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Tracking the World’s Largest Salmon With Sonar

 

Members of the Sarufutsu Itou Conservation Group work on building a frame on the river bank to support the acoustic camera.
Members of the Sarufutsu Itou Conservation Group work on building a frame on the river bank to support the acoustic camera. (Photograph by Pete Rand)

Onishibetsu, Japan – I’ve learned to be patient.  A skill honed as an obsessed fly fisherman years ago.

Lately, though, I don’t use a rod and reel to stalk fish.  The challenge of “catching” them with sonar I find much more gratifying.  Consider it the most benign form of “catch and release.”

I’m in a corner of northern Japan that is home to one of the most enigmatic fish around – known locally as itou (“ee-toe”).  These fish, more widely known as taimen (“TIE-men”), split early from the salmon evolutionary tree.  These ancient fish are found only in Asia. One characteristic certainly sets them apart from all others in the great salmon family – they are the biggest, capable of reaching over 2 meters (6 feet) in length and living over 30 years.

I think it was an historic accident that we gave the largest North American salmon the common name of king salmon.  Taimen are much more deserving of the crown, in my humble opinion.  They are, however, endangered.

My Japanese colleague, Michio Fukushima, and I have been working together for some years now, devising a more foolproof method of counting these fish.  Conservation is a tricky enough profession, but when you are dealing with fish, it’s very hard, if not downright impossible, to get solid data on numbers in the population.  It is not like counting trees or deer… fish are basically invisible and most migrate in mysterious ways.  Devising ways of counting fish is an obsession to many fishery scientists, myself included.

Michio started years ago on foot, hiking along headwater streams looking for itou nests (small gravel depressions on the river bottom created by females), carefully recording their location and mapping them – thus providing some rough measure of how many adults there are in the river.  Realizing first-hand how hard this was, and recognizing the limitations of this method, he then explored a different method to count itou from a plane.  That didn’t work out.

Trying Sonar

I first met Michio back in 2006, and suggested we might try sonar.  It has been used for many years in the great salmon rivers in North America, but I was not aware of any work of this type in Asia.

Fast forward to spring 2014, and we are poised to count the entire spawning run in one of the best itou rivers in Japan, the Sarufutsu.  The river is now under conservation protection by the largest paper company in Japan and it holds the greatest hope for saving the species here.  They have lost ground over the last 50 years and the threats continue to mount.  Saving the best of what’s left is a smart conservation strategy.

Sonar image of fish
The acoustic camera sends out 128 narrow beams of high-frequency sound, and the echos received are assembled into a stunning, high resolution video image. (Image by Katsunori Mizuno/University of Tokyo)

Our objective is simple: establish a current abundance “baseline,” and use that as a reference as we work to improve the situation for itou.  Emboldened by our success last spring, we are feeling confident that we’re on the right track now.  Last weekend, with the help of the devoted members of the local itou conservation group here, we got our “magic camera” in the water.  This sonar is capable of producing high-resolution video images from sound.

It sounds gee-whizzy (and it is!), but it turns out to be the ultimate fish finder for us in our quest to count itou.  There are great video cameras on the market now, but none can see through muddy water or search the bottom of a river at night.  Our “magic camera” can.

So, with the sonar now in position just downstream of the spawning grounds, we wait for the arrival of itou.  Last year our first itou arrived on Earth Day (April 22).  I write this dispatch on April 21, with no sightings yet.  As the days get longer, the snow melts and the water warms, I suspect we’ll see our first itou in the next couple of days.  Until then, I wait patiently.

Taimen in Sarufutsu River Japan
Once through the fishway and counted by our sonar, spawners enter a beautiful forest. Shown here are two itou spawners (male on the left, female on the right). The Sarufutsu River is one of the largest, undammed river systems remaining in Hokkaido. The river is now under permanent protection by the largest paper company in Japan. (Photograph by Satoshi Adachi)

 

Comments

  1. Cj Simmons
    Ny
    April 25, 2:59 pm

    Pete..you should set up machine vision stations using fiber optics as a cold light source. These systems are used by manufactures looking for defects in products like burned corn flakes..