A workshop on the “Status and Applications of Acoustic Mitigation and Monitoring Systems for Marine Mammals” was held November 17-19, 2009, sponsored by the Bureau of Energy Management, Regulation and Enforcement (BOEMRE) and attended by over 200 participants. The objectives of the workshop were stated as follows:
“Learn about, discuss, and better understand the current status of acoustic hardware and software tools for marine mammal monitoring and mitigation as applied to offshore industries. This will include the capability, applicability, feasibility, availability, cost and other benefits and limitations of acoustic systems as they pertain to different marine mammal and operational contexts. The discussion will focus on currently available acoustic systems, along with some potentially beneficial applications under development.”
Following a workshop with such ambitious objectives, consolidation of key conclusions is obviously valuable, but taking a step towards closure is a challenge, due to the inherent complexity of the subject matter. These brief notes represent an attempt by the workshop’s technical advisors to capture key conclusions.
Conclusion 1: Many of the basic software and hardware technologies to meet marine mammal monitoring and mitigation requirements exist, but most of these technologies have not been specifically designed for offshore industrial development. The appropriate combination of technologies for a project will likely require a site/case-specific, integrated approach because no one technical approach will satisfy all or even most marine mammal monitoring and mitigation requirements for the offshore industry. Simply put, “one size does not fit all.” Furthermore, it should be clearly noted that all PAM systems (e.g., fixed, towed, or drifting) only work if an animal produces a sound that can be detected with the system. An active acoustic monitoring system circumvents this limitation, but raises some concern because it also introduces sound into the environment.
Conclusion 2: Choosing and evaluating the best acoustic monitoring system for a specific project requires a thoughtful and thorough assessment of a project’s objectives, coupled with a thorough evaluation of the regulatory monitoring and mitigation requirements, and the capabilities of the available acoustic technologies. This coupling of objectives with regulations and technical capabilities is an ongoing iterative process, where objectives may have to be modified as a result of specific monitoring and mitigation regulatory requirements and/or the inherent limitations of available systems.
Conclusion 3: Three general types of acoustic systems are available: fixed passive acoustic monitoring (fixed PAM), towed passive acoustic monitoring (towed PAM), and active acoustic monitoring (AAM) systems. Each of these system types has somewhat unique data processing (including signal processing) requirements. Data processing needs and capabilities are an integral requirement in the design, operation, and evaluation of acoustic systems. As an example, most data processing software that is well suited to a fixed PAM system is not usually designed to work with a towed PAM system, and data processing software that is designed to work with one particular towed PAM system may not work at all with a different towed PAM system.
Conclusion 4: Fixed PAM technologies appear to be more mature than towed PAM or AAM technologies, although this does not necessarily indicate that a fixed PAM approach is the most effective in all situations. Fixed PAM has been used with great success in many settings, including predevelopment baseline studies, assessment of marine mammal responses to offshore facilities, and management of ship traffic to reduce the risk of collisions with whales. Despite these successes, a number of limitations and challenges were highlighted (see Conclusions section at end of report).
Conclusion 5: Towed PAM technology seems to be somewhat less mature than fixed PAM technologies, but more mature than AAM technologies. Towed PAM systems have been used with some success to supplement visual monitoring of exclusion zones in the North Sea, the Gulf of Mexico, and elsewhere. Despite these successes, a number of limitations and challenges were highlighted (see Conclusions section at end of report).
Conclusion 6: The AAM technology is less mature than either fixed PAM or towed PAM technologies. However, active acoustics is the only acoustic method capable of detecting animals that are not producing sounds. Despite the relative immaturity of active acoustics, recent tests indicate that it can be useful in some circumstances. Limitations or challenges associated with active acoustic systems are provided in the Conclusions section at end of report.
Conclusion 7: In some circumstances, the effectiveness of marine mammal monitoring and mitigation could be increased by using a combination of approaches. For example, a combination of marine mammal observers, towed PAM, and active acoustics would improve the likelihood of detecting and identifying marine mammals in the vicinity of potentially harmful activities. Similarly, a combination of fixed PAM and active acoustics may provide an improved understanding of apparent changes in the distribution of calling whales responding to industry sounds, a problem that has plagued at least some studies that relied only on a fixed PAM system.
Conclusion 8: The effectiveness of the marine mammal monitoring and mitigation process would significantly benefit from the development, establishment, and maintenance of a national(at least) or international (preferable) standardized, web-accessible ecosystem database (consisting of species seasonal presence/abundance and as many other important behavioral features as possible), coupled with a marine acoustics database (including marine mammal sounds, natural abiotic sounds, and anthropogenic sounds). This conclusion is consistent with many previous recommendations (e.g., NRC, 1994; 2000; 2003; Southall et al., 2007), including those expressed as a high priority by a task force of U.S. federal agencies considering this subject (Southall et al., 2009).