Biological parameters of franciscana dolphins, Pontoporia blainvillei, by-caught in artisanal fisheries off southern Buenos Aires, Argentina

The franciscana dolphin (Pontoporia blainvillei) is a small coastal dolphin endemic to the south-western Atlantic Ocean. Incidental captures in fishing gillnets is possibly the greatest conservation concern for this species, and occurs within most of its geographical distribution. The aim of this paper is to determine the biological parameters of franciscana dolphin by-caught from artisanal coastal fisheries of the southern Buenos Aires province, Argentina. Between 2003 and 2009, carcasses of 54 incidentally captured franciscanas were collected. The age, sexual and physical maturity and body condition of each specimen was determined. The sex-ratio of the by-caught dolphins did not differ from parity and, consistent with other areas, juveniles younger than 4 yr old were captured in higher proportion (69%). In addition, 74% of the entangled animals were sexually immature and 85% physically immature. Sexually immature dolphins were predominant in the spring, a period which coincides with the breeding season. An assessment of the body condition of captured franciscanas suggests that entanglements were not associated with a disease or physiological disorder. The results presented here are important to assess the impact of artisanal fisheries on the population of franciscana dolphins in the southernmost area of its distribution.