In this post Debbie Russell discusses her paper ‘Avoidance of windfarms by harbour seals is limited to pile driving activities‘ published today in Journal of Applied Ecology.
Marine renewables in the fight against climate change
To fight climate change we have to cut our carbon emissions. One of the main sources of carbon emissions results from burning coal to make electricity. Thus a key weapon in our fight against climate change is the development of a renewable development industry. This can include harnessing energy from the sun, wind, and even tide. Building the number of wind turbines required to support our energy demands would take up a lot of our countryside and thus understandably there is a push to build large windfarms offshore.
Both the construction of these windfarms and their operation can have an effect on marine wildlife. The foundations of turbines are installed using pile drivers – essentially large hammers that drive the foundation posts into the sea bed – which produces very loud sounds which can scare off animals. Even when the turbines have been installed, there is still potential disturbance to animals through operational noise and the boat traffic required for maintenance purposes. However, due to the relatively small space between the rows of turbines, large ships and many types of commercial fishing are excluded, which in turn can result in reduced disturbance and increased prey availability. In fact, the structures themselves can become artificial reeds – they can attract algal growth which leads to a concentration of animals including fish species.
Using mobile phones to understand the impact of windfarms on seals
Many marine animals are also being affected by climate change and it is difficult to reconcile the long term benefits of marine renewables (through reduced climate change) with their potential negative impacts on wildlife. Understanding the impact of these developments on marine animals is problematic due to the difficulties in monitoring these animals beneath the water surface. This is where your mobile phone comes in! We attach adapted mobile phones onto the back of the necks of seals, which unlike most mobiles are reliably waterproof. Like in your phone the GPS can record their location. The seals regularly come to shore, where they normally manage to get some phone signal. The track of the seal at sea is then transmitted to us via the mobile phone system. It is the seal equivalent of ET phone home!
To understand the impact of windfarms and to inform the positioning and process of constructing windfarms, we attached these “mobile phone tags” to 50 harbour seals in The Wash, south-east UK. We attached around half of these devices prior to any windfarm development, and the other half when one windfarm in the area was under construction and another was operational. We found that the seals did not appear to avoid the windfarm which was operational or even for the most part the windfarm under construction. However during the noisy pile driving of foundations, the use of the 20 km area surrounding the windfarm greatly decreased. Some animals did still enter this area to travel to or from where they haul out on land.
What happens now?
These findings suggest that any energetic costs of displacement, in terms of increased travelling time or exclusion from a foraging area, are likely to be restricted to pile driving activities. However, the motivation to forage or haul out likely causes some individuals to continue to enter high noise areas. A previous study on the same individuals showed that such behaviour may result in seals incurring hearing damage. We were able to calculate a relationship between the noise levels we expected seals to hear and to what degree they were excluded. Seals are protected by European law and our findings will be used by the regulators and the marine renewable industry to more accurately predict the effect of particular windfarms on seals. Furthermore, the results can also be used to minimise the effects of windfarm construction on seals. For example now we have a good idea of what sound levels cause seals to be displaced, where possible bubble curtains (literally curtains of air bubbles coming from a hose with holes in it!) can be placed around the pile driving activity to reduce the noise to levels which do not scare seals away. Further studies are required to understand if there is an effect of windfarm construction on the population size of seals.