The National Academy of Science recently released a report concerning the “cumulative effects of stressors on marine mammals” that illustrates the difficulty of science in providing definitive evidence on threats to species. The report begins by stating that “assessing the cumulative effects of multiple stressors” is a “top-priority problem in marine biology.” A survey of 2000 ocean scientists declared that their “top priority” research question is “How will the individual
and interactive effects of multiple stressors (e.g., ocean acidification, anoxia, warming, fishing, and pollution) affect the capacity of marine ecosystems and species to adapt to changing oceans?” I read this report hoping to benefit from a statement about substantive findings on cumulative effects. However, the report does not provide such an assessment because it turns out that identifying cumulative effects is very difficult to do. A previous 2005 National Academy report stated that “no scientific studies have conclusively demonstrated a link between sound and adverse effects on a marine mammal population.” This report states that this statement remains true concerning a “population” but, they state, in more recent years, studies have shown effects “on individual marine mammals.” The report states several reasons why it is so difficult to assess the effects of sound (and other stressors) on populations. One limitation is that most studies establish a “threshold” so that they are measuring the effects of sound in an “all or nothing” approach that thus underestimates the impact of sound. They conclude that the effects of sound “cannot be reliably be condensed into a single estimate” because individual animals respond differently” and, statements about the effects are subject to uncertainty so that at best “confidence intervals” would be “more consistent with the state of knowledge” about predicted impacts. It goes on to state that once researchers try to estimate the cumulative impacts of additional stressors that the research is much more complex and it is even more difficult to reach firm conclusions. They state that to study this issue “rigorously” would require a factorial experiment that could detect the “interactive effects of multiple stressors” but that for both “practical and ethical reasons, such experimental approaches are not possible” and consequently conclusions must be based on “quasi-experiments.” In my Wildlife Politics book, I have an entire chapter devoted to science and its role in wildlife conservation policy. I point out that the Endangered Species Act (and major treaties such as CITES) state that policy should be based on the “best available science” but I demonstrate in the chapter how the role of uncertainty as well as values (e.g., how and where to draw lines) and the use of complex models based on assumptions has meant that often researchers disagree on substantive conclusions about wildlife conservation. This National Academy Report reaffirms my Ch.2 conclusion about the limitations of science. Of course, science does play a key role in making decisions but, as I show in my book, it is often a “supporting” not a leading role in many decisions. The report is available as follows: National Academies of Sciences, Engineering, and Medicine. 2017. Approaches to Understanding the Cumulative Effects of Stressors on Marine Mammals. Washington, DC: The National Academies Press. doi: https://doi.org/10.17226/23479
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