Rhinoptera steindachneri is a commercially important, medium-sized, pelagic migratory batoid fish with benthic feeding habits. It has been considered a specialized predator that feeds on molluscs as well as benthic ophiurids and arthropods off the Mexican Pacific coast. Most biological aspects of this species in La Paz Bay are unknown, despite its being a commercially important species of conservation interest. Therefore, the aim of this study was to characterize the feeding habits of R. steindachneri based on specimens caught in artisanal fisheries. The stomach contents of 310 specimens (146 females and 164 males) were analysed, all captured from 2013 to 2015. The vacuity index was 97.1%, and the most important prey species were Mysidium spp. and Cylichna spp. Because of the high frequency of empty stomachs recorded, it was not possible to describe with precision the general diet of the species. Three hypotheses were developed to try to explain why this characteristic occurred in this species, ranging from eating habits to physiology and prey digestion and geographic location of the study. However, considering the mechanical process of prey handling of R. steindachneri, several hypotheses were formulated, with the hour of capture, chemical processes and physiology and prey digestion being the most probable to explain this high vacuity index reported in this study.

The taxonomic status of butterfly rays within the genus Gymnura remains a subject of ongoing debate among researchers. Some authors recognize up to five valid species for the Americas, while others considered several to be synonyms, which has posed a persistent challenge. We aimed to shed light on this complexity by employing molecular operational taxonomic units (MOTUs) based on the mitochondrial gene cytochrome oxidase I (COI). Genetic sequences were obtained from fresh muscle tissue collected in the marine ecoregions corresponding to the type locality from all the nominal butterfly ray species distributed along the Eastern Tropical Pacific (ETP). Our results unveiled compelling findings; all the species delimitation models used consistently identified seven MOTUs for the American continent and an extra G. altavela MOTU restricted to Africa. In addition, our results and models exceeded the worldwide accepted interspecific threshold of 2.0%. Remarkably, our results support the taxonomic reinstatement of Gymnura afuerae (Hildebrand, 1946) as a valid species, with a range expanding into the ETP in the Southern Hemisphere. Similarly, our data support the recent suggestion of resurrecting Gymnura valenciennii (Duméril, 1865) as a valid species in the western Atlantic. These findings urge a reassessment of the conservation status and a comprehensive taxonomic revision of American butterfly rays.