Since the inception of the Adriatic Dolphin Project, dolphin behaviour research was integral part. As dolphins spend most of their time under water, observations made on the surface give only an indication what is actually happening. Still, understanding their behaviour is important to understand habitat use, population health and threats, etc. The goal is to understand the amount of time an individual spends doing one activity, creating a “behavioural budget” for an individual or group. Some activities aim at researching changes in the behaviour of individual dolphins in the vicinity of different vessels. This enables us to find relationships between types of behaviour and location, and to find, measure and understand behavioural responses to boat presence. Understanding these relationships can help develop conservation measures to reduce negative impacts that boat traffic might have on this vulnerable population. A significant increase in boat traffic in Croatian near-shore waters has taken place since the 1990s. It is known that dolphin reactions to boat presence can vary from habituation and short-term behavioural responses to long-term consequences affecting their activity, distribution, reproductive success, and fitness. Although many behavioural studies worldwide describe unique cases, the majority found negative impacts of boat traffic on cetacean species in general.
In our study, we use two sampling protocols: “group follow” and “individual follow”. The “group follow” protocol is used to collect data on the behaviour of the whole group; group size, age composition, formation and unusual activities are also noted. For example, dolphins can have different responses to boat presence if they are in a small or a large group, or if calves are present in the group. The “individual follow” is used to monitor the behaviour of a single animal and record the inter-breathing intervals (IBI) – the time interval between two successive surfaces. Changes in respiration patterns may reflect a change in behaviour which helps recognise various behavioural states with more certainty. The analysis of the data since 2006 has shown that the most significant factors generating negative behavioural response are: boat type (e.g. speedboats and motor-yachts), boat speed, the duration of encounter, and boat approach (aggressive approaches cause more intense avoidance reactions). Dolphins try to avoid boats by prolonging dives or changing their behavioural state into “travel” mode resulting in an increase in swimming speed. These short-term responses can have a negative effect on dolphin energy expenditure and stress levels. Unfortunately, little is known about how these short-term effects transfer into long-term consequences. Please see The Blue World Institute’s code of conduct for boat owners and skippers encouraging the reduction of negative impact.