SC/F14/J18

Preliminary analysis of changes in spatial distribution of
Antarctic minke and humpback whales in Area IV during
the period of JARPA and JARPAII from 1989 to 2006
HIROTO MURASE1, KOJI MATSUOKA2, TAKASHI HAKAMADA2 AND TOSHIHIDE KITAKADO3
1 National Research Institute of Far Seas Fisheries, 2-12-4 Fukuura, Yokohama, Kanagawa, 236-8648, Japan
2 The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan
3 Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo, 108-8477, Japan
ABSTRACT
Changes in spatial distribution of Antarctic minke whales and humpback whales in Area IV during the period of JARPA and
JARPAII were examined. To elucidate temporal changes of their spatial distribution, data obtained in JARPA-JARPAII was
divided into three periods: early (1989/1990, 1991/1992 and 1993/1994), middle (1995/1996, 1997/1998 and 1999/2000) and late(2001/2002, 2003/2004 and 2005/2006). Spatial distribution was estimated using generalized additive models (GAM). The
presence or absence of whales was used as a response variable while seafloor depth, distance from shelf break and longitude wereused as explanatory variables. Mean probabilities of the occurrence of Antarctic minke whales in the survey area in early, middle
and late periods were 0.41, 0.46 and 0.41 while those of humpback whales were 0.14, 0.35 and 0.46. Occupied area indices(probabilities of the occurrence of Antarctic minke whales minus probabilities of the occurrence of humpback whales) were also
calculated. If the index was 1, only Antarctic minke whales were presented in a grid cell while only humpback whales were
presented if the index was -1. If the index was 0, probabilities of the presence of Antarctic minke whales and humpback whales ina grid cell were identical. Mean occupied area indices in early, middle and late periods were 0.28, 0.11 and -0.07, respectively.
The spatial distribution of humpback whales was expanded during the period of JARPA and JARPAII while that of Antarctic
minke whales remained stable. The results indicated that competition between humpback and Antarctic minke whales for habitatin Area IV during the period of JARPA and JARPAII was intensified as abundance of humpback whales increased.

INTRODUCTION
Humpback whales (Megaptera novaeangliae) in the Southern Hemisphere had been exploited commerciallysince the early 1900’s. The International Whaling Commission (IWC) protected humpback whales fromcommercial whaling in the Southern Hemisphere in 1963. The Scientific Committee of the IWC (IWC/SC) now
recognizes eight major breeding stocks in the Southern Hemisphere, namely Breeding Stocks A, B, C, D, E, F, G
and X (IWC, 2011). The Indian sector of the Antarctic between 70°E and 130°E, also defined as Area IV of the
IWC baleen whale management area (Donovan, 1992), is used by breeding stock D (BSD) as its main summer
feeding ground (Pastene et al. 2013). The Breeding ground of BSD is located in Western Australia. It wasreported that abundance of BSD in feeding (from 1989 to 2004: Matsuoka et al., 2011) and breeding ground(from 1999 to 2008: Hedley et al. 2011) was increased. The results of population assessment of BSD by the
IWC/SC indicated the population size in 2006 was 60-80% of pre-exploitation (IWC, 2007) although further
assessment is still undergoing. Habitat expansion of BSD in the feeding ground was observed qualitatively as theabundance was increased (Matsuoka et al., 2011). However, it has not been tested quantitatively.
In contrast to humpback whales, abundance of Antarctic minke whales (Balaenoptera bonaerensis) in
Area IV did not show any significant trend from late 1980’s to mid-2000’s (Hakamada et al. 2014a; Okamura
and Kitakado, 2012). However, it was reported that the energy storage and stomach contents weight of Antarctic
minke whales in the same period were declined (Konishi and Walløe 2014a;b). The results indicated there was a
possibility of competition between humpback and Antarctic minke whales for their major prey, krill.
The objectives of this paper are two folds. Firstly, it is investigated that whether habitat of humpback
whales in Area IV is expanded from late 1980’s to mid-2000’s. Secondary, it is investigated that whether
changes in overlapping spatial distribution of humpback and Antarctic minke whales in Area IV from the late1980’s to the mid-2000’s have occurred. Data obtained by Japanese Whale Research Program under Special
Permit in the Antarctic (JARPA) and its phase II (JARPAII) was used in the analysis.
MATERIALS AND METHODSJARPA was conducted from the 1987/1988 to the 2004/2005 season. JARPAII has been conducted since
2005/2006. Among them, the surveys were conducted in Area IV in nine seasons (1989/1990, 1991/1992,
1993/1994, 1995/1996, 1997/1998, 1999/2000, 2001/2002, 2003/2004 and 2005/2006). A general map of thesurvey area is shown in Fig. 1. Sighting survey data obtained in these years were used in the analysis. Data usedin the abundance estimation of humpback (Hakamada et al. 2014b) and Antarctic minke (Hakamada et al. 2014a)1whales were used in this analysis. Details of survey methods and data are described in these two papers. Sighting
survey efforts in the northern part of the survey area was sparse (e.g. about two transects in each 10 degree
longitudinal sector) in each year. Estimation of the distribution of whales between transects is difficult by using
such data sets. To deal with the difficulty, data were pooled according to time periods: early (1989/1990,
1991/1992 and 1993/1994) middle (1995/1996, 1997/1998 and 1999/2000) and late (2001/2002, 2003/2004 and2005/2006) periods.
The survey areas were divided into 30×30 km grid cells in the South Pole Lambert azimuthal equal area
projection with central meridian at 100°E and latitude of origin at 65°S. The effort data were separated in 1 km
segments and then aggregated in the grid cells. The sighting data were allocated to 30×30 km grid cells based on
the geographic coordinates of the sighting positions. Let Yi be the number of schools of whales in the i-th gridcell, and Xi denote the presence or absence of whales as

1 if Yi > 0,
Xi = 
0 o.w.
Then a spatial smoother using GAM having a binomial error distribution with the logistic link function isconsidered as,logpi= θ o + ∑ f k ( zik ) ,1 − pikwherepi = E[Xi]: probability of occurrence of humpback/Antarctic minke whales in the i-th grid cell

θ o : an intercept
f k : a nonparametric smooth function of the k-th explanatory variablezik : the value of the k-th covariate in the i-th grid cell
The probabilities of the occurrence of humpback and Antarctic minke whales were estimated separately.
Seafloor depth, distance from the shelf break (800m isobath) and longitude are used as explanatory variables.
ETOPO1 Global Relief Model (Amante and Eakins, 2009) is used as seafloor depth. Original resolution of
ETOPO1 is 1x1 arc minute grid cell. The location of the shelf break is identified by using this data. Mean depth
in each 30x30 km grid cell and distance between the shelf break and each grid cell are calculated using ageographic information system (GIS), ArcGIS version 10.1 (ESRI, Redlands, CA, USA). Latitudinal
heterogeneity of the distribution of whales can be captured by these two variables. Longitude is also used as acovariate because the environmental covariates used in this analysis might not capture longitudinal heterogeneityof the distribution of whales.
Smoothness parameters were estimated with the generalized cross-validation (GCV). For these analyses,
the mgcv package (Wood, 2006) version 1.7-27 of R software version 3.0.2 (R Development Core Team 2013)
was used. Probabilities of the presence of humpback and Antarctic minke whales in unsurveyed gird cells were
estimated using the fitted model.
To investigate the extent of overlapping spatial distribution between humpback and Antarctic minke
whales, an index, the occupied area index, was calculated as:zi = p x , i − p y , iwherezi : occupied area index in the i-th grid cell
p x, i : probability of presence of Antarctic minke whales in the i-th grid cellp y , i probability of presence of humpback whales in the i-th grid cellIf the index was 1, only Antarctic minke whales were present in the i-th grid cell while only humpback whales
were present if the index was -1. If the index was 0, probabilities of the presence of Antarctic minke andhumpback whales in the i-th grid cell were identical.

2

RESULTS AND DISCUSSION
A summary of number of grid cells used in the analysis is shown in Table 1. Selected GAMs are summarized inTable 2. Smoothed fits of selected covariate modeling the probability of occurrences of humpback and Antarctic
minke whales in early, middle and late periods are shown in Figs. 2-7.
Survey effort and sighting positions of Antarctic minke whales in Area IV in early, middle and lateperiods is shown Fig. 8 while estimated spatial distribution is shown in Fig. 9. Overall, spatial distribution of
Antarctic minke whales was consistent throughout the three periods. Densities of Antarctic minke whales werehigh in the western part of the survey area where Prydz Bay is located. Antarctic minke whales were mainly
distributed south of the shelf break where seafloor depth is shallow. The relationship between bottom topography
and the distribution of Antarctic minke whales revealed by this study is consistent with past studies (Ainley et al.
2012; Kasamatsu et al. 1996; Murase et al. 2002; 2013). Frequency distributions of probabilities of occurrence ofAntarctic minke whales in the survey area in early, middle and late periods are shown in Fig. 10. Means ofprobabilities of occurrence of Antarctic minke whales in the survey area in early, middle and late periods were0.41, 0.46 and 0.41, respectively. Probabilities of occurrence of Antarctic minke whales were also consistentthroughout the three periods.
Survey effort and sighting positions of humpback whales in Area IV in early, middle and late periods isshown Fig. 11 while estimated spatial distribution is shown in Fig. 12. In the early period, humpback whales
were mainly distributed in the northern part of the survey area between 80°E and 100°E. In the middle period,
humpback whales expanded their habitat closer to the shelf break between 80°E and 120°E. In the late period,
humpback whales were distributed in the entire survey area along the shelf break. Frequency distributions ofprobabilities of occurrence of humpback whales in the survey area in early, middle and late periods are shown in
Fig. 13. Means of probabilities of occurrence of humpback whales in the survey area in early, middle and lateperiods were 0.14, 0.35 and 0.46, respectively. Probabilities of the occurrence of humpback whales increased
from the early to late periods. Past studies using data obtained in the 1980’s and early 1990’s demonstrated that
humpback whales were distributed in the northern part of the study area (Kasamatsu et al. 1996; Murase et al.
2002). However, results of this study suggested humpback whales expanded their habitat closer to the shelf
break as their abundance rebounded. The results of this study suggested that humpback whales were rarely
distributed on the shelf in the feeding season. The finding contrasted with other results in the feeding season in
the North Atlantic (Paxton et al. 2007) and the nursing/breeding seasons when they were distributed in shallow
seafloor depth areas (Ernst and Rosenbaum 2003; Paxton et al. 2011).
Estimated spatial distribution of occupied area indices of Antarctic minke whales and humpback whales
in Area IV in early, middle and late periods is shown in Fig. 14. The figure suggested that the habitats of
humpback whales expanded both in the longitudinal and latitudinal direction while that of Antarctic minke
whales remained stable. Frequency distributions of occupied area indices in early, middle and late periods shiftedfrom positive values to negative values (Fig. 15). Means of occupied area indices in early, middle and lateperiods were 0.28, 0.11 and -0.07, respectively. These results indicated that competition between humpback andAntarctic minke whales for habitats in Area IV during the period of JARPA and JARPAII was intensified asabundance of humpback whales increased. The results of competition for habitats could be reflected in biologicalparameters of Antarctic minke whales such as the energy storage and stomach contents weight.
ACKNOWLEDGEMENT
The authors would like to express their thanks to the crews, researchers and scientists who engaged in thesurveys to plan and collect valuable data.
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Amante, C. and Eakins, B. W. 2009. ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis. NOAA Technical
Memorandum NESDIS NGDC-24, 19 pp.
Donovan, G.P. 1991. A review of IWC stock boundaries. Rep. Int. Whaling Commn. (Special Issue) 13: 39-68.
Ernst, P.J. and Rosenbaum, H.C. 2003. Habitat preference reflects the social organisation of humpback whales (Megaptera novaeangliae) ona wintering ground. J. Zool. 260: 337–345.
Hakamada, T. and Matsuoka, K. 2014a. Estimates of abundance and abundance trend of the Antarctic minke whale in Areas IIIE-VIW, southof 60ºS, based on JARPA and JARPAII sighting data (1989/90-2008/09). Paper SC/F14/J3 presented to the Japanese Whale Research
Program under Special Permit in the Antarctic phase II (JARPAII) Expert Panel Review Workshop, Tokyo, February 2014. 11pp.
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JARPA and JARPAII sighting data (1989/90-2008/09). Paper SC/F14/J4 presented to the Japanese Whale Research Program under Special
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Report to the Australian Marine Mammal Centre on work done to 6th May, 2011, p. 28.
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(Special Issue) 3: 1-50.
Kasamatsu, F., Joyce, G.G., Ensor, P. and Mermoz, J. 1996. Current occurrence of baleen whales in antarctic waters. Rep. Int. Whal. Comm.
46: 293-304.
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periods. Paper SC/F14/J13 presented to the Japanese Whale Research Program under Special Permit in the Antarctic phase II (JARPAII)
Expert Panel Review Workshop, Tokyo, February 2014.
Konishi, K. and Walløe, L. 2014b. Time trends in the stomach content weight in the Antarctic minke whales during the JARPA and JARPAII
research periods. Paper SC/F14/J14 presented to the Japanese Whale Research Program under Special Permit in the Antarctic phase II(JARPAII) Expert Panel Review Workshop, Tokyo, February 2014.
Matsuoka, K., Hakamada, T., Kiwada, H., Murase, H. and Nishiwaki, S. 2011. Abundance estimates and trends for humpback whales(Megaptera novaeangliae) in Antarctic Areas IV and V based on JARPA sighting data. J. Cetacean Res. Manage. (Special Issue) 3: 75-94.
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Antarctic (35ºE-145ºW). Polar Biol. 25: 135-145.
Murase, H., Kitakado, T., Hakamada, T., Matsuoka, K., Nishiwaki, S. and Naganobu, M. 2013. Spatial distribution of Antarctic minke
whales (Balaenoptera bonaerensis) in relation to spatial distributions of krill in the Ross Sea, Antarctica. Fish. Oceanogr. 22: 154-173.
Okamura, H. and Kitakado, T. Abundance estimates of Antarctic minke whales using the OK method. Paper SC/64/IA3 presented to the 64th
IWC Scientific Committee, June 2012. 24pp
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grounds based on mitochondrial DNA analyses. Paper SC/65a/SH13 presented to the 65th IWC Scientific Committee, June 2013
(unpublished). 11pp.
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Publications 7: 143–160.
Paxton, C.G.M., Hedley, S.L. and Bannister, J.L. 2011. Group IV humpback whales: their status from aerial and land-based surveys off
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Wood, S., N. 2006 Generalized additive models: an introduction with R. Boca Raton: Chapman & Hall.

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Table 1. .Number of grid cells used in modeling.
PeriodEarly(1989/1990, 1991/1992, 1993/1994)
Middle(1995/1996, 1997/1998, 1999/2000)
Late(2001/2002, 2003/2004, 2005/2006)

Grid cell insruvey area

Grid cellwith effort

Grid cell withminke whale

Grid cell withhumpback whale

2,209

1,324

582

184

2,207

1,286

639

455

2,345

1,134

518

565

Table 2. Results of GAM modelling. Approximate significance levels (p-value) and effective degrees of freedom(edf) are shown for each of the covariates.
PeriodEarly

MiddleLate

Species

Minke
whale

Humpback
whale

Minke
whale

Humpback
whale

Minke
whale

Humpback
whale

FamilyBinomial

Binomial

Binomial

Binomial

Binomial

Binomial

Link function

Logit

Logit

Logit

Logit

Logit

Logit

Adjusted R2

0.13

0.13

0.20

0.20

0.16

0.30

Deviance explained (%)

10.1

18.6

16.0

17.8

12.7

25.7

GCV score

1.25

0.68

1.19

1.09

1.21

1.06

Covariates

edf

p valueedf

p valueedf

p valueedf

p valueedf

p valueedf

Longitude

3.43

<0.01

7.88

<0.01

8.59

<0.01

5.71

<0.01

1.00

<0.01

7.92

<0.01

Distance from shelf break

5.05

<0.01

8.24

<0.01

1.77

<0.01

1.93

0.02

1.00

<0.01

4.06

<0.01

Seafloor depth

1.00

<0.01

6.32

0.13

3.08

<0.01

5.67

<0.01

1.00

<0.01

5.00

<0.01

5

p valueFig. 1. General map of the survey area. Area bounded by yellow line is the survey area (Area IV of the IWC baleen whale management area). Seafloor depth and the locationof shelf break (800m isobaths; purple line) are also shown.

6

3
2
-1

0

1

s(depth,5.05)

0.6
0.2

s(lon,3.43)

-0.2
-0.6
70

80

90

100

110

120

130

-5000

-4000

-3000

-2000

-1000

0.5

depth

-1.5 -1.0 -0.5 0.0s(dist.shelf.km,1)

lon

0

200

400

600

dist.shelf.km

20s(depth,8.24)

-4
-6

-3
70

80

90

100

110

120

130

-5000

-4000

-3000

-2000

-1000

depth

-4

-2

0

2

lon

s(dist.shelf.km,6.32)

-2

1
0
-2

-1

s(lon,7.88)

2

Fig. 2. Smoothed fits of selected covariate modeling the probability of occurrences of Antarctic minke whales inearly period (1989/1990, 1991/1992 and 1993/1994). Tick marks on the x-axis are observed data points. The
shaded areas indicate the 95% confidence bounds. lon: longitude, depth: seafloor depth (m), dist.shelf.km:
distance from the shelf break (km).

0

200

400

600

dist.shelf.km

Fig. 3. Smoothed fits of selected covariate modeling the probability of occurrences of humpback whales in early
period (1989/1990, 1991/1992 and 1993/1994). Tick marks on the x-axis are observed data points. The shaded
areas indicate the 95% confidence bounds. lon: longitude, depth: seafloor depth (m), dist.shelf.km: distance fromthe shelf break (km).

7

1.5
1.0

s(depth,1.77)-0.5 0.0

0.5

2.0
1.0

s(lon,8.59)

0.0
-1.0
70

80

90

100

110

120

130

-4000

-3000

-2000

-1000

-1

0

1

2

depth

-4

-3

-2

s(dist.shelf.km,3.08)

lon

0

200

400

600

dist.shelf.km

0.0 0.5
-1.0

0
-1
-3

-2.0

-2

s(lon,5.71)

1s(depth,1.93)

Fig. 4. Smoothed fits of selected covariate modeling the probability of occurrences of Antarctic minke whales in
middle period (1995/1996, 1997/1998 and 1999/2000). Tick marks on the x-axis are observed data points. The
shaded areas indicate the 95% confidence bounds. lon: longitude, depth: seafloor depth (m), dist.shelf.km:
distance from the shelf break (km).

70

80

90

100

110

120

130

-4000

-3000

-2000

-1000

0

1

2

depth

-2

-1

s(dist.shelf.km,5.67)

lon

0

200

400

600

dist.shelf.km

Fig. 5. Smoothed fits of selected covariate modeling the probability of occurrences of humpback whales in
middle period (1995/1996, 1997/1998 and 1999/2000). Tick marks on the x-axis are observed data points. The
shaded areas indicate the 95% confidence bounds. lon: longitude, depth: seafloor depth (m), dist.shelf.km:
distance from the shelf break (km).

8s(depth,1)-1.0

0.0 0.5 1.0 1.5

0.6
0.2

s(lon,1)

-0.2
-0.6
70

80

90

100

110

120

130

-5000 -4000 -3000-2000 -1000 0

-0.5

0.0

0.5

depth

-1.5

-1.0

s(dist.shelf.km,1)

lon

0

100

300

500

700

dist.shelf.km

0-1s(depth,4.06)

-5

-3

-4

-2

-3

-2

1
0
-1

s(lon,7.92)

1

2

Fig. 6. Smoothed fits of selected covariate modeling the probability of occurrences of Antarctic minke whales inlate period (2001/2002, 2003/2004 and 2005/2006). Tick marks on the x-axis are observed data points. The
shaded areas indicate the 95% confidence bounds. lon: longitude, depth: seafloor depth (m), dist.shelf.km:
distance from the shelf break (km).

70

80

90

100

110

120

130

-5000 -4000 -3000-2000 -1000 0

1

2

depth

-2

-1

0

s(dist.shelf.km,5)

lon

0

100

300

500

700

dist.shelf.km

Fig. 7. Smoothed fits of selected covariate modeling the probability of occurrences of Antarctic minke whales inlate period (2001/2002, 2003/2004 and 2005/2006). Tick marks on the x-axis are observed data points. The
shaded areas indicate the 95% confidence bounds. lon: longitude, depth: seafloor depth (m), dist.shelf.km:
distance from the shelf break (km).

9Fig. 8. Surveyed tracklines (black line) and sighting positions of Antarctic minke whales (pink circle) in Area IV
in early (1989/1990, 1991/1992 and 1993/1994) middle (1995/1996, 1997/1998 and 1999/2000) and late(2001/2002, 2003/2004 and 2005/2006) periods. Location of the shelf break (800m isobaths; purple line) is also
shown.

10

Fig. 9. Estimated probabilities of occurrence of Antarctic minke whales in Area IV in early (1989/1990,
1991/1992 and 1993/1994) middle (1995/1996, 1997/1998 and 1999/2000) and late (2001/2002, 2003/2004 and2005/2006) periods. Location of the shelf break (800m isobaths; purple line) is also shown.

11

Fig. 10. Frequency distributions of probabilities of occurrence of Antarctic minke whales in Area IV in early,
middle and late periods.

12Fig. 11. Surveyed tracklines (black line) and sighting positions of humpback whales (sky blue circle) in Area IV
in early (1989/1990, 1991/1992 and 1993/1994) middle (1995/1996, 1997/1998 and 1999/2000) and late(2001/2002, 2003/2004 and 2005/2006) periods. Location of the shelf break (800m isobaths; purple line) is also
shown.

13

Fig.12. Estimated probabilities of occurrence of humpback whales in Area IV in early (1989/1990, 1991/1992
and 1993/1994) middle (1995/1996, 1997/1998 and 1999/2000) and late (2001/2002, 2003/2004 and 2005/2006)
periods. Location of the shelf break (800m isobaths; purple line) is also shown.

14

Fig. 13. Frequency distributions of probabilities of occurrence of humback whales in Area IV in early, middle
and late periods.

15

Fig. 14. Occupied area indices of Antarctic minke and humpback whales in Area IV in early (1989/1990,
1991/1992 and 1993/1994) middle (1995/1996, 1997/1998 and 1999/2000) and late (2001/2002, 2003/2004 and2005/2006) periods. If the index was 1, only Antarctic minke whales were present in a grid cell while only
humpback whales were present if the index was -1. If the index was 0, probabilities of the presence of Antarctic
minke and humpback whales in a grid cell were identical.

16

Fig. 15. Frequency distributions of occupied area indices of Antarctic minke and humpback whales in Area IV inearly (1989/1990, 1991/1992 and 1993/1994) middle (1995/1996, 1997/1998 and 1999/2000) and late(2001/2002, 2003/2004 and 2005/2006) periods. If the index was 1, only Antarctic minke whales were present ina grid cell while only humpback whales were present if the index was -1. If the index was 0, probabilities of thepresence of Antarctic minke and humpback whales in a grid cell were identical.

17