State of conservation report of Shiretoko
In response to the World Heritage Committee Decision 36COM7B.12

Ministry of the Environment
Forestry Agency
January 2015

I ．Update statistics on annual Steller sea lion quotas and numberscaught and report on population trends within the property(decision:Item4)
Update statistics on annual Steller sea lion quotas and numberscaught
1. With respect to Steller sea lions (SSLs) that migrate to Hokkaido, the Fisheries
Agency of Japan (FAJ) provides the Hokkaido Government every year with anannual allowable catch number, which serves as the scientific basis for
management purposes. The Hokkaido Fishing Zone Coordination Commission,under the supervision of the Hokkaido Government, then sets annual catch
limits.

The annual allowable catch numbers were calculated on the basis of the PBR(Potential Biological Removal) level for the migration seasons from 2007/08 to
2013/14. For the migration seasons from 2010 to 2014, a block quota(i.e. anaggregate quota) was originally set for the five-year period based on the PBRlevel, and catch has been managed in accordance with that quota. The annual
allowable catch numbers have therefore been calculated by reference to thedegree as to how much the PBR and block quotas have been used up.

However, for the 2014/15 migration season, which is the last year of the current
block quota period, the annual allowable catch numbers were presented
separately for the Sea of Japan migrating group and the Nemuro (Shiretoko)
migrating group. For the Sea of Japan migrating group, the population has
recovered rapidly in recent years and increased enough to be downgraded fromthe threatened species. On the other hand, such population recovery has started
causing serious damage to the fisheries. Against this background, the annual
allowable catch numbers were recalculated scientifically in accordance with abasic management approach that had been newly presented by FAJ ((i) the
objective should be to minimize damage to the fisheries caused by SSLs to theextent of posing no risk of SSL extinction; and (ii) in light of the past experienceof letting the population decrease to be listed as threatened species, SSLs
should be managed based on the precautionary and adaptive approach).

For

the Nemuro (Shiretoko) migrating group, the annual allowable catch number was
set to be the same as the most recent catch quota for the Nemuro district set by
the Hokkaido Government within the annual catch limit.

Table 1

Annual allowable catch numbers(Number of individuals)
2009/102010/112011/122012/132013/142014/15

Sea of Japanmigrating

501

group
Nemuro

144

156

197

(Shiretoko)
migrating

257

257
15

group
(Fisheries Agency)

2.

The Hokkaido Government manages catches by allocating the catch quota foreach district within the annual catch limits of SSL set by the Hokkaido Fishing
Zone Coordination Commission (Table 2), and on the basis of the catch records
from the previous year and the state of damage to the fisheries, as well as
information on SSL spotting from fishermen. For the Nemuro district, the catch
quotas have been set at a level similar to, or not substantially exceeding, thecatch records for the previous year (Table 3), in spite of the fact that fisheries
damage has been growing year after year.

Note that up until 2013/14, figures set for the respective districts were changed(upwards or downwards) midterm on an as-needed basis, considering the catch
numbers and fisheries damage of given season, as well as information on SSL
spotting from fishermen, that were relevant to the respective districts. The
numbers were managed thereby to the extent that they should not exceed theprefecture-wide quota. However, as the annual catch limits have been presented
separately for the Sea of Japan migrating group and for the Nemuro migratinggroup - an approach that has started from 2014/15 as described earlier - proper
catch management is now slated to continue so that catches should not exceed
the respective catch limit (501 for the Sea of Japan migrating group and 15 for
the Nemuro migrating group).

Table 2

Annual catch limits of SSL in Hokkaido offshore waters(Number of individuals)
2009/102010/112011/122012/132013/142014/15(2009.10.1(2010.10.1(2011.10.1(2012.10.1(2013.10.1(2014.9.1-2010.6.30)-2011.6.30)-2012.6.30)-2013.6.30)-2014.6.30)-2015.6.30)

144

156

197

253

253

516

Hokkaido(Hokkaido Fishing Zone Coordination Commission)

Table 3Catch quota or Annual catch limit for the Nemuro district within the annual
catch limits shown in Table 2(Number of individuals)
2009/102010/112011/122012/132013/142014/15(2009.10.1(2010.10.1(2011.10.1(2012.10.1(2013.10.1(2014.9.1-2010.6.30)-2011.6.30)-2012.6.30)-2013.6.30)-2014.6.30)-2015.6.30)

12(*1)

10

12

12→15(*2)

12→15

15

Nemurodistrict(Hokkaido Government)* Catch figures set for the Nemuro district containing the Shiretoko World Natural
Heritage Site(*1) The 2009/10 figures are the numbers set for "Other districts" excluding Soya,
Rumoi, Ishikari and Shiribeshi(*2) (→) indicates a change in the set figure made midterm in consideration of thestate of fisheries damage, etc.

Table 4

State of catches(Number of individuals)

Hokkaido
Nemurodistrict2009/102010/112011/122012/132013/14(2009.10(2010.10(2011.10(2012.10(2013.10-2010.6)-2011.6)-2012.6)-2013.6)-2014.6)

122

115

195

249

253

8

6

10

14

13

* This shows the catch records for the Nemuro district and is not limited to thearea within the Shiretoko World Natural Heritage Site.
(Hokkaido Government)Report on population trends within the property
3.

The population of the Eastern subspecies, found to the east of Cape Suckling in
Alaska, has been on the rise since the mid 1970s at the rate of approximately
3% per year. The population of the Central in the vicinity of the Aleutian Islands,
belonging to the Western subspecies found to the west of the same cape,dropped rapidly in the 1970s, but has been increasing slightly (1% yr -1 ) since
2000. The Asian group, another among the Western subspecies that occurs to
the west of the Commander Islands, experienced a rapid population decline up
until the 1980s, but it has then either remained stable or decreased in the westof the Bering Sea and to the east of the Kamchatka Peninsula, while showing an
upward trend in recent years in the Kuril Islands and the Sea of Okhotsk at therate of 4% yr -1 . In particular, a sharp increase in pup number has been marked
on Tuleny Island in the vicinity of Sakhalin.

In the red list revision in 2012, the International Union for Conservation of
Nature (IUCN) lowered the category of the species from Vulnerableto Near
Threatened. In Japan, SSLs were assessed as Vulnerable (VU) on the red lists
issued by the Ministry of the Environment but the category was lowered to Near
Threatened (NT) in the red lists revised in 2012 (the 4th Version of the Japanese
Red Lists, released on August 28, 2012). The reasons include: it is estimatedthat there are roughly 5,800 SSLs migrating to Japan (FY2009, Fisheries
Agency) and; the population of their origin, the Asian group, has been on theincrease since the 1990s (Fisheries Agency and Fisheries Research Agency,"FY2013 Current Status of International Fishery Stocks").

4. The state of SSL migration on the east coast of the Shiretoko Peninsula issurveyed by frequent land-based sighting survey in the winter season between
November and February, with six fixed observation points set along the coastlineof Rausu Town and the northern part of Shibetsu Town. Ever since the largest
count (*3) attained 126 in 2009/10 (between November 16, 2009 and February
15, 2010), the spotting of over 100 migrating SSLs is confirmed every year.

(*3) A series of land-based observation on swimming SSLs were performed at a
total of 6 fixed observation points along the eastern coast of the Shiretoko
Peninsula including the Heritage area. Sequential counts were taken whenswimming SSLs were found during a 5-10 minutes of scanning of the sea surface
from each observation point, using 8x to 10x binoculars. After a series of counts
continuing 10-30 minutes, a maximum count was adopted as the data of the day

at each point. The numbers of SSLs counted on the same day at the six points
were summed up (a daily count). The survey was performed for multiple days
including the peak period of SSLs’ sighting (between mid-Dec. and mid-Jan.) ineach year, the largest value of the daily counts for each season was defined as
the "largest count." Note that on the east coast of Shiretoko Peninsula, there is no
SSL hauling out while they float and rest in groups off the coast of each of theparticular locations (which match the observation points described above) during
daytime between November and February. For that reason, any count of SSLs
landing occasionally at some locations is not appropriate as a means of studying
SSLs as far as Shiretoko is concerned.

Table 5

State of SSL wintering migration on the east coast of Shiretoko Peninsula

after the World Heritage List inscription (Largest count by survey year)(Number of individuals)
2006/07

2007/08

2008/09

2009/102010/112011/122012/132013/14

winterwinterwinterwinterwinterwinterwinterwinterseasonseasonseasonseasonseasonseasonseasonseason(2006.10.21(2007.9.30(2008.11.3(2009.11.16(2010.11.15(2011.10.22(2012.11.21(2013.11.2-2007.4.26)-2008.3.8)-2009.3.10)-2010.2.15)-2011.2.14)-2012.2.4)-2013.2.12 )-2014.2.7)

95

98

60

126

179

128

131

110

(Ishinazaka et al. (2009), Bulletin of the Shiretoko Museum 30:27-53.; Shiretoko
Nature Foundation independent research project data (Proceedings of the 17th
Conference of the Wildlife Conservation Society of Japan, pp. 85-86, etc.),
Ishinazaka (2009) Eumetopias jubatus (Schreber, 1776) In: The Wild Mammals ofJapan. Shoukadoh, Kyoto, pp. 284-285)

II ．R eport on the state of conservation of the property, including progressachieved in addressing the conflict between fishers and Steller sea
lion (Decision:Item6)
1.

Damage to the fisheries caused by SSLs consists of direct damage in the formof broken nets and indirect damage due to lost fishery incomes resulting fromdamaged catches and loss of fishing opportunity by broken nets. The amount of
those damages to the coastal fisheries in Hokkaido has exceeded one billion yen
for 20 years, and the situation has become increasingly serious in recent years,
especially due to the growing population of migrating SSLs and theirextendedmigration periods, among other factors.

Table 6

State of fisheries damage caused by SSLs (Hokkaido)(In millions of yen)
FY2009FY2010FY2011FY2012FY2013

661

710

680

530

529

5

－

－

－

55

693

898

818

1,082

1,449

11

51

63

209

302

1,354

1,608

1,497

1,612

1,979

16

51

63

209

357

Amount ofdamage tofishing gear
Nemurodistrict
portionAmount ofdamage tocatches
Nemurodistrict
portionSum total
Nemurodistrict
portion* The amounts of damage for the Nemuro district is not limited to the area within the
Shiretoko World Natural Heritage Site.
(Hokkaido Government)

2.

In Hokkaido, there are prefecture-wide efforts under which the

LiaisonCommittee for Mammal Damage Prevention was set up in the government's
headquarters, as well as a

Liaison Council for Marine Mammal Damage

Prevention in each (general) subprefectural bureau

including in the Nemuro

Subprefectural Bureau, and comprehensive marine mammal-control steps arepushed forward in partnership with groups associated with the fisheries,
municipal governments, associated prefectural government bodies and otherorganizations, working to ensure accurate comprehension of the state ofdamage through fisheries damage surveys and to provide support for actions
being taken to address the damage, including introducing reinforced bottom
pound nets and implementing capture procedures.

In the Nemuro district, Rausu Town developed a wildlife damage prevention planin an effort to address fisheries damage, including implementing repelling or
capture procedures, and is planning to continue taking further steps aimed at thecoexistence of SSLs and fisheries, with various organizations working incooperation.

Furthermore, the Ministry of the Environment and the Hokkaido Government
have also established the Multiple Use Integrated Marine Management Plan for
Shiretoko World Natural Heritage Site with the aim of achieving two goals
together: the conservation of the marine ecosystem and the lasting andproductive fisheries through the sustainable use of marine resources in thewaters within the heritage site.
With the SSL designated as one of the indicator species characterizing themarine ecosystem of Shiretoko in the course of those actions, monitoring
surveys, including counting the number of migrating SSLs, are carried out andtheir findings are reported to the Shiretoko World Natural Heritage Site ScientificCouncil, which then provides advice from scientific perspectives: efforts are thus
being made for the purpose of marine ecosystem conservation and managementin the waters within the heritage site.

III ． To continue monitoring the status of salmonid migration andspawning, and consider further river construction modifications
including other appropriate measures, as needed, on the Rusha River inorder to ensure natural salmonid migration and spawning (Decision:
Item5)
The continuation of monitoring
1. For the purpose of verifying whether salmonid migration and spawning have been
improved as a result of modifications made to 13 river structures built on five rivers(see Appendix 1: Shiretoko River Position Map), monitoring (including number of
upstream runs of salmonid species, number of spawning beds, riverbed gradient,particle size distribution of the gravel bed, and flow velocity) has been conducted for aperiod of three years after the modifications. Nearly all of the monitoring wascompleted by 2013, but to verify whether the modifications continue to be effective,
monitoring will be conducted for the periods 2013 - 2014 and 2019 - 2020 as well (theresults of monitoring conducted so far are shown in Appendix 2: Effects ofModifications to River Structures).
2. Furthermore, long-term monitoring of the number of fish runs and the number ofspawning beds for pink salmon, a salmonid species with a large number of individuals
migrating upstream in Shiretoko, has been conducted since 2013 on three rivers(Rusha River, Teppanbetsu River, and Rusa River) in the property’s core area.
This monitoring, which was developed for the purpose of managing the heritage site
adaptively based on scientific knowledge for the period from FY2012 to FY2021, isbeing conducted based on the Long-term Monitoring Plan for the Shiretoko World
Natural Heritage Site.

Concerning the Rusha River
3. Of the three check dams*1 in place on the Rusha River, the two upstream dams weremodified in 2006. The results of monitoring conducted subsequently show that ratio ofchum salmon spawning beds made on the upstream side of the dams had increased
compared to before the modifications, indicating that the modifications were effective
to a certain extent. The salmon and trout hatchery facilities at the mouth of the river
were removed in 2012.
4. While the modifications have shown to have positive effects, the following issues
have also arisen.
i. The river bed on the downstream side of Dam No. 1, which is the farthest checkdam downstream, has been degrading in recent years, and there are concernsthat this may have an adverse effect on upstream runs of salmonid species.
ii. The number of spawning beds in the reaches between the dams (from Dam No. 1
through Dam No. 3) is roughly half that of the beds in the reaches upstream or
downstream of the check dams. One possible reason is that channels suited tospawning have not formed because of fixation of the watercourses and blockageof hyporheic flow caused by the dams.
5. For these reasons, beginning in 2012 the River Construction Advisory Committee*2
and Hokkaido Government, while exchanging views with local parties concerned,
have been studying the possibility of further modifications to these river structures on
the condition that a balance can be struck between improving the spawningenvironment of salmonids and maintaining the disaster-prevention role of the checkdams for set net fishing grounds around the mouth of the river. The Committee andHokkaido Government are working towards a decision on specific further modification
methods, with the aim of reaching that decision in 2015.
6. Some ideas have been suggested, including removing the middle part (including thefoundation) of all three check dams, as well as lowering the height. It has also beensuggested, in the case modifications are to be implemented, to implement them overthe course of at least several years sequentially from the upper-most dam, while
carefully monitoring the impact on objects that need to be protected and theimprovements to the spawning environment.

Scientific advice and the cooperation of local parties concerned
7. In studying and implementing these measures, the Forestry Agency and Hokkaido
Government have asked experts in the committee for scientific advice, and local
parties concerned for understanding and cooperation.
*1. The three river structures, i.e. the check dams, on the Rusha River were built by
Hokkaido Government from 1974 to 1979 in response to demands from the community
in the wake of damage to salmon and trout hatcheries, set net fishing grounds locatednear the mouth of the river caused by debris flow during torrential rainfalls in 1972 and1973.
In 2005, the River Construction Working Group (see next item), which consisted ofexperts in the fields of river environment conservation, fish, erosion-control engineeringand other areas, and related administrative authorities, made the assessment
concerning the two check dams upstream that salmonids (especially chum salmon)

were either unable or just barely able to migrate upstream. For this reason, in 2006,
Hokkaido Government carried out structure modifications on these two check dams that
included cutting parts of them down.
*2. The River Construction Advisory Committee is a committee established under the
Shiretoko World Natural Heritage Site Scientific Council. The Committee provides
technical advice on modifications and scientific advice concerning the implementationof appropriate monitoring and assessments. The Committee is the successor of theRiver Construction Working Group (FY2005 - 2007).

IV ．To submit a report on the state of conservation of the property,
including on progress achieved in improving natural salmonid
migration and spawning within the property (Decision: Item6)
1．The Forestry Agency and the Hokkaido Government, which were the builders of theriver structures, held meetings of the River Construction Working Group* from
FY2005 to FY2007, and made decisions on the propriety of modifications to 100 river
structures in the property, based on assessments of the impact on the upstream
migration of salmonids and the changes to the disaster-prevention role of the river
structures for local residents resulting from modifications to them.
It was decided that modifications should be implemented for 13 river structures,and in accordance with the basic principles of making salmonid migration possible
just by modifying existing facilities and avoiding to the extent possible theconstruction of new facilities associated with these modifications, all modifications
were completed by the respective builders by 2013.
2．The results of salmonids monitoring conducted after the modifications to the river
structures clearly demonstrate the effectiveness of modifications. As an example,
they show that the ratio of spawning beds in the areas upstream of the modified river
structures had increased (see Appendix 2: Effects of Modifications to River
Structures). Although modifications were carried out with priority placed on the
migration of salmonids, there were instances in which the river environments did notchange to more appropriate conditions for spawning because, when deciding on themodification to make, insufficient consideration was given to how flow velocity would
be inhibited upstream and downstream of the structures and how gravel composition
upstream and downstream would be altered by the modifications. For this reason, it
was decided that the effects of the modifications should be evaluated over the longterm through continued monitoring (as described in III. 1).
3．Furthermore, beginning in 2013, the River Construction Advisory Committee has
been studying the possibility of modifications to 35 river structures which, in theassessments mentioned above, were deemed to have potential in terms of improving
the upstream migration and spawning of salmonids but for which the decision wasmade to maintain their current state because of the large impact on theirdisaster-prevention and other roles. These potential modifications have been studied
with a view to creating river environments more appropriate for spawning by making
the best possible use of the outcome and assessments of the 13 structure
modifications.

*The River Construction Working Group was established under the Shiretoko World
Natural Heritage Site Scientific Council in 2005 simultaneously with the listing ofShiretoko as a World Natural Heritage Site. It was formed for the purpose obtaining
expert advice on 1) assessing environments around river structures, 2) assessing river
structures in terms of salmonid habitats and continued disaster-prevention, and 3)
studying potential modification methods based on those assessments. The River
Construction Working Group has now been succeeded by the River Construction
Advisory Committee.

Appendix 2
Effects of Modifications to River Structures

1. Background
The River Construction Working Group of theShiretoko World Natural Heritage Site ScientificCouncil found that it was appropriate to makedeliberate modifications to 13 river structures on fiverivers within the Shiretoko World Natural Heritage
Site (Fig. 1).
These structures were modified during the period
from 2006 to 2012. The status of the upstream runsof salmonid species and the number of spawning
beds have been monitored on a continuing basis.

Fig. 1 Rivers in the Shiretoko World Natural Heritage Site

2. Effects of modifications to river structures
Below we describe the effects of modifications to the 13 river structures, according to eachtarget river.
1) Sashirui River
Year of modification

No. of structures modified

Modification method

2007

2

Modification of existing fishways

There had been two existing fishways on the Sashirui River, but their structures had notbeen sufficiently conducive to fish runs. These structures were therefore modified to makethem suitable for upstream runs (Fig. 2).
A

B

Fig. 2 Fishway at a check dam before and after modification
A: Before modification, B: After modification

Modification image◆Effects of modifications
The beneficial effects of fishway modifications were verified by observing the number of
salmonid spawning beds upstream of the modifications. The ratio of the number of spawning
beds observed upstream of the check dams to the total number of spawning beds observed
had increased after the 2007 modifications (Fig. 3).
No. of spawning beds
upstream/total no. of
spawning beds (%)

100%
Pink salmon
ｶﾗﾌﾄﾏｽ

80%

Chum salmon
ｼﾛｻﾞｹ

60%
40%
20%
0%
2007

2008

2009

2010

2013

Year

Fig. 3 Sashirui River: Changes in the ratio of the number of spawning beds observed upstream of
the check dams to the total number of spawning beds observed(2007 data indicates the ratio of the number of spawning beds before the fishway modifications)
The fishways were modified in 2007.

2) Chienbetsu River
Years of modification

No. of structures modified

Modification method

2008, 20092

Installation of new fishways

Two check dams had been built on the Chienbetsu River but no fishways had been installed,
rendering the upstream runs for salmonid species impossible. For this reason, new fishways
were installed (Fig. 4).

A

B

Fig. 4 Check dam before and after modification by installation of a fishway
A: Before modification, B: After modification◆Effects of modifications
The beneficial effects of the fishway modifications were verified by observing the number of
salmonid spawning beds upstream of the modifications. The ratio of the number of spawning
beds observed upstream of the check dams to the total number of spawning beds observed
had increased after the 2008-2009 modifications (Fig. 5).
No. of spawning beds
upstream/total no. of
spawning beds (%)

100%

ｶﾗﾌﾄﾏｽ
Pink salmon
Chum salmon
ｼﾛｻﾞｹ

80%
60%
40%
20%
0%

2008

2009

2010

Year

2011

2012

2013

Fig. 5 Chienbetsu River: Changes in the ratio of the number of spawning beds observed upstreamof the check dams to the total number of spawning beds observed(2008 data indicates the ratio of the number of spawning beds before the fishway installations)
The fishways were installed in 2008 and 2009.

3) Iwaubetsu River
Years of modification

No. of structures modified

Modification method

2006–2010

6

Making slits and lowering dam height

Five check dams and one water channel had been built on tributaries of the Iwaubetsu River,
rendering the salmonids’ upstream runs impossible. These six structures were therefore
modified by making slits and lowering dam height (Fig. 6).
A

B

Fig. 6 Check dam before and after modification by making slits and lowering dam height
A: Before modification, B: After modification◆Effects of modifications
The beneficial effects of making slits and lowering dam height were verified by observing thenumber of salmonid spawning beds upstream of the modifications. The ratio of the numberof spawning beds observed upstream of the check dams to the total number of spawning
beds observed had increased after the 2006–2010 modifications (Fig. 7).
No. of spawning beds
upstream/total no. of
spawning beds (%)

60%
Pink salmon
ｶﾗﾌﾄﾏｽｼﾛｻﾞｹ
Chum salmon

40%

20%

0%
2007

2008

2009

2010

2011

2012

2013

Year

Fig. 7 Iwaubetsu River: Changes in the ratio of the number of spawning beds observed upstreamof the check dams to the total number of spawning beds observed
The modifications were made from 2006 to 2010.

4) Rusha River
Year of modification

No. of structures modified

Modification method

2006

2

Making slits and notches

Three check dams had been built on the Rusha River. Two upstream structures weremodified by making slits and notches in them to enable freer upstream migrations ofsalmonid species (Fig. 8).

A

B

Fig. 8 Check dam before and after modification by making slits and notches
A: Before modification, B: After modification◆Effects of modifications
The beneficial effects of making slits and notches were verified by observing the number of
salmonid spawning beds upstream of the modifications. The ratio of the number of spawning
beds observed upstream of the check dams to the total number of spawning beds observed
had increased after the 2006 modifications (Fig. 9).
No. of spawning beds
upstream/total no. of
spawning beds (%)

80%

Pink salmon
ｶﾗﾌﾄﾏｽChum salmon
ｼﾛｻﾞｹ

60%
40%
20%
0%
2006

2007

2008

2009

2012

2013

Year

Fig. 9 Rusha River: Changes in the ratio of the number of spawning beds observed upstream of
the check dams to the total number of spawning beds observed
The modifications were made in 2006.
No surveys were conducted in 2010 and 2011 for either species, and no chum salmon surveys
were conducted in 2012 and 2013.

5) Rausu River
Years of modification

No. of structures modified

Modification method

2009–2012

1

Making slits

Twenty-eight river structures had been built on the main stream of the Rausu River, andmodifications had been made to 18 of these structures from the river mouth upward by
installing fishways. These modifications had been started in advance of the area’s
inscription on the World Heritage List and had been completed by 2007. Although thesalmonids’ upstream runs had been extended and the extent of their spawning beds
increased as a result, the salmonids had remained unable to run upstream of a check dam
built about 3.3 km from the river mouth. For this reason, the check dam was modified bymaking slits (Fig. 10).
A

B

Fig. 10 Check dam before and after modification by making slits
A: Before modification B: After modification◆Effects of modifications
The beneficial effects of making slits were verified by observing the number of salmonid
spawning beds upstream of the modification. After 2009, the salmonid upstream runs andthe spawning beds began to extend upstream beyond the modified check dam (about 3.5
km from the river mouth).
In contrast, the ratio of the number of salmonid spawning beds upstream of the modified
check dam to the total number of spawning beds did not change significantly from the firstyear after the modification ended because of the presence of a salmon and trout capture
project at the river mouth; as part of this project, hatchery weirs (urai in Japanese) had beenplaced on the river. The beneficial effects of the modification will be continuously monitored(Fig. 11).
Distance from rivermouth (m)

3000

3,104

3,336

3,554

3,554

3,554

2,355

2000

1000

3,336

1,227

1,227

0
2005

2006

2007

2008

2009

2010

2011

2012

2013

Year

Fig. 11 Changes in the greatest distance upstream from the mouth of the Rausu River where
spawning beds were confirmed to be present
The modification by making slits was made from 2009 to 2012.

Note 1: Area in which salmonid spawning beds were confirmed
2: In the Rausu River, modifications to downstream river structures by installing
fishways began before the area’s inscription on the World Heritage List. As a result, theextents of the upstream runs and the spawning beds increased consecutively up until
2009, when modification of the check dam by making slits was begun.
3: In 2012, the upstream runs were difficult because spring floods increased the drop
height at the downstream river structure. The following year this problem was resolved
and the salmonid species once again ran upstream beyond the structure.