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The conservation of humpback dolphins, distributed in coastal waters of the Indo-West Pacific and eastern Atlantic Oceans, has been hindered by a lack of understanding about the number of species in the genus ( Sousa) and their population structure. To address this issue, we present a combined analysis of genetic and morphologic data collected from beach-cast, remote-biopsied and museum specimens from throughout the known Sousa range. We extracted genetic sequence data from 235 samples from extant populations and explored the mitochondrial control region and four nuclear introns through phylogenetic, population-level and population aggregation frameworks. In addition, 180 cranial specimens from the same geographical regions allowed comparisons of 24 morphological characters through multivariate analyses. The genetic and morphological data showed significant and concordant patterns of geographical segregation, which are typical for the kind of demographic isolation displayed by species units, across the Sousa genus distribution range. Based on our combined genetic and morphological analyses, there is convincing evidence for at least four species within the genus ( S. teuszii in the Atlantic off West Africa, S. plumbea in the central and western Indian Ocean, S. chinensis in the eastern Indian and West Pacific Oceans, and a new as-yet-unnamed species off northern Australia). [ABSTRACT FROM AUTHOR]

Due to indications that misidentification (largely confusion among dolphins of the genera Delphinus and Stenella) in the past had led to erroneous assumptions of distribution of the two species of common dolphins ( Delphinus delphis and D. capensis) in the western Atlantic Ocean, we conducted a critical re-examination of records of the genus Delphinus from this region. We compiled 460 ‘plottable’ records, required support for confirmation of genus and species identifications, and found many records lacking (and some clearly misidentified). When we plotted only the valid records ( n = 364), we found evidence of populations in only three areas, and apparent absence throughout much of the tropical/subtropical regions. Off the east coast of the US and Canada, D. delphis is found from the Georgia/South Carolina border (32°N) north to about 47–50°N off Newfoundland. Since the 1960s, they have apparently been absent from Florida waters. There is no evidence that dolphins of the genus occur in the Gulf of Mexico. Reports of common dolphins from most of the Caribbean Basin are also rejected, and the only place in that region where they are confirmed to occur is off central-eastern Venezuela (a coastal D. capensis population). Off eastern South America, common dolphins appear to be restricted to south of 20°S. There is a coastal long-beaked population found in the South Brazil Bight, and one or more short-beaked populations south and offshore of this (ranging south to at least northern Argentina). The results are very different from commonly-accepted patterns of distribution for the genus in the Atlantic. Most areas of distribution coincide with moderate to strong upwelling and common dolphins appear to avoid warm, tropical waters. This study shows that great care must be taken in identification of similar-appearing long-beaked delphinids, and that uncritical acceptance of records at face value can lead to incorrect assumptions about the ranges of the species involved. [ABSTRACT FROM AUTHOR]

ABSTRACT 1. The Clymene dolphin Stenella clymene is found in tropical and warm temperate waters of both the North and South Atlantic Oceans. Confusion surrounding the identifying characteristics of this species has contributed to a general lack of knowledge of this species. 2. We collected and verified a total of 195 records (109 sightings, 67 strandings, and 19 captures) of Clymene dolphins. Twenty-five per cent (n = 49) of these records were previously unpublished. Rejected records are discussed in order to clarify the literature. 3. The northernmost locations for the Clymene dolphin are 39°17′N, 74°35′W (NJ, USA) and 19°1.9′N, 16°13.5′W (113 km north of Nouakchott, Mauritania). The southernmost locations are 29°58′S, 50°07′W (Tramandaí, Rio Grande do Sul, Brazil) and 3°40′S, 18°5′W (off Ascension Island). 4. Clymene dolphins were found in waters with bottom depths ranging from 44 to 4500 m (mean = 1870 m; SE = 110 m; median = 1675 m; n = 94). A single sighting reported at a location with a bottom depth of 44 m is considered to be atypical, as this species has an otherwise exclusively oceanic distribution. 5. Group sizes ranged from at least one individual in a mixed-species school of spinner dolphins Stenella longirostris to a group of an estimated 1000 animals (mean = 76.1; SE = 11; median = 47; n = 105). Stranding group size ranged from 1 to 46 individuals (n = 67), with single individuals being most common (n = 60). There is information available for seven mass strandings, all of which occurred in the south-eastern USA. [ABSTRACT FROM AUTHOR]