Abstract: Research on the feeding habits of Franciscana dolphins (Pontoporia blainvillei) in waters along the Uruguayan coast was carried out using stomach contents from 41 individuals that were incidentally entangled in artisanal fishing nets or were stranded on the beach. A total of nine prey species were identified: eight teleosts and one squid. Teleosts were identified in 99.8% of the 37 stomach samples, corresponding to a total of 342 individuals. The striped weakfish (Cynoscion guatucupa) was the most important teleost by index of relative importance (IRI) (n = 127; IRI = 49.4%), followed by the toadfish (Porichthys porosissimus) (n = 90; IRI = 26.6%) and the whitemouth croaker (Micropogonias furnieri) (n = 66; IRI = 17.3%); whereas the remaining fish species represented less than 6.5% IRI. From eight species of fish found in stomach contents, four of them (striped weakfish, toadfish, whitemouth croaker, and Argentine croaker [Umbrina canossai]) actively produce sound. Fish, particularly those emitting sound, were the most important food content, representing 97.4% IRI. The Levin’s index of niche breadth shows a specialist feeding strategy, and data indicated that the Franciscana chooses soniferous prey along the Uruguayan coast. Therefore, we suggest that Franciscana dolphins find their prey in the low visibility waters of the Rio de la Plata estuary and the murky waters of the Uruguayan ocean coast through passive listening. However, this behavior may also lead Franciscana dolphins to be attracted to artisanal fishing nets because of the sounds produced by the fish caught in nets, which puts them in danger of becoming entangled.
Key Words: Franciscana dolphins, Pontoporia blainvillei, diet, Uruguay coast, passive listening, soniferous fishes
Document Type: Research Article
DOI: https://doi.org/10.1578/AM.43.4.2017.430
Page Numbers: 430-438

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