Subject: population estimates

Tori (cullins@hawaii.edu)
Thu, 22 May 1997 16:34:48 -1000

I am a student at Brushton Moira Central, in our class we are doing 
research on humpback and mink whale's population,We are trying to figure 
out why the population changes on the coast from year to year, one year 
the population is very high then it either drops or it rises with out 
warning any info. would be of great help. 



Aloha Brushton Moira,

Here is a question for you. Let's say you and your classmates want to go
count how many humpback or minke whales are on the East Coast. How would
you go about doing that? Dont' forget they are under water more than on
top, andd how would you tell one from the other?
Whale researchers have this same problem and that is why when you are
reading about the population sizes of these whales you see the word
"estimate" being used. Nobody knows exactly how many whales are out there.
Different methods are used to estimate the populations. Here in Hawaii,
Iknow of three different ones. 1) Counting whales by use of an airplane. A
few years back, the airplane used to fly around the coast of the islands
and count the whales below. The problem is you can't always see the whales
underwater and also the airplane speed is faster than the whales swimming
speed. So, if the whale is under water, you may fly right over and past it
before it comes up for air. Recently, better methods have been used to
correct this problem. Check this out, when the better methods were used,
the estimated population of humpback whales went from approximately 1,500
to 3,500! Keep in mind that even at this population size of humpbacks in
Hawaii, they would still be endangered. 2) Shore observations. Researchers
sit at a good vantage point and track and count whales. Problem - the
visibilty range is limited, they may be counting whales more than once, or
not enough. 3) Acoustic tracking. The researchers have hydrophone arrays
(like microphones) in the water and count humpbacks by their "songs" as
they pass by. Problem - only males are singing, and not all of the males
sing, noe do singing males sing constantly. 
I have simplified the description of these methods for you, math formulas
are also used to guess how many whales were not counted. With this
information, it is easy to see how population estimates could differ from
year to year, method to method, and researcher to researcher. Usually,
froma a varitey of estimates, one will be accepted.
Beyond what I have told above, population sizes can be naturally affected
by birth and death rates. Humpbacks and minke whales only have one baby
(calf) about every two or three years. So the natural increase of
population size by birth rates will be rather slow, considering if the
calf lives and other such factors. Whales are rather long lived, so the
birth rate should be greater than the death rate, if they were allowed to
live out their natural life span. Sadly, this hasn't been their fate for
quite some time now.
This should be a good start for you all to form a good hypothesis of why
the population estimates fluctuate as they do. Aloha!

Tori