Tugged Sonar, Source: Wikimedia Commons
A lot has been said and discussed in regard to how Navy’s Mid-Frequency (MF) and Low-Frequency (LF) sonars can affect marine mammals. The discussion has been mainly focused on physiological effects, such as hemorrhage, ear damage, gas embolism, etc. Even though media, officials, rescues rarely discuss these effects with the public, another aspect of how Navy’s sonar and other anthropogenic noise activities can cause mass strandings has been missing entirely from the conversation on strandings. One major phenomenon of mass strandings is that animals are seemingly healthy, without any serious illnesses or impairments and when released, can survive and thrive with no issues whatsoever (Bogomolni et al., 2010 ). This is why acoustic barrier hypothesis proposed by Dr. Brownell requires more attention than it currently attracts.
In 2008 Brownell et al., published a very comprehensive reviewpaper on how sound has been historically used to hunt not only small dolphins, but also large whales. In a nutshell, the article describes various methods that have been used since 14th century to hunt cetaceans with sounds. Ancient fishermen were well-aware of these properties of sounds and used it to drive pods ashore in Japan, Solomon Islands, Denmark, Canada, Faroe Islands and so on. Remarkable, there are also evidences that a fin whale (species that strand very often) was also successfully driven ashore in 1903 by using sound in New England, USA. So from this review it is abundantly clear that sound can indeed be successfully used to drive cetaceans ashore. But what does it have to do with Navy sonar or oil/gas industry seismic surveys airguns?
Killer Whales. Source: Wikimedia Commons
In another paper published in 2009 by Brownell et al., a curious case of nearstranding of melon-headed whales (Peponocephala electra) is described. Nearstranding is another phenomenon that will be discussed in this blog soon, however in this paper the stranding was prevented by human intervention where the pod was basically herded out of the bay in Hawaii. This is another, highly recommended and fascinating read, but in short on July 3-4, 2004 a pod of melon-headed whales entered Hanalei Bay, Hawaii (similar to recent Cape Cod case). The pod moved into very shallow waters and exhibited very typical prestranding behavior, such as erratic milling, and other behavioral manifestations. Prior and during this stranding the Navy was operating its Mid-Frequency (MF) sonar in the area. The situation got so bad, that NMFS was forced to request the Navy to stop operating its sonar and only then “the whales were successfully moved out to sea by two canoes using a traditional lau (a strand of woven beach morning glory vines[= pohuehue, Ipomoea pes-caprae] ∼700 ft (213 m) in length floating on the surface of the water that was tied between the two canoes), which were assisted by an additional 30–40 kayaks as the animals moved toward open waters.” (Brownell et al., 2009, p. 14). The only casualties of this nearstranding was one calf that was found dead later and most likely got lost or separated from his mom and died of dehydration.
While the Navy vehemently denied any involvement and NOAA produced a document trying to mitigate the accusations (Southall et al., 2006), other researchers indicated that the sonar in this case acted as an acoustic barrier forcing pod to flee, preventing whales from leaving the area or going towards sonar. The history of drive fisheries that used sound supports this notion and indeed offers another possible mechanism of how the sonar or seismic exploration airguns can cause mass strandings. If a pod is in position between the coast and the sound source it will flee the sound source because it cannot move towards it. It will not flee sideways, but will flee in the opposite direction basically hitting the coast sooner than later. And indeed, in case of melon-headed whales, a pod turned out at the entrance of Hanalei Bay while the MF sonar was still very much active. Brownell et al., (2009) proposed that the sonar acted as an acoustic barrier (similar to drive fisheries) and forced the pod to flee and refuse to leave the harbor. This fits very well in the notion that mass stranded whales are not sick, unlike the rescues and gov. officials want us to believe. Nor they are lost, or disoriented. They just flee the sound source and die on our shores.
There are some reports that the Navy exercises were underway even before the first dolphin stranded in Cape Cod in mid-January, 2012. These exercises involved “combat acoustics” which very well might acted once again as an acoustic barrier and induced the common dolphins to flee it, entering Cape Cod Bay, strand and die. Because the exercises were underway on 27th of January and possible even now, it might as well explain why common dolphins have been stranding for weeks now (it has to be noted that the current location where the “combat acoustic” was used is unknown apart from broad “Atlantic Ocean” description). Now, unlike with the case with melon-headed whales, nobody asked the Navy to stop or even talked about Navy Comptuex exercises. This is extremely sad and disturbing. We already have scientific reports in place that talk about the acoustic barrier and yet, the media, rescues and government officials keep talking about irrelevant stuff, blaming strandings on sociality of common dolphins, errors in navigation and other nonsense alike. The situation with mass strandings worldwide is one hot mess and unless we start questioning everything we have been told so far, it is not going to change.
References:
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By: Alfombra Bird Observatory, Costa Rica on April 12, 2012
at 11:30 pm