Trophic Dynamics and Feeding Ecology of Skipjack Tuna (Katsuwonus pelamis) off Eastern and Western Taiwan

Abstract

The skipjack tuna (Katsuwonus pelamis) is a mesopredator fish species with seasonal abundance in waters off Taiwan. Regional ecological and life-history information has been historically lacking for this species. In recent years, stable isotope analysis (SIA) of carbon and nitrogen has been used to assess predator feeding ecology and broader ecosystem trophic dynamics. This study evaluated comparative skipjack feeding ecology in distinct regions off Taiwan, combining traditional stomach content analysis with SIA of individuals off western (n = 43; 2020) and eastern (n = 347; 2012–2014 and n = 167; 2020) Taiwan. The stomach content analysis showed the most important prey to be ponyfish (Photopectoralis bindus) in western Taiwan and epipelagic squids (Myopsina spp.) and carangids (Decapterus macrosoma;) in eastern Taiwan from 2012 to 2014 and epipelagic carangids (Decapterus spp.) and flying fishes (Cheilopogon spp.) in eastern Taiwan in 2020, suggesting that the skipjack tuna is a generalist predator across regions. In contrast, time-integrated diet estimates from Bayesian mixing models indicated the importance of cephalopods and crustaceans as prey, potentially demonstrating more mesopelagic feeding in less productive waters during skipjack migrations outside the study regions. Skipjack off western Taiwan had a slightly higher estimated trophic position than in the waters off eastern Taiwan, potentially driven by the varying nutrient-driven pelagic food web structures. Skipjack SI values increased with body size off eastern Taiwan but not in western waters, suggesting that opportunistic predation can still result in different predator–prey size dynamics between regions.

Special Issue “Applications of Stable Isotope Analysis”

“…Thanks to this study, the authors were able to conclude that skipjack tuna in western Taiwan had a slightly higher trophic position and that opportunistic predation may result in different predator–prey size dynamics between regions (stable isotope values increased with body size in eastern Taiwan). These data complemented previous research regarding other pelagic predators such as black and blue marlin, yellowfin and Pacific bluefin tuna, and sailfish in Kuroshio Current [ 7 ].…”

“…This Special Issue aims to provide an updated view and highlight the advances in the application of stable isotope analysis (SIA) in the different fields of chemistry. It includes five research articles and two review papers dealing with the use of this technique in geochemical [ 2 , 3 ], archaeological [ 4 , 5 , 6 ], environmental [ 7 ], and food [ 4 , 8 ] studies.…”

“…The combination of SIA and stomach content analysis provides a powerful tool to assess trophic dynamics. In this regard, Chang et al [ 7 ] used the SIA of C and N to evaluate the predatory feeding ecology of skipjack tuna in Taiwanese waters. For this purpose, the stomach contents from individuals from eastern ( n = 347) and western ( n = 43) Taiwan were analysed.…”

The Effects of Trans-Basin Climate Variability on Skipjack Tuna in the Northwest Pacific Ocean: Causal and Nonstationary

“…As the opportunistic feeder, SKJ could consume various preys, such as squid, crustaceans, and some mackerel or perciform fish during migration (Aoki et al, 2017). Such region-dependent feeding could probably moderate the down-top biotic effect on SKJ through the food chain, while the inverse control from predators (like sharks and billfishes in the eastern tropical Pacific Ocean, (Hunsicker et al, 2012;Chang et al, 2022) is unclear in the NWP.…”

First record of skipjack tuna (Katsuwonus pelamis) from Dahab in the Gulf of Aqaba, Red Sea, Egypt

“…The skipjack tuna (K. pelamis) is a mesopredator fish with seasonal prevalence and little life-history knowledge. It is a highly migratory fish species that may be found in subtropical and tropical seas, the primary fishing area for tuna purse-seine fisheries, with skipjack making up the majority of the catch (Chang et al, 2022). Tunas are thought to be predators and opportunistic eaters in general.…”