Report of the Working Group on Vital Parameters and Demography

Abstract

Age distribution of franciscanas incidentally caught in northern Rio de Janeiro State, southeastern Brazil, was reported for 62 males and 57 females (Di Beneditto and Ramos, 2000). Males ranged from 0 to 5 years but were mostly of age 2. Females ranged from 0 to 9 years and were mostly of ages 2 and 3. Overall, 74% of all captured animals were of three years or younger. Age distribution of 260 franciscanas from incidental captures and strandings were obtained from three regions in southeastern Brazil: Espirito Santo State (ES) (n = 14), northern Rio de Janeiro State (NRJ) (n = 141) and Sao Paulo State (SP) (n = 105) (Ramos et al., 2000). A comparison between the age distribution of incidental catches in NRJ and strandings in SP indicated a higher percentage of older animals in SP: 73% were between 0-3 years in NRJ (incidental captures); the same percentage was between 36 years in SP (strandings) (K-S Test, n=164, P≤0.05). Since both samples are from different regions, it is unclear how to interpret the observed difference in age composition. However, similarities have been detected in the age structure of incidentally caught franciscana when compared over the complete distribution. Age classes up to 3 years were the most representative in southern Brazil (Pinedo, 1994; Ott, 1998; Ott et al., 2000), Uruguay (Kasuya and Brownell, 1979; Crespo et al., 1986) and Argentina (Perez Macri and Crespo, 1989, Corcuera et al., 1994). This suggests that captures are biased towards juveniles (see also IWC, 1994). Age distribution patterns for stranded franciscanas in other regions are unknown. A summary on information of age structure of the southern franciscana incidentally caught or stranded is given in Table 1.