Feeding Habits Variability and Trophic Position of Dolphinfish in Waters South of the Baja California Peninsula, Mexico

Using data from analyses of stomach contents and stable isotopes, we examined high-resolution variations in the feeding habits and trophic position of Dolphinfish Coryphaena hippurus during 2005-2007. In total, 418 specimens were collected off the southern Baja California peninsula, Mexico. Based on analysis of stomach contents (% index of relative importance [%IRI]), Dolphinfish consumed mainly epipelagic prey, with the red crab Pleuroncodes planipes as the most abundant prey species. The diet was highly similar between sexes but differed between size-classes: Dolphinfish smaller than 65 cm FL fed mainly on Pacific Sardine Sardinops sagax caeruleus (%IRI = 30), whereas those larger than 110 cm FL fed mainly on jumbo squid Dosidicus gigas (%IRI = 45) in addition to red crabs. Dietary differences between the smallest and largest specimens were mainly related to changes in morphology and spatial stratification by size (i.e., to avoid cannibalism). Trophic positions estimated by both methods indicated that the Dolphinfish is a secondary to tertiary carnivore with a high degree of trophic plasticity, and thus it plays different trophic roles within the area. Elevated variability in δ¹⁵N and Shannon-Wiener diversity index values on an annual scale revealed that Dolphinfish are opportunistic predators. Interannual diet variation related to the availability and abundance of prey species can be explained by changes in environmental conditions due to climate anomalies associated with El Niño-Southern Oscillation events. We highlight that the Dolphinfish is a good indicator of changes occurring in the food web structure of pelagic ecosystems. The observed variations in feeding habits and trophic position are critical to understanding the ecology and role of Dolphinfish in marine ecosystems by providing knowledge on feeding locations, seasonal prey utilization, and prey availability and allowing predictions of possible ecological responses to environmental change. Received January 11, 2013; accepted November 12, 2013.