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

Abstract

The Yellowfin Tuna Thunnus albacares is one of the major fish species caught around subsurface fish aggregation devices (FADs) in the waters southwest of Taiwan. However, how it interacts with other organisms around FADs is poorly known. In this study, the diet and feeding habits of juvenile Yellowfin Tuna were estimated from the analysis of stomach contents from 1,477 specimens with FLs ranging from 24 to 108 cm and stable isotope analysis (202 specimens) collected around FADs in the waters southwest of Taiwan. The analysis of stomach contents indicated that juvenile Yellowfin Tuna with FL < 50 cm mainly feed on larval purpleback flying squid Sthenoteuthis oualaniensis, larval shrimps, and zooplanktonic organisms such as amphipods. Yellowfin Tuna with FL of ∼50 cm switch their diet to teleost fishes such as Japanese Barracudina Lestrolepis japonica, Skinnycheek Lanternfish Benthosema pterotum, and fishes in the families Exocoetidae and Scombridae. Stable isotope analysis indicated that the δ15N values ranged between 6.2‰ and 12.6‰, and the estimated trophic position varied from 3.18 ± 0.24 for tuna with FL < 30 cm, while it reached 4.59 ± 0.50 for those with FL > 50 cm and 4.75 ± 0.06 for those with FL > 90 cm. Based on the distinct diet shift of the juvenile Yellowfin Tuna, demonstrated by both stomach contents and stable isotope analyses, this study concluded that the tuna shift their diet at approximately 50 cm FL. Received March 31, 2015; accepted September 9, 2015

Diet composition of bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) caught on aggregated schools in the western equatorial Atlantic Ocean

“…Although several authors have reported the preference of yellowfin tuna for diverse fish families, the overwhelming contribution of flying fishes (Exocoetidae) found in this study were previously reported by Vaske‐Jr et al () and Ruderhausen et al () in the western Atlantic, and by Weng et al () from pre‐adults (90–110 cm in fork length) in the western Pacific, off Taiwan.…”

Annual variability in dentin δ15N and δ13C reveal sex differences in weaning age and feeding habits in Risso's dolphins (Grampus griseus)

“…, Weng et al . ) may indicate that these individuals were not from the population in Taiwanese waters.…”

“…Although samples from the western coast were limited, the distinct isotopic ratios, particularly those from Penghu, suggest that they were from a different, spatially segregated population than those individuals stranded or caught on the eastern or northern coasts. However, the comparable stable isotope ratios of plankton and cephalopods collected from the southwestern and southeastern waters of Taiwan (Tsai et al 2015, Weng et al 2015) may indicate that these individuals were not from the population in Taiwanese waters.…”

Ontogenetic change in the amount and position of slow‐oxidative myotomal muscle in relationship to regional endothermy in juvenile yellowfin tuna Thunnus albacares

“…Weng et al . () also found evidence of a diet shift in juvenile T. albacares at c . 500 mm L F , to faster moving, surface‐associated prey.…”

“…Similarly, dietary shifts to a mesopelagic shrimp found at depths of 200–700 m and to a more piscivorous diet were documented, based on analyses of both stomach contents and stable‐isotope composition, in T. albacares juveniles, but at a larger size of c . 500 mm L F (B. S. Graham et al ., ; Weng et al ., ). B. S. Graham et al .…”