Abundance and distribution of an isolated population of franciscana dolphins (Pontoporia blainvillei) in southeastern Brazil: red alert for FMA I?

DANILEWICZ, D.; ZERVINI, A.; ANDRIOLO, A.; SECCHI, E.; SUCUNZA, F. ; FERREIRA,E. ; DENUNCIO, P. ; FLORES, P.A.

2011-12-15/2012-01-15

1-11

Biológica

Prom.Gral.del Conoc.-Cs.Exactas y Naturales

The franciscana (Pontoporia blainvillei) is endemic of the eastern coast of Brazil, Uruguay and Argentina and inhabits coastal waters from Brazil (18o25’S) to Argentina (41o10’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. In December 2011 and January 2012 design-based aerial surveys were conducted to assess the distribution and to estimate abundance of franciscanas in FMA I in three coastal (coastline to 30m isobath). One of this strata corresponded to an area believed to represent a hiatus in the species distribution between RJ and ES. 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) with the most supported detection probability model. 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. It is 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. It is also recommended that research to estimate bycatch is resumed in FMA I.