This report should be read in conjunction with Harwood et al. (2014), which describes an interim protocol for implementing the Population Consequences of Disturbance approach for quantifying and assessing the effects of UK offshore renewable energy developments on marine mammal populations. Together, these reports should enable developers to be confident that the information on marine mammals that they provide in their ESs and HRAs is relevant and appropriate, and to help regulators and their advisors ensure that the assessments of the potential population consequences of these developments are consistent and comprehensive.
We review the potential threats to five marine mammal species (grey seals, harbour seals, minke whales, bottlenose dolphins and harbour porpoises) that may be associated with offshore renewable energy developments. We conclude that the most important risk is of disturbance from the noise associated with the construction of such developments, because of the large numbers of animals that may be affected and the fact that the resulting changes in behaviour may affect individual vital rates (the probabilities of survival and giving birth in a particular year for individual animals).
We develop a stochastic framework for modelling the population dynamics of these five species that can be used to assess the potential consequences of any changes in vital rates that may occur as a result of disturbance. We also suggest an appropriate set of demographic rates (the mean values of individual vital rates, averaged across all members of a population) for each of the different Management Units of these five species that have been identified by Anon. (2014).
We used this model framework to determine the sensitivity of the growth rate of these populations to changes in demographic rates that may occur as a result of disturbance. We confirmed the results of previous analyses that have suggested that the growth rate of marine mammal populations is most sensitive to changes in adult survival. However, when we reviewed the likely sensitivity of individual vital rates to the effects of disturbance, we concluded that the survival of dependent young (calves or pups) and fertility (the probability that an individual female will give birth in a particular year) were most likely to be affected for all species except harbour porpoise. Harbour porpoises carry much smaller energy reserves than the other four species and, as a result, adult and juvenile survival could also be affected by disturbance.
Finally, we consider how the approach described in this report and in Harwood et al. (2014) could be extended to other marine mammal species in UK waters. We conclude that the only species which could be assessed in the same way using currently available information is the killer whale.