Comparison of the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus) tuna associated with drifting FADs in the equatorial central Pacific Ocean

Abstract

We evaluated the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) associated with drifting fish aggregating devices (FADs) in the equatorial central Pacific Ocean. A total of 30 skipjack [34.5–65.0 cm in fork length (FL)], 43 yellowfin (31.6–93.5 cm FL) and 32 bigeye tuna (33.5–85.5 cm FL) were tagged with coded transmitters and released near two drifting FADs. At one of the two FADs, we successfully monitored the behavior of all three species simultaneously. Several individuals remained around the same FAD for 10 or more days. Occasional excursions from the FAD were observed for all three species, some of which occurred concurrently for multiple individuals. The detection rate was higher during the daytime than the nighttime for all the species, and the detection rate for bigeye tuna was higher than for yellowfin or skipjack tuna. The swimming depth was deeper during the daytime than nighttime for all species. The fish usually remained shallower than 100 m, but occasionally dived to around 150 m or deeper, most often for bigeye and yellowfin tuna during the daytime. The swimming depth for skipjack tuna was shallower than that for bigeye and yellowfin tuna, although the difference was not large, and is probably not sufficient to allow the selective harvest of skipjack and yellowfin tuna by the purse seine fishery. From the detection rate of the signals, bigeye tuna is considered to be more vulnerable to the FAD sets than yellowfin and skipjack tuna.

Association dynamics of tuna and purse seine bycatch species with drifting fish aggregating devices (FADs) in the tropical eastern Atlantic Ocean

“…Therefore, the maximum TRT of 55 days is likely underestimated. In any case, the values observed here for yellowfin and bigeye tuna are comparable to what was observed in other studies on anchored FADs (Dagorn et al, 2007a;Ohta and Kakuma, 2005;Rodriguez-Tress et al, 2017), but were never observed for drifting FADs (Dagorn et al, 2007b;Matsumoto et al, 2016;Schaefer and Fuller, 2010). It is also worth noting that these previously reported TRTs were calculated at the scale of an array of anchored FADs and not on a single drifting FAD, as in our study.…”

“…Skipjack tuna did not remain associated with the FADs for such long periods and the maximum observed TRT for this species was 15 days. Most studies have observed that skipjack tuna generally associate with FADs for shorter periods of time, with reported maximum TRTs varying from 6.4 to 12.8days (Govinden et al, 2013;Matsumoto et al, 2016Matsumoto et al, , 2014. As an exception to this general finding, a skipjack tuna remained associated for a record of 40.9 days at an array of anchored FADs in Mauritius (Rodriguez-Tress et al, 2017).…”

“…The amount of time a fish tends to remain in FAD-associated and non-associated states can also be used to model the dynamics of fish abundance and thus provide fishery-independent abundance indices (Capello et al, 2016). Electronic tagging studies have successfully measured the residence and absence times of tropical tunas and other species associated with drifting and anchored FADs, although most of the studies have been conducted on anchored FADs (Dagorn et al, 2007b(Dagorn et al, , 2007aFilmalter et al, 2015;Govinden et al, 2013;Matsumoto et al, 2016Matsumoto et al, , 2014Mitsunaga et al, 2012;Ohta and Kakuma, 2005;Robert et al, 2013;Rodriguez-Tress et al, 2017;Fuller, 2013, 2010). Nonetheless, all of these studies were conducted in the Pacific and Indian Oceans, and the dynamics of FAD-associated species in Atlantic are yet to be described.…”

Detection of pelagic habitat hotspots for skipjack tuna in the Gulf of Bone-Flores Sea, southwestern Coral Triangle tuna, Indonesia

“…The Chl-a front appears to coincide with the shelfbreak position (approximately 350 m isobath) of both Flores Sea and Bone Gulf (Figs 1 , 5 and 10 ). Highest skipjack CPUEs are concentrated near the shelfbreak location [ 17 ] during the daytime [ 55 ]. Our empirical fishing data (2007–2011) confirm that fishermen consistently exploit the forage habitat during the daytime and, using the fishing data in 2012, we showed that our prediction models have been substantially verified (Figs 5 , 8 and 9 ).…”

Towards acoustic discrimination of tropical tuna associated with Fish Aggregating Devices

“…Thus, in order to concentrate on tuna species presence and abundance on DFADs, targeting depths below that occupied by the non-target species may be an effective strategy. Although tuna species could also be found at shallower depths and some by-catch species can have a partially overlapping vertical distribution during some hours of the day, studies using tag sensors have shown that tuna species generally remain deeper than non-target species [53,54]. The few studies that have assessed the presence of tuna at DFADs using echo-sounders have not considered data above 25 m to avoid targeting non-tuna species [51, 55].…”