Re: Strandings

From: Phil Clapham (phillip.clapham@noaa.gov)
Date: Mon Apr 24 2000 - 06:58:06 EDT


Hi:

Sorry to take so long to answer your question (especially since you
asked so nicely!)

Yes, pilot whales are probably the most commonly mass-stranded cetacean;
other species that do this (come up in large numbers) are false killer
whales, sperm whales and some dolphins. The causes are probably varied,
but with pilot whales here on Cape Cod it seems to be a combination of
things. Cape Cod Bay (where most of the mass strandings occur) is a
natural trap, not only because it has land on three sides but because
the water is very shallow at low tide in some places. So poor old pilot
whales (which aren't a coastal species anyway, so they're perhaps not as
familiar with coastal navigation) come in at high tide, with plenty of
water. Suddnely - and this happens mostly at spring/neap tides, where
the tidal range is so large - the tide goes out and they find themselves
in a maze of shallows and sand bars. This is probably enough to cause a
stranding, but if you then add in a storm - which happens with most
strandings of this type - you almost certainly have a stranding on your
hands. It may well be that the social structure of the group makes
things worse; perhaps a lead animal gets trapped, and everyone else
follows.

The same general scenario - navigational error and tide made worse by a
storm - may apply to false killer whales. It's not clear why sperm
whales sometimes mass strand; they're very deep-water animals and so
aren't use to shallow water, but still - they're powerful enough that
you'd think they could power their way out of any problems. But then if
you don't know which way to go, and you're in a mass of sand bars, maybe
not...

Single strandings are usually animals that are sick and on the way out
anyway, and this can happen with any cetacean. Baleen whales (like
humpbacks) never strand together in large numbers, although we did have
a case in 1987 of a mass mortality - a lot of humpbacks died
(separately) after being poisoned by red tide, picked up through
mackerel they'd been eating.

Hope this helps!

Phil Clapham

> Carol Shaughnessy wrote:
>
> Hi Mr.Clapham, I am a sixth grader at Thayer Academy, and I am
> recently doing a project on the pilot whale. I know pilot whales have
> stranded themselves on beaches many times, but I was wondering which
> species of whale has committed the most strandings. I f you can
> answere, that would be great, if you have no time on your hands to
> answer this question, it is fine with me! Thankyou so much. Bye!

-- 

Phillip J. Clapham, Ph.D. Large Whale Biology Program Northeast Fisheries Science Center 166 Water Street Woods Hole, MA 02543

tel (508) 495-2316 fax (508) 495-2066 Internet: phillip.clapham@noaa.gov



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