Strandings are common and every year, thousands of whales, dolphins, and porpoises are found on coastlines throughout the world. Cape Cod, USA and New Zealand experience more frequent strandings than anywhere else. When a single cetacean is stranded it is normally due weak conditions caused by old age, sickness, and disorientation.In March and April 2004, more than 100 dolphins were stranded and died around the Florida panhandle. Tissue samples and stomach contents were sent for study in labs. The research conducted by Naomi Rose outlines four possible reasons for this odd and frightening occurance.
Social Bonds
When dolphins spend their lives within a single group, they may be reluctant to leave behind a sick group member. For example, in 1994, there was a mass stranding of white-sided dolphins in which all the animals were found to be healthy except one exceptionally ill individual.
Geography
Some researchers theorize that distortions in the earth's magnetic field may result in animals stranding if they are using magnetic fields to migrate. Otherwise healthy dolphins have also been found stranded in areas such as Cape Cod, where some believe that the gently sloping beaches and rapidly changing tides lead to navigational miscalculations that result in animals becoming trapped in shallow, enclosed areas.
Acoustic Testing
Whales and dolphins rely heavily on the use of sound to survive. Loud noises from naval sonar and seismic testing have been implicated in recent mass strandings. For example, in the Mediterranean in the 1990s and in the Bahamas in 2000, examinations revealed hemorrhages in the ears and brains of many stranded animals, as one might expect to see following intense acoustic or pressure pulses. Marine mammal scientist Naomi Rose represents the HSUS on a national advisory committee convened by the U.S. Marine Mammal Commission that is looking into this area of growing concern.
Biotoxins
Some marine algae (plant plankton) produce toxins. At times these algae grow rapidly in what are called harmful algal blooms—what we know as "red tide" is one such bloom. Toxins from these blooms build up in the sardines and anchovies who feed on them; the toxins can then accumulate in animals like the sea lions and dolphins who feed on the smaller species. As these biotoxins are passed up the food chain they may lead to sudden death when an animal's nervous system is damaged. In other cases, the toxins may weaken the animal's immune system, leaving the animal vulnerable to other infections that may cause stranding. Large numbers of animals may be affected in an area with a harmful algal bloom. These biotoxins can also affect human health if people eat small fish and shellfish with accumulated toxins.
