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Figuring the sounds in Arctic offshore Scientists seek ways to estimate the environmental impacts of multiple sound sources as industrial and vessel activity builds up Alan Bailey Petroleum News
While oil spill concerns often grab the headlines when it comes to potential environmental impacts from Arctic offshore oil exploration and development, worries about the possible effects of industrial noise on marine wildlife also figure high on the priority lists of those who plan, monitor or regulate offshore activities, and of those who hunt for marine mammals as a subsistence food source.
During this year’s National Marine Fisheries Service Arctic Open Water Meeting, held in early March, several presentations focused on the tricky question of how to assess noise impacts on marine mammals, to achieve an appropriate balance between economic needs and environmental protection.
Noisy ocean During a talk on the impacts of offshore seismic sound on marine mammals, Amy Scholik-Schlomer, acoustic coordinator in the National Marine Fisheries Service Office of Protected Resources, commented that, while marine mammals use sound for communication, navigation and prey detection, the ocean is inherently noisy, with sounds coming from both natural and manmade sources.
The Fisheries Service, while allowing activities vital to security and the national economy to take place, tries to address concerns about manmade noise becoming a threat to marine life, Scholik-Schlomer said.
Although mitigation measures enforced during seismic operations try to ensure that animals are not exposed to sound loud enough to cause hearing damage, there is a more general question of the impact of manmade sound on animal behavior, in situations where an animal is not directly injured by the noise but where behavioral changes may impact the animal’s ability to reproduce, grow or even survive, she said.
Pervasive sound And human sound can pervade the ocean.
In the mid-Atlantic people have recorded seismic sounds at distance of up to 4,000 kilometers from a seismic vessel, Scholik-Schlomer said. And in the Gulf of Mexico, where seismic sound can be near continuous, animal vocalization has been observed to change, although the reasons for the change are unknown, she said.
Simple vessel traffic can itself create noise problems. Scholik-Schlomer demonstrated a computer simulation of the underwater sounds from commercial shipping in the north Atlantic: This model suggests noise from the ships overwhelms or “masks” natural sounds used by North Atlantic right whales for 50 percent of the time, and sometimes for as much as 80 percent of the time, Scholik-Schlomer said.
Modeling technique Melania Guerra, a scientist from Cornell University, described a new research program, evaluating a modeling technique for assessing the cumulative impacts of multiple sound sources in the Alaska Arctic offshore. The research program, with funding from BP and the involvement of the North Slope Borough, is developing a computer application that simulates the potential behavior of animals such as whales under different sound scenarios.
Given the complexity of the issues being addressed, the research program involves a working group of multi-disciplinary experts from a variety of backgrounds and affiliations, Guerra said.
Essentially, the group’s approach involves deciding on a region and time period to assess, identifying all known significant sources of human ocean noise in that region and period, and then using the data to model the human “acoustic footprint,” the pattern of both continuous and impulsive underwater sound that would permeate various parts of the region as a consequence of human activities.
The idea then is to assemble information about what is known about the ways in which an animal species responds to sound, so that the model can simulate animals’ behavior as they swim through the acoustic footprint, enabling the scientists to assess any significant or adverse impacts from the human-generated noise.
Beaufort Sea test As a test for its simulator system, the group decided on a case study loosely based on activities in the western Beaufort Sea during the summer open water season of 2008, Guerra said. And the group chose to use the system to assess the impact of the activities on the east to west migration of bowhead whales between Sept. 1 and Oct. 23 of that year, she said.
At that time five seismic surveys were in progress in the Beaufort Sea, with two surveys using powerful air guns and three using smaller air guns, Guerra said. In addition, two offshore islands had oil operations that created some subsea sound, and two barge tows were in progress, she said. The incorporation of sound characteristics from all of these sources into a marine sound propagation model enabled the simulation of the subsea acoustic footprint, as it developed over the time period under investigation.
To simulate the whale behavior, the scientists gathered data about what is known about how bowhead whales respond to sound, including Alaska Native traditional knowledge about the whales’ behavior and sound avoidance responses. By plugging all of this information into the computer system the scientists created what they called “animats,” simulated animals rather like avatars in an electronic game. By then having a population of animats “swim” through the acoustic footprint, with different animats taking different routes but all animats motivated by a desire to move east to west through the Beaufort, it became possible to observe simulated animal movements and measure potential animal sound exposures. The simulation could be run with or without sound avoidance behavior built into the animat characteristics, Guerra explained.
Exposure data With sound avoidance included, causing sound to deflect the whales’ migration paths, 99 percent of the animats took action to avoid sound levels of 180 decibels or higher; 85 percent avoided sounds greater than 170 decibels and 60 percent avoided 160-decibel noise, Guerra said. And the model provided data about how much noise each animat encountered along its route through the sea, with the sound exposure for different animats at different times from different sound sources depending on the distance from shore of each animat’s migration path.
Potential animal sound exposure histories derived from a simulator system like this demonstrate how sound exposures from multiples sound sources can be just as important as the type of single-source sound exposure typically assessed when regulating industrial activities, Guerra said. However, although the research group has discussed the future possibility of government agencies using this type of simulator system for regulatory decision making, presumably enabling assessments of the cumulative impacts of multiple, concurrent activities, Guerra stressed that the research program remains far from reaching a point where the simulator tool could be used for this purpose.
For example, in running the Beaufort Sea simulation the researchers made several simplifying assumptions about the various sound sources, Guerra said. The simulator model could incorporate much greater complexity. And, with scientific papers on the research in progress, the scientists have not yet finalized the modeling method, she said.
The research is a work in progress, a simple first step towards a potentially useful tool, as activity levels in the Arctic increase, Guerra said.
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