Incidental catches of franciscana (Pontoporia blainvillei) on the southern coast of São Paulo State and the coast of Paraná State, Brazil

F. C. W. Rosas, E. L. A. Monteiro-Filho, M. R. Oliveira

Abstract


A total of 40 individuals of P. blainvillei, incidentally caught on the southern coast of São Paulo State (region of Cananéia) (25°00'S, 47°54'W and 25°04'S, 47°56'W) and on the coast of Paraná State (25°18'S, 48°05'W and 25°58'S, 48°35'W), were recorded between 1997 and 1999. The average mortality of franciscanas incidentally caught by the only fishing boat sampled on the southern coast of São Paulo State, which operated up to 40 nautical miles (nm) from the coast, was 11 individuals/year, with a proportion of 2.3 males for every female. An average mortality of 10 franciscanas/year was estimated for several artisanal fishing communities sampled on the coast of Paraná State, where fishing activities usually are not further than 5nm from the coast. There was no significant difference (P>0.05) between the proportion of males and females incidentally caught by the artisanal fisheries on the Paraná coast. The proportion of sexually immature franciscanas reached 55%; in southern São Paulo State, compared with 76.2%; for the coast of Paraná. Bottom-set gillnets, with a stretched mesh size of 7.0 and 13.0cm, recorded the greatest number of individuals incidentally caught in the Cananéia region. However, on the Paraná coast, the greatest number of franciscanas was incidentally caught in driftnets with a stretched mesh size of 10.0cm. Comparing these mesh sizes with those presented in the literature for franciscanas incidentally caught in other places, it seems that other fishery characteristics (e.g. distance from the coast, depth, fishing effort, and season) are more important than the mesh size itself. The predominance of captured males in the fisheries further away from the coast, and the greatest proportion of sexually immature franciscanas incidentally caught in the fisheries closer to the coast, suggest spatial segregation between some age groups and sexes for this species in the study area. The results also suggest that the fisheries with industrial fishing characteristics, carried out by the boats in the Cananéia region, could be causing a strong impact on the populations of P. blainvillei. This means that a continuous surveillance of fishing activity is necessary for a greater period, including as many boats as possible, in order to certify the mortality estimates in that region.

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DOI: http://dx.doi.org/10.5597/lajam00020

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