Rodrigo H. Tardin

Coordinated feeding tactics of the Guiana dolphin, Sotalia guianensis (Cetacea: Delphinidae), in Ilha Grande Bay, Rio de Janeiro, Brazil

Differences in distribution, prey species, season and social learning opportunities influence the feeding tactics used by marine mammals. Here, we analyze the coordinated feeding behavior of the Guiana dolphin, Sotalia guianensis (Van Beneden, 1864, Delphinidae) and its relation to seasonality and the presence of calves. In a total of 201 feeding bouts, we observed four types of coordinated feeding tactics, which differed in frequency and in mean number of engaged individuals. Tactics in which dolphins used their bodies to herd and capture prey were the most frequent, presenting a higher frequency and engaging a higher number of individuals, suggesting that these tactics are better for capturing fishes which form larger schools. Furthermore, the seasons influenced the feeding behavior used by dolphins. During spring-summer, a longer duration of bouts and a larger number of individuals engaged in the feeding tactics was observed, which may be related to the seasonal spawning of larger schooling fish, such as Sardinella brasiliensis (Steindachner, 1879). Calves were present in 95% of all coordinated feeding tactic occurrences. This study indicates a complete preference of dolphins for coordinating their actions to capture prey and for the first time reports the presence of calves in the coordinated tactics and jumps. This broadens the current knowledge of the Guiana dolphin feeding tactics.

Bryde's whale (Cetartiodactyla: Balaenopteridae) occurrence and movements in coastal areas of southeastern Brazil

Brydes whales, Balaenoptera edeni Anderson, 1879, were observed on 17 occasions (N = 21 surveys) in the coastal waters off Rio de Janeiro in southeastern Brazil during austral summer through autumn 2014. Five whales were individually identified using photo-identification techniques. The mean interval between resightings for all individuals was 12.8 days, with a minimum of one day and a maximum of 48 days. The comparison between the catalogs of Brydes whales off Rio de Janeiro and the Cabo Frio region revealed matches for three individuals. The resightings show movements of up to 149.6 km along the coastal waters off the state of Rio de Janeiro. Most of the observations consisted of solitary individuals (82.3% of sightings). Feeding was the predominant behavior observed (47%), followed by milling (35.3%) and travelling (17.6%) in waters up to 48 m deep. Direct observations resulted in the addition of new prey, such as snubnose anchovy, Anchoviella brevirostris (Gunther, 1868) and white snake mackerel, Thyrsitops lepidopoides (Cuvier, 1832), to the known diet of the Brydes whale. A long time series of photo-identification efforts in the Rio de Janeiro, the Cabo Frio region and other areas can elucidate fundamental aspects of spatial and temporal site fidelity knowledge of Brydes whales in southeastern Brazil.

Behavioral event occurrence differs between behavioral states in Sotalia guianensis (Cetarctiodactyla: Delphinidae) dolphins: a multivariate approach

Difficulties in quantifying behavioral events can cause loss of information about cetacean behavior, especially behaviors whose functions are still debated. The lack of knowledge is greater for South American species such as Sotalia guianensis (Van Beneden, 1864). Our objective was to contextualize the behavioral events inside behavioral states using a Permutational Multivariate Analysis of Variance (MANOVA). Three events occurred in the Feeding, Socio-Sexual and Travelling states (Porpoising, Side flop, Tail out dive), and five events occurred in the Feeding and Travelling states (Back flop, Horizontal jump, Lobtail, Spy-hop, Partial flop ahead). Three events (Belly exposure, Club, and Heading) occurred exclusively in the Socio-sexual state. Partial Back flop and Head flop occurred exclusively in the Feeding state. For the events that occurred in multiple states, we observed that some events occurred more frequently in one of the states (p < 0.001), such as Lobtail, Tail out dive horizontal Jump, Partial flop ahead and Side flop. Our multivariate analysis, which separated Socio-sexual behavior from Feeding and Travelling, showed that the abundance of behavioral events differs between states. This differentiation indicates that some events are associated with specific behavioral states. Almost 40% of the events observed were exclusively performed in one state, which indicates a high specialization for some events. Proper discrimination and contextualization of behavioral events may be efficient tools to better understand dolphin behaviors. Similar studies in other habitats and with other species, will help build a broader scenario to aid our understanding of the functions of dolphin behavioral events.

Coordinated feeding behavior of the Guiana dolphin, Sotalia guianensis (Cetacea: Delphinidae), in southeastern Brazil: a comparison between populations

The coordinated feeding tactics used by delphinids are influenced by differences in the distribution of prey species, season, and opportunities for social learning. In the present study, we compared the coordinated feeding behavior of two populations of the Guiana dolphin, Sotalia guianensis, in southeastern Brazil, and how these feeding tactics vary seasonality and in the presence of calves. We observed eight types of coordinated feeding tactics, which differed in frequency and in the mean number of individuals engaged in them, and between both areas. Feeding tactics used to herd and capture prey were the most frequent and engaged a greater number of individuals, suggesting that these tactics are better for capturing fish that gather in larger schools. Furthermore, the seasons influenced the occurrence of different prey items, which in turn modified the feeding tactics of the dolphins. In the Ilha Grande Bay we observed that bouts lasted longer and larger groups engaged in the feeding tactics, which may be associated with the seasonal spawning of larger schooling fish such as Sardinella brasiliensis (Steindachner, 1879) (Teleostei: Clupeidae). However, in the Sepetiba Bay, we observed longer feeding bouts and a smaller number of individuals engaged in the feeding tactics during autumn-winter. This may be associated with the fact that the most abundant prey species, Micropogonias furnieri (Desmarest, 1823) (Teleostei: Sciaenidae), gathers in small schools. Calves were present in 95% of all coordinated feeding tactics that occurred in the Ilha Grande Bay and in approximately 61% of feeding tactics in the Sepetiba Bay, suggesting that these areas are important for social learning. This study provides more information about feeding tactics and improves knowledge of the coordinated behavior of Sotalia guianensis (Van Beneden, 1864).