Setúbal Dolphins
Bottlenose dolphins (Tursiops truncatus). illustration NOAA Fisheries .
Evolution and Anatomy
Measures and Behaviors
of the Sado Population
scientific articles and others
Setúbal Dolphins
Biology
Tursiops truncatus
Common name: Bottlenose dolphin
Scientific name: Tursiops truncatus
Common bottlenose dolphins are probably the best-known species of dolphin and get their name from their short, thick snout (or rostrum).
They are distinguished from other species for their darker color (dark gray) and for being large animals. Adults range from 1.9 to 3.8 m and there is a wide variation between different populations.
Communication | Guidance
Dolphins are acoustic specialists. How they interact with each other and with the environment depends on their sensory system.
It is through the lower jaw that they receive the sound, as the outer ears are not functional. They use Ecolocation to detect their position and / or the distance between objects and other animals (for example, schools of fish). They do this through the emission of ultrasonic waves, which reflect on the target and return to the dolphin again in the form of an echo.
They communicate through whistles, clicks or other sounds (click on the player to listen).
Social Animals
Bottlenose dolphins are pretty sociable animals and they live mostly in groups. It’s common to see them socialize with other coastal dolphins. They are very active at the surface, that’s why we can observe some jumps and acrobatic movements.
They are for sure very curious, what makes them approach to boats and in some times they go with the boat, like a race for them.
Sado dolphins have 4 main activity patterns: traveling, foraging, socializing and resting.
- Traveling is the most frequently observed pattern. It is characterized by submersions of dolphins in a single group and in a generally well-defined swimming direction, usually with short submersions.
- Foraging, perhaps the second most frequent pattern, is characterized by fast and erratic movements on the surface, sometimes with hunting cooperation between individuals.
- During Socialization it is usual to observe interaction behaviors between them, such as synchronized jumping and physical contact, usually in small groups of 2 or 3 individuals.
- When very slow movements are noticed on the surface just to breathe, in a cohesive group with a constant direction, the dolphins are at Resting.
In 2017 were born 3 dolphins
Between 8 and 12 years of age, dolphins reach sexual maturity and are ready to mate. The gestation period lasts 12 months, where only a single calf is born.
All efforts are made to ensure the survival of the offspring and their development. Dependence on the mothers can last between 2 to 6 years, which implies long time gaps between each pregnancy.
All is grist to the mill
They are considered an opportunistic and generalist species, due to their ability to adapt their diet to the availability of prey. In the Sado estuary it is common to see them eating mullets, sea bass, cuttlefish, octopuses, crustaceans, among others.
Sometimes they hunt in groups, cooperating with each other. They often hunt in shallow areas, such as the sand banks of the estuarine delta, trapping the fish against the banks, with rapid movements on the surface. It is common to see individuals flinging prey through the air.
The main reason why they chose the Sado estuary to settle was for its biodiversity, abundance and biomass of its prey.
Setúbal Dolphins
Conservation
"The sea, once it casts its spell, holds one in its net of wonder forever."
Jacques Yves Cousteau
Despite the bottle nose dolphins are classified as “non endangered species”, in Portugal the resident population of dolphins are considered “fragile” because it’s low number of individuals, consanguinity problems and other factors of the population like slow reproduction.
It’s the only resident population of dolphins living in Portugal and one of the few 3 in all Europe. That’s why it as so much protection and all studies for now aim to their well being and conservation.
“Know to protect” is the goal, and all the dolphin watching activities should be regulated and managed by the “code of conduct”.
"The sea unifies, it's men's last hope. Now more than ever the meaning of this words aims to alert us that "we are all in the same boat."
Jacques Yves Cousteau
Bottlenose dolphin is classified as “non endangered species” (UICN, 2003) in Portugal and Europe.
The species is protected by international, European and national legislation:
- Convention on International Trade in Endangered Species of Wild Fauna and Flora” (CITES);
- Bern Convention -a binding international legal instrument in the field of nature conservation;
- The Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and contiguous Atlantic area (ACCOBAMS);
- European Directive 2009/147/EC.
- And Whale watching national mainland legislation published in January 2006 (Decree-Law nr. 9/2006).
"Since birth, men carries the weight of gravity on its shoulder. It's stuck to Earth. But man only needs to dive below surface and it's free."
MAHATMA GANDHI
The Action Plan for the conservation of wildlife and the resident population of dolphins in Sado estuary, aims to define a set of strategies for the conservation and protection of the population.
On this sense the Natural reserve of Sado estuary (RNES) as gathered since 2008 some meeting with partners in order to define the basis of this plan of action.
One of the projects developed in this plan is “Roazes do Sado project” that aims to alert all navigators before and during the dolphin watching.
Setúbal Dolphins
History
Oldest record in history
José Vicente Barbosa du Bocage was the first writer who described the existence of dolphins in Sado estuary.
First scientific records
The first scientific records about the dolphins in Sado estuary began in 1980 with the works of Teixeira & Duguy (1981), Hussenot (1982), Dos Santos (1985) e Dos Santos & Lacerda (1987).
In 1981 is officially published the first Regulation for Protection of Marine Mammals on the Portugue coast (in portuguese).
the day a dolphin flew
Twenty years ago one of the Sado dolphins, “Asa”, flew over the Sado estuary, hoisted by a Portuguese Air Force helicopter. This was the solution to save him after he was trapped in a river mat, most likely while hunting.
Population decreased to the smallest number
In 2005 the population of dolphins in Sado estuary decreased to 22 individuals.
However we can consider this year as a wind of change, because from this date on the population increased its numbers and mortality rates of calf’s decreased, since 2005 have born 17 dolphins and only 4 are not present in the population.
BEGINNING OF THE Awareness Project
From 2015 the project “Sado Dolphins” was put in works, promoted by “Tróia Natura” in partnership with ICNF (Natural park reservation), this project aims to alert all navigators in Sado estuary to adopt good behaviour and attitude in the presence of dolphins.
During the summer months is very common to see the protection team in action.
THEY'RE ABOUT 30 DOLPHINS
The resident population of dolphins from Sado estuary as nowadays about 30 dolphins. 22 adults, from which 8 females, 5 males and 9 of them not yet sexual known. 4 Juveniles and 4 calf’s complete the population.
chronologically ordered
Bibliography
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Underwater vocalization of bottlenose dolphins in the region of the Sado estuary: acoustic features and occurence patterns
Alves, I.S.C. 2017. Tese de Mestrado, Faculdade de Ciências da Universidade de Lisboa. 38 pp.
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Estudo da utilização espácio-temporal do estuário do Sado pela população residente de roazes (Tursiops truncatus), com recurso a um método goniométrico.
Costa, M. 2017. Tese de Mestrado, Faculdade de Ciências da Universidade de Lisboa. 60 pp.
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A Quantitative Analysis of Pulsed Signals Emitted by Wild Bottlenose Dolphins
Luís, A. R., Couchinho, M. N., & Dos Santos, M. E. (2016). PloS one, 11(7), e0157781. doi:10.1371/journal.pone.0157781
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Avaliação de potenciais impactos da actividade da pesca na população de roazes do Estuário do Sado
Ferreira, P.A.C., 2012.Tese de Mestrado, Faculdade de Ciências da Universidade de Lisboa. 39 pp.
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Residency and behavioural patterns of coastal bottlenose dolphins (Tursiops truncatus) in the Arrábida and Tróia shores (Portugal)
Martinho, F.O.M.M., 2012. Tese de Mestrado, Faculdade de Ciências da Universidade de Lisboa. 80 pp.
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Vocalizações dos golfinhos-razes (Tursiops truncatus) residentes na região do estuário do sado e estudo da influência do tráfego marítimo nos padrões de emissão dos assobios
Rocha, A.I.L. 2012. Dissertação de Mestrado em Ciências do Mar – Recursos Marinhos, Instituto de Ciências Biomédicas Abel Salazar, da Universidade do Porto. 97 pp.
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The environmental history of cetaceans in Portugal: ten centuries of whale and dolphin records.
Brito, C., & Sousa, A. 2011. PLoS ONE 6(9): e23951. doi:10.1371/journal.pone.0023951
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Movimentos e atividades dos golfinhos-roazes (Tursiops truncatus) na zona terminal do estuário do Sado e possíveis influências ecológicas.
Ferreira, M.C.V. 2010. Mestrado em Ecologia Marinha. Universidade de Lisboa, Faculdade de Ciências, Departamento de Biologia Animal, Lisboa. 56 pp.
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Estudo da utilização do território pela população de roazes (Tursiops truncatus) do estuário do Sado a partir de dados obtidos em embarcações de Dolphin Watch.
Grilo, S.I.B.E., 2010. Tese de Mestrado, Faculdade de Ciências da Universidade de Lisboa. 86 pp.
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Bases para o plano de ação para a salvaguarda e monitorização da população de roazes do estuário do Sado.
Sequeira, M.; Matias S., Farinha J.C., Gaspar R., Silva C., Augusto J., Ferreira C., Fonseca M.J., Narra P. e Luís, A.R. 2009. Instituto da Conservação da Natureza e da Biodiversidade: 80 pp.
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Avaliação do impacto de construções portuárias no comportamento e no ambiente acústico da população de golfinhos-roazes (Tursiops truncatus) do estuário do Sado.
Luís, A.R.F. 2008. Mestrado em Ecologia e Gestão Ambiental. Universidade de Lisboa, Faculdade de Ciências, Departamento de Biologia Animal, Lisboa. 110 pp.
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A população residente de Tursiops truncatus num quadro de gestão integrada do estuário do Sado: Proposta de um acordo voluntário.
Silva, C. 2008. Tese de Mestrado, Faculdade de Ciências da Universidade de Lisboa. 114 pp.
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Análise da estrutura social, da composição dos grupos e associações nos golfinhos-roazes (Tursiops truncatus) residentes na região do Sado.
Augusto, J.F.F. 2007. Mestrado em Ecologia Marinha. Universidade de Lisboa, Faculdade de Ciências, Departamento de Biologia Animal, Lisboa. 65 pp.