Fish Sci
DOI 10.1007/s12562-015-0946-8

Biology

ORIGINAL ARTICLE

Satellite tracking of Bryde’s whales Balaenoptera edeni
in the offshore western North Pacific in summer 2006 and 2008
Hiroto Murase1,2 · Tsutomu Tamura1 · Seiji Otani1 · Shigetoshi Nishiwaki1

Received: 19 February 2015 / Accepted: 16 October 2015
© Japanese Society of Fisheries Science 2015

Abstract Movements of two individual Bryde’s whales(Balaenoptera edeni) were recorded using satellite-monitored radio tags in the offshore western North Pacificwhere no such data had been recorded. One individual
was recorded for 13 days 4 h 57 min from 13 to 26 July
2006. The total traveled distance of the individual was
917.3 km with a mean speed of 2.9 km/h. The other individual was recorded for 20 days 5 h 5 min from 24 July to
13 August 2008. The total traveled distance of the individual was 2649.7 km with a mean speed of 5.5 km/h. It has
been documented that the subarctic-subtropical transitionarea (around 40°N) is one of the feeding areas of Bryde’s
whales in summer. However, the results revealed that someindividual Bryde’s whales moved from the subarcticsubtropical transition area to the subtropical area even insummer. The observation indicated Bryde’s whales did notstay in a feeding area persistently throughout summer. This
study provides the first information regarding the continuous movement of Bryde’s whales in the offshore western
North Pacific in summer which enhances understanding of
their life history.
Keywords Distribution · Feeding ground · Habitat ·Marine mammal · Migration · Movement · Telemetry* Hiroto Murase
muraseh@affrc.go.jp
1

The Institute of Cetacean Research, 4‑5 Toyomi‑cho,
Chuo‑ku, Tokyo 104‑0055, Japan

2

Present Address: National Research Institute of Far Seas
Fisheries, Fisheries Research Agency, 2‑12‑4 Fukuura,
Kanazawa, Yokohama, Kanagawa 236‑8648, Japan

Introduction
Information regarding the movement of baleen whales isimportant to understanding their crucial distribution areas
and for their management. Long-term (weeks to months)
study is required to reveal distribution areas of baleen
whales as they migrate long distances between breeding
and feeding grounds. Marking tags, known as “Discoverytags”, were used to study whale movement in earlier years[1]. However, the practice was ended as a moratorium ofcommercial whaling was imposed in the 1980s because
the tags shot into the bodies of whales had to be recoveredby catching these individuals. The tags could only provide
two locations (locations of deployment and recovery) andpaths between two locations were unknown. Photographic
matching of natural external markings has also been used
to study movement of whales with successful results [2, 3].
However, as in the case of the Discovery tags, photographic
matching could only provide locations where photographs
were taken and movement between these locations was
unknown. Moreover, recapturing of tagged and photographed individuals is difficult if target species are abundant and/or distributed in areas remote from land. Attempts
to monitor continuous movement of baleen whales using
satellite-monitored radio tags was started in the 1980s [4]and they have been deployed to most baleen whale species,
such as right Eubalaena spp. [5–8], bowhead Balaena mysticetus [9–14], blue Balaenoptera musculus [15–20], fin
B. physalus [20–25], sei B. borealis [26], common minke
B. acutorostrata [27, 28], humpback Megaptera novaeangliae [11, 29–35] and gray Eschrichtius robustus [36–39]
whales. However, no result for Bryde’s whales Balaenoptera edeni has been reported in scientific literature, except
for a doctoral thesis [40], probably because their oceanic
distribution inhibits access from scientists.

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Fish Sci

Though the occurrence of three species of the Bryde’s
whale complex, namely, Bryde’s whale B. brydei, Eden’s
whale B. edeni and Omura’s whale B. omurai has been
indicated [41], some scientists consider the former two
forms to be subspecies, B. e. brydei and B. e. edeni, rather
than species, as indicated by the Committee on Taxonomyof the Society for Marine Mammalogy (Committee on Taxonomy, "List of Marine Mammal Species and Subspecies",
Society for Marine Mammalogy: http://www.marinemammalscience.org “accessed on 19 February 2015”) and Katoand Perrin [42]. The scientific committee of the International Whaling Commission (IWC/SC) treats these taxa
(apart from Omura’s whale) as B. edeni with Bryde’s whaleas the common name, but recognizes that more than one
species exists [43]. It was reported that the species distributed in our study area (i.e. offshore western North Pacific)
was identified as B. brydei while those in coastal areas ofsouthwestern Japan were identified as B. edeni based on a
genetic study [44] in the sense of Wada et al. [41]. However, other authors treated them as two different stocks of
B. edeni in the sense of the IWC, namely the western North
Pacific and East China Sea stocks, respectively [40, 45].
Furthermore, differences between Bryde’s whales in various regions of the world have not been investigated fully
on a global basis [42], although relationships between
geographic sampling locations and the phylogenetic position for Bryde’s whale control-region haplotypes have been
investigated on a global basis using published data [46]. We
follow the nomenclature defined by the IWC because taxonomy is not the main subject of this paper.
In the offshore western North Pacific, Bryde’s whales
are distributed in the subarctic-subtropical transition area
in summer [47, 48] as one of the feeding grounds [49–51].
Past studies of Bryde’s whale movement in the offshore
western North Pacific using the Discovery tags suggested
they stayed in the low latitudes (0°–10°N) in winter (January to March) and then migrated to middle latitudes (20–40°N) in spring and summer (April to August), althoughsome individuals stayed in the middle latitudes from winterto summer [40]. The estimated abundance of the western
North Pacific stock in the period of 1998–2002 was 20,501
individuals [52]. The estimated rate of annual increase
from 1988 to 2002 was 4.1 % [53]. Based on photographic
matching of individuals, local movement of Bryde’s whales
was identified in coastal areas of southwestern Japan [40],the Gulf of California [54] and south eastern Brazil [55].
These individuals could be considered as local residents. It
is expected that photographic matching in offshore regions
is technically and logistically difficult because the abundance and target area are large in comparison with coastal
areas. These could be some of the reasons why such an
attempt has not been made. There is no information on thecontinuous movement of Bryde’s whales in the offshore
western North Pacific during summer. Understanding of
movement Bryde’s whales in the offshore western North
Pacific is important for management of this species distributed in this area. It should be noted that Kishiro [40]deployed satellite tags to individuals belonging to the East
China Sea stock of this species.
In this paper, movement of Bryde’s whales in the offshore western North Pacific in summer 2006 and 2008 wasstudied by using satellite-monitored radio tags. Satellitederived sea surface temperature (SST), sea surface chlorophyll-a concentration (CHL) and sea surface height anomaly (SSHA) data were used to understand oceanographic
conditions encountered by the tagged individuals. It is
expected that distribution of Bryde’s whales is related to
distribution of their prey, but such data are not available forthis study. These environmental data are commonly used inhabitat modelling studies of cetaceans as proxies for theirprey abundance or availability [56]. This is the first reportof satellite tracking of Bryde’s whales in this region.

Materials and methods
Two satellite tags were attached to Bryde’s whales in theoffshore western North Pacific in 2006 and 2008 (one tagfor each year) as a part of the second phase of the “Japanese Whale Research Program under Special Permit in
the western North Pacific” (JARPNII; Table 1; Figs. 1, 2).
The program was conducted under a permit issued by thegovernment of Japan. The individual in 2006 was accompanied by a calf with an estimated body length of 8.7 m,
as estimated visually from the research vessel. The transmitters used in the study were the “TCU-150 Argos Platform Transmitter Terminal System” (PTT, Telonics Inc.,
Arizona, USA) equipped with salt water switches. Locations of the Argos satellite transmitters were provided
through the “Collecte Localisation Satellites” (CLSs,

Table 1  Summary of satellite tracking of two individual Bryde’s whales in 2006 and 2008
Year Attachment

Duration

Traveled distance(km)

Mean speed(km/h)

31°16.3ʹN 153°34.4ʹE 12.5

13 days 4 h 57 min

917.3

2.9

2008 24 Jul. 38°00.1ʹN 147°51.5ʹE 13 Aug. 24°02.1ʹN 164°46.4ʹE 12.6

20 days 5 h 5 min

2649.7

5.5

Date

LatitudeEnd
Longitude

Date2006 13 Jul. 37°36.5ʹN 155°10.4ʹE 26 Jul.

13

LatitudeLongitude

Body length(m)Fish Sci
Fig. 1  Movements of two individual Bryde’s whales in 2006
and 2008 monitored by satellite
tags. Circles represent positionsof signals. Location classes 1–3
are used in the figure. (A color
version of this figure is available
in the portable document format(PDF) version of this article)

Seafloor
depth (m)-1

40°N

Deployed
24 Jul. 2008

-10900

Deployed
13 Jul. 2006

30°N
End
26 Jul. 2006End
13 Aug. 2008

130°E

Fig. 2  Bryde’s whales tagged in 2006 (a) and 2008 [b; A color version of this figure is available in the portable document format (PDF)
version of this article]

Ramonville-Saint-Agne, France). The switches allowedtransmissions when the tags were out of the waters. The
transmitters were encapsulated in polycarbonate cylinders
with stainless harpoon heads (Fig. 3). The harpoon heads
were tethered to the stainless shaft with an expectation

140°E

150°E

160°E

170°E

180°

that the harpoon heads were fixed in the body tightly. The
antennas of the transmitters were covered by other polycarbonate cylinders when the tags were deployed fromthe gun. The covers could be detached once it hit whales.
The nylon strings were attached to the tags so that they
could be retrieved when the shots were missed. The tags
were deployed by an air gun, called as the ICR (Instituteof Cetacean Research, Tokyo, Japan) gun, which was amodification of the marine safety pneumatic line thrower[57]. The tags were shot from the bow deck of the survey
vessels. Yushin Maru No. 2 (747GT) and Yushin Maru
(720GT) were used in 2006 and 2008, respectively. The
lengths of the vessels are about 70 m and the height ofthe bow decks from sea surface is about 8 m. The effective shooting range of the gun is approximately 25 m.
The shooting distance between the gun and the individuals in 2006 and 2008 were approximately 10 and 20 m,
respectively.
The CLSs provide theoretical accuracy of locations(location class: LC), as shown in Table 2. The CLSs do notprovide the accuracy for LCs-0, A and B. Several at-sea
measurements of the accuracy were conducted as reviewed
by Costa et al. [58] and their estimated accuracy is also
shown in Table 2. In this paper, only LCs-1, 2 and 3 wereconsidered to calculate distance and time of travel between
consecutive points.
SST data (4 × 4 km grid) obtained by a moderate resolution imaging spectroradiometer aboard the Terra satellite (Terra MODIS) were used. CHL data (4 × 4 km grid)obtained by a sea-viewing wide field-of-view sensor (SeaWiFS) aboard GeoEye’s OrbView-2 were used. Monthly
means of July 2006 and rolling 32-day composites (19July–19 August 2008) in level 3 SST and CHL products
were downloaded from “Ocean Color Web” (http://oceancolor.gsfc.nasa.gov/, NASA Goddard Space Flight Center,“last accessed on 22 December 2013”) were used. Missing

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Fish Sci
Fig. 3  The tag attached to
Bryde’s whales in 2006 and2008. The satellite transmitterwas encapsulated in a polycarbonate cylinder with a stainlessharpoon head (bottom). The
antenna of the transmitter wascovered by another polycarbonate cylinder when the tag was
deployed from the gun (top).
The cover could be detachedonce it hit whales. The harpoon
heads were tethered to the stainless shaft with an expectationthat the harpoon heads were
fixed in the body tightly. [Acolor version of this figure isavailable in the portable document format (PDF) version ofthis article]

Table 2  Accuracy of satellite tag locations (latitude/longitude in km)
provided by the CLSs and measured by Costa et al. [58]Table 3  Number of received signals from two individual Bryde’s
whales in 2006 and 2008 by location class

Location class (LC)

Location class (LC)

Accuracy (km)CLS

Costa et al. [58]

Statistics
LC-3
LC-2
LC-1
LC-0
LC-A
LC-B

68th percentile
0.15/0.15
0.35/0.35
1.00/1.00–––

68th percentile
0.225/0.340
0.468/0.729
0.574/0.879
1.795/2.855
2.788/4.373
4.642/8.253

LC-Z

No location

No location

data in these data were estimated by ordinary kriging withthe aid of the geographic information system (GIS), ArcGIS 10.1 (ESRI, California, USA). Maps of sea levelanomalies and geostrophic velocity anomalies (MSLAs)
were also used in this study. Daily data of sea surface
height anomalies (SSHAs) recorded on the middle dayof the data recording periods (19 July 2006 and 6 August2008) were used in the paper because only daily data wereavailable. The altimeter products were produced by Ssalto/
Duacs and distributed by Aviso, with support from Cnes
(http://www.aviso.oceanobs.com/duacs/ “accessed on 29
January 2010”). Cross-sections of SSTs, CHLs and SSHAs
encountered by the tagged individuals were also preparedby using ArcGIS. The “ETOPO1 Global Relief Model forbottom topography” [59] was used as seafloor depth datafor illustrative purpose. “A Global Self-consistent, Hierarchical, High-resolution Geography Database” [60] wasused in figures to depict coastlines.

13

Number of signals
2006

2008

LC-3
LC-2
LC-1
Subtotal
LC-0
LC-A
LC-B
LC-Z

1
8
15
24
14
48
67
5

1%
5%
9%
15 %
9%
30 %
42 %
3%

4
27
33
64
27
63
74
88

1%
9%
10 %
20 %
9%
20 %
23 %
28 %

Subtotal

134

85 %

252

80 %

Total

158

100 %

316

100 %

Results
Movement of one Bryde’s whale (estimated body length:12.5 m) was recorded for 13 days 4 h 57 min from 13
to 26 July 2006 (Table 1). A total of 158 signals werereceived (Table 3). Among them, 24 signals were LCs
1–3 (15 % of total signals). Daily means (minimum andmaximum) of signal numbers (all classes) was 10.33(4–17). The number of signals (excluding LC-Z) in daytime (sunrise to sunset) and nighttime (sunset to sunrise)
was 90 and 59, respectively. LC-Z was excluded because
location data were necessary to calculate local time.
Speed of movement in Table 1 was calculated using total
traveled distance divided by total traveled time. The total
traveled distance of the individual was 917.3 km with amean speed of 2.9 km/h. Mean (minimum and maximum)

Fish Sci
Table 4  Means (minimum and maximum) of distance and duration
between two consecutive locations calculated by received signals
from two individual Bryde’s whales in 2006 and 2008
Distance (km)Duration

2006

2008

2006

2008

SST, SSHAs and CHLs were 25.7 °C (23.3–28.7), 6.5 cm(−30.9 to 35.9) and 0.09 mg/m3 (0.03–0.15), respectively.
The mean speed for the two individuals calculated using
total traveled distance divided by total traveled time was
4.4 km/h.

MeanStandard
deviation

20
58

41
42

6 h 59 min
19 h 0 min

7 h 34 min
7 h 41 min

Discussion

Maximum

261

210

74 h 8 min

33 h 34 min

Minimum

0.4

0.6

25 min

1 min

Year

Location classes 1–3 are used for the calculations

distance and duration between two consecutive locations
were 20 km (0–261) and 6 h 59 min (25 min–74 h 8 min),respectively (Table 4). Minimum and maximum speeds
between two consecutive locations were 0.1 and 6.5 km/h,
respectively. It should be noted that the distance between
the positions of the satellite tags might not be actual
movement path of the whale as two consecutive points
had long time durations. Therefore, the speed of movements calculated by using distance between two consecutive positions can be considered as not actual but minimum speed. Principally, the individual moved southward(Fig. 4). SSTs encounter by the individual increased as it
moved south. SSHAs encounter by the individual showed
no consistent changes. CHLs encounter by the individual
decreased as it moved south. Summary statistics of SSTs,
SSHAs and CHLs encountered by the tagged individual
are shown in Table 5. Mean (minimum and maximum)
SSTs, SSHAs and CHLs were 22.6 °C (19.0–24.9),
1.2 cm (−29.2 to 30.2) and 0.13 mg/m3 (0.07–0.18),
respectively.
Movement of the other Bryde’s whale (estimated bodylength: 12.6 m) was recorded for 20 days 5 h 5 min from24 July to 13 August 2008. A total of 316 signals werereceived. Among them, 64 signals were LCs 1–3 (20 % of
total signals). The daily mean (minimum and maximum) of
signal numbers (all classes) was 14.36 (1–20). The number of signals (excluding LC-Z) in the daytime and nighttime were 114 and 110, respectively. The total traveled distance of the individual was 2649.7 km with a mean speedof 5.5 km/h. Mean (minimum and maximum) distance andduration between two consecutive locations were 41 km(1–210) and 7 h 34 min (1 min–33 h 34 min), respectively.
Minimum and maximum speeds between two consecutive
locations were 1.4 and 26.4 km/h, respectively. Principally,
the individual moved eastward then southward (Fig. 5).
SSTs encounter by the individual increased as it moved
south. SSHAs encounter by the individual showed no consistent change. CHLs encounter by the individual decreased
as it moved south. Means (minimum and maximum) of

The results of this study showed two Bryde’s whales monitored by satellite tags moved southward from the subarcticsubtropical transition area (around 40°N) to the subtropicalarea of the offshore western North Pacific in summer (Julyand August). The approximate location of the subarctic
front is around 40°N in this area [61]. The subarctic-subtropical transition area of the western North Pacific can beconsidered as one of the feeding areas of Bryde’s whales insummer. However, this study revealed that some individual
Bryde’s whales moved from the subarctic-subtropical transition area to the subtropical area, even in summer. The
observations indicated that Bryde’s whales did not stay ina feeding area persistently throughout summer. Historicalcommercial catch and sighting data indicated that Bryde’s
whales were also distributed to the equator in the offshore
western North Pacific in summer [62]. The results of a species distribution model (SDM) using a generalized linear
model (GLM) indicated that the subarctic-subtropical transition area was the northern edge of Bryde’s whale distribution in the western North Pacific in the summer, and theestimated probability of occurrence was high in the southof the area [48]. The results of the Discovery tags indicated that Bryde’s whales did not migrate north of 40°N
[40]. Combining the past knowledge and the results of thisstudy, the subarctic front can be considered as the northern
limit of the distribution area of Bryde’s whales in the western North Pacific. The results of this study indicate that thenorthbound migrants of Bryde’s whales could change theirswimming direction southward after they encounter thefront. In the subarctic-subtropical transition area, Bryde’s
whales mainly fed on krill and Japanese anchovy Engraulisjaponicus [49–51]. In the south of the area (area approximately bounded by 20°N, 35°N, 160°E and 170°W), theymainly fed on krill, Euphausia similis and Nematoscelis
difficilis, and oceanic lightfish Vinciguerria nimbaria, butthey also fed on a variety of fish species such as Indianscad Decapterus lajang, synonym for Decapterus russelli,
Lovely hatchetfish Argyropelecus aculeatus, Prickly lanternfish Myctophum asperum, Bertelsen’s lanternfish Diaphus bertelseni and Polypnus (note: the spelling is shownin the reference but it could be Polyipnus) matsubarai [63].
The feeding area of Bryde’s whales might not be restricted
to the subarctic-subtropical transition area in summer as
they feed on a variety of prey species (krill, small pelagic

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Fish Sci

(a)

(b)

SST (°C)
35
0Deployed
13 July 2006

End
26 July 2006

Deployed
13 July 2006

SST

40°N

30°N

End
26 July 2006

140°E

150°E

160°E

170°E

(c)

(d)

SSHA (cm)
75
-92

40°N
SSHA

Deployed
13 July 2006

End
26 July 2006

30°N

140°E

(e)

150°E

CHL (mg/m^3)
0.01
0.05

160°E

0.1

0.5

1

170°E

5

10

20

(f)
End
26 July 2006

CHL

40°N
Deployed
13 July 2006

30°N

140°E

150°E

160°E

170°E

Fig. 4  Sea surface temperature (SST; a, b), sea surface height anomaly (SSHA; c, d) and sea surface chlorophyll-a concentration (CHL;e, f) encountered by a Bryde’s whale in 2006. Black line in the map

Table 5  Means (minimum
and maximum) of sea surface
temperature (SST), sea surface
height anomalies (SSHAs)
and sea surface chlorophyll-aconcentrations (CHLs)
encountered by two individuals
Bryde’s whales in 2006 and
2008

13

Year

represents the track of movement of the individual [A color version ofthis figure is available in the Portable Document Format (PDF) version of this article]

SST (°C)

CHL (mg/m3)

SSHA (cm)

2006

2008

2006

2008

2006

2008

Mean

22.6

25.7

Standard deviation
Maximum

1.6
24.9

1.4
28.7

1.2

6.5

0.134

0.087

16.4
30.2

15.8
35.9

0.033
0.180

0.039
0.153

Minimum

19.0

23.3

−29.2

−30.9

0.069

0.034

Fish Sci(a)

SST (°C)
34

(b)

6

Deployed
24 July 2008End
13 August 2008

SST

40°N

Deployed
24 July 2008

30°N
End
13 August 2008

140°E

150°E

160°E

170°E

(c)

SSHA (cm)
122

(d)

End
13 August 2008

-82

SSHA

40°N

30°N

140°E

(e)

Deployed
24 July 2008

150°E

CHL (mg/m^3)
0.01
0.05

160°E

0.1

0.5

1

170°E

5

10

20

(f)

CHL

40°N

30°N

140°E

150°E

160°E

Deployed
24 July 2008End
13 August 2008

170°E

Fig. 5  Sea surface temperature (SST; a, b), sea surface height anomaly (SSHA; c, d) and sea surface chlorophyll-a concentration (CHL;e, f) encountered by a Bryde’s whale in 2008. The black line in the

map represents the track of movement of the individual. [A color version of this figure is available in the portable document format (PDF)
version of this article]

and mesopelagic fishes) in various parts of the western North Pacific. The southward movement observed inthis study could be (1) seasonal migration, (2) movement
within feeding areas and/or (3) other reasons (e.g. associated with social behavior). However, it is difficult to makeany conclusion based only on data from two individuals
with a relatively short tracking duration.
Reported swimming speeds of baleen whales estimatedby using satellite tag data are summarized in Table 6.
Because calculation methods of the speeds were varied

from paper to paper, and the speeds calculated using satellite tag data might not be actual swimming speeds, comparison of swimming speeds among baleen whales basedon this table is only for reference. Nevertheless, swimming
speeds of Bryde’s whales calculated in this study are comparable to other baleen whales.
It was expected that Bryde’s whales stayed around thesubarctic-subtropical transition area of the western North
Pacific in summer as the area was considered as their important feeding ground. However, this study revealed that the13

Fish Sci
Table 6  Comparison ofswimming speed (km/h) ofbaleen whales from different
studies calculated by using dataobtained by satellite tags

Species

Right whale

Bowhead whale
Blue whale

Mean

Standard deviation

Humpback whale

Gray whale

References

Maximum

Minimum
–
1.1
0.8
0.9
1.1
1.1
–
2.4
4.2
2.5
0.5
–
–
2.9
2.7
0.3
0.7
4.3
1.0
2.5
0.8

[5]
[6]
[7]
[10]
[13]
[15]
[17]
[19]
[20]
[20]
[23]
[25]
[26]
This study
[27]
[28]
[29]
[31]
[33]
[34]
[35]

3.3
–
2.7
–
3.8
–
2.5
4.5
–

–
–
1.3
–
1.4
–
2.7
1.4
–

–
1.5
3.7
4.4
–
–
1.3
5.4
–
3.8
–

–
–
4.0
–
–
–
0.7
–
–
0.6
–

–
6.5
4.6
4.5
5.8
3.7
–
7.2
6.5
7.7
0.8
–
–
5.5
3.3
7.3
3.1
6.5
5.9
6.3
3.8

–
1.0

–
–

5.9
2.2

1.1
0.4

[36]
[37]

5.6

–

–

–

[38]

Fin whale

Sei whale
Bryde’s whale
Common minke whale

Range

Mean swimming speed and the range (maximum and minimum) is summarized in the table. Note that
because calculation methods of the speeds were varied from paper to paper and the speeds calculated byusing satellite tag data might not be actual swimming speeds, comparison of swimming speeds among
baleen whales based on this table is only for reference

tagged individuals showed southward movement even insummer. The results implicate the limitations of interpreting SDM results (e.g. Sasaki et al. [48]) as pointed out by
Palacios et al. [64]. SDMs may only estimate spatial distribution of individuals given certain environmental conditions
at a certain time period. In that sense, SDMs are consideredsnapshot models that could overlook the dynamics of anindividual whale’s movement, as indicated by satellite tracking studies. However, it should be note that data obtained bysatellite tags only provides the locations where tagged individuals are present. In addition, the number of satellite tags
attached to baleen whales is still limited at this stage. Generally, data for SDMs of baleen whales obtained through conventional line transect surveys and locations where the target species is absent can be obtained in addition to presence
locations. Data obtained by SDMs and satellite tags is complementary information which will improve our understating of the spatial distribution of baleen whales. The resultsof this study showed that the tagged individuals encounteredvarious environmental conditions while they were moving,

13

though it was difficult to make any conclusion regarding their habitat choice as only two satellite tracking data
streams with relatively short time durations were available.
It was reported that Bryde’s whales in the waters around
Madeira Island (southeast North Atlantic) showed diurnalchanges in diving depth which was presumable linked toavailability of prey [65]. Simultaneous recording of whale
movement in four dimensional space (longitude, latitude,
depth and time) and prey availability will enhance ourknowledge regarding the habitat choices of Bryde’s whales.
The mean swimming speed of the individual in 2006
(2.9 km/h) was slower than that of the individual in 2008
(5.5 km/h). The individual in 2006 could swim slowly
because it was accompanied by a calf. The breeding season of Bryde’s whales in the western North Pacific is long
but winter appears to be the peak [66, 67]. It was estimatedthat gestation and lactation periods last 12 and 6 months,
respectively in Bryde’s whales as in the case of sei whales[68]. Because only estimated body size was available forthe calf, it is difficult to determine the timing of the calving.

Fish Sci

This study provides the first information on the movement of Bryde’s whales in the offshore western North
Pacific in summer and sheds light on an aspect of their life
history. However, relatively short transmission durations inthis study (13 and 20 days) could not address such a question fully. It was reported that the length of transmissions
for humpback whales in the Gulf of Maine was related tothe design of the tags [69]. Improvement of the tagging system used in our study should be considered in future study
to increase transmission duration. Obtaining more satellite
tracking data of Bryde’s whales in the area will enhance
understanding of the life history and contribute to the conservation and management of this species distributed in thatarea.
Acknowledgments The authors express their thanks to the crews
and researchers onboard the research vessels who deployed the satellite tags. The study was supported by the Fisheries Agency of Japan,
Kyodo Senpaku Co. Ltd. and the Institute of Cetacean Research.

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