As Reported in the OffShore Energy Panel in 1211
Birds and bats represent the organisms presumed to be at greatest risk of harm from wind turbines over water, based upon their distribution and abundance patterns and behavioral responses, and based upon observations made on wind-turbine impacts on land. Summering and especially overwintering waterbirds are ubiquitous in the sounds, and the near-shore coastal ocean out to at least 2 miles is heavily used by fish-eating waterbirds and probably occasionally transited by migratory songbirds and shorebirds of concern. Compared to reported minimum densities of birds on land around an existing Minnesota wind farm of about 600 individuals per km2, the Duke Energy-funded UNC surveys in 2010 demonstrated an average bird density in Pamlico Sound of only 12.9 individuals per km2 and on the transects in the coastal shelf out Hatteras Inlet and Beaufort Inlet of 5.0 individuals per km2. To the degree that abundances imply relative risk, the risks to birds would be judged as much lower over North Carolina’s near-shore continental shelf than over land where wind farms exist. The pattern of bird abundance over the near-shore continental shelf exhibits large declines with distance from the shore, such that bird density declines by about two thirds from the highest density within the first 10 km of the beach to the average of the zone from 10-40 km. True pelagic seabirds remain uncommon and only begin to increase in abundance past the 40 km point as one approaches the Gulf Stream, where true pelagic seabirds and many endangered marine mammals exist in substantial abundance off of North Carolina’s coast. The year-long UNC surveys of birds over the eastern Pamlico Sound and on the continental shelf into Onslow Bay and Raleigh Bay failed to encounter even a single individual of an endangered bird species. No bats were detected even though surveys began at first light and ended at dusk daily. Bird abundance is not the only factor determining risk of encounter with a spinning rotor blade. Behavior must also be considered. Night flying would elevate risk because of the difficulty in detecting the spinning rotor blades. Passerine birds (neotropical migrants) make inter-continental migrations during spring and fall, tracking the coastline along the coastal North American flyway. These migrations occur at night, raising concern about these valued terrestrial species. The UNC year-long surveying detected very few passerines and revealed no evidence that the migratory pathway extended out over the continental shelf into areas that would place these birds at risk from wind turbines. In the Duke Energy study, flight elevations of each species of bird were estimated for replicate numbers of individual birds and compared to the heights swept by a standard 3.6 MW wind turbine (26.5 – 135.5 m). Half the species of birds never flew as high off the water as the minimum height swept by the turbine blade. Of those species whose flight altitudes overlapped the rotor-swept elevations, only a small percentage flew within the risky altitudes. Finally, UNC assessed risks of collision of birds with vehicles crossing the 22-m tall Bonner Bridge by comparing counts of dead birds and of live birds by species. 70 W InD e n eR G Y Re s oU Rc e s Brown pelican and juvenile gulls and terns exhibited higher mortality than other species, implying that they might also exhibit similarly risky behavior around spinning rotors of wind turbines. The only reliable means of determining true risk of bird mortality from encountering spinning rotors blades is to conduct an assessment of impact on an installed wind turbine in the geographic area of concern. Nevertheless, existing evidence implies that risks to birds and bats may be lower, even substantially lower, over the N.C. continental shelf 10-40 km from land than on land where existing wind farms are found. In contrast to the elevated bird abundances in the Pamlico Sound relative to the coastal shelf in the Atlantic Ocean, the patterns in absolute abundances of marine mammals and sea turtles spotted during the UNC 2010 surveys reflect substantially higher abundances in the coastal ocean than in the Pamlico Sound. The coastal ocean sampling revealed 0.41 marine mammals per km2, as compared to only 0.013 per km2 in the Pamlico Sound. Sea turtle abundances were also 35 times higher in the coastal ocean at 0.035 per km2 versus 0.001 per km2 in Pamlico Sound. Consequently, absolute risk of interactions between energy-production facilities and both marine mammals and sea turtles is much greater in the coastal ocean. All the sea turtles observed are federally listed under the Endangered Species Act as either threatened (loggerhead, with a current review of evolutionary separate units for potential endangered status) or endangered (Kemp’s ridley and leatherback), so require special consideration and federal agency consultation wherever a development project poses any potential risk to them. Similarly, marine mammals observed in the coastal ocean include at least one species listed under ESA (humpback whale, and possibly also an unidentified cetacean), and require similarly comprehensive federal agency review of development plans. Obviously, marine mammals and sea turtles do not run a risk of death from encounters with rotating rotor blades of wind turbines. The risk of potential concern to marine mammals, and perhaps also to sea turtles, is a risk of noise, especially during installation of piles, which may be forced as much as 30 m deep into the sedimentary sea floor to stabilize the wind turbine above. Bottlenose dolphins have been observed to retreat to a distance of 10 km away from similar noises, thereby temporarily depriving them of use of that habitat area. If this problem is judged to be serious or if any endangered marine mammal proves similarly sensitive, then mitigation during construction may be required. This could conceivably be achieved by doing the construction during a season of low use by marine mammals or by employing gravity-based foundations on the wind turbines, a more expensive design suitable for sites where the sea floor is hard rather than comprised of sandy sediments. Marine mammals and sea turtles may also be affected by the EM fields around the transmission cables running from the wind farm into shore. Sea turtles are known to navigate back to natal beaches based on detecting and following the earth’s magnetic field. This may imply navigation disruptions from the EM fields – an issue that still needs study. Some fishes also use electromagnetic fields for navigation, communication, or aggression, notably the American (and European) eel, and certain rays and other elasmobranchs. A report 4 prepared as a part of the environmental impact assessment (EIA) for the Cape Wind project in Massachusetts suggests that while the magnitude of the EM and induced electric fields from buried transmission cables may exceed the detection threshold for marine organisms, the 50-60 Hz frequency from an AC cable may be imperceptible because many organisms are only able to detect frequencies of 10 Hz or less. No problem has been reported from existing European wind farms that relates to EM fields and their effects on fish or wildlife. Many positive environmental synergies can be associated with the presence and operation of wind turbines on the nearshore continental shelf. The foundation of each wind turbine is usually stabilized with a rock anti-scour apron, built up 1-2 m from the seabed using large rocks, ideal for creation of habitat for rocky reef fishes. The species of the snapper-grouper complex that occupy rocky reef habitat on the North Carolina continental shelf include some of the most depleted fishery stocks. Provision of new habitat that would occur through construction of the anti-scour aprons would benefit these valuable fish stocks and the fisheries based upon them. The presence of a wind farm on the continental shelf could also facilitate the ocean mariculture industry. There exists strong interest in shellfish and finfish culture on the continental shelf as a means of escaping risk of escalating water-quality problems inside our estuaries and as a means of minimizing environmental effects of finfish-generated wastes, which can be diluted and dispersed in shelf waters with strong currents. Nevertheless, a major impediment to ocean mariculture is solving the problem of how to protect the pens and nets from being damaged by ship traffic. The presence of a wind farm, with its necessarily well-lit, charted, and visually obvious structures, could offer mariculture pens protection from collisions with ships. 4 http://www.boemre.gov/offshore/PDFs/CWFiles/141.pdf71 W InD e n eR G Y Re s oU Rc e s Several large coastal areas offshore in federal waters off North Carolina were identified as locations where wind farms would not pose excessive risk to birds and wildlife. The coastal zone out to at least 2 miles, the areas within a 5-mile radius around each inlet, the three Capes (Fear, Lookout, and Hatteras), “The Point” northeast of Cape Hatteras, all waters shallower than 4 m in depth, and the entire area swept by the Gulf Stream are characterized by unacceptably high risk to birds, sea turtles, and/or marine mammals and are not compatible with the presence of a wind farm. On the remainder of the N.C. continental shelf, wind farms would not pose high risk to birds and wildlife.