engleski

Use of underwater stereoscopic camera in assessment of live bluefin tuna captured for farming purposes

Caging practices of live bluefin tuna (Thunnus thynnus) captured by purse seines for fattening and/or farming purposes, become an important fishery based aquaculture practice. However, it has been observed that this practice include uncertainties about number and size of seed fish captured and stocked into growth out floating cages, and also problems in collection of purse seine catch-at-size data. To solve this problem, ICCAT made recommendation (Rec. 10-04) asking all contracting parties to use stereoscopic cameras in order to assess initial capture-at-size information of the live fish placed in the fattening and/or farming cages. Its usefulness has been studied in the Adriatic Sea area, where mostly small bluefin tuna have been used as seed fish for eventual farming purposes. Underwater stereoscopic camera system together with an appropriate image analysing software was used to determine individual fish lengths, eventually used to calculate tuna weights using given length-weight relationship. Number of fish has been obtained by direct counting of specimens on slow-motion video records (frame-by-frame) made during fish transfer from transporting cage into anchored growing cage. It has been observed that weight estimates may vary according to length-weight relationship chosen, as well as due to different individual fish positions or camera motions. Difficulties in assessment of fish numbers by direct counting have been observed, mainly due to fast swimming and schooling behaviour of small tunas. The quality of images recorded was also an important factor for eventual analyses. Therefore, with aim to ensure good image quality, use of white background, a rigid frame to fix camera at appropriate distance from fish and good lightning conditions (i.e. avoid camera use at dawn and dusk) is needed.

Bluefin tuna; cageing; size measurements; stereoscopic camera

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