Rough-toothed dolphins (Cetartiodactyla: Delphinidae) habitat use in coastal urban waters of the South-western Atlantic

Abstract

Rough-toothed dolphins (Steno bredanensis) are regularly present in continental shelf areas of the South-western Atlantic. However, there is little information on the natural history and ecology of these delphinids. This study evaluated the occurrence, habitat use and individual movements of the species in coastal waters off Rio de Janeiro, south-eastern Brazil. Data were obtained from boat surveys between August 2011 and May 2018, during which rough-toothed dolphins were sighted in 21 distinct events, predominantly in autumn and winter. The mean group size was 29 individuals. Rough-toothed dolphins were usually recorded 130 to 2300 m from the coast, between 7.6 and 28 m depths. In total, 115 individuals were catalogued through dorsal fin marks and 61 (53%) were resighted between one (47.5%) and four (9.8%) occasions. The interval between resightings ranged from seven to 2087 days (mean = 268). Agglomerative hierarchical clustering indicated 30 individuals (49.2%) in low degree, 12 (19.7%) in medium degree and 19 (31.1%) in high degree of site fidelity. Dolphins showed a higher frequency of low degree of habitat use, despite the presence of multiyear recaptures, which may be related to the prevalence of dolphin occurrence in autumn and winter, a large home range and/or the abundance and distribution of food resources. Dedicated surveys and regional collaboration are needed to evaluate the home range and population status of this species for their effective conservation. Our findings enhanced knowledge of this little studied species facing increasing anthropogenic threats in coastal waters off Rio de Janeiro.

Shallow‐water habitat use and population parameters of rough‐toothed dolphins, Steno bredanensis (G. Cuvier in Lesson, 1828) in southeastern Brazil

“…The inner portions of GB could constitute important feeding grounds for S. bredanensis , as recently observed by Lodi and Maricato (2020). Off‐effort sightings suggested that this species could be using the area more than expected.…”

“…In Brazil, one study has investigated the population structure of S. bredanensis and documented the presence of a southeastern population (Silva et al, 2015). However, mark-recapture efforts with the sole aim of investigating nearshore occurrences are still scarce, and only a few records have been documented, which have suggested that individual site fidelity is linked to aspects of habitat use (Lodi & Maricato, 2020). Furthermore, dedicated efforts to investigate population abundance are lacking in the SWAO.…”

Long-Term Consequences of High Polychlorinated Biphenyl Exposure: Projected Decline of Delphinid Populations in a Hotspot for Chemical Pollution

“…Certain overlaps observed between rough-toothed dolphins and Guiana dolphins raise concerns about the long-term viability of rough-toothed dolphin populations inhabiting coastal areas, such as site fidelity to polluted areas and in foraging grounds . Rough-toothed dolphins from SE Brazil are observed year-round in the coast of RJ state using enclosed bays, as the GB, which are relevant foraging areas for this apex predator, but also increase the risk of exposure to pollutants. Therefore, assessing the damage that such pollutants may cause to coastal populations of rough-toothed dolphins becomes imperative.…”

“…These areas are also important for several cetacean species. The Guanabara Bay, for example, located in the metropolitan area of Rio de Janeiro state, in SE Brazil, is one of the most degraded environments on the Brazilian coast, highly eutrophic, and yet an important resource supplier to rough-toothed dolphins. , Most samples from this site were collected inside or around the area of the Guanabara Bay.…”

A solitary rough-toothed dolphin (Steno bredanensis) in a superport area on northern Rio de Janeiro State, SE Brazil

“…The rough-toothed dolphin inhabits tropical, subtropical and warm-temperate waters in all three major oceans, mostly between 40°N and 35°S. This species usually occurs in oceanic waters deeper than 1,000 m, but also in shallower waters (until 30 m or less) (West et al 2011;Jefferson 2018;Lodi & Maricato 2020). This species lives in relatively small groups, mostly ranging from 10-20 individuals, although larger groups up to 50 or more individuals and mixed groups in association with other species have been documented (Jefferson 2018).…”