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Scientists Call Strongly for More Stringent Safety Thresholds for Sonar Exposure

Ocean, Science, Sonar Add comments


This is an AEI lay summary of the following academic paper:
Parsons, Dolman, Wright, Rose, Burns. Navy sonar and cetaceans: Just how much does the gun need to smoke before we act? Marine Pollution Bulletin 56 (2008) 1248–1257.
This paper represents a clarion call by several biologists who are convinced that we now have enough information about the impacts of sonar on whales to justify the imposition of more stringent safety measures. In contrast to Navy insistence that there is no widespread problem, and to the slow and patient progression of scientific data to clarify exactly what the mechanisms that lead to strandings may be, these authors lay out a compelling case for a change in course.

The paper begins with a litany of strandings that have stayed below the radar of most observers, including noting that there have been eight mass strandings in the Canary Islands in recent years, as well as little-studied multiple events in Japan and Taiwan, near US and Chinese training grounds. While delving into the current theories about what may cause the physical injuries seen in many stranded animals, they stress that these injuries, as well as less severe injuries, are likely triggered by avoidance reactions to sonar sounds. Strikingly, they detail several events in which it appears that animals found on the beach died at sea, and question why ocean biologists do not follow the standard used in terrestrial biology, where it is widely acknowledged that only a small proportion of animals that die are actually found by humans, and each body found is considered likely to be indicative of many others never discovered.

The authors stress that current safety standards, based on avoiding temporary or permanent hearing loss, are clearly inadequate, pointing out that likely population-level effects are much more apt to involve sub-lethal and non-physcially injurious exposure levels that trigger behavioral and subtle physical changes, “e.g., repeated and widespread reduction in foraging or reproductive success, widespread impaired immune function, or large-scale displacement.” They express particular concern about the conclusions of a recent US Noise Criteria Panel, which recommended modest increases in the allowable sound exposure levels, based on improved data about what sound levels can cause temporary hearing loss. (To read the post summarizing the panel’s conclusions, click here.) Here, they also make a fairly strong case that our reliance on hearing and behavioral tests using captive animals is likely producing distorted results (they note in particular studies that suggest belugas hear shipping traffic at 80km (rather than the 20km suggested by captive studies), and that common dolphins may avoid seismic surveys when sound levels are only 48dB, orders of magnitude lower than captive studies suggest they’d respond to. They conclude that “it must be assumed that military exercises involving sonar are not just affecting a small number of beaked whales, but are likely to be having wider effects on the ecosystem and quite possibly causing loss of biodiversity (at least locally, as appears to be the case in the Bahamas).”

The paper continues with a summary of the many statements of concern that have been issued by international bodies since 2001, though so far only the Canary Islands have responded with concrete policy changes (banning active sonar off its coasts). Noting that low-frequency sonars are likely to create both physiological and behavioral reactions at much greater distances, the authors conclude their paper with this statement: “we contend that there is already enough evidence to know that the current efforts to protect cetaceans from the consequences of exposure to sonar and undoubtedly other intense anthropogenic sound are inadequate and that additional protection measures are therefore required.”


2 Responses to “Scientists Call Strongly for More Stringent Safety Thresholds for Sonar Exposure”

  1. Robin Says:

    What can concerned citizens of North Florida do right now to help with this cause?

  2. aeinews Says:

    The Navy is currently considering building an Undersea Warfare Training Range off the coast near Jacksonville.
    A draft EIS was released this fall, and public comments are now closed. But you could stay in touch with that process and encourage state agencies to take a close look (when it was proposed in NC, state agencies were active in the commenting process). The range is a mixed bag: it may help concentrate activity, since they’ll have instruments installed on the seabed to make more use of the exercises, but there are concerns about whether it’s too close to right whale calving areas. So far, no record of notable reactions by right whales due to sonar, but this needs to be considered.

    Also, Jacksonville has its own larger “Range Complex” that is undergoing an EIS process