“Mass strandings of whales occur periodically in Australia and New Zealand for reasons that are not entirely understood. Theories include disturbance of echo-location, possibly by interference from sound produced by human activities at sea.”

Dolphin serial killers?: “Dead porpoises (and other cetaceans) turn up regularly on beaches around Britain. According to a Defra report last year, the cause of death of 15 out of 56 porpoise bodies found – the majority – was ‘physical trauma (bottlenose dolphin attack)’. [A photo accompanying the article] shows the rake marks on a harbour porpoise caused by a bottlenose dolphin.” (New Scientist Environment Blog)