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Why do whales and dolphins strand?

What is a stranding?

According to the U.S. Marine Mammal Protection Act, a stranded marine mammal is not only a living marine mammal on land that needs medical assistance or is unable to return to the water without assistance, but also includes any dead marine mammal (at sea or on land).

While it’s fairly easy to determine if a whale or dolphin is stranded, it’s rarely easy to understand why.

Stranded pilot whales

Fascinating Fact

There is a species of beaked whale, Perrin’s beaked whale, that was first identified from a few stranded individuals and has only recently been seen at sea!

Types of strandings

Single Strandings

This can include a living or dead baleen or toothed whale species and includes either a single individual or a mother and her calf.  Since a calf is still dependent on his or her mom, stranding with mom is considered a single event.

Spirtle survived a stranding on a beach

Mass Strandings

Mass strandings primarily occur when 2 or more (not including a mom and calf) whales or dolphins strand together.  These are typically social groups of toothed whales (dolphins, pilot whales, sperm whales, etc) who are usually alive when the stranding occurs.

Navigational Errors

Whales and dolphins are more likely to strand on some types of shore and coastline than others. Shallow, sloping shores made of soft sediment can confuse the “echolocation” used by whales and dolphins to find their way around.

A combination of factors may cause whales and dolphins to strand and one theory relates to them navigating using the earth’s magnetic field. Crystals of magnetite - which react to a weak magnetic field - have been detected in the brains and skulls of some whales and dolphins and a magnetic “sense” could be an important navigational aid, especially in the deep oceans.

Whether caused by human activity or as a result of something natural, strandings are tragic, but they, can tell us a lot, about the biology of the animals, the state of the population it came from and the marine environment.

What to do if you find a stranded whale or dolphins?

WDC staff attend and help with many live strandings, and lots of ‘dead’ ones too. Our experts are often involved in the post-mortem examination. It’s a grisly task, but we do it, because it gives us information: Information we use to get conservation measures put in place.

A live whale or dolphin beached on the shore is almost always in danger of its life. If you find a stranded whale or dolphin, whether it is alive or dead, please report it as soon as possible.

If you find a LIVE stranded or injured whale, dolphin or porpoise on the beach or in the shallows, you must act quickly. The appropriate emergency numbers to call in such an event and which can be used 24 hours a day are:

Northeast Region, United States

Marine Mammal and Sea Turtle Stranding and Entanglement Hotline

Phone: (866) 755-NOAA (866-755-6622)

West Coast Region, United States

Marine Mammal and Sea Turtle Stranding and Entanglement Hotline

Phone: (866) 767-6114

 

For additional information stranding or entangelement locations in the United States, check out the NOAA page.

For additional information stranding or entangelement locations in Canada, check out the Marine Mammal Center page.

British Columbia, Canada

To report stranded marine mammals

DFO hotline: 800-465-4336

Nova Scotia, Canada

To report a stranded, injured or dead marine mammal

Marine Animal Response Society Hotline at:  866-567-6277

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