Vessel -Induced Behavioural Changes in Striped and Bottlenose Dolphins in Southern Spain

Abstract

The interactions of commercial vessels that operate by sighting dolphins and other types of vessels can have detrimental effects on cetacean populations. Dolphins may suffer short-term effects that could trigger other long-term and even irreversible effects. Behavioural changes in groups of striped dolphins, Stenella coeruleoalba, and bottlenose dolphins, Tursiops truncatus, were analysed in the Bay of Algeciras, Gibraltar, southern Spain. The reactions (Approach, Elusive and Indifference) of the dolphins to the boats were observed before each sighting began. The data was analysed only when the dolphins interacted with the boat collecting the data (Control situation) and when they interacted with more than one boat (Impact Situation). We distinguished between the sightings that complied with the cetacean approach protocol (regulated) and those that did not (unregulated). The behavioural states were classified into 5 categories: Feeding (F), Milling (M), Socialising (S), Travelling (T) and Diving (D), although it was not always possible to observe them all. It was concluded that the presence of boats and the failure to comply with the protocol for approaching cetaceans were the main causes of the behavioural transitions that led to an absorbing diving state in the Markov chains. The results showed that feeding behaviour was significantly altered, which can have negative consequences for the dolphins. The results obtained highlight the importance of implementing conservation plans that regulate maritime traffic, establish protection zones, and develop continuous monitoring programmes to ensure the survival of these species in their natural habitat.