The cephalopod beats the elasmobranch

Abstract

Three major taxa comprise the bulk of the diet of the common octopus Octopus vulgaris (class Cephalopoda). Besides mollusks and crustaceans, some small fishes (infraclass Teleostei) are also typically found in octopus stomachs (Thalassas 2018; doi.org/10.1007/s41208-018-0084-z). In June 2020, we witnessed a predation event of O vulgaris on the common guitarfish or shovelnose ray Rhinobatos rhinobatos (class Chondrichthyes, subclass Elasmobranchii) off the coast of Cabo de Palos (southeastern Spain, western Mediterranean). To the best of our knowledge, this observation is the first documented record of predation between these two species.

We observed the predation event while hovering at a depth of 15 m in the ecotone between a seagrass (Posidonia oceanica) meadow and the sandy bottom. The very large octopus had completely immobilized the guitarfish, which was on its back on the seafloor with no chance of escape. How did these two animals initially encounter each other? Did the octopus actively prey on the fish? Given the peculiarity of the event, we hypothesize that the guitarfish was presumably injured or weak, especially considering the opportunistic feeding behavior of the octopus. This recorded event is especially relevant from a conservation viewpoint, given that R rhinobatos is considered extirpated from Spanish Mediterranean waters and is globally cataloged as Critically Endangered on the IUCN Red List of Threatened Species (see also Newell 2017; https://repository.library.noaa.gov/view/noaa/16215).