DOI

https://doi.org/10.34331/cpops.2022S003

J-STAGE Advance published date: June 13, 2023

KATSUMATA, ISODA, MATSUNO, MURASE AND MATSUOKAOBSERVATION OF FIN WHALE (BALAENOPTERAPHYSALUS) FEEDING BEHAVIOR IN THE AUSTRALSUMMER SOUTHERN HEMISPHERE MID-LATITUDES
Taiki KATSUMATA1*, Tatsuya ISODA1, Kohei MATSUNO2,
Hiroto MURASE3 and Koji MATSUOKA1
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan
2
Faculty/Graduate School of Fisheries Sciences, Hokkaido University,
3–1–1 Minato-cho, Hakodate, Hokkaido 041–8611, Japan
3
Laboratory of Cetacean Biology, Tokyo University of Marine Science and Technology,
4–5–7 Konan, Minato-ku, Tokyo 108–8477, Japan*Corresponding author: katsumata@cetacean.jp
1

Abstract
In the Southern Hemisphere, ﬁn whales (Balaenoptera physalus) feed mainly in the latitudinal range between 50°S and 60°S during the austral summer. In February 2021, ﬁve ﬁnwhales were sighted about 1,000 km south of the Cape of Good Hope, South Africa at position
43°49′S, 19°12′E. Feeding behavior was evident as the whales were lunging laterally into surrounding red patches with their mouth open. Examination of sampled red patches revealed thatthe ﬁn whales were feeding on either Calanus australis or C. agulhensis. This is the ﬁrst reportof ﬁn whales preying on Calanus spp. in this sea area and time of the year.
Key words:

Balaenoptera physalus, Southern Hemisphere, ﬁn whale, distribution, feeding
behavior.

In austral summer, ﬁn whales (Balaenoptera physalus) mainly distribute in the latitudinal range between 50°S–60°S for feeding (Mackintosh, 1966; Miyashita et al., 1995; Edwards et al., 2015; Aguilar
and Garcia-Vernet, 2018). They prey on krill, mostly Euphausia valentini and E. superba, and rarely on copepods and amphipods in the Southern Hemisphere (Kawamura, 1980). In recent years, ﬁnwhales have been reported to feed on krill between 29°S and 43°S, along the coast of Chile (Perez etal., 2006; Toro et al., 2016; Buchan et al., 2021).
On 13 February, 2021, one school of ﬁve ﬁn whales was ﬁrst sighted at position 43°49′S, 19°12′E,
approximately 1,000 km south of the Cape of Good Hope, South Africa by the captain (Nobuo Abe)on board the Yushin Maru No.2 (747GT), a research vessel engaged in the 2020/21 austral summer
survey of the Japanese Abundance and Stock-structure Surveys in the Antarctic (JASS-A; Isoda etal., 2021) program. The sighting was made during the vessel’s transit between the Antarctic and thehome port in Shiogama, Japan.
At the time of the observations, visibility was 5 n. miles, and the wind speed was 14 knots in direction southeast. Air and sea surface temperatures were 9.9°C and 10.9°C, respectively. Each of the ﬁve
whales was swimming in separate directions about 200 m apart. The behavior of two of them (designated as Whale-A and Whale-B) was observed from the upper deck of the vessel and aerial video
footage was recorded using an unmanned aerial vehicle (UAV; Phantom Pro4 Ver2.0, DJI, China).
The body lengths of the two whales recorded in the UAV footage were visually estimated by an experienced observer onboard: 19.7 m (Whale-A) and 19.3 m (Whale-B). The other three individuals were
estimated to be 20.3 m, 18.5 m and 17.2 m, but were not videotaped because they were too spread apartto be spotted by the UAV monitor.
According to UAV observation, multiple reddish patches approximately 20–50 m long scattered on

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Fig. 1. Lateral lunge feeding of a ﬁn whale (Whale-A) with its right jaw down. A detailed behavior sequenceand the shape of prey patches are shown in the supplement video.

Fig. 2.

Lunge feeding of Whale-A without turning the body sideways.

the sea surface around the whales. Both whales A and B were feeding on the sea surface and no deep
diving was observed. The swimming direction of Whale-B was not constant, and the feeding was
made in circular movements. When the patch formed longitudinally on the sea surface, the whales
were either lunging parallel to it or passing through when they were intersecting perpendicular to thepatch. The change in the direction of lunging relative to the patch could be for increasing prey capture eﬃciency. More detailed observation of the feeding behavior indicated the whales were lunging
laterally with their right jaw down (Fig. 1). A total of four blows and six lateral lunge feedings wereobserved in Whale-A during a period of 225 seconds for a distance of about 620 m (distance calculated
from the UAV ﬂight log). Most of the time, lunge feeding was carried out laterally, however, non-lateral lunge feeding was observed twice on Whale-A (Fig. 2). Whale-B made lateral lunge feedings
three times and blew twice during a period of 143 seconds for a distance of approximately 280 m withno display of non-lateral lunge feeding.
Samples of sea surface red patch at the location of the sighting were collected using 10 L buckets.
Identiﬁcation of the prey species in the red patches was subsequently conducted in the laboratory
through morphological examination. The result suggested the occurrence of either Calanus australis
or C. agulhensis at its stage C5 (Fig. 3). The identiﬁcation was based on the characteristics of the
prosome, which was rounded in the posterior end and measured 2.65–2.70 mm. According to BradCetacean Popul. Stud. (CPOPS), Short noteVol. 4, 2023, 34–39

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Fig. 3. Copepod sampled at 43°47′S, 19°14′E on 13 February, 2021, and identiﬁed as either Calanus australis
or C. agulhensis.

ford-Grieve et al. (1999), the candidate species that ﬁt the prosome length in stage C5 are C. australis and C. agulhensis. Eﬀort was made to discern between the two species by examining the ﬁfth
swimming leg and the arrangement of the inner spines, but results were not conclusive. Therefore,
it was not possible to discern between these two species using morphology, conﬁrming the diﬃculty mentioned by Bradford-Grieve (1994) for the identiﬁcation of C. australis from C. agulhensis.
Furthermore, the location of the sampling corresponded to the distribution areas of both species. The
copepod species that have been reported as prey of ﬁn whales include C. tonsus (Neocalanus tonsus)
in the Southern Ocean and oﬀ South Africa (Kawamura, 1980) and Calanoides carinatus and Nannocalanus minor oﬀ South Africa (32°40′S–36°30′S) (Best, 1967), and C. chilensis oﬀ northern Chile(43°S) (Buchan et al., 2021). According to Best (1967), 94.1% of ﬁn whales caught oﬀ South Africa
fed on krill, 3.8% on copepods, and 2.0% on amphipods. Kawamura (1980) discussed that rorquals oﬀ
South Africa have a highly variable species composition because of their feeding grounds were concentrated in small areas. The location where ﬁn whales were sighted in this study is within a narrowand productive area due to the Agulhas Current System (Fig. 4). It is considered that ﬁn whales in thisarea feed not only on krill but also several available species, including copepods as a secondary preysource. However, recent information on the prey species of ﬁn whales in the Southern Hemisphere islimited, and their diet may have changed from the time when the previous studies had been conducted.
In the Northern Hemisphere, Jory et al. (2021) reported an expanded dietary niche for ﬁn whales in
the St. Lawrence Estuary due to changes in the marine environment caused by climate change in the
2000s. On the other hand, the major whaling grounds of ﬁn whales in the past were reported on the
coast of South Africa and south of 50°S (Mackintosh, 1966). The small catches of ﬁn whales around
45°S might have made it unknown that copepods possibly are major prey items for ﬁn whales in theSouthern Hemisphere mid-latitudes.
Fin whale feeding behavior in non-Antarctic Ocean waters in austral summer was reported for anear-shore productive zone in the Humboldt Current System oﬀ Chile (Perez et al., 2006; Toro et al.,2016; Buchan et al., 2021).
Chlorophyll-a (Chl-a) concentration at the sighting position of ﬁn whales in this study (43°49′S,
19°12′E) was relatively high. The monthly average Chl-a concentration in February 2021 observedby MODIS-Aqua at the location of the ﬁn whale sighting is shown in Fig. 4. The Chl-a concentration
missing values were complemented using the ﬁll no data feature with default values in QGIS (Version
3.16.13-Hannover). The concentration of Chl-a at the sighting position was 0.35 mg/m3. The Chl-a
concentration in the latitudinal range between 40°S–45°S is relatively higher than that outside of thisrange (Fig. 4). In the latitudinal range between 40°S–44°S between South Africa and Antarctica, the36

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Fig. 4. The sighting location of a ﬁve-ﬁn whale school (red circle) on 13 February, 2021 with searching tracks(black lines) of the survey vessel. Monthly average chlorophyll-a concentration for February 2021 is also
shown (Original data: Ocean color web, from https://oceancolor.gsfc.nasa.gov/ (Accessed 2022-7-8)).

eddies that separated from the Agulhas Current System transported nutrient-rich water southwardand mixed with the surrounding water in a shallow depth (the mixed layer was formed at 35 m depth,
on average) resulting in the high concentration of Chl-a (Luis and Lotlicar, 2021). Read et al. (2000)
reported high concentrations of surface Chl-a (in the range 0.5–0.8 mg/m3) between 41°S–44°S and
35°E–45°E where diﬀerent currents converge. These studies have shown that oﬀshore waters of South
African middle latitudes are highly productive and are likely an important feeding area for ﬁn whales.
Venkataramana et al. (2020) investigated the community of zooplankton using the horizontal towing bongo net (200 µm mesh) and the multiple plankton sampler (upper 1000 m) between 40°S–56°S
and 47°E–57°E from January to February and reported copepods were the dominant group across theentire region. In addition, past commercial catches and post-whaling sighting information have also
shown that ﬁn whales distribute oﬀshore South Africa, around 45°S, from December to February(Miyashita et al., 1995; Matsuoka et al., 2006; Edwards et al., 2015). These results suggested thatﬁn whales may be using copepods as prey in this area, as reported in this study. Fin whales in the
Northern Hemisphere have been associated with copepod concentrations (Nemoto, 1963; Flinn et al.,
2002; Baraﬀ, 2006), and copepods are considered the second most abundant prey after krill (Flinn etal., 2002; Baraﬀ, 2006; García-Vernet et al., 2021), or the primary prey for ﬁn whales (Witteveen and
Wynne, 2016).
The oﬀshore waters of South Africa are possibly an important feeding area for ﬁn whales. However, few survey eﬀorts have been made in this area; most sighting surveys after the late 1970s wereconducted south of 60°S (Branch and Butterworth, 2001; Matsuoka and Hakamada, 2014) targeting
mainly Antarctic minke whales (B. bonaerensis). Additional sighting survey eﬀort in mid-latitude
waters (i.e., 35°S–50°S) would warrant further understanding the feeding ecology of ﬁn whales in theSouthern Hemisphere.

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Supplement
Video footage of the feeding observations of whales A and B is available at: https://cpops.jp/archive/
2022S003Whale-A.mp4 and https://cpops.jp/archive/2022S003Whale-B.mp4.
Acknowledgements

We thank Captain Nobuo Abe and oﬃcers and crew of the Yushin-Maru No.2 for their hard work and dedication that led
to the successful observations reported in this paper. We express our deep gratitude to Drs. Yoshihiro Fujise and Tsutomu Tamura and the staﬀ of the Institute of Cetacean Research and Kyodo Senpaku Co. Ltd. for their assistance in arrangements andsupport for the cruise. Finally, we thank Dr. Luis A. Pastene (Institute of Cetacean Research) for his assistance in preparing
this paper.

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Received: November 26, 2022
Accepted: April 20, 2023
Published online: June 13, 2023

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