Distribution, habitat use, and abundance of the endangered franciscana in southeastern and southern Brazil

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 South America due to high bycatch levels. Four management units (FMAs) were defined throughout the species’ range. FMA II includes states along southeastern and southern Brazil, and represents one of the least known units. Recently, genetic analysis proposed that FMA II comprises two distinct populations and its range should be divided into FMA IIa and IIb. In December 2008 and January 2009 aerial surveys were conducted to assess the distribution and to estimate abundance of franciscanas off FMA II. A total of 54 groups were seen (average group size = 2.76, SE = 0.17) in shallow (mean depth = 7.15 m, SE = 7.08) coastal habitats (average distance from the shore = 6.48 km, SE = 6.28). Abundance corrected for perception and availability bias was estimated at 6,827 ( CV = 0.26) franciscanas in FMA II, and at 1,915 ( CV = 0.32) and 4,353 ( CV = 0.24) franciscanas in FMA IIa and FMA IIb, respectively. This study indicates that, at least during the summer, franciscanas aggregate in shallow coastal habitats. Current estimates of incidental mortality in FMA II correspond to 4.4%–7.3% of the estimated stock size, suggesting high, likely unsustainable bycatch.

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