A guest post by Andrew McQueen, US Army Corps of Engineers
Researchers around the world are focusing more on the role of anthropogenic (human-made) sounds in marine ecosystems. In the last half century, as we have industrialized and expanded our use of the “blue” ocean economy (maritime transport, fisheries, and renewable energy), some regions have observed incremental increases of anthropogenic underwater sounds. However, the ecological consequences, or risks, of these changing underwater soundscapes remain largely unknown.
Some regions are introducing policies that factor impacts of underwater sounds as physical stressors to marine habitats. For example, the European Union has adopted the Marine Strategy Framework Directive and the International Maritime Organization proposed guidance for reducing underwater sounds from commercial shipping. In the U.S., the National Oceanic and Atmospheric Administration (NOAA) released technical guidance for assessing effects of anthropogenic sounds on selected marine mammals. The marine coastline is particularly vulnerable, due to the intensity and overlap of human activities within critical nearshore habitats. Therefore, the development and application of risk-based tools will aid in our understanding and management of the underwater soundscapes in these complex marine ecosystems.
Researchers frequently confront challenges when assessing potential ecological impacts of underwater sounds. Sound waves traveling in water behave differently than in air and are not directly comparable. Underwater sound waves can have complex waveforms that vary greatly among sound sources, in terms of intensity (decibel level), frequency (hertz), duration, and distance traveled. Much progress has been made to understand impacts of underwater sound on marine species. In the past two decades, the number of studies exploring adverse impacts of underwater sounds on marine life has drastically increased. Consequently, we are in a unique position to apply this new scientific knowledge to more advanced risk-based concepts and principles to enhance our progress toward understanding impacts.
The future success of the blue economy will require port infrastructure maintenance and expansion and dredging to maintain safe and navigable waterways. Yet, like many anthropogenic activities in marine environments, dredging introduces underwater sounds from engines, propellers, and operational equipment. A recent U.S. Army Engineer Research and Development Center (ERDC) research initiative conducted to support the U.S. Army Corps of Engineers provided an opportunity to develop and demonstrate a risk-based approach for assessing and managing risks associated with underwater sounds. The objective of the study was to assess impacts associated with underwater sounds in the marine environment.
A large-scale port expansion dredging project was used as a practical example; the project involved publicly available sound exposure modeling tools (see the NOAA National Marine Fisheries Service [NMFS] web calculator) and published biological effects for select marine species. A key beneficial component of the framework presented in the study is the use of a phased approach (Figure 1), whereby a screening step utilizes readily available information to evaluate risks, and a more comprehensive step to further refine the assessment and to be subsequently used by managers to determine whether measures are needed to reduce the impacts. This framework offers flexibility and transparency for assessing impacts within the rapidly evolving field of underwater sound and provides a system to apply the existing scientific information we currently have.
Although many challenges remain toward a more complete understanding of how human-induced changes in the marine soundscape affect ecosystems, a risk-based approach provides a path forward to making scientifically defensible management decisions. The information resulting from this approach can be combined with other threats to the marine ecosystem—increased demand on resources, climate change and emerging contaminates—to paint a more complete picture of ongoing threats and to help meet the future challenges of an environmentally sustainable blue economy.
Articles referenced in this post
McQueen, A.D., Suedel, B.C., de Jong, C. and Thomsen, F. (2020), Ecological Risk Assessment of Underwater Sounds from Dredging Operations. Integr Environ Assess Manag, 16: 481-493. https://doi.org/10.1002/ieam.4261
Miller, P.J.O., Johnson, M.P., Madsen, P.T., Biassoni, N., Quero, M., Tyack, P.L. (2009)
Using at-sea experiments to study the effects of airguns on the foraging behavior of sperm whales in the Gulf of Mexico. Deep Sea Research Part I: Oceanographic Research Papers 56(7): 1168-1181. https://doi.org/10.1016/j.dsr.2009.02.008