Estimating the geographic range of a threatened shark in a data-poor region: Cetorhinus maximus in the South Atlantic Ocean

LUCIFORA, LUIS O.; BARBINI, SANTIAGO A.; DI GIÁCOMO E.; WAESSLE J.; FIGUEROA, DANIEL E.

Congreso; Joint Meeting of Ichthyologists & Herpetologists, Albuquerque, E.E.U.U; 2013

The basking shark, Cetorhinus maximus, is widely distributed in temperate regions of all oceans except the Indian Ocean. In the southern hemisphere there is a large gap in the information on distribution, especially in the South Atlantic. We compiled all the records of basking sharks in the South Atlantic and used them in a recently developed tool for estimating geographic ranges of species, maximum-entropy distribution modelling (MaxEnt). Basking sharks records used in this study came from different sources: for the southwest Atlantic from scientific literature providing occurrence data, and the database of Onboard Fishery Observers Program of the Instituto Nacional de Investigación y Desarrollo Pesquero (Argentina); for the southeast Atlantic, the data came from the databases of the Fish Collection and the Shark Collection of the Iziko South African Museum, accessed from http://www.gbif.org/. Environmental data used as predictors were obtained from the Bio-Oracle database. Occurrence and environmental data were used in MaxEnt models. The model that best fit the data included four variables: chlorophyll minimum concentration, dissolved oxygen concentration, salinity, and sea surface temperature range. Our results indicated that basking sharks inhabit temperate to subtropical continental shelf waters. In the southeast Atlantic, basking sharks inhabited the cool waters from off southern South Africa to northern Namibia, and were absent in the subtropical waters off KwaZulu-Natal (South Africa). In the southwest Atlantic, basking sharks occurred on continental shelves from off Tierra del Fuego (Argentina) to off Rio de Janeiro (Brazil), being absent from waters north of Rio de Janeiro.