Christina Murdock, of Westland High School, asks :-

Why do whales beach themselves?

Mike Donoghue, a marine zoologist with the Department of Conservation, responded.

The explanation for the stranding of whales on beaches all over the world is likely to remain a secret. No one theory explains all strandings.

Some strandings involve single whales which are old, sick or injured and generally they die.

Theories of group strandings include confusion and mistakes in navigation caused by local coastal conditions. It appears that some areas act as whale traps. Long protruding spits with gently sloping beaches seem to pose special hazards for offshore species such as pilot whales (which make up 50 per cent of all group strandings). The gently sloping sand does not reflect a whale's sonar well. The whale, already confused by a spit across its path, may simply not `see' the beach with its sonar.

Once the whale is in shallow water it cannot turn without swimming forward into even shallower water where it can easily be rolled over by waves. Add a falling tide and it is easy to see how a stranding could occur.

A further complication is the strong bonding amongst the whales in a herd which can create a herd stranding when one whale gets into difficulty and calls for help. Others will go to its aid.

Of the 1140 strandings recorded for New Zealand to 1992 (8287 whales) there have been 163 herd strandings. One involved 72 sperm whales. The largest recorded stranding involved 450 pilot whales.