Periodic behavior and residence time of yellowfin and bigeye tuna associated with fish aggregating devices around Okinawa Islands, as identified with automated listening stations

-In the Western and Central Pacific Ocean (WCPO), which accounts for over half of world tuna production, purse seine effort and catch on floating objects have increased significantly due to a rapid increase in the use of fixed and free-floating fish aggregation devices (FADs). FAD fishing has had an impact on the current status of the stocks of the three main target tunas in the equatorial WCPO, skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus). FADs have been shown to influence the behaviour and movement patterns of the three tuna species with the juveniles of each species occupying shallower habitats when associated with FADs. Aggregation of tunas around drifting objects increases their vulnerability to purse seine gear, particularly for juvenile and small size classes. Further to the impacts on the target stocks, the use of FADs has increased the vulnerability of other fishes to the purse seine method, including some shark and billfish species. Given the concern over FAD-related fishing effort on target and bycatch species, there is a need to understand how FAD use affects target and bycatch stocks. Science needs to better support management decisions are highlighted including the need to identify the magnitude of broader community-level affects.

Section: Fads and Prey Landscapessupporting

confidence: 64%

Section: Fads and Prey Landscapesmentioning

confidence: 82%

A critique of the ecosystem impacts of drifting and anchored FADs use by purse-seine tuna fisheries in the Western and Central Pacific Ocean

Leroy

Phillips

Nicol

et al. 2012

“…The hourly detection rate and continuous residence time (CRT) as defined by Ohta and Kakuma (2005) were calculated to relate the horizontal swimming patterns. CRT indicates the duration for which a tagged fish was continuously monitored at a single FAD without interruption over 24 h. To examine diurnal swimming patterns, daytime was defined from sunrise (05:40) to sunset (18:30) in local time astronomically.…”

Section: Discussionmentioning

confidence: 99%

“…They swam within a limited shallow range during nighttime and dived to deeper water up to 100 m during daytime, while an adult individual dived over 1000 m (Dagorn et al 2006). All juveniles stayed around a single payao or associated with a network of payaos for less than 6 days, while adult yellowfin tuna stayed around a single FAD for a maximum of 55 days (Ohta and Kakuma 2005) and 151 days with a network of FADs (Dagorn et al 2007). During the short stay, some juveniles showed a synchronized horizontal swimming pattern, assuming that they stayed near a payao during daytime and away from the payao at night time simultaneously.…”

Section: Introductionmentioning

confidence: 99%

Schooling behavior of juvenile yellowfin tunaThunnus albacaresaround a fish aggregating device (FAD) in the Philippines

Mitsunaga

Endo

Babaran

2012

-A fish aggregating device (FAD) called a payao is conventionally installed to catch pelagic species in the Philippines. The waters around the Philippines are important regions for yellowfin tuna stocks because they include spawning grounds and nurseries. To understand the schooling behavior of juvenile yellowfin tuna Thunnus albacares around a payao, 13 juveniles (20.5−24.0 cm fork length) double tagged with ultrasonic transmitters (V7-2L-R256; Vemco Ltd.) and data loggers (DST-micro; Star-Oddi Ltd.) were released around a payao. A self-recording receiver (VR2-DEL; Vemco Ltd.) was attached on the mooring rope of the payao to follow the horizontal movements and data loggers recorded the vertical movements of tagged juveniles. Nine juveniles were recaptured simultaneously by ring net at the same payao after 4-7 days. One juvenile was recaptured by hand line at another payao 12 km away from the tagging site after 6 days. Recaptured juveniles showed a diurnal schooling pattern suggesting different school shape and foraging strategy between daytime and nighttime. Juveniles showed a diurnal horizontal moving pattern, concentrated near the payao during daytime, while they were distributed around the payao at nighttime. The fluctuations of swimming depth were synchronized among fish. Juveniles also showed a diurnal vertical movement pattern in surface mixed layer. They concentrated in a shallow and narrow range (11.2 ± 8.2 m, mean ± SD) at nighttime, while they were distributed to a deep and wide range (20.0 ± 11.8 m) during daytime. The maximum vertical neighbor distance indicated the vertical thickness of the school and showed a peak around noon. Higher vertical movement speed during daytime indicated vertical foraging in a water column, while at nighttime the juveniles might forage horizontally following the diurnal migration patterns of prey in the surface layer.

“…With the increasing use of drifting FADs by industrial purse seiners all over the world, the scientific community has questioned the effects of FADs on the behaviour of fish (Marsac et al 2000;Hallier and Gaertner 2008). So far, most behavioural studies have been conducted on tropical tunas mainly Thunnus albacares, but also Katsuwonus pelamis and Thunnus obesus (Dempster and Taquet 2004) and their movements within FAD arrays (Klimley and Holloway 1999;Ohta andKakuma 2005, Dagorn et al 2007). However, studies on smaller species around shallow coastal FADs (Soria et al 2009;Capello et al 2011) have recently revealed the a Corresponding author: manuela.capello@ird.fr potential of using fine-scale data (often difficult to obtain on larger species in the open ocean) to understand behavioural processes.…”

Section: Introductionmentioning

confidence: 99%

Effect of current and daylight variations on small-pelagic fish aggregations (Selar crumenophthalmus) around a coastal fish aggregating device studied by fine-scale acoustic tracking

Capello

Soria

Potin

et al. 2012

-Several pelagic fish species are known to associate with floating objects. However, quantitative information on the main factors that drive this associative behaviour is still lacking. Small pelagic fish offer a particularly interesting case study for this phenomenon, since the small spatial scales involved in their association with floating objects allow experimental data to be collected at a fine scale. Here, we monitored twelve acoustically-tagged bigeye scads, Selar crumenophthalmus (Carangidae), (mean fork length 16.4 cm, SD 2.1 cm) around a floating object moored in shallow water (15 m depth) playing the role of a coastal fish aggregating device (FAD). To quantify the role played by variations in current and daylight, we calculated the speed distribution, pair correlation function and group polarization for the tagged fish hourly, from midday to dusk (13:00−18:00), for varying current strengths and daylight conditions. We found that the current induced a shift in the position of the aggregation upstream of the FAD, at distances that increased with the current strength. We found evidence of an expansion and a higher coordination in the aggregation at dusk, with increasing speed, distance among conspecifics and alignment. We discuss possible scenarios in which group polarization increases at dusk and suggest complementary measurements for future experiments that could confirm our findings.