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January 29, 2010
Article

Fathoming: What are the marine impacts of offshore wind turbines?

by Dr. Heather Deese and Catherine Schmitt

Editor's note: We're introducing a new feature called Fathoming. These articles will explore scientific topics pertinent to Maine's coastal waters. The articles are made possible, in part, by funds from Maine Sea Grant.

Today there aren't any wind turbines off Maine's coast, but there may be in the next few years.  Maine is actively pursuing ocean wind energy, as are other states, and European nations have already installed over 700 offshore turbines.

This flurry of activity is raising questions about potential impacts on marine species and habitats. Turbines would mean new structures, noise, vibrations, and induced electric and magnetic fields around submarine power cables (the turbines in a wind farm are typically connected by a network of buried submarine power cables to a transformer that sits on the edge of the array, which is connected to land by a larger, buried cable). How would all of these features affect lobsters? Whales? Seals? Herring? Groundfish? What would be the cumulative impact if a development involved one, 10, or 100 turbines? (There are also questions about impacts on birds and bats, and human activities, but these are beyond the scope of this article.)

There has been relatively little study of the ecological effects of offshore turbines on marine species, but we can gain insight from existing offshore turbines and ecological knowledge of local species.

Specific impacts will depend on the type and number of turbines. There are two types of offshore wind turbines: bottom-mounted (installed on or in the seafloor) and floating.

Virtually all existing offshore turbines are bottom-mounted in areas less than 50 feet deep, although a few are in waters 150 feet deep. The proposed Cape Wind project would include 130 bottom-mounted turbines in waters up to 60 feet deep. In Maine, this type of turbine could be constructed along the relatively shallow southern coast or, potentially, on offshore rocky ledges.

The technology for floating platforms is at an early stage of development. The only operational full-scale floating wind turbine is the Hywind project off Norway's coast. The only concrete plan for offshore wind power in Maine is a proposal for the University of Maine-led DeepCWind consortium to erect prototype floating turbines in a recently designated test site south of Monhegan Island.

Construction of bottom-mounted turbines will involve installation in or on the seafloor and laying or burying cable, leading to sediment suspension and noise that could interfere with animal behavior, communication and physiology. More frequent ship traffic could pose a collision risk for marine mammals. Construction of floating wind turbines would have similar impacts in terms of power cables, but would be expected to have less direct impact on the seafloor (except for anchors).

Once operating, the turbines will interact with the undersea environment in complex ways. The amount of noise they generate will depend on the location, number, and design of the turbines. The structures will displace some seafloor habitat but will create additional hard-surface habitat, similar to the introduction of pilings under a pier. Field studies in Europe have indicated that some offshore wind turbines act as artificial reefs and fish aggregation devices (FADs), according to Dan Wilhelmsson, Department of Zoology, Stockholm University.

One key question is whether turbines will be surrounded by no-go zones for boat traffic and fishing. Offshore wind farms in Europe are no-dragging zones (due to interconnecting submarine cables), but in some cases fixed-gear fishing is allowed between the turbines. There are setbacks around each turbine in line with insurance requirements related to issues such as ice throw from the blades. Any major changes in fishing due to new turbines would likely lead to a different mix of species living on, in, or near the seafloor.

Another question is how electro-magnetic fields induced around submarine power cables will impact marine species. While there are multiple cables already in the water (including those that connect islands to mainland), the ecological effects of the electro-magnetic fields are not well known. According to Win Watson, who studies lobster physiology at the University of New Hampshire, the sensitivity of American lobster to magnetic fields is unknown, but some invertebrates, including spiny lobsters, are known to be magneto-sensitive. Some fish species are magneto- or electro-sensitive, such as sharks and rays. In a series of experiments involving large underwater net cages, Dr. Andrew Gill, of Cranfield University, UK, found that some small sharks and rays display statistically significant changes in behavior around submarine power cables.

What about noise from construction and ongoing operation? Dr. Watson notes that lobsters appear to "hear" or "feel" sounds in their environment, but have not been found to respond to sounds in a consistent fashion. He therefore supposes that "at first glance, manmade underwater sounds are probably not too much of a problem for lobsters".

Construction and operational noise could be a concern for large whales, such as the humpback, fin, and the critically endangered North Atlantic right whales that frequent the Gulf of Maine. Man-made sounds that mask the whale's own sounds could complicate whale mating, migration, mother-calf interactions, and possibly feeding. Sounds that are loud enough could damage an animal's hearing. According to Sean Todd, director of Allied Whale at the College of the Atlantic, at certain frequencies, a signal at 90 decibels is loud enough to disrupt whale behavior and 130 decibels can cause injury. Sharp, sudden sounds are more harmful. (Decibels represent volume or loudness, and hertz is the frequency or pitch.) The monitoring studies from offshore wind turbines in Europe have not conclusively shown whether or not noises from similar turbines would negatively impact the large whale species in the Gulf of Maine.

To get a handle on current whale distributions prior to energy development, Dr. Todd is working with other researchers at College of the Atlantic, Cornell University, and the Maine Department of Marine Resources to establish an underwater network of acoustic monitoring buoys in the waters of Downeast Maine. "Because whales are acoustically active, we can use sound to document their presence, and it allows us to get data during bad weather when it wouldn't otherwise be possible to observe whales. By linking those data with ship and aerial observation effort, we will have a much more complete model of where whales can be found," said Todd.

And what do the researchers and their students hear? "It's actually a fairly noisy environment," said Todd. The listening devices pick up everything from boat traffic to fish to whale vocalizations to the Rice Krispie-like crackling of oxygen escaping from the cells of seaweed. "There is nothing silent about the sea," said Todd.

Needless to say, there are a lot of unanswered questions. All we know for sure is that the introduction of wind turbines (and exclusion of some types of fishing) will bring about some changes for species and habitats, but nobody can say for sure at this point what those changes will be.

As Pete Jumars, Director of the School of Marine Sciences at the University of Maine puts it, "one floating wind turbine is not likely to have substantial local environmental impacts, but 10 turbines might, and 100 almost certainly will."

The question will be whether the impacts of tens or hundreds of offshore wind turbines is deemed worth the environmental, economic, and security benefits associated with generating electricity from renewable resources.

Heather Deese, Ph.D in oceanography, is the Island Institute's director of marine programs. Catherine Schmitt is communications coordinator for Maine Sea Grant.

click to enlargeDevelopment of large net cage off west coast of Scotland to test effect of electro-magnetic fields on sharks and rays.
Development of large net cage off west coast of Scotland to test effect of electro-magnetic fields on sharks and rays. PHOTO: DR. ANDREW GILL, CRANFIELD UNIVERSITY, U.K.

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