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SC/69A/CMP/13
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Resource ID
19968
Access
Open
Document Number
SC/69A/CMP/13
Full Title
Adapting an acoustic sailboat survey to estimate the distribution and abundance of a fringe population of franciscana dolphin (Pontoporia blainvillei) (FMA Ia)
Author
A. Andriolo, F. Sucunza, A.N. Zerbini, D. Danilewicz, T.O.S. Amorim, F.R. De Castro, G.A. Ferriera, J. Pedro Mura, J. Gomes, J. Luis Pizzorno
Authors Summary
The manuscript documented the use of an acoustic sailboat survey to estimate the distribution and abundance of a fringe population of franciscana dolphin (Pontoporia blainvillei) (FMA Ia), Brazil. The main conclusions are:
1. Expansion of the distribution limits for FMA Ia to support better conservation strategies.
2. Despite the broad distribution range in the study area, the FMA Ia franciscana population is significantly concentrated around the Rio Doce mouth.
3. The franciscana dolphin population at FMA Ia was estimated through the acoustic method in 1256 (CV=0.69)
4. The possibility of implementing autonomous and automated systems for data collection and analysis exists.
5. It demonstrated the effectiveness of a completely independent system for abundance estimation supplanting human perception biases and enhancing reproducibility.
In conclusion, the potential loss of FMA Ia is a stark reminder of the urgent need for conservation efforts. By protecting these isolated groups, we can help ensure the survival and recovery of endangered species and the ecosystems they inhabit.
Publisher
IWC
Publication Year
2023
Abstract
The franciscana (Pontoporia blainvillei) is a small endemic dolphin found only in the coastal waters off the eastern coast of South America (Brazil, Uruguay, and Argentina). Its distribution has been divided into management areas, known as Franciscana Management Areas (FMAs). The FMA Ia in Brazil is the northernmost isolated population unit. This study aimed to collect data on franciscana at FMA Ia using a sailboat equipped with an acoustic towed array, with the objectives of documenting the method to address detection probability and provide reliable estimates of distribution and abundance. The data was collected on a 40-foot sailboat between February 22nd and May 23rd, 2019. The acoustic recording was conducted continuously with the sailboat towing a 50m linear array of four-element) omnidirectional hydrophones encompassing the cities of Vitória, ES (20°18’S, 40°15’W) and the northern limit of the State of Espírito Santo (18°19’S, 39°39’W). The conductivity (converted to salinity), temperature, and depth data were collected using the Conductivity, Temperature, and Depth (CTD) profiler SBE 19plus (Sea-bird Electronics) with the support of auxiliary sensors at 37 stations. The audio processing was conducted with the software PAMGuard version 2.02. Perpendicular distances were calculated from the sailboat to the transect line. Truncation was applied to discard all observations beyond 100 meters. Abundance was estimated using standard line-transect methods, and detection probability was estimated using Conventional (CDS) and Multiple Covariate Distance Sampling methods. The corrected density estimate (Dc) was computed by dividing Du by 3.48 (Var=4.2) from Mura et al. (this meeting). The northern boundaries of FMA Ia could be maintained as Amaral et al. (2018) (18º20'S), and the southern limit can be extended and placed at 20°01’S. The coastline corresponding with these new proposed boundaries is 220 km. The FMA Ia population density was estimated at 0.29 (CV=0.69) individuals per km2 for the whole area. The total abundance number was 1256 (CV=0.69) individuals in this study. The study area faced serious habitat degradation due to the iron ore tailings reaching the coast, and the need for continuous monitoring was highlighted. The study also demonstrated the effectiveness of using an autonomous and automated system for abundance estimation, suppressing human perception biases and enhancing reproducibility.