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SC/69A/ASI/19/Rev2
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Resource ID
19948
Access
Open
Document Number
SC/69A/ASI/19/Rev2
Full Title
First Range-Wide Aerial Survey off South Brazilian and Uruguayan Waters for Density and Abundance Estimates of the Threatened Franciscana Dolphin
Author
F. Sucunza, D.J. Alvares, D. Danilewicz, C. Dimitriades, E. Ferreira, V. Franco-Trecu, P.H. Ott, C. Passadore, M.S. Perez, J. Ribeiro, A.N. Zerbini
Authors Summary
The franciscana (Pontoporia blainvillei) is endemic to coastal waters from Brazil to Argentina. The species is regarded as one of the most threatened cetaceans in the South Atlantic Ocean due to high bycatch levels. Four management units "FMAs" were defined throughout the species' range. FMA III includes states along southern Brazil and the whole Uruguayan coast. Aerial surveys to estimate density and abundance of franciscanas throughout the whole latitudinal range of FMA III were conducted in two periods: from February 20th to March 14th 2021 (Brazilian sector of FMA III) and from March 01th to April 04th 2023 (Uruguayan sector). A total of 5,312 km of tracklines were surveyed over a total area of 80,342 km2, and a total of 96 franciscana groups (199 individuals) was recorded on effort by front observers with an average group size of 2.07 (SE = 1.09, median = 2, range = 1-5). Overall density and abundance corrected for visibility bias and group size bias were estimated at 0.54 individuals/km2 (CV=0.3) and 43,148 individuals (CV = 0.3, 95% CI = 23,786 – 78,271). Because aerial surveys were carried out in 2021 in Brazil and in 2023 in Uruguay, the present density and abundance estimates could be regarded as a 2022 estimate. This is the first study to estimate abundance of franciscana dolphins in the whole of FMA III. The results suggest that this is the most abundant franciscana stock. Available bycatch estimates (from the early 2000s) for this management area correspond to 2-4% of the estimated stock size, suggesting the possibility that bycatch is unsustainable. Continued population monitoring is essential to assess the long-term viability of franciscana dolphins inhabiting southern Brazilian and Uruguayan waters.
Publisher
IWC
Publication Year
2023
Abstract
The franciscana (Pontoporia blainvillei) is endemic to coastal waters from Brazil to Argentina. The species is regarded as one of the most threatened cetaceans in the South Atlantic Ocean due to high bycatch levels. Four management units "FMAs" were defined throughout the species' range. FMA III includes states along southern Brazil and the whole Uruguayan coast. Aerial surveys to estimate density and abundance of franciscanas throughout the whole latitudinal range of FMA III were conducted in two periods: from February 20th to March 14th 2021 (Brazilian sector of FMA III) and from March 01th to April 04th 2023 (Uruguayan sector). A total of 5,312 km of tracklines were surveyed over a total area of 80,342 km2, and a total of 96 franciscana groups (199 individuals) was recorded on effort by front observers with an average group size of 2.07 (SE = 1.09, median = 2, range = 1-5). Overall density and abundance corrected for visibility bias and group size bias were estimated at 0.54 individuals/km2 (CV=0.3) and 43,148 individuals (CV = 0.3, 95% CI = 23,786 – 78,271). Because aerial surveys were carried out in 2021 in Brazil and in 2023 in Uruguay, the present density and abundance estimates could be regarded as a 2022 estimate. This is the first study to estimate abundance of franciscana dolphins in the whole of FMA III. The results suggest that this is the most abundant franciscana stock. Available bycatch estimates (from the early 2000s) for this management area correspond to 2-4% of the estimated stock size, suggesting the possibility that bycatch is unsustainable. Continued population monitoring is essential to assess the long-term viability of franciscana dolphins inhabiting southern Brazilian and Uruguayan waters.