Feeding ecology and trophic level of the banded guitarfish, Zapteryx exasperata, inferred from stable isotopes and stomach contents analysis

The feeding ecology and trophic level of the banded guitarfish, Zapteryx exasperata, from the Gulf of California, were assessed using stable isotope analysis (SIA) of carbon and nitrogen in muscle samples, and stomach contents analysis (SCA). Males and females showed similar diet preferences with a high diet overlap (Cλ = 0.99) and similar values of δ13C and δ15N (ANOVA, F = 0.0 p = 0.94 for δ13C; F = 0.1 p = 0.78 for δ15N). The main prey groups found were demersal fishes dominated by the daisy midshipman, Porichthys margaritatus, (>90%IRI), however, pelagic fishes were also found (Engraulis mordax 2%IRI). An ontogenetic diet shift was found, indicated by the importance of crustaceans in the juvenile diet and the significant isotopic differences between juveniles and adults (δ13C, ANOVA, F = 13.3 p = 0.0004 and δ15N, ANOVA, F = 4.7 p = 0.03). An overall trend of increase in δ15N values with increasing body length (F = 8.15 p = 0.005) was observed. The mean trophic level estimated in this work by the two methods was ~4.1, indicating that this species is a top predator in the Gulf of California. Zapteryx exasperata is a specialist feeder (Bi = 0.11, H’ = 2.32), consuming mainly benthic fishes in coastal areas of the Gulf of California. The importance of this species in the benthic ecosystem equilibrium as a top predator is an important point to keep in mind when developing future management plans of the batoid fishery in the Gulf of California.