Technical Reports of the Ins�tute of Cetacean Research (2023)

pp. 1–7

Technical Report (not peer reviewed)

What do we know about whales and the ecosystem in the western
North Paciﬁc Ocean? Part 4: Summary of results on chemical pollu�on
Genta Yasunaga* and Yoshihiro Fujise
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan*Contact e-mail: yasunaga@cetacean.jp

ABSTRACT

Three baleen whale species, common minke, sei and Brydeʼs whales were surveyed during the former Japanese whale research under special scien�ﬁc permit programs in the western North Paciﬁc Ocean. They wereconducted from 1994 to 2019. The Ins�tute of Cetacean Research collected and analyzed samples in order toinves�gate the concentra�on of chemical pollutants and the eﬀect of those pollutants on the health of thewhales. This paper summarizes the results found for mercury (Hg), Persistent Organic Pollutants (POPs) andradioisotope concentra�ons in the whales collected during the research programs. Whales are suited as biological indicators of environmental condi�ons because they are long-living animals with the ability to migrate
long-distances. In par�cular, the former JARPNII research program inves�gated pollutant concentra�ons of
the sampled baleen and toothed whales in rela�on to their sex and maturity. In addi�on, JARPNII inves�gatedpollu�on concentra�ons in prey species collected from the stomach contents of whales as well as those insamples of seawater and air obtained from the research area at the �me of survey. The results from direct
examina�ons of diﬀerent types of bio�c and abio�c sources revealed very important informa�on in furthering
our understanding of the bioaccumula�on process through the marine food chain.

INTRODUCTION
Pollutants such as Persistent Organic Pollutants (POPs)and mercury (Hg) are generally released from land andtransported to coastal and pelagic waters in run-oﬀs as
well as by atmospheric dissemina�on and other ways.
Higher trophic animals such as cetaceans generally accumulate POPs through the marine food web (Sanpera
et al., 1993; Borrell and Reijnders, 1999). The monitoringof pollutants concentra�ons in the marine environment
through the examina�on of biological �ssues of marine
mammals is important, since marine mammals can serveas biological indicators of environmental condi�ons.
Large cetaceans may be par�cularly useful as they are
long-living animals migra�ng long distances.
In 1995, the Interna�onal Whaling Commission (IWC)
decided to ʻgive priority to research on the eﬀects ofenvironmental changes on cetaceans …ʼ (IWC Resolu�on
1995/10), and its Scien�ﬁc Commi�ee (SC) decided totreat the adverse eﬀects of pollutants in cetaceans as oneof its highest priority issues.
Japanʼs whale research programs under special permit in the western North Paciﬁc were conducted forapproximately 25 years, from 1994 and 2019. The main

target species of the programs were the common minke(Balaenoptera acutorostrata), Brydeʼs (B. edeni) and sei(B. borealis) whales. During the surveys, the Ins�tute of
Cetacean Research (ICR) collected and analyzed samples
in order to inves�gate the concentra�on of chemical pollutants and the eﬀect of those pollutants on the health of
the whales.
At this point, it was considered important to summarize the knowledge on whales and their environment
accumulated so far by Japanʼs whale research in thewestern North Paciﬁc. The objec�ve of this paper is tosummarize the most relevant outputs of pollutant studies
based on samples and data collected during the former
whale research programs under special permit in thewestern North Paciﬁc.

SUMMARY OF POLLUTANT MONITORING IN
THREE BALEEN WHALE SPECIESThe ICR uses a cold-vapor atomic absorp�on spectrometry, ELISA, UPLC-MS/MS and UPLC-FDA for measurementsof pollu�on and biomarker concentra�ons in whales(Figure 1).
Table 1 shows the measurement systems and the standard procedures used at the ICR in recent chemical pol1

Technical Reports of the Ins�tute of Cetacean Research (2023)

lutant studies of North Paciﬁc baleen whales. Results on
chemical pollutants in whales presented in this paper are
based on those systems and procedures.
Laboratory and analy�cal procedures to determine
pollutant concentra�ons in baleen whales have been
described in previous documents (Yasunaga et al., 2016;
Yasunaga and Fujise, 2016a; b). Details of the procedures
are not repeated here for the sake of brevity. The main results are presented in this sec�on for three baleen whale
species, by type of chemical pollutant.
Mercury (Hg)
It is known that Hg is mainly released on land as elemental Hg from natural sources such as volcanic ac�vi�es
and anthropogenic sources, e.g. thermal power plants.
Once released, elemental Hg is transported to the pelagic
ocean and pelagic surface water (Fitzgerald et al., 1998).
In the pelagic ocean, elemental Hg is converted into

methyl Hg and bioconcentrated at moderate levels inanimals of high trophic level, such as cetaceans, throughthe food chain (Knauer and Mar�n, 1972). Therefore, inpredic�ng changes in Hg concentra�ons in baleen whales
and their environment, factors such as food habitat ofwhales and biological informa�on such as sex, age andpregnancy, are important.
Yasunaga et al. (2016) examined temporal changes
in Hg concentra�ons (including all chemical forms ofHg such as methyl Hg and inorganic Hg, i.e. total Hg) of
baleen whales using muscle samples of mature malesof common minke whales for the period 1994–2014, sei
whales for the period 2002–2014 and Brydeʼs whales forthe period 2002–2014 from the western North Paciﬁc.
The research areas surveyed are shown in Figure 2. The

Figure 2.
Figure 1.

UPLC-MS/MS and FDA system at the environmental
chemistry laboratory of the Ins�tute of Cetacean
Research.

Sub-areas surveyed by the former Japanese whale
research program under special permit. Sub-areas
are based on IWC (1994), and they have been usedby the IWC for the management of common minke
whales.

Table 1
Measurement systems and the standard procedures used at the Ins�tute of Cetacean Research in the recent chemical pollutant
studies of North Paciﬁc baleen whales.
Substances

Total Hg

Direct Thermal
Measurement
Decomposi�on-Goldsystems
Amalgama�on-CVAAS

Standard
procedures

2

Provisional regula�onlevels of Hg in ﬁsheries
by Ministry of Health andWelfare Japan (1972)

Total PCB

Legacy POPs fordetermina�on of each isomerRadioisotopes(the I131, Cs134 and Cs137)

Analy�cal methodof PCBs using
GC-ECD with apacked colomun

A sample decomposedwith alkaline solu�on andextracted with hexane aremeasured by GC/MS-SIM

Containers were placed in
0.04-mm thick polyethylenebags and a germanium semiconductor detector

The public analy�cal
method of Japan by
Ministry of Welfare
Japan (1973)

Analy�cal Manual for endocrine disrupter chemicals
by Japan Environmental
Agency (1998)

The analy�cal manual forradioac�ve materials in foods inemergency by Ministry of Health,Labour and Welfare (2002)

What do we know about whales and the ecosystem in the western North Pacific? Part 4

reason for using only mature males was to exclude theeﬀects of pregnancy in case of females and growth, andto be less suscep�ble to age-related Hg accumula�on(Braune et al., 2015).
Concentrations of Hg through the trophic chain
To understand the bioaccumula�on process, it is necessary to examine Hg concentra�ons not only in whales but
also in their prey species. Figure 3 shows the rela�onships
between Hg concentra�ons in common minke, sei and
Brydeʼs whales in the western North Paciﬁc, and those in
their main prey species (two zooplanktons and six pelagicﬁsh species) during the period 1995–2007. The Hg concentra�ons were in the order of:Common minke whales (0.22±0.07 ppm wetwt.)>sei whales (0.052±0.009)≒Brydeʼs whales(0.046±0.008).
The Hg concentra�ons in krill and copepods ranged
from <0.001–0.013 and 0.003–0.010 ppm dry wt.,
respec�vely. Mercury concentra�ons in the pelagicﬁshes were in the order of:
Paciﬁc pomfret (0.232±0.027)>walleye pollock(0.045)=Paciﬁc saury (0.039±0.016)=Japanese anchovy (adult) (0.037±0.025)>Japanese anchovy(larval ﬁsh) (0.005±0.003).
It is known that common minke whales selec�vely feed
on rela�vely higher trophic organisms, mainly pelagic ﬁshsuch as Paciﬁc saury and Japanese anchovy (Tamura andFujise, 2002). This is diﬀerent from sei and Brydeʼs whales
which feed mainly on krill and copepod (Tamura andFujise, 2002; Tamura et al., 2009). Diﬀerences in feeding
habitat among whale species and trophic levels of prey
would be one of the reasons for higher Hg concentra�ons
in common minke whales than in sei and Brydeʼs whales.
The Hg concentra�ons in common minke whales from

Figure 3.

oﬀshore, however, would be aﬀected by changes in thefood habitat during the research period.
Temporal trend in Hg concentrations
To examine yearly changes of Hg in common minke, sei
and Brydeʼs whales in the western North Paciﬁc, mul�ple
linear regression analyses were carried out including adjustment for confounders, i.e. sampling years, sampling
longitude, sampling la�tude, sampling date, body length,
blubber thickness and main prey item.
Results indicated that Hg concentra�ons observed in
the muscle of common minke whales oﬀ Kushiro andSanriku (part of sub-area 7) and sub-area 8, and Brydeʼswhales in sub-areas 8 and 9 were rela�vely stable in thewestern North Paciﬁc during the research periods.
On the other hand, the associa�on of Hg concentra�ons with sampling year was sta�s�cally signiﬁcant incommon minke whales from sub-areas 7 and 9, and sei
whales from sub-area 9. A slight ﬂexion point of yearly
trends of Hg was observed in 2008 for common minke
whales from sub-area 9, and in 2012 for sei whales fromsub-area 9 (Figure 4). The results of mul�ple linear regression analyses showed that the main prey items (subarea 7= walleye pollock, sub-aera 9= Paciﬁc pomfret and
Paciﬁc saury) were associated with Hg concentra�ons
in common minke whales. This associa�on was not observed in the case of sei whales. Hg concentra�ons in sei
whales, having sardine and saury in their stomachs, wereslightly lower than those in common minke whales fromsub-area 9. Therefore, Hg concentra�ons of sei whales
from sub-area 9 may be less aﬀected by Hg in the fooditems (Figure 4).
Thus, the yearly trend of Hg in sea surface water andthe baleen whales from the North Paciﬁc remain stable
for the research period. This is also supported by the

Rela�onships between Hg concentra�ons in muscle �ssues of common minke, sei and Brydeʼs whales in
the western North Paciﬁc, and those in their prey species.
3Technical Reports of the Ins�tute of Cetacean Research (2023)

Figure 4.

Simple plots (le� sides) and smoothing plots using the GAM (right sides) of Hg concentra�ons in muscle �ssues of common minke whales in sub-areas 7 (a: 1996–2012) and 9 (b: 1994–2013), sei whales in sub-area
9 (c: 2002–2014) and Brydeʼs whales in sub-areas 8 and 9 during research years.

results of monitoring studies on Hg concentra�ons from1980s in the nearby waters (Laurier et al., 2004; Sunderland et al., 2009).
POPs
POPs are organic compounds that are resistant to environmental degrada�on that occur through chemical andbiological processes. Therefore, they have the poten�al
to be transported over long distances. The manufacturing, use and import/export of the speciﬁed compounds
4

have been strictly restricted since the adop�on of theStockholm Conven�on on POPs by the United Na�ons Environment Programme in 2001 (Hagen and Walls, 2005).
Among them, polychlorinated biphenyls (PCBs), dichlorodiphenyl-trichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB) and chlordanes(CHLs) are commonly called ʻlegacy POPsʼ (French
et al., 2006). These legacy POPs had been produced andused in large quan��es worldwide in the middle of lastcentury. However, they remain a major environmental

What do we know about whales and the ecosystem in the western North Pacific? Part 4

Figure 5.

Composi�ons of a) DDTs and b) HCHs in the blubber of common minke, sei, Brydeʼs whales from the western North Paciﬁc and Antarc�c minke whales.

Figure 6.

Simple plots of PCB concentra�ons in blubber of common minke whales (mature males) in sub-areas 7(coastal) and 9 (oﬀshore).

challenge for human health and risk to wildlife due totheir toxicity and persistency.
Accumulation features
Yasunaga and Fujise (2020) examined accumula�on
features of PCB congeners and DDT, HCH, HCB and CHL
isomers in the blubber of common minke, sei and Brydeʼswhales from the western North Paciﬁc. DDT and HCH,
the main components contained in pes�cide products
released into the environment, were hardly present in
the samples. Concentra�on levels of ﬁve mature malesof common minke, sei and Brydeʼs whales taken by the
JARPNII in 2011 were compared with those in Antarc�cminke whales. Results showed that, among the legacy
POPs, concentra�on levels of PCBs were the highest in
the whales from the western North Paciﬁc, whereas in
Antarc�c minke whales from the Antarc�c Ocean, thelevels were lower than those of HCB and DDTs.
The average percentage of p,pʹ-DDT (which is primarily released into the environment) in the three whale
species from the western North Paciﬁc was lower thanthat of Antarc�c minke whales (Figure 5). The p,pʹ-DDT
has been used to control malaria (De Jager et al., 2006),
and is metabolized into p,pʹ-DDE in the animal body andthe environment over a long period of �me (Okonkwo
et al., 2008). The percentage of β-HCH accounted forover 90% of total HCHs in common minke, sei and Brydeʼswhales from the western North Paciﬁc, whereas thepercentage of γ-HCH was the dominant isomer of total
HCHs in Antarc�c minke whales (Figure 5). Technical HCH,
called Lindane, had been released into the environment.
Almost all of those consisted of γ-HCH from the 1950s
and 1970s (Walker et al., 1999). However, in Australia, it
was used a�er that period (Tanabe et al., 1982). These
results suggest that in the western North Paciﬁc, a great
deal of �me had passed from the release of DDTs andHCHs into the environment.
Yearly trend
Yasunaga and Fujise (2016a) examined yearly changes of
PCBs in the western North Paciﬁc. Mul�ple linear regression analysis was carried out, including adjustment for
confounders, i.e. sampling years, sampling longitude, la�tude, sampling date, body length, blubber thickness andmain prey species. Results indicated no signiﬁcant correla�ons between year and food items in all areas. It wassuggested that PCB concentra�ons in minke whales fromthe western North Paciﬁc were stable during 2002–2014.
Results for common minke whales in coastal and oﬀshore
waters are shown in Figure 6.

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Technical Reports of the Ins�tute of Cetacean Research (2023)

Figure 7.

Concentra�ons of Cs 134+137 in muscle of common minke, sei and Brydeʼs whales taken from the western
North Paciﬁc from 2011 to 2015.

Radio Isotope
On 11 March 2011, the Great East Japan Earthquake andthe tsunami that followed destroyed the nuclear power
plant in Fukushima. This accident led to the release oflarge amounts of radioac�ve materials into the environment.
To monitor the impact of this incident on large whalesin the western North Paciﬁc, Yasunaga and Fujise (2016b)
inves�gated the I131, Cs134 and Cs137 concentra�ons inmuscle samples of 53 common minke, 16 Brydeʼs, 32 sei
and 3 sperm whales sampled in the period 2011–2015.
Results are shown in Figure 7. Iodine131 was not detected in Brydeʼs, sei and sperm whales, with the excep�on of two common minke whales taken from Kushiro
in 2012. The ranges of Cs134 + Cs137 concentra�ons incommon minke, sei, Brydeʼs and sperm whales were ND(not detected)-31, ND-9.8, ND-7.1 and ND-0.59 Bq/kg
wet wt., respec�vely. The radioisotope concentra�ons
in all four whale species examined have been decreasing
since 2011.

CONCLUDING REMARKS
It is important to monitor the concentra�ons of diﬀerent chemical pollutants in whale �ssues and their environment, and the possible eﬀect of such pollutants on
whales. The ICR has contributed to this monitoring by analyzing samples and data collected over a long period in
the western North Paciﬁc, not only from whales but also
from their prey species and their environment. Biological
data available from the whales are important for the in6

terpreta�on of the concentra�ons of chemical pollutants
found. The results from the direct analyses of samples
from bio�c and abio�c sources revealed very important
informa�on in furthering our understanding of the bioaccumula�on process through the marine food chain.
The Minamata Conven�on on Mercury is a global
treaty which aims to protect human health and the environment from the adverse eﬀects of mercury. The monitoring of the marine environment using bioindicatorsfrom marine mammals is encouraged by the Conven�on
as one of the recommended ac�ons in the Hg reduc�onplans (UNEP, 2019). Thus, the ﬁndings from this study
are expected to contribute directly to such monitoring
programs.

ACKNOWLEDGEMENTS
We thank Luis A. Pastene (ICR) for his assistance in preparing this document and the Editorial Team of TEREP-ICR
for editorial work.

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