Cuvier beaked knife, part of the mass fence that occurred in 1996 in the Greek bay Kyparissiakos.
Credits: Alexandros Frantzis / Splashdowndirect / Shutterstock
The ship's sonar was associated with massive firing of wholesome whales for almost two decades, but precise mechanisms affecting whales have been avoided by scientists. Now the researchers have explained the key details of how this disruptive signal provokes behavior in some whales ending with death.
Before the necropsy of spotted whales from multiple stranded deposits found nitrogen bubbles in their body tissues, signs of decompression sickness, or "bends." This dangerous condition also affects divers when they suddenly rise from deep water; it can cause pain, paralysis, and even death.
The kits are tailor-made for deep diving, and beak whales are recorders for the longest and deepest diving. But new research explains how the sonar at certain frequencies disorientates and intimidates some jumbo kits so much that experience overcomes important adaptation to deep diving: slower heart work. Extreme fear accelerates the heart rate of the whale, which can lead to decompression sickness; the intense pain of this condition disables kits so that they are stranded on the beaches and eventually die, scientists reported in a new study. [Whale Photos: Giants of the Deep]
Massage of Cuvier beak whales (Ziphius cavirostris) before the 1960s were almost unknown, but this changed with the introduction of an active sonar (MFAS) into marine exercise in the open ocean. This type of sonar, developed in the 1950s to detect submarines, ranges from 4.5 to 5.5 kHz, according to the study. After this sonar appeared, massive settling events soon jumped for juniper kits, with 121 such austerities that occurred between 1960 and 2004, the researchers wrote.
Scientists first noted the link between the mass stranding of Cuvier whale kits and marine exercises using sonar at the end of the 1980s, lead author Yare Bernaldo de Quirós, a researcher at the Institute of Animal Health and Food Safety at Las Palmas de Gran Canaria, Spain, said Live Science in Email.
This relationship strengthened after similar events in Greece in 1996 and in the Bahamas in 2000, de Quíros added. And in September 2002, when 14 beaked kites were stranded in the Canary Islands during NATO's naval exercise, veterinary pathologists discovered animal lesions that were "consistent with decompression sickness," de Quirós said.
Fight or escape
In 2017, biologists studied juniper kits in order to analyze the finds on wrecks from the past decade on the workshops, observing mass strata that were associated with nearby naval exercises with the aid of a sonar.
Between 2002 and 2014, six mass strata occurred in Greece, the Canary Islands and Almeria in Southeastern Spain, but the dead whales do not appear to be afflicted or ill. However, they have shown "abundant gas bubbles" through veins, blood clots in multiple organs, and microscopic bleeding "of different weight" in the body tissues.
Copied kits may have experienced a "fight or escape" that overpowered the key diving adaptation: lowering the heart rate, reducing oxygen consumption and preventing nitrogen buildup. The result was bleeding and "creating massive bubbles in their tissues," explained de Quirós.
These symptoms of decompression sickness were probably hit by whales after they were scared by acoustic shocks, according to the study.
"Time and space connectivity with marine exercises with the use of a sonar is very clear," de Quíros said in an e-mail. Moreover, behavioral studies have shown that whales who have never encountered a sonar (or who have been exposed only occasionally) usually show a stronger response from animals living near military establishments, she added.
In 2004, Spain banned a sonar in the waters of the Canary Islands. After the ban was issued, mass strikes did not occur, "proving the effectiveness of this alleviation," de Quíros said.
Based on their findings, the authors of the study recommended a widespread prohibition of military exercises through a sonar over the Mediterranean Sea, where atypical mass stings of beaked kits are still taking place. Further research will determine the long-term impact of mass strata on poplar whale populations, authors wrote in the study.
The findings were published online (January 30th) in Proceedings of the Royal Society B.
Originally posted on the day Live Science.