Habitat use patterns of franciscana dolphins(Pontoporia blainvillei)off southern Brazil in relation to water depth

Abstract

The patterns of habitat use by the franciscana dolphins (Pontoporia blainvillei) along its distribution are poorly known. This study investigates the patterns of habitat use with respect to depth for 181 individuals of different age, size, gender and reproductive condition off Rio Grande do Sul, southern Brazil. The results reveal that franciscanas are very homogeneously distributed according to depth. Individuals from all lengths utilize nearly the entire range of depths of the surveyed area. Larger or older animals do not use deeper waters than younger animals, indicating that body size and age are not limiting factors for franciscanas that occupy deeper or offshore waters. Gestation seems to not cause a change in the distribution of females. Although the sex-ratio of the overall data did not vary from 1:1 in different depth intervals, a small-scale comparison between the northern and southern coast demonstrated the existence of some kind of sexual segregation. Franciscana by-catch in Rio Grande do Sul is not sustainable and it is agreed that management procedures are needed. Nevertheless, the available data on species distribution do not allow the designing of a protected area in order to minimize the by-catches of a particular sex/reproductive class.

Ontogenetic and sexual characterization of the feeding habits of franciscanas, Pontoporia blainvillei, based on tooth dentin carbon and nitrogen stable isotopes

“…, Secchi ) and dolphins of all age classes occur homogeneously throughout the area (Danilewicz et al . ). Therefore, variation in δ 13 C should indeed be small and differences in carbon might reflect some small interindividual variation in dietary preferences along the ages (see discussion on SIAR outcomes below).…”

Towards a Standardized Approach of Cetacean Habitat: Past Achievements and Future Directions

“…In comparison, water temperature measurements accessed from remote sensing data was used to investigate seasonal distribution changes in striped dolphins (Stenella coeruleoalba) in the Ligurian Sea [41]. Of further note is the typically small number of environmental variables measured in many studies despite the high plausibility of other factors being instructive in describing habitat [42]- [44]. This consideration and narrowed selection of assessed variables should therefore caution our application of some habitat studies for progressing management objectives and conservation strategies.…”

Interação com a pesca: implicações na conservação da toninha, Pontoporia blainvillei (Cetacea, Pontoporiidae) no litoral do estado de São Paulo, SP

“…Recentemente a partir de um maior número de dados de captura acidental no litoral do Rio Grande do Sul foi verificado que não ocorre segregação das toninhas quanto ao gênero, estado de maturidade e idade em relação a profundidade (Danilewicz et al, 2009). Na costa do Uruguai também não foi constatado uso diferencial do habitat pelas toninhas de diferentes idades (Praderi et al, 1994;Pinedo, 1994).…”

“…A frota pesqueira monitorada no presente trabalho operou em águas costeiras, da zona de arrebentação até a isóbata de 20 metros, sendo esta faixa considerada como a área preferencial de uso pelas toninhas (Pinedo et al, 1989;Bordino et.al., 1999;Di Beneditto e Ramos, 2001;Siciliano et al, 2000;Danilewicz et al, 2009). E embora não tenha sido realizado nenhum aprofundamento dos dados de captura acidental em relação a área e considerando que a frota monitorada operou na área preferencial das toninhas, (Botta, 2005), porém nessa área a idade média de maturidade gonadal tanto para machos quanto para fêmeas é superior (2,1 a 3,6 anos para os machos e 3,3 a 3,7 anos para fêmeas) (Danilewicz et al, 2000;Danilewicz et al, 2004;Botta, 2005).…”