Whale strandings are complex events with various causes. Illness and old age can play a part, as can extreme weather and the make-up of coastlines:
- Illness: A stranded whale might be infested with parasites, poisoned by industrial or natural toxins, or have had problems during birthing.
- Social Cohesion: Group strandings may be a consequence for open-ocean species that are highly social. At sea, a whale may signal for help if in trouble. Closer to shore, this survival strategy may be disastrous, drawing the rest of the pod into the stranding.
- Magnetic Phenomena: Some people have suggested that abnormalities in the Earth’s magnetic field may cause strandings. However, this does not appear to hold true in all parts of the world.
- Coastline Composition: Whales chasing prey near shallow sloping beaches can strand. They can also be trapped by receding tides or swept off course and onto the shore by strong currents.
Due to its tidal extremes and unusually irregular coastline that spans a wide range of ocean waters—both sub-tropical and polar—New Zealand has one of the highest whale stranding rates in the world. But it also has a high rescue success rate, and has led the development of several rescue techniques.