INTRODUCTION
The populations of the genus Delphinus are distributed in tropical, subtropical and temperate waters worldwide (Jefferson et al., Reference Jefferson, Leatherwood and Webber1993) and show a high degree of morphological variation. Their taxonomy has undergone numerous revisions, with at least 30 nominal species described for the genus (Hershkovitz, Reference Hershkovitz1966). Genetic (Rosel et al., Reference Rosel, Dizon and Heyning1994) and morphological (Heyning & Perrin, Reference Heyning and Perrin1994) evidence for the existence of two species of common dolphins: a short beaked form (Delphinus delphis Linnaeus, 1758) and a long beaked one (Delphinus capensis Gray, 1828) was found in the north-eastern Pacific populations. Heyning & Perrin (Reference Heyning and Perrin1994) also proposed wide global distributions for both species. However, genetic (Natoli et al., Reference Natoli, Cañadas, Peddemors, Aguilar, Vaquero, Fernández-Piqueras and Hoelzel2006) and morphological (Bell et al., Reference Bell, Kemper and Conran2002; Murphy et al., Reference Murphy, Herman, Pierce, Rogan and Kitchener2006; Tavares, Reference Tavares2006; Westgate, Reference Westgate2007) studies are not consistent with the conclusions of Heyning & Perrin (Reference Heyning and Perrin1994).
Natoli et al. (Reference Natoli, Cañadas, Peddemors, Aguilar, Vaquero, Fernández-Piqueras and Hoelzel2006) found that the oceanic short beaked form (D. delphis) is a well-defined species, contrary to the coastal long beaked form (D. capensis sensu Heyning & Perrin, Reference Heyning and Perrin1994), which suggests that different populations may have evolved independently converging in the same morphotype.
While the taxonomic status of the south-western Atlantic population(s) of the long beaked morphotype is not clearly established, we will refer to it as Delphinus capensis, following the current diagnostic criteria used by Heyning & Perrin (Reference Heyning and Perrin1994) to distinguish D. capensis from D. delphis.
In the south-western Atlantic Ocean, D. delphis has been cited for Argentinean waters (Crespo et al., Reference Crespo, Koen Alonso, Dans, García, Pedraza, Coscarella and González2000; Bastida & Rodríguez, Reference Bastida, Rodríguez, Barquez, Díaz and Ojeda2006) and D. capensis for southern and south-eastern Brazilian waters: São Paulo, Paraná and Santa Catarina States (Santos et al., Reference Santos, de, Rosso and Ramos2002; Cherem et al., Reference Cherem, Simões-Lopes, Althoff and Graipel2004; Zerbini et al., Reference Zerbini, Secchi, Bassoi, Dalla-Rosa, Higa, Sousa, Moreno, Moller and Caon2004). Moreover, Martins et al. (Reference Martins, Ott and Danilewicz1995) reported a stranded D. delphis at the southernmost State of Rio Grande do Sul (Brazil).
Tavares et al. (Reference Tavares, Moreno, Siciliano, Rodríguez, Santos, de and Fabián2010) reviewed the biogeography of the genus Delphinus in the south-western Atlantic Ocean and proposed three stocks: one located in northern Brazil (Pará State, Stock 1: 0–1°S) and two from south-eastern Brazil (Rio de Janeiro ≈ 22°S) to central Argentina (Patagonia ≈ 42°S). These authors found two distinct patterns in habitat use stratified by water depth: in south-eastern Brazil (from 22°S to 28°S, Stock 2) sightings were restricted to coastal waters with depths ranging from 18 to 70 m, which is similar to the reported habitat for D. capensis in other parts of the world. 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 71 to 1435 m (Stock 3), which resembles the pattern observed for D. delphis (see Figure 1). According to Tavares et al. (Reference Tavares, Moreno, Siciliano, Rodríguez, Santos, de and Fabián2010), Stocks 2 and 3 include both forms (D. delphis and D. capensis) sensu Heyning & Perrin (Reference Heyning and Perrin1994).
Fig. 1. Proposed scheme of distribution of Stock 2 and Stock 3 of common dolphins in south-western Atlantic waters (Tavares et al., Reference Tavares, Moreno, Siciliano, Rodríguez, Santos, de and Fabián2010). Red patch, Stock 2; blue patch, Stock 3. States of Brazil: RJ, Rio de Janeiro; SP, São Paulo; PR, Paraná; SC, Santa Catarina; RS, Rio Grande do Sul. Provinces of Argentina: BA, Buenos Aires; RN, Río Negro; CH, Chubut.
Early Uruguayan mammals’ lists cited D. microps (Arechavaleta, Reference Arechavaleta1882; Figueira, Reference Figueira1894), a synonym of D. capensis (Heyning & Perrin, Reference Heyning and Perrin1994; Mead & Brownell, Reference Mead, Brownell, Wilson and Reeder2005). Ximénez et al. (Reference Ximénez, Langguth and Praderi1972) and Pilleri (Reference Pilleri1977) replaced that name by D. delphis. González (Reference González2001) returned to D. capensis based on Heyning & Perrin's propositions (Reference Heyning and Perrin1994). However, these last authors did not directly examine the south-western Atlantic specimens. Their results were only based on the craniometric measurements published by Casinos (Reference Casinos1984) of three specimens from Brazil, five from Argentina and two from Venezuela.
In a recent revision, Tavares et al. (Reference Tavares, Moreno, Siciliano, Rodríguez, Santos, de and Fabián2010) only found D. capensis in Uruguay (≈34°S) based on the examination of three skulls. According to the same author, there were very few records and little information was available in the scientific collections visited.
The oceanographic dynamics must be taken into account if we deal with cetacean distributions. The most relevant feature of the south-western Atlantic waters is the Subtropical Convergence (SC): cold sub-Antarctic waters from the Malvinas/Falkland Current encounter warm waters of the Brazil Current (Seeliger et al., Reference Seeliger, Odebrecht and Castello1997). This system is dynamic throughout the year. During the austral winter, the Malvinas/Falkland Current reaches lower latitudes, bathing the Uruguayan and Rio Grande do Sul State (southern Brazil) coasts. During the summer, the SC moves to the south, and the warmer Brazil Current washes the shores of Uruguay and Buenos Aires Province (Argentina) (Wainer et al., Reference Wainer, Gent and Goni2000).
The geographical closeness of the proposed stocks of Delphinus, the complex dynamics of the SC and the little information of the specific allocation of the specimens from Uruguay, lead to the question whether both forms of Delphinus occur in Uruguayan waters.
MATERIALS AND METHODS
All available Uruguayan specimens of the genus Delphinus held in national collections were reviewed. Twelve skulls were examined, but only ten were included in the analysis because of the cranial maturity: MMPE 016 (Museo del Mar de Punta del Este); MNHN 5760, 5819, 5820, 6105, 6133 (Museo Nacional de Historia Natural); ZVCM 459, 1089, 2108 (Facultad de Ciencias, Universidad de la República) and DINARA w/n (Dirección Nacional de Recursos Acuáticos). As distal fusion is not an accurate marker of cranial maturity in D. delphis (Perrin & Heyning, Reference Perrin and Heyning1993), the specimens were identified as adults based on Tavares et al. (Reference Tavares, Moreno, Siciliano, Rodríguez, Santos, de and Fabián2010): ‘fused and secure, closed sutures, closed alveoli, and distal fusion between the premaxillae and maxillae at the tip of the rostrum’. The cranial measurements were taken with a 0.1 mm precision calliper according to Perrin (Reference Perrin1975). Each measurement was repeated three times in order to obtain mean values. The diagnostic tool to discriminate the short and long beaked forms was the rostral ratio (RR) criteria presented by Heyning & Perrin (Reference Heyning and Perrin1994). The RR was calculated as the ratio of length of rostrum/zygomatic width (1.21–1.47 for Delphinus delphis and 1.52–1.77 for Delphinus capensis).
RESULTS
Four specimens were identified as Delphinus capensis, three as Delphinus delphis and three could not be determined (Delphinus sp.) because of broken beaks or intermediate value of RR (Table 1).
Table 1. Identification of Delphinus sp. specimens from Uruguay based on Heyning & Perrin (Reference Heyning and Perrin1994) criteria.
CBL, condylobasal length; r, right; l, left; LR, length of rostrum; RR, rostral ratio; ZW, zygomatic width. DINARA, Dirección Nacional de Recursos Acuáticos (Montevideo); MMPE, Museo del Mar de Punta del Este (Maldonado); MNHN, Museo Nacional de Historia Natural (Montevideo); ZVCM, Sección Zoología—Vertebrados of the Facultad de Ciencias, Universidad de la República (Montevideo).
For the specimen MNHN 5819, the value of the RR lies between long and short beaked ranges and therefore is not useful to identify it at specific level. In the case of MNHN 5760 and MNHN 5820, the RR could not be calculated because of their broken beaks. As the coloration pattern and total length of the two forms may vary from the criteria presented by Heyning & Perrin (Reference Heyning and Perrin1994), especially in the south-western Atlantic (Tavares et al., Reference Tavares, Moreno, Siciliano, Rodríguez, Santos, de and Fabián2010), these individuals were identified as Delphinus sp.
Despite the low number of specimens available, we found both forms of Delphinus in Uruguay.
DISCUSSION
The occurrence of both forms of Delphinus in Uruguayan waters does not indicate per se to which stock(s) they belong. Since Stock 2 does not reach latitudes higher than 28°S and the distribution of Stock 3 includes Uruguay (Tavares et al., Reference Tavares, Moreno, Siciliano, Rodríguez, Santos, de and Fabián2010), we confirm the existence of D. capensis and report D. delphis, not already communicated for Uruguay.
Our result is consistent with the hypothesis that the occurrence of both forms of Delphinus in Uruguayan waters could be the result of displacements of Stock 3 of short and long beaked common dolphins, probably associated with the dynamics of the SC and storms. The scarcity of records for Uruguay is consistent with the fact that Stock 3 distributes in deeper waters, far from the coastline.
The existence of intermedial RR values between the two recognized species for the Uruguayan specimens was already found for other areas in the south-western Atlantic (Tavares et al., Reference Tavares, Moreno, Siciliano, Rodríguez, Santos, de and Fabián2010), North Atlantic (Murphy et al., Reference Murphy, Herman, Pierce, Rogan and Kitchener2006; Westgate, Reference Westgate2007) and Australia (Bell et al., Reference Bell, Kemper and Conran2002). The presence of these intermedial values could respond to the fact that RR ranges proposed by Heyning & Perrin (Reference Heyning and Perrin1994) may not apply exactly to the specimens of the south-western Atlantic (see discussion in Tavares et al., Reference Tavares, Moreno, Siciliano, Rodríguez, Santos, de and Fabián2010).
On the other hand, as our information comes mostly from strandings, it provides a lineal view of the population ranges. Despite the scarcity of data and lack of reported sightings, we can draw the following conclusion: the presence of both species in Uruguayan waters is confirmed. This finding is a relevant input for a re-examination of the current approach on the distribution of the genus Delphinus in the south-western Atlantic.
ACKNOWLEDGEMENTS
We appreciate the cooperation shown by Maurício Tavares for the comments that helped to improve the manuscript. We are indebted to Julio Chocca, Bernardo González, Yamandú Marin and Gastón Beathyate (Laboratorio de Tecnología Pesquera, DINARA), Alberto Ponce de León and Cesar Barreiro (Departamento de Mamíferos Marinos, DINARA), Pablo Etchegaray (Museo del Mar of Punta del Este) and Melitta Meneghel (Facultad de Ciencias, Universidad de la República), who allowed us to examine skulls and catalogues; Enrique A. Crespo and Diego Rodríguez for literature support. This work would not have been possible without the permanent support and encouragement of Ricardo Praderi and Enrique M. González.
This contribution is dedicated to Ing. Agr. Ricardo Praderi, researcher at the Museo Nacional de Historia Natural of Montevideo. Pioneer in the cetacean studies in Uruguay, with more than 50 years dedicated to research, excellent professor and beloved friend.
