Diet of the stone scorpionfish (Scorpaena mystes) from the coastal region of Santa Rosalia, Gulf of California, Mexico using stomach contents and stable isotope analyses

In Santa Rosalia, stone scorpionfish, Scorpaena mystes, is an important part of the benthic community, hence its ecology regarding food habits by means of stomach contents and isotope signal were studied. Stone scorpionfish were captured during an annual cycle, from May 2015 through April 2016 in waters off Santa Rosalia, Baja California Sur, Mexico. Stomach contents and muscle samples were analyzed for δ¹³C and δ¹⁵N isotopic signature in order to describe the trophic niche of the stone scorpionfish both in terms of the prey items consumed and the assimilated items. The diet comprised 22 items: cephalopods, bivalves, crustaceans, seaweeds, and unidentified organic matter (UOM). The most important preys according to the %IRI (Index of Relative Importance) were the cephalopod Octopus hubbsorum (19.5%), non-identified crustaceans (18.8%), brachyuran crabs (15.9%), Serranus psittacinus (9.3%), Dosidicus gigas (8.8%) and Cronius ruber (7.3%). No significant differences were found between the diet of females and males, sizes or seasons. The mean of the δ¹⁵N was 19.07 ± 0.63‰ and for the δ¹³C was of −14.76 ± 0.81. The main contributors to the diet, according to the Stable Isotope Mixing Model in R (SIMMR), were the cephalopod Octopus hubbsorum with a mean contribution of 32% followed by demersal fishes with 31%. No significant differences were found between the sexes, sizes or seasons, or in the isotopic niche. The Amundsen plot shows that the stone scorpion fish is a generalist predator, while the trophic level was 4.3 with stomach contents and 4.0 by means of the isotopic signature. This is the first study of stone scorpionfish involving its trophic niche.