Trophic assessment and isotopic niche of three sympatric ray species of western Baja California Sur, Mexico

Abstract

Along the Pacific coast of Baja California Sur (PCBCS), the banded guitarfish (Zapteryx exasperata), shovelnose guitarfish (Pseudobatos productus) and bat ray (Myliobatis californica) are highly abundant. Their ecological roles as predators in demersal communities can be key in this ecosystem. To better understand their trophic relationship in the PCBCS, stable isotopes analysis of carbon (ẟ13C) and nitrogen (ẟ15N) were used. Muscle samples (n\u2009=\u2009265) were collected from shovelnose guitarfish (n\u2009=\u200994), banded guitarfish (n\u2009=\u200987) and bat ray (n\u2009=\u200984). We observed high variability in stable isotopes values, ẟ13C and ẟ15N of shovelnose guitarfish ranged from −18.53 to −12.85‰ and 15.93‰ to 20.37‰, respectively; banded guitarfish from −18.12‰ to −13.57‰ and 14.41‰ to 19.26‰, respectively; and bat ray from −17.73‰ to −13.98‰ and 13.97‰ to 18.46, respectively. Statistically significant interspecific differences were found (p\u2009<\u20090.05) for ẟ13C and ẟ15N values, as bat ray showed a lower mean ẟ15N value and less negative mean ẟ13C value. Mature male (MM) bat ray) showed significantly higher ẟ15N values and shovelnose guitarfish (MM) significantly lower ẟ13C values compared to other cohorts. Isotopic niche analysis using Bayesian ellipses (SEAc) indicated shovelnose guitarfish occupies the widest isotopic niche compared with bat ray and banded guitarfish. Based on SEAc, the banded guitarfish overlapped 0.46 with the shovelnose guitarfish, while the bat ray overlapped 0.38 and 0.39 with banded and shovelnose guitarfish, respectively. Reported data suggest there is a relative overlap among all species, with probably greater amount of partitioning between the bat ray and the other two species.