Biogeography of common dolphins (genus Delphinus) in the Southwestern Atlantic Ocean

Abstract

1. The common dolphins (genus Delphinus) have one of most problematic taxonomies and complex distribution patterns of all cetaceans. Although the taxonomy and the distribution seem to have been clarified somewhat in the eastern North Pacific and Indo-Pacific Oceans, many questions remain in the Southwestern Atlantic Ocean (SWA). We review the biogeography of Delphinus in the SWA. 2. We reviewed data from strandings, incidental catches and sightings since 1922. Systematic surveys were conducted in five major areas. Twenty-one natural history collections were examined, and 135 skulls were measured. 3. A total of 184 records of common dolphins were compiled. Delphinus apparently occurs in three stocks in the SWA: one located in northern Brazil and two from southeastern Brazil (~22°S) to central Argentina (~42°S). Two distinct patterns in habitat use were observed by depth: in southeastern Brazil, sightings were restricted to coastal waters with water depths ranging from 18m to 70m. On the other hand, in the area that extends from southern Brazil to Central Argentina (from 28°S to 42°S), sightings were recorded in deeper waters, ranging from 71m to 1435m, with the exception of occasional coastal sightings. The cranial analyses demonstrated that both short-beaked common dolphins Delphinus delphis and long-beaked common dolphins Dephinus capensis occur in the SWA. 4.In the SWA, Delphinus seems to occur near areas of high productivity. One stock is associated with the productive waters discharged by the Amazon River and possibily with the coastal upwelling system off the coast of Venezuela, while the other stocks are associated with the Cabo Frio upwelling system and the Subtropical Convergence. Our results indicate that the current taxonomy does not adequately reflect the amount of variation within the genus in the world.

Cetacean records along São Paulo state coast, Southeastern Brazil

“…With the discovery of a main breeding area off southern Brazil (~27 o S) (OTT et al, 2008), the recovery of the right whale population from past exploitation may be expanding the breeding area to include protected bays in southeastern Brazil. The northern coast of SP state has shallow protected bays which have been used by female-calf pairs during the last 20 years (see LODI et al, 1996;SANTOS et al, 2001a (see ZERBINI et al, 2004;MORENO et al, 2005;TAVARES et al, 2010), as well as for the higher incidence of these species' strandings. A few records have related to strays from their currently known range -such as B. arnuxii, M. europaeus and L. peronii.…”

Ecological niche modeling of Stenella dolphins (Cetartiodactyla: Delphinidae) in the southwestern Atlantic Ocean

“…This area is under the domain of the high pressure center of the Atlantic anticyclone which controls the climate and determines the large-scale oceanographic circulation. The main currents of the SWA are the South Equatorial, Brazil and Malvinas Currents (Moreno et al, 2005;Seeliger et al, 1997;Tavares et al, 2010).…”

“…Considering the large cetaceans dispersal ability and not obvious geographical barriers to dolphins, the geographical extent of the models and the background sampling was restrict to the SWA, which comprises waters south of Equator and west of 20°W (Moreno et al, 2005;Tavares et al, 2010). This area is under the domain of the high pressure center of the Atlantic anticyclone which controls the climate and determines the large-scale oceanographic circulation.…”

Post-glacial habitat release and incipient speciation in the genus Delphinus

“…Elsewhere in the world there are long-beaked populations (of the 'capensis' type) proposed to occur off Peru, Chile, Venezuela, Brazil, Argentina, South Africa, Madagascar, India, Indonesia, China, Korea and southern Japan (see Hammond et al, 2008;Jefferson et al, 2008), although for a number of these locations occurrence is not well documented. Based on the 'rostral index' (rostrum length/zygomatic width ratio, see below), Cunha et al (2015) identified 5 'delphis' and 9 'capensis' types off Brazil and Argentina among the 14 skulls they measured, and Tavares et al (2010) identified 47 of 59 measured skulls from this region as the 'capensis' type. However, Cunha et al (2015) suggest that D. capensis should not be used to refer to the long-beaked form, and instead the lbENP form should again be recognized as D. bairdii and all other populations recognized as D. delphis.…”