Effects of Modifications to River Constructions
1. Background
The River Construction Working Group of theShiretoko World Natural Heritage Site ScientificCouncil found that 13 river constructions on fiverivers within the Shiretoko World Natural Heritage
Site required modification, and these structures weremodified starting in 2006 (Fig. 1), with the status of
salmonid species upstream run and number ofspawning

beds

monitored

threeyears

aftermodification.

Fig. 1 Rivers in the Shiretoko World Natural Heritage Site
2. Effects of modifications to river constructionsThe following is a description of the modifications to riverconstructions on four rivers that were completed by 2010, and their effects.
1) Sashirui River
Year of modification

No. of structures modified

Modification method

2007

2Modification of existing fishways

There were two existing fishways on the Sashirui River, but their structure was not conducive to fish run.
The structures were modified so as to be suitable for upstream run (Fig. 2).

Ａ

Ｂ

Fig. 2 Before and after dam modification (modifications to existing fishways)
A: Before modification, B: After modification◆Effects of modification
The beneficial effects of the modification of the fishways were verified through observation of the numberof salmonid species spawning beds upstream from the modified river constructions. The number ofsalmonid species spawning beds upstream from the constructions had increased (Fig. 3).

Number of spawning beds

Number of spawning beds

a2007

2008
Year

2009

100

b
500
2007

2010

2008

2009

2010

YearFig. 3 Change in number of salmonid species spawning beds on the Sashirui River after modification ofriver constructions(2007 data indicates the number of spawning beds before fishways were modified)a: Pink salmon (Oncorhynchus gorbuscha) b: Chum salmon (Oncorhynchus keta)

Fishwaysmodified in 2007.

2) Chienbetsu River
Year of modification

No. of structures modified

Modification method

2008, 2009

2New fishways installed

There were two erosion-control dams built on the Chienbetsu River, but no fishways were installed,
rendering salmonid species upstream migration difficult. For this reason, new fishways were installed(Fig. 4).

Ａ

Ｂ

Fig. 4 Before and after dam modification (installation of new fishways)
A: Before modification, B: After modification◆Effects of modification
The beneficial effects of the modification of the fishways were verified through observation of the numberof salmonid species spawning beds upstream from the modified river constructions. The number ofsalmonid species spawning beds upstream from the constructions had increased (Fig. 5).

Fig. 5

Change in number of salmonid species spawning beds on the Chienbetsu River after
modification of river constructions(2008 data indicates the number of spawning beds before fishways were modified)a: Pink salmon

b: Chum salmon

Fishways modified in 2008 and 2009.

3) Iwaubetsu River
Year of modification

No. of structures modified

Modification Method

2006 – 2010

6

Opening slits and cutting down height

Five erosion-control dams and one water channel were built on the tributaries of the Iwaubetsu River,
rendering salmonid species upstream run impossible. For this reason modifications to these six
structures were performed, consisting of opening slits and cutting down height of dams (Fig. 6).

Ａ

Ｂ

Fig.6 Before and after dam modification (opening slits)
A: Before modification, B: After modification◆Effects of modification
The beneficial effects of opening slits and cutting down height were verified through observation of thenumber of salmonid species spawning beds upstream from the modified river constructions. The numberof salmonid species spawning beds upstream from the constructions had increased (Fig. 7).

Fig. 7 Change in number of salmonid species spawning beds on the Iwaubetsu River after modificationof river constructions(No data on the number of spawning beds in 2007)
a: Pink salmon b: Chum salmon

Fishways modified from 2006 to 2010.

4) Rusha River
Year of modification

No. of structures modified

Modification method

2006

2

Opening slits

There were three dams built on the Rusha River, and the two upstream dams were cut down and/or had
openings cut in them to enable freer migration for salmonid species which run upstream (Fig. 8).

A

B

Fig. 8 Before and after dam modification (cutting down height and creating opening)
A: Before modification, B: After modification◆Effects of modification
The beneficial effects of cutting down height and creating openings were verified through observation of
the number of salmonid species spawning beds upstream from the modified river constructions. The
number of salmonid species spawning beds upstream from the constructions had increased (Fig. 9).

Fig. 9 Change in number of salmonid species spawning beds on the Rusha River after modification ofriver constructions
a: Pink salmon, b: Chum salmon

Fishways modified in 2006.