Reassessment of the franciscana Pontoporia blainvillei (Gervais & d'Orbigny, 1844) distribution and niche characteristics in Brazil

The franciscana (Pontoporia blainvillei) is the most threatened small cetacean of South America. The species is endemic to coastal waters of the western South Atlantic Ocean, where it is distributed from Itaúnas (Brazil) to Golfo San Matias (Argentina). Its range was divided in four Franciscana Management Areas (FMAs) for conservation purposes. However, the distribution of the franciscana is not continuous along its range, with two hiatuses proposed in southeastern Brazilian coast. The absence of franciscana records in these regions has been confirmed by multiple years of research, however the reasons for this discontinuous distribution is not well understood. In this study, information on the distribution of the franciscana in south and southeastern Brazil is updated and new limits for FMAs are proposed. NicheA 3.0 software was used to investigate the environmental suitability of distributional gaps in relation to four weakly correlated, allegedly relevant descriptors of franciscana´s distribution. In total, 788 records from dedicated aerial and boat surveys and bycatch were used to verify and to confirm the new FMAs limits proposed by franciscana´s experts previously. The distributional gaps were reshaped and defined as following: Gap I from Piraquê-Açu River Mouth, Santa Cruz (19°57′S) in the state of Espírito Santo to Barra de Itabapoana (21°18′S) in the state of Rio de Janeiro; and Gap II from Armação dos Búzios (22°44′S) to Piraquara de Dentro (22°59′S) in Rio de Janeiro. The ecological niche model indicated that distributional gaps are inside franciscana´s fundamental niche, and are relatively suitable in terms of salinity, temperature, diffuse attenuation and bathymetry. However, the narrow of continental shelf seems to be the main factor explaining the absence of franciscanas in the distributional gaps as well as for the differentiation of some of the FMAs proposed. Narrowness of continental shelf seems to be intensifying the dynamics of biotic interactions promoting food competition for example, and/or causing geographic limitation to maintain minimal viable population size in present or past times periods.Fil: do Amaral, Karina Bohrer. Laboratório de Sistemática e Ecologia de Aves e Mamíferos Marinhos, Universidade Federal do Rio Grande do Sul; BrasilFil: Danilewicz, Daniel. Grupo de Estudos de Mamíferos Aquáticos do Rio Grande do Sul ; BrasilFil: Zerbini, Alexandre. Instituto Aqualie; BrasilFil: Di Beneditto, Ana Paula. Universidade Estadual do Norte Fluminense, Laboratório de Ciências Ambientais; BrasilFil: Andriolo, Artur. Instituto Aqualie; BrasilFil: Alvares, Diego Janisch. Universidade Federal do Rio Grande do Sul, Programa de Pós-Graduação em Biologia Animal, Instituto de Biociências; BrasilFil: Secchi, Eduardo Resende. Universidade Federal do Rio Grande, Instituto de Oceanografia, Laboratório de Ecologia e Conservação da Megafauna Marinha-EcoMega; BrasilFil: Ferreira, Emanuel. Entrada do Parque Estadual do Rio Vermelho - Associação R3 Animal, Rodovia João Gualberto Soares; BrasilFil: Sucunza, Federico. Grupo de Estudos de Mamíferos Aquáticos do Rio Grande do Sul; BrasilFil: Borges Martins, Márcio. Universidade Federal do Rio Grande do Sul, Programa de Pós-Graduação em Biologia Animal, Instituto de Biociências; BrasilFil: de Oliveira Santos, Marcos César. Universidade de São Paulo, Departamento de Oceanografia Biológica, Instituto Oceanográfico, Laboratório de Biologia da Conservação de Mamíferos Aquáticos; BrasilFil: Cremer, Marta. Universidade da Região de Joinville, Projeto Toninhas; BrasilFil: Denuncio, Pablo Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Ott, Paulo Henrique. Grupo de Estudos de Mamíferos Aquáticos do Rio Grande do Sul; BrasilFil: Moreno, Ignacio Benites. Universidade Federal do Rio Grande do Sul, Laboratório de Sistemática e Ecologia de Aves e Mamíferos Marinhos; Brasi