Applying HEP to Evaluate Impacts of Kuma River Dam Removal Projects on Japanese Eel Populations

Hongwei Shi1 Hiroto Yagi2  Akira Tanaka1

1Tokyo City University Graduate Division, Graduate School of Environmental and Information Studies Yokohama, Japan

2EA International

Keyword: Dam Removal, Japanese Eel, Ecological Impact Assessment, Alternatives Analysis


1 Introduction

Yagi, Tsuru, Tanaka (2013) used Habitat Evaluation Procedures (HEP) to evaluate the potential effects on Ayu (Plecoglossus altivelis) habitats from removing the Arase and Setoishi dams on the Kuma River in Kumamoto, Japan.  The researchers determined that HEP was very effective method for studying habitat changes on a representative specie in an ecosystem.  This study used HEP to determine the potential effects of Kuma River dam removal projects on habitats of the IUCN-protected Japanese eel (Anguilla japonica).

The Japanese eel population is declining rapidly due to overfishing, the human destruction of eel habitats and impacts of global climate change.  More specifically, water quality deterioration and artificial river control projects have had a major impact on eel population (Tsukamoto, 2008).  Local fishermen and residents on the Kuma River have been concerned about the effects of dams the on the eel population since the dam construction projects started in the 1950s.  Until the recent introduction of HEP to Japan there was no objective method to study these effects.  This paper uses HEP to analyze the potential influences of Arase and Setoishi dam removal projects on Japanese eel habitats and makes recommendations to increase the quality of the habitats.

2 Methods

HEP can be used compare both qualities and sizes of species habitats in two ways: 1) simultaneously studying of multiple habitats in different locations, or 2) studying one location over a fixed period (Tanaka, 2012).  HEP study results are expressed in “Total Habitat Units” (THU) where:



HU   =    Habitat Unit

HSI   =    Habitat Suitability Index (0 to 1)


THU is the viability score of the total studied habitat area.  HU is the viability score for each subsample of the studied area. HSI is a composite value of several environmental factors which affect the viability of the subject species.  An HSI score of 1 is considered a ‘perfect’ environment, whereas a score of 0 is considered non-viable.  Five HSI factors considered in this study were: distance of upstream migration pathways; obstructions to migration pathways; concentrations of dissolved oxygen; and, pH and temperature factors.


3 Evaluation

The river supports eel populations in both the yellow and silver stages of maturation.  The primary factors affecting these eel populations are distance of upstream migration pathways and obstructions to migration pathways. This study considered three different scenarios and their potential effects on THU: 1) continued power generation at Arase and Setoishi dams; 2) demolition of only the Arase dam; and, 3) demolition of both the Arase and Setoishi dams.  This study used HSI models and normalized THU scores for each scenario in accordance with HEP procedures.  (See Table 1)


4 Conclusions

It is possible to use the HEP process to evaluate the effects of dam removal on Japanese eel populations and to quantify the qualities of specific habitats. HEP study results can be used when considering future river works. Specifically, HEP can be used as an alternative to, or in consonance with other Environmental Impact Assessments to determine habitat impacts of dam removal projects.


Table 1


Remove Arase Dam

Remove Arase Dam and Setoishi Dam

Quality of Habitat (THU)

Status Quo

To Be Good

To Be

Very Good



Hiroto Yagi, Shouko Tsuru & Akira Tanaka (2013), Applying HEP to Quantitative Habitat Impact Assessment for Dam Removal Projects – Case Study of Arase Dam Removal Project in the Kumagawa river;

J. .Japanese Soc. Shiranui &Kumagawa Reg.Stu Vol.7.No.1, 2013 pp.2-7

Katsumi Tsukamoto(2008), Present status and conservation of eel resources, Ocean Extra (48), 5-8

Akira Tanaka(2012)Theory and Practices for Habitat Evaluation Procedure in Japan

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