Edison D. Macusi | Ricardo P. Babaran | Jose T. Ingles
Discipline: Fisheries, Ecology, Environmental Conservation
This paper describes the vertical movements, behavior and habitat utilization of an electronically tagged adult yellowfin tuna (Thunnus albacares) after 17 days of liberty in the Philippines based on analyses of 23,845 datapoints recorded from a recovered electronic popup tag. The exhaustive set provides a way to describe the vertical movement as well as a range of behaviors exhibited by the fish. We used the daily time records of depth and temperature from the vertical dives of the fish at different times of the day (nocturnal, dawn, diurnal, dusk) to describe fish behavior and to characterize its three deep dives. The fish stayed 23% and 24% of its time at warmer waters of 28 0C and 30 0C. It also spent 15% of its time at 26 0C and 10% of its time at colder waters of 20 0C and 22 0C. The daily differences in temperatures fluctuated from 12.10C to 30.1 0C with the daily average temperature of 24.2 0C. Swimming speeds determined show the maximum vertical ascent speed that the fish registered reached 1.53m/s swimming from a depth of 195m to 104m during a dusk. The maximum vertical descent speed reached 1.38m/s from a depth of 78m down to 161m. The deepest dive of the fish started from a U-shaped diving profile that lasted for almost 32 minutes and then followed by another U-shaped dive for 12 minutes before a deep dive and fast vertical ascent. The total duration of its dives differ with water depth: 0-50m (1.89 hours), 50-75m (4.78 hours), 75-100m (3.35 hours), 100- 125m (1.69 hours), 125-150m (1.69 hours). Such swimming behavior provides valuable information on the vulnerability of tunas particularly the juvenile fishery.