How does the use of mid-frequency sonar by the world’s navies affect marine mammals? Rocket science may help biologists to understand the effects of these systems by allowing them to virtually look inside the head of whales.
An industrial sized X-ray scanner, the same kind that NASA uses for detecting flaws in solid fuel rockets, is now providing 3D images of the hearing anatomy of whales, using a method developed by a marine biologist, Dr. Ted Cranford. The research, sponsored by the Office of Naval Research (ONR) and the Chief of Naval Operations Environmental Readiness Division (N45), uses a simulated model of a beaked whale’s head.
The research team’s initial data suggests that mid-frequency active sonar sounds are largely muffled before reaching the whale’s ears, but that the higher frequencies used by whales to hunt are heard at amplified levels without any dampening.
“Even though these findings are promising, our next step is to reproduce the study with a similar species for which hearing tests are available, such as the bottlenose dolphin. If we obtain like results, it will help to validate this new discovery.” – Cranford
The new approach to the investigation of mid-frequency sonar effects on marine mammals uses advanced computing in conjunction with outsized X-ray CT scanners to generate the reproductions in minute detail. The simulation is referred to as a “finite element model” or FEM, and according to the researchers, it accurately describes the interactions of sound with the hearing anatomy of whales.
“The simulation technology is powerful because it provides a means to look at a broad range of species, from whales to fish, for which we may not otherwise be able to study hearing. Virtual experiments can also provide potential for evaluating and directing mitigation efforts.” – Dr. Michael Weise, ONR program manager
According to an article at NRDC, the most widely used sonar systems operate in the mid-frequency range, and evidence of the danger caused by these surfaced in 2000, when whales of four different species stranded themselves on beaches in the Bahamas. The Navy denied responsibility, but the government’s investigation established that mid-frequency sonar caused the strandings.
In 2005, the Navy was sued by a coalition of conservation and animal welfare organizations because of the use of mid-frequency sonar, saying that it “can emit continuous sound above 235 decibels, an intensity roughly comparable to a Saturn V rocket at blastoff.”
Again, from the NRDC:
“The Navy also admitted that training exercises off the coast of southern California posed dangers to marine life. It estimated that exercises planned between January 2007 and 2009 would disturb 170,000 marine mammals, permanently injure more than 500 whales and cause temporary hearing impairment in at least 8,000 others.”
[Via US Navy]