189

Predicted Changes on the Distribution Areas of Marine Organisms
around Japan Caused by the Global Warming
Hisami KUWAHARA1*, Sadamitsu AKEDA1, Satoshi KOBAYASHI2, Akira TAKESHITA2,
Yoh YAMASHITA3 and Katsutoshi KIDO4
1National Research Institute of Fisheries Engineering, Fisheries Research Agency
7620-7 Hasaki, Kamisu, Ibaraki 314-0408, Japane-mail: kwhr@fra.affrc.go.jp
2
Tokyo Kyuei Co., Ltd.
3
Kyoto University
4
Marine Ecology Research Institute*corresponding author

Abstract
The IPCC report published in April 2001, predicted sea surface water temperatures to increase by
3°C or so by 2100. This rise in seawater temperature is expected to have a significant impact on marineorganisms distributed around Japan. In order to estimate the influence of warmer water, we performed asimulation study based on the assumption that sea surface water temperatures will increase by 1.0°C in
30 years (short-term), 1.4°C in 50 years (medium-term), and 2.9°C in 100 years (long-term). Data on
the range of water temperatures marine organisms can inhabit were collected from previous studies andreports, and those data were applied to maps of seawater temperatures predicted over the short, medium,and long-term to study the changes in the distribution of areas of inhabitation.
The results showed that a shift in the 29°C isothermal line (i.e., the line at which the maximum annual sea water temperature is 29°C) significantly influences the distribution of marine organisms, because the line coincides with the boundary between the zone of temperate marine organisms and that of
sub-tropical ones. Though the isothermal line currently stays south of the island of Kyushu, it will supposedly move north as global warming proceeds, reaching the coasts of the Chugoku district and theisland of Shikoku in 50 years, and those of the Kanto and Hokuriku districts in 100 years. The northward-shift of the 29°C isothermal line will not affect pelagic fish, such as mackerel, bonito, and Pacificsaury, because they have strong swimming abilities, although their catch and fishing seasons will haveto change somewhat, Demersal organisms like Alaska pollock and tanner crab will also not be influenced because water temperatures will rise only slightly in water deeper than 100 m.
However, our simulation showed that the number of coastal marine organisms such as bastard halibut, red sea bream, abalone, and sea urchin will decrease significantly and the cultivation of Japaneseamberjack, puffer, and seaweeds will also be impacted, especially in southern Japan, where these bad
influences will be observed early in the future. These results indicate that we must urgently considerplans to protect fishery resources against global warming.
Key words: impact assessment, global warming, marine organism

1. Introduction
The IPCC (Intergovernmental Panel on Climate
Changes) report (IPCC, 2001) issued on April 2001
predicted air temperature rises of 5.8°C at the
maximum by 2100, which will be accompanied byincreased sea surface water temperatures rising about
3°C, and an 88 cm rise in the sea level.
Since Japan is one of the major fishery nations of
the world, the fishing industry will be drastically afGlobal Environmental Research
10(2)/2006: 189-199
printed in Japanfected by the changes in water temperatures and sea
level caused by global warming, and we will have tospend huge amounts of money and time on countermeasures. However, studies on this subject have been
insufficient, with just fragmented research done in thepast (National Research Institute of Fisheries Science,1989). Therefore, there is an urgent need to understand the effects of global warming on the fishingindustry and consider how to deal with this problem.
Ideally, studies on the effects of global warming©2006 AIRIES190

H. KUWAHARA et al.

should take into account various factors of the physical environment, including sea currents, material
circulation, ecological systems, and so on. We cannot,
however, conduct such ideal research at present because there has been insufficient study of many of theinterrelated factors.
Hence, as an initial approach to predicting the influence of the global warming on marine organisms,
we limited the purpose of this study to elucidating
suitable water temperatures for inhabitation of usefulmarine species and revealing the effects of warmer
water on them (i.e., changes of their areas of distribution). The marine organisms selected for the study
were 34 of the main species currently caught in Japan.
Based on the assumption that water temperatures willrise by 2.9°C (the maximal value predicted by the
IPCC) in the next 100 years (long-term), we madeshort-term, medium-term, and long-term predictions
and compared them with the present state.

2. Assumption of Increasing Sea Water Temperatures
Because the IPCC prediction was made on a gridof a few hundred kilometers (latitude, about 2 degrees;
longitude, about 2 degrees) using a whole-globe model,
it was too coarse in spatial resolution to predict
regional effects of global warming on the coastal regions of Japan.
To supplement the IPCC data, the Japan Meteorological Agency (JMA) started preparing 20 km-gridmaps of predicted sea surface temperatures using
NOAA data (Prediction Information on the Global
Warming, Vol. 5, JMA), which were limited to thecoastal area around Japan. The Agency kindly provided us with monthly average data at present and 100
years in the future, which were used for our study.
The JMA predicts that water temperatures will increase by 1.4°C in 100 years (long-term), which issmaller than the 2.9°C indicated by the IPCC. In our
simulation study, we assumed that water temperatures
around Japan would increase by 2.9°C (the maximal

1.5℃

Increase in seawatertemperature (°C)

3.0
IPCC prediction
2.8
IPCC
予 測
(maximum)
2.6
Japan
2.4
Meteorological
気象庁
2.2
Agency prediction
2.0
1.8
medium term
1.6
1.4
short term
1.2
1.0
0.8
0.6 1.0℃
0.4
0.2
0.0
Present state 0 10 20 30 40 50 60 70 80
Years predicted (years later)

Fig. 1 Sea water temperature increases chosen.

90 100value predicted by the IPCC) in 100 years (long-term)
and the rate of increase of the temperatures would
be constant (see Fig. 1). The words “short-term,”“medium-term,” and “long-term” are here defined asfollows: (1) short-term, the point in time when watertemperatures will be 1.0°C higher than present values
calculated by the JMA; (2) medium-term, the point intime when water temperatures will be at levels predicted by the JMA for 100 years in the future (i.e.,
1.4°C higher than present water temperatures); and (3)long-term, the point in time when water temperatures
will be 1.5°C higher than medium-term water temperatures (i.e., 2.9°C higher than present water temperatures). Consequently, “short-term,” “mediumterm,” and “long-term” mean about 30, 50 and 100
years later, respectively. Underwater temperatures
were calculated by the conversion equation, against
sea surface temperatures, derived from vertical watertemperature profile which were obtained from thevalues measured by the MIRC (Foundation, Japan
Hydrographic Association).

3. Marine Organisms Selected as Objects ofStudy
We selected 34 species of marine organisms tostudy the effects of warmer water in consideration of
the following conditions:a) Their distributions exhibited no regional biases;
otherwise we could not observe the overall trendsof the effects of warmer water in the sea surrounding Japan.
b) Their fishing grounds (coasts, offshores, or tidelands) or aquaculture farms (including seaweedbeds) were located evenly around Japan.
c) They were commercially valuable marine organisms, specified as “marine organism resources,” included among Total Allowable Catch (TAC) or
Total Allowance Effort (TAE) species and were
subjects of agriculture, forestry and fishery statistics.
In general, the responses of marine organisms toincreases in water temperature are supposed to beclosely related to their “mobility.” Therefore, we divided these 34 species into the following four groups
based on the differences in mobility:① mass-caught species which are migratory andreadily move to other habitats when water temperatures rise: Japanese sardine, chub mackerel, bonito,
Pacific saury, Japanese jack mackerel, chum salmon,
Alaska pollock, tanner crab and Japanese common
squid (nine species);② coastal, stationary species, which stick tenaciously to certain coastal habitats and an unable tomove far away from their original homes: bastard
halibut, red sea bream, Haliotis discus, disk abalone,northern hard-spined sea urchin, Japanese sea tangle,
surf clam and short-necked clam (eight species);③ cultured species, which are cultivated using

Predicted Changes on the Distribution Areas of Marine Organisms

fish-preserves or rafts: Japanese amberjack, tiger
puffer, Yezo giant scallop, giant Pacific oyster,
Porphyra yezoensis (nori) and Cladosiphon
okumurans (six species);④ seaweed species: Eisenia bicyclis, Echlonia
cava, Cystoseira hakodatensis, Sargassa patens,
Sargassa macrocarpum, Laminaria angustana,Laminaria ochotensis, Laminaria longissima, eelgrass, Zostera asiatica and Thalassia hemprichii(eleven species).

191

4. Water Temperatures Focused on
In order to decide what temperatures we should
focus on in the simulation studies, we prepared databases on temperature ranges suitable for the 34 marineorganisms, which were based on past culturing experiments and field surveys, taking their life histories into
consideration. Table 1 shows an example of the database (on bastard halibut). From the databases, we estimated the upper and lower limits of the inhabitable

Table 1 Example of preparation of database on the resistance of subject marine organisms to water temperatures (for bastard
halibut).

192

H. KUWAHARA et al.

temperature range for each organism and focused on
those temperatures to predict changes in each distribution area which would occur with an increase in watertemperature. Although the limit temperatures were
estimated based on data on adults, they were adequately modified for the species for which ecologicalcircumstances in early stages of life histories were
important. These limit temperatures were then plottedon water temperature maps (present state) producedby the JMA, to find the present expected distribution
area. If the plotted lines coincided well with theboundaries of distribution areas revealed by fieldsurveys, we judged the estimate valid; and if not, we
modified the limit values so that the estimate would
become valid.

(1989-2001) in the stick-held dip net fishery season(i.e., from August to November) which were provided
by JAFIC (Japan Fisheries Information Service
Center).
Figure 2 represents changes in the fishing groundsof Pacific saury according to water temperature
increase. The four pictures on the left side display
present and future (short-term, medium-term andlong-term) states in September, and the ones on theright represent those in November. As shown in theleft maps (September), the fishing grounds (regions
surrounded by the red line) are now found off the
Nemuro peninsula in the eastern part of Hokkaido.
However, they move north as water temperature rises(see the short- and medium-term maps). No fishinggrounds appear in sea regions near Japan on thelong-term map (fishing grounds are found near thefour islands of the Northern Territories but they areoutside the Japanese economic zone). The maps on theright (November) indicate that, in the present state,fishing grounds are found offshore from the Sanriku
district to Choshi City in Chiba Prefecture. They
ascend to the north with an increase in watertemperature and are expected to distribute offshore
from Nemuro City to Iwaki City in the future (see thelong-term map). There will be no fishing grounds thenaround Choshi City.

5. Prediction of Changes in Distribution
Area
Firstly, we predicted changes in the fishinggrounds of Pacific saury caused by warming of water
as an example of a “mass-caught species” (see Fig. 2).
In this simulation, the range of water temperatures in
the fishing grounds was assumed to be 16°C-20°C in
August, 16°C-19°C in September, 12°C-23°C in
October, and 12°C-22°C in November. These values
were based upon data on sea surface temperatures
Table 2 Table of water temperatures chosen for focus of shudy.

Coastal, stationary species

Species of ample catch

Classification by
migration

Species
Japanese sardine
Chub mackerel
BonitoPacific saury
Japanese jack mackerel
Salmon (chum salmon)
Alaska pollock
Tanner crab
Japanese common squid
Bastard halibut
Red sea bream
Haliotis discus
Disk abalone
Northern hard-spined
sea urchin
Japanese sea tangle
Surf clam
Short-necked clam

Cultured species

Japanese amberjack
Tiger puffer
Yezo giant scallop
Giant Pacific oyster
Porphyra yezoensis (nori)
Cladosiphon okumurans
Eisenia bicyclis

Seaweed bed species

Ecklonia cava
Cystoseira hakodatensis
Sargassa paten
Sargassa macrocarpum
Laminaria angustana
Laminaria ochotensis
Laminaria longissima
Eel grass
Zostera asiatica
Thalassia hemprichii

Life history

Water temperature
focused on
Lower
Upper
tempera- temperture side ature side

Remarks

Adult fish

JAFIC
JAFIC
data used data used

(Experimental data)

Adult fish
Fry
Adult fish

8
12
–1

18
18
12

Adult crab
Adult squid
Adult fish
Adult fish
Adult shellfish
Juvenile shellfish (settling period)
Adult shellfish
Juvenile shellfish (settling period)
Adult sea urchin
Fry (hatching period)
Spore
Gamete (maturing period)
Adult shellfish
Juvenile shellfish (settling period)
Adult shellfish
Juvenile shellfish (settling period)
Adult fish
Nnon-adult fish (fry)Adult fish
Adult shellfish
Shellfish fry (attaching period)
Adult shellfish
Shellfish fry (attaching period)
gameteConchospore (seed-collecting period)
Spore
Spore
Gamete (maturing period)
Spore
Gamete (maturing period)
Spore
ThallusThallus
Spore
Spore

1
2
5
7
4
10
7
12
–1
19
2
5
5
15
0
0
7
20.8
4
–3
6
–1
15
5
10
18
10
10
10
10
–2
6
6
–2
3.5

17
28
27.5
28
28
25
28
24
25
24.5
25
18
28
28
35
34
30
27.2
28
23
20
31
25
20
25
30
25
25
25
25
24
28
28
20
20

Zoospore (forming period)
Spore
Gamete (maturing period)
Vegetative stock
Seed (germinating period)
Vegetative stock
Vegetative stock

1
4
0
4
5
not clear
19

12
10
10
28
24
25
29

Shimo et al., 2000; Ochiai & Tanaka, 1985
Shimo et al., 2000; Ochiai & Tanaka, 1985; Fishery Enhancement Division, Fisheries
Agency, 2002
Fishery Enhancement Division, Fisheries Agency, 2002; Japan Fisheries Resource
Conservation Association, 1980; 1981; 1983; 1988
Shimo et al., 2000; Fishery Enhancement Division, Fisheries Agency, 2002
Shimo et al., 2000; Ochiai & Tanaka, 1985; Marui et al., 1981
Shimo et al., 2000; Ochiai & Tanaka, 1985
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000; Ochiai & Tanaka, 1985; Marui et al., 1981
Shimo et al., 2000; Ochiai & Tanaka, 1985; Marui et al., 1981
Shimo et al., 2000; Ochiai & Tanaka, 1985; Marui et al., 1981
Shimo et al., 2000; Japan Resource Association, 1986
Shimo et al., 2000; Japan Resource Association, 1986
Shimo et al., 2000; Japan Resource Association, 1986
Shimo et al., 2000; Japan Resource Association, 1986
Shimo et al., 2000; Japan Resource Association, 1986
Shimo et al., 2000; Japan Resource Association, 1986
Japan Resource Association, 1986
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Shimo et al., 2000
Sudo, 1992; Marui et al., 1981
Sudo, 1992; Taniguchi & Yamada, 1978
Sudo, 1992; Murase & Kito, 1998; Murase, 2000
Sudo, 1992
Japan Fisheries Resource Conservation Association, 1983; Kaneko & Niihara, 1977;
Ueda et al., 1963; Kinoshita et al., 1935; 1936
Japan Fisheries Resource Conservation Association, 1983; Kaneko & Niihara, 1977;
Ueda et al., 1963; Kinoshita et al., 1935; 1936
Sasaki, 1977
Sasaki, 1977
Shimo et al., 2000; Kawasaki et al., 1988
Shimo et al., 2000; Kawasaki et al., 1988
Miki, 1933; Oomori 2000
Kawasaki et al., 1988; Tanaka et al., 1962

Predicted Changes on the Distribution Areas of Marine Organisms

193

Fig. 2 Prediction of changes in fishing grounds for Pacific saury.

Fig. 3 Prediction of changes in inhabitation areas of bastard halibut.

Mass-caught species of a pelagic nature, such as
Japanese sardine, chub mackerel, Japanese jack mackerel and the like, tended to show simulation results
similar to that of Pacific saury. On the other hand,
Alaska pollock and tanner crab, which are distributed
in deep water, proved to be little affected by warm
water on the assumption that their habitats were at thedepth of 200 m.
Secondly, we simulated results for bastard halibut
as an example of a “coastal, stationary species.” Basedon the data on adults, we assumed that the lower limitof their inhabitable water temperature during the minimum water temperature period (February) was 5°C
and the upper limit during the maximum water tem-

194

H. KUWAHARA et al.

perature period (August) was 27.5°C. Because the sea
surface temperature in summer is thought to be 1.5°C
higher than the deep water temperature (at about
30 m) which bastard halibut inhabit, we focused on
29°C (not 27.5°C) in the simulation.
Figure 3 shows changes in the fishing grounds ofbastard halibut caused by increases in water temperature. The maps on the left are simulation results forthe minimum water temperature period (February) andthe ones on the right are those for the maximum watertemperature period (August). The former indicate ashift in its northern limit of distribution due to lowtemperatures, and the latter indicate a similar shift inthe southern limit due to high temperatures.
Bastard halibut are now caught nationwide from
Hokkaido to Kyushu (see the “present state” maps in
Fig. 3). The prefectures in red indicate that the fish iscaught in their neighboring waters. The map of the“present state” on the left indicates that the 5°C isothermal line, which should be the northern limit of the
fish’s distribution, lies in the Soya district and Cape
Erimo during the minimum water temperature period.
This result accords well with the actual distribution of
the fish. Because water temperatures rise as time proceeds, the bastard halibut fishery in the future shouldbe less restricted by low temperatures. The pictures on
the right show that the 29°C isothermal line (blue line),
the high temperature limit for bastard halibut, lies atthe southern tip of Kyushu island in the present state
during the maximum water temperature period. As
water temperatures increase, the line moves north, inother words, the areas uninhabitable for bastard halibut (i.e., below the line) gradually expand. The entire
island of Kyushu and the southern part of Shikoku lie
in uninhabitable areas in the short-term future, and in
addition, all prefectures around the Inland Sea ofJapan in the medium-term future (prefectures in grayindicate that their neighboring waters will be uninhabitable for the fish). In the long-term future, thelimit line will reach southern part of Niigata Prefecture in the Sea of Japan and southern part of Chiba
Prefecture in the Pacific Ocean.
Simulation studies for the other coastal stationary
species indicated that, except the short-necked clam,
they are strongly affected by warmer water as bastard
halibut is. The southern limits of their distribution
move drastically north, whereas the northern limits
shift just somewhat north. In other words, their habitable areas tend to shrink as the result of global warming. On the other hand, the short-necked clam is not
influenced so much by increases in water temperature
because their adults can live in a wide range of watertemperatures, 0°C-35°C. However, it is possible thatthe growth of larvae spawned in spring would bedelayed or hampered in sea areas with water temperatures of 30°C or higher.
Thirdly, we simulated results for tiger puffer as an
example of a “cultured species.” Based on the data on
adults, we assumed that the lower limit of their in-habitable water temperatures during the minimum
water temperature period (February) was 4°C and theupper limit during the maximum water temperature
period (August) was 29°C. This 29°C is a modified
value (see Table 2, indicating that the upper limit is28°C) which takes into consideration that the sea surface is warmer than where tiger puffer lives.
Figure 4 shows the predicted change in the area
where the tiger puffer can be cultivated, caused bywarming of water. The pictures on the left are for theminimum water temperature period (February) and theones on the right are for the maximum water temperature period (August).
In the present state, tiger puffers are cultured in sea
areas adjacent to Fukui Prefecture and west ward in
the Sea of Japan, where water temperatures are over
12°C even during the low water temperature period,
and those neighboring Shizuoka Prefecture and west
ward in the Pacific Ocean, where the lowest watertemperature is 16°C. Because the lower limit of thetemperature range which tiger puffers can tolerate 4°C,
it might be practicable to cultivate the fish to the northof (namely, in regions colder than) the above areas.
However, the actual northern limits of the areas ofcultivation are the lines at 12°C or 16°C, whereas the
4°C-isothermal line that should be the theoretical
northern limit does not pertain to the distribution ofcultivation. This fact seems to be the result of the economic necessity to raise the fish as quickly as possible
in aquaculture. On the other hand, the isothermal line
at 29°C, the upper limit of inhabitation for tiger puffer,
restricts the areas of cultivation during the maximum
water temperature period (see the pictures on the rightin Fig. 4). As water temperatures increase, the 29°C
line moves north, and consequently, the present cultivation areas become unsuitable. However, it is also
anticipated that new areas which are suitable to thefish’s culture would appear in the Hokuriku andTohoku districts because of warmer water.
Other “cultured species,” except the giant Pacificoyster and nori (P. yezoensis), tended to show almost
the same simulation results as the tiger puffer, although the sensitivity to warmer water differed from
one to another. Cultivation areas of to the giant Pacificoyster and nori were predicted to change little andincrease slightly, respectively.
Finally, we simulated results for E. bicyclis as an
example of a “seaweed species.” Taking into consideration its biology in the spore stage and during gamete maturation, we focused on water temperatures of
10°C for the minimum water temperature period(February) and 28°C for the maximum water temperature period (August). Previous studies (available
literature and information) suggest that the upper limit
of water temperature suitable for the inhabitation of
E. bicyclis is 25°C. However, because the southernborder of its present distribution coincided well withthe 28°C-isothermal line during the high water temperature period, we decided to focus on 28°C, rather

Predicted Changes on the Distribution Areas of Marine Organisms

195

Fig. 4 Prediction of changes in culture areas of tiger puffer.

Winter (February)

Summer (August)Fig. 5 Prediction of changes in inhabitation areas of E. bicyclis.

than 25°C.
Figure 5 shows changes in the distribution of
E. bicyclis caused by water temperature increases. The
maps on the left represent the simulation results during the minimum water temperature period (February)
and the ones on the right show those during the maxi-

mum water temperature period (August). The red, yellow, and blue lines designate the present distributionof E. bicyclis, the 10°C isothermal line in the minimum water temperature period, and the 28°C isothermal lines in the maximum water temperature period.
As shown in the left pictures, the northern distribu-

196

H. KUWAHARA et al.

tion limit of E. bicyclis, which is on the coast of Iwate
Prefecture to Miyagi Prefecture in the present state, isanticipated to move north as water temperatures keep
rising and reach the southern part of Hokkaido in thelong-term future. The pictures on the right reveal thatthe southern limit of its distribution lies at the southern tip of Wakayama Prefecture in the present state
and, as water temperatures increase, ascends north toreach the coast of Fukushima Prefecture in thelong-term future.
The other seaweed species, in our simulations,showed tendencies similar to that of E. bicyclis withregard to the effect of warmer water: T. hemprichii ispredicted to be affected in the short-term future andthe influences on L. angustana, L. ochotensis and
L. Longissima should be observed in the medium-term
future.

6. Predictions of Influence in Each Sea
RegionTables 3 to 6 show predicted changes in distribution regions (sea districts), caused by increases inwater temperature, for the 34 commercially valuablespecies selected as research subjects. Tables 3 to 6

correspond to mass-caught, coastal and stationary,cultured and seaweed species, in that order.
With regard to the amply caught pelagic fish, thefishing grounds, fishing seasons, fishing times andcatches are expected to change somewhat. However,
because they are generally strong swimmers and areagile in response to changes in water temperature,they are predicted to be affected relatively little. In
addition, those inhabiting deep spots are not influenced much, since temperatures of deep water layers
do not fluctuate easily.
Changes in water temperature are predicted to exert greater effects mainly on the coastal, stationary andcultured species in the southern Pacific and East
China Sea districts; such effects will begin to appear
in the short-term future. Similar influences are anticipated in the Seto Inland Sea district, too.
In the northern Pacific and Hokkaido districts, seaweeds are expected to proliferate and expand theirhabitats as water temperatures rise; new entry of nonnative species and increased harvests (including of
cultured species) are also expected.
The northern and western districts of the Sea ofJapan are anticipated to suffer decreasing catches in
the long-term future, although they may enjoy some

Table 3 Prediction of influence on ample catch species.
Sea district

Prefecture

Species
Prediction time

Japanesesardineshort medium
term
term

long
term

Chub mackerel

Bonito (fishing Pacific suary(fishing groundground off
off Sanriku)
Sanriku)Japanese jackmackerelChum salmon

Alaska pollock

short medium
term
term

short medium long
term
term
term

short medium long
term
term
term

short medium long
term
term
term

short medium
term
term

long
term

Hokkaido
district
Hokkaido
Pacific north Aomori (Pacific side), Iwate,
district
Miyagi, Fukushima, Ibaraki
Pacific middle Chiba, Tokyo, Kanagawa,district
Shizuoka, Aichi, Mie
Pacific south Wakayama, Tokushima,
Kochi, Miyazaki
districtFukuoka, Saga, Nagasaki,
East China
Kumamoto, Kagoshima,
Sea district
Okinawa
Aomori (Japan Sea side),
Japan Sea
north district Akita, Yamagata, Niigata,
Toyama, Ishikawa
Fukui, Kyoto, Hyogo (Japan
Japan Sea
west district Sea side), Tottori, Shimane,
Yamaguchi (Japan Sea side)
Osaka, Hyogo (Inland Sea
Inland Seaside), Okayama, Hiroshima,
district
Yamaguchi (Inland Sea side),
Kagawa, Ehime, Oita

Table 4

Prediction of influence on coastal stationary species.

short medium long
term
term
term

long
term

Tanner crab
short medium
term
term

long
term

Japanesecommon squid
short medium
term
term

long
term

Predicted Changes on the Distribution Areas of Marine Organisms

197

Table 5 Prediction of influence on cultured species.

Table 6 Prediction of influence on seaweed bed species.

positive effects of increased water temperature, suchas new entry of nonnative species (Japanese amberjack as a cultured species, for example).

7. Northward Movement of Sub-tropicalSpecies
The above description concerns the influence of increased water temperatures mainly on marine organisms that are caught in Japan at present. In this section,
we examine subtropical species that are not caught
much at present, but are expected to ascend northernfrom southerly regions to sea regions around Japan in
the future.
The FAO Species Catalogue (Heemstra et al.,
1989; Carpenter & Allen, 1989; Allen, 1985; Russell,1990) shows distribution areas of marine organisms
by species in addition to giving morphological descriptions. It includes the seas around Japan in Major
Fishing Area 61 (the Pacific, Northwest) that isbounded by latitude 20°00’ north (the southern limit)
and longitude 175°00’ west (the eastern limit). It has
tables summarizing information regarding which

major fishing areas are the habitat for each species.
We have little knowledge about the tolerance limits
and suitable range of water temperature for individual
southern fish species. Hence, we made the assumptionthat the lower water temperature limits which eachspecies can inhabit is the present water temperature in
February at the northern limit of its distribution, as
shown in the FAO Species Catalogue, and we focusedon the temperature in February in order to judge
whether the fish could inhabit it in winter. Then we
attempted predictions on the northward ascents oflimit-temperature isothermal lines for the future(short-term, medium-term, and long-term).
Figure 6 shows examples of predicted changes fora Serranidae species (honeycomb grouper) and a
Nemipteridae species (Scolopsis monograma). We
focused on a water temperature of 20°C as the estimated lower limit for inhabitation in the minimum
water temperature period (February). In the present
state, the northern limit for Serranidae species (i.e.,the 20°C isothermal line) lies south of the islands of
Kyushu and Shikoku; it is expected to move north aswater temperatures rise and this fish species is198

H. KUWAHARA et al.

Fig. 6 Changes in the distribution areas of southern fish
species.

expected to be caught around those islands in thelong-term future.
Similar analyses revealed that 61 of 171 species
belonging to the families of Serranidae, Lutjanidae,
Nemipteridae, or Letherimidae may move north fromsouthernly sea regions, including those around
Okinawa Prefecture, and make new entries into waters
off the southern part of Kyushu in the short-term
future. Moreover, 27 species of the aforementioned
four families, which are thought already to be distributed around the western part of Japan, may possibly
expand their distribution areas. Therefore, as many as
88 species in all are expected to make new entries or
expand their distribution around the western part ofJapan. Among them, 47 species have been caught formarkets of Southeast Asia and utilized as food.
Because many of the sub-tropical species inhabit
coral reefs, the ascent of coral reefs to the north also
needs to be investigated. At present, the northern limitof stone corals that build reefs in sea regions around
Japan lies at Tateyama City in Chiba Prefecture. It is
expected to move north as water temperatures increase,and environments suitable for coral inhabitation are
expected to appear in the western part of Japan.

8. Conclusion
The Japanese Archipelago extends in a long arc
from north to south and includes geographical districts
from semi-frigid to sub-tropical zones. A rise in watertemperature due to global warming would transformparts of the semi-frigid zone to the temperate zone, thetemperate zone to the sub-tropical zone and the
sub-tropical zone to the tropical zone. Therefore, themain marine organisms that are distributed around
Japan at present will be influenced by climate changes
and the southern and northern limits of their habitats
will move north.
Except for northern species such as chum salmon,
Pacific saury, Alaska pollock, northern hard-spine sea
urchin, and so on, many marine organisms inhabiting
seas near Japan are widely distributed around Honshu,
Shikoku, and Kyushu, as well as part of Hokkaido,
and thus can be classified as temperate species.
The upper limits of water temperature suitable forinhabitation by such typical temperate species as red
sea bream, bastard halibut, Japanese amberjack, tiger
puffer, and the like lie in the range of 28°C-30°C.
When comparing actual distributions of their habitats
and aquaculture regions with the present state of watertemperature distribution, we see that the southern limits for those species coincide with the 29°C isothermalline in August. At present the 29°C isothermal line inAugust lies at the southern tip of Kyushu and closely
agrees with Watase’s line, which separates the temperate-zone fauna from the sub-tropical. Geographically,
it is a line between the island of Yakushima andAmami-Oshima. This isothermal line will move northand reach the northern part of Kyushu (on the Sea ofJapan side) and the Kii Peninsula (on the Pacific side)in the short-term future (30 years later), Yamaguchi
Prefecture (on the Sea of Japan side) in the mediumterm future (50 years later), and the northern part of
Niigata Prefecture (on the Sea of Japan side) and thenorthern part of Chiba Prefecture (on the Pacific side)in the long-term future.
This ascending isothermal line will force temperatemarine organisms now caught in Japan to shift theirdistribution north. The effects are expected to manifest
differently depending on the response characteristics(mobility) of the marine organisms to increased watertemperatures, as described above.
This study showed that global warming mightchange the distribution of marine organisms and exert
a great influence on fishery industries, although factors other than water temperature were not dealt with,as stated initially. Hence, it will be necessary to makepredictions in greater detail and to study possible
countermeasures in the future. It will be important tomonitor environmental data including water temperatures and detailed data on catches. The catch data ofcertain kinds of species, even if small in volume, may
serve as indicators of global warming. Therefore, theyshould not be rounded up in the category of “others”
but be provided in detail. Furthermore, it is desirable
to share such data with as many people as possible
and use them as basic information for making predictions of and contemplating measures against global
warming.

Predicted Changes on the Distribution Areas of Marine Organisms

Acknowledgement
This study was performed as part of “Surveys andCountermeasures for Fishing Grounds, Fishing Ports,
and Fishing Villages against the Global Warming of
the Earth” (under the Fisheries Agency). Professor
Ichiro Deguchi (Osaka University), chairman of the
Research Committee, and the committee members
kindly gave us a great deal of advice. Valuable data
were also readily provided us by the JMA, JAFIC(Japan Fisheries Information Service Center) andmany municipalities. We wish to mention our gratitude for their kindness here. Also we thank emeritus
Professor Muneo Okiyama of Tokyo University andMiss Hiroko Gohda of the Ocean Engineering Division, Tokyo Kyuei Co., Ltd., for the critical reading of
the manuscript.
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