J-STAGE Advance published date: December 8, 2021

ISODA, MATSUOKA, TAMURA AND PASTENESPATIAL AND TEMPORAL DISTRIBUTION OF
FLOATING MARINE MACRO DEBRIS IN
THE INDO-PACIFIC REGION OF THE ANTARCTIC
Tatsuya ISODA1*, Koji MATSUOKA1, Tsutomu TAMURA1 andLuis 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
Marine debris can aﬀect marine species including whales through ingestion and entanglements.
Surveys of marine debris in the Antarctic waters are very limited. This study investigated theﬂoating marine macro debris occurring in the Indo-Paciﬁc sector of the Antarctic (35°E–145°W),
south of 60°S, based on Japanese sighting surveys conducted between the austral summer seasons
1991/92 and 2018/19. In order to examine the spatial diﬀerences in distribution and density, themarine macro debris data were divided into IWC management Areas IIIE, IV, V and VIW as wellas into CCAMLR Convention Areas. Furthermore, to investigate temporal diﬀerences, the data
were divided into two periods: 1991/92–2004/05 and 2005/06–2018/19. A total of 175 objects
were found, consisting mainly of metal and polymer products. Buoys/ﬂoats constituted the mostfrequent sightings, representing 67% of all marine macro debris found. The density indices (number of marine macro debris observed by 100 n.miles) increased from the ﬁrst to the second period
in all Areas. The increase in the number of marine macro debris between the ﬁrst and second periods was statistically signiﬁcant in Areas IV and V. The larger number of marine macro debris in
the second period (represented predominantly by buoys/ﬂoats) coincides with an increase in ﬁshing activities in the surveyed area. However, the overall number of ﬂoating marine macro debris
in the Indo-Paciﬁc sector of the Antarctic is low and much lower than that reported for the North
Paciﬁc and North Atlantic, and this result is consistent with the low incidence of marine macrodebris found in the stomach of Antarctic minke whales reported for the same sector. Continued
monitoring of ﬂoating marine macro debris is recommended given the increasing trend in thenumber of ﬁsheries and tourist activities in the Antarctic.
Key words:

Antarctic, Japanese sighting survey, marine macro debris, ﬁshing buoy.

Introduction
Marine pollution is deﬁned as the introduction by man, directly or indirectly, of substance or energy into the marine environment (including estuaries) resulting in such deleterious eﬀects as harm toliving resources, hazards to human health, hindrance to marine activities including ﬁshing, impairment of quality for use of sea water and reduction of amenities (GESAMP, 1991). Marine debris, also
known as marine litter, is a kind of pollutant including, among many others, man-made objects suchas polymer bags, buoys, rope, lost ﬁshing lines and nets. Once in the sea, such debris becomes mobile
and their movement, distribution and accumulation pattern depend on oceanic currents and gyres.
A workshop of the International Whaling Commission Scientiﬁc Committee (IWC/SC) agreed that

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marine debris, and its contributions to entanglements, exposures including ingestions, and associatedimpacts, including toxicity, is both a welfare and a conservation issue for cetaceans on a global scale(IWC, 2014). Naturally, marine debris can aﬀect other pelagic species as well.
The problem of pollution by marine debris is more frequent and critical in populated areas. Evidence from remote oceanic islands suggests a southward-decreasing, strong latitudinal gradient inlitter densities from subtropical and temperate waters through the subtropical convergence to the Antarctic Polar Front and beyond. That is, there is a clear decreasing trend in marine debris accumulation
with latitude (Gregory and Ryan, 1997; Barnes, 2005). However, in recent years, marine debris has
been recorded in remote places such as sub-Antarctic and Antarctic regions (Barnes et al., 2010; Ivar
do Sul et al., 2011). The sources of this pollutant in the Antarctic could be global oceanic debris drifting across the Antarctic Polar Front or debris from tourism and ﬁsheries activities, which have been
increasing in sub-Antarctic and Antarctic areas (Lamers et al., 2008; CCAMLR, 2012).
As indicated above, ﬂoating marine debris could be a threat aﬀecting the welfare and conservationof large whales migrating to the Antarctic each austral summer for feeding. Such threats could bethrough entanglements, ingestions, and associated impacts, including toxicity (IWC, 2014; Baulch andPerry, 2014). For this reason, it is important to monitor the type, number and distribution of ﬂoating
marine debris in the Antarctic feeding grounds. Unfortunately, previous studies of this kind are very
scarce in the Antarctic. Suaria et al. (2020) investigated the abundance of ﬂoating plastics aroundthe Southern Ocean from a survey conducted during the Antarctic Circumnavigation Expedition in
2016/17, and the authors conﬁrmed the Southern Ocean as the region with the lowest concentrationof plastic globally. The IWC International Decade for Cetacean Research-Southern Ocean Whale andEcosystem Research (IDCR-SOWER) conducted observations on ﬂoating macro debris in 1987/88(Matsuoka et al., 2003) and up to 2009/10 when the survey was completed (Murase et al., 2020). Although a brief summary was presented in Murase et al. (2020), analyses of the data collected are yet tobe conducted. The authors found low occurrence of marine macro debris in the Antarctic.
The main objective of this study was the investigation of the spatial and temporal distribution of
ﬂoating marine macro debris in the Indo-Paciﬁc sector of the Antarctic. The study is based on observations conducted from systematic vessel-based sighting surveys of the former research programs
JARPA/JARPAII (Japanese Whale Research Program under Special Permit in the Antarctic, Phases I
and II) (Government of Japan, 1987, 1989, 2005) and NEWREP-A (New Scientiﬁc Whale Research
Program in the Antarctic Ocean) (Government of Japan, 2015), over a period of 28 years. Outputs
from this study could provide valuable information for the development of conservation policies ofwhales and the Antarctic ecosystem.

Materials and methods
Research area
The marine macro debris observations were conducted along the surveys of the JARPA, JARPAII
and NEWREP-A, which had as the main objective the systematic collection of sighting and biological
data of whales in IWC Antarctic management Areas III (0°–70°E), IV (70°–130°E), V (130°E–170°W)
and VI (170°–120°W). The marine macro debris data analyzed in this study were from the eastern partof Area III (IIIE) (35°–70°E), Area IV, Area V and the western part of Area VI (VIW) (170°–145°W),
from 60°S to the ice edge, from where data for a longer period were available (Figs. 1A and 1B). The
marine macro debris data were also summarized according to the Convention Areas of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Figs. 1A and 1B show
the geographical boundaries of the IWC and CCAMLR management areas used for the analyses inthis study. IWC Area IIIE overlaps partially with CCAMLR Divisions 58.4.2–4; Area IV with 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
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Fig. 1A. The sighting eﬀort (n.miles surveyed by Lat. 1°×Long. 1° square) of the JARPA survey in the
Indo-Paciﬁc sector of the Antarctic during the austral summer seasons 1995/96 to 2004/05 (ﬁrst period, a totalof 50,476 n.miles surveyed). The ﬁgure also shows the geographical boundaries of the IWC and CCAMLR
management areas used for the analyses in this study.

Fig. 1B. The sighting eﬀort (n.miles surveyed by Lat. 1°×Long. 1° square) of the JARPAII and NEWREP-A
surveys in the Indo-Paciﬁc sector of the Antarctic during the austral summer seasons 2005/06 to 2018/19 (second period, a total of 52,328 n.miles surveyed). The ﬁgure also shows the geographical boundaries of the IWC
and CCAMLR management areas used for the analyses in this study.

this regard, the data of marine macro debris collected in the Indo-Paciﬁc sector of the Antarctic can be
useful for these two international organizations. CCAMLR management areas involve the terminology‘Areas,’ ‘Divisions’ and ‘Sub-areas.’ For practical purposes, in this study these are referred simply as
CCAMLR ‘Areas.’
As the surveys were limited to waters south of 60°S, i.e., south of the Antarctic Polar Front, whichacts as a barrier of debris movement from lower latitude waters to the Antarctic (see above), the emphasis of this study was on longitudinal diﬀerences in the distribution of marine macro debris, given
the wide longitudinal span of the surveys in the Indo-Paciﬁc sector.
Research period
Marine macro debris surveys were conducted mainly during January–February, in the austral summer seasons between 1991/92 and 2018/19.
Survey procedure
Observation of marine macro debris was carried out from the platform of sighting vessels participating in JARPA, JARPAII and NEWREP-A. The main objective of the sighting vessels was the200

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collection of sighting data of whales for abundance estimation purposes. Although the protocol of thesurveys included the observation of ﬂoating marine macro debris along the track-lines, they could not
be considered as dedicated marine macro debris surveys. Details of the general sighting survey procedures can be found in Nishiwaki et al. (2006) and Nishiwaki et al. (2014). Basically, the sighting
vessels followed a pre-determined zig-zag track-line at a speed of 11.5 knots. The sighting surveys
involved two observers on the top platform (19 m high from the sea level) and ﬁve observers on theupper bridge platform (11 m high from the sea level). Sighting surveys, including the observationsof marine macro debris on the sea surface, were carried out from the platforms using a scaled binocular developed by the Institute of Cetacean Research and FUJINON (FUJINON 7×50 FMT-SX;
7×50 mm, ICR model). The vessel did not deviate from the track-line when an item of marine macrodebris was sighted.
Marine macro debris data were recorded separately for sighting surveys conducted ‘on eﬀort’ (primary observers were present at the relevant observation platforms) and ‘oﬀ eﬀort’ (marine macro debris recorded during drifting, transit and experiments). For each observation, the type of marine macrodebris, the sighting date and the geographical position were recorded. When feasible, pictures weretaken.
The surveys focused on marine macro debris objects of sizes approximately 300 mm or larger (estimated visually by experienced observers). It should be noted that the sighting probability of small objects decreases with distance from the vessels. As a consequence, some small objects occurring at long
distances could have been missed. However, the survey procedures were exactly the same for each annual survey in the 28-year period, so the comparison of density indices (see below) between temporal
strata is still a valid approach in relative terms.
Data analysis
To examine geographical diﬀerences in distribution, marine macro debris data were grouped by
IWC management Area and CCAMLR Convention Areas. To investigate temporal trends in the Areas, marine macro debris data were grouped into two periods: 1991/92–2004/05 (ﬁrst period) and2005/06–2018/19 (second period). This temporal division was made so that the sighting eﬀort (searching nautical miles) was evenly distributed between the two periods. In making this temporal division
it was also considered that ﬁshery and tourist activities in the Antarctic had increased from the 2000’s(see Fig. 1 in Lamers et al., 2008 and Figs. 6 and 7 in CCAMLR, 2012), and therefore an increase in
the number of marine macro debris was expected for the second period.
No sighting survey was conducted in the seasons 2010/11, 2011/12 and 2013/14. Observations ofmarine macro debris between the seasons 1991/92 and 1994/95 were made under both ‘on eﬀort’ and‘oﬀ eﬀort,’ however, the type of eﬀort was not recorded. Therefore data in this period were not used
when the density indices (see below) were calculated.
The density index (the number of marine macro debris observed per 100 n.miles) was calculated foreach management Area in each of the two periods, based on the marine macro debris data collectedunder ‘on eﬀort’ mode. The number of marine macro debris per unit area is an alternative method toassess its geographical and temporal distribution. Given the number and complexity of each IWC andCCAMLR area examined, the density index was selected for practical purposes.
A chi-square test was used to assess the diﬀerences in the number of marine macro debris between
periods based on the expected frequency of 50 : 50.

Results
Sighting eﬀort
Figs. 1A and 1B show the sighting eﬀort expressed in nautical miles, surveyed in the ﬁrst andCetacean Popul. Stud. (CPOPS), Full paper
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second periods, respectively. The searching eﬀort was similar in both periods, 50,476 n.miles and52,328 n.miles in the ﬁrst and second periods, respectively.
Floating marine macro debris
Tables 1A–1C show the number of marine macro debris in the whole (A), ﬁrst (B) and second (C)periods, respectively, grouped by the IWC Areas. A total of 175 observations of marine macro debris
were recorded between 1991/92 and 2018/19 (15 metallic objects, 159 polymer products and one
object of unknown material). Buoys/ﬂoats made of polymer (Fig. 2) accounted for 67% of all marine
macro debris. Most buoys/ﬂoats observed were single objects. The total numbers of marine macro
Table 1A. Summary of ﬂoating marine macro debris recorded during systematic sighting surveys in the
Indo-Paciﬁc sector of the Antarctic by JARPA, JARPAII and NEWREP-A between the austral summer
seasons 1991/92 and 2018/19, by IWC Area and eﬀort (on and oﬀ).

*Observed on the surface as single objects, however, at least in eight cases, several objects were observed; those cases were counted as a single observation. Material ofbuoys/ﬂoats was considered to be polymer, in addition to Styrofoam and rubber.
**Two ropes, two tanks, one ball, one sheet, and two unknown products.
***A squared box of unknown material.

Table 1B. Summary of ﬂoating marine macro debris recorded during systematic sighting surveys in the
Indo-Paciﬁc sector of the Antarctic by JARPA, between the austral summer seasons 1991/92 and 2004/05(ﬁrst period), by IWC Area and eﬀort (on and oﬀ).

Table 1C. Summary of ﬂoating marine macro debris recorded during systematic sighting surveys in the
Indo-Paciﬁc sector of the Antarctic by JARPAII and NEWREP-A, between the austral summer seasons
2005/06 and 2018/19 (second period), by IWC Area and eﬀort (on and oﬀ).

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Fig. 2. Example of a single ﬂoating marine macro debris observed at two distances from the vessel at position
67°S, 179°W (IWC Area V; CCAMLR Sub-area 88.1) during the 2013/14 austral summer season. Picture by
one of the authors (KM).
Table 2A. Summary of ﬂoating marine macro debris recorded during systematic sighting surveys in the
Indo-Paciﬁc sector of the Antarctic by JARPA, JARPAII and NEWREP-A between the austral summer
seasons 1991/92 and 2018/19, by CCAMLR Area and eﬀort (on and oﬀ).

Table 2B. Summary of ﬂoating marine macro debris recorded during systematic sighting surveys in the
Indo-Paciﬁc sector of the Antarctic by JARPA, between the austral summer seasons 1991/92 and 2004/05(ﬁrst period), by CCAMLR Area and eﬀort (on and oﬀ).

Table 2C. Summary of ﬂoating marine macro debris recorded during systematic sighting surveys in the
Indo-Paciﬁc sector of the Antarctic by JARPAII and NEWREP-A, between the austral summer seasons
2005/06 and 2018/19 (second period), by CCAMLR Area and eﬀort (on and oﬀ).

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debris were 48 and 127 in the ﬁrst and second periods, respectively. The buoys/ﬂoats were the main
marine macro debris in both periods but its percentage was higher in the second period (52% and 73%
in the ﬁrst and second period, respectively).
A similar pattern was observed when the data were grouped by CCAMLR Areas (Tables 2A–2C).
Geographical distribution of marine macro debris
Figs. 3A and 3B show the geographical distribution of marine macro debris in the ﬁrst and second
periods, respectively, in both IWC and CCAMLR Areas. In the ﬁrst period, the marine macro debris(mainly buoys/ﬂoats) were concentrated near the borders between IWC Areas but they were more
widely distributed through the CCAMLR Areas. In the second period, the distribution of marine macro debris (mainly buoys/ﬂoats) was notably wider in both IWC and CCAMLR Areas, and they wereconcentrated mainly in Areas IV (CCAMLR Areas 58.4.1–3) and V (CCAMLR Areas 58.4.1 and88.1), reﬂecting perhaps the larger searching eﬀort spent in those Areas.
The most southerly marine macro debris sighting was a buoy in the Ross Sea, at position 76°S,
171°W (IWC Area V, CCAMLR Area 88.1).
Density index
Tables 3A–3C show the density indices in the whole (A), ﬁrst (B) and second (C) periods, respec-

Fig. 3A. Distribution of marine macro debris sighted by JARPA survey in the Indo-Paciﬁc sector of the Antarctic during the austral summer seasons 1991/92 to 2004/05 (ﬁrst period) (on and oﬀ eﬀort), by IWC andCCAMLR management areas.

Fig. 3B. Distribution of marine macro debris sighted by JARPAII and NEWREP-A surveys in the Indo-Paciﬁc
sector of the Antarctic during the austral summer seasons 2005/06 to 2018/19 (second period) (on and oﬀ
eﬀort), by IWC and CCAMLR management areas.

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tively, grouped by the IWC Areas. The index for all Areas and period was 0.12. The largest index wasin Area V and the smallest in Area IIIE. The density indices increased between the ﬁrst and second
period in all Areas. A chi-square test resulted in signiﬁcant temporal diﬀerences in the number of marine macro debris in Areas IV (chi-square=7.36, df=1, p=0.007) and V (chi-square=20.25, df=1,
p＜0.001). However no signiﬁcant diﬀerences were found between periods when the density indiceswere used. It is likely that the values of density are too low to detect any diﬀerence. No signiﬁcantdiﬀerences were found in the number of marine macro debris between the ﬁrst and second periods inAreas IIIE (chi-square=0.50, df=1, p=0.480) and VIW (chi-square=0.33, df=1, p=0.564).
Tables 4A–4C show the density indices in the whole (A), ﬁrst (B) and second (C) periods, respectively, grouped by the CCAMLR Areas. The pattern found is very similar to the analysis of IWC
Areas. The largest index was in Area 58.4.1 and the smallest in Area 58.4.2–4. The density indicesincreased between the ﬁrst and second periods in all Areas. A chi-square test resulted in signiﬁcanttemporal diﬀerences in the number of marine macro debris in Area 58.4.1 (chi-square=19.93, df=1,
p＜0.001) and 88.1 (chi-square=9.26, df=1, P=0.002). However no signiﬁcant diﬀerences were
found between the two periods when the density indices were used. No signiﬁcant diﬀerences in the
Table 3A. The searching distance (n.miles), number of marine macro debris and density indices (numberof marine macro debris observed per 100 n.miles) during JARPA, JARPAII and NEWREP-A surveys in the
Indo-Paciﬁc sector of the Antarctic during the austral summer seasons 1995/96 to 2018/19, by IWC Area (datafor the period 1991/92–1994/95 were not used for the reasons explained in the ‘Data analysis’ section).

Table 3B. The searching distance (n.miles), number of marine macro debris and density indices (number ofmarine macro debris observed per 100 n.miles) during JARPA survey in the Indo-Paciﬁc sector of the Antarctic during the austral summer seasons 1995/96 to 2004/05 (ﬁrst period), by IWC Area (data for the period
1991/92–1994/95 were not used for the reasons explained in the ‘Data analysis’ section).

Table 3C. The searching distance (n.miles), number of marine macro debris and density indices (number ofmarine macro debris observed per 100 n.miles) during JARPAII and NEWREP-A surveys in the Indo-Paciﬁc
sector of the Antarctic during the austral summer seasons 2005/06 to 2018/19 (second period), by IWC Area.

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Table 4A. The searching distance (n.miles), number of marine macro debris and density indices (numberof marine macro debris observed per 100 n.miles) during JARPA, JARPAII and NEWREP-A surveys in the
Indo-Paciﬁc sector of the Antarctic during the austral summer seasons 1995/96 to 2018/19, by CCAMLR Area
(data for the period 1991/92–1994/95 were not used for the reasons explained in the ‘Data analysis’ section).

Table 4B. The searching distance (n.miles), number of marine macro debris and density indices (number ofmarine macro debris observed per 100 n.miles) during JARPA survey in the Indo-Paciﬁc sector of the Antarctic during the austral summer seasons 1995/96 to 2004/05 (ﬁrst period), by CCAMLR Area (data for the period 1991/92–1994/95 were not used for the reasons explained in the ‘Data analysis’ section).

Table 4C. The searching distance (n.miles), number of marine macro debris and density indices (number of marine macro debris observed per 100 n.miles) during JARPAII and NEWREP-A surveys in the Indo-Paciﬁc sectorof the Antarctic during the austral summer seasons 2005/06 to 2018/19 (second period), by CCAMLR Area.

number of marine macro debris were found between the ﬁrst and second periods in Areas 58.4.2–4(chi-square=0.47, df=1, p=0.491) and 88.2 (chi-square=0.33, df=1, p=0.564).

Discussion
The present study summarized the spatial and temporal distribution of marine macro debris in
the Indo-Paciﬁc sector of the Antarctic based on data collected systematically over a period of 28
years. The data were organized based on the management areas of two international organizations incharge of the conservation and management of Antarctic marine living resources, the IWC and the
CCAMLR. Although similar surveys have been conducted previously in the Antarctic (e.g., Matsuoka
et al., 2003; Suaria et al., 2020), the present study is the ﬁrst to report marine macro debris information which were collected along systematic sighting surveys in the same region (Indo-Paciﬁc sector of
the Antarctic) over a long period of time (28 years).

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Marine debris has been increasing worldwide and one of the main concerns is the negative eﬀect of
this kind of pollutant on marine species through ingestion and entanglements (see reviews by Panti etal., 2019; IWC, 2020). Emphasizing the importance of this subject, two international workshops were
held recently to discuss the interaction between marine mammal and marine debris, and to deﬁne future research plans (Panti et al., 2019; IWC, 2020).
The main results of the present study can be summarized as follows: i) the occurrence of ﬂoating
marine macro debris in the Indo-Paciﬁc sector of the Antarctic is low, and much lower in comparison
with the occurrence in other oceans of the world; ii) buoys/ﬂoats made of polymer were the main marine macro debris found in this sector of the Antarctic, comprising 67% of all marine macro debris observed; iii) the largest density indices were found in IWC Areas IV and V (and CCAMLR Areas 58.4.1
and 88.1); and iv) there is an increasing temporal trend of marine macro debris (particularly buoys/
ﬂoats) in all Areas, which was statistically signiﬁcant in IWC Areas IV and V (and CCAMLR Areas
58.4.1 and 88.1).
Regarding i) above, the results of low occurrence of marine macro debris in the Antarctic are consistent with the results of Suaria et al., (2020) and the preliminary results of IWC/IDCR-SOWER(Murase et al., 2020). Matsumura and Nasu (1997) reported ﬂoating marine macro debris in the North
Paciﬁc Ocean and its adjacent waters for the period 1987–1991. Their surveys covered approximately 926,000 n.miles and recorded 136,338 pieces of marine macro debris (including natural objects).
About 60% of marine macro debris were polymer products (e.g., ﬁshing gear, Styrofoam products,
and other polymer products). Total densities expressed in number of objects observed per 1 n.mile2
were 20–40 in coastal waters, 0.2 in the north equatorial current area (5°–15°N, across the central Paciﬁc), and 1–3 in the subarctic boundary area (35°–45°N). Barnes and Milner (2005) reported the results of ﬂoating marine macro debris across the entire latitudinal range from the Antarctic to the North
Atlantic. Densities of marine macro debris ranged from 0 to 5 items/km2 in sub-Antarctic and Antarctic waters. Marine macro debris density values have a peak of 10 to 100+ items/km2 in the North Atlantic (English Channel). Clearly, the number of marine macro debris in the Indo-Paciﬁc sector of the
Antarctic is much lower than those observed in the North Paciﬁc and North Atlantic oceans, although
it should be noted that the density index used in the present study is not directly comparable with thedensities reported in other studies.
Points ii), iii) and iv) above are related with the occurrence of buoys/ﬂoats, the main marine macrodebris observed in the Indo-Paciﬁc sector of the Antarctic. Buoys/ﬂoats accounted for about 67% of
all sighted ﬂoating marine macro debris and its density indices increased between the ﬁrst and second
periods. It should be noted that Barnes et al. (2010) recorded three pieces of marine macro debris (apolymer cup and two ﬁshing buoys) in the Dumont d’Urville and Davis Seas (i.e. Areas IV and V)
during a survey conducted in the 2007/08 austral summer season. Figs. 4A and 4B show the annual
trend of the density indices for buoys/ﬂoats in each of the management Areas of IWC and CCAMLR,
respectively. An increasing trend is observed, particularly in IWC Area IV and V (Fig. 4A); and in
CCAMLR Areas 58.4.1 and 88.1 (Fig. 4B), after the 2005/06 austral summer season. It is important toinvestigate the source of the buoys/ﬂoats observed and the reasons for the increasing trend in density
after this season.
Oceanic fronts, such as the subtropical Convergence and Antarctic Polar Front, act as barriers forthe movement of marine debris from low latitude waters to polar areas (Gregory and Ryan, 1997).
Although these barriers are considered permeable by some authors (e.g. Gregory, 2009), the hypothesis that all buoys/ﬂoats observed in the Indo-Paciﬁc sector of the Antarctic were transported fromlower latitudes has a low plausibility. Since the season 2004/05, licensed longline vessels have conducted exploratory ﬁshery for Antarctic toothﬁsh (Dissostichus mawsoni) in CCAMLR Area 58.4.1,
which overlaps partially with IWC management Areas IV and V. The number of licensed vessels in
Area 58.4.1 was four to seven in 2004/05 to 2007/08 seasons, however it decreased to one to three in
2008/09 to 2014/15 seasons (SC-CAMLR, 2012a; CCAMLR, 2013, 2014, 2015). In Area 88.1, which
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Fig. 4A. The trend of the density indices of sighted buoys/ﬂoats by austral summer season and IWC Area,
between 1995/96 and 2018/19 (data for the period 1991/92–1994/95 were not used for the reasons explainedin the ‘Data analysis’ section).

Fig. 4B. The trend of the density indices of sighted buoys/ﬂoats by austral summer season and CCAMLR
Area, between 1995/96 and 2018/19 (data for the period 1991/92–1994/95 were not used for the reasons
explained in the ‘Data analysis’ section).

overlaps partially with IWC management Areas V, one to three licensed longline vessels ﬁshed in the
exploratory ﬁshery for Dissostichus spp. from 1996/97 to 2001/02 (except 10 vessels in 2000/01).
This number increased to more than 10 in 2002/03 to 2011/12 (SC-CAMLR, 2012b), 16 in 2016/17
and 25 in 2017/18 (CCAMLR, 2017, 2018). The number of sighted buoys/ﬂoats increased signiﬁcantly in Areas IV and V after the 2005/06 season, peaked in the 2007/08 season, and then decreased.
However, the decrease in Area V was less prominent than in Area IV (Fig. 4A). The pattern exhibitedin Figs. 4A and 4B mimics the ﬂuctuations of longline ﬁshing operations in these Areas. In addition
to this, operations by IUU (illegal, unreported and unregulated) vessels have been reported in theseareas (SC-CAMLR, 2012a, 2012b). Therefore, it is likely that the buoys/ﬂoats debris observed in the

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present study come from ﬁshing vessels operating in Areas 58.4.1 and 88.1. Although not statisticallysigniﬁcant, the density index increased between the ﬁrst and second period in Area 88.2, where ﬁshingactivities were also reported (see Fig. 1 in Brooks et al., 2020). It should be noted that a loss of ﬁshinggears from bottom longline ﬁsheries targeting Antarctic toothﬁsh operating in Areas 88.1 and 88.2 wasreported in Webber and Parker (2012).
Fishing operations are a source of marine macro debris in the Antarctic, contributing not only to
direct ﬁshing-related debris but also miscellaneous debris items (Ivar do Sul et al., 2011). Webberand Parker (2012) recommended that ﬁshing vessels and/or the CCAMLR observers should record
detailed information on gear loss, in order to estimate unaccounted ﬁshing mortality and to reduce theloss of ﬁshing gear. Such information is also essential to understanding the interaction among whales,ﬁsheries and marine debris.
Despite the increasing trend observed in some areas, the overall number of ﬂoating marine macrodebris in the Indo-Paciﬁc sector of the Antarctic is very low, and this result is consistent with the low
incidence of marine macro debris and entanglements found in the stomach of Antarctic minke whalesin the same sector of the Antarctic (see Isoda et al., this issue).

Conclusions
This study provided the results of the ﬁrst systematic and comprehensive surveys of ﬂoating marine
macro debris in the Indo-Paciﬁc sector of the Antarctic conducted for a period of 28 years. The occurrence of ﬂoating marine macro debris (metal and polymer products mainly) was generally low. The
level of occurrence was substantially lower in comparison with the information reported for other oceanic basins, and this result is consistent with the low incidence of marine macro debris and entanglements found in the stomach of Antarctic minke whales in the same sector of the Antarctic. The main
ﬂoating marine macro debris was ﬁshing buoys/ﬂoats, which increased during the second half of thesurvey period. The probable source of the buoys/ﬂoats are ﬁshing vessels operating in the Antarctic.
Long-term surveys (e.g., JARPA, JARPAII and NEWREP-A) proved to be very useful for collecting
information of marine debris in the Antarctic. This monitoring of marine macro debris is continuing inthe same region under the Japanese Abundance and Stock-structure Surveys in the Antarctic (JASS-A)
program (Government of Japan, 2019) since the 2019/20 season. It is recommended that periodical
analyses of marine macro debris are conducted and reported in the future.
Acknowledgements

We would like to thank all of the captains, crew members, cruise leaders and researchers onboard the research vessels of
JARPA, JARPAII and NEWREP-A surveys for their contributions in collecting the data used in this study. We also thank theanonymous reviewers for useful comments that improved the manuscript notably.

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Received: December 12, 2020
Accepted: September 29, 2021
Published online: December 8, 2021

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