Age and growth of franciscana dolphin, Pontoporia blainvillei, (Cetacea) incidentally caught off southern Brazil and northern Argentina.

BOTTA, SILVINA; MUELBERT, M.; SECCHI, EDUARDO R.; DANILEWICZ, DANIEL; NEGRI, MARÍA FERNANDA; CAPPOZZO, HUMBERTO LUIS; HOHN, ALETA A.

Fortaleza, Ceará, Brasil

Congreso; III Congresso Brasileiro de Oceanografia; 2008

The franciscana, Pontoporia blainvillei, is possibly the cetacean most vulnerable to incidental catch in coastal gillnets in the western South Atlantic. Four Franciscana Management Areas (FMA I-IV) have been proposed based on differences including genetics, morphometrics, and population parameters. Evidence for splitting FMAIII and FMAIV is weak. We compared age and growth of animals bycaught from FMAIII (Rio Grande do Sul (RS), Brazil) and FMAIV (Buenos Aires coast (BA), Argentina) as possible support for maintaining these two FMAs. Data on body length (BL) and age from 155 males and 134 females from RS and 19 males and 14 females from BAwere used for growth analysis. Ages were estimated by counting growth layer groups (GLGs) in teeth (1GLG=1yr). The von Bertalanffy growth model was fit to length-at-age data. A large proportion of the specimens (83% of RS and 77% of BA) were less than three years old. A 17-year-old male from Brazil was found, representing the oldest franciscana male ever reported. No between-region differences were observed in asymptotic lengths of males (p=0.11, RS=131.46 cm and BA=138.34) or of females (p=0.80, RS=153,67 cm and BA=151.10 cm). Females had a greater asymptotic body length than males (p<0.001). Our findings, do not support splitting FMAIII and FMAIV into separate units.