An exciting new study was recently published by researchers from Aberdeen, St Andrews and Washington State that will help improve how we assess population effects for bottlenose dolphins in the Moray Firth, with some lessons on improving these models going forward.

It is difficult to predict the long term consequences of impacts on marine mammals from human activities. We need to use statistical modelling tools to help us assess the potential population consequences from disturbance. Population models, such as PCoD, work on a three step process: 1) how disturbance changes behaviour, 2) how behavioural changes influence vital rates and 3) how changes in vital rates affect population dynamics. We have a good understanding on how disturbance can cause behavioural changes and how changes in vital rates can affect a population, but we are missing the middle step of how behavioural changes affect vital rates. This new study is a great step towards addressing this. It uses an individual based model to predict how bottlenose dolphins behavioural dynamics and motivational state change as a result of shipping and dredging activities and how this can link to changes in an an individual’s condition and vital rates.

The study aimed to create a model to link individual dolphin behavioural and motivational states then predict changes in exposure and motivational states as a result of disturbance from industrial developments. The East coast of Scotland bottlenose dolphin population was used as there is long term data available such as distribution, habitat use and the reproductive history of individual dolphins. The individual based model assigned 1 of 2 motivational states to a dolphin at any one time: to gain energy (foraging) or to spend energy (travelling, mating, resting etc.). The disturbance activities used in the model included developments at the port of Ardersier, Invergordon and Nigg Bay, each of which involved increased boat traffic and dredging activities.

The results of the modelling showed that there was no significant predicted change in dolphin motivational states with the increased boat and dredging from the construction of the three developments. However, it was shown that increased boat traffic during the operational phase of the developments can cause a motivational change which could impact on an individual’s condition and vital rates, thus affecting the population.

Full details of the models used can be seen in the paper here.

Check out more work by the lead author Enrico Pirotta.

Why is this work important?

In order for effective regulation of offshore developments we need to understand how individuals are expected to react to differing levels of disturbance and how these changes in behaviour and motivational states affect their vital rates (such as survival and reproduction), which will in turn affect the population dynamics.

Check out SMRU Consultings work in this area: