Interim Findings on the Stranding of Beaked Whales in the Bahamas
December 20, 2001

NOAA Fisheries and the U.S. Navy today released the interim report on the March 2000 stranding of 17 marine mammals in the Bahamas.

The report states that this stranding event was caused by the unusual combination of several contributory factors acting together: specific oceanographic features, unusual bathymetry, presence of beaked whales and a specific sound source. Review of passive acoustic data ruled out volcanic eruptions, landslides, other seismic events, and explosive blasts. The unusual extended use of Navy midrange tactical sonars operating in the area is the most plausible acoustic source.

On March 15 and 16, 2000, a stranding of seventeen marine mammals of several species was discovered along the Northeast and Northwest Providence Channels on Bahamian Islands. The strandings took place within 24 hours of U.S. Navy ships using active midrange sonar for an unusually extended period, as they passed through the Northeast and Northwest Providence Channels. Six of the whales died after stranding on beaches. One dolphin stranded and died of unrelated causes. Ten whales were returned to the sea alive. Specimen samples were collected from four dead whales. Three whales showed signs of bleeding in the inner ears and one whale showed signs of bleeding around the brain.

An unusual combination of specific physical oceanographic features, bathymetry, presence of beaked whales, and specific sound sources were present. While the precise causal mechanisms of tissue damage are unknown, available evidence points to acoustic or impulse trauma. Review of passive acoustic data ruled out volcanic eruptions, landslides, other seismic events, and explosive blasts. The unusual extended use of Navy midrange tactical sonars operating in the area is the most plausible acoustic source.

The investigation team concludes that the cause of this stranding event was the confluence of these contributory factors acting together. Research should focus on identifying such highly unusual but problematic combinations so they can be avoided. The actual mechanisms by which these sonar sounds could have caused animals to strand, or their tissues to be damaged, have not yet been determined, but research is under way. This research, along with other research on the impacts of sonar sounds on marine mammals, increased knowledge of marine mammal densities, increased knowledge of causes of beaked whale strandings, increased knowledge of beaked whale anatomy, physiology and medicine, and further research on sonar propagation, will provide valuable information for determining which combinations of factors are most likely to cause another mass stranding event. Low Frequency Active sonar had no involvement in this event.

To the maximum extent practical, the Navy will adopt measures in its future peacetime operations and training, including the use of tactical mid-range sonars, to avoid injuring or harassing marine mammals. The report recommends the Navy and NOAA research the mechanisms by which sonar sounds affect marine mammal tissue or behavior (the report lists 15 different projects). The report also recommends the Navy put into place mitigation measures that will protect animals but not jeopardize national security. The Navy will include, when possible, Bahamian scientists and qualified individuals as participants in future surveys involving marine mammal research in Bahamian territorial waters. Navy and NOAA will also invite Bahamian participation in future marine mammal workshops and conferences.

This is an interim report; Conclusions and recommendations appearing therein could change somewhat as final results become available.

For further information regarding the biological studies contact:

Gordon Helm or Connie Barclay - NOAA Fisheries (301)713-2370

For further information regarding the Navy’s use of sonar and the recommended mitigation measures contact:

Lt. Pauline Storum or Lt. Patrick McNally - U.S. Navy (703)692-6705/6706/6707