Estimates of collision risk of harbour porpoises and marine renewable energy devices at sites of high tidal-stream energy.

Extracting renewable energy from the sea is an attractive alternative to burning fossil fuels. Like any marine industry, obtaining energy from wind, waves or tidal-streams could have impacts on the marine environment (positive or otherwise). One frequently cited area of uncertainty for extracting energy from fast flowing tidal currents is the possibility of large marine vertebrates (including whales, dolphins, porpoises [collectively cetaceans], seals, sharks, turtles, and diving birds) colliding with submerged tidal-turbines – a scenario with parallels to the issues surrounding bird strikes by wind turbines.
Preliminary modelling work has suggested that interactions between tidal turbines and harbour porpoises (Scotland‟s most abundant cetacean) may be common, assuming porpoises occur in tidal-stream areas at densities similar to other Scottish coastal habitats. However, it remains unclear how true this assumption is, and particularly whether porpoises avoid or are attracted to these areas. The aim of this study, therefore, was to investigate how often porpoises occurred in two areas of immediate interest for tidal-stream development on the west coast of Scotland. These two sites were the tidal narrows of the Sound of Islay (between the islands of Islay and Jura) and the Kyle Rhea (between Skye and the mainland).
Surveys were carried out during the summers of 2009 and 2010 using a variety of standard and specifically adapted techniques. The primary tool was the use of a research boat (the Hebridean Whale and Dolphin Trust‟s RV Silurian) which was used to criss-cross the sites with observers visually scanning for......