Threatened franciscanas: improving estimates of abundance to guide conservation actions
Zerbini, Secchi, Danilewicz, Andriolo, Flores
Description
The franciscana (Pontoporia blainvillei) is endemic to the eastern coast of Brazil, Uruguay and Argentina and inhabits coastal waters from Brazil (18°25’S) to Argentina (41°10’S). The species is currently regarded as the most threatened small cetacean in South America due to high bycatch levels throughout its range. Recently, four management stocks (known as Franciscana Management Areas or FMAs) were defined: two in Brazil (FMA I-III), one in Brazil/Uruguay (FMA III) and one in Argentina (FMA IV). FMA I corresponds to the coasts of the Brazilian states of Rio de Janeiro (RJ) and Espirito Santo (ES) and represents one of the least known stocks. This population faces a number of conservation threats including bycatch in fisheries and habitat degradation, but the magnitude of these threats have not yet been well understood because of lack of information on population size.
Aerial surveys are a reliable way to estimate abundance of coastal cetaceans and knowledge of abundance and trends is essential to evaluating threats and mitigation measures. The main objective of the project was to:
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conduct simultaneous boat and aerial surveys to determine the correction factors to allow complete abundance estimates to be obtained with appropriate levels of uncertainty. These factors relate to: estimated school size; time spent at the surface; time an animal is visible to observers.
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to use these to develop appropriate monitoring to evaluate effects of human impacts (bycatch and habitat degradation); and
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to build up local expertise in monitoring and improve international collaboration.
Results
In December 2011 and January 2012 surveys were conducted to assess the distribution and to estimate abundance of franciscanas in FMA I in three coastal (coastline to 30m isobath). A total of 20 franciscana groups (46 individuals) were seen, including in the proposed hiatus. Average group size was 2.2 (SE = 0.305). Abundance corrected for perception and availability bias was estimated to be 1,998 (CV=0.48, 95% CI: 796-5,013). Franciscanas were recorded from very coastal and turbid waters near the shore (just behind the surf zone) to clearer waters as far as 13km from the shore.
The most recent (2001-2002) estimates of incidental mortality in FMA I correspond to 5.5% (2.2-13.8%) of the estimated population size presented here, possibly indicating high and unsustainable bycatch. The researchers strongly recommended that new aerial surveys with increased sampling effort be conducted in order to produce more robust population estimates and further assess the species distribution. They also recommended that research to estimate bycatch is resumed in FMA I.
These recommendations were endorsed by the Scientific Committee at its 2012 Annual Meeting in Panama.
The full results can be found in SC/64/SM17
