Military sonar disrupts whales

Bardock, Wal Cuviera, CC BY 3.0

 

It is no secret that everyday human activity is continuously destroying the Earth’s environment and atmosphere.

A recent study suggests that carbon emissions and disposed trash in the oceans, among other prominent forms of pollution, are not the only factors contributing to environmental peril; something unexpected is now harming animals in the ocean.

In a study conducted by Erin A. Falcone et al. and published by Royal Society Publishing, it is shown that mid-frequency sonar used by the military to track submarines is beginning to negatively affect Cuvier’s beaked whales. The scientists tagged and studied 16 whales off the coast of Southern California and noticed this species of whale will beach themselves when they come in contact with these mid-frequency sonars. Upon further study of the beached whales, scientists discovered what resembled decompression sickness. This discovery is groundbreaking, as it was believed that decompression sickness — more commonly known as the bends — was not possible in marine mammals.

According to the study, scientists had a difficult time researching these whales due to the amount of information that is unknown about them. They have not been observed much over the years, and their basic behavior was relatively undocumented prior to the beginning of the studies regarding the beaching of these whales due to sonar contact. Cuvier’s beaked whales are known “to perform a stereotypic [sic] pattern of deep, foraging dives separated by a series of shallower, non-foraging dives,” per the study. Two specific whales were tagged for controlled exposure, and upon exposure to the mid-frequency sonars, the whales were observed to completely change their behavior. At times, they stopped foraging mid dive. On other occasions, the whales would dive deeper and longer than normal and rush back to the surface too quickly. The whales, in some instances, were known to stop diving completely. One rare occasion showed a whale completely unaffected by the sonar; however, this whale was farther out of the sonar’s range.

After compiling the data regarding deeper dives made by the whales post-contact with the mid-frequency sonars, these were the results.

“Deep dives became longer as the distance to the nearest mid-power MFAS decreased. Using the Complete dataset [sic], the mean deep dive duration was predicted to increase with proximity to mid-power MFAS from approximately 60 min to approximately 90 min beginning at around 40 km. The SOAR dataset [sic] predicted that the mean deep dive duration returned to MFAS-free levels by approximately 20 km, after increasing to approximately 107 min with mid-power MFAS at approximately 5 km. The second-ranked models added distance to the nearest high-power source, with a comparable AIC weight for the Complete dataset [sic] (0.224) but a weight roughly half that of the best model in the SOAR dataset [sic].”

The study also showed data about length of surface intervals as well.

“Surface intervals tended to be longer, but also more variable in duration, during either type of MFAS use. This effect was most apparent on SOAR, where predicted surface time during confirmed MFAS-free periods was brief and constrained to a very narrow interval, relative to both periods with MFAS use on SOAR and periods with no reported MFAS use in the Complete dataset [sic].”

The study concluded the sonar is — in fact — the cause of the behavioral changes in Cuvier’s beaked whales. Although high frequency sonar was tested as well, the mid-frequency sonar showed higher levels of response. The full study can be found here.