Prey consumed by Guiana dolphin Sotalia guianensis (Cetacea, Delphinidae) and franciscana dolphin Pontoporia blainvillei (Cetacea, Pontoporiidae) in an estuarine environment in southern Brazil

Abstract

ABSTRACT. The present study provides information about the diet of sympatric populations of small cetaceans in the Babitonga Bay estuary. This is the first study on the diet of these species in direct sympatry. The stomach contents of seven Guiana dolphins Sotalia guianensis and eight franciscanas Pontoporia blainvillei were analyzed. The prey of both cetaceans was mostly teleost fishes, followed by cephalopods. We identified 13 teleost fishes as part of the diet of the franciscanas, and 20 as part of the diet of Guiana dolphins. Lolliguncula brevis was the only cephalopod recorded, and was the most important prey for both cetaceans. Stellifer rastrifer and Gobionellus oceanicus were also important for franciscana, so as Mugil curema and Micropogonias furnieri were important for Guiana dolphins. Stellifer rastrifer and Cetengraulis edentulus were the fishes with the highest frequency of occurrence for franciscana (50%), while Achirus lineatus, C. edentulus, S. brasiliensis, Cynoscion leiarchus, M. furnieri, M. curema, Diapterus rhombeus, Eugerres brasilianus and G. oceanicus showed 28.6% of frequency of occurrence for Guiana dolphins. Franciscanas captured greater cephalopods than the Guiana dolphins in both total length (z= -3.38; n= 40; p< 0.05) and biomass (z = -2.46; n = 40; p<0.05). All of the prey species identified occur inside the estuary, which represents a safe habitat against predators and food availability, reinforcing the importance of the Babitonga Bay for these cetacean populations.KEYWORDS. Diet, Babitonga Bay, cetacean, fish, cephalopod. RESUMO. Presas consumidas pelo boto-cinzaSotalia guianensis (Cetacea, Delphinidae) e pela toninha Pontoporia blainvillei (Cetacea, Pontoporiidae) em ambiente estuarino no sul do Brasil. O presente estudo fornece informações sobre a dieta de populações simpátricas de pequenos cetáceos no estuário da Baía da Babitonga. Este é o primeiro estudo sobre a dieta destas espécies em simpatria direta. Foi analisado o conteúdo estomacal de sete botos-cinza Sotalia guianensis e oito toninhas Pontoporia blainvillei. As presas de ambos cetáceos foram principalmente peixes teleósteos, seguida de cefalópodes. Foram identificadas 13 espécies de peixes teleósteos como parte da dieta de toninhas e 20 como parte da dieta de botos-cinza. Lolliguncula brevis foi o único cefalópode registrado e foi a presa mais importante para ambos cetáceos.Stellifer rastrifer e Gobionellus oceanicus foram também importantes para a toninha, assim como Mugil curema e Micropogonias furnieri foram importantes para os botos-cinza. Stellifer rastrifer e Cetengraulis edentulus foram as espécies de peixes com maior frequencia de ocorrência para a toninha (50%), enquanto Achirus lineatus, C. edentulus, S. brasiliensis, Cynoscion leiarchus, M. furnieri, M. curema, Diapterus rhombeus, Eugerres brasilianus e G. oceanicus apresentaram 28,6 % de frequência de ocorrência para os botos-cinza. As toninhas capturaram cefalópodes maiores do que os botos-cinza, tanto em comprimento total (z= -3,38; n= 40; p< 0,05) como...

Use of carbon and nitrogen stable isotopes to study the feeding ecology of small coastal cetacean populations in southern Brazil

“…Although the study involves a small number of samples, any available information on the foraging habits of these species is beneficial for establishing conservation measures (Cremer et al 2012, Owen et al 2011. Nonetheless, results found in this study may not represent the diet behaviour of a large population and conclusions should be drawn with caution.…”

“…Although relatively important for both species, it was not possible to capture Gobionellus oceanicus individuals for analysis. Prey samples were selected based on the specific total length that both dolphins consume (Cremer et al 2012). Samples of muscle tissue were collected from the dorsal area of each specimen and frozen immediately.…”

“…Based on stomach content analysis of individuals collected in the Babitonga Bay area, Cremer et al (2012) concluded that both species exhibit a generalist diet that includes several teleost fish and one cephalopod species, which are important food sources for both species. Correspondingly, similar results have been found in other regions of the Brazilian coast (Santos et al 2002, Di Beneditto & Siciliano 2007, Di Beneditto et al 2009, Daura-Jorge et al 2011.…”

“…One approach for studying animal feeding behavior is to examine stomach contents, as performed by Cremer et al (2012). This technique is very useful, although stomach content analyses represent just a "snapshot" of a brief period in the lifecycle of animals like cetaceans.…”

“…Franciscana individuals from a separate population found in the nearshore area, located outside of the bay, were also included in the analysis in order to check for variation in feeding strategies of the same species in relation to habitat differences (Ford et al 1998). The diet of these populations was characterized to complement the findings of a recent study on their feeding strategies, which analyzed the stomach contents of specimens collected in Babitonga Bay (Cremer et al 2012). Additionally, a second objective of this study was to investigate whether the use of stable isotopes could effectively distinguish nearshore Franciscana specimens from estuarine individuals.…”