Short-term variability but long-term consistency in diets of dolphinfish Coryphaena hippurus in the western North Atlantic

Temporal variation in fish predator diets can indicate changes in community trophic structure. Opportunistically feeding predators can serve as samplers through which foraging ecology or changes in relative abundances of prey can be studied. We sampled a sportfishing tournament in the western North Atlantic (WNA) over 23 yr (2003-2025) to identify trends in diets of dolphinfish Coryphaena hippurus , an opportunistic pelagic predator. Analyses focused on prey that substantially contributed to diets by percent frequency of occurrence or percent weight: scombrids, exocoetids, cannibalized conspecifics, a multi-taxa group of prey associated with pelagic Sargassum algae, and ingested Sargassum . Analysis of similarities (ANOSIM) and non-metric multi-dimensional scaling (NMDS) were conducted to determine any interannual differences in diet communities. Binomially distributed generalized additive models (GAMs) were fitted to prey presence/absence data for the 5 aforementioned prey types and gamma-distributed GAMs fitted to positive (non-zero) prey weight data for the 4 animal prey types. GAM fitting was used to determine whether dietary patterns were related to year or predator length. ANOSIM and NMDS found interannual variability of prey communities but without a consistent trend through time. GAMs fitted to presence/absence data showed no long-term trends. These models also showed declining scombrid and exocoetid prey presence but increasing cannibalized prey presence at larger predator lengths. GAMs fitted to weight data showed no long-term trends but decreasing and increasing trends in weight of scombrid and cannibalized prey with predator length, respectively. Results indicate stable dolphinfish diets and thus likely stable abundances of its important prey in the WNA.