The diet was analyzed by calculating three methods for each prey taxon. We calculated (1) frequency of occurrence (%FO), (2) by using gravimetric methods (%W), and (3) numerical (%N) following Hyslop (1980). We also combined these methods to calculate the index of relative importance of Pinkas et al. (1971). IRI is a commonly used measure that provides a summary of dietary composition (Cailliet et al. 1986).