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

Abstract

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.

How do tuna schools associate to dFADs? A study using echo-sounder buoys to identify global patterns

“…For example, Robert et al (2012) found size dependent differences in the time yellowfin spent around an anchored FAD, with smaller individuals (< 50cm fork length) spending about four times as much time around the FAD than larger individuals. Similarly, differences in the CRT skipjack, yellowfin and bigeye tuna have been observed across oceans (Govinden et al, 2021;Schaefer and Fuller, 2005;Tolotti et al, 2020).…”

“…Although extensive literature has been dedicated to examining the time spent by tunas both near and away from floating objects, most work has been conducted on individually tagged tunas at a limited number of study sites (Govinden et al, 2021;Schaefer and Fuller, 2005;Tolotti et al, 2020;Dagorn et al, 2007;Ohta and Kakuma, 2004;Chiang et al, 2021;Matsumoto et al, 2016Matsumoto et al, , 2014Rodriguez-Tress et al, 2017). These methods provide high levels of detail, but also may not be representative of overarching trends across all dFADs, nor even the general patterns of an entire school of tuna.…”

Schooling in habitats with aggregative sites: The case of tropical tuna and floating objects

“…For a non-social model defined in an array of 10 FADs, these parameters imply average residence times and absence times of 10 days. Here, the choice of the model parameters h and l aimed at ensuring average residence and absence times of the same order of magnitude of those observed in past electronic tagging studies (Govinden et al, 2013(Govinden et al, , 2021Robert et al, 2013;Rodriguez-Tress et al, 2017;Tolotti et al, 2020). These parameters were kept fixed, in order to study the model sensitivity to other parameters, whose ranges of values are unknown.…”

“…Field studies also demonstrated that the associative behavior of tuna can be species and size-specific (Robert et al, 2012;Rodriguez-Tress et al, 2017). The choice of considering constant l stems from previous electronic tagging studies, which demonstrated that the time that tagged individuals spent between two FAD associations follows exponential survival curves (Govinden et al, 2021;Robert et al, 2013;Rodriguez-Tress et al, 2017;Tolotti et al, 2020) and random walk types of movements (Girard, 2004;Pérez et al, 2020). Because the equilibrium solutions of the model depend on the ratio l/h and to reduce the number of free parameters, the values of l and h were considered constant and fixed to plausible values (average association/ absence time of 10 days in an array of 10 FADs for the non-social model).…”

Recommendations towards the establishment of best practice standards for handling and intracoelomic implantation of data-storage and telemetry tags in tropical tunas

“…Data-storage and telemetry tags (emitting either radio or acoustic signals) are designed for intracoelomic implantation (hereafter collectively referred to as "body cavity tag" or BCT) and are battery-powered electronic devices encased in biologically inert resin, stainless-steel, or ceramic. Acoustic BCTs have been deployed in marine fisheries research since the 1960s [6,10,16,28,103] and are now commonly used to monitor movements and behaviors at locations of aggregation or confinement [33,34,37,43,52,81,95] or along corridors of seasonal movement [14]. Data-storage BCTs (referred to as Archival or Data Storage Tags) were developed in the 1990s [7,39].…”