Comparison between acoustic Target Strength of Yellowfin Tuna (Thunnus albacares) and Longtail Tuna (Thunnus tonggol)

Abstract

Yellowfin Tuna (Thunnus albacares) and Longtail Tuna (Thunnus tonggol) are among the two commercially important fishes and highly migratory species, subject to be conserved by the convention on the law of the sea in Annex I of the 1982 Convention on the Law of the Sea (FAO, Fisheries Department 1994). Morphologically, T. albacares and T. tonggol have a striking difference, where the former has swim bladder while the latter has not. This paper comparing the result of acoustic target strength (TS) measurement of the two species using SIMRAD EY 60 scientific acoustic instrument. The in-situ measurement was conducted on each species for two different fish length. The fish is tethered using a monofilament string and the distance between the surface of the transducer to fish is ± 4 m. The result showed that the value of T≐ Albacares1 (51.70 cm) is -40.46 dB and T. Albacares2 (29.20 cm) is -43.70 dB, whereas value of T. tonggol1 (19.4 cm) is -46.53 dB and T. tonggol2 (17.1 cm) is -49.29 dB. Therefore, teh presence of swim bladder made a difference on the measured mean between T. albacares and T. tonggol. Whilw for the length of fish, is not always the case.