Population structure, distribution and habitat use of the Critically Endangered Angelshark, Squatina squatina, in the Canary Islands

Abstract

Angel sharks are among the most threatened fish worldwide, facing regional and global extinction. In Europe, populations of the three Critically Endangered angel sharks (Squatina aculeata, Squatina oculata and Squatina squatina) have been severely depleted. Taking advantage of the last global ‘hotspot’ of the angelshark, Squatina squatina, this study gathered data through a citizen science programme to describe the occurrence of this shark in the coastal waters of the Canary Islands. Specifically, this study described (1) the population structure, and (2) habitat use of this species, which was used in a Species Distribution Model to (3) examine realized and potential distribution patterns, and to (4) determine the relative importance of environmental predictors on the occurrence of S. squatina. Over the 12 months sampling period (April 2014 – March 2015), 678 sightings were reported. Individuals ranged from 20 to 200 cm (total length). Larger sightings of both females and neonates occurred mostly in April to July, i.e. during the pupping season. Males were significantly more frequent in November to January, i.e. during the mating season. Angelsharks were encountered at depths from <1 m to a maximum of 45 m. Small‐sized individuals (i.e. neonates) exclusively occurred in shallow water (0–25 m). Most sharks occurred on sandy bottoms adjacent to reefs. Even though sightings were recorded at all seven islands in the archipelago, there were fewer encounters in the western than the eastern islands. The Species Distribution Model indicated that the probability of occurrence mainly correlated with sea surface temperature, chlorophyll, salinity and depth. Areas with the greatest habitat suitability were in shallow water. The angelshark displayed spatial (vertical and horizontal) and temporal segregation by size and sex. This information is vital to inform conservation of this Critically Endangered shark in its last stronghold.

Integrating local ecological knowledge, citizen science and long‐term historical data for endangered species conservation: Additional records of angel sharks (Chondrichthyes: Squatinidae) in the Mediterranean Sea

“…This work, additionally, provides evidence of the important role that citizen science, social media and LEK can play in data gathering, but also in the conservation of rare and endangered species. The value of citizen science and social media for data gathering has already been proven for angel sharks (Holcer & Lazar, ; Meyers et al, ), as well as for other elasmobranch species in the Mediterranean Sea (Giovos et al, ); the same is true for LEK (Barash, Pickholtz, Pickholtz, Blaustein, & Rilov, ; Coll et al, ; Fortibuoni, Borme, Franceschini, Giovanardi, & Raicevich, ; Gonzalvo, Giovos, & Moutopoulos, ). In this work, citizen‐science data accompanied with the current knowledge and the official fisheries catch reports provided important information about an extremely threatened family of species.…”

“…These are frequently used as alternative sources of information when conventional data are not available (Moutopoulos, Dimitriou, Katselis, & Koutsikopoulos, ), supplementing and validating scientific knowledge, thus empowering marine scientists and managers to improve conservation and policy (e.g. Giovos, Chatzispyrou, Doumpas, Stoilas, & Moutopoulos, ; Johannes, Freeman, & Hamilton, ) even in the case of the extremely rare angel sharks in the Canary Islands (Meyers et al, ) and the Adriatic Sea (Holcer & Lazar, ).…”

Near disappearance of the Angelshark Squatina squatina over half a century of observations

“…The coastal seas of Wales, United Kingdom and Ireland appear to be the only locations with regular Angelshark sightings in western Europe, although no Angelsharks have been observed in Ireland since 2011 (Meyers et al, ). Designing effective conservation measures for last remaining populations requires an understanding of the population trend and spatial distribution, and an identification of the factors that have been driving their decline (Gordon et al, ; Shephard, Wögerbauer, Green, Ellis, & Roche, ).…”

Opportunities from citizen science for shark conservation, with a focus on the Mediterranean Sea

“…Although several CS initiatives for shark research are taking place worldwide both with a global and local scope (www.sharkpulse.org, www.eoceans. org), and focused on single species or broader taxonomic groups (Davies et al 2013;Andrzejaczek et al 2016;Araujo et al 2017;Meyers et al 2017;Norman et al 2017), these initiatives are lagging in terms of scientific output in comparison with other similar projects on other groups of animals ( Figure 1). In the Mediterranean Sea, 33 CS initiatives on sharks have been launched since the 1980s (Table II).…”

“…Among ocean users, scuba divers are the greatest contributors to shark CS; 60% of shark CS publications are from scuba divers. Scuba divers have successfully contributed to a variety of CS projects, including the study of endangered shark species such as the angelshark (Squatina squatina) for zoning (Meyers et al 2017) and valid investigations on long-term distributions of the whitetip reef shark (Triaenodon obesus) and the grey reef shark (Carcharhinus amblyrhynchos) (Whitney et al 2012;Vianna et al 2014). Scuba divers are generally considered ideal citizen scientists, thanks to some key characteristics such as the ability to access and monitor underwater environments, a general commitment to protect the ecosystems scuba diving depends on, and a desire to grow and to learn (Lucrezi et al 2018b).…”