Fish Ladders vs. Flying Fish, Which Works Better?

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The sight of a Chinook Salmon being shot out of a duct on a river in the Pacific Northwest would probably startle famous early 20th century conservationist Aldo Leopold. But then, the massive number of dams on U.S. waterways in the 21st century would probably shock him as well. This modern age has brought many changes. The rampant development, damming and, sadly, destruction of wild rivers demands attention and a bit of ingenuity. And yes, these modern inventions can also be astonishing.

Ladders and Lifts

There are some 80,000 dams in the United States. Of these, about 10% have fish ladders. In a February 2015 post I discussed the value of hydraulic numerical modeling in the design of fish passages and ladders using US Army Corps of Engineers HEC-RAS water surface profile software. The fact is that fish ladders and lifts are still the primary way of helping fish move upstream and it is worth designing them as efficiently as possible. But, the first ladders were installed some 60 years ago and there lies the problem. The design of the fish ladder has remained substantially the same over that same span of time.

Alternatives to the traditional methods of moving fish have lately appeared. Whoosh Innovations, LLC, headquartered in Seattle, Washington has been quietly working on a fish transport system over the past four years that moves fish with minimal stress and minimal human intervention. How do the two systems of moving fish compare?

Do Fish Ladders Work?

Recent research shows that fish ladders are actually pretty poor at moving fish. A team of scientists examined the rate at which Atlantic salmon, American shad, river herring and other species were able to make the trip from the ocean to historic spawning grounds on the Susquehanna, Connecticut and Merrimack river in the Northeastern U.S., notwithstanding the stretch of dams in between. (Visit the article here for the full text.)

Poor Rates of Clearance

An analysis of historic records spanning a period of 30 years showed that in fact only a fraction of the fish successfully completed the trip. Less than 3 percent of one species, American Shad, made it past all of these dams. Other fish that migrate up river to spawn fared equally poorly. Biologist and co-author John Walden points out that the total number of fish being tracked is already much lower than the historic numbers of fish that migrated prior to European colonization. While there are a number of variables that might explain these declines, Walden suggests that the general consensus among fish biologists is that dams are primarily responsible. Fish may successfully navigate one ladder, but the likelihood of successfully clearing all of them is much less.

How the Wooshh System Works

The system is quite simple and consists of only a few key parts. At first, flowing water attracts the fish to the entrance of the system. Then a small blower gently pulls the fish into the flexible conduit and in so doing triggers the deployment of an air tube attached to the blower. The tube introduces positive pressure behind the fish and the seal that is created within the tube, combined with the pressure differentials, pushes the fish up the conduit. The fish travel at about 20 feet per second (i.e., 13 mph) which means that most of their trips are just a few seconds long. The FDA approved tube is kept moist although the method of transport is actually quite dry and uses little water.

Although the basic technology was first developed for the fruit processing industry, its application for fish transport is actually quite new. Extensive research in 2015 by a number of private and public agencies has confirmed that Wooshh Transport in most cases performs as well as or better than most other methods. Studies have confirmed that the fish experience minimal stress or injury, no mortality and that their reproductive condition is unaffected.

Changing the Fortunes of Fish?

Following the many positive results established by independent studies, the idea now only has to gain momentum. Two Wooshh conduits have been purchased by Troutlodge, Inc., the world’s principal producer of trout eggs, and were installed early in 2016 for the transport of Rainbow Trout broodstock. Other projects are in development. Let’s see this technology make a difference. Let’s see those fish fly!

Also Read: Design of Fish Passages & Ladders with HEC-RAS