Abstract
Oceanic waters are difficult to assess, and there are many gaps in knowledge regarding cetacean occurrence. To fill some of these gaps, this article provides important cetacean records obtained in the winter of 2010 during a dedicated expedition to collect visual and acoustic information in the Vitória-Trindade seamounts. We observed 19 groups of cetaceans along a 1300-km search trajectory, with six species being identified: the humpback whale (Megaptera novaeangliae, N = 9 groups), the fin whale (Balaenoptera physalus, N = 1), the Antarctic minke whale (Balaenoptera bonaerensis, N = 1), the rough-toothed dolphin (Steno bredanensis, N = 1), the bottlenose dolphin (Tursiops truncatus, N = 2), and the killer whale (Orcinus orca, N = 1). Most humpback whale groups (N = 7; 78%) were observed in the Vitória-Trindade seamounts, especially the mounts close to the Abrolhos Bank. Only one lone humpback whale was observed near Trindade Island after a search effort encompassing more than 520 km. From a total of 28 acoustic stations, humpback whale songs were only detected near the seamounts close to the Abrolhos Bank, where most groups of this species were visually detected (including a competitive group and groups with calves). The presence of humpback whales at the Trindade Island and surroundings is most likely occasional, with few sightings and low density. Finally, we observed a significant number of humpback whales along the seamounts close to the Abrolhos Bank, which may function as a breeding habitat for this species. We also added important records regarding the occurrence of cetaceans in these mounts and in the Western South Atlantic, including the endangered fin whale.
Highlights
The majority of cetacean species (~53%) are classified as “Data Deficient” by the International Union for Conservation of Nature (IUCN, 2012)
The large and shallow Abrolhos Bank is the area of highest density within the known distribution of humpback whales in Brazil (Andriolo et al, 2010a), but additional records have been made near oceanic islands, such as the Archipelago of Fernando de Noronha (Lodi, 1994) and the Trindade Island (Townsend, 1935; Siciliano, 1997)
The Vitória-Trindade Chain is a range of seamounts that stretches linearly from west to east at ~21° S, beginning in the southeastern Abrolhos Bank (~38° W) and reaching its easternmost point at the Martin Vaz Archipelago and Trindade Island (~29° W) (Figure 1)
Summary
The majority of cetacean species (~53%) are classified as “Data Deficient” by the International Union for Conservation of Nature (IUCN, 2012). This lack of knowledge is partly due to the inherent difficulties of studying marine mammals, especially those inhabiting offshore waters. One of the humpback whale’s seven breeding areas in the Southern Hemisphere is located in the coastal waters of Brazil (IWC, 1998). Breeding stock A (IWC, 1998) refers to the population wintering along the eastern and northeastern coast of Brazil, from 6° to 24° S (Andriolo et al, 2010a). The large and shallow Abrolhos Bank is the area of highest density within the known distribution of humpback whales in Brazil (Andriolo et al, 2010a), but additional records have been made near oceanic islands, such as the Archipelago of Fernando de Noronha (Lodi, 1994) and the Trindade Island (Townsend, 1935; Siciliano, 1997)
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