HN Reader

I have a guy in my family who worked to remove dams over a small tributary river of the Seine, in Normandy, France. It took him several years to remove the 300+ dams, the oldest ones being easily 150 years old. The very first year after his work was completed the salmons came back.

Now he works in the environmental police, and is often called to handle cetaceans getting lost in the Seine delta. People freak out because it is an unusual sight nowadays, but he told me this is just a return to how things were. They are stories of dolphins swimming as far back as Paris in the past centuries.

I guess this means we're doing something right, I hope one day we'll be rid of this poisonous brown opaque water flowing through our cities. I really hope one day to be able to see this "clear water" my grandpa told me he learned to swim in.

Lots of discussion about salmon memory and such, but is it possible this is just Salmon finding "hey this is a great spot"? It is hard to imagine salmon not being flexible to some extent, and still surviving.

>Less than a month after four towering dams on the Klamath River were demolished, hundreds of salmon made it into waters they have been cut off from for decades to spawn in cool creeks

Do we understand the mechanisms of this "genetic memory" (my words, no idea if its accurate or if there is a better word for it)? Butterflies knowing where to fly even though it was their grandparents that last did it - eels traveling thousands of miles to breed in a place theyve never seen - countless bird migrations - even something as simple as how it takes a human baby 12-18 months to walk but many animals walk as soon as they are born. I would love to understand better how this knowledge is inherited

I read a fascinating article on this dam removal last week! https://hakaimagazine.com/features/the-other-side-of-the-wor...

The article tells both sides of the story of the dam removal in as fair a way as I think is possible. Many of the locals were against it and there was a strong advocacy group that fought for it, including a tribal constituency.

I came away from the article feeling I understood both sides better but with less certainty about what was the right choice.

Animal behavior usually has a weird combination of inborn instinct and learned behavior.

The one I've read about that stuck with me was dam building by beavers. Some part of the behavior is driven by a dislike of the sound of running water. Someone did an experiment with speakers playing the sound of running water and the beavers near the speakers would attempt to cover them with sticks and mud.

In my head I'm imaging that sound is like nails on a chalkboard to beaver.

I'm surprised we could never engineer a proper salmon "elevator" to bypass the damn. Given the price of removing the damn, there seems to be a huge budget for creating some sort of high-tech Robo-elevator to scoop the fish out and drive them way upstream in a robo-vehicle.

Maybe a giant net that lies at the base of the damn, and periodically lifts out of the water to catch the fish and automate the transportation of them to ideal next step drop.

I'm lucky enough to have a salmon-bearing stream on my property here in the northwest. They are an extremely inspiring species to watch through their lifecycle. Tenacious.

All these dams on the Klamath river did have fish ladders where the salmon could go upstream and spawn. Removing the dams just increased the number of fish swimming upstream. Some of the fish ladders had glass walls and people could watch the fish going up & down the ladder.

Here in coastal British Columbia, it’s the removal of ocean fish farms that has sent the dwindling numbers of pink salmon soaring again!

I'm most curious about how the salmon found it so fast.. Did their instincts predispose them to go there, if they were in the area? or was there some physical trace they were following? or is there some weird lamarkian genetic memory thing going on? .. In fact do we know now salmon normally navigate 1000's of miles back to their spawn location?

FYI the podcast Gastropod did a really good episode on the dams & the salmon

[1] https://gastropod.com/bringing-salmon-home-the-story-of-the-...

There are systems to allow salmon to go over dams. From ladders to cannons.

I hope they are right about this dam not needed for flood prevention. Spain just lost hundreds of people and suffered billions in damages because these kinds of policies.

Hydropower is the only true renewable green energy that we have. It's ironic that dam removal is so popular with people who claim to care about green energy and the environment.

for the past few years i've been watching the salmon return to a spot in the uk they've not been to for over 200 years. i had no idea growing up there that these were salmon spawning grounds, then some wiers were removed. such a wonderful thing to see. i don't think it's memory!

How do they know? I thought salmon always return to the same river, so a river no salmon come from won't get any returning, but I guess a certain percent are adventurous?

I thought that project already had salmon spillway weirs.

I wish the environmentalists would make up their minds.

Either they want clean power from hydroelectric dams or the don't.

salmon have the right to return.. but humans don't?.. watermelon..

Hopefully the Snake river is next.

This is only tangential but with more solar and nuclear, more and more projects like this will become possible.