Dam dynamics often fail fish

It seems strange how little we know about fish, their habits and whether the help we’re trying to give them is actually helpful

Allan BonnerMany of us who received our education on fish migration via TV nature programs have missed a few important things.

All I remember is that salmon can leap several feet in the air over cascades to get upstream to spawn.

Somewhere in these documentaries I recall an industrialist taking full credit for installing a fishway at a dam so we could have hydroelectric power, a lake for recreation and happy fish.

What I and the TV documentaries missed is all the kinds of help we’ve tried to give fish and how a lot of it doesn’t work. What’s also interesting is how little we’ve known about fish behaviour and how neglected serious study of it has been until recently.

The help we’ve tried to give fish may go back as far as the Middle Ages, when millers built dams to store water and to turn waterwheels. This helped supply food to a community by grinding farmers’ grain. But it interfered with another food source: fish. It evolved that millers had an obligation to provide a passage to help fish get up, around or over a dam.

There may have been lots of these passages built in the Middle Ages. The Doomsday Book, written after the Norman Conquest of 1066, mentions mills and dams in its survey of England and Wales.

The Canadian Maritime provinces and the New England states have plenty of small dams because of early industrialization and settlement by Europeans. Most now generate relatively small amounts of electricity.

Some old and small dams produce less electricity than a few solar panels or one windmill. And the cost of maintenance far exceeds the benefits of many small dams.

An open river with fish swimming freely may be the greatest benefit.

Laws evolved in some jurisdictions to require dam operators to compensate landowners if the dam blocked their access to fish. Some dam owners also had to construct fishways.

There are a lot of types of fishways, depending on the topography, height of dam, species of fish and other factors. Fishways have been built so fish can swim beyond a barrier to reproduce, rest, or spend the winter or summer in a suitable part of the waterway.

There are several fish ladder designs. One is a pool and weir (little dam). To go up a pool and weir ladder, fish have to rise above or leap up a series of relatively low steps into the waters above and on the other side of the weir.

There are other terms such as fish pass, fish passageway, and fish steps. Other designs look like locks, natural waterways and metal slides the fish swim up. All help the fish get up, through or over the big dam.

What seems strange is how little we know about fish, their habits and whether the help we’re trying to give them is actually helpful.

It’s been 1,500 years since the start of the Middle Ages and almost 1,000 years since the Doomsday Book’s reference to dams in England and Wales. Yet researcher John F. Orsborn of Washington State University, writing in 1987, noted we may be basing our help on “unproven fish swimming and leaping capabilities.”

Worse, he quotes mid-20th-century research indicating “it is almost impossible to prophesy the behaviour of fish and quite impossible to anticipate the vagaries of water.”

So other than not knowing much about fish and water, we were in good shape when most fishways were built.

Through trial and error, we found out there’s often more error. Quoting other research, Orsborn notes there is “much about it yet to be learnt – and unlearnt” and “many fishways were unsuccessful based more on intuition than on scientific and engineering endeavour.”

Prior to the construction of a dam, fish have the whole river to navigate their way upstream and downstream. The best fish passageway is an open river.

The entrance to a constructed passageway at a dam is small and hard for fish to find. Many never find it.

We build passageways based on many variables – topography, design, location, fish swimming ability, materials used, height of the dam and so on. Yet even in the 20th century, researchers documented that we knew little about what works or why.

It seems we spent lots of engineering time and money building fishways without considering “fish behaviour and preference,” according to Orsborn.

Something as simple as the number of fish expected wasn’t taken into serious consideration until the Hell’s Gate fishway was built in the mid-20th century on the Fraser River in British Columbia.

When those TV documentaries I saw as a kid showed fish leaping, apparently nobody was really sure why some fish leap. Some research suggested they prefer swimming, and there’s some evidence they can be encouraged to leap by shadows and the undulation of the water.

We’re now pretty sure some fish leap out of the water to avoid predators. Sturgeon leap to fill their bodies with air, perhaps to maintain buoyancy. Salmon leap to get over an obstacle on their way to spawning grounds.

But until recently, we inadvertently built some fishways to help fish do what they don’t normally do. We built others to do what they don’t want to do. Others are in the wrong spot or of a design that’s not enticing.

We seem to be learning in the 21st century, with some government guidelines based on interdisciplinary studies. But it’s ironic that this was after hundreds of years of building dams and fishways.

Canadian researcher C.M. Bunt from Kitchener, Ont., and some American colleagues have also called the design of fishways into question. Writing in 2011, they note that fish may be enticed into fishways more because of their own behaviour and biology “than structure type or hydraulics.”

So try as we might to build something that helps, the fish ultimately decide what works. In fact, these researchers say “data do not clearly justify recommendations for any particular fishway type.”

Worse, “the vast majority of fishway structures do not effectively mitigate the effects of barriers.” Even some early research results fall short. We can tell if fish approach a fishway, but without high-tech gear to measure, we can’t be certain “whether they actually entered the structure.” We’ve not been sure if fish don’t like the fishway entrance or the water flow inside.

Why bother with these complex calculations?

It turns out that the value of the fish and tourism may exceed the value of the electricity generated by many small dams. The cost of dam maintenance, safety and fishways may be far more than removing the dam and restoring a river, and replenishing the wild fish populations.

Getting it right is good business, economics and stewardship.

Ecologist Barry Commoner often gets the last word when I think of these kinds of issues. He coined four laws of ecology in the early 1970s:

  • Everything is connected to everything else.
  • Everything must go somewhere.
  • Nature knows best.
  • There is no such thing as a free lunch.

Relevant here is that our need for power is connected to our need for wild fish as part of the natural ecology. Dams were not a free lunch. We paid a huge price for many that are now abandoned, unsafe or provide small amounts of electricity.

And even after 1,500 years of trial and error, nature – and its fish – really do know best.

Dr. Allan Bonner, MSc, DBA, is a crisis manager based in Toronto.

Allan is a Troy Media Thought Leader. Why aren’t you?

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