title: The Devil We Don't Know: Investigating Habitat and Abundance of Endangered Giant Devil Rays in the North-Western Mediterranean Sea.
abstract: The giant devil ray Mobula mobular, the only Mediterranean mobulid, is subject to mortality caused by directed and accidental captures in fisheries throughout the region. Whilst the combination of human impacts, limited range and a low reproductive potential is not inconsistent with its endangered listing, there are insufficient data to enable a quantitative assessment of trends. Without this, it is difficult to assess and prioritise threats and develop effective conservation actions. Using results from aerial surveys conducted between 2009 and 2014 over the Ligurian, Corsican, Sardinian, northern and central Tyrrhenian seas (626,228 km2), this study provides the first quantitative information on giant devil ray abundance and habitat choice in the western Mediterranean. Devil rays were observed in all seasons except winter, with their estimated abundance in the study area peaking in summer. The overall uncorrected mean density in the study area during summer was estimated at 0.0257 individuals km-2 (range: 0.017-0.044), resulting in a total abundance estimate of 6,092 (12.7%CV) individuals at the surface; once corrected for availability bias, this estimate indicates a summer presence of >12,700 devil rays in the study area. Rays were mostly observed alone even if occasionally, larger aggregations up to a maximum of 18 individuals were observed. Although observed throughout the study area, spatial modelling identified their preferred habitat to be over a broad strip connecting the Tuscan Archipelago to Eastern Sardinia, over a wide range of water depths ranging from 10 to 2000m. The observed seasonal changes in giant devil ray distribution in this study, combined with similar evidence from other areas in the Mediterranean, support the hypothesis that the species undertakes latitudinal migrations across the region, taking advantage of highly productive waters in the north during summer, and warmer southern waters during winter.
authors.affiliation: Tethys Research Institute, Viale G.B. Gadio 2, 20121, Milano, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Notarbartolo di Sciara
authors.affiliation: Istituto Superiore per la Protezione e la Ricerca Ambientale, Via Vitaliano Brancati 48, 00144, Roma, Italy.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Lauriano
authors.affiliation: Tethys Research Institute, Viale G.B. Gadio 2, 20121, Milano, Italy.
authors.forename: Nino
authors.initials: N
authors.lastname: Pierantonio
authors.affiliation: ALNILAM Research and Conservation Ltd, Cándamo 116, 28240 Hoyo de Manzanares, Madrid, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Cañadas
authors.affiliation: The International Whaling Commission, The Red House, 135 Station Road, Impington, Cambridge, Cambridgeshire, CB24 9NP, United Kingdom.
authors.forename: Greg
authors.initials: G
authors.lastname: Donovan
authors.affiliation: Tethys Research Institute, Viale G.B. Gadio 2, 20121, Milano, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Panigada
mesh_terms: D063147:Animal Distribution / Q000502:physiology*; D000818:Animals; D003247:Conservation of Natural Resources; D017753:Ecosystem; D056727:Endangered Species; D005260:Female; D008297:Male; D008522:Mediterranean Sea; D011156:Population Density; D012098:Reproduction / Q000502:physiology*; D012621:Seasons; D012860:Skates, Fish / Q000502:physiology*