Trophic level and isotopic composition of δ¹³C and δ¹⁵N of pacific angel shark, Squatina californica (Ayres, 1859), in the southern Gulf of California, Mexico

δ¹³C and δ¹⁵N stable isotopes were used to determine trophic level and the assimilated food components of Pacific angel shark, Squatina californica and its variation between size, sexes and seasonally in the southern Gulf of California, Mexico. Muscle tissues were collected during 2001 to 2003. The quantification of δ¹³C and δ¹⁵N stable isotopes was realized by isotope ratio mass spectrometry. The values of stable isotope of carbon (δ¹³C) ranged from -16.55 to -15.06‰ (average -15.94‰ ±0.34) and nitrogen (δ¹⁵N) was between 18.30 to 19.52‰ (average 18.90‰ ±0.27), we found that as male as female feeds on same zones and not differences were found among years and seasons, therefore the angel shark present a same trophic level to feed on benthic prey in the coast zone. The trophic level was determined for S. californica with 4.5, therefore is considered a tertiary consumer in the southern Gulf of California. We concluded that Pacific angel shark present a same trophic pattern during migration to deep areas en the Gulf of California, feeding on benthic species with same trophic level.