Isotopic niche overlap of four large pelagic predatory fish species in the northwest Atlantic ocean

Understanding trophic dynamics and the potential for competition among pelagic predators is critical to managing multi-species fisheries. We estimated trophic position and isotopic niche overlap for albacore (Thunnus alalunga; n = 63), Atlantic bluefin tuna (Thunnus thynnus; n = 16), bigeye tuna (Thunnus obesus; n = 70) and swordfish (Xiphias gladius; n = 20) collected from the northwest Atlantic in 2022 using stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) in muscle. Atlantic bluefin tuna showed low overlap with other species, while bigeye tuna had high overlap with albacore and swordfish (particularly swordfish ≤ 175 cm in length). Large swordfish may avoid competition with other predators by foraging on deeper prey based on higher δ¹³C values. Different size incorporation methods differentially affected overlap estimates, necessitating careful consideration of methodology. Trophic position estimates were similar to results from 14 - 21 years ago (except for bigeye tuna), despite ecological changes in the region. Understanding trophic dynamics among pelagic predators is essential to managing a system expected to undergo further shifts caused by climate change.