Cetacean stranding
Beached whales often die due to dehydration, collapsing under their own weight, or drowning when high tide covers the blowhole.
[2] Several explanations for why cetaceans strand themselves have been proposed, including changes in water temperatures,[3] peculiarities of whales' echolocation in certain surroundings,[4] and geomagnetic disturbances,[5] but none have so far been universally accepted as a definitive reason for the behavior.
[6] Whales that die due to stranding can subsequently decay and bloat to the point where they can explode, causing gas and their internal organs to fly out.
[2] Some strandings can be attributed to natural and environmental factors, such as rough weather, weakness due to old age or infection, difficulty giving birth,[9] hunting too close to shore, or navigation errors.
The University of Western Australia Bioacoustics group proposes that repeated reflections between the surface and ocean bottom in gently sloping shallow water may attenuate sound so much that the echo is inaudible to the whales.
A 2017 study by scientists from Germany's University of Kiel suggests that large geomagnetic disruptions of the Earth's magnetic field, brought on through solar storms, could be another cause for whale beachings.
The solar storms cause anomalies in the field, which may disturb the whales' ability to navigate, sending them into shallow waters where they get trapped.
However, killer whales in Península Valdés, Argentina, and the Crozet Islands in the Indian Ocean have learned how to operate in shallow waters, particularly in their pursuit of seals.
The killer whales regularly demonstrate their competence by chasing seals up shelving gravel beaches, up to the edge of the water.
[12] In Argentina, killer whales are known to hunt on the shore by intentionally beaching themselves and then lunging at nearby seals before riding the next wave safely back into deeper waters.
[6] Theories describing how sonar may cause whale deaths have also been advanced after necropsies found internal injuries in stranded cetaceans.
At an amplitude of two hundred forty decibels, it is loud enough to kill whales and dolphins and has already caused mass strandings and deaths in areas where U.S. and/or NATO forces have conducted exercises.
Ken Balcomb, a cetologist, specializes in the killer whale populations that inhabit the Strait of Juan de Fuca between Washington and Vancouver Island.
[15] He investigated these beachings and argues that the powerful sonar pulses resonated with airspaces in the dolphins, tearing tissue around the ears and brain.
The stranding happened on 24 September 2002, close to the operating area of Neo Tapon, an international naval exercise, about four hours after the activation of mid-frequency sonar.
There is also a theoretical basis by which sonar vibrations can cause supersaturated gas to nucleate, forming bubbles, which are responsible for decompression sickness.
They noted that over the past decade there had been a number of mass strandings of beaked whales in the Canary Islands, and each time the Spanish Navy was conducting exercises.
Fernández et al. in a 2013 letter to Nature reported that there had been no further mass strandings in that area, following a 2004 ban by the Spanish government on military exercises in that region.
Data tags have shown that Cuvier's dive considerably deeper than previously thought, and are in fact the deepest-diving species of marine mammal yet known.
De Quirós et al. (2019)[22] published a review of evidence on the mass strandings of beaked whale linked to naval exercises where sonar was used.
[45] Three hundred and five bodies and 32 skeletons were identified by aerial and satellite photography between the Gulf of Penas and Puerto Natales, near the southern tip of South America.
[48] On the evening of November 2, 2020, over 100 short-finned pilot whales were stranded on the Panadura Beach in western coast of Sri Lanka.
