Rising levels of noise in the ocean have been identified as a growing concern for the well-being of marine mammals, but other threats such as pollution, climate change, and prey depletion by fisheries may also be harming marine mammals.
A major new report by the National Academies of Sciences, Engineering, and Medicine has concluded that current knowledge and data are insufficient to determine what combination of factors cause the greatest concern.
The study, by a committee of experts chaired by professor of marine biology at the University of St Andrews Peter L Tyack, includes a newly developed conceptual framework model to help federal agencies and research communities explore the potential cumulative effects of human activities on marine mammals.
The report, which was launched in Washington DC, found that although the impacts from some stressors such as persistent chemical pollutants or ocean climate cannot be readily reduced, others like noise, fisheries, or shipping routes can be managed to reduce their impact.
One tool recommended in the report is a real-time, centralised system for reporting health data of different populations.
Professor Tyack said:
“Current scientific theory and data for individual marine mammals or their population is not enough to predict the total risk from a combination of threats.
“The model we developed in this report provides a way to examine the effects associated with the exposure to a single stressor in the context of the cumulative effect of other stressors in the animal’s environment.”
The committee, which included St Andrews biology professor John Harwood and ecological statistician Len Thomas, also recommended using a framework that assesses the health of individual mammals impacted by an activity, and using changes in health to determine how it could eventually affect populations.
For example, North Atlantic right whales, a protected species since the 1930s, still have an extremely low population size, are exposed to noise and chemical pollutants, and also encounter physical injury during their lengthy migration due to entanglement in fishing gear and collisions with shipping vessels. Archived records of their life histories, including photos and drawings, have helped provide information on health variations and locations over time.
Researchers have used these data to determine certain causes of decline in the population, such as a dramatic decrease in the health of female whales and low reproduction coinciding with reduced prey availability.
The report recommends building affordable surveillance systems that can detect changes in population parameters such as size or reproductive rate and hence indicate when populations may be at risk due to exposure to stressors.
Notes to news editors
The study was sponsored by the Office of Naval Research, the National Oceanic and Atmospheric Administration, the Bureau of Ocean Energy Management, and the Marine Mammal Commission. The National Academies of Sciences, Engineering, and Medicine are private, non-profit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln.
Copies of Approaches to Understanding the Cumulative Effects of Stressors on Marine Mammals are available at www.nap.edu.
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