Fish Ladder: fairground for fish

Fairground for fish: a solution to help navigate man-made barriers

Image credit: Whooshh Innovations

A new solution to help fish navigate man-made barriers in our rivers whisks fish over dams in seconds almost before the fish are aware of it.

Many fish species such as salmon or eels must complete journeys of thousands of kilometres, returning upriver from the sea to spawn as part of their life cycle. On their way, they must overcome man-made barriers like hydroelectric dams, locks, sluices, or weirs that block their passage to the spawning grounds upstream. There are about 85,000 dams in the US, and 600,000 barriers to migration along the rivers of Europe, an obstacle at almost every kilometre of river. It’s not easy for migratory fish. Their numbers have declined by 75 per cent over the last 50 years. They need all the help we can give them.

Originally designed to help fish traverse weirs or dams, fish ladders or fishways have been around since the 19th century. They do not always work effectively for all fish species or even in both directions. Some species need to travel upstream then return downstream, but hydropower companies were still installing one-way systems into the 1960s, effectively evolving animals from spawning many times over the course of their lifetimes into one shot breeders. Even if the design and installation of a fishway is passable in both directions, an installation that works for Atlantic Salmon might be impenetrable to an eel or sea trout with quite different swimming abilities.

To find out how salmon in one river coped at a fish ladder, William Twardek of Carleton University in Canada studied how Chinook salmon in the Yukon River in Alaska fared as they used a fish ladder to circumnavigate the Whitehorse Hydroelectric Dam – some 3,000km into one of the world’s longest fish migration and the last obstacle on the river before their spawning grounds. The fish ladder was built in 1959, completed soon after they finished the dam, and is the longest wooden fish ladder in the world, according to Yukon Energy. Using telemetry to track tagged fish, Twardek discovered that only a third of the fish attempting the ladder actually made it past the dam to spawn. “These salmon made it all the way upstream from the ocean and were so close, but then didn’t get to reproduce like they should have. Anything we could do to help get them to their spawning sites so that they reproduce would be useful,” he says.

Those that make it can exhaust themselves – traversing a fish ladder can leave them energy depleted at a critical time when they need to be fit to breed. Jumping up a fish ladder alongside a dam is a bit like a marathon gym workout for a fish, much like someone choosing to climb the stairs in a tall building versus jumping in the lift.

E&T spoke to co-founder of aptly named Whooshh Innovations, Vince Bryan III in Seattle, US, about his fish-friendly transporter. Recognising the scale of the problems facing migratory fish, whose numbers are falling across the world, Whooshh Innovations devoted themselves to developing new, lower-cost technology and solutions.

Essentially, Whooshh is a flexible tube with an entry point at the bottom of the barrier. Here, they photograph the fish in a wet airlock component at high speed, and machine learning measures each fish and directs it to a best-fit tube, the transport tube itself, and an ejection zone where the fish might be braked to ensure a safe re-entry to the river above the dam. “It’s a voluntary process for the fish. We create an attraction flow or current where we want the fish to enter the system. We sit it in an area where the fish will naturally aggregate or rest in front of the barrier. They will find the entrance by themselves,” Bryan explains.

Once inside, the fish enter a dewatered and misted wet airlock where they are photographed at high resolution at high speed 18 times from three angles, using both infrared and visible light. In less than half a second, the technology identifies the fish by species, and its girth measured. It is important to dewater the photography area to enable its use in even turbid waters. One unexpected result of the library of high-resolution images has been that fish biologists have been able to quantify sea lion and seal attacks on the beleaguered fish, helping to inform fisheries policies on predator control. A sorting algorithm then either sends the fish forward to an appropriate diameter tube for its journey up and over the barrier or rejects it as an undesirable alien species and sends it back to the river, denying it passage. The company must train the algorithm on hundreds of images of fish from each river over a period of months. This is important so that fisheries authorities can stop invasive species continuing upriver and competing with the valued native species like Atlantic salmon or Chinook for food and spawning sites. Fisheries managers will decide whether to remove the invasive species altogether, or return them to the river. The system can handle 60 fish a minute, more than enough for a busy migration.

Once in the Whooshh system, fish glide through a soft and flexible misted tube that conforms to the fish’s body, forming a seal around it. A pneumatic pressure differential in front of and behind the fish whisks it along at about 8m/s. On the Priest River rapids and dam on the Columbia river, Washington State, the average passage time for a fish heading up the fish ladder is over 23 hours, the Whooshh system whizzes them through in an effortless and stress-free 2.55 minutes. The fish move through the minimal friction system so fast that they barely know that they are out of the water, and their gills remain healthy in the mist. Towards the end of their brief traverse the fish pass a speed trap, which measures their speed. They bleed pressure off to slow the fish before they squirt out of the system in a gentle re-entry to the river and swim off obliviously upstream to complete their life cycle. The short duration transit means more of the animal’s energy is available for better spawning success upstream. As Bryan says: “They swim in, they slide, they glide, and they swim off. There’s no shock to their system.

“There is virtually no theoretical limit to the height that Whooshh can move fish over a barrier. We could send them up vertically, but our specifications call for a 40-degree angle or less. We do this to assure the fish are not stressed and to increase the size range of fish for a single tube. If the fish were to go straight up it could stress them as their circulatory systems are not designed to counter gravity and their blood could pool toward the tail,” says Bryan. 

The tallest dams in the world are almost 300m high, easily surmountable for the technology. Another benefit to hydropower users of the system is that it uses very little water. The fish-friendly tube transporter is also quick to install, and costs 20 per cent of a conventional concrete fish ladder and has considerably less environmental impact on often remote riverside sites. Being whizzed through a tube in seconds is an easy ride for fish, and that reduced energy use translates into more spawning success, helping to replenish depleted fish stocks.

The Whooshh Innovations system caught the attention of Marco Blixt, fisheries biologist at Finnish energy company Fortum, who had a very specific situation at the Höljes Forshaga Hydroelectric power station on the river Klarälven in Sweden. The complex is only 5-6m high, but there are eight consecutive dams between Lake Vänern and the remaining spawning grounds. The company had been trapping and transporting fish by truck over the 80km span of barriers since the 1930s as swimming up conventional fish ladders over such a length of obstacle would exhaust the fish. “We installed the system in 2020, it is a low stress on the fish, and on our staff. Some big salmon weigh 8kg, handling them manually was labour intensive, and stressful for the fish,” says Blixt.

During the spawning run, Fortum see 30-60 Atlantic salmon and trout every 24 hours attempt to pass the power station. Using the first Whooshh installation in Europe, last year saw the company move 1,600 spawners, or about five tonnes of fish, around the Höljes Forshaga dams. During the off season, Blixt just rolls up the flexible tube and stores it until next year. “It is very easy to use,” he explains, “and is very site specific. We are looking at other sites where we might lift the fish over our other dams.”

One thing that Fortum had not anticipated was the keen media interest in the project. “We had local and national news organisations keen to cover the story, generating a lot of good PR for us. As an energy company positive PR is sometimes in short supply,” he says wryly. “I think that it’s the concept of squirting fish through a tube that captures the public’s imagination. The reaction certainly took us by surprise.”

The real beneficiaries of the technology are our freshwater fish. Their populations have declined catastrophically over the last four decades across the globe. Dams are a critical component for green power generation, and there is no reason they cannot coexist alongside healthy fish populations aided by a helping hand up and over exhausting barriers.

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