●Research Trends and Results

Predicting the impact of water temperature increase on
cold water fish that may be induced by climate change
AMANO Kunihiko (Dr.(Eng.)), HeadMOCHIZUKI Takafumi, ResearcherEnvironment Department, River Environment Division(Key Words) Climate change, global warming, river water temperature, cold water fish
1. Introduction
It is predicted that global warming will beaccompanied by climate change, but it is difficult toquantitatively evaluate its impacts on river ecosystems.
This research hypothesized that global warming will
increase river water temperature to study its impact on
the fish species inhabiting rivers.
2. Evaluation of water temperature dependency offish species
Data representing river water quality and thenational survey for river and riparian ecosystems wereanalyzed for 109 Class A river systems in Japan. The
frequency distribution of river water temperature
values at locations confirmed to be habitats of 5common fish species and 6 stenothermal cold water
fish species were obtained, then compared with thefrequency distribution of all measured river watertemperatures nationwide, to analyze water temperaturedependency of these fish species. We have used
24-year period data for river water temperature
analysis.
The frequency distributions of water temperature
measured at confirmed locations of 5 common fish
species were almost identical to the frequency
distribution of all data, but the measured watertemperatures at locations where yamame trout or othercold water fish were confirmed were biased towards
low temperature and the frequency it exceeded 25C°
was particularly low (Fig. 1). When the mean annual
maximum temperature was obtained and analyzed, atconfirmed, the temperature never exceeded 26C°, and it
can be concluded that the surrounding watertemperature is the limit for the habitation of cold water
fish 1).
3. Sensitivity analysis of water temperature
increase and summary
Figure 2 shows the estimated mean annual
maximum water temperature distribution based on
the results of the nationwide water quality survey of
public water bodies. The mean annual maximum watertemperature is below 26C° in and north of Tohoku ,and in regions to the west, it is partially distributed in
Shinshu or in mountainous regions.
If we assume the mean annual maximum watertemperature increases by 1C° nationwide, focusing on
the change of the area with temperature below 26C°
where cold water fish will be able to live, theirhabitable range which equals about 9% of the national
land will be lost, with possible negative impact on thehabitats of cold water fish such as cherry salmon thatare widely distributed in western Japan 1). And if themaximum temperature rises by 5 C°, the area of thenational land where rivers in which cold water fish canlive are distributed will fall to about 5%, so they will（℃）
‐20
20‐21

0.06
0.05

Water temperature histogram (Yamame trout)
水温ヒストグラム（ヤマメ）confirmed

21‐22
22‐23

Water temperature distribution at
全地点の水温分布(S59～H19)

0.04

all locations (1984 to 2007)

0.03

23‐24

0.02

24‐25

0.01

25‐26

0.00

t<-4-4≦t<-3-3≦t<-2-2≦t<-1-1≦t<00≦t<1
1≦t<22≦t<3
3≦t<4
4≦t<55≦t<66≦t<7
7≦t<88≦t<99≦t<1010≦t<1111≦t<12
12≦t<13
13≦t<14
14≦t<15
15≦t<1616≦t<1717≦t<1818≦t<19
19≦t<2020≦t<2121≦t<2222≦t<2323≦t<2424≦t<2525≦t<2626≦t<2727≦t<2828≦t<2929≦t<3030≦t<3131≦t<3232≦t<3333≦t<3434≦t<3535≦t<3636≦t<3737≦t<3838≦t<3939≦t<40Frequency
頻度

Water temperature distribution of

ヤマメ確認箇所の水温分布
places where yamame trout were

26‐27

Water水温（℃）
temperature (C°)

28‐29

27‐28

29‐30

Figure 1.Water Temperature Frequency
Distribution at Locations Where the Cold Water
Fish, Yamame Trout, were Confirmed (Blue) and
Water Temperature Distribution in Rivers
Nationwide (Red)locations where cherry salmon or yamame trout were30‐3131‐32
32‐33
33‐Figure 2. Nationwide Distribution of EstimatedMean Annual Maximum Water Temperature

●Research Trends and Results
no longer exist anywhere in Honshu, making it very
difficult for cold water fish to survive.
[Reference]
1) Amano, K. and T. Mochizuki: An assessment of thedependency of fish and aquatic invertebrates on water
quality using the national survey for river and riparian
environment, Advances in River Engineering, JSCE,
Vol.17, 2011.