Minke population in No. Atlantic

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Mon, 24 May 1994 08:21:20

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Subject: Minke population in No. Atlantic
 
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Subj:	Minke Whale population
 
Date:         Mon, 23 May 1994 20:40:59 BST
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From:         Michael Halford <mchalford@gn.apc.org>
Subject:      Minke Whale population
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IFAW Technical Briefing  94:8  May 1994
 
How Many Minke Whales  in the Northeast Atlantic?
 
SUMMARY
 
 
Dr Justin Cooke has presented to the Scientific Committee a
re-analysis of some of the Northeast Atlantic minke whale
sightings data obtained by Norwegian scientists.
 If Cooke is right there are about 53,000 minke whales in
the Northeast Atlantic, not 87,000 as claimed by Norwegian
scientists. Calculation of a catch limit from each of these
numbers leads to very different results; about 250 animals
from the Norwegian estimate close to zero from Cooke's.
 
Cooke has calculated a new value for  g(0), a critical number
used in the calculations which lead to population estimates.
g(0) is a measure of the chance that a whale on the track of
the survey vessel will be seen. It can range from zero to one.
If all whales present are seen then g(0) = 1. If g(0) is 0.5
then the raw estimate is doubled. Cooke's best estimate is
0.59, compared with the earlier Norwegian estimate of 0.36.
 
The difference between the estimates of g(0) arises mainly
from differences in numbers of whales identified as duplicates
[ie the same whale seen by different observers] in the data
from experiments carried out especially to estimate g(0).
Discrepancies arise from a combination of poor specification
of criteria for such identifications, subjective judgements
that cannot be reproduced, inadequate specification of their
methods by Norwegian scientists.  It seems that the Norwegian
scientists were careless in their analyses of their own data
in that they missed many duplicates.
 
It also seems that the majority of the Scientific Committee
acted irresponsibly in uncritically 'accepting' the Norwegian
analyses in 1992, and in not attempting to verify them in
1993. While the RMP itself may be a finely tuned and
exhaustively tested instrument, the casual approach that the
Scientific Committee appears to have taken in advising how it
might be implemented (should the Commission so decide) clearly
leaves much to be desired.