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We quantified the diet of juvenile, scalloped hammerhead shark Sphyrna lewini in the area off Mazatlan, Sinaloa, Mexico, to understand their feeding ecology this shark. The prey species of Sphyrna lewini were identified and quantified from stomach content analysis. In addition, we determined the variations between genders. During two fishing seasons (2000-2001 and 2001-2002), we analyzed 232 stomachs, of which 85% contained food. The trophic spectrum was composed of three species of cephalopods, six of crustaceans and 19 species of fish from mainly pelagic and benthic habitats. According to the Index of Relative Importance (%IRI), the cephalopod Loliolopsis diomedeae with IRI = 18%, fish of the family Carangidae IRI = 25% and family Synodontidae IRI = 19% constituted the main prey in general. The trophic niche width was \0.4, which indicated that S. lewini juveniles in this area feed on a wide range of prey items, though they showed a preference for a few prey items.

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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.

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The isotopic ratios from statoliths and beaks indicate that D. gigas has changed its spatial and trophic preferences, a shift that is probably related to changes in the species' diet. This intraspecific variation in preferences could be related to characteristics such as size, which may influence squid distribution preferences.