Summary of Abstract Submission

Abstract Submission No. IO50-08-0021PresentationOral


Nimit Kumar*1, Nagaraja Kumar M1, Srinivas Kumar T1, Satya Prakash1, Uday Bhaskar TVS1

1 INCOIS, India


Tuna are known for their international demand and attractive market value, resulting most tuna stocks under high exploitation pressure. However, their movement and environmental preferences are little understood in Indian Ocean. We tagged a total of 42 Yellowfin tuna (Thunnus albacares) with PSATs (Pop-up Satellite Archival Tags) to study its ecology. The tags contained timer, pressure, temperature and communication (ARGOS) sensor. Half of the tags also had a light sensor for underwater tracking. We found the tuna stock being localized and undergo homing behavior. Tuna in this region exhibited neither significant diurnal pattern nor deep diving behavior even though deeper waters having temperatures within range of preference as known from studies in other oceans. Ambient temperature-range preferred by tuna in Arabian Sea and Bay of Bengal basins were 26-30 C and 25-29 C, respectively. We also noted tuna accessing areas with negative Sea Surface Height but limit its movements within 5 cm for most (70%) of the time. To probe this, we used SSH-based estimation of oxycline depth and found that during boreal winter, tuna avoid diving often below the oxycline. With the fact that tuna has high oxygen demand, dissolved oxygen might be factor that governs movement of tuna. Also, we propose that these habits account for stratified waters of these basins, which disproportionate food availability within upper waters only. With these first insights to the tuna stock of the region, we believe this will enable resource managers pursue their policies effectively.