Environmental Assessment for a Marine Geophysical Survey of Parts of the Arctic Ocean, August–September 2010

ABSTRACT

According to the United Nations Convention on the Law of the Sea (UNCLOS), individual nations’ sovereign rights extend to 200 nautical miles (n.mi.) (370 km) offshore or to a maritime boundary in an area called the continental shelf. These rights include jurisdiction over all resources in the water column and on and beneath the seabed. Article 76 of UNCLOS also establishes the criteria to determine areas beyond the 200 n.mi. (370 km) limit that could be defined as “extended continental shelf,” where a nation could extend its sovereign rights over the seafloor and sub-seafloor (As used in UNCLOS, “continental shelf” refers to a legally defined region of the sea floor rather than a morphological shallow-water area adjacent to continents commonly used by geologists and hydrographers.). This jurisdiction provided in Article 76 includes resources on and below the seafloor but not in the water column. The United States has been acquiring data to determine the outer limits of its extended continental shelf in the Arctic and has a vested interest in declaring and receiving international recognition of the reach of its extended continental shelf.

The U.S. collaborated with Canada in 2008 and 2009 on extended continental shelf studies in the Arctic Ocean. The U.S. Coast Guard (USCG) Cutter Healy worked with the Canadian Coast Guard ship Louis S. St. Laurent to map the continental shelf beyond 200 n.mi. (370 km) in the Arctic. Each icebreaking vessel contributed different capabilities in order to collect data needed by both nations more efficiently in order to save money, avoid redundancy, and foster cooperation. Generally, the Healy collects bathymetric (sea-floor topography) data and the Louis S. St. Laurent collects seismic reflection profile data. The vessels work in concert when ice conditions are heavy, with one vessel breaking ice for the ship collecting data. The Canadian Environmental Assessments for these projects are available on line at http://www.ceaa.gc.ca/052/details-eng.cfm?pid=38185 (2008) and http://www.ceaa.gc.ca/052/details-eng.cfm?pid=46518 (2009).

The U.S. Geological Survey (USGS) and Geological Survey of Canada (GSC) are undertaking a similar partnership again for 2010 in a limited area of U.S. waters during the period between ~10 and 16 August. The survey vessels will then proceed to international or Canadian waters where surveying will proceed until ~3 September, when the two icebreakers will separate to conduct independent work. The survey area of the joint work will be bounded approximately by 145° to 158° W longitude and 71° to 84° N latitude in water depths ranging from ~2,000 to 4,000 m (fig. 1). Ice conditions are expected to range from open water to 10/10 ice cover. The Louis S. St. Laurent will join accompanying vessel Healy in or near the survey area around 10 August to begin the joint survey work.

As its energy source, the seismic system aboard Louis S. St. Laurent will employ a 3-airgun array consisting of three Sercel G-airguns. Two guns will have a discharge volume of 500 in3 and the third a discharge volume of 150 in³ for a total array discharge volume of 1,150 in³. The seismic survey will take place in water depths 2,000–4,000 m. This airgun array is identical to the system used in the 2008 and 2009 field programs by the Geological Survey of Canada.

The USGS requested that the National Marine Fisheries Service (NMFS) issue an Incidental Harassment Authorization (IHA) to authorize the incidental, that is, not intentional, harassment of small numbers of cetaceans and seals should this occur during the seismic survey in U.S. waters. USGS is also consulting with the U.S. Fish and Wildlife Service (USFWS) regarding concerns about disturbance to walruses and polar bears. Through informal consultation with the Office of Protected Resources with the National Oceanic and Atmospheric Administration (NOAA), USGS proposes that no ESA-listed marine species—bowhead, fin, humpback or sperm whale—will be adversely affected by this project during the survey or transit to the survey area from Dutch Harbor. The information in this Environmental Assessment (EA) supports the IHA Application process, consultation with the USFWS, and provides information on marine species, some of which is also contained in the IHA Application to NMFS. Alternatives addressed in this EA consist of a similar program during a different time period along with issuance of an associated IHA, and the no action alternative, with no IHA and no seismic survey.

Several species of cetaceans and pinnipeds inhabit the Arctic Ocean. Few species that may be found in the survey area are listed as Endangered under the U.S. Endangered Species Act (ESA). The bowhead whale is the endangered species most likely to occur within the survey area. The polar bear, which was recently listed as Threatened under the ESA, may also occur in the survey area. The survey has been scheduled specifically to avoid the spring and fall bowhead whale migrations north of Barrow. Two additional species of special concern (birds) that might be encountered are the spectacled and Steller’s eiders, which are listed as “threatened.”

Potential impacts on the environment due to the seismic survey would be primarily a result of the operation of the airgun source. In addition to the airgun array, a Chirp pulse echo sounder will be operated on the Louis S. St. Laurent. The Louis S. St. Laurent will also tow a 3–5 kHz subbottom profiler while in open water and when not working with the Healy. The Healy will use a multibeam echo sounder, a subbottom profiler and a “piloting” echo sounder continuously when underway and during the seismic profiling. Acoustic Doppler current profilers may also be used on the Healy. The project will also involve vessel and helicopter traffic. Increased underwater noise from vessel traffic and use of geophysical equipment may result in avoidance behavior or other disturbance to some marine mammals and fish. An integral part of the planned survey is a monitoring and mitigation program to minimize impacts of the proposed activities on marine species and on fishing and subsistence activities and to document the nature and extent of any effects. Injurious impacts to marine mammals have not been demonstrated to occur near airgun arrays, and the planned monitoring and mitigation measures would minimize the possibility of such effects should they occur.

Protection measures designed to mitigate the potential environmental impacts will include the following: a minimum of one dedicated protected species observer (PSO) maintaining a visual watch during all daylight airgun operations; two observers (when possible, otherwise a single observer) on watch 30 min before airgun operations start; and power downs or shut downs of the airgun array when mammals are detected in, or about to enter, designated safety radii. USGS and its collaborators are committed to apply these measures in order to minimize disturbance of marine mammals and to minimize the risk of injuries or other environmental impacts.

With the planned monitoring and mitigation measures, unavoidable impacts to each of the species of marine mammal that might be encountered are expected to be limited to short-term localized changes in behavior and distribution near the seismic vessel. At most, such effects may be interpreted as falling within the Marine Mammal Protection Act (MMPA) definition of “Level B Harassment”. No long-term or significant effects are expected on individual marine mammals or marine mammal populations, or their habitats.

A draft version of this environmental assessment was posted for public comment on the USGS web site from June 11–July 12, 2010. Comments received during this period and USGS responses to the comments are summarized at the end of this document in appendix K. While the comments resulted in clarifications being added to the draft EA, none of the changes developed from the comments or from discussions with the other agencies substantively changed the conclusions of the draft EA.

Last modified August 5, 2010
First posted June 8, 2010 as a draft document