“Urbanite” rays and sharks: Presence, habitat use and population structure in an urban semi-enclosed lagoon

Abstract

There is a vital necessity to provide more biological data on rays and sharks to promote efficient conservation. In this study, we assembled a database of weekly sightings to describe temporal (seasonal) patterns in the presence of elasmobranchs within an urban, semi-enclosed, landscape (Las Canteras beach, Gran Canaria Island, eastern Atlantic). Data also provided insight into their habitat use and population structure. From October 2015 to October 2018, eight species, either endangered or “data deficient” according to the IUCN red list, were reported, including: the common eagle ray, Myliobatis aquila, the common stingray, Dasyatis pastinaca, the round stingray, Taeniurops grabatus, the spiny butterfly ray, Gymnura altavela, the bull ray, Aetomylaeus bovinus, the angel shark, Squatina squatina, the marbled electric ray, Torpedo marmorata and the hammerhead shark, Sphyrna zygaena. All species were predominantly observed at night. The species varied in their habitat use; D. pastinaca, G. altavela and S. squatina dominated in sandy and mixed bottoms, while M. aquila and T. grabatus were mostly found in rocky and mixed bottoms. Both D. pastinaca and T. grabatus did not show any seasonal pattern, with consistent records all year around. In contrast, M. aquila, G. altavela and S. squatina showed some degree of seasonality. For five species, small-sized individuals were observed. If semi-enclosed embayments at oceanic islands, under intense human presence, are used by juveniles of endangered rays and sharks, proper management, e.g. limitation of putative human interactions, need to be considered to avoid disturbances.