THIS PAPER CAN NOT BE CITED EXCEPT IN THE CONTEXT OF IWC MEETINGS
SC/56/BRG33

Preliminary investigation of stock structure of B-C-B
bowhead whales based on analyses of biological parameters
Takeharu Bando, Ryoko Zenitani and Seiji Ohsumi
The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan
ABSTRACTThe possibility of more than one stock mixing within B-C-B stock of bowhead whales was examinedusing biological parameters such as conception date, body length distribution of mature whales, migration
period and mean cycle of δ13C oscillation in baleen. Heterogeneity was found in some of the parameters
but statistical tests were not conducted due to the small sample size. To elucidate the stock structure of
B-C-B bowhead whales, further research and samples are needed.
KEYWORDS: BOWHEAD WHALE; STOCK IDENTITY; BIOLOGICAL PARAMETERSINTRODUCTION
The comprehensive assessment of the bowhead whale conducted in 1991 identified five stocks ofbowhead whales including the B-C-B stock (IWC, 1992). Since then, the Committee addressed the issueof stock identity of the B-C-B stock on several occasions (DeMaster et al., 2000). However, those
discussions were based on very limited data and no comprehensive analyses on stock identity within the
B-C-B have been presented. Despite the limited availability of data and comparative analyses, theCommittee recommended a single B-C-B stock scenario for management in 2002, which is the only stock
scenario being considered by the Aboriginal Whaling Management Procedure (AWMP).
Accurate elucidation of the stock structure of the large whales requires not only genetic data
but also non-genetic data (Donovan, 1991; Fujise et al., 2001; Perrin, 2001; Rugh et al., 2003, Pastene,2003). For example, the stock structure of the North Pacific common minke whale has been examined bygenetic data (Goto et al., 2000), conception date (Kato, 1992), body length at physical maturity (Zenitani
et al., 2000), scars on the skin (Fujise et al., 2001) and pollutant (Fujise et al., 2000). Some heterogeneity
was found in these parameters and two stocks, the Okhotsk Sea-Western Pacific stock (the ‘O’ stock) andthe Sea of Japan-Yellow sea-East China Sea stock (the ‘J’ stock) were identified. A review of the studies
on stock identity was conducted by Pastene et al. (2000).
Pastene et al. (this meeting) have suggested the possibility of more than one stock mixing
within the B-C-B bowhead whale stock as a result of genetic analysis of samples from the Alaskan
aboriginal whaling. If more than one stock exists and mixing occurs in the Bering-Chukchi-Beaufort Sea,
their breeding area and breeding period might differ resulting in differences of conception dates. Further,
if the migration period and course differs for each stock, distribution and migration route in the feeding
season may differ between them. Growth rate may also differ between each stock as the result ofdifference of nutritional condition. Variation of δ13C value in the baleen was thought to result from1

different nutritional condition (Schell et al., 1989) and differences in the cycle of δ13C oscillation in eachindividual would be the result of difference of migration pattern, feeding record or heretic growth rate ofbaleen.
In this paper, we attempt to examine the stock structure of B-C-B bowhead whales by using
biological data such as conception date, growth curve, body length distribution of mature whales,
migration period and cycle of δ13C oscillation in baleen, which were derived from data and samples ofwhales taken in the aboriginal whaling off the Alaska mainland.
MATERIALS AND METHODS
Data used in this study
Following the guidelines on data availability agreed by the Scientific Committee of the IWC, thefollowing biological data from bowhead whales caught in aboriginal whaling in 1973-2003 was provided
by data owners:
Archive 1: Basic data for the animals caught (date and position of catch, sex, body length).
Archive 3: Date on which whales were seen during aerial survey/ photogrammetry work; dates
on which whales were caught at Barrow.
Archive 6: Corpora counts.
Archive 7: Baleen measurements for age determination.
Archive 8: Aspartic acid measurements for age determination.
Archive 16: Data for fetuses and reproductive females.
Data used in this study is shown in Table 1. All year and area are combined due to the small sample size.
Method to estimate the conception date
Conception date was estimated from the date of catch and body length of fetus using the formula ofHuggett and Widdas (1951). Body length at birth was assumed as 4.3m (Philo et al., 1992).
Method to estimate age
Age was estimated from D/L ratio for aspartic acid of eye lens nucleus by the formula of George et al.
(1999).

Age =1 + ( D / L) 0 
1 + D / L ln  − ln 1 − D / L 1 − ( D / L) 0 
2k AspD/L: D/L ratio for aspartic acid of eye lens(D/L)0: D/L ratio at birth 0.0285 (George et al. 1999)
kAsp: Rate of racemization 1.18×10-3 (George et al. 1999)
Determination of sexual maturity
Male
Following O’Hara et al. (2002), body length of less than 12.5m were identified as immature, 12.5m to
13.0m were identified as maturing and greater than 13.0m were identified as mature.
FemaleWhales with one or more corpora lutea or albicantia were identified as mature and whales with fetus
record were also identified as mature. Whales with no corpora lutea or albicantia in each ovary were2

identified as immature. For the whales with no corpora counts or fetus record, body length of greater than
14.0m were identified as mature and less than 14.0m were identified as immature (Nerini et al., 1984).
Method to examine stock structure
If all whales in the sample belonged to a single stock, the distribution of the plot of each biologicalparameter must become a normal distribution with a single median, despite the occurrence of someindividual variation. If whales from another stock with differences in biological parameters were mixed in
the samples, the distribution of the plots would deviate from a normal distribution. So, we checked the
distribution of the plot of each parameter to examine the possibility of mixing of more than one stock.
RESULT
Conception date
Catch date and body length of fetus are plotted in Fig. 1. In spring, body length of fetus shows two modesof 0-100cm and greater than 350cm. The former was assumed to have conceived in the latest breeding
season and the latter was assumed to have conceived in the previous breeding season. So, they wereplotted separately. From the regression curve and formula of Huggett and Widdas (1951), fetus growth
was shown as follows.
T=BL/1.017+42
T: date from conception
BL: body length of fetus
Estimated conception date of each whale is shown in Fig. 2. Breeding season was assumed from late
December to early April with a peak in mid February. Some whales such as 88G1, 92B8, 83KK1 and
02S3 deviated from the normal distribution but too small sample size did not allow use of statistical tests.
Growth curve
Estimated age and body length are plotted in Fig. 3. A precise growth curve was not obtained due to thesmall sample size and large individual variation. Individual variation was greater in female than in male.
The coarse accuracy of age determination (George et al., 1999) would also prevent obtaining an accurate
growth curve.
Body length distribution of mature whales
Body length distribution of female bowhead whales, whose maturity status was identified by corpora
counts or fetus record, is plotted in Fig. 4. Body length of the smallest mature whale was 13.0m andlargest immature whale was 14.2m.
Body length distribution of male and female whales, whose maturity status was identified bycorpora counts, fetus record or body length are plotted in Fig. 5. Two peaks of 14-15m and 16-17m wereobserved in body length distribution of mature female whales. This could represent mixing of more than
one stock, or considering the longevity of bowhead whales, the larger peak might be physically mature
whales.
Migration period
Spring migration season observed at Barrow is plotted in Fig. 6 with sighting record in Anadyrskiy Gulf
in April to June obtained from Melinikov et al. (1998). The last day of whale sighting at Barrow differsfrom 5/24 to 6/15 but is concentrated around early June. Melinikov et al. (1998; 2002) showed that many
bowhead whale are distributed near the Sireniki area in the Gulf of Anadyr in late May, which contradicts
the single stock scenario of almost all whales migrating to the Beaufort Sea in summer.

3

Cycle of δ13C oscillation in baleen
73 mean cycles of δ13C oscillation in baleen was obtained from 123 records in Archive 7. Mean cycle ofδ13C oscillation becomes lower as the number of oscillations increase and invariable at more than 5
oscillations (Fig. 7). Distribution of mean cycles of δ13C oscillation in each oscillation number is plottedin Fig. 8. Two peaks of short (20-40cm) and long (40-60cm) cycles were found in oscillation number one
and two. This might be the result of differences of migration pattern, feeding record or heretic growth rateof baleen, which leads to the possibility of more than one stock of bowhead whales included in thesesamples.
DISCUSSION
Conception date, growth curve, body length distribution of mature whales, migration season and cycle ofδ13C oscillation, which were considered as indicator of stock structure, were examined in this paper. Ageat sexual maturity and accumulation rate of corpora are also an effective indicator of stock structure, but
we did not examine them due to the small sample size. Rooney et al. (2002) reported a morphologicalvariant of bowhead whale ‘ingutuk’, but we could not identify them from the database.
Mark recapture, Photo ID, distribution, density of distribution, migration pattern, body length
at physical maturity, fat index, body color, body proportion, sound, diet, pollutant loads, parasites andpresence of scars on the skin are also useful to identify stock structure (Rugh et al., 2003), but no data
was obtained.
In this study, we were unable to derive definitive conclusions about the stock structure of
B-C-B bowhead whales caught around the Alaska mainland. The main cause for this is the small numberof samples and scarcity of data. Too small sample sizes prevented the use of statistical tests on data usedin this study. Rate of investigation for each parameter is plotted in Fig. 9. Samples such as reproductive
organ were not collected with sufficient frequency to allow detailed data analysis. Increased sample size
may reveal heterogeneity in biological parameters in B-C-B bowhead whales, as was the case withheterogeneity found in the genetic study (Pastene et al., this meeting).
Bowhead whales are distributed year-round in the Chukchi peninsula and concentrated inAnadyrskiy Gulf at late May (Melinikov et al., 1998; 2002). Some bowhead whales were reported in the
Bering Sea in summer (Dalheim et al., 1980; Bogoslovskaya et al., 1982). Two or more peaks wereobserved in spring migration to the Beaufort Sea by the sighting survey conducted at Barrow (Braham etal. 1979). This information suggests the possibility of more than one stock of bowhead whale distributedin the Bering-Chukchi-Beaufort Sea region.
More data collection and research is required on all whales caught by aboriginal whaling.
Additional research, such as satellite telemetry, sighting surveys in all distribution areas in summer,
examination of variation of sea ice conditions, biopsy sampling and research at the breeding area would
be useful to accumulate knowledge about the stock structure of B-C-B bowhead whales.
CONCLUSION
Some heterogeneity was found in some parameters but the small sample size prevents confirmation. To
elucidate the stock structure of B-C-B bowhead whales, analysis of biological parameters is required
together with genetic studies. It is possible that catch quotas calculated using the single stock scenario for4B-C-B bowhead whales assumed by the Scientific Committee could threaten other mixed and depleted
small stocks. We recommend further research be conducted on bowhead whales caught in aboriginal
whaling and that research be conducted in the Bering Sea and Chukchi Sea in both the summer feeding
season and winter breeding season.
ACKNOWLEDGMENTS
We would like to thank all researchers and hunters to investigate whales and to collect samples in hardenvironment. We also thank to Dr T. Smith to arrange data request. Dr Geof Givens allowed us to use dataof migration period (Archive 3). Dr Judy Zeh, Dr Cheryl Rosa and Susan Lubetkin allowed us to use dataof stable isotope (Archive 7). Dr. John C. George provided useful comments and allowed us to use data ofbasic data (Archive 1), corpora counts (Archive 6), baleen measurements (Archive 7), aspartic acidmeasurements (Archive 8) and data for fetuses and reproductive females (Archive 16). We thank to Dr
Hiroshi Hatanaka and Dr Luis A. Pastene of the Institute of Cetacean Research, for providing usefulcomments. Dan Goodman kindly reviewed and corrected English.
REFERENCES
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Migrations and aboriginal whaling. Rep. int. Whal. Commn 32:391-9.
Braham, H.W., Krogman, B., Leatherwood, S., Marquette, W., Rugh, D., Tillman, M., Johnson, J. andCarroll, G. 1979. Preliminary report of the 1978 spring bowhead whale research program results. Rep.
int. Whal. Commn 29:291-306.
Dahlheim, M., Bray, T. and Braham, H. 1980. Vessel survey for bowhead whales in the Bering and
Chukchi Seas, June-July 1978. Mar. Fish Rev. 42(9-10):51-57.
DeMaster, D., Ruh, D., Rooney, A., Breiwick, J., Shelden, K. and Moore, S. 2000. Review of studies on
stock identity of the bowhead whale from the western Arctic. IWC/SC/52/SD4:24pp.
Donovan, G.P. 1991. A review of IWC stock boundaries. Rep. int. Whal. Commn (special issue) 13:39-68.
Fujise, Y., Hakamada, T., Aoki, M., Niimi, S., Nakata, S., Honda, K. 2000 An attempt to identify stocks inthe western North Pacific minke whale (Balaenoptera acutorostrata) using the accumulation levels ofheavy metals and organochlorines as ecological tracers. Paper SC/F2K/J18 presented to the IWC
Scientific Committee Workshop to Review the Japanese Whale Research Programme under special
permit for North Pacific Minke Whales (JARPN), Tokyo, 7-10 February 2000 (unpublished). 18pp.
Fujise, Y., Zenitani, R., Goto, M. 2001. Utility of non-genetic information for stock identification –Thecase of the western North Pacific minke whale-. Paper SC/53/SD5 presented to the IWC ScientificCommittee, May 2001 (unpublished).9pp.
George, J.C., Bada, J., Zeh, J., Scott, L., Brown, S.E., O’Hara, T. and Suydam, R. 1999. Age and growthestimates of bowhead whales (Balaena mysticetus) via aspartic acid racemization. Can. J. Zool.
77:571-80.
Goto, M., Pastene, L. A., 2000 Population structure in the western North Pacific minke whale based on
RFLP and sequencing analyses of mtDNA control region, using data from the 1994-1999 JARPN
surveys. Paper SC/F2K/J11 presented to the IWC Scientific Committee Workshop to Review theJapanese Whale Research Programme under special permit for North Pacific Minke Whales (JARPN),Tokyo, 7-10 February 2000 (unpublished). 15pp.
Huggett, A.St.G. and Widdas, W.F. 1951. The relationship between mammalian foetal weight andconception age. J. Phyaiol. 114:306-17.
International Whaling Commission. 1992. Report of the Bowhead Whale Assessment Meeting. Rep. int.
Whal. Commn 42:137-55.

5

Kato, H. 1992. Body length, reproduction and stock separation of minke whales off northern Japan. Rep.
int. Whal. Commn 42:443-53.
Melnikov, V.V., Zelensky, M.A. and Ainana. L.I. 1998. Observations on distribution and migration of
bowhead whales (Balaena mysticetus) in the Bering and Chukchi Seas. Paper SC/50/AS3 presented to
the IWC Scientific Committee, May 1998 (unpublished).31pp.
Melnikov, V.V., Litovka, D.I., Zagrebin, I.A., Zelensky, M.A. and Ainana. L.I. 2002. Results ofshore-based counts of bowhead whales in Chukotka: At the western Bering strait, and the eastern Gulfof Anadyr; in May and June 1999 to 2001. Paper SC/54/BRG15 presented to the IWC ScientificCommittee, May 2002 (unpublished).19pp.
Nerini, M.I., Braham, H.W., Marquette, W.M. and Rugh, D.J. 1984. Life history of the bowhead whale,
Balaena mysticetus (Mammalia: Cetacea). J. Jool. Lond. 204:443-68.
O’Hara, T.M., George, J.C., Tarpley, R.J., Burek, K. and Suydam, R.S. 2002. Sexual maturation in malebowhead whales (Balaena mysticetus) of the Bering-Chukchi-Beaufort Seas stock. J. Cetacean
Manage. 4(2):143-8.
Pastene, L.A., Goto, M., Fujise, Y. 1999 Review of the studies on stock identity in the minke whale
Balaenoptera acutorostrata from the North Pacific. Paper SC/51/RMP15 presented to the IWC
Scientific Committee, May 1999 (unpublished).28pp.
Pastene, L.A 2003. On the different criteria used by the IWC/Scientific Committee for defining stocks inbowhead and western North Pacific minke whales. Paper SC/55/RMP9 presented to the IWC ScientificCommittee, May 2003 (unpublished).7pp.
Pastene et al. (in this meeting)
Pastene, L.A., Goto, M., Fujise, Y. 2000 Review of the studies on stock identity in the minke whale
Balaenoptera acutorostrata from the North Pacific. Paper SC/F2K/J1 presented to the IWC ScientificCommittee Workshop to Review the Japanese Whale Research Programme under special permit for
North Pacific Minke Whales (JARPN), Tokyo, 7-10 February 2000 (unpublished). 22pp.
Perrin, W.F. 2001. Draft review of the utility of non-genetic data for differentiating stocks of whales.
IWC/SC/53/SC2: 10pp.
Philo, L.M., George, C., Tarpley, R., Zeh, J. and Albert, T. 1992. Synopsis of mortality, morbility andfoetal growth rate of the bowhead whale. Rep. int. Whal. Commn 42:154-5.
Rooney, A.P., George, J.C. and Tarpley, R.J. 2002. Phylogenetic and morphometric analysis of the ingutuk,
a morphological variant of the bowhead whale (Balaena mysticetus). Paper SC/54/BRG19 presented to
the IWC Scientific Committee, May 2002 (unpublished).14pp.
Rugh, D., DeMaster, D., Rooney, A., Breiwick, J., Shelden, K. and Moore, S. 2003. A review of bowhead
whale (Balaena mysticetus) stock identity. J. Cetacean Res. Manage. 5(3):267-79.
Schell, D.M., Saupe, S.M. and Haubenstock, N. 1989. Bowhead whale (Balaena mysticetus) growth andfeeding as estimated by δ13C techniques. Marine Biology 103:433-43.
Suydam, R.S., Angliss, R.P., George, J.C., Braund, S.R. and DeMaster D.P. 1995. Revised data on thesubsistence harvest of bowhead whales (Balaena mysticetus) by Alaska Eskimos, 1973-1993. Rep. Int.
Whal. Commn. 45:335-7.
Zenitani, R., Kato, H., Fujise, Y., 2000 Some analyses on biological parameters of western North Pacificminke whales, from a view point of stock identification. Paper SC/F2K/J13 presented to the IWC
Scientific Committee Workshop to Review the Japanese Whale Research Programme under special
permit for North Pacific Minke Whales (JARPN), Tokyo, 7-10 February 2000 (unpublished). 18pp.

6

Table 1. Sample size used in the analysis of biological parameters.
Body
NumberAspartic acid
Body length
lengthof corpora
racemizationof fetus
M
F
Full Part
M
F
2
1
Gambell
20 27
2
1
2
2
1
Savoonga
20 32
2
1
1
Wales
2
5
Kivalina
4
3
2
Point Hope
44 41
2
1
7
Wainwright
36 42
2
2
3
Barrow
199 209
18
53
10
32
33
1
Nuiqsut
20 161
61
Kaktovik
34 30
3
2
2
Unknown
Total
379 405
28
72
14
40
42
*1
13
Baleen plates which has more than one δ C oscillation were used.

7

δ13C
oscillation*1
M F Uk
4

3 1
4 1
24 21
1
6 5
1
37 34

1
1

2

500
y = 1.017x - 89.618

450

88G1

2

R = 0.9717

Body length of fetus (cm)

400
350
300
250
200
02S3

150
100

83KK1
92B8
92B7

50
0
0

30

60

90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540

Accumulative date (days from 1/1)
Fig. 1. Fetul growth curve of bowhead whale. Large fetus (more than 350cm) caught in springwere plotted separately (see text). Legends in figure shows whale ID.

12Frequency

10
8
6
4
2
0
Dec-M Dec-L

Jan-E

Jan-M Jan-L

Feb-E Feb-M Feb-L Mar-E Mar-M Mar-L Apr-E Apr-M
Conception dateFig. 2. Estimated conception date of Bowhead whales.

8

20.0

Male
18.0

Body length (m)

16.0
14.0
12.0
10.0
8.0
6.0
-50

0

50

100

150

200

250

Estimated age
20.0

Female18.0

Body length (m)

16.0
14.0

12.0
10.0

8.0
6.0
-50

0

50

100

150

200

Estimated age
Fig. 3. Estimated age and body length of male(upper) and female (lower) Bowhead
whales.

9

250

10
Female:Immature by corpora counts and fetus record

Frequency

8

Female:Mature by corpora counts and fetus record
n=97

6
4
2

19.1

18.1

17.1

16.1

15.1

14.1

13.1

12.1

11.1

10.1

9.1

8.1

7.1

6.1

5.1

0

Body length (m)Fig. 4. Body length distribution and maturity status of Bowhead whales.
Maturity status was identified by corpora counts and fetus record.

40

Male:Mature

Male

35

Male:Maturing

Frequency

30

Male:Immature

25

n=380

20
15
10
5

19.1

18.1

17.1

16.1

15.1

14.1

13.1

12.1

11.1

10.1

9.1

8.1

7.1

6.1

5.1

0

Body length (m)40Female35

Female:Immature
Female:Mature

Frequency

30
25

n=405

20
15
10
5

Body length (m)Fig. 5. Body length distribution and maturity status of Bowhead whales.
Maturity status was identified by corpora counts, fetus record or body length.

10

19.1

18.1

17.1

16.1

15.1

14.1

13.1

12.1

11.1

10.1

9.1

8.1

7.1

6.1

5.1

0

April

May

11

1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
1994*1
1995*1
1996*1*1： Sighting of bowhead whales in Sireniki area (Anadyrskiy Gulf) extracted from Melinikov et al. (1998).
Fig. 6. Migration season of Bowhead whales investigated at Barrow and sightings in Sireniki area.
11

June

Mean oscillation cycle (cm)

80.0
Male
Female

60.0

40.0

20.0

0.0
0

4

8

12

16

20

13

Number of Oscillation in δ C
Fig. 7. Number of oscillation and mean cycle of δ13C in baleen of Bowhead whales.

Frequency

10

Number of oscillation = 1

8
6
4
2
0
0-5

5-10

10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70
Mean cylcle of δ13C oscillation (cm)10

Number of oscillation = 2

Frequency

8
6
4
2
0
0-5

5-10

10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70
Mean cylcle of δ13C oscillation (cm)Frequency

10

Number of oscillation = 3

8
6
4
2
0
0-5

5-10

10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70
Mean cylcle of δ13C oscillation (cm)10

Number of oscillation = 4

Frequency

8
6
4
2
0
0-5

5-10

10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70
Mean cylcle of δ13C oscillation (cm)Frequency

40

Number of oscillation >= 5

30
20
10
0
0-5

5-10

10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70
13

Mean cylcle of δ13C oscillation (cm)Fig. 8. Distribution of mean δ C oscillation cycle in baleen of Bowhead whales.

1224

Number of landed whales in Alaska
Body length measurment
Identification of sex
Baleen length measurment
Corpora count
120.0

60

Aspartic acid measurment

Number of catch

2002

2000

1998

0
1996

0.0
1994

10

1992

20.0

1990

20

1988

40.0

1986

30

1984

60.0

1982

40

1980

80.0

1978

50

1976

100.0

1974

Ratio(%)

δ13C measurment of baleen

Year
Fig. 9. Catch history and rate of investigation in each parameter. Data of landed whale from 1974 to 1993 arefrom Suydam et al . (1995), data from 1994 to 2002 are recompiled from the annual report of the Scientific Committee.

13