How do fish react to wind farms and cables?

Mon, 04/12/2010 - 4:00am

4/10/10 — The electromagnetic fields generated by underwater electric transmission cables from offshore wind farms and pile driving during wind turbine construction may have major effects on fish, according to two British researchers who spoke March 31 at the University of Rhode Island’s Bay Campus in Narragansett.

Sharks, skates and rays are attracted to underwater electric cables, according to Professor Andrew Gill of Cranfield University in the United Kingdom. Related research by Frank Thomsen, scientific program manager for the British government’s Center for Environment, Fisheries and Aquaculture Science, found that pile driving noise repels cod and sole and makes both species swim more quickly. The effects of the altered behavior on ecosystems surrounding wind turbines is unclear, both scientists say, and requires additional research.

The Coastal Resources Management Council, which is in the midst of designing a use plan for the ocean south of Rhode Island, and the Rhode Island Natural History Survey sponsored the presentation by the two researchers.

The U.K. currently has nine operational offshore wind farms and plans for many more, Gill noted. In addition, nearby Denmark is the world leader in offshore wind farm construction. Gill and Thomsen, however, lament that the boom in construction has not generated enough environmental scientific research on offshore energy developments. To conduct their experiments, they built two 15-foot high, 120-foot in diameter underwater cages. Fish placed in the cages were outfitted with transmitters, so that onshore researchers could track their movements.

Gill’s research focused on the electromagnetic fields created generated by electricity passing through underwater cables. Many marine species, including seals, whales, eels, lobster and crabs use the Earth’s electromagnetic field to guide their migration patterns, but sharks, skates and rays were selected for the experiments because they have sensors near their mouths to detect electric magnetic fields generated by their prey.

Gill found three of the five species tested were more attracted to a live cable, which generates an electromagnetic field, than an inactive cable. In addition, a German study found that migrating eels slow down when passing over a live cable, but that it does not cause them to change direction, he added. That information is a small part of measuring the impact of wind farms on fish populations, he noted. While an active cable might distract sharks from successfully foraging for food, wind farms could also have positive effects for the fish, Gill said, such as discouraging fishing or attracting smaller fish that provide sharks’ food supply. Also unclear is whether the cables’ effects on the fish would diminish over time as they become accustomed to it. “The basic thing is,” Gill commented, “we know next to nothing.”

Thomsen also used the large underwater cages for his experiments. He measured fish responses to recordings of recorded pile driving sounds. Other European scientists have reported fewer porpoise sightings and heard fewer of the mammal’s clicking noises during pile driving for wind turbines, Thomsen said. His experiments tested the noise’s effect on two commercially valuable fish — cod and sole — reasoning that if the fish moved away from the sounds, scientists could argue either that wind farms should not be located in spawning areas or not constructed during spawning season.

When the sound was turned on, Thomsen says, cod froze, then they started swimming more rapidly while moving away from the noise. Sole also moved away from the sound and started swimming more rapidly.

Those findings are just the beginning of valuable research, Thomsen says, noting, “What that means in terms of biological impact is unknown.” At what distance fish are affected by the pile driving noise is also uncertain, although research suggests cod still change their behavior when more than 20 kilometers away from the construction site. Also unknown is whether fish initially move away from the noise, but then return as they become accustomed to it.

Other related research is underway. In Germany, for example, scientists are testing whether a curtain of bubbles will significantly muffle the sound of pile driving. In response to a question, Thomsen also said the dust raised by pile driving should be studied.

The two men also criticized current environmental monitoring of British wind turbine projects with Gill calling them “a bit of a waste.” With only guidelines, not strict requirements, monitoring varies from project to project. “In Germany, as you might imagine, it’s different,” Thomsen noted with a smile, “There’s one standard and it’s followed.”

Britain has taken steps to move turbines further offshore. The first round of wind farms were built from five to 10 kilometers from shore, Gill noted. In response to concerns about impacts on birds, however, the second round of projects was limited to three specific ocean areas and required to be built at least 12 kilometers offshore.