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A new way of assessing wildlife takes NMFS is revisiting how to estimate how many marine mammals are impacted by the sound from activities such as seismic surveys Alan Bailey Petroleum News
The National Marine Fisheries Service, or NMFS, is in the process of revising the criteria that it uses to estimate the extent to which sound from offshore industrial activities such as marine seismic surveys and offshore drilling disturb marine mammals, NMFS staff told the annual Arctic Open Water Meeting on March 6.
Critical importance
The acoustic disturbance criteria are of critical importance in the process of applying to NMFS for incidental harassment authorizations, the permits that allow the minor disturbance, or “take,” of small numbers of animals during industrial operations. Without a government authorization, a take of a marine mammal would normally violate the Marine Mammals Protection Act and, depending on the species of mammal involved, could also contravene the Endangered Species Act.
The acoustic criteria are essential to the calculations used to estimate how many takes an activity might cause, and are also used in designing mitigation measures to avoid wildlife disturbance. An harassment authorization will normally prohibit the exposure of animals to sound that might cause injury and will limit the number of minor takes allowed.
NMFS administers incidental harassment authorizations for whales and seals, while the U.S. Fish and Wildlife Service administers similar authorizations for polar bears and walruses. The intention is to ensure that offshore activities do not harm the various mammals that live in the ocean.
New criteria Amy Scholik-Schlomer, acoustic coordinator with the NMFS Office of Protected Resources, told the Open Water Meeting that NMFS has been working on new sound disturbance criteria for some time, to take account of new science and to put in place a consistent set of criteria throughout NMFS.
“There has been a lot of new science since our original criteria were first derived,” Scholik-Schlomer said.
The new criteria are still undergoing internal review in NMFS and are being documented as a set of guidelines for eventual publication. Before final publication, the guidelines will be subject to a peer review and will go through a public comment process.
“The goal is to have these guidelines issued by late 2013,” Scholik-Schlomer said.
Current guidelines The current guidelines spell out a series of sound levels, specified in decibels, at which broad categories of animal such as whales and seals are likely to be impacted. Depending on the level of sound, impacts can range from minor behavioral disturbance through temporary hearing impairment to permanent hearing damage. Companies conducting offshore activities are only allowed to disturb small numbers of animals at the lower levels of disturbance, without causing injury.
NMFS mandates two sets of sound levels: one for impulse sounds such as seismic shots and another for continuous sounds, such as the noise from a drilling rig. And, with an absence of data about hearing loss in marine mammals, the sound levels have been based on expert opinion, Scholik-Schlomer said.
To assure that an activity operates within acceptable levels of animal disturbance, the acoustic disturbance criteria are used in conjunction with estimates of sound propagation from the activity and estimates of likely animal population distributions. Then, when conducting an activity, a “safety circle” is defined around the sound source, outside which the sound level is below the relevant disturbance threshold. The activity has to stop if an animal enters the safety circle.
Estimating takes Initially, the new acoustic criteria will only apply to the estimating of takes for an activity, with the existing criteria continuing to be used for the time being in the establishment of safety circles for mitigating animal disturbance, Jolie Harrison, NMFS incidental take team supervisor, explained.
The new criteria, which attempt to more realistically model how sound impacts animals, separately consider sound levels that might injure animals and the sound levels which, while possibly not causing injury, would cause some significant change to animal behavior — cause an animal to flee from an area, for example.
For its injury-causing sound criteria, NMFS has used a variety of data about marine mammal sensitivity to noise and extrapolated this data to estimate sound levels that would cause permanent hearing loss for a variety of mammal species, Scholik-Schlomer said.
Types of impact The criteria for injury-causing sound levels continue to distinguish between impulsive sound and continuous sound, but they also consider two distinct potential impacts to animals: the peak pressure of the sound waves passing through the water and the cumulative amount of sound that an animal might experience over time. That latter consideration, the cumulative impact, recognizes the importance of the duration of sound as well as the sound level, Scholik-Schlomer explained.
In assessing the potential for injury, NMFS also wants to take a much more focused approach by recognizing the different hearing characteristics of different animals, even within broad animal classifications such as whales or seals. Individual whale species, for example, are being placed into groups based on whether their hearing responds to low, medium or high frequency sound, and with weightings applied to adjust the sound criteria for a species, based on how well that species can hear, Scholik-Schlomer said.
Thus the frequency characteristics of the sound and the characteristics of a species’ hearing will both play into estimates of potential marine mammal takes. Seismic sound, for example, tends to have quite a low frequency and would have less impact on whales with mid-frequency hearing than on animals with lower frequency hearing, Scholik-Schlomer explained.
NMFS realizes the complexities of this new approach and is working on tools and a user guide, to help people understand the techniques, she said.
Behavioral impacts In determining acoustic criteria for animal behavior impacts, as distinct from impacts that can cause injury, NMFS is distinguishing between different types of activity such as seismic surveying, drilling, impact pile driving and so on, Scholik-Schlomer said. This approach recognizes that animal behavior reacts to the overall nature of an activity, and not just to the sound that it emits, she said. The same sound level may have different impacts, depending on what is being done.
NMFS is using data from marine mammal monitoring during industrial projects to derive behavioral information.
For the initial implementation of the new guidelines, NMFS is only considering the behavioral impacts of seismic surveys. If the approach works out, NMFS will apply the same procedures for other types of activity, Scholik-Schlomer said.
Fundamentally different And the new approach is fundamentally different from what has been done in the past.
Rather than, as is done now, taking an all-or-nothing approach, in which all animals inside a zone where sound is above a certain level are assumed to be impacted while no impacts are assumed to occur to animals outside the zone, NMFS wants to use a statistical technique to develop an “exposure response curve,” a curve that plots the proportion of animals likely to be impacted by the sound over a range of distances from the sound source.
“I think it more accurately reflects what we know about (animal) behavior,” Scholik-Schlomer said.
NMFS is also categorizing animals into broad species groups, recognizing that different types of animal use sound and respond to sound in different ways, she said.
A further twist in the new approach is the consideration of some animal vocal and respiratory responses that can happen at relatively low sound levels. NMFS is also developing sound criteria for species that appear especially sensitive to sound, with the bowhead whale being a possible example of this, Scholik-Schlomer said.
Threshold sound exposure levels will be specified for the various permutations of animal types, sound types and types of harassment, such that any exposures of the relevant animals to sound levels above any of the thresholds would constitute takes. Hence, it will be possible to estimate the total number of animal takes likely from a specific offshore activity.
Although the new sound thresholds will be expressed in decibel values, in the same manner as in the old criteria, Scholik-Schlomer cautioned about trying to make comparisons between the sound level thresholds in the old and new systems. The criteria cannot be directly compared, especially because the new criteria use cumulative sound exposures, taking into account the sound duration, she said.
“We’ve never taken duration into account like that before,” she said.
Complicated Some people at the meeting questioned the feasibility of using the new scheme at some point in future for mitigating animal disturbance, rather than just for estimating takes — the new scheme is significantly more complex than the current procedure. And whereas the current procedure simply involves establishing a safety circle using a standard set of sound level thresholds, the new acoustic disturbance criteria involve subtleties such as sound durations and exposure response curves.
However, Harrison said that she thought that it would ultimately be possible to adapt the new methods for mitigation use.
Some people questioned how traditional Native knowledge might be incorporated into the procedures. Native subsistence hunters worry about the potential impacts of industrial noise on the wildlife that they hunt for food. Would impacts on the subsistence harvest be evaluated as part of take estimating, one questioner asked.
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