J-STAGE Advance published date: December 8, 2021

ISODA, TAMURA AND PASTENEINGESTION OF MARINE DEBRIS AND EVIDENCE OFENTANGLEMENTS INVOLVING ANTARCTIC MINKEWHALES (BALAENOPTERA BONAERENSIS) SAMPLED
IN THE INDO-PACIFIC SECTOR OF THE ANTARCTIC
Tatsuya ISODA1*, Tsutomu TAMURA1 and Luis A. PASTENE1, 2
2

1
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan
Project Microbiomes as Bioindicators of the Aquatic Ecosystem Health in Chilean Patagonia, Centro deEstudios del Cuaternario de Fuego-Patagonia y Antártica (CEQUA), Punta Arenas, Chile*Corresponding author: isoda@cetacean.jp

Abstract
This study presents the results of an examination of marine macro debris ingested by Antarctic minke whales (Balaenoptera bonaerensis) in the Indo-Paciﬁc sector of the Antarctic in
the period 1987/88–2018/19. Whales used in this study were sampled by surveys of the former
Japanese whale research programs under special permit in the Antarctic. Also, this study examines evidence of past and present entanglements around the body of the animals. Of a totalof 11,992 whales examined, 19 had ingested macro debris (0.16%) such as polymer products
and wood. Only four cases of entanglements were recorded in the 11,992 whales examined(0.03%). Of 5,215 whales examined from the period of 2005/06 onward, six whales presented
body marks associated with past entanglements (0.12%). It was concluded that the frequency
of macro debris ingested as well as the number of entanglement cases involving Antarctic minke whales sampled in the Indo-Paciﬁc sector of the Antarctic are extremely low in comparison
with whales in the North Atlantic. These low frequencies of ingested debris and entanglements
are unlikely to have a negative eﬀect on the conservation of the Antarctic minke whale populations in this sector of the Antarctic.
Key words:

Antarctic, Antarctic minke whale, marine macro debris, ingestion, entanglements.

Marine debris is a kind of pollutant aﬀecting marine wildlife. Among the marine debris types,
plastics have a more negative impact on marine wildlife than others. Plastics include microplastic
particles (with a diameter <5 mm, Arthur et al., 2009) and macroplastic particles (>20 mm, Barnes
et al., 2009). Such marine debris could cause disease or be ingested and lead to starvation (Gregory, 2009). Recently, two workshops (Panti et al., 2019; IWC, 2020) were held to discuss the current
status of the interaction between marine debris and marine mammals. The objectives of the workshops
were to identify negative eﬀects on the animals; to identify possible areas of research to assess the impact of marine debris on this group of animals; and to propose ways to alleviate the problem. So far,detection of debris interactions in cetaceans has largely depended on data collected from small sample
sizes provided by stranded animals. Therefore it has been diﬃcult to determine the implications of debris interactions at a population level (Baulch and Perry, 2014).
The present study focuses on the Antarctic, one of the most isolated places on earth where the eﬀectof human activities and the occurrence of marine debris are assumed to be limited (see also Isoda etal., this issue). There is limited information regarding interaction between marine debris and whalesin the Antarctic. This study investigates the occurrence of marine macro debris ingested by Antarctic
minke whales (Balaenoptera bonaerensis) based on whales sampled over a period of more than 30
years in the Indo-Paciﬁc sector of the Antarctic by surveys of the former JARPA/JARPAII (Japanese

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MARINE DEBRIS AND EVIDENCE OF ENTANGLEMENTS OF ANTARCTIC MINKE WHALES

Table 1. Number of macro debris ingested by Antarctic minke whales and frequencies (number of whales
with debris ingestion per 100 Antarctic minke whales) in the Indo-Paciﬁc sector of the Antarctic in the australsummer seasons 1987/88–2018/19 (JARPA, JARPAII and NEWREP-A). In parentheses are the numbers ofmarine debris found in the forestomach and main stomach when only those two compartments were examinedin the 2005/06–2013/14 seasons (JARPAII).

* All items found in stomach and duodenal ampulla except one polymer product found in the anus of one whale. Category‘others’ includes one small black piece of carbonized object (research season: 2002/03) and one small rubber piece (research season: 2003/04).

Research Program under Special Permit in the Antarctic, Phases I and II) and NEWREP-A (NewScientiﬁc Whale Research Program in the Antarctic Ocean). The Antarctic minke whale is a smallbaleen whale species, which migrates between low latitude winter breeding grounds and high latitude
summer feeding grounds in the Antarctic where it is widely distributed (Kasamatsu et al., 1995). The
species feed mainly on Antarctic krill (Euphausia superba) but also on ice krill (E. crystallorophias)
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Fig. 1. A piece of polymer product found in the stomach of an Antarctic minke whale sampled during the
2002/03 austral summer season at position 76°S; 175°E (IWC Area V; CCAMLR sub-area 88.1).
Table 2. Ingestion of macro debris by Antarctic minke whales by sex and sexual maturity in the Indo-Paciﬁc
sector of the Antarctic in the austral summer seasons 1987/88–2018/19 (JARPA, JARPAII and NEWREP-A).
In parentheses are the sample sizes examined by sex and sexual maturity.

* Includes one male and one female of unknown sexual maturity status.

in some areas of the Antarctic (Ichii and Kato, 1991; Tamura and Konishi, 2009). It has been assumed
that these whales ingested debris mixed in with food during the austral summer feeding period in the
Antarctic waters.
This study also examines the body surface of the whales to identify entanglements, i.e., objects
attached to the body (from the period of JARPA, JARPAII and NEWREP-A) or evidence from scars
and marks of past entanglement events (from the period of JARPAII and NEWREP-A when more detailed photographic records were available). This is a unique study because it examines ingestion andentanglements in the Antarctic minke whale based on a series of surveys conducted over 31 years, and
it is the ﬁrst study to provide a summary of information regarding interaction between marine macrodebris and whales in the Antarctic.
The surveys were conducted during the austral summer seasons from 1987/88 to 2018/19. Table
1 shows the details of the survey years and the number of samples for each year. The research area
comprised the Indo-Paciﬁc sector of the Antarctic, speciﬁcally the International Whaling Commission(IWC) Antarctic Management Areas III East (IIIE) (35°–70°E), IV (70°–130°E), V (130°E–170°W)
and VI West (VIW) (170°–145°W), south of 60°S (JARPA and NEWREP-A) and south of 62°S (JAR-

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Fig. 2. Size of marine debris ingested by Antarctic minke whales in the Indo-Paciﬁc sector of the Antarctic(1987/88–2004/05). The sample size of debris in this ﬁgure is diﬀerent from that in Table 1 (no size information was available for two polymer products and three wood pieces).

PAII). These areas overlap partially with the Convention Areas of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR): Area IIIE with Divisions 58.4.2–4, Area IVwith Divisions 58.4.1–3, Area V with Division 58.4.1 and sub-area 88.1, and Area VIW with sub-area
88.2.
In order to obtain samples representative of the populations, Antarctic minke whales were sampled
randomly on predetermined track-lines (Nishiwaki et al., 2006; Nishiwaki et al., 2014). Sampledwhales were examined onboard of the research base vessel where several biological measurements
and samples were collected. Body length was measured to the nearest 1 cm from the tip of snout to thedeepest part of the notch of the ﬂukes along a straight line parallel to the body axis. Body weight was
obtained using a large weighing scale installed on the ﬂensing deck. Sex of the whales was determinedby researchers on board. Sexual maturity in females was determined by the presence of at least one
corpus luteum or albicans in the ovaries and for males a single testis weight of 400 g or more was used
as a criterion (Kato, 1982).
The stomachs of 11,992 Antarctic minke whales were examined. Examination of macro debris was
conducted during the routine analysis of stomach contents following established protocols (Tamura
and Konishi, 2009). The three stomach chambers and the duodenal ampulla were examined macroscopically during the period 1987/88–2004/05 (JARPA) and 2015/16–2018/19 (NEWREP-A). Only
the fore and main stomachs were examined during the period 2005/06–2013/14 (JARPAII). Macro debris and objects other than preys were recorded. The sizes of solid objects were estimated from scaled
photographic records.
Out of the 11,992 Antarctic minke whales examined, a total of 19 whales had ingested macro debris(Table 1). None of the whales had multiple marine debris in their stomachs. Fig. 1 shows an example
of marine debris (polymer product) found in the stomach of an Antarctic minke whale. There werenine cases of polymer product ingestion and eight cases of wood ingestion. Macro debris ingestion
was not observed after the 2005/06 season and there was no temporal increasing trend over the reCetacean Popul. Stud. (CPOPS), Short noteVol. 3, 2021, 286–294

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Table 3. List of entanglement cases in the Antarctic minke whales in the Indo-Paciﬁc sector of the Antarctic in
the austral summer seasons 1987/88–2018/19 (JARPA, JARPAII and NEWREP-A) (see Fig. 3).

Fig. 3. Four cases of entanglement in the Antarctic minke whales in the Indo-Paciﬁc sector of the Antarctic in the austral summer seasons 1987/88–2018/19 (JARPA, JARPAII and NEWREP-A). a: ﬁshing hook;b: monoﬁlament ﬁshing line; c: rope; d: packing band (the band was lost when the whale was transported to
the research base vessel).

search period. The frequency of stomachs with debris per 100 Antarctic minke whales examined wasvery low (0.16%) and the frequency of polymer products was 0.08%. Around 68.4% of all macro debris was ingested by mature males (Table 2). Most macro debris (75.0%) was less than 100 mm in size
(Fig. 2). There were three debris, one polymer bag and two small wood pieces with sizes of more than
100×100 mm. Apart from debris, stones were found in six whales (in six austral seasons) and feathers
in 37 whales (in thirteen austral seasons).
The frequency of ingested debris per 100 Antarctic minke whales was very low in comparison withdebris found in whales from the North Atlantic. For example, six of 82 Icelandic ﬁn whales (B. physalus) examined had debris in their stomachs while on the eastern coast of the United States, three of
19 mysticetes examined contained synthetic objects in their gut (Sadove and Morreale, 1990). The
frequencies of marine debris ingestion obtained from stranded animals in the UK were 2.2% in the
harbour porpoise (Phocoena phocoena) and 2.3% in the short-beaked common dolphin (Delphinusdelphis) (Deaville and Jepson, 2010). For the Indo-Paciﬁc sector of the Antarctic, our study found that
only 19 Antarctic minke whales out of 11,992 examined had macro debris in their stomachs (0.16%).
The Antarctic minke whale is a ﬁlter feeder species with swallowing behavior (Nemoto, 1970), and290

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Fig. 4. Six cases of Antarctic minke whales in the austral summer seasons 2005/06–2018/19 (JARPAII and
NEWREP-A) presenting marks and scars possibly produced by past entanglements. a: healed injury of ﬂukes;
b: healed injury of snout; c: healed injury of ﬂukes; d: healed injury of ﬂukes (rope used in the whale processing is also shown); e: healed injury of dorsal ﬁn; f: unhealed injury of head.

this foraging behavior of Antarctic minke whales is associated with shallow waters (less than 100 m indepth) (Friedlaender et al., 2014), which increases the chance of ingesting debris ﬂoating on the surface or in layers just under the surface.
Regarding entanglements, only four cases were found in the total sample of 11,992 whales (0.03%)(Table 3, Fig. 3). These included a ﬁshing hook, a monoﬁlament ﬁshing line, a rope and a packing
band. Six out of 5,215 Antarctic minke whales examined from the period of 2005/06 onward presented scars and marks likely to be associated with past entanglements (0.12%) (Fig. 4). It was assumed
that scars were healed injuries (ﬁve cases) while unhealed marks were considered as injuries (onecase). The unhealed injury was observed during the most recent survey under NEWREP-A. The possibility of these scars being produced by attacks from killer whales (Orcinus orca) is low. Scars observed in the present study were not consistent with the dentition of killer whales which comprise linear, parallel scars spaced 2.5–5.0 cm apart (Naessig and Lanyon, 2004). As in the case of debris, casesof entanglements with dangerous objects were extremely low in the Antarctic minke whales fromthe Indo-Paciﬁc sector of the Antarctic when compared to the North Atlantic. For example, along theeastern coast of the United States and Canada during 2002–2006, 27 and 77 cases of entanglements
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Fig. 5. Relationship between body length and body weight in the Antarctic minke whales (n=10,037) including whales ingesting debris and cases of entanglement. The sample size in this ﬁgure is diﬀerent from those in
Tables 1 and 3 (no body weight was available for one animal that ingested polymer product and two entangled
animals).

were reported for common minke whales (B. acutorostrata) and humpback whales (Megaptera novaeangliae), respectively (Glass et al., 2008). In Iceland, ﬁve of 95 ﬁn whales examined showed signs ofprevious entanglements (Sadove and Morreale, 1990). It was reported that entanglement of Antarctic
fur seals (Arctocephalus gazella) was caused mostly by loop shaped debris such as packing bands(Croxall et al., 1990; Arnould and Croxall, 1995). Similar cases were reported for common minke
whales in the Atlantic (Gill et al. 2000). In the present study, one of the four cases of entanglement in
the Antarctic minke whale was from a packing band (Fig. 3d). CCAMLR has prohibited the dischargeof plastics and restricted the use of packing bands on ﬁshing vessels through Conservation Measure
26–01 (CCAMLR, 2006). Fishing gear is the most signiﬁcant source of entanglements for whales
and such entanglements have been reported in various waters (Laist, 1997; Simmonds, 2012). In the
Antarctic, reports of mortality of whales attributed to entanglements related to ﬁsheries operations are
rare. One of those reports informed of the mortality of a sperm whale and another one possibly of an
Antarctic minke whale (SC-CAMLR 2004; 2012). In the present study, only three cases of entanglements occurred, possibly from ﬁshing gears (derelict or active) (Fig. 3).
In the cases involving both macro debris ingested and entanglements, it was shown that whales
were not emaciated according to the usual body-length-weight relationship (Fig. 5). In conclusion thefrequencies of marine macro debris ingested as well the cases of entanglements involving Antarctic
minke whales in the Indo-Paciﬁc sector of the Antarctic are extremely low, and much lower in comparison with cases reported in the North Atlantic. These low frequencies of ingested debris and entanglements are unlikely to have a negative eﬀect on the conservation of the populations of Antarctic
minke whales in the Indo-Paciﬁc sector of the Antarctic.
Acknowledgements

We would like to thank all of the captains, crew members, cruise leaders and researchers onboard the research vessels of292

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MARINE DEBRIS AND EVIDENCE OF ENTANGLEMENTS OF ANTARCTIC MINKE WHALESJARPA, JARPAII and NEWREP-A for their contributions in collecting the data used in this study. Also, we are grateful tothe anonymous reviewers for their helpful comments.

References
Arnould, J.P.Y. and Croxall, J.P. 1995. Trends in entanglement of Antarctic fur seals (Arctocephalus gazella) in man-madedebris at South Georgia. Mar. Poll. Bull. 30 (11): 707–712. doi: 10.1016/0025-326X(95)00054-Q.
Arthur, C.A., Baker, J. and Bamford, H. 2009. Proceedings of the International Research Workshop on the Occurrence, Effects, and fate of Microplastic Marine Debris. September 9–11. NOAA Technical Memorandum NOS-OR&R-30, 2009,
Washington.
Barnes, D.K.A., Galgani, F., Thompson, R.C. and Barlaz, M. 2009. Accumulation and fragmentation of plastic debris inglobal environments. Philos. Trans. R. Soc. B 364: 1985–1998. doi: 10.1098/rstb.2008.0205.
Baulch, S. and Perry, C. 2014. Evaluating the impacts of marine debris on cetaceans. Mar. Poll. Bull. 80(1–2): 210–221.
CCAMLR. 2006. Schedule of Conservation Measures in Force in 2006/07 season. CCAMLR, Hobart, Australia: 192 pp.
Croxall, J.P., Rodwell, S. and Boyd, I.L. 1990. Entanglement in man-made debris of Antarctic fur seals at Bird Island, South
Georgia. Mar. Mamm. Sci. 6: 221–233. doi: 10.1111/j.1748-7692.1990.tb00246.x.
Deaville, R. and Jepson, P.D. (eds.). 2010. UK Cetacean Strandings Investigation Programme (CSIP)—Final Report for theperiod 1st January 2005–31st December 2010. CSIP, Institute of Zoology, Zoological Society of London, UK. 98 pp.
Friedlaender, A.S., Goldbogen, J.A., Nowacek, D.P., Read, A.J., Johnston, D. and Gales, N. 2014. Feeding rates and under-ice foraging strategies of the smallest lunge ﬁlter feeder, the Antarctic minke whale (Balaenoptera bonaerensis). J.
Exp. Biol. 217(16): 2851–2854. doi: 10.1242/jeb.106682.
Gill, A., Fairbairns, B. and Fairbairns, R. 2000. Photo-identiﬁcation of the minke whale (Balaenoptera acutorostrata) aroundthe Isle of Mull, Scotland. Report to the Hebridean Whale and Dolphin Trust. 88 pp.
Glass, A.H., Cole, T.V.N., Garron, M., Merrick, R.L. and Pace III, R.M. 2008. Mortality and serious injury determinations forbaleen whale stocks along the United States eastern seaboard and adjacent Canadian Maritimes, 2002–2006. U.S. Dept.
Commerce., Northeast Fish. Sci. Cent. Ref. Doc. 08–04. 18 pp.
Gregory, M.R. 2009. Environmental implications of plastic debris in marine settings-entanglement, ingestion, smothering,hangers-on, hitch-hiking and alien invasions. Philos. Trans. R. Soc. B 364: 2013–2025. doi: 10.1098/rstb.2008.0265.
Ichii, T. and Kato, H. 1991. Food and daily food consumption of southern minke whales in the Antarctic. Polar Biol. 11:
479–487. doi: 10.1007/BF00233083.
International Whaling Commission. 2020. Report of the IWC Workshop on Marine Debris: The Way Forward, 3–5 December 2019, La Garriga, Catalonia, Spain. Paper SC/68B/REP/03 presented to the IWC Scientiﬁc Committee, May 2020
(unpublished). 38 pp. [Paper available from the Oﬃce of the IWC].
Kasamatsu, F., Nishiwaki, S. and Ishikawa, H. 1995. Breeding areas and southbound migrations of southern minke whales
Balaenoptera acutorostrata. Mar. Ecol. Prog. Ser. 119: 1–10.
Kato, H. 1982. Some biological parameters for the Antarctic minke whale. Rep. int. Whal. Commn. 32: 935–945.
Laist, D.W. 1997. Impacts of marine debris: entanglement of marine life in marine debris including a comprehensive list of
species with entanglement and ingestion records. pp. 99–139. In: Coe J. M. and Rogers D. B. (eds.) Marine Debris,
Sources, Impacts, and Solutions. New York. Springer-Verlag. 432 pp. doi: 10.1007/978-1-4613-8486-1_10.
Naessig, P.J. and Lanyon, J.M. 2004. Levels and probable origin of predatory scarring on humpback whales (Megaptera novaeangliae) in east Australian waters. Wildl. Res. 31: 163–170. doi: 10.1071/WR03086.
Nemoto, T. 1970. Feeding pattern of baleen whales in the ocean. pp. 241–252. In: Steele, J.H. (ed.) Marine Food Chains.
University of California Press, Berkeley. 552 pp.
Nishiwaki, S., Ishikawa, H. and Fujise, Y. 2006. Review of general methodology and survey procedure under the JARPA. Paper SC/D06/J2 presented to the IWC JARPA review meeting, December 2006, (unpublished). 47 pp. [Paper available
from the Oﬃce of the IWC].
Nishiwaki, S., Ishikawa, H., Goto, M., Matsuoka, K. and Tamura, T. 2014. Review of general methodology and survey procedure under the JARPAII. Paper SC/F14/J2 presented to the IWC JARPAII review meeting, February 2014, (unpublished). 34 pp. [Paper available from the Oﬃce of the IWC].
Panti, C., Baini, M., Lusher, A., Hernandez-Milan, G., Bravo Rebolledo, E.L., Unger, B., Syberg, K. and Simmonds, M. P.
2019. Marine litter: One of the major threats for marine mammals. Outcomes from the European Cetacean Society
workshop. Environ. Pollut. 247: 72–79. doi: 10.1016/j.envpol.2019.01.029.
Sadove, S.S. and Morreale, S.J. 1990. Marine mammal and sea turtle encounters with marine debris in the New York Bight
and the northeast Atlantic. pp. 562–570. In: Shomura, R. S. and Godfrey, M. L. (eds.) Proceedings of the Second International Conference on Marine Debris, 2–7 April 1989, Honolulu, Hawaii. NOAA Tech. Memo. NMFS-SWFSC-154.
SC-CAMLR. 2004. Report of the Working Group on Fish Stock Assessment. pp. 340–657. In: Report of the Twenty-Third
Meeting of the Scientiﬁc Committee (SC-CAMLR-XXIII), Annex 5. CCAMLR, Hobart, Australia.
SC-CAMLR. 2012. Report of the Working Group on Fish Stock Assessment. pp. 265–377. In: Report of the Thirty-First
Meeting of the Scientiﬁc Committee (SC-CAMLR-XXXI), Annex 7. CCAMLR, Hobart, Australia.
Simmonds, M.P. 2012. Cetaceans and Marine Debris: The Great Unknown. J. Mar. Biol. Vol. 2012 Article ID 684279, 8 pp.
doi: 10.1155/2012/684279.

Cetacean Popul. Stud. (CPOPS), Short noteVol. 3, 2021, 286–294

293

ISODA, TAMURA AND PASTENE
Tamura, T. and Konishi, K. 2009. Feeding habits and prey consumption of Antarctic minke whale (Balaenoptera bonaerensis) in the Southern Ocean. J. Northwest Atl. Fish. Sci. 42: 13–25. doi: 10.2960/J.v42.m652.

Received: December 25, 2020
Accepted: June 10, 2021
Published online: December 8, 2021

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