Fine-scale vertical and horizontal movements of juvenile yellowfin tuna (Thunnus albacares ) associated with a subsurface fish aggregating device (FAD) off southwestern Taiwan

Abstract

Summary An increase in yellowfin tuna (Thunnus albacares) catch by danish seine fisheries around the subsurface fish aggregating devices (FADs) in southern Taiwan waters has been a concern of local government and environmental groups. However, the attraction mechanism of aggregating tunas at the subsurface FADs is still poorly understood. The objective of this study is to examine the fine‐scale vertical and horizontal movements of juvenile yellowfin tunas around a subsurface FAD. In total, 53 tunas (35–81 cm fork length) were tagged with ultrasonic telemetry tags and released at a subsurface FAD in the waters off Shiao‐Liu‐Chiu Island, southwestern Taiwan from October 2008 to December 2009. These tunas stayed at the subsurface FAD for up to 31 days, with daytime vertical movement depths averaging 60–80 m at a maximum depth of 250 m. At night, the tuna gathered at a shallow depth of 40 m. The mean depth of vertical movement in the daytime is significantly different from that of the nighttime (P < 0.05). The maximum detectable distance of horizontal movement was 1.6 km, with 80% of the long horizontal movements occurring in the daytime. It is likely that the purpose of these vertical and horizontal movements was for feeding or avoiding predators. Moreover, the tagged tunas did not depart from the subsurface FAD simultaneously, suggesting distinct behaviors in their movements.

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

“…() (skipjack tuna: 0.20–3.75 days, yellowfin tuna: 0.61–0.70 days) and Weng et al . () (yellowfin tuna: up to 31 days, mostly <10 days). In the present study, we observed large temporal changes in species composition and fish size in the catch at FAD6.…”

“…There is potential for the selective harvest of tuna species if their swimming depth differs around FADs. A number of studies have evaluated the vertical behavior of the aforementioned tuna species (the so‐called ‘tropical tunas’) associated with floating objects, including FADs (Cayré and Chabanne, ; Holland et al ., ; Cayré, ; Marsac and Cayré, ; Klimley and Holloway, ; Dagorn et al ., ; Schaefer and Fuller, , , , ; Musyl et al ., ; Ohta and Kakuma, ; Leroy et al ., ; Schaefer et al ., ; Mitsunaga et al ., , ; Matsumoto et al ., ; Weng et al ., ). Most of these studies evaluated the behavior of tropical tunas around anchored FADs whereas few have evaluated behavior around drifting FADs because of the difficulty and expense of tracking FADs.…”

Feeding Ecology of Juvenile Yellowfin Tuna from Waters Southwest of Taiwan Inferred from Stomach Contents and Stable Isotope Analysis

“…Graham (2008) estimated the half-life turnover rate of the liver to be shorter than that of muscle tissue (12 versus 63 d), because the metabolic rate of the liver is higher than that of muscle tissue (Suzuki et al 2005;Guelinckx et al 2007). Weng et al (2013) reported that juvenile Yellowfin Tuna that lingered around a single FAD in the waters southwest of Taiwan for >31 d fed on various types of prey during this period and their muscle tissue exhibited varied stable isotope N and C values. The movement of juvenile Yellowfin Tuna from other waters to Taiwanese waters may alter their food intake and increase their nutrient supply.…”

Habitat and behaviour of adult yellowfin tuna (Thunnus albacares) in the waters off southwestern Taiwan determined by pop-up satellite archival tags

“…According to local fishermen's experience, adult yellowfin tuna migrate from the South China Sea to the waters off southwestern Taiwan during the same period. The feeding behaviour of juvenile yellowfin tuna around subsurface FADs in the waters off southwestern Taiwan has been documented (Weng et al, 2013(Weng et al, , 2015. The authors found that juvenile yellowfin tuna aggregated at a depth of 60-80 m in the daytime and at a depth of 40 m at nighttime, and fish stayed near the subsurface FADs for up to 31 days.…”