Effects of vessels on common dolphin activity patterns in a critical area for the species. Conservation implications

Although whale-watching tourism makes it easier for humans to learn about these animals in the wild, interactions with boats can trigger temporary or even permanent behavioural changes in their populations. In this work we studied the potential effect of boats on the welfare of common dolphins, Delphinus delphis, a protected species in the Mediterranean, as well as a female bottlenose dolphin (Billie-Tursiops truncatus) that coexists with them in the bay of Algeciras-Gibraltar (BA-G), Southern Spain and that gave birth to the first known hybrid between both species in the wild. First, the reaction of the animals (Approach, Elusive and Indifference) to the presence of boats was observed. Subsequently, we have classified the sightings into four situations: Control (C) and Impact (I) with Regulated (RS) and Unregulated (US) sightings. In each situation, six behavioural states were distinguished: Feeding (F), Resting (R), Milling (M), Socialising (S), Travelling (T) and Diving (D). It was concluded that the presence of boats and non-compliance with the protocol for approaching cetaceans were the main causes of the behavioural transitions and that they led to an absorbing D state in the Markov chains. The results showed that the feeding and resting behaviours of the dolphins were significantly altered. Possible alteration of these behaviours may have negative effects on the animals. Our results are further evidence of the need to regulate and monitor vessel activities to protect common dolphins in BA-G, a critical area for this species, which still lacks specific conservation plans.