engleski

Some field observations on usefulness of searchlight sonar during bluefin tuna (Thunnus thynnus L.) fishing activities in the Adriatic Sea

The first field observations regarding to use of a searchlight sonar in the commercial fisheries, as well as some practical limitations that could appear are described in this paper. Some problems in sonar use, regarding to bluefin tuna purse-seine fisheries in Adriatic Sea, are presented. The data presented in this paper was collected on board of the commercial purse-seiner while fishing bluefin tunas during July-August in the Adriatic Sea (Jabuka Pit). This fishing vessel was equipped with FURUNO CH-24 Colour PPI searchlight single-beam sonar system made for commercial purposes. The importance of proper placement of the transducer on the hull, and disturbances that raised from its improper placement are noticed. The presence of wakes made by fishing vessels cruising over the fishing ground, were the main limitation for making acoustic observations in the surface layer. Also, in comparison to the ability of fishermen to spot the bluefin tunas close to the sea surface at more than 2000 meters, the effective ranges from 300 to 1200 meters achieved by this sonar was relatively short, and made no significant contribution to the search for fish. Under rough sea conditions (sea state: ĄÝ4 Beauforts), it was impossible to use sonar, due to pitching and rolling of the vessel.

sonar; bluefin tuna (Thunnus thynnus L.); fishing; Adriatic Sea

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