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When fish meet a trawling vessel: examining the behaviour of gadoids using a free-floating buoy and acoustic split-beam tracking

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Abstract:

The reaction of individual gadoids to a bottom-trawling vessel has been observed in situ in the Barents Sea using a free-floating buoy and acoustic target-tracking methods. More than 20 000 tracks were analysed in terms of velocity changes in vertical, athwarthship, and alongship direction relative to the vessel, the warps, and the trawl, respectively. The fish starts diving about 15 min before vessel passing. This coincides with the time the trawl is running and not with the gradual increase in vessel noise caused by the approaching vessel. The change in horizontal movement is more gradual and is directed away from the vessel in the alongship direction, but towards the vessel in the athwarthship direction. The strongest and sharpest response is related to the trawl warps. A strong herding in front of the warps is seen. Closer to the bottom, an athwarthship herding reaction is seen away from the trawl doors or possibly the lower parts of the warps. There were only minor differences when grouping the tracks according to light level, fish size, and fish density.

L'utilisation d'une bouée dérivante et de méthodes acoustiques de suivi de cibles dans la mer de Barents a permis d'observer in situ la réaction de gadoïdes individuels à un chalutier de fond. Nous avons ainsi analysé plus de 20&000 trajectoires en ce qui a trait aux changements de vitesse en directions verticale, perpendiculaire et parallèle au navire, aux aussières et au chalut. Le poisson commence à plonger environ 15 min avant le passage du navire. Cela coïncide avec le temps d'utilisation du chalut et non avec l'accroissement graduel du bruit causé par l'approche du navire. Le changement dans le déplacement horizontal est plus graduel et il est orienté en direction opposée au navire chez les poissons qui se déplacent parallèlement au navire et en direction du navire chez les poissons qui se déplacent perpendiculairement au navire. Les réactions les plus fortes et les plus marquées sont associées aux aussières du chalut. On observe de forts rassemblements devant les aussières. Plus près du fond, il se fait une réaction de rassemblement vers le navire pour fuir les portes du chalut ou peut-être les parties plus basses des aussières. Il n'y a que des différences mineures lorsqu'on regroupe les trajectoires en fonction du niveau de lumière, de la taille des poissons et de la densité des poissons. [Traduit par la rédaction]

Document Type: Research Article

Publication date: October 1, 2005

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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