Acoustic Assessments

Acoustic Assessment

Before BOEM authorizes offshore activities, the bureau and industry applicants must assess the potential risk of acoustic impacts to marine species. As regulatory requirements and technical capabilities change, BOEM’s underwater acoustic analysis and assessments must become both more complex and more flexible to meet changing demands.  

Typically, researchers combine acoustic propagation models and animal movement models to generate a predicted number of “takes” by harassment under the Endangered Species Act, the Marine Mammal Protection Act, or both. Under these statutes, harassment does not allow for species mortality but includes the potential to injure hearing or disrupt important behaviors. These estimates tend to produce very high take numbers because the assumptions built into the calculations are highly conservative by design. Estimates also do not incorporate other relevant information (e.g., life history, species status, and behavioral context), which is essential for realistically assessing actual impacts on population sustainability. BOEM will incorporate these important contextual factors as we advance our in-house capacity for underwater acoustic modeling. This improvement includes utilizing a risk assessment framework that has recently been developed by external experts.

BOEM’s Acoustic Modeling Approach

Currently, BOEM relies on external modeling for formal analysis of the acoustic and biological effects of anthropogenic sound on marine species. While some current models approximate various phenomena and predict effects, there is no comprehensive model that meets BOEM’s long-term needs. 

Consequently, the CMA is building a “Workbench” – a dynamic tool for predicting acoustic and biological effects of anthropogenic sound on the Outer Continental Shelf. This model will be particularly useful for answering current needs and driving next-generation regulatory approaches.

The CMA Workbench will address these challenges through an integrated framework of models, tools, and analytic processes that yield results consistently recognized as high-quality by experts in the field. The Workbench will be certified as part of an initial capabilities review but will grow to meet emergent scientific discoveries and regulatory requirements and future needs.

The new model aims to provide the following:

  • In-house capability to reliably estimate the effects of anthropogenic sound on marine life  
  • Capability to integrate various models, giving flexibility to develop new techniques and answer new questions as regulatory requirements and technical capabilities evolve
  • Internal expertise to use Workbench to drive more complex questioning, interpret results, and contribute reliable quantitative assessments to recommendations for BOEM-regulated activities
  • Ability to conduct formal and defensible analysis, as well as informal exploration by a variety of stakeholders and quality control oversight of contractors
  • Substantiation that the CMA possesses legitimate and trusted expertise on the acoustic impacts of BOEM activities

The CMA has also developed recommendations for modeling impact pile driving noise. This document provides industry an overview of BOEM’s expectations during the Construction and Operations Plan (COP) review process and also explains BOEM’s expectations for sound field verification during impact pile driving. 

New Risk Assessment Framework

BOEM supported the development of a customized, quantifiable risk assessment framework for evaluating the relative level of risk of each of the noise-producing activities that BOEM authorizes (e.g., seismic surveys and pile driving). This framework integrates relevant information about species vulnerability (e.g., population size, habitat use, environmental context) and exposure to noise (e.g., pile driving, vessel noise, wind turbine operations) to provide an overall assessment of risk to a species when exposed to a particular sound-generating activity. Using the framework, BOEM – along with developers – can consider aggregate impacts of multiple overlapping activities, such as the concurrent construction of multiple offshore wind farm facilities. The result: identification of high-risk areas, times, and species where BOEM should focus its regulatory attention. This holistic risk assessment is more informative/comprehensive to decision making than relying solely on simple take numbers.  

Framework Case Studies