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Temporal trends in mortality and effects of by-catch on common bottlenose dolphins, Tursiops truncatus, in southern Brazil

Published online by Cambridge University Press:  09 December 2010

Pedro F. Fruet ,
Paul G. Kinas ,
Kleber G. da Silva ,
Juliana C. Di Tullio ,
Daniele S. Monteiro ,
Luciano Dalla Rosa ,
Sérgio C. Estima  and
Eduardo R. Secchi
Pedro F. Fruet*
Affiliation:
Pós-Graduação em Oceanografia Biológica, Instituto de Oceanografia, Universidade Federal do Rio Grande-FURG, RS, Brazil Museu Oceanográfico ‘Prof. Eliézer C. Rios’, Universidade Federal do Rio Grande (FURG), Caixa Postal 379, Rio Grande, RS, Brazil Laboratório de Tartarugas e Mamíferos Marinhos/Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), 96500-970 Caixa Postal 474, Rio Grande, RS, Brazil
Paul G. Kinas
Affiliation:
Laboratório de Estatística Ambiental/Instituto de Matemática, Estatística e Física, Universidade Federal do Rio Grande (FURG), 96200-970, Caixa Postal 474, Rio Grande, RS, Brazil
Kleber G. da Silva
Affiliation:
Núcleo de Educação e Monitoramento Ambiental (NEMA), Rua Maria Araújo, 450, Cassino, Rio Grande, RS, Brazil
Juliana C. Di Tullio
Affiliation:
Pós-Graduação em Oceanografia Biológica, Instituto de Oceanografia, Universidade Federal do Rio Grande-FURG, RS, Brazil Museu Oceanográfico ‘Prof. Eliézer C. Rios’, Universidade Federal do Rio Grande (FURG), Caixa Postal 379, Rio Grande, RS, Brazil Laboratório de Tartarugas e Mamíferos Marinhos/Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), 96500-970 Caixa Postal 474, Rio Grande, RS, Brazil
Daniele S. Monteiro
Affiliation:
Núcleo de Educação e Monitoramento Ambiental (NEMA), Rua Maria Araújo, 450, Cassino, Rio Grande, RS, Brazil
Luciano Dalla Rosa
Affiliation:
Museu Oceanográfico ‘Prof. Eliézer C. Rios’, Universidade Federal do Rio Grande (FURG), Caixa Postal 379, Rio Grande, RS, Brazil
Sérgio C. Estima
Affiliation:
Núcleo de Educação e Monitoramento Ambiental (NEMA), Rua Maria Araújo, 450, Cassino, Rio Grande, RS, Brazil
Eduardo R. Secchi
Affiliation:
Museu Oceanográfico ‘Prof. Eliézer C. Rios’, Universidade Federal do Rio Grande (FURG), Caixa Postal 379, Rio Grande, RS, Brazil Laboratório de Tartarugas e Mamíferos Marinhos/Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), 96500-970 Caixa Postal 474, Rio Grande, RS, Brazil
*
Correspondence should be addressed to: P.F. Fruet, Museu Oceanográfico ‘Prof. Eliézer C. Rios’, Rua Cap. Heitor Perdigão, 10 Caixa Postal 379, Rio Grande, RS, Brazil email: [email protected]
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Abstract

The mortality of the bottlenose dolphin, Tursiops truncatus, on the southern portion of Rio Grande do Sul State coast was investigated based on 914 beach surveys conducted between 1969 and 2006. A total of 188 stranded bottlenose dolphins were recorded during this period, indicating a 1.8M:1F sex-ratio of those animals sexed (N = 79). Mortality was low in calves, high in juveniles and sub-adults and slightly lower than in adults. The overall mortality was clearly seasonal overlapping with higher fishing efforts in the Patos Lagoon Estuary and adjacent coastal areas, where most individuals washed ashore. Analysis of a continuous 14-year long subset (1993–2006) of the data indicated relatively low levels of mortality between 1995 and 2000 and a marked increase between 2002 and 2005 followed by an apparent drop in 2006. By-catch was responsible for at least 43% of the recorded mortality between 2002 and 2006. Juvenile males were more susceptible to incidental catches. Among females, by-catch of adults represented 75%. Results of a potential biological removal analysis suggest that current levels of fishing-related mortality are unsustainable for the small resident population of bottlenose dolphins that inhabits the Patos Lagoon Estuary, and that this population may be declining.

Keywords

conservationtime series analysissex-ratioTursiops truncatuspotential biological removalRio Grande do Sul
Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 92 , Issue 8: Marine Mammals , December 2012 , pp. 1865 - 1876
Copyright
Copyright © Marine Biological Association of the United Kingdom 2010

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