Magnetism from underwater power cables doesn’t deter sea life
Trio of studies show marine animals will cross and even colonize high-voltage cables
ON THE LINE Power cables ferry electricity to islands and from offshore energy plants such as this wind farm off the coast of Denmark. Underwater electric power cables don’t trouble local marine life, new studies suggest.
NEW ORLEANS — High-voltage electricity surging through undersea power cables doesn’t bother local sea life, three new studies suggest. The work eases concerns that planned offshore power production from wind turbines and tidal generators would disrupt marine communities.
Tracking the movements of fish and crabs around underwater power cables, the new studies reveal that marine critters don’t shy away from the magnetic fields put off by the cables. One study even found that the thick cables can serve as artificial habitats and host undersea communities.
“There’s much less of a concern now,” said Ann Bull, a marine biologist at the Bureau of Ocean Energy Management in Camarillo, Calif., who presented two of the studies February 26 at the American Geophysical Union’s Ocean Sciences Meeting.
In the 1980s, the first underwater telecommunications cables clashed with marine life: Sharks intrigued by electric fields put off by the wires would gnaw on the cables, often leaving teeth behind. Wrapping the cables in insulating material blocked the electric fields and stemmed shark attacks, but magnetic fields generated by the cables remained. Laboratory experiments show that many marine creatures can sense even relatively weak magnetism, sparking fears that the cables serve as “electric fences” that disrupt sea life.
Commercial fishers particularly worried that crabs wouldn’t cross undersea cables to find bait in crab traps. To test this, Bull and her colleagues built cages with two baited traps, one of which required crabs to pass over an active power line. Both Dungeness crabs (Metacarcinus magister) and rock crabs (Romaleon antennarium) had no problem crossing the line: In hundreds of trials, the crabs chose each trap around half the time.
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In another study, Bull and her colleagues monitored the marine life around three parts of the seafloor over three years. One area had a powered cable, another, an unpowered cable, and the third area had no cables at all. Both cabled areas attracted similar kinds and numbers of anemones and other sea life. In fact, more than twice as many fish and four times as many invertebrates hung around the cables than in the area with unaltered seafloor.
Measuring the magnetic field generated by the powered cable, Bull and colleagues found that the field quickly weakened with distance. By a meter away, the magnetic field was too meager to distinguish from background noise, Bull said. Even where the magnetic field was strongest, right on top of the cable, sea creatures didn’t seem bothered.
In the third study, also presented February 26, Megan Wyman, an animal behaviorist at the University of California, Davis, and colleagues looked at an 85-kilometer-long, high-voltage power cable that bisects the San Francisco Bay. The team used acoustic sensors to monitor whether the activation of this cable in 2010 affected salmon migration. They found that the cable did not hinder young Chinook salmon (Oncorhynchus tshawytscha) from migrating through the bay from inland rivers.
“It’s great to hear that they don’t seem to see any impact,” said Genevra Harker-Klimes, a marine scientist at the Pacific Northwest National Laboratory in Sequim, Wash. “There are a few loose ends that need to be tied up, but overall this is very positive” news for offshore energy production.
