Distribution, population size and IUCN Red Listing of an isolated population of the threatened franciscana

Abstract

The franciscana Pontoporia blainvillei is the only extant member of the family Pontoporiidae, and its occurrence is restricted to coastal waters from Brazil to Argentina. The species is one of the most threatened cetaceans in the southwestern Atlantic Ocean, due to unsustainable bycatch levels. A total of 11 Franciscana Management Areas (FMAs) have been defined throughout the species’ range. FMA Ia represents the northernmost franciscana population, demographically isolated on the north coast of Espírito Santo State, Brazil. In March 2018, aerial surveys were conducted to assess the distribution and estimate the abundance of franciscanas in FMA Ia. A total of 2986 km of survey effort was conducted, and 27 groups were seen (average group size: 2.52 ind., coefficient of variation [CV] = 0.50) in coastal habitats (average distance from the shore: 3.3 km, CV = 0.70). Abundance, corrected for visibility bias and group size bias, was estimated at 1183 (CV = 0.76) individuals, and the potential biological removal was computed at 1. Results suggest that at least during the summer, franciscanas in ES are distributed in coastal habitats between Conceição da Barra and Santa Cruz, with a high-density area observed near the estuary mouth of the Doce River. This is one of the smallest of all franciscana populations and one with a restricted range. The estimated abundance indicates that the ES population qualifies for listing as Endangered under IUCN Red List criterion C2a(ii). In order to reduce threats to this population, management actions are urgently needed.

Trophic ecology and small‐scale differentiation of ecological groups of franciscana dolphin, Pontoporia blainvillei, in southeastern Brazil, revealed by carbon and nitrogen stable isotopes

“…The population of franciscana dolphins in FMA Ia, on the coast of Espírito Santo, inhabits the northern region of the coastline, ranging from the municipality of Conceição da Barra to Aracruz (Sucunza et al, 2023).…”

“…The study area was subdivided into three subareas, according to the locations where the carcasses were collected: in the north (subarea 1), in the center (subarea 2), and in the south (subarea 3) of the distribution of the franciscana dolphins along the northern coast of the state of Espírito Santo, with each subarea mainly being associated with the mouths of the São Mateus River, Ipiranga River, and Doce River, respectively. In addition, the separation of samples between subareas took into account information on the area occupied by the species in the study area, with the lowest population densities separating subareas 1 and 2 and the highest densities in subarea 3 (Sucunza et al, 2023).…”

Report of the Abundance Steering Group (Bled, Slovenia, 21-23 April 2023)

“…The correction factor for both visibility and group size bias was revised to 4.76 (CV=0.25). Previous estimates for FMA Ia (Sucunza et al, 2020c) and Ib (Danilewicz et al, 2020) had been discussed during the 2021 pre-meeting Workshop (IWC, 2022b, items 3.2.and 3.3) but categorised as Provisional until those new correction factors could be applied. As a result, estimates of abundance were last revised for FMA Ia in 2018 and Ib in 2011 and 2017.…”