Subject: Whales- defenses

Mike Williamson (m.dalebout@auckland.ac.nz)
Wed, 24 Sep 1997 3:28:22 GMT+1200

Dear brimmer, 

You asked how whales protect themselves.

The answer to this of course depends on what the threat is. 
						
If faced with a fast catcher boat armed with a harpoon gun, a whale's 
only defense would be to try to outrun it. How successful this strategy
would be is hard to say.  As far as I'm aware, historical whaling records
do not include mention of those that got away, and I am not sure the
Japanese and Norwegians whalers who are still hunting minke whales today
post that information either. 
					
Modern catcher boats are able to move faster through the water than whales
are able to swim, although swimming speed varies with species.  Right whales
for example are slow swimmers, rarely exceeding 5 knots, with an average 
speed of only 2 knots.  Gray whales are also not too fast, clocking a maximum
speed of only 6.5 knots.  Humpback whales do about 5 knots on average, but
can put on bursts of 9-10 knots.  Sperm whales are much faster, doing about
10 knots on average, and able to accelerate up to 20 knots or so if pushed,
though only able to maintain this speed for a short period.  Speeds of
14 -18 knots have been reported for the minke whale.  The sei whale appears
to be the fastest of the lot, able to achieve a sprint of about 32 knots, 
although again for only a short stretch. Some dolphin species can also go 
this fast, and are generally a lot faster than whales on average.

Other threats to whales include nets, other fishing gear and pollution. Whales
will avoid nets if they can sense them, but often appear unaware of them 
(inattentiveness? inability to sense some types of nets?).They may also be
lured closer by curiosity or the fish etc trapped in them, and so can also get 
into trouble that way. The same goes for other fishing gear such as lobster 
pots. 

Pollution is a more difficult problem. 
				
Sharks may also prey on whales (as may killer whales), with groups often 
mobbing a lone animal.  Again, the whale's main defense would be to try to
outrun its aggressors. Dolphins have been frequently documented successfully
driving sharks away with head butts and bites, but for baleen whales this is
obviously not an option.

Aggression or threat from members of the same species is also common eg 
male-male aggression during the breeding season, but in many species this will
take the form of ritualised displays (eg breaching, tail slapping),
and protagonists will not make actual physical contact up to a certain point. 
If the encounter becomes more serious, the whales may charge each other.
						
The linear scars on male beaked whales are also attributed to intra-specific 
fighting. Most species of beaked whales have only one pair of teeth which
erupt from the gum only in the adult males. The males appear to use these teeth
as weapons when fighting males of the same species.

Thanks for your question.

Cheers


merel




***********************************
Ms. Merel Dalebout
Ecology & Evolution Research Group
Thomas Building, Level 1
School of Biological Sciences
University of Auckland
Private Bag 92-019
Wellesley Street
Auckland, N.Z.
Ph:09-373-7599 ext. 4588
Fax: 09-373-7417
e-mail: m.dalebout@auckland.ac.nz