound levels. In the absence of boat noise, tuna assumed a concentratedudcoordinated school structure with unidirectional swimming and without a precise shape.udWhen a car ferry approached, tuna changed swimming direction and increased their vertical movementudtoward surface or bottom; the school exhibited an unconcentrated structure and uncoordinatedudswimming behaviour. Hydrofoils appeared to elicit a similar response, but for shorter periods. Agonisticudbehaviour was more evident when exposed to sounds from outboard motors of small boats. Thisudstudy showed that local noise pollution generated by boats produced behavioural deviations in tunaudschools. Schooling enhances tuna homing accuracy during their spawning migration, and an alterationudin schooling behaviour can affect the accuracy of their migration to spawning and feedingudgrounds.