| Affiliation: | 1. Eastern Marine Biology Research Center, Fisheries Research Institute, Taitung, Taiwan;2. Institute of Oceanography, National Taiwan University, Taipei, Taiwan;3. Pelagic Research Group LLC, Honolulu, Hawaii, USA;4. Institute of Oceanography, National Taiwan University, Taipei, Taiwan Center of Excellent for the Oceans, National Taiwan Ocean University, Keelung, Taiwan;5. Gulf of California International Research Center, Santa Rosalia, Mexico;6. School of Marine Science and Policy, University of Delaware, Lewes, Delaware, USA;7. Department of Environmental Biology and Fishery Science, National Taiwan Ocean University, Keelung, Taiwan;8. Fisheries Research Institute, Keelung, Taiwan |
| Abstract: | To gain a better understanding of the trophic ecology of Pacific blue marlin Makaira nigricans off eastern Taiwan, nitrogen and carbon stable isotopes (δ15N and δ13C) and Bayesian mixing models were used to explore trophic dynamics and potential ontogenetic feeding shifts across M. nigricans of different size classes. Makaira nigricans samples from east of Taiwan (n = 213) and Palau (n = 37), as well as their prey (n = 70), were collected during 2012 and 2013. Results indicated increases in δ15N with size, with values of larger size classes (> 200 cm eye-to-fork length; LEF) significantly higher than those < 200 cm LEF. Values of δ13C were negatively correlated with size. Makaira nigricans > 200 cm LEF had the highest estimated trophic position (4.44) and also exhibited ontogenetic changes in trophic position. Large M. nigricans fed more on dolphinfish Coryphaena hippurus and hairtail Trichiurus lepturus, while smaller M. nigricans consumed smaller forage fish (e.g., moonfish Mene maculata) and cephalopods. These changes may relate to greater swimming speeds and vertical habitat use in larger M. nigricans, allowing capture and consumption of larger prey items at higher trophic positions. The high trophic level of M. nigricans east of Taiwan confirms its important role as an apex predator in marine food webs and how ecological role changes with size. |
