We reviewed prominent emerging infectious diseases of cetaceans, examined their potential to impact populations, re-assessed zoonotic risk and evaluated the role of environmental stressors. Cetacean morbilliviruses and papillomaviruses as well as Brucella spp. and Toxoplasma gondii are thought to interfere with population abundance by inducing high mortalities, lowering reproductive success or by synergistically increasing the virulence of other diseases. Severe cases of lobomycosis and lobomycosis-like disease (LLD) may contribute to the death of some dolphins. The zoonotic hazard of marine mammal brucellosis and toxoplasmosis may have been underestimated, attributable to frequent misdiagnoses and underreporting, particularly in developing countries and remote areas where carcass handling without protective gear and human consumption of fresh cetacean products are commonplace. Environmental factors seem to play a role in the emergence and pathogenicity of morbillivirus epidemics, lobomycosis/LLD, toxoplasmosis, poxvirus-associated tattoo skin disease and, in harbour porpoises, infectious diseases of multifactorial aetiology. Inshore and estuarine cetaceans incur higher risks than pelagic cetaceans due to habitats often severely altered by anthropogenic factors such as chemical and biological contamination, direct and indirect fisheries interactions, traumatic injuries from vessel collisions and climate change.

The distribution of dolphins of the genus Stenella is poorly known in the southwest Atlantic Ocean. A complete review of records (n = 311) of these dolphin species was performed to describe distribution and habitat. Atlantic spotted dolphins S. frontalis occur in both southern (21 to 33°S) and northern Brazil (north of 06°S), with a hiatus in its distribution off eastern South America. This species presents the highest preference for nearshore habitats, restricted to waters within the 1000 m isobath. Pantropical spotted dolphins S. attenuata are found in tropical waters as far south as 22°S and are mainly observed off northeastern South America. They occur beyond the continental shelf break in depths > 850 m. Clymene dolphins S. clymene are distributed in deep waters (1390 to 4500 m) as far south as 30°S. Strandings are more common where the continental shelf is narrower. Spinner dolphins S. longirostris are found in oceanic waters as far south as 30°S. They inhabit tropical waters over the shelf and slope (depths ranging from 170 to 2700 m). The striped dolphin S. coeruleoalba is the least known species of the genus in the western South Atlantic. Most records are from temperate waters in southern Brazil and Argentina. The distributions of S. attenuata, S. clymene and S. longirostris overlap to a great extent and are predominantly oceanic and associated with warm ocean currents. S. frontalis seems to prefer a different, coastal habitat, influenced both by warm currents and upwelling areas. The discontinuous distribution of this species suggests that an isolated population inhabits the southern coast of Brazil.

Dolphins of the genus Sotalia are found along the Caribbean and Atlantic coasts of Central and South America and in the Amazon River and most of its tributaries. At present, the taxonomy of these dolphins remains unresolved. Although five species were described in the late 1800s, only one species is recognized currently (Sotalia fluviatilis) with two ecotypes or subspecies, the coastal subspecies (Sotalia fluviatilis guianensis) and the riverine subspecies (Sotalia fluviatilis fluviatilis). Recent morphometric analyses, as well as mitochondrial DNA analysis, suggested recognition of each subspecies as separate species. Here we review the history of the classification of this genus and present new genetic evidence from ten nuclear and three mitochondrial genes supporting the elevation of each subspecies to the species level under the Genealogical/Lineage Concordance Species Concept and the criterion of irreversible divergence. We also review additional evidence for this taxonomic revision from previously published and unpublished genetic, morphological, and ecological studies. We propose the common name “costero” for the coastal species, Sotalia guianensis (Van Bénéden 1864), and accept the previously proposed “tucuxi” dolphin, Sotalia fluviatilis (Gervais, 1853), for the riverine species.

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