Behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares), and bigeye (T. obsesus) tunas associated with drifting fish aggregating devices (dFADs) in the Indian Ocean, assessed through acoustic telemetry

We investigated the associative behavior of skipjack (Katsuwonus pelamis), yellowfin
(Thunnus albacares), and bigeye (T. obsesus) tuna within multi-species
aggregations associated
with drifting fish aggregating devices (dFADs) in two different regions of the
western Indian Ocean: the Mozambique Channel and the Seychelles, using acoustic
telemetry. We documented the residence and absence times of tunas at two temporal
scales (coarse and fine scale) and made comparisons between regions. A total
of 56 tunas were tagged and released at 7 different dFADs (4 in the Mozambique
Channel and 3 in the Seychelles) during four research cruises. We recorded the first
observations of skipjack tuna making excursions of more than 24 hours away from
dFADs before returning and confirmed findings of other studies showing that yellowfin
tuna can make long excursions (4.07 days) before returning to their home dFADs.
Combining both studied regions, average residence times were 7.59 days (min 0.03;
max 16.49), 6.64 days (min 0.01; max 26.72), and 4.58 days (min 0.09; max 18.33) for
bigeye, yellowfin, and skipjack tuna, respectively. Exponential models best fitted the
residence times for all three tuna species, indicating time-independent
probabilities
of departure from dFADs. For yellowfin tuna, at a coarse temporal scale, no regional
differences were observed in the residence times. However, at a fine temporal scale,
regional differences were apparent in both residence and absence times. This study
provides new information on the associative behavior of tunas at dFADs in the Indian
Ocean which is key to improving the science-based
management of dFADs.