Dolphin stranding was of interest as long ago as in the time of Ancient
Greece. Aristotle stated, "It is not known why they sometimes run aground on the seashore; for it is asserted that this happens
rather frequently when the fancy takes them and with no apparent reason."
Today, there continues to be much interest in and conjecture about dolphin
"stranding", or ending up on dry land to die. Stranding of both single dolphins and groups of dolphins has been recorded.
We know that some stranding behavior is a result of certain diseases (the dying body actually washing up onto the
shore, instead of the animal coming by its own power on shore to die). Often such stranding involves multiple dolphins.
Over the two year period of 1987-1988 thousands of dolphins stranded along the U.S. Atlantic Coast. This mass stranding
was attributed to Morbillivirus infection. Morbillavirus is often attributed to disease-related mass
stranding. This virus is easily passed from one dolphin to another because dolphins are a very social animal. They swim close
to and breath on each other. The virus enters the dolphin body through the respiratory system's blowhole. Because dolphins
are constantly on the move, developing a strategy to treat these infections is nearly impossible.
Stranding of multiple dolphins may be caused by forced submergence due to an acute toxic event (such as an oil
spill or a spill of other hazardous materials). Stranding by injury or entanglement with various ocean artifacts
(fishing lines, plastic waste, and crab pot ropes, such as in this photo) usually involves single dolphins.
From February
2010 to April 2011, 406 baby Bottlenose dolphins washed up on the shores of the Gulf of Mexico. The National Oceanic and Atmospheric
Administration (NOAA) called these deaths an "unusual mortality event", or UME. A UME is defined as a stranding incident that
is unexpected or one which involves a significant loss of any particular marine mammal population. NOAA investigated
the cause(s) of both the number of dolphins stranded as well as why the dolphins were so young. Most of the stranded
animals were pre-term, newborn or very young (under 4 feet in length). This event coincided with the April 2010 British
Petroleum oil rig explosion in the Gulf, the worst oil spill in U.S. history. The investigation did not determine if
this UME was associated with the oil rig disaster, just that a number of the stranded animals had oil on and inside their
bodies. Samples of tissue from these animals were carefully documented as part of the on-going criminal litigation against
BP.
Populations of stranded dolphins often are predominantly males and calves.
Males do not have any way to shed contaminants, unlike females. Females shed large amounts of contaminants through their breast
milk. This helps to protect the female, but the contaminated breast milk is passed to the nursing calf, possibly resulting
in its death.
Researchers believe stranding may also
be a result of faulty echolocation processing, where the animal interprets a sloping beach ahead as an area of open ocean
and ends up swimming onto the beach accidently, unable to get back to the water. The gentle slopes of such beaches may provide
poor surfaces for the reflection of their biosonar waves. Perhaps dolphins make mistakes in navigation due to magnetic disturbances
while following the earth's geo-magnetic contours. A predator chasing a dolphin could cause it to strand. Or, severe weather
conditions, military activity (explosions
and sonar), or loud sounds produced by construction or dredging could confuse the animals and force dolphins onto the
shore to die.
Marine Stranding Networks have been organized to report cases of stranding and initiate appropriate rescue efforts.
These networks exist along the entire U.S. range of the Atlantic Bottlenose Dolphin and have been effective in reducing deaths
due to stranding. Recent data from the NOAA Stranding Network Report list the number of dolphins stranded in the
U.S. during a three year period as follows: 750 dolphins stranded in 1996, 564 in 1997, and 593 in 1998.
A stranding occurred in January, 2012 with 40-50 common and white-sided dolphins washing up on Cape Cod. A number
were saved due to the efforts of the International Fund for Animal Welfare. Along the NE U.S. coast the stranding season is
from January to April each year. Experts state it may be the unusual topography of the Cape Cod coastline that may be the
cause of stranding frequently seen in this area.
In April, 2012 a number of bathers on a Brazilian beach reacted when about 30 dolphins began stranding right
in front of them. The dolphins were quickly and carefully assisted back into more navigatable waters.
Site Content
Understanddolphins.com contains information condensed from a number of reputable technical sources,
peer reviewed journal articles, and respected dolphin research facilities, as well as from my personal experiences and
observations as a dolphin VIP Tour Guide and Educator.
I have made every attempt to support the information presented in this site with video and still
photographic images. On a regular basis I plan to produce more of these images and will continue to update the site with these
as well as with any new and scientifically verified information which becomes available.
