Whales May Suffer From Decompression Sickness
Study Provides Clues to How Navy Sonar Affects Rare Beaked Whales
Jul 7, 2009
As part of the effort to prevent further losses of rare whales during navy sonar testing, researchers have been looking into the reasons that beaked whales, and Cuvier’s beaked whales (Ziphius cavirostris) in particular, have been so heavily affected.
Ocean Noise Affects Many Whales and Dolphins
It is not just navy exercises at sea that are having a negative effect on whales and dolphins. Seismic testing for undersea oil and natural gas, as well as shipping traffic also contribute to the ocean noise pollution faced by marine mammals everyday. Noise affects the whales’ ability to communicate and to find food, as many species, including sperm whales (Physeter macrocephalus) use sound to capture prey.
What makes the navy sonar testing situation unusual is that several rare beaked whale species appear to be most heavily affected. This has lead researchers to try to determine what it is that makes these whales so vulnerable, and how further deaths can be prevented.
Navy Sonar Testing Linked to Beaked Whale Strandings
The question of why beaked whales in particular were being affected is one that needed to be looked at closely. Most beaked whale species are poorly understood. The IUCN lists all but the Cuvier’s beaked whale as data deficient, largely because these whales tend to be found far offshore and are difficult to study.
The Cuvier’s beaked whale is known to have a reasonably large population, which is spread around the globe. But even with this species, it is not clear whether the population is increasing or decreasing.
Beaked Whale Diving Behavior Offers Clues to Mass Stranding Cases
The recent study by Hooker et al, “Could beaked whales get the bends?” can be viewed at the Cascadia Research Collective website. It looks at decompression sickness as a possible cause for the deaths of beaked whales following navy exercises. The study was funded in part by the US Navy.
The researchers studied diving behavior and physiology for three species, Cuvier’s and Blainville’s (Mesoplodon densirostris) beaked whales and the northern bottlenose whale (Hyperoodon ampullatus).
One finding was that these beaked whales tend to perform a series of short, shallow dives after long deep dive foraging dives. It is hypothesized that these shallow dives are deep enough to reduce supersaturation but shallow enough to all allow removal of nitrogen, thus preventing the bends.
It was found that diving behavior for Cuvier’s beaked whale was significantly different from that of the northern bottlenose whale or the Blaineville’s beaked whale. This may result in higher levels of nitrogen (N2) in the blood and tissues, possibly making them more susceptible to decompression sickness. It is possible that the navy sonar testing prevents the whales from performing the needed series of shallow, nitrogen-clearing dives, resulting in nitrogen narcosis and death.
Further Research Needed on Navy Sonar and Whale Mass Strandings
While this study provided some possible reasons for the predominance of Cuvier’s beaked whales in navy sonar related mass strandings, it is still not known how the sound waves affect the dive behavior of these beaked whales. More information on those effects will be needed to understand why the strandings occur.
There are also many unanswered questions about the anatomy and physiology of deep diving marine mammals and birds, such as the effects of underwater sound waves on bubble formation within blood vessels, which may provide clues to the navy sonar related mass stranding problem.
What is clear is that there is a connection between beaked whale mass strandings and sonar testing and that further deaths should be avoided.
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