Population size and IUCN Red Listing of the isolated northern population of the franciscana (Pontoporia blainvillei)
Federico Sucunza, Daniel Danilewicz, Paulo H Ott, Mariana Neves, Natalia Berchieri, Ana Paula Farro, Agnaldo Martins, Alexandre N. Zerbini
International Whaling Commission
The franciscana (Pontoporia blainvillei) is endemic of coastal waters from Brazil (18o25'S) to Argentina (42o10'S). The species is regarded as the most threatened small cetacean in the western South Atlantic Ocean due to high bycatch levels and habitat degradation. The franciscana is listed as Vulnerable in the IUCN Red List of Threatened Species. Recent analysis of mtDNA suggested that individuals found in the species??? northern range (Brazilian State of Esp??rito Santo, ES) represent an isolated population. Aerial surveys following design-based line transect methods were conducted on March 2018 to assess distribution and estimate abundance of franciscanas off ES. A total of 2,986 km on sighting effort was carried out from the shore up to 16.5 km from the coast between Itaǧnas (18o25'S) and Presidente Kennedy (21o17'S), north and south ES boundaries respectively. A total of 17 franciscana groups were seen (average group size = 2.41, CV=0.14) in coastal habitats (average distance from the shore = 3.3 km, SE = 2.3 km, range = 0.4 - 8 km). Abundance corrected for visibility and group size biases was estimated at 595 individuals (CV = 0.44, 95% CI = 203 - 1,200). Results suggest that, at least during the summer, franciscanas in ES are distributed in very coastal habitats between Concei??ǜo da Barra (18o35'S) and Santa Cruz (19o56'S). This is probably the smallest and the one presenting the most restricted range among all franciscana populations. The estimated abundance indicate that the ES population qualifies for listing as ???Endangered??? under the IUCN Red List criterion C2a(ii) because of the small size (less than 2,500 mature individuals) and because of an inferred decline in abundance as a consequence of bycatch and habitat degradation. In order to reduce threats to this population management actions are urgently needed.