It's not only whales that are affected by military sonar, but California sea lions respond to the underwater noise as well, according to a new study in the journal Marine Environmental Research. Experiments with captive sea lions show that the louder the military style sonar signals the marine mammals are exposed to, the more they react, particularly if they are younger sea lions.
In the experiment, fifteen sea lions were exposed to a simulated tactical sonar signal (not directly physically harmful) for one second at varying levels of loudness. The sea lions were trained to swim across an enclosure, touch a paddle and return to the starting point.
The simulated sonar was turned on when the sea lions crossed the middle of the enclosure. Among the sea lion reactions were such things as refusing to participate, hauling out of the water to avoid the noise, changes in their breathing rate and staying underwater longer. The experiment was conducted using methods based on pharmaceutical studies on “dose and response” to medications.
The work is part of the ongoing effort by the Navy and independent scientists to learn how sonar affects marine mammals and makes some species apparently lose their way and get beached, as has believed to have happened when Navy ships have employed the sonar technology they use to detect enemy submarines.
“The problem is that there isn't much data out there,” said the National Marine Mammal Foundation's Dorian Houser, the lead author of the study. What scientists and the Navy have had is a hodgepodge of data that has amounted to little more than wild guesses about how specific animals respond to the military sonar. “The regulatory agency is forced to make this decision based on very little information.”
And so they throw together what little is known about large baleen whales with toothed whales, for instance, despite the vast differences in the animals and extrapolate.
“It's a tough issue to crack,” agreed Brandon Southall, a marine mammal researcher at the University of California at Santa Cruz, and president of Southall Environmental Associates. “You're asking how a pattern of behavior changes with different species and different individuals.”
Right now there are basically two lines of research underway. One is with captive animals, like what Houser and his colleagues are doing. The other is studying wild animals in the oceans, which is Southall's specialty.
“The hard part is controlling for variables in the wild,” said Houser, who has a great deal of control with captive animals. The downside of that, however, is that captive species are limited, mostly just sea lions and bottlenose dolphins, and they are used to human activities.
On the other hand, Southall studies wild animals with a real sonar-equipped ship in the ocean, and so better reproduces what animals experience from Navy vessels. Both approaches have strengths and weaknesses and will, said Southall, complement each other.