Towards regionalization of the chondrichthyan fauna of the Southwest Atlantic: a spatial framework for conservation planning

SABADIN, DAVID E.; LUCIFORA, LUIS O.; BARBINI, SANTIAGO A.; KITTLEIN, MARCELO; FIGUEROA, DANIEL E.

ICES JOURNAL OF MARINE SCIENCE

OXFORD UNIV PRESS

Año: 2020 vol. 77 p. 1093 - 1905

1054-3139

Biogeographic regionalization identifies natural species assemblages that characterize a geographic region. In this study, the geographic distribution of chondrichthyan species richness and species assemblages for the Southwestern Atlantic was identified. The geographic distributionof 103 chondrichthyans was estimated using the MaxLike species distribution model. Binary maps (presence?absence) of each species were obtained by applying a threshold to the estimated probability of occurrence. Based on the binary maps, the sum of all species per pixel was calculated to determine the patterns of chondrichthyan richness at four taxonomic levels: (i) class Chondrichthyes, (ii) subclass Holocephali(chimaeras), (iii) division Selachii (sharks), and (iv) division Batomorphi (batoids). The continental shelf off Uruguay and southern Brazil, be-tween 29 S and 36 S, from the coast to 200 m depth, presented the highest levels of chondrichthyan richness, and a smaller peak in richnesswas found in El Rincón (northern Argentina). Sharks concentrated mainly off Lagoa dos Patos (southern Brazil). Batoid richness was maximal off Uruguay and northern Argentina, including modes in El Rincón, the San Jorge Gulf, and slope of the Argentine shelf. Classification analyses revealed the presence of a hierarchical regionalization. The biogeographic scheme found has three main and six minor assemblage areas. Main areas are hierarchically identifiable as provinces and minor as ecoregions or districts. Two of the main assemblages had spatial correspondence with the Argentine and Magellanic Provinces of the biogeographic scheme currently accepted, while the third one is a biogeographic unit identified here for the first time, the Patagonian Slope Province. Biogeographical studies are necessary tools to promote management and conservation since regional differentiation means distinctive biological communities. The regionalization found provides the basis for the design of protected area networks for conservation or management resources, such as fishing effort zoning.