OBSERVATIONS ON THE OCCURRENCE AND
BEHAVIOUR OF MINKE WHALES OFF
THE COAST OF BRAZIL
K. V. SINGARAJAHLaboratory of Marine Biology & Comparative Physiology, Department of Systematics & &ology, CCEN,
Federal Universify of Paraiba, Joao Pessoa-58000, BRAZIL
ABSTRACT

Field observations on minke whale morphology and physiology, the hydrography and topography of the Brazilian whaling ground and catch statistics from 1963 to 1982 are presented.
In the past 20 years, 12,494 minke whales have been taken off Brazil;
only 3 were taken prior to 1963. Of those animals thought to be mature,
females predominate in the catch (sex ratio, 2 females: 1 male). The population appears to remain at an exploitable level, although other species in thearea have been considerably reduced.
The most important environmental conditions associated with the arrivalof the minke whale in these tropical breeding grounds appear to be an optimum temperature of 26-27°C, day-length, reduced turbulence and an amiablesurface current.
The behaviour of minke whales in response to various stimuli is described,
and in particular their escape reactions, normal swimming speeds, co-ordinated swimming, affinity for mates and response to electric shocks.
INTRODUCTION

The minke whale, Balaenoptera acutorostrata (Plate I), is one of the most valuable
marine mammals and is now the most common species of baleen whales in the
Antarctic. Perhaps, due to its high yield of meat, relative to the rest of the components (Table 1), this species has become an important natural food resource andthus making the commercial whaling economically viable. Despite the claims thatthe minke whales are increasing in the Antarctic and now considerably more abundant as they were in 1910 (FAO, 1982), the exploitation of this species is regulated
by IWC.
The minke whales taken off Brazil are considered as a part of the Area II
management stock as defined by the IWC (0°-60°W) although there is some controversy over the applicability of these Areas (originally developed for blue and fin
whales) to minke whales (IWC, 1981; 1982). However, much of the whaling
would depend on natural population which varies both geographically and seasonally due to fluctuations in the rate of recruitment, mortality, including level of exploitation, growth rate, supply of planktonic krill as food (Ohsumi, Masaki and
Kawamura, 1970; Ohsumi, 1979) and other causes of environmental factors. The
catch statistics and catch per unit effort (CPUE) values over the past 20 years have
Sci. Rep. Whales Res. Inst.,
No. 35, 1984, 17-38

18

SINGARAJAHTABLE 1.

PRIMARY MATERIALS DERIVED FROM MINKE WHALES BASED ON
ACCUMULATED FACTORY DATA

Primary Products

1.
2,
3.
4.
5.

6.
7.
8.

Mean Weight (Kg/Whale)

%

Meat
Bone
Cartilage
Baleen plates
Viscera: Tongue
Lungs
Heart
Kidneys
Liver
StomachIntestine
Blubber : Dorsal
VentralFins
Lost Materials: Blood etc at sea & factory

3,500
l,260
7
35
70
56
21
14
63
14
63
980
280
42
595

50.00
18.00
0.10
0.50
l.00
0.80
0.30
0.20
0.90
0.20
0.90
14.00
4.00
0.60
8.50

Total

7,000

100.00

shown that the recruitment of this species in this area has remained very constant(Singarajah, 1983). With the advent of their breeding seasons, the minke whales
arriving off Brazil are characteristically migratory, but the reasons to select thisarea as their breeding ground with such regularity are little understood.
Previous work on Brazilian minke whales is scanty (Williamson, 1975) and in
this paper some aspects of minke whale biology are examined and the feasibility ofcontinuing to exploit this species, together with some of the factors which may
influence their migratory behaviour to the breeding ground off Brazil, are discussed.
MATERIALS AND METHODS

Field observations were made on board the catcher boat Caho Branco. The normal
operation pattern is that the boat leaves port at about 0330-0400 hours and returns to the factory with its catch at about 2230-2300 hours. Samples were taken
both on board the catcher and at the factory though most measurements were madeat the latter.
Past data on catches, lengths, reproductive state of the whales and information on stomach contents were kindly provided by SUDEPE (Superintendencia Do
Desenvolvimento Da Pesca) but some of the early data were missing or consideredunreliable. The selected data, covering the whole period of minke whaling, werethen transferred to an IBM computer for processing. Blood counts were made on
board the catcher; most observations on behaviour patterns were confirmed byphotographs, 35 mm colour slides and "Super 8" cine films. Where necessary,
appropriate parts of the whale, including entire baleen series, were transported to
the laboratory for confirmation.
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

BEHAVIOUR OF MINKE WHALES

19

RESULTS
MORPHOLOGY

General appearance:

The minke whales are the smallest of the rorqual whales which
are well adapted for exclusively marine life. The body is somewhat less streamlined with triangular and dorsoventrally compressed head with a strong central
ridge (see Plate I). The paired nostrils or "blow holes" are situated at thesummit of the head about a metre from behind the tip of the snout which isabout 8 cm shorter than the lower jaw. The blow holes are highly dilatable, especially when the animal gasps for breath, which otherwise remain closed by valvelike muscular folds of skin. The blow holes lead to a common median tubular
canal about 50 cm long and 8 cm in diameter before leading to the tracheae.
The eyes are small, when compared to the huge body, and dorsolaterally
placed. The eye-ball, on dissecting out, measures about 10 cm in diameter andwell controlled by the powerful eye muscles and the optic nerve.
No external ear is visible, but the external ear aperture is a horizontal slit ofextremely small size, about 5 mm long; normally remains closed by valvular folds
within a narrow groove about 9 mm wide and 9 cm long. The centre of theaperture lies about 44 cm behind and on the same level as the eye. The external
aperture leads into a complicated tubular canal which is about 6 mm in diameterand its inner surface is lined by fine longitudinal grooves and ridges and having
the same colour as the skin, perhaps due to invagination of the skin. The canal,
after running about 8 cm towards the tympanic bulla, leads into a "gizzard-like"structure which is often filled with bone marrow-like substance. The canal is now
continued from the centre of one side of the muscular gizzard structure and extends
until it establishes contact with the ear plug. The conical ear plug (Plate II) fitsclosely over a membranous, but strong, teat-like structure or "glove finger" (Plate
III) and similarity in ear aperture was noticed in fin whales (Laws & Purves, 1956).
The broad margin of the glove finger is attached to the hollow part and surroundedby the bony elements in the posterior-ventral region of the tympanic bulla. The
canal, connecting the gizzard-like structure and the ear plug, is smooth and devoidof any ridge or groove and the grey colour is generally lacking. The ear bones or
tympanic bullae are kidney-shaped, each about 9 cm long and 6 cm broad andweighing 450 g wet and 250 g dry weight. It is perhaps the hardest part of thewhole body and is located just anteriodorsal to the foramen magnum and is separated from the external aperture by about 50 cm, on each side.
Ventral grooves: The ventral grooves run lengthwise and parallel to one anotherreaching anteriorly the chin and posteriorly close to the umbilicus, and extend
laterally to a line between the eye and the flipper insertion. The median groove
extends from the posterior end of the mandibular symphysis to just short of theumbilicus. This distance between the end of the median groove and the umbilicus has a mean of 84.9 cm, though it varies in the different sexes. However,
the minimum distance between the umbilicus and the nearest 6th groove, on either
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SINGARAJAH

20

side of the median groove, remains constant in both sexes at 40.7 cm. This observation is in close agreement with measurement given by Ohsumi et al. (1970) to
the Antarctic minke whales.
The number of ventral grooves of 660 animals (223 males and 437 females)
were counted in 1979 and the mean number in both males and females was 47 (8).
Da Rocha (1980) examined 220 males and 452 females and her values (for half thetotal number) were 21 for males (range 16-35) and 22 for females (range 15-31 ).
The difference in the values may be due to differences in the method of counting; in da Rocha's study, the grooves were counted while the whales were lying
in their sides on the flensing platform; while in the present study the grooves werecounted while the whale was tied by its tail alongside the vessel, which facilitatedthe counting.
Skin and colour pattern: The skin is about 3 mm thick, smooth and slippery, supported by a thick layer of panniculus adiposus or the "blubber" from below(Fig. 1). The colour of the skin changes from dark grey on the dorsal aspect of
the body to creamy white ventrally. The dark grey colour continues from tip of
the snout to the dorsal surface of the caudal fluke, but dips down just below theeye and the dorsal end of the flipper insertion to form a small arch and again midway between the flipper and the caudal fluke thus forming a wider arch; the end
6

5

E

0

Cl)
Cl)

0
... ....
'

4

UJ

z

@
..... ....

........ ....

~

0

®

.... .....

-.....

:c

~

a:

UJ

3

@

@

0

..... d-- ------------

@

@

G3)

@

@

@

J

A

s

0

N

D

CD
CD

:::>

...J
CD

MONTH
Fig. 1. Blubber thickness of males and females of the same whaling season.
bers shown within circles represent mean sample.

Num-

Sci. Rep. Whales Res. Inst.,
No. 35, 1984

BEHAVIOUR OF MINKE WHALES

21of this second arch then curves up, like a broad inverted dorsal fin, to a medianlateral line to merge with the dorsal surface of the fluke, on each side. The cream
colour extends from chin to the caudal end, including the ventral surface of the
fluke though the margins of the latter are usually edged with dark grey. The
creamy bracket marks above the flipper are usually inconspicuous.
These colour patterns are essential in identifying the Antarctic stocks of minke
whales, and seem to be of adaptive value. Usually with the slightest tilt of the
body in the water, these peculiar colour patterns cause to reflect a bright bluishgreen light, particularly when the whales swim up side down, which enables them
to be easily recognized from a distance of about 800 meters.
Jaws: The two jaws are symmetrical, but the lower jaw is about 8 cm longer
than, and protrudes beyond, the upper jaw (see Plate I). The upper jaw on eachside measures, on an average, 186 cm between the tip of the snout and the gape ofthe mouth. But, beyond this point, the baleen laminae are carried in by a shortsegment, about 28 cm long, which curves inward and terminates bluntly as a triangular end. It is along this rear end that the greatest number of smaller baleen
laminae are arranged in multiple rows.
Baleen plates: The strongly keratinized horny structures though called baleen
plates, all are not truly plates. These horny structures are fused together attheir top ends by interlaminar cement-like substance to form the " baleen series "(Plate IV) and suspended from each side of the upper jaw. The cemented part,which apparently represents the "gum", varies in height and width according to
the size of the plates inserted.
On the basic characteristics of size, shape and position, the plates could begrouped into mainly four categories:
1. The smallest rod-like structures in the anterior segment of the jaw, usually
8 in number, are arranged in double rows fairly close to each other. Each ofthese rod-like structures measures about one cm from below the line of fusionand provided with usually 4 very stiff filaments (Plate VA).
2. These are followed by the transitional plates which are small rectangularlaminae and variable in number (Plate V B).
3. Next in series, occupying the major part of the jaw, are the larger plates, on
an average 237 of them, arranged transversely at intervals of 0.4--1 cm between laminae. They are inserted by the smallest side and run undivided
between lingual and labial margins in a single row (see Plate IV). However,the size of the individual plates varies and the largest plates are always confined to the mid-region while others, in gradually diminishing order of size,
run towards both extremities of the jaw until they merge with the transitionallaminae. These laminae are not typically triangular as commonly described,
but rather combinations of inverted triangles and rectangles; the triangularpart increases in size at the expense of rectangular part as the plates reach the
mid-region of the jaw. The labial side of the largest plates measures about
40 cm and is smooth and devoid of any filaments, but on the lingual side only
the hypotenuse, just below the rectangualr part, is frayed out into fine flexible
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

22

SINGARAJAH

filaments (see Plate IV). The filaments also vary in number and length; thelargest plate on the average consists of 380 filaments and the longest of thesebeing 10 cm.
4. By contrast, the " plates " on the rear end of the baleen series are very much
reduced in size, about 2 cm tall and rectangular type of laminae which aredisproportionally numerous and grossly overlap and relatively difficult tocount, unless the series is cut into segments. The bristles are less stiff andvary between 4 and 12 per plate (Plate V C).
Perhaps for this reason, Williamson (1973) concluded that for rorquals, it was
too difficult to accurately count the rear plates and he called them, including theanterior rod-like plates, as "hairs". Previous studies (van Utrech et al. 1978;
Ohsumi et al. 1970; da Rocha, 1980) have clearly not included all the "hairs"in their counts. Best (1978) followed the procedure followed by Williamson (1983).
During the 1981 season, the baleen plates from 26 whales, 13 males and 13
females, were examined. Except for the colour pattern, no asymmetry was observed between the right and the left hand side of the blaeen series. The baleen
laminae can be further divided into 3 on the basis of colour: (i) creamy white;(ii) creamy white with black edge and (iii) black (see Plates IV & V). The results
are given in Table 2. The baleen series on the right side comprised an average of
111 all white plates, including the rod-like "plates" or "hairs", at the anterior
end, covering about 50 cm of the jaw. The plates in the mid-region comprised
an average of 127 white/black plates. The posterior all black laminae include
about 87 plates and about 2,050 smaller laminae. The pattern on the left handside is the same but the proportion of all white plates is lower; on average there are
only 63 all white plates covering 20 cm.
While the function of the colour difference on the two sides remains curious,
but the enormous number of the smaller laminae, though look vestigeal in form,
are adaptations that are functionally more evolved to increase the efficiency andrapidity perhaps during filter-feeding.
Flippers: Between 1979 and 1981, 1,745 animals, 619 males and 1126 females,
were examined for flipper colouration. The flippers are elongated and more winglike. There appeared to be no difference between the sexes; the flippers are about
1 m in length (Plate VI) and 30 cm wide, being light grey apart from a dark grey
calyx shaped on the dorsal surface next to the body. No white stripes were observed in Brazilian minke stock, but the under margins turn out to be slightly
TABLE 2.

MEAN NUMBER OF BALEEN LAMINAE FOR MINKE WHALES FROM BRAZIL
Colour pattern

Males
Females

right
left
right
left

(i)

(ii)

(iii)*

106.6

128.3

73.7

156.7

116.0
51.8

126.3

2131.5
1913.02051.02112.0187.5* posterior black laminae are from approximate estimates.

Sci. Rep. Whales Res. Inst.,
No. 35, 1984

23

BEHAVIOUR OF MINKE WHALES

whitish.
Flukes: In 1980, the flukes from 49 animals, 20 males and 29 females, were examined. The flukes were on average about 118 cm in length, and narrower inmales than in females. The notch was about 7 cm deep and 4 cm at its widest
part. A considerable strength is centered just anterior to the fluke, the tail-stock(Pl. VII).
Dorsal fin: A fleshy dorsal fin about 38 cm in height is situated about two thirdsof the length of the body, more proximal to the flukes, and neatly curved (Pl.
VIII) pointing caudally. Both dorsal fins and caudal flukes are devoid of any
bony elements.

.,.
Fig. 2. Positions of minke whales caught during 1980 season, superimposed on tract
chart. The broken line represents the continental edge of Brazil and the discrete
numbers indicate depths in meters.
Sci. Rep, Whales Res. Inst.,
No. 35, 1984

24

SINGARAJAH

Hairs: Very few hairs were seen; usually on the rostrum and on the sides of themandible. The hairs, particularly from the latter, arise from 7 small pits (each*0//......_____... ,,..

40

/

/

cTP
~

80

tsO

40

20

0

20

Fig. 3. Surface currents and an isothermic stretch of the whaling area off Brazil, in
the Southwest Atlantic. Surface temperature distributions are based on 20 years
daily recordings during each whaling season.
* Since this paper going to the press, asymmetrical disposition and variation of number of pits, particularly
in a few females had been observed.

Sci. Rep. Whales Res. Inst.
No. 35, 1984

BEHAVIOUR OF MINKE WHALES

25side). The hairs are creamy colour and about 4 cm tall and can be easily pulled out.
External sexual characteristics: As in the other whale species, the vaginal orifice lies
immediately anterior to the anus whereas the penal slit is clearly separated fromthe anus. In many females a creamy yellow substance was found in the vagina;
which may have meant that they had recently copulated. Histological analysis
is required to confirm this ..
WHALING AREA

Topography and hydrography: The tract records of the whaling boats over several
years reveal the whaling grounds off Brazil, which extend from 6°-8°lO'S and
32°20'-35°00'W, to have remained very constant. The continental shelf extends to about 20 miles from the coast where it drops abruptly from 60 m to
3-4,000 m (Fig. 2). The sea floor in the shelf area is irregular and rocky. The
most important hydrographic feature of the area is its proximity to the equatorial
current systems. The south equatorial current flows westwards near the equator
towards South America. On reaching the Brazilian coast it divides into two:most of the warm water moves northwards towards the Caribbean while theremainder turns south forming the weak Brazil current. This meets the cold
Falkland current (Fig. 3). The whaling area is largely under the influence of thesouth equatorial current. From June, when it is particularly strong, to September,
TABLE 3. MONTHLY MEAN TMPERATURES (°C) BASED ON DAILY RECORDINGSFROM JUNE TO DECEMBER EACH YEAR OF THE WHALING AREA, LAT.
6°S-8°10'S AND LONG. 32°20'W-35°00'W.
Year
July
June
26.10
1963
*25.00
27.12
27.23
1964
26.98
1965
27.35
27.14
1966
27.70
26.70
1967
27.45
26.41
1968
26.10
26.42
1969
27.73
26.80
1970
27.20
27.10
1971
27.80
27.60
1972
28.00
27.60
1973
28.10
27.60
1974
27.80
27.50
1975
27.90
26.90
1976
27.30
1977
28.30
28.30
1978
1979
27.40
27.80
1980
28.50
1981
27.62
1982
27.89
* Based on only 4 days recordings.
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

August
26.05
27.74
26.26
26.64
26.16
26.01
26.77
26.40
26.50
27 .10
26.40
26.40
26.70
26.60
28.00
26.90
27.50
27.70
26.86
27.38

September
27.74
27.00
26.97
26.15
26.13
26.01
26.80
26.40
26.40
26.90
26.80
26.80
26.60
26.60
26.60
27.00
27.70
27.40
26.91
27.25

October
26.35
26.35
26.71
27.01
26.95
26.80
26.74
26.90
26.50
27.00
27.00
27.00
27.10
27.00
26.90
27.40
27.80
27.60
27.77
27.53

November

26.71
26.42
27.02
27.03
27.90
26.90
27.30
27.90
27.90
27.60
27.40
27.70
27.70
28.00
27.90
27.84
27.70

December

27.56
27.00
27.80
27.80
27.80
27.80
27.80
27.80
28.40
28.10
27.83

SINGARAJAH

26

TABLE 4. SOME ENVIRONMENTAL PARAMETERS OF THE WHALING AREA OFF THE
COAST OF BRAZIL (LAT. 6°S-8°10'S AND LONG. 32°20'W-35°00'W), AVERAGE BASEDON *DAILY AND **MONTHLY RECORDINGS DURING 4 YEARS 1979-1982.
Month

Current velocity*
Knot/Hr

Salinity**%0

Oxygen**ml/I

Extinction**
Coefficient

June
July
AugustSeptember
OctoberNovember
December

1.04
0.97
0.83
0.98
0.74
0.60
0.60

34.60
34.82
35.00
35.00
35.40
35.50
35.50

7.80
8.04
7.60
8.20
7.90
8.00
8.20

0.15
0.90
0.11
0.09
0.10
0.14
0.17

there is a strong southerly wind, which from mid-September until December becomes easterly.
Measurements of temperature, current velocity and salinity (Tables 3 and 4)
reveal that the temperature and salinity remain fairly constant throughout theyear. The velocity of the current decreases from 1.04 knots in June to 0.60 in
December. Visibility under water improves considerably after July partly due todecrease in precipitation.
Biotic factors: Flying fish, Exocoetus sp., are very common in the whaling grounds
and schools of dolphins (12-20 animals) are also often seen. The whale louse,
Ovamus balaenopterae, is- found on minke whales (Ohsumi et al., 1970). As thewhales move into warmer waters, these ectoparasites fall off, probably in response to the warmer water, leaving small oval shaped scars which are about
5 cm X 4 cm X 4 cm. The large white shark, Carchardon carcharias and the hammerhead shark, Spkvrna zvgaena are quite common in the whaling area, and often tear
chunks of meat from the ventral side of dead, buoyed whales. Occasionally, Remoras or suckerfish and lampreys were seen to be attached towards the ventral
side of the buoyed whales.
BEHAVIOUR

Behaviour during the hunt: Off Brazil, minke whales are commonly seen in small
groups, 2-6 animals, and only rarely as singles or in larger groups, about 10-14
animals. The animals in pairs swim fairly close to one another (10-12 m) andsometimes very close. Undisturbed minke whales swam at about 8-10 knots;
estimated by comparison with the velocity of the boat. Some authors (Kasuya
et al, 1965; Mitchell, 1978) have reported "ship seeking" behaviour for minke
whales although no such evidence was found in tropical waters and the minke
whales off Brazil appeared to be indifferent to the presence of the vessels.
Absence of" ship seeking" behaviour in the Antarctic minke whales also has beenreported particularly during the last IWC/IDCR cruise (IWC, 1982).
During chasing, the whales can swim faster than the boat (17 knots) for shortperiods. However, after about 10-12 n miles they surface regularly and more
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

BEHAVIOUR OF MINKE WHALES

27

frequently, often cutting right across the bow of the ship, when, of course, they areeasy to harpoon. When hit with the harpoon some animals attempt to escapewith such force that they break the loop encl of the whale line and swim rapidly(estimated at about 24 knots) away, usually following a fairly straight course andprofusely bleeding which was traceable for more than a killometer. In all harpooned whales, it was noticed that the spray of water during blowing was mixed
with blood. Direct evidence indicated that this was due largely to rupture ofblood vessesls, even though an explosive charge in the lungs could not be ruled out.
Epimeletic behaviour: On one occasion, a pod of three whales, later found to be
two females and one male, were pursued at full speed. A female was harpooned
and was eventually brought to the ship, during which time the other two whales
remained with the female, swimming in large circles around her. Within anhour the second female was harpooned and took out the full 700 m whale line,
diving and circling in an attempt to escape. During this time the male swam close
to the female, diving and blowing in synchrony. This continued for some 13
minutes before the female was brought to the side of the boat and killed by electricution. Even then the male made no attempt to escape and fell easy prey tothe gunner.
Electric shocks: Most of the harpooned whales do not die instantly and are
frequently winched back and shot a second or even a third time after which an
TABLE 5. COMPARISON OF CATCHES, SEX RATIOS AND PERCENTAGESOF MINKE WHALES FOR THE PERIOD FROM 1963 TO 1982.
Year

Male

Female

1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
Total

16
26
119
154
151
204
227
330
231
210
246
380
279
330
225
242
315
244
288
4,217

2
28
42
233
334
305
413
474
570
470
440
515
658
497
664
463
496
587
504
566
8,261

* Due to loss
Sci. Rep. Whales Res. Inst.,

No. 35, 1981

In determinate*

4

6
2

16

Total

Sex Ratio
Male : Female

CHI Square/P
Values

2
44
68
352
488
456
617
701
900
702
650
765
1,309
776
1,000
690
739
902
749
854
12,494

1 : 1. 75
1 : 1.62
I : 1.96
1 : 2.17
1 : 2.02
1 : 2.02
1 : 2.09
1 : I. 70
l : 2.03
l : 2.10
l : 2.09
I : I. 73
l : I. 78
I : 2.01
l : 2.05
1 : 2.05
1 : 1.86
I : 2.25
I : 1.96
1 : 1.95

0.06<0.8
0. 73>0.5
0.04<0.9
0.69<0.5
0.01>0.9
0.02<0.9
0.28<0. 7
4.01<0.5
0.33>0.5
0.15<0. 7
0.87>0.5
5.21<0.l
2.04>0.2
0.01>0.9
0.92<0.8
0.09<0.8
1.03<0.3
0.17<0.7
0.06<0.9

SINGARAJAH

28

electric shock is applied. Initially intermittent shocks are applied to which thewhales respond violently. After these, a continuous current is applied for threeminutes during which even the strongest whale becomes restrained, apart fromsome lashing of the flukes. This is soon followed by the drooping of the lower jaw.
Perhaps, it might be safest for the crew to wait until the lower jaw droops before
tying the whale to the ship.
CATCH STATISTICS FOR BRAZIL

Paiva (1961) and Williamson (1975) gave some details of catches from Brazil forthe period of 1910, when whaling began, to 1974, but these include mostly thelarger species. Prior to 1966, larger whales (humpbacks up to 1928 and then sei
and Bryde's whales and occasional blue, fin and sperm whales) dominated the
1963
1965
1967
1969
1971
1973
1975=---~.:...:,-:-_:_~-'-"r'-=--~...:...:;-::_:__~---.
197'7
1979
1981
1800 r---.~~-r~~-.~~--.~~~-'--'--~---'-'-i-'----'--~_:_:_r,

~

•I

,'''

.

' ',

1600

,
,
/

'

,,di
;"

1200

• •, ••-•, -- • •, •• J

J•I••••',\•-04-:-.-:0.'". • • • • •

,..

..

9....

'

:

: .

I

'

I

·I

\

I

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Fig. 4. The relationship between catch (e) and sighting (O); the pattern of minke
whales caught fluctuates almost correspondingly with changes in population sighted.
M indicates means.

Sci. Rep. Whales Res. Inst.,
No. 35, 1984

BEHAVIOUR OF MINKE WHALES

29

catch. Only 3 minke whales were taken prior to 1963. However, catches of minke
whales increased only during the last 20 years (Singarajah, 1983) while most of
the others are now protected.
Table 5 gives details of Brazilian catches between 1963 and 1982. The season
generally lasts from June to December but for a variety of reasons no whaling occurred in either of those months in 1967, 1968, 1971, 1976, 1978, 1979 or 1981.
During the period 1963-1982, 12,494 minke whales have been caught: prior to1963 3 were caught making a total for the area of 12,497.
Fig. 4 shows the number of minke whales sighted and the number of minke
whales caught between 1963-1982.
SEX RATIO

Fig. 5 shows the catch composition by year and month for the greater period ofminke whaling and the average lengths of males and females. There is a significant difference between .the number of males and females in the catches and theoverall ratio is 1 male: 1.95 females; not significantly different from 1: 2. Thisremains fairly constant by month although the percentage of females is lowest at
the beginning of the season (Fig. 5). This factor, along with the sex ratio in
captured schools, often 1 male: 2 females or 2 males: 3 +females, may suggestthat minke whale are not monogamous.
DISCUSSION

Although a comprehensive anatomical description of southern minke whales has
been given by Ohsumi et al., (1970), the present study has provided additional information with respect to the whales off Brazil. Despite somewhat vestigeal inform and character, the omission by previous workers (Williamson, 1961; van
Utrecht et al, 1962; Ohsumi et al, 1970; da Rocha, 1980) to include in the countof the very large number of the baleen plates of the posterior segment was perhaps
solely due to their size. Nevertheless, these are true baleen plates and they could
not be justifiable excluded.
Variation in flipper colour patterns have been described by several authors(Taylor, 1957; Williamson, 1959; Ohsumi et al, 1970; Doroshenkho, 1975; Best,1978). Data from Brazilian operations show that a single flipper type, devoid ofa white stripe, predominates. However, on rare occasions (e.g. in 1980 and 1981,
about 0.2% of the annual catch) a second type, with a white stripe, was recorded.
The animals were small, about 7 m, and Best (pers. commun.) informed me that" they might be a diminutive form of the species ".
The morphology of minke whales off Brazil and in the Antarctic and the temporal distribution of the whales strongly suggest that the whales migrate between
these two areas. Data collected over several years on the distribution of minke
whales off Brazil clearly show that they generally occur in a relatively small area(< 15,000 n. miles 2 ). Their high density in this tropical habitat is further confirmed by the CPUE estimates.
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

~.:~

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Fig. 5. Relationship between numbers of males (solid line) and females (brokenline) minke whales taken monthly. Open histograms compare the mean lengthsof males and females on yearly basis.

197.3

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BEHAVIOUR OF MINKE WHALES

31

The concentration of the minke whales into this area for breeding is presumably a result of the physical and biotic characteristics of the environment. Temperature and perhaps day length seem likely to be important factors influencing
the migrations of whales. Minke whales begin to arrive in the region in the latterpart of June, although the peak months are September, October and November bywhich time:1) precipitation has considerably diminished;2) the strong SE wind has changed to a moderate E wind concomitant with
reduced turbulence;3) the water is more transparent;4) the temperature has dropped very slightly (perhaps to an optimal level);5) the surface current is less strong;
and these factors may influence the minke whales. However, it must be remembered that the first three points also have the practical effect on making the whales
easier to see and so the increase in sightings may to some extent be due to this. In
addition, the increasing numbers of whales from June to September may in fact
have more to do with the conditions in the Antarctic which affect the rate of leaving there rather than the prevalent conditions on arrival off Brazil.
It is interesting to note that the testes from males which were caught in thepeak period are generally larger than those taken earlier (Table 6 and Fig. 6). A
similar trend is seen in ovary weights although the range is greater.
As yet, we have not found a satisfactory technique for estimating the age ofthe minke whales taken off Brazil: Christensen's (1980) method using the tympanic bullae was tried but found to be too tedious for routine samples; problems
were also found with the reading of ear plugs, particularly of younger animals, andoften the counts of the left and the right plugs were different. As a result of thiswe have no estimate of age at sexual maturity for the animals off Brazil.
Masaki (1979) examined age at sexual maturity in minke whales taken by
Japanese expeditions in the Antarctic using four techniques: (i) the age (from ear
plugs) at which 50% of the animals are sexually mature, i.e. have either at least
one corpus luteum or albicans, or have one testis of at least 0.4 kg; (ii) the relationship between age (from ear plugs) and the number of ovulations; (iii) using
length at sexual maturity and the growth curve (age from ear plug); (iv) from thetransition phase of the ear plug. The results from all four methods suggested afemale age at sexual maturity of about 6-7 years. Direct evidence for males wasmore limited due to the scarcity of immature animals in the catches and the need forfurther histological analyses to confirm to 0.04 kg criterion of Ohsumi et al. (1970).
However, assuming that the transition phase in the ear plug was formed at sexual
maturity then the age at sexual maturity for males was about 6 years. If the 0.4 kg
criterion is true then almost all the males caught in Brazilia:n waters are mature(Table 6). Using the maturity criterion of technique 1, da Rocha (1980) estimated the lengths at maturity of males and females off Brazil to be about 25 ft and26.5 ft respectively. This is slightly higher than Masaki's Area II values of 23.3 ft
and 26.1 ft.
Sci. Rep. Whales Res. Inst.,
No. 38, 1984

32

SINGARAJAHTABLE 6.
Weight
(g)
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1,000
1, 100
1,200
1,300
1,400
1,500
1,600
1,700
1,800
1,900
2,000
2,100
2,200
2,300
2,400
2,500
2,600
2,700
2,800
2,900
3,000
3,200
3,400
3,600
3,800
4,000'
4,200
4,400
4,600
~
Mean
Combined Mean
Overall Mean=FREQUENCY DISTRIBUTIONS OF WEIGHTS OF TESTES
August

July
Left

Right

1
2

I
I

1

2

September

Left

Right

1
1
3
I
I
4
3

1
3

Left

Right

2
I
1

1

2
4
2

2
I

3

2
1
4
I
2

4
2
3

2
2
I
2

1
2

3

1

2
2

1

2
1

2
2

3
1

2
2
2
1
1
1
2
2
1

1
4
2
3
2
1
2
1
2
1

1

1

8
1
1
3
1
1

1
1
1

3
1
2

4

3
1

2

2
1
2

20
1,052.5
1,076.320
1,100.043
42*
1,296.5 1,207.5
1,252.4
1,428.53

41*
1,237.8
1,240.4

42
1,242.9* 1 lost during !lensing.

Sci. Rep. Whales Res. Inst.,
No. 35, 1984

BEHAVlQUR OF MINKE WHALES

33

OF BRAZILIAN MINKE WHALES BASED ON 1979 SEASON
OctoberNovember

Left

Right

2

2

December

Left

Right

2
2

2
2
I
2
2
3

Left

Right

I

2

2
4
2
I
3
I
4
II
3
2
6
2
2
6
I
3
2
I
1

I
I
3
I

3
I
4
I
I

ti
12
3
2
8
I
2
2
2
6
2
4
I
2

I
1
2
1
1

75

75

1,386.7
1,408.0

1,429.3

Sci, Rep. Whales Res. Inst.,
N. 35, 1984

I

2
I
2
4
4
3
6
3
3
2
2

2

2
I
I

2
2
I

2
I

1
2

14
1,877 .4
1,867 .9

14
1,864.3

8
3
4
I
5
2
1

2
3
2

2
3

47
1,839.4
1,836.147
1,833.3

SINGARAJAH

34
JULY

Ali GUSTSEPTEMBEROCTOBER!o:oo_

2500

20.oO

! ooo -

50 0

10 0

,

r

-~,,~~-,;--~--.',,r-~-,,-~~~,,,--~~o:--~-.,,~~~-,c--~--,>--~----0~~~,<5~--,;--~--,.,,NUMBERQF

TESTES

EXAMINED

Fig. 6. Weight frequency histogram for the testes of minke whales caught off thecoast of Brazil during the 1980 season.

Masaki (1979) estimated the gestation period for minke whales to be about 9
l /2 months, with the peak mating period in early to mid-October and the peakcalving period in late July using the method of Laws (1959), and data from thewhole Antarctic. If this is true, then if the waters off Brazil were calving grounds,
one might expect to see large numbers of calves in the area. However this is not
the case. This may be because the females calve elsewhere or because calving occurs much later in the season. If the latter is true then one might expect to finda high proportion of pregnant (near term) females in the catch in the early part ofthe season, decreasing as the season progresses. Unfortunately, there are few reliable records on pregnancy off Brazil to date.
Population estimates of minke whales in southern hemisphere is far fromcomplete at the present; and there is no close agreement among previous estimates(Ohsumi et al, 1970; Williamson, 1975; Best, 1979; Chapman, 1979; Holt, 1980).
Although minke whales in the Antarctic are claimed to be increasing (FAO, 1982),
Watson & Riche (1981) place the population of southern minke whales at
150,000-300,000. However, the minke whales arriving off the coast of Brazil tobreed are variations of the southern stock (Williamson, 1975), but no estimates on
absolute population for the Southwest Atlantic has been worked out. Recent
Sci. Rep. Whales Res. Inst.,
No. 35, 1981-

BEHAVIOUR OF MINKE WHALES
30.17

34.51

38. 84

43. 184 7. 52

56. 2051 .86

35
60.53

64.87

69. 211975 •

61 18. 00

5732. 30
•

!977

1982
1980-

5346. 60

4960.90
1978

•

1976

;;;

"z 4575. 20
;;\

1979
1974

:0

~
!::; 4243.95'\

"'z

•1901

1972

4189.50
.1971

g

=:

... 3803. 80
"'
!ii

1969

"'

3418.103032.402646. 70.
2539,33..J:

2261. 00

•1968

196 6

20~.-oo--''--3-z.~34~'--=,-s~.6-8~-4-,~.0~1--'---,-4~5.~35~----:-4~9.~ss=--~5~4~.o-3~-5~0~.3~7~-:c62~.1~0~----=-6~1.~04-;---"--:;1~1.38
G /~Fig. 7. Correlation between the catch per unit effort (C/E) and the abundance ofminke whales. Regression line calculated from 17 years consistent data.

marking experiments to relate stock identity and estimates of its population have
met with only limited success; of the 29 minke whales marked off the coast of
Brazil (Butterworth & Best, 1982) none so far has been recaptured.
The regression line (Fig. 7) for the more consistent peak seasons, covering
almost the entire minke whaling period from t.he Brazilian whaling ground, showsthat the relationship between catch per unit effort and abundance is fairly constant with a few exceptions. The significant variablity in abundance particularly
during 1966, 1971, 1977 and 1981 might be due to a variety of causes, the chief
being operational and other factors peculiar to Brazil, including the quota system
imposed by IWC.
Sex data, throughout the whaling period, both monthly and annual catch,show characteristically that the females far out number the males, and these observations are quite contrary to those reported in the Antarctic (Kasuya & Ichihara, 1965; Ohsumi et al, 1970). The reversal of the sex ratio of the same species
in varying geographical conditions perhaps suggests the segregation of the sexuallymature whales which may be associated with hormonal state of the individuals.
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

36

SINGARAJAH

In respect of the sex ratio, the Brazilian minke whales resemble the population of
the Arctic pattern where Jonsgard (1951) noted that the females numerically dominated the males.
Several lines of evidence indicate that the Brazilian minke whales could be
regarded as spatial and temporal stock in a transient habitat, but their biotic potential or capacity to increase in population will very much depend on the limiting
factors which prevail in their native relatively stable Antarctic habitat.
ACKNOWLEDGEMENTS

The majority of this work was carried out on board the catcher boat Caho Brancoand at Costinha Whale Factory and it is a pleasure to acknowledge the hospitality
and assistance of the Captain, A. Sato, and his crew, and the factory manager, Mr
S. M. Saito.
I also wish to thank Dr G. Rabay of COPESBRA and Mr R. Sampaia of
SUDEPE for their interests; the former supplied me with many original IWC
reports on minke whales.
This work was carried out during the tenure of a Senior Research Fellowshipfrom the National Council for Development of Science and Technology (CNPq),
REFERENCES
BEST, P. B., 1978. External character5 of minke whales landed at Durban. SI, 25 pp., Document submitted to special meeting on southern hemisphere minke whales, IWC. Seattle.
BEsT, P. B., and D.S. Butterworth 1980. Report on the southern hemisphere minke whales assessment
eruise, 1978/1979. Rep. int. Whal. Commn., 30: 257-283.
BUTTERWORTH, D.S. & BEsT, P. B., 1982. Assessment of minke whales stocks in Antarctic Area II. Prog.
Report. MI 24: 1-12.
CHAPMAN, D. G., 1979. Stratified estimate of Area IV series B minke whale population from sightings dataof assessment cruise 1978/1979 and estimate varience. IWC/31/4, Annex G, Appendix I: 13-15.
CHRISTENSEN, I., 1980. Age determination of minke whales Balaenoptera acutorostrata, from laminated structures in the tympanic bullae. Rep. int. Whal. Commn., 31: 245-253.
DA RocHA, J., 1980. Progress report on Brazilian minke whaling. Rep. int. Whal. Commn., 30: 379-384.
DoROSHENKO, N. V., 1975. Body proportions of the minke whales from the Antarctic. In marine mammals. Mater 6, Vses. Soveshch. po izuc. morsh. mlekopitayushchikh. Kiev. Naukova Dumka. I: 108110.
F.A.O., 1981. Review of the state of world fishery resources. COFI/81/INF., 5: 19-21.
HOLT, S., 1980. Southern minke whales, stock assessments, replacement yield and management procedures.
IWC/Sc/32/Mi4 48 pp.
IWC., 1981. Report of the planning meeting for the IWC/IDCR minke whale assessment cruise, 1981/
1982.
IWC., 1982. Cruise report of the 1980/1981 minke whale assessment cruise.
.JoNSGARD, A., 1951. Studies on the little picked minke whale (Balaenoptera acutorostrata Lacepede). Reporton the Norwegian investigations carried out in the years 1943-1950. Norsk Havalfangst-Tid. 40 (3):209-2,'32.
KAsuYA, T. & T. lcHIHARA, 1965. Some informations on minke whales from the Antarctic. Sci. Rep.
Whales Res. Inst., 19: 37-43.
LAws, R. M., 1959. The foetal growth rates of whales with special reference to the fin whale, Balaenoptera
Sci. Rep. Whales Res. Inst.,
No. 35, 198~

BEHAVIOUR OF MINKE WHALES

37

physalus Linn. Discovery Rep., 29: 281-308.
LAws, R. M. & P. E. PuRvEs, 1956. The ear plug of the Mysticeti as an indication of age with special reference to the North Atlantic Fin whale (Balaenoptera physalus Linn.). Norsk. Havaifangst-Tid. 45 (8):413-425.
MASAKI, Y., 1979. Yearly change of biological parameters for the Antarctic minke whales. Rep. int. Whal.
Commn., 29: 375-395.
MITCHELL, E., 1978. Minority statement of southern minke stock assessment. Rep. int. Whal. Commn.,
28, 84-85.
0HSUMI, S., Y. Masaki, & A. Kawamura, 1970. Stock of the Antarctic minke whales. Sci. Rep. Whales
Res. Inst., 22: 75-125.
OHsUMI, S., 1979. Feeding habits of the minke whales in Antarctic. Rep. int. Whal. Commn., 29: 473-476.
PAIVA, M. P., 1961. Recursos basicos da pesca maritima no nordeste Brasileiro. Bol. Est. Biol. Mar. Univ.
Ceara, 3: 1-10.
SINGARAJAH, K. V., 1983. Behavioural observations and estimates of relative abundance of minke whales
based at Costinha land station-Brazil. Proceeding Sympos. Marine Mammals. Colombo, Feb. 1983. (inpress).
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sea-ice. Proc. Z,ool. Soc. Lond., 1929: 325-331.
VAN UTRECHT, W. L. & S. VAN DER sPOEL, 1962. Observations on a minke whale (Mammalia, Cetacea)
from Antarctic. Z,eith.fur Sudnertierk. 27 (4): 217-221.
WATSON, L. & T. RITCHE, 1981. Whales of the world. 302 p. Hutchinson, London.
WILLIAMSON, G. R., 1959. Three unusual rorqual whales from the Antarctic. Proc. Z,ool. Soc. Lond., 133:
135-144.
WILLIAMSON, G. R., 1961. Two kinds of minke whales in the Antarctic. Norsk. Hvalfangst-Tid., 50 (4):133-141.
WILLIAMSON, G. R., 1973. Counting and measuring baleen and ventral grooves of whales. Sci. Rep.
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Sci. Rep. Whales Res. Inst.,
No. 35, 1984

38

SINGARAJAH

EXPLANATION OF PLATESPLATE I
Breathing and escape reaction of a female minke whale for harpoon shot. Also, notethe difference of length between the lower and upper jaw and the triangular rostrum
with the strong central ridge.
PLATE II
The ear-plugs which fit snugly upon the conical end of the "glove-finger"; the rightand the left side plugs often vary considerably in size.
PLATF III-A & B
The pair of ear bones or tympanic bullae of the same female whale measuring 9.20 m
body length. Macrophotography; the marker represents 1 cm. The surface viewof the photograph is actually the vertical plane of the tympanic bullae, facing eachother in the natural position, with their membranous "glove finger" pointing posterior and ventrally. A: inner aspect. B: outer aspect.
PLATE IV
A small segment of the baleen series just anterior to mid-region of the jaw. Note thecolour pattern (black/white); the lingual margin of the hypotenuse of the triangularpart of the plate is frayed out into fine flexible filaments. Note also the height ofthe cementation.
PLATE VThe different types of reduced baleen plates. A; anterior rod-like plates ("hairs"),
B ; the transitional rectangular laminae, C ; the posterior reduced rectangularlaminae (see text).
PLATE VI
The flipper, more like a wing and a calyx shaped mark on the dorsal surface next
to the body. Note the distinct absence of stripes or patches on the flipper of theBrazilian minke whales.
PLATE VII
The fluke of a male which is usually narrower than that of the female. The whale
strikes the tailstock in response to harpoon shot and in an atttempt to escape.
PLATE VIII
The dorsal fin; situated more toward the caudal end of the body.

Sci. Rep. Whales Res. Inst.,
No. 35, 1984

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