Effects of tourist boats on the behaviour of  Indo-Pacific bottlenose dolphins off the south coast of Zanzibar

Abstract

The short-term effects of tourist boats on the behaviour of Indo-Pacific bottlenose dolphins Tursiops aduncus were investigated off the south coast of Zanzibar, Tanzania, by comparing dolphin group behaviour in the presence (impact) and absence (control) of tourist boats. Groupfollows were conducted from a carefully maneuvered (non-invasive) independent research vessel and behavioural data on group activity were collected using scan sampling methods. By using a timediscrete Markov chain model, the transition probabilities of passing/changing from one behavioural state to another were calculated and compared between impact and control situations. The data were further used to construct behavioural budgets. In the presence of tourist boats, dolphins were less likely to stay in a resting or socialising activity but were more likely to start travelling or foraging, as inferred from the Markov chain model. The behavioral budgets showed that foraging, resting and socialising all decreased as an effect of tourist boat presence, while travelling increased. The behavioural responses are likely to have energetic implications, mainly by increasing physical demands.Further, the results demonstrate that the current level of tourism intensity off the south coast of Zanzibar affects the dolphins' cumulative behavioural budget. Regulations on dolphin tourism are therefore urgently needed to minimise potential long-term negative effects on the dolphins.

Changes in bottlenose dolphin whistle parameters related to vessel presence, surface behaviour and group composition

“…Our results are therefore consistent with a short-term acoustic behavioural response, with animals shifting the frequency of their whistle vocalizations upwards when boats are close by. Although the 200 m radius we used to determine tour boat presence is lower than the 400 m radius used in some studies (Buckstaff, 2004;Lusseau, 2003a), it is somewhat greater than the criteria used in others (Christiansen, Lusseau, Stensland, & Berggren, 2010). We consider our results to be conservative.…”

Marine vessels alter the behaviour of bottlenose dolphins Tursiops truncatus in the Istanbul Strait, Turkey

“…Definition of each behavioural state (Lusseau 2003, Constantine et al 2004, Christiansen et al 2010 the behavioural states to be assessed (Lusseau 2003, Stockin et al 2008. Therefore, the preceding and following behavioural states were recorded for control and impact situations in order to create the transition probability matrix for the Markov chains.…”

“…To determine the behaviour demonstrated by the focal group, a focal 'group' scan sampling method was adopted (Christiansen et al 2010, Meissner et al 2015. Behaviours of individuals in a group were scanned from one side of the group to the other, and the predominant behaviour (the behavioural state that > 50% of the group was engaged in) of the group was recorded every 3 min after their initial sighting.…”

“…Dusky dolphins Lagenorhynchus obscurus (Barr & Slooten 1999, Dans et al 2008, common dolphins Delphinus delphis (Stockin et al 2008, Meissner et al 2015, Indo-Pacific humpback dolphins Sousa chinensis (Van Parijs & Corkeron 2001), sperm whales Physeter macrocephalus (Gordon et al 1992), minke whales Balaenoptera acutorostrata (Christiansen et al 2013), Hector's dolphins Cephalorhynchus hectori (Bejder et al 1999) and bottlenose dolphins (Nowacek et al 2001, Hastie et al 2003, Lusseau 2004, Christiansen et al 2010, Pirotta et al 2015, Perez-Jorge et al 2017, have demonstrated both short-and longterm behavioural changes in response to marine vessels within a wide range of ecological settings. Such changes can take on various forms, with the most frequent being variations in vocalization, an increase in dive intervals, both vertical and horizontal avoidance behaviour, an increase in swimming speed, and a decrease in foraging and resting behaviour (Lusseau 2004, Stockin et al 2008, Christiansen et al 2010, 2013, Meissner et al 2015. By contrast, cases exist whereby habituation may be particularly advantageous to the population as a whole.…”

“…Various authors (e.g. Saulitis et al 2000, Lusseau 2003, Stockin et al 2008, Christiansen et al 2010, Meissner et al 2015 have utilized behavioural budgets via the creation of Markov chains as a tool to assess disturbances in various cetacean populations, with particular focus on marine vessel pressure. However, it is important to keep in mind that studying the effect of marine traffic can involve some limitations, given that cetaceans spend most of their time underwater and some of their behavioural reactions might be elusive to the observer (New et al 2014, Pirotta et al 2015.…”