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

Published online by Cambridge University Press:  15 May 2009

Daniel Danilewicz*
Affiliation:
Grupo de Estudos de Mamíferos Aquáticos do Rio Grande do Sul (GEMARS), Rua Felipe Neri, 382/203, Porto Alegre 90440-150, Brazil Grupo de Ecologia e Conservação de Megafauna Marinha-EcoMega
Eduardo R. Secchi
Affiliation:
Laboratory of Marine Mammals, Museu Oceanográfico ‘Prof. Eliézer C. Rios’, Universidade Federal do Rio Grande, Cx P 379, CEP 96200, Rio Grande, Brazil Grupo de Ecologia e Conservação de Megafauna Marinha-EcoMega
Paulo H. Ott
Affiliation:
Grupo de Estudos de Mamíferos Aquáticos do Rio Grande do Sul (GEMARS), Rua Felipe Neri, 382/203, Porto Alegre 90440-150, Brazil Universidade Estadual do Rio Grande do Sul (UERGS), Cidreira, Rio Grande do Sul, Brazil Grupo de Ecologia e Conservação de Megafauna Marinha-EcoMega
Ignacio B. Moreno
Affiliation:
Grupo de Estudos de Mamíferos Aquáticos do Rio Grande do Sul (GEMARS), Rua Felipe Neri, 382/203, Porto Alegre 90440-150, Brazil
Manuela Bassoi
Affiliation:
Laboratory of Marine Mammals, Museu Oceanográfico ‘Prof. Eliézer C. Rios’, Universidade Federal do Rio Grande, Cx P 379, CEP 96200, Rio Grande, Brazil National Oceanography Centre, Southampton, European Way, SO14 3ZH, Southampton, UK Grupo de Ecologia e Conservação de Megafauna Marinha-EcoMega
Márcio Borges-Martins
Affiliation:
Grupo de Estudos de Mamíferos Aquáticos do Rio Grande do Sul (GEMARS), Rua Felipe Neri, 382/203, Porto Alegre 90440-150, Brazil Departamento de Zoologia, Universidade Federal do Rio Grande do Sul, Brazil
*
Correspondence should be addressed to: D. Danilewicz, Grupo de Estudos de Mamíferos Aquáticos do Rio, Grande do Sul (GEMARS), Rua Felipe Neri, 382/203, Porto Alegre 90440-150, Brazil email: [email protected]

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.

Type
Research Article
Copyright
Copyright © Marine Biological Association of the United Kingdom 2009

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