This is a web page of the following research project:

The Sumitomo Foundation Research Project
A novel monitoring technique for the endangered Sakhalin taimen (Salmonidae)
Project leader: Michio Fukushima (The National institute for Environmental Studies, Japan)
Research period: Apr. 2012- Mar. 2014

Project Outline

This project aims to develop a technique to monitor the endangered Sakhalin taimen populations in Hokkaido, Japan. We deployed a high resolution sonar video camera, DIDSON, in a small stream in Hokkaido, Japan, to count upstream migrants of this species. The DIDSON enables accurate enumeration of fish in highly turbid waters and/or during night time, the conditions under which ordinary video cameras such as the ones with CCD fail. The DIDSON data and the resulting scientific findings will be used to improve our understanding of the ecology of this rare salmonid as well as to improve the fish passage structure (i.e., fish ladder) at the monitoring site and to propose a time period when people, especially fishermen, are discouraged to disturb their spawning activities. We started the field survey in early April 2013 and finished in late May, producing some interesting findings with respect to the migration and spawning behavior of the species.

Cooperative institutes/ Co-funder

What is Sakhalin taimen?

Sakhalin taimen, or “itou” in Japanese, are a salmonid inhabiting Hokkaido and Far East Russia. They are recognized as the largest freshwater fish in Japan. They spawn in spring and are the only spring spawner among all the native salmonids living in Japan. Their distribution and abundance have shrunk and dwindled in recent years, leading to their red list status of Critically Endangered by IUCN and Endangered by the Ministry of Environment, Japan.

For additional information about itou, visit “Sarufutsu Itou Conservation Council” web page.

Sakhalin taimen(photo by Mikio Abe)

A female itou digging the gravel to lay eggs while guarded by a male spawner.
(May 11th, 2013, photo by Dr. Pete Rand)

Pictures of DIDSON deployment in 2013

In spring, stream and river water rapidly increases due to melting snow in Hokkaido. This is when Sakhalin taimen begin their upstream migration for spawning. Their population size has never been accurately counted even though they have long been believed to be in danger of extinction. We deployed DIDSON at two locations in a small stream in northern Hokkaido to count the number of individuals in the spawning run and to explore how migration behavior might be influenced by environmental factors like temperature and flow.

DIDSON (Dual Frequency IDentification SONar)
Courtesy of TOYO Corporation


A metal frame is being built for DIDSON installation with the help of a local conservation group “Itou-no-kai”


The site for installation (a surveillance camera was also installed).


There is some risk in deploying the equipment.


On the left is an under-water CCD camera, and on the right is the DIDSON (both beneath the wooden board).


Checking a computer monitor for correct setting using an “itou model”.

Sarufutsu_More 037_S.jpg

Here is a problem! One of the culverts located upstream from the installation site was completely clogged with woody debris.

A video clip from the DIDSON data

Courtesy of TOYO Corporation

You may need to install a plug-in to watch this video depending on the browser

Two itou recorded by DIDSON at around 10pm on May 7, 2013. Both are close to 1 meter long. This fan-shaped image of DIDSON output is akin to a sonogram you can find in a hospital. The principle is basically the same: the DIDSON sees a fish in the complete darkness in the river just like a sonogram reveals the image of a human fetus in a women’s womb. DIDSON operates at 1.8 MHz and uses 96 beams each spaced at 0.3° to produce a high resolution image of underwater objects. It is interesting to see the “shadow” of sound as shown in this video clip. Being able to study a rare aquatic species such as itou without putting any stress on them is one of the great merits of this technique.

Other videos

Hit the buttons to watch.

Recorded on May 7, 2013
(courtesy of TOYO Corporation)

A synthesized video clip from a side-view image and a longitudinal view from upstream
(Courtesy of Asada Laboratory, Institute of Industrial Science, University of Tokyo).

Count results of migrating itou in 2013

Itou counts 2013_s2.jpg

Seven individuals of itou were the first detected by DIDSON on April 23, 2013, and the last was on May 14 with a total number of 335 itou enumerated over a period of approximately 3 weeks. The daily counts (and the total) encompass nearly 100 percent of the itou that up-migrated. This is because the narrow upstream outlet of the fishladder where the DIDSON was installed guarantees the detection of all the individuals passing in front of the sonar and because no individuals were detected down-migrating until the end of the spawning season. Therefore, this technique provides nearly a complete census of the spawning population, a feat rarely accomplished in fisheries research.

There were two peaks in the daily counts; the first occurred on April 29 with 47 fish passing upstream and the second on May 4 with 54 fish passing upstream. Water temperature fluctuated between 3 °C in the evening and 8 °C in the daytime during the spawning season. However, the water temperature declined precipitously from May 1 to 2, and this was accompanied by a marked decrease in fish passage at our site. We hypothesize that this reduction in water temperature slowed the upstream progress of spawners.

Although being in danger of extinction in many rivers throughout their natural range, our work suggested the population in this Hokkaido river may actually be flourishing. We should consider this great news and a positive conservation story! However, it is important to realize that the range of the species in Japan has shrunk dramatically over the past 50 years. The species used to be found in nearly 50 river systems in Japan; today, the species can be found in only about a dozen rivers and the habitat in many of those rivers are in a very degraded condition. Some think it is a miracle that the species, one of the largest salmonids in the world, still survives at all in Japan. Through our study we hope to learn more about why the population in our study river continues to remain healthy, and how we can keep it that way. In addition, we hope this work will help us develop more effective ways to recover populations that are close to extinction.

Last updated 2013-June-18