Technical Reports of the Ins�tute of Cetacean Research (2022)

pp. 52–55

Technical Report (not peer reviewed)

Long-term track movement of Antarc�c minke whales revealed bysatellite-monitored tag experiments conducted by the Ins�tute ofCetacean ResearchKenji Konishi* and Tatsuya Isoda
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan*Contact e-mail: konishi@cetacean.jp

ABSTRACTThis paper presents progress of the work on long-term track movement of Antarc�c minke whales based onsatellite tagging experiments conducted by the Ins�tute of Cetacean Research. In par�cular, the experiments
focused on inves�ga�ng the migratory links between whales in the feeding and breeding areas. Five examplesof northward tracks from Antarc�c feeding areas in the Indo-Paciﬁc sector of the Antarc�c to lower la�tudes
areas are presented. The ﬁve tracks suggested some migra�on pa�erns in the Indian and Paciﬁc Oceans.
These results showed that tracking of Antarc�c minke whales by satellite-monitored tags provides precise anddirect evidence of migratory links. This work should be con�nued and the number of whales tagged should beincreased. This informa�on will greatly assist the interpreta�on of the stock structure hypothesis of Antarc�cminke whales derived from gene�c and sigh�ng data analyses.

INTRODUCTION
Understanding the stock structure of whales is crucial forassessment and management purposes. The Antarc�cminke whale Balaenoptera bonaerensis (herea�er AMW)
is one of the most abundant species in the Southern
Hemisphere, and its abundance exceeds 500,000 animals(IWC, 2012). As in the case of other rorqual whales, theAMW is assumed to migrate between winter tropical andsub-tropical breeding areas and summer Antarc�c feeding areas (Kasamatsu et al., 1995). However, evidences ofdirect links are scarce. Only three Discovery tag-marked
AMWs were recovered at lower la�tude areas, showing movements from feeding to breeding areas. AnAMW marked at 35°W (east of Antarc�c Peninsula) andtwo AMWs marked at 19°E were recaptured oﬀ Brazil
at la�tude 6°S–7°S in the Atlan�c Ocean (Buckland andDuﬀ, 1989). These were the only cases showing direct evidence of links between breeding and feeding grounds forthis species.
The Ins�tute of Cetacean Research (ICR) has conducted
detailed research of the AMW and its ecosystem in theIndo-Paciﬁc sector of the Antarc�c in austral summer,
through the former programs JARPA (Japanese Whale
Research Program under Special Permit in the Antarc�c),
JARPAII (the second phase of JARPA) and the NEWREP-A(New Scien�ﬁc Whale Research Program in the Antarc52

�c Ocean). A summary of the biological and ecologicalresearch outputs from these programs is available inMurase et al. (2020). In the austral summer 2019/20
the ICR commenced a new non-lethal research programin the Indo-Paciﬁc sector of the Antarc�c called JASS-A(Japanese Abundance and Stock-structure Surveys in theAntarc�c). The main objec�ve of the JASS-A is the es�ma�on of the abundance and abundance trends of the AMW
and other large whale species. Research on the stockstructure of large whales is the other main objec�ve ofthe JASS-A, which is essen�al for appropriately interpreting the results of abundance es�mates.
A review of the stock structure studies on the AMW
in the Indo-Paciﬁc sector was provided by Murase et al.
(2020). The current stock structure hypothesis of the AMW
in the Indo-Paciﬁc sector of the Antarc�c involves the occurrence of at least two stocks, the eastern Indian Oceanstock (I-stock) and the western South Paciﬁc stock (P-stock)(IWC, 2008; Pastene and Goto, 2016; Kitakado et al., 2014;
Murase et al., 2020). These stocks are presumed to berelated to the breeding areas for this species suggested byKasamatsu et al. (1995) based on sigh�ng density indices.
Figure 1 shows a schema�c representa�on of the distribu�on of the I- and P-stocks in the Antarc�c feeding grounds
and the geographical loca�ons of the low la�tude breedingareas suggested by Kasamatsu et al. (1995).
One of the important aspects to be inves�gated is theLong-term track movement of Antarctic minke whales revealed by satellite-monitored tag experiments conducted by the InstituteFigure 1.

Hypothesis on stock structure of Antarc�c minke whales in the feeding grounds of the Indo-Paciﬁc sector ofthe Antarc�c derived from gene�c analyses (I- and P- stocks) (IWC, 2008; Pastene and Goto, 2016; Kitakado
et al., 2014) and loca�on of breeding areas of this species suggested by the sigh�ng records (Kasamatsuet al., 1995). The ﬁgure shows the distribu�on of the eastern Indian Ocean stock (I-stock) and westernSouth Paciﬁc stock (P-stock) (Pastene and Goto, 2016), and an overlap sector (Kitakado et al., 2014). The
four breeding areas suggested by sigh�ng density indices (Kasamatsu et al., 1995) are also shown withdashes-line, and the highest density parts are marked with the le�er “H”. Ver�cal bars represent possible
boundaries (Kasamatsu et al., 1995).

links between the hypothesized stocks in the feedingareas and breeding areas. Satellite tracking of whales
can be useful for this purpose. Long-term tracking ofAMWs were previously reported (Lee et al., 2017; Konishi
et al., 2020). However only a few tracks showed evidenceof northward migra�on pa�ern from the Antarc�c Peninsula (Lee et al., 2017).
This paper presents the progress on the work of longterm track movement of AMWs based on satellite tagging
experiments conducted by the ICR. Informa�on on thelink between whales in the feeding and breeding areas
will greatly assist the interpreta�on of the stock structure hypothesis in the feeding ground based on gene�canalyses.

Figure 2.

SPOT6-type tags (Wildlife Computers Inc.) connected to ICRʼs ISOD-type anchor and LK-Carrier.

Figure 3.

Whale tagger LK-ARTS used during the NEWREP-A
and JASS-A tagging experiments.

TAGGING EXPERIMENTS ON ANTARCTIC MINKEWHALES BY THE ICR
In this report, tagging results using SPOT6-type tags,
which are designed to inves�gate horizontal movement,
are presented (Wildlife Computers Inc.; Figure 2). Thetags were deployed using an air compressed launcher
LK-ARTS (Figure 3), ﬁred from the research vessel YushinMaru No.2 (Konishi et al., 2020). Five tracking records
with clear northward migra�on movements were selected for this paper.
Long-term track movement of AMWs
The ﬁve northward tracking movements of AMWs areshown in Figure 4 and the relevant data are presented

in Table 1. The tag deployments were made in the sector
10°E–30°E (west of Indian Ocean Sector) and in the sector
170°W–140°W (Paciﬁc Sector), south of 60°S. These records indicated that the western and eastern movements
seem to be closely related to the direc�on of westward
Antarc�c Coastal Current and eastward Circumpolar Current, respec�vely (see Nicol et al., 2000).
Two AMWs in the Indian Ocean Sector were tagged in53

Technical Reports of the Ins�tute of Cetacean Research (2022)

Figure 4.

Five cases of northward tracking movement of Antarc�c minke whales tagged during the NEWREP-A andJASS-A programs. All deployments were conducted during the austral summer on the feeding ground. Twoformer whaling loca�ons in South Africa and Brazil are also shown.

Table 1
Relevant data of ﬁve satellite-tracked Antarc�c minke whales in Figure 4 during the NEWREP-A and JASS-A programs.
Tracking colour

Tracking periods

Loca�ons of deployments

Loca�on of last transmission

GreenBlueRedPurple
Yellow

2 Feb. 2020–2 Sept. 2020
28 Jan. 2021–1 Jul. 2021
27 Feb. 2018–3 Jun. 2018
6 Feb. 2022–6 Aug. 2022
28 Jan. 2022–1 Jul. 2022

68.5°S; 14.6°E
69.2°S; 19.4°E
76.7°S; 163.9°W
71.5°S; 133.4°W
66.6°S; 129.8°W

30.5°S; 35.1°E
40.2°S; 67.5°E
46.7°S; 140.7°W
15.9°S; 109.2°W
59.9°S; 104.3°W

a similar longitudinal sector, however they showed different movement pa�erns. One animal moved eastward
and started migra�ng to the north around 70°E (blue inFigure 4). The other animal showed a westward movement along the Antarc�c coast, then changed its course
to the east at 45°W in the oﬀshore area, then started
migra�ng in the northeast direc�on. This animal ﬁnallyarrived at the area oﬀ the coast of Durban, South Africa,in September (green in Figure 4).
In the Paciﬁc Sector, AMWs moved into the Ross Sea
at ﬁrst, then one whale started migra�ng to the east (yellow in Figure 4). Two others moved ﬁrst to the east andthen to the north (red and purple in Figure 4). The longest
tracked animal showed northward migra�on and ﬁnallyarrived at 16°S; 109°W in August.
In the previous study by Lee et al. (2017), two AMWs
tagged in the west of the Antarc�c Peninsula showednorthward migra�on at diﬀerent longitudinal bands inthe Paciﬁc Sector, while another one moved into theAtlan�c Sector.
Interpreta�on of movements in the context of stockstructure
The ﬁve cases of tracking AMWs presented in this paper
demonstrated that their longitudinal range of movement
at the feeding area are wider than previously reported
54(up to 80°). On the other hand, the migratory corridors
to breeding areas involve a wide longitudinal range. Inaddi�on, AMWs appear to move in the northeast direc�on when they start the migra�on to the breeding areas.
These la�tudinal movement pa�erns will assist the interpreta�on of the stock structure hypothesis of this species
in the Indo-Paciﬁc sector of the Antarc�c derived fromgene�c analyses.
As indicated earlier, the current hypothesis on stock
structure by gene�c evidence in the Indo-Paciﬁc sector ofthe Antarc�c feeding grounds involves at least two stocks,
the I-stock and the P-stock (Pastene and Goto, 2016) (Figure 1). These authors suggested that the former could berelated to the breeding area in the eastern Indian Ocean
while the la�er could be related to the breeding area inthe western South Paciﬁc suggested by sigh�ng densityindices examined by Kasamatsu et al. (1995). It is important to note that no gene�c analysis has been conducted
on whales in the hypothesized breeding areas at lower
la�tudes and that the gene�c rela�onship among theproposed breeding areas remains unknown.
Indian Ocean sector
One of the whales tagged in the Indian Ocean Sector ofthe Antarc�c reached the coast of Durban, in South Africa(Figure 4). This loca�on corresponds to the western Indian

Long-term track movement of Antarctic minke whales revealed by satellite-monitored tag experiments conducted by the InstituteOcean breeding area proposed by Kasamatsu et al. (1995)
and Best (1982). This is a cri�cal piece of evidence on
movement from the tagging program conducted by theICR. The migratory track of the second whale tagged in theIndian Ocean sector of the Antarc�c is not complete therefore the migratory des�na�on of this whale in the IndianOcean is unknown. It should be noted that the two tracked
AMWs were both at 0–10°E in the feeding ground.
Paciﬁc sector
The migratory pa�erns of the three AMWs tagged in thePaciﬁc sector of the Antarc�c (Ross Sea) to lower la�tudes
were diﬀerent from each other, however, they all moved
in a northeast direc�on (Figure 4). The whale with the longest tracking record arrived at la�tudes<20°S, in the eastern Paciﬁc Ocean breeding area proposed by Kasamatsu
et al. (1995). The ﬁnal migratory des�na�ons of the othertwo whales are unknown. However, the incomplete movement pa�ern, in par�cular that of the ʻyellowʼ whale,suggests that it is unlikely that they reached the westernSouth Paciﬁc breeding area (Figures 1 and 4).
The three whales were tagged ini�ally in the Antarc�cin a sector corresponding to the P-stock (Figure 1). Assuming that whales in the proposed breeding areas of thewestern and eastern South Paciﬁc Ocean are diﬀeren�ated gene�cally, the tagging data are consistent with theno�on that whales from gene�cally diﬀeren�ated breeding stocks mix spa�ally in the feeding grounds, in this casein the Ross Sea. Mark-recovery tags in the past showedthat AMWs marked in the Atlan�c feeding ground at35°W were recovered in the breeding area oﬀ Cos�nha,Brazil in the Atlan�c Ocean (Buckland and Duﬀ, 1989),
sugges�ng that whales from a breeding ground (Brazil)
could be distributed in a very distant feeding ground.
Future works
The number of tagged whales should be increased in theIndo-Paciﬁc sector of the Antarc�c. In par�cular, Antarc�c minke whales in the core areas of distribu�on of thehypothesized I- and P- stocks should be targeted in thefuture. Technological improvement of the satellite tagging is also required in order to increase the dura�on oftracking whales.

ACKNOWLEDGEMENTS
The authors would like to thank the vessel crews and ICR
members involved in the tagging experiments in the ﬁeld.
We also thank Mutsuo Goto and Mioko Taguchi (ICR)
for providing explana�on of the current stock structure
hypothesis of AMWs in the Indo-Paciﬁc sector of the Ant-arc�c. Our gra�tude to Luis A. Pastene (ICR) for his input
in the interpreta�on of the tagging data in the context
of the stock structure and for his assistance in preparing
this manuscript. Finally, we thank the Editorial Team ofTEREP-ICR for the editorial work on this manuscript

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