Keyword: Cetacea

Distribution patterns of Risso’s Dolphin, Grampus griseus, in offshore waters of Southeast Brazil assessed by aerial surveys

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The Risso’s dolphin, Grampus griseus, is widely distributed in temperate and tropical ocean waters around the world. Despite the known occurrence along the Brazilian coast, information regarding the spatial distribution of the species is scarce. Here we evaluated the distribution pattern of Risso’s dolphins using records obtained through 200 h of dedicated aerial surveys for marine mammals off the slope and outer continental shelf of Southeast Brazil, conducted between March and May 2012. A total of 16 groups of Risso’s dolphins was recorded with a median group size of 35 individuals (range = 1–300). Environmental variables (i.e., depth, slope, distance to the coast and to the shelf break, and sea surface temperature) associated with the Risso’s dolphin groups recorded indicate an oceanic distribution pattern, occurring close to the shelf break, what is probably related with foraging activity. This study provides new information about the distribution of Risso’s dolphins in Brazilian waters, and could be used as basis to plan conservation actions.

Padrões de distribuição do golfinho-de-Risso, Grampus griseus, em águas oceânicas do sudeste do Brasil, avaliado através de levantamentos aéreos. O golfinho-de-Risso, Grampus griseus, apresenta ampla distribuição em águas tropicais e temperadas ao redor do mundo. Apesar da ocorrência conhecida ao longo da costa brasileira, informações a respeito da distribuição espacial da espécie são escassas. Neste estudo, avaliamos o padrão de distribuição do golfinho-de-Risso usando registros obtidos através de 200 h de sobrevoos dedicados para observação de mamíferos marinhos no talude e plataforma externa do sudeste do Brasil, conduzidos entre março e maio de 2012. Um total de 16 grupos de golfinhos-de-Risso foi registrado com uma mediana de tamanho de grupo de 35 indivíduos (variação = 1–300). Variáveis ambientais (i.e., profundidade, declividade, distância da costa e para a quebra da plataforma, e temperatura superficial da água) associadas aos grupos de golfinhos-de-Risso registrados indicaram um padrão de distribuição oceânico, ocorrendo próximo da quebra da plataforma continental, o que está provavelmente relacionado com atividade de forrageio. Este estudo fornece novas informações sobre a distribuição dos golfinhos-de-Risso em águas brasileiras, e pode ser usado como base para planejamento de medidas de conservação.

Graphical abstract for the article “Distribution patterns of Risso’s Dolphin, Grampus griseus, in offshore waters of Southeast Brazil assessed by aerial surveys” (Portal et al., 2022)

Revisión y actualización de la colección de mamíferos marinos del Museo Argentino de Ciencias Naturales «Bernardino Rivadavia» (Buenos Aires, Argentina)

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Se realizó una revisión de los ejemplares de la Colección de Mamíferos Marinos del Museo Argentino de Ciencias Naturales «Bernardino Rivadavia». La misma indicó que del total de ejemplares catalogados (n = 378), el 56.9% corresponde a Cetacea mientras que el 43.1% restante corresponde a Pinnipedia. Dentro de Cetacea la familia más representada es Delphinidae, y el género con más ejemplares, Pontoporia (Pontoporidae); se reportan además, en forma complementaria, tres ejemplares tipo que no fueron listados en un trabajo previo. Dentro de los Pinnipedia, la familia mejor representada es Otariidae, y el género con mayor número de ejemplares, Otaria.

Updated revision of the marine mammals collection housed at the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (Buenos Aires, Argentina). A thorough revision of the specimens housed at the Marine Mammals collection of the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” indicated that 56.9% (n = 378) of the total number of specimens catalogued belongs to Cetacea, and the remainder (43.1%) to Pinnipedia. Among Cetacea, Delphinidae is the best represented family, whereas Pontoporia (Pontoporidae) is the genus which comprises the major number of specimens. Furthermore, we report three type specimens which were not cited in a previous work. As regards to Pinnipedia, the best represented family corresponds to Otariidae, Otaria being the genus with the highest number of specimens.

La presencia del delfín listado, Stenella coeruleoalba (Meyen, 1833), en el Mar Argentino

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El conocimiento del género Stenella en el Atlántico Sudoccidental ha sido muy limitado. A pesar que el holotipo fuera capturado por Meyen (1833) en el estuario del Río de la Plata, solo unos pocos especímenes se registraron en el sector durante las últimas décadas. El presente estudio analiza la distribución y ocurrencia de delfines listados en el Mar Argentino, y sintetiza el conocimiento sobre su presencia en el Atlántico Sudoccidental. Stenella coeruleoalba se registra entre los 7° y 42° S, aunque la mayoría de los ejemplares se hallaron entre los 30° y 40° S. Cerca del 70% de los ejemplares hallados correspondieron a varamientos solitarios y, en todos los casos en que pudo determinarse el sexo, correspondieron a machos subadultos o adultos (205–242 cm). Un total de 10 cráneos se encuentran depositados actualmente en museos de Brasil, Uruguay y Argentina (LCB 402–471 mm). Los avistajes predominaron entre fines de primavera y verano (octubre–febrero), comprendiendo grupos reducidos (1–4 delfines) en aguas relativamente poco profundas (30–100 m). Un único ejemplar de esta especie fue capturado incidentalmente en operaciones de pesca de anchoíta en el norte de Patagonia y asociado con delfines comunes. Los patrones de coloración observados fueron el gris azulado en ejemplares varados y pardusco en ejemplares avistados, con la combinación característica de bandas laterales y la mancha dorsal. La corriente cálida del Brasil podría estar influenciando la presencia de delfines listados en Uruguay y Argentina durante el verano, a pesar que algunos de los ejemplares fueron registrados en aguas de temperaturas inferiores a los 20° C, las cuales están influenciadas por la Corriente de Malvinas. Las investigaciones futuras deberían focalizarse en la relación entre las condiciones ambientales y la distribución del género Stenella en el Atlántico Sudoccidental.

The presence of striped dolphins, Stenella coeruleoalba (Meyen,1833), in the Argentine Sea. The knowledge about the presence of striped dolphins (Stenella coeruleoalba) in the South Western Atlantic Ocean (SWAO) is very limited. Although the holotype was captured by Meyen (1833) in the La Plata River Estuary, only a few museum specimens and isolated strandings were recorded in the area. This study presents the distribution and occurrence of striped dolphins in the Argentine Sea and reviews its presence in the SWAO. S. coeruleoalba is found from 7° to 42° S, although most of the sixteen records were found between 30° and 40° S. Seventy percent of the dolphins were single stranded animals, and in the cases that sex was determined, all of them were juvenile to adult males (205–242 cm). A total amount of 10 skulls are deposited in museum collections of Brazil, Uruguay and Argentina (CBL 402–471 mm). The sightings were concentrated in late spring and summer (October–February), comprising small groups (1–4 dolphins) in relatively shallow water (30–100 m). Only a single incidental catch was recorded, being a dolphin associated with common dolphins feeding on anchovies in northern Patagonia. The colour pattern found was bluish grey in stranded animals and brownish in live dolphins, with the characteristic combination of lateral stripes and spinal blaze. The southbound warm Brazil Current may influence in the presence of striped dolphins in Uruguay and Argentina during austral summer, even though some animals were found during winter in waters of temperatures below 20° C clearly associated with the northbound cold Malvinas-Falkland Current. Future research should focus on the relationship between the environmental conditions and the distribution of the genus Stenella in the South Western Atlantic.