8108

• UCREFRP Catalog Number: 8108
• Author: Dizon, A. E., C. Lockyer, W. F. Perrin, D. P. Demaster and J. Sisson
• Title: Rethinking the Stock Concept
• USFW Year: 1992
• USFW - Doc Type: A Phylogeographic Approach
• Copyright Material: YES

~.,

,
'-":\

Dizon et Ill.

ppm wet weight) in blubber of Antarctic Area IV and V
minke whales to be mostly lower than those observed
for the Northern Hemisphere, where levels are 0.14-1.1
ppm wet weight for PCBs and 0.21-2.6 ppm DDT off
West Greenland Oohansen et al. 1980), and 27.45 ppm
PCBs and 1.09 ppm DDT in the St. Lawrence estuary,
Canada (Sergeant 1980). The differences are clearly due
to feeding ground separation, and show clear distinc-
tions between the hemispheres.
3. Parasites
Comparison of infestation rates of ectoparasites in ad-
jacent Antarctic Areas I, II, and III (Bushuev 1986,
1988) suggest that differences exist between popula-
tions. In Area III, 34-57% of the whales are infested,
compared with 2-1l% in Area II (with variable inci-
dence from east to west) and almost zero infestation in
Area I. Ohsumi et al. ( 1970) reported very low ectopar-
asite infestation in Area IV, and later investigation over 3
years showed significant differences between Areas I,
III, and IV. The differences were interpreted as indicat-
ing that stocks are separated on the feeding grounds.
B. Population response
The Southern Hemisphere minke whales have been
documented to respond indirectly to exploitation of
competitor species in a density-dependent manner, with
consequent reduction in the age at sexual maturation
from about 12-13 years to 7-8 years during a 30-year
period (Area III) (Kato 1987), Masaki (1978, 1979),
Kato (1983), Kato et al, (1984), and Ohsumi (1986)
reported similar changes in age at sexual maturation for
Areas III and IV combined. The pattern of trends and
values of biological parameters seems similar for the
Areas, but perhaps the response has been greatest in the
most heavily exploited Areas, I, II, and III (Horwood
1990).
Rather less is known for the Northern Hemisphere
because of difficulties in age determination, Still, sexual
maturation is reported to be about 7.3 years in the
North Atlantic.
C. Phenotypic Data
The Northern and Southern Hemisphere forms of the
minke whale are different in coloration (flippers, baleen,
etc.) size, and skeletal morphology, the southern form
being designated as the bonaerensis form. With the ex-
ception of the newly described dwarf form, mature an-
imals from the southern population are generally larger
than those from the northern populations (Lockyer
1984). The Atlantic minke is also slightly larger than the
Pacific minke.
In the Southern Hemisphere, two morphological
types were traditionally reported, one with plainly pig-
mented flippers and the other with asymmetrical two-
tone coloration; both belong to the bonaerensis form
(Williamson 1959; Ohsumi et al. 1970; Taylor 1957;
Aguayo 1974; Baker 1983; Gaskin 1972; Kasuya& Icru-

Rethinking the Stock Concept

33

hara 1965). Currently, there are tJ;1ree reported color
forms of minke whale, mainly defined on the basis of
extent and symmetry (left and right sides) of flipper
coloration-the presence, absencc;-or intermediary of a
white band, the extent of pale coloration of the baleen,
and dark pigmentation around the neck and throat re-
gion (Best 1985). The new evidence for a diminutive or
dwarf form in the southern oceans, mainly reported
from South Africa, Australia, New Zealand, and Brazil
(Best 1985), is largely based on the definition of a third
color morph characterized by symmetry of coloration
and white flippers. In addition, the third form is consis-
tently smaller, Best (1985) concluded that the dwarf
form was also sufficiently different in skull characters
from the southern bonaerensis subspecies that it was at
least as distinct as the northern davidsoni form from the
bonaerensis one,
D. Genotypic Data
Restriction fragment analyses using 14 restriction en-
zymes of minke whale intDNA D-loop from four popu-
lations-Antarctic Areas IV and V, bonaerensis type,
Antarctic Area IV dw~ form, Sea of Japan and western
North Pacific (davidsoni type )-indicated 4-11 % ge-
netic nucleotide diversity (Wada et al. 1991). In Areas
IV and V (bonaerensis form) the genetic diversity
within populations is only 0.17%, compared with 0.05%
within the western North Pacific and 0.00% within the
Sea of Japan, Nucleotide diversity shows no significant
differences between Areas IV and V, but significant dif-
ferences between the bonaerensis, dwarf, and david-
soni forms, the latter two being relatively more closely
related, with genetic diversity of about 4% (Fig. 4).
The diversity between the Sea of Japan and the west-
ern North Pacific is only 0,06%, but is >10% between
Northern and Southern Hemisphere minke populations.
Wada and Numachi ( 1991 ) presented results of enzyme
electrophoresis on tissue proteins from different bal-
aenopterid whales that indicated that genetic differen-
tiation between Antarctic and western North Pacific Sea
of Japan and Korean stocks was about seven times

Dwarf form

Western North Pacific
( davidsoni.type)

Sea of Japan
( davidsoni-type)

Antarctic
( bonaerensis-type)

I
12

I I I
10 8 6 4 2
Nucleotide diversity (%)

I
o

Figure 4. mtDNA sequence divergence among four
minke whale samples. After Wada et at (1991).

CoasemadoD BJoJosy
Volume 6, No, I, March 1992