1Departamento de Patologia, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, São Paulo, State of São Paulo, Brazil; 2Instituto Nacional de Pesquisa da Amazônia, Manaus, State of Amazonas, Brazil; 3Instituto de Biologia, Universidade Federal de Pelotas, Pelotas, State of Rio Grande do Sul, Brazil; 4Departamento de Zoologia, Universidade Federal do Paraná, Curitiba, State of Paraná, Brazil; 5Projeto BioPesca, Praia Grande, State of São Paulo, Brazil; 6Departamento de Medicina Veterinária Preventiva e Saúde Animal, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, São Paulo, State of São Paulo, Brazil; 7Fundação Parque Zoológico de São Paulo, São Paulo, State of São Paulo, Brazil
Abstract
The franciscana dolphin (Pontoporia blainvillei) is considered to be one of the most threatened small cetaceans in the western South Atlantic Ocean and is the most common cetacean caught incidentally in fishing nets along its distribution.5 Studies on the stock structure and abundance of the franciscana dolphin in its home range are needed to evaluate the impact of this incidental mortality on the population.2
Parasites have been useful as an additional source of information regarding various aspects of host biology, including stock identity.1 Therefore, detailed studies regarding parasite burden of P. blainvillei have been recommended as a tool to evaluate ecological segregation and stock structure.3
In the present study, we analyzed metazoan parasites from the stomach, intestines, and lungs of 41 franciscana dolphins caught incidentally in fishing nets or stranded in beaches from three geographically close areas: group 1, Guarujá and Praia Grande (São Paulo State), n=12 (24°00’ S, 46°17’ W); group 2, Cananéia (São Paulo State), n=17 (25°00’ S, 47°56’ W); and group 3 (Paraná State), n=12 (25°30’ S, 48°23’ W). The sample population consisted primarily of immature animals between 0–3 years of age.
No parasites were found in the lungs. Acanthocephalans (Polymorphus sp.) were found in the stomachs of two animals and were considered an incidental finding. The trematode Hadwenius pontoporiae (Digenea: Campulidae) was the only parasite found in the intestines, with a prevalence of 100% for group 1, 82.35% for group 2, and 58.33% for group 3. The mean intensity of H. pontoporiae for groups 1, 2, and 3 was 39.5, 25.05, and 13.5 parasites per host, respectively.
Because the sampling of wild animals is often opportunistic, samples obtained are rarely age-stratified or diverse enough to detect heterogeneity in host-parasite associations.4 No significant correlation between total body length and infection levels (Pearson’s correlation coefficient = 0.51, p>0.01) were observed. Franciscana dolphins from Rio Grande do Sul State showed a negative correlation between mean intensity and total body length and age of the host, suggesting that immune response may increase with age.1
In this study there was a significant difference in number of parasites among the three groups (Kruskal-Wallis test, p=0.012). Groups 2 and 3 were geographically close and exhibited nonsignificant differences in the total number of parasites found (Mann-Whitney test, p=0.063). Groups 1 and 3 were further apart geographically and differed significantly in total number of parasites (Mann-Whitney test, p=0.003).
Analysis of data from areas where H. pontoporiae has already been found, including those of this study (Rio Grande do Sul State1 and Argentina2), demonstrates an increasing prevalence and mean intensity of parasite infection with increasing latitude. Therefore, H. pontoporiae may continue to be used as a biological tag for franciscana dolphin stock studies, with standardized methodology throughout its distribution, along with other characteristics, always considering the number of factors that may affect the results.
Acknowledgment
This work was supported by Fundação de Ampara à Pesquisa do Estado de São Paulo (FAPESP, grant #00/14669-0).
Literature Cited
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3. Aznar, F.J., J.A. Raga, J. Corcuera, and F. Monzón. 1995. Helminths as biological tags for franciscana (Pontoporia blainvillei) (Cetacea: Pontoporiidae) in Argentinean and Uruguayan waters. Mamm. 59:427–435.
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5. Secchi, E.R., P.H. Ott, E.A. Crespo, P.G. Kinas, S.N. Pedraza, and P. Bordino. 2001. A first estimate of franciscana (Pontoporia blainvillei) abundance of southern Brazil. J Cetacean Res Manage. 3:95–100.