The use of stable isotopes and mixing models to determine the feeding habits of soft-bottom fishes in the southern Gulf of California

Recently, stable-isotope analyses have been coupled with mixing models to determine trophic relationships by identifying the most important types of prey and assessing their relative contribution to the diet. This method has advantages over stomach-content analysis and is emerging as a powerful tool to determine trophic relationships. We analysed the stable-isotope ratios of 15N and carbon 13C in the muscle tissue of 19 soft-bottom fish species found in shrimp-fishing bycatch along the coast of Nayarit, Mexico. An elemental analyser was used, connected to an isotope-ratio mass spectrometer. We processed the isotope data with a Bayesian mixing models using SIAR model. We identified five trophic guilds (crustacean eaters, fish eaters, molluscs eaters, echinoderms eaters and crustacean-fish eaters) based on their principal prey types. Crustacean consumers were the dominant group. The calculated trophic levels of the five guilds ranged from 3.1 to 4.8. Stable-isotope analyses coupled with mixing models are useful in determining diets and trophic relationships and can be used to analyse the trophic webs of some ecosystems.