Loading...
Publication
The effects of vessel traffic on the behavioural patterns of common dolphins, in Tagus estuary, Portugal
| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 1016.19 KB | Adobe PDF |
Advisor(s)
Abstract(s)
O impacto das embarcações nas populações de golfinhos tem sido extensivamente
estudado a nível mundial. O golfinho-comum, Delphinus delphis, tem visitado o estuário do
Tejo nos últimos dois séculos e, nos últimos anos, tem existido um aumento dos avistamentos.
Esta área possui elevados níveis de tráfego marítimo ao longo do ano, onde tanto embarcações
comerciais quanto de lazer são frequentes. Este estudo fornece os primeiros dados relativos às
interações entre golfinhos e embarcações. Para compreender os possíveis efeitos da presença
de embarcações no comportamento dos golfinhos, foram realizadas observações a partir de terra
de março de 2022 a março de 2023. O tempo despendido em cada comportamento foi diferente
quando as embarcações estavam próximas dos golfinhos: os golfinhos-comuns passaram menos
tempo em alimentação e deslocação, enquanto o tempo gasto em busca de presas e socialização
aumentou. No entanto, não foram encontradas diferenças significativas. A reação neutra foi a
mais observada, sendo que o modelo GEE mostrou diferenças estatísticas entre as diferentes
reações (positiva, neutra e negativa). Utilizando as cadeias de Markov, as probabilidades de
transição comportamental observadas foram diferentes em ambos os cenários (ausência vs
presença de embarcações): a probabilidade de transição para um estado de deslocação aumentou
quando as embarcações estavam por perto. Este estudo é o primeiro passo para compreender
uma potencial fonte de impacto, uma vez que se espera que as empresas de turismo se expandam
devido ao aumento de avistamentos de golfinhos.
ABSTRACT: The impact of vessels on dolphins' populations has been extensively studied worldwide. The common dolphin, Delphinus delphis, has been visiting the Tagus estuary for the past two centuries, and during the last years, the sightings seem to have increased. This area has high levels of maritime traffic throughout the year, where both commercial and recreational vessels are frequent. This study provides the first insight into the interaction between dolphins and vessels. To understand the possible effects of vessel traffic on the dolphins’ behaviour, land-based observations were carried out from March 2022 to March 2023. The behavioural budgets were different when vessels were in the vicinity of dolphins: common dolphins spent less time surface feeding and travelling, while the time spent foraging and socializing increased. However, no statistical differences were found. The neutral reaction was the most observed reaction, and the GEE model showed statistical differences between the different reactions (positive, neutral and negative). Using Markov chains, behavioural transition probabilities were different in both scenarios (absence vs presence of vessels): the dolphins were more likely to transition to a travelling state when vessels were nearby. This study is the first step towards understanding a potential impact source since it is expected that tourism companies expand due to the increase in dolphin’ sightings.
ABSTRACT: The impact of vessels on dolphins' populations has been extensively studied worldwide. The common dolphin, Delphinus delphis, has been visiting the Tagus estuary for the past two centuries, and during the last years, the sightings seem to have increased. This area has high levels of maritime traffic throughout the year, where both commercial and recreational vessels are frequent. This study provides the first insight into the interaction between dolphins and vessels. To understand the possible effects of vessel traffic on the dolphins’ behaviour, land-based observations were carried out from March 2022 to March 2023. The behavioural budgets were different when vessels were in the vicinity of dolphins: common dolphins spent less time surface feeding and travelling, while the time spent foraging and socializing increased. However, no statistical differences were found. The neutral reaction was the most observed reaction, and the GEE model showed statistical differences between the different reactions (positive, neutral and negative). Using Markov chains, behavioural transition probabilities were different in both scenarios (absence vs presence of vessels): the dolphins were more likely to transition to a travelling state when vessels were nearby. This study is the first step towards understanding a potential impact source since it is expected that tourism companies expand due to the increase in dolphin’ sightings.
Description
Dissertação de Mestrado realizada sob a
orientação de Professora Doutora Ana Rita Francisco Luís,
apresentada no Ispa - Instituto Universitário para
a obtenção de grau de Mestre na especialidade
de Biologia Marinha e Conservação.
Keywords
Golfinhos-comuns Embarcações Behavioural budgets Estuário do Tejo Cadeias de Markov Common dolphins Vessel traffic Behavioural budgets Tagus estuary Markov chains