Undersea turbines – are they friend or foe?

I follow CECHR – a twitter account run on behalf of the University of Dundee. It is an environmental department within the university and frequently tweets pictures of stuff of an environmentally friendly nature. Sometimes I disagree with the things they tweet, sometimes I don’t. Sometimes I even like the comments or technology on display. Today they tweeted this photo:

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I do not know how big the blades on these turbines are, but this other photo from CECHR suggests that they may be very large.

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Furthermore, the first image suggests that they are planted on the seabed in arrays. The whole set-up seems analogous to the huge arrays of wind turbines that I see every time I trundle up the A30. I don’t like the wind turbines and I do not like the look of these sea-bed types either, and my reasons for doing so are much the same.

Yesterday, I was walking part of the coast path near Mousehole. As I came back to the car, I looked out across Mounts Bay and saw an area of white disturbance on the sea about a mile away. The sea was calm at the time. Closer inspection with the binoculars and then with the telescope revealed a patch of sea which had turned almost white with gulls and Gannets diving into the sea. As I watched, I was even more pleased to see three Sooty Shearwaters sitting on the surface and occasionally taking off and diving just like the Gannets. What was happening is that a shoal of pilchards or something had come inshore and everyone was having a feast. As I watched, I noticed that there was also some curious splashing that was not caused by the Gannets. It swiftly became apparent that a pod of about a dozen Common Dolphins had joined in the fun. So there it was, huge group of dolphins, Gannets, Herring Gulls, Black-Backed Gulls and Sooty Shearwaters. All turning the sea a boiling white by catching pilchards. We need to understand that this was an awful lot of activity going on in a very small patch of sea. Big things – Gannets have a wingspan of two metres, dolphins are up to 2.7 metres long – are diving very fast into a small volume of water. This kind of sight is fairly regular along the Cornish coast as well as elsewhere.

Now imagine that same shoal of pilchards caught up in one the proposed arrays of under-sea turbines and it is possible to imagine the carnage that may ensue. The more fish that are chopped up, the greater will be the frenzy of diving, feeding birds and cetaceans. Imagine a pod of whales caught up in one these arrays and the horrible mess that might ensue. For example, for many years there was a particular Bottle-nosed Dolphin who used to come inshore. He was well known because he had a chunk missing from his dorsal fin:

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Of course, no-one knows how he sustained this damage, but the most likely explanation is that he got too close to a ship’s propeller. So imagine that there are a whole series of these things and the underwater hazard that they pose.

CECHR have been helpful in that they have linked me to a series of papers on this kind of subject, but in the end very little is actually known about the impact this kind of turbine will have on fish, cetaceans and diving birds. One paper in the selection seems to be relevant and that is this one which concerns fish. However there are a number of caveats to be applied to drawing any conclusions from this paper;

  • The depth of the turbines may affect different species in a different way.
  • Their position close to or well above the sea bed may affect some diving species differently e.g. whales are able to dive to any depth, Gannets mostly dive to depths of 15 metres, but may regularly dive up to 30 metres.
  • If the arrays operate as a sanctuary for prey species – e.g squid, this may make make them even more of a death trap for whales.
  • The rpm and the diameter of the turbines affects the peripheral speed of the ends of the turbine blades and this can affect the strike rate depending upon the size of the animal passing between the blades – a Mackerel is less likely to be hit than a whale, because the whale takes much longer to pass through the swept area of the turbine.
  • The above paper is based upon a model. All models are only as good as the assumptions that are put into them in the first place. If the assumptions are over simplistic, then the models will not only be wrong (all models are wrong) but they will be massively wrong.

This list will not be exhaustive but gives an indicator as to a fraction of the likely problems that will be experienced by diving birds and cetaceans when a shoal of fish passes into the array.

It seems to me that fish, birds and cetaceans already have enough man-made hazards to cope with already without coping with yet another threat to their lives. Given the over fishing in UK waters provided by the Common Fisheries Policy, this looks like just one step too far in the pursuit of so-called ‘Green’ energy.

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