The Species
Introduction
Lahille's bottlenose dolphin (Tursiops truncatus gephyreus or Tursiops gephyreus), also known as bottlenose dolphin, mullet dolphin, or fishing dolphin, is a medium-sized dolphin from the Delphinidae family, found exclusively in shallow waters along the Atlantic coast of South America (Brazil, Uruguay, and Argentina).
Its common name honors the naturalist who first described the species in 1908 in Argentina. These dolphins can reach up to 4 meters in length and weigh up to 400 kg. They have a rounded head, a maxilla slightly shorter than the mandible, a short rostrum, and a well-defined melon. Their coloration features a gradient of gray tones, dark on the back and gradually lightening towards the belly. The dorsal fin is triangular with a broad base, often displaying natural long-lasting marks used to distinguish individuals. Their reproductive season occurs between spring and summer.
Lahille's bottlenose dolphins can live up to approximately 50 years, with females typically living longer than males. They live in complex societies and exhibit specific cultural behaviors, such as cooperative fishing
Distribution
Lahille's bottlenose dolphin is endemic to the coastal waters of the Southwestern South Atlantic Ocean, distributed between southern Brazil, Uruguay, and Argentina, within latitudes 25°S and 46°S.
It inhabits shallow marine waters up to 30 meters deep, near the surf zone, typically within 3 km of the shore, and is associated with coastal water bodies such as lagoons, bays, and estuaries, where it forms resident populations year-round.
Although Lahille's bottlenose dolphins tend to show long-term and intergenerational fidelity to the areas where they are born, data from the Gephyreus Project has revealed movements of individuals between some Management Units, ranging from tens to hundreds of kilometers within a few days.
At the Gephyreus Project, we monitor 10 study areas:
- In Brazil: the coastal areas of Itajaí and Florianópolis (Baía Norte), the Laguna estuary, the mouths of the Araranguá, Mampituba, and Tramandaí rivers, and the estuarine and coastal areas of Lagoa dos Patos.
- In Uruguay: coastal areas between La Coronilla and La Paloma/Cabo Polonio.
- In Argentina: areas between Bahía Blanca and Bahía de San Antonio.
Population and Abundance
Two genetically and geographically isolated subpopulations of Lahille's bottlenose dolphin are known. The southern Brazil-Uruguay subpopulation ranges from the state of Paraná to the Uruguayan coast. The Argentine subpopulation occurs from the southern part of Buenos Aires Province to Chubut Province. The Rio de la Plata estuary and the northern coast of Buenos Aires Province mark the geographic boundary between these populations.
In Argentina, there is one Management Unit (Bahía San Antonio), while the southern Brazil-Uruguay subpopulation consists of at least five: southern Lagoa dos Patos-Uruguay, Lagoa dos Patos estuary, northern Lagoa dos Patos, Laguna, and Florianópolis.
Abundance estimates indicate a total population size of fewer than 500 individuals across the species' entire distribution. The total abundance for the Argentine subpopulation is estimated to be below 200 individuals, while the southern Brazil-Uruguay subpopulation is estimated at approximately 300 individuals.
In Brazil, Lagoa dos Patos hosts the largest known population of Lahille's bottlenose dolphins. Cooperative fishing between dolphins and artisanal cast-net fishers actively and frequently occurs in the Laguna estuary and Barra do Rio Tramandaí.
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Cooperative Fishing
Cooperative fishing is a specialized foraging tactic unique to Lahille's bottlenose dolphin. It involves a rare interaction of cooperation with artisanal cast-net fishing.
Cooperative fishing occurs actively and frequently only in the Laguna estuary (Santa Catarina) and Barra de Tramandaí (Rio Grande do Sul), with historical and occasional records at the mouths of the Araranguá (SC) and Mampituba (RS) rivers. It is also known as "dolphin fishing" or "dolphin run."
In this interaction, dolphins and fishers move in sync to catch mullet (Mugil liza), benefiting both parties. The dolphins herd the schools of fish toward the shore, where the fishers are positioned. With characteristic body signals, the dolphins indicate the best moment for the cast-net fishers to throw their nets. The mullet are corralled and captured more easily by both the dolphins and the fishers, ensuring greater fishing success with less effort!
Mutualistic interactions between humans and cetaceans are extremely rare worldwide. Currently, this occurs only in southern Brazil and Myanmar, on the coast of Asia, involving another dolphin species (Orcaella brevirostris).
Threats
Evidence indicates that Lahille's bottlenose dolphin is declining across its distribution range, primarily due to bycatch in fishing nets and the degradation of its habitats.
Pollution (chemical, waste, and noise), depletion of prey, rapid and unregulated urban growth (such as infrastructure projects and coastal industrial activities), accidental vessel collisions, and the lack of coastal management represent significant threats to Lahille's bottlenose dolphin. Each subpopulation faces unique conservation concerns.
The Argentine subpopulation is particularly notable for its small size, historically observed range reduction, apparent genetic and geographic isolation, and low genetic diversity. Meanwhile, the southern Brazil-Uruguay subpopulation could decline by approximately 23% within a single generation if current environmental conditions and bycatch rates do not improve.
The small population size and restricted distribution in coastal waters, which are heavily impacted by human activities, justify the inclusion of Lahille's bottlenose dolphin in threatened species categories.
Status de Conservação
Currently, Lahille's bottlenose dolphin is globally classified as “Vulnerable” according to the criteria of the International Union for Conservation of Nature (IUCN).
In Brazil, Argentina, and Uruguay, Lahille's bottlenose dolphin is considered “Endangered.” This means that, without protection, there is a possibility that this species could disappear in the not-too-distant future.
For this reason, initiatives like the Gephyreus Project are underway! By systematizing and sharing population data among study areas, it is possible to monitor the status of subpopulations and gain deeper insights into Lahille's bottlenose dolphin. This information aims to support national and international conservation strategies and public policies.
These efforts are also communicated and shared with local communities, mobilizing partner stakeholders and contributing through environmental education to foster an appreciation for nature and socio-environmental culture.
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