Abundance and distribution of franciscanas (Pontoporia blainvillei) in northern Rio de Janeiro (FMA Ib), Brazil
Daniel Danilewicz, Federico Sucunza, Paulo H. Ott, Emanuel Ferreira, Martin S. Perez, Natalia Berchieri, Diego Alvares, Artur Andriolo, Eduardo R. Secchi, Paulo A. C. Flores, Ana Paula Farro, Agnaldo Martins, Alexandre N. Zerbini
International Whaling Commission
The franciscana dolphin (Pontoporia blainvillei) is endemic to the coast of Brazil, Uruguay and Argentina and is regarded as the most threatened small cetacean in South America primarily due to high levels of fishery bycatch. There is evidence for the existence of one peripheral and isolated franciscana populations in northern Rio de Janeiro, na area known as Franciscana Management Area (FMA) Ib. In 2012, 2017 and 2019 aerial surveys were conducted to assess abundance and distribution in FMA Ib. Abundance corrected for visibility and group size bias was estimated at 1,692 franciscanas in 2011 (Dc=0.30, CV=0.47, 95% CI: 706-4,055) and at 1,280 franciscanas in 2017 (Dc=0.32, CV=0.43, 95% CI: 566-2,445) with the most parsimonious detection probability models. Density is the second lowest in the entire franciscana range, which is consistent with the remarkable low genetic diversity observed in this population. The extent of occurrence (EOO) of franciscanas in FMA Ib was calculated as 1,665 km2. Franciscanas were observed from turbid waters near the surf zone to clearer waters up to 15.1nm offshore. Population concentration is inversely correlated to distance from shore, with 50% and 70% of the groups located within 3nm and 4nm from shore, respectively. Potential Biological Removal for FMA Ib was computed as 8.1 and 1.6, suggesting that any human-induced mortality higher than those numbers per year (8 or 2, depending on the Recovering Factor criteria) could lead to depletion of this isolated population.