Hallier Jean-Pierre, Fonteneau Alain. (2015). Tuna aggregation and movement from tagging data : a tuna "hub" in the Indian Ocean. In :
Murua H. (ed.), Marsac Francis (ed.), Eveson J.P. (ed.). IO Tuna tagging. Fisheries Research, 163 (SI), p. 34-43. ISSN 0165-7836.
Titre du document
Tuna aggregation and movement from tagging data : a tuna "hub" in the Indian Ocean
Murua H. (ed.), Marsac Francis (ed.), Eveson J.P. (ed.) IO Tuna tagging
Source
Fisheries Research, 2015,
163 (SI), p. 34-43 ISSN 0165-7836
The majority of the tuna tagged during the IOTC Regional Tuna Tagging Project of the Indian Ocean (RTTP-IO) were released in tuna schools associated with tagging vessels (72% of all RTTP-IO tagged tuna) implementing the Associated School Fishing Technique (ASFT). This fishing technique was first developed off Mauritania Senegal by local pole-and-line vessels in the 1980s. During the program the ASFT was implemented by the two RTTP-IO tagging vessels over a period of 71/2 months in 2006 and three months in 2007 generating release of 121,068 tuna with a well-balanced species composition between the 3 species tagged (33.3% yellowfin, 39.5% skipjack and 27.2% bigeye). Fishing without using any live bait (only lures on the hooks) was also possible and very productive as 56% of all tagged tuna were caught that way, The consequences of using ASFT on the results of the RTTP-IO are presented. While fishing associated schools (AS), 11,016 recaptures of tagged tuna (61% yellowfin, 18% skipjack, 21% bigeye) were registered by the tagging vessels and some tuna were recaptured several times, one tagged skipjack was caught nine times during a period of two months. This paper analyses the contribution of the ASFT within the overall RTTP-IO tagging program and the characteristics of the recoveries of tagged tuna by the tagging vessels fishing AS. The quite low level of local recaptures in AS fishing underlined a high turn-over of the three species in AS in particular, and in this area in general. This place was like a hub for tuna coming in and going out at a high rate, indicating a rapid and good dispersion of the tagged fish into the rest of the population. These results are compared with recoveries observed in the Atlantic Ocean, where similar tagging operations were carried out in the 1990s, revealing disparate results in the two oceans.
