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SC/69A/CMP/20
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Resource ID
19972
Access
Open
Document Number
SC/69A/CMP/20
Full Title
Distribution and abundance of Franciscana (Pontoporia blainvillei) in northern Rio de Janeiro, Brazil: core habitat and density decline
Author
Daniel Danilewicz, Federico Sucunza, Diego Janisch Alvares, Paulo H. Ott, Emanuel Ferreira, Martin Perez, Artur Andriolo, Eduardo R. Secchi, Paulo A. C. Flores, Ana Paula Farro, Agnaldo Martins, Alexandre N. Zerbini
Authors Summary
This paper describes the results of three aerial surveys conducted to assess the distribution and abundance of the franciscana population in the northern Rio de Janeiro region. The study found that the population's distribution range is limited to a 125 km stretch of coastline, with the highest densities observed in the southern region. The core habitat in the southern region covers a 780 km2 area and is critical for the population's long-term viability. The study also detected a seasonal expansion-retraction distribution model, possibly driven by reproduction. The estimated abundance of the population was 1,104 individuals in 2017, with an 11% decrease in density observed over a six-year period. The study recommends continuous monitoring of the population's abundance and trends and discuss the implementation of a marine protected area as a conservation strategy while considering the limits of the proposed core area.
Publisher
IWC
Publication Year
2023
Abstract
Here we present information on the results of three dedicated aerial surveys to assess the at-sea distribution of franciscanas and estimate its abundance applying line-transect distance sampling in northern Rio de Janeiro population (Franciscana Management Area Ib). This study found that the distribution range of this franciscana population is limited to a 125 km stretch of coastline, with much higher densities in the southern region. The core habitat located in the southern region encompasses a 780 km2 area. All indications point to this area being where the franciscana has its highest densities and must be considered critical for this population long-term viability. The possible establishment of a marine protected area as a conservation strategy for this population must consider the limits of the proposed core area. While there is still no evidence of seasonal inshore-offshore movements, a more dispersed distribution of groups was observed during winter. This seasonal expansion-retraction distribution model may be driven primarily by reproduction and requires further investigation to be validated. The decline in franciscana densities with distance from shore is less pronounced compared to other populations. Using the most parsimonious detection probability models, the abundance was estimated at 1,104 in 2017 (Dc=0.27, CV=0.50, 95% CI: 0.12-0.69). A 11% decrease in the density of was detected over a six-year interval (2011-17), which raises the concerns with this isolated population. The potential biological removal (PBR) x’was calculated at 8 franciscanas, lower than historical annual mortality in FMA Ib. Implementation of continuous monitoring of the abundance and trends of this threatened population is recommended.