Cetacean stranding is a phenomenon in which cetaceans strand themselves on land, usually on a beach. Beached whales often die due to dehydration, collapsing under their own weight, or drowning when high tide covers the blowhole.
Species susceptible to stranding:
Whales, dolphins and porpoises. Among them toothed whales, sperm whale, pilot and killer whales, few beaked whale species, and oceanic dolphins are most susceptible to stranding.
Causes of Stranding:
Natural Reasons include rough weather, weakness due to old age or infection, difficulty giving birth, hunting too close to shore, or navigation errors. Some standing may be caused by larger cetaceans following dolphins and porpoises into shallow coastal waters. The larger animals may habituate to following faster-moving dolphins. If they encounter an adverse combination of tidal flow and seabed topography, the larger species may become trapped.
Human-related issues including by catch, vessel collisions and environmental degradation. Natural and human-related factors can also interact to cause stranding. Noise from naval exercises and active sonar can cause the stranding.
1. Most strandings occur on gently sloping beaches. Cetaceans may not be adapted to shallow water and get themselves into shallow water because their sonar may not detect gentle smooth slopes up to shallow areas. Evidence against this theory is that the greater incidence of strandings on sandy beaches may be due to the fact that there are more sandy than rocky beaches in the world and animals are easier to find on sandy beaches. Also, when stranded animals are pushed back out to sea they tend to return to the beach. However, if one persists in pushing them out, they tend to eventually return to sea. There have been no records of mass strandings of Mysticete whales.
2. Parasites in the ears; ova in the brain.
3. Cetaceans may revert to primitive instincts under stress. Under stress, behavior may be dominated by the subcortex, overruling the rational cortex. Strandings are lethally non-adaptive and should have evolved out, however they have remained. Panic may be a factor.
4. Mass strandings may be due to social cohesiveness, where cetaceans follow each other. Evidence against this is the presence of single strandings and the finding of mass strandings spread along an entire beach.