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

Abstract

The effect of boat noise on the behaviour of bluefin tuna Thunnus thynnus was investigated\ud in the Egadi Islands, Sicily, during spring 2005 using a fixed tuna trap set near shipping routes.\ud Tuna behaviour was observed when exposed to both natural ambient sound and sound generated by\ud hydrofoil passenger ferries, small boats and large car ferries. Acoustical and behavioural analyses\ud were conducted with and without extraneous sound to define a list of behavioural categories. Each\ud vessel produced different engine sounds with regard to their composition and bandwidth, and all\ud were distinctly different from ambient sound levels. In the absence of boat noise, tuna assumed a concentrated\ud coordinated school structure with unidirectional swimming and without a precise shape.\ud When a car ferry approached, tuna changed swimming direction and increased their vertical movement\ud toward surface or bottom; the school exhibited an unconcentrated structure and uncoordinated\ud swimming behaviour. Hydrofoils appeared to elicit a similar response, but for shorter periods. Agonistic\ud behaviour was more evident when exposed to sounds from outboard motors of small boats. This\ud study showed that local noise pollution generated by boats produced behavioural deviations in tuna\ud schools. Schooling enhances tuna homing accuracy during their spawning migration, and an alteration\ud in schooling behaviour can affect the accuracy of their migration to spawning and feeding\ud grounds

Aggregations of wild Atlantic Bluefin Tuna (Thunnus thynnus L.) at Mediterranean offshore fish farm sites: Environmental and management considerations

“…The constant feed availability at fish farm sites leads to behavioural changes in the tuna, which could lead to potential modifications on schooling behaviour, a key strategy for gregarious species. Consequently, an alteration in schooling behaviour could affect the tuna's homing accuracy to spawning and feeding grounds during migration (Sarà et al, 2007), potentially resulting in new coastal migratory routes or resident populations, at least at a local or regional scale. In as much, there is a need for research that should be directed towards understanding the extent of the influence of offshore fish farms on the biology and ecology of this very important natural marine resource.…”

“…Individuals which would have inhabited an on-growing cage for some time may have their migratory behaviour modified, given that they show some affinity to the fish farms by remaining aggregated there or visit the surrounding facilities. Sarà et al (2007) suggested that tuna behaviour can be altered by anthropogenic disturbances, such as boat noise, which can modify swimming and schooling patterns, thereby affecting their natural migratory behaviour, including migration to spawning and feeding grounds. However, based on daily observations by the fish farm divers, the wild ABT aggregated around fish farms are recorded throughout the year, except during harvesting time (January to February) and during the spawning period (June) of the species.…”

A noisy spring: the impact of globally rising underwater sound levels on fish

“…Another example concerns effects of nearby boating noise on blue-fin tuna (Thunnus thynnus) in large oceanic pens. In the presence of boat noise, tuna schools were less coherent than when the noise was not present and individual fish often swam independently towards the surface or the bottom [19]. Fish have also been reported to flee from seismic shooting areas as inferred from decreased catch…”

Ambient noise and temporal patterns of boat activity in the US Virgin Islands National Park

“…However, there is growing evidence that small boat noise can impact fishes. Exposure to boat noise from a range of vessels disrupted schooling behavior in captive bluefin tuna, which the authors argued could affect feeding if a similar response occurred in wild tuna (Sara et al, 2007). Playbacks of vessel noise in the lab raised hearing thresholds for three species of Mediterranean fish, particularly in the frequency range where acoustic communication takes place (Codarin et al, 2009).…”