Abstract

It is commonly accepted that cetaceans are descended from land-living ancestors. At some time intermediate ancestral forms must have been amphibious, and during this period it was presumably critically important for them to seek safety on land when injured, afflicted with disease, attacked by aquatic predators, or otherwise severely stressed. "Under stress the organism regresses." In the case of organisms with a highly developed central nervous system, behavior may be dominated by responses associated with the primitive and very basic motivations and emotions regulated by subcortical structures, instead of following a more rational course under control of the cerebral cortex. The basic drives (hunger, thirst, sex, etc.) and emotions (anger, fear, pleasure) are evolutionarily conservative.

It is suggested that the requirement to seek safety on land early in cetacean history became a response that also was mediated by subcortical structures, that the response manifests itself under conditions of stress, of whatever nature, and has persisted to the present despite the fact that it long ago became maladaptive. No other hypothesis appears to account for as many of the known facts on stranding behavior.

Notes

Theories

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.

Animals can slowly and deliberately strand or they can quite violently do so.

None of the above theories fully explains the stranding phenomenon. One of the unanswered questions which remain is from how far do the at-sea animals come to get stranded?