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Making decisions for fish without thinking like them


I got to sit down with my wildlife enthusiast, lover-of-learning, friend Jes Welles, and pick her brain about fish. Jes is a biologist with an avid fondness for the Delaware River and its incredible natural history. One thing in particular that fascinates her is fish and how they interpret and live in their aquatic world—or, what she would call “fish intelligence.”

“The more I learn about them, the more I’m blown away, and left thinking... fish are pretty smart. It’s a different kind of smart, but, nonetheless, there is some kind of intelligence in fish. The way they can read cues in the water, remember good spots for food or cold water, find their way back to the water they hatched in, communicate with each other, avoid predation, change sex if they need to. They feel pain, they learn… just wow, right?” she said.

She would even argue that, as humans, we may not always make the right decisions in regards to fish, because we can’t possibly understand the world they live in the way they do. We can try to understand to the best of our abilities, but the way we interpret our world and theirs is through completely different sensory pathways. Although some of our intentions might be in the right place, humans might not be thinking like a fish as much as we should when we make decisions for them.

One of the biggest impacts she thinks humans have had on fish is our alteration of waterways that interrupt aquatic connectivity. What does this mean? Humans have altered waterways with road construction, bridge construction, culverts and a whole lot of dams. In doing so, waterways lose their aquatic connectivity, and the aquatic life that used to flow up and down is interrupted. Sometimes, whole populations of organisms get stranded and are cut off from their natural way of life.

“Imagine you’re just hanging out in the water, staying away from all of that noise/vibration downstream of you, and when it finally settles down you start swimming back downstream and bam! Now there’s a dam there and you’re stuck living above it,” she said. “Regardless of whether you’ll be living in a lake now with some streams trickling in, or you’re just stuck in a section of a stream or river, doesn’t’ seem very fair to the fish.”

Both reservoirs and hydropower often have minimum flows that must be met, but in systems where water is being conserved for specific purposes, fish are often not high on the list of priorities. In the case of hydropower, she thinks that has to be a confusing situation for fish trying to reach their natal waters, especially if that natal water is above that dam.

“To a fish trying to get upstream, I would think that the water being churned out for hydropower must ‘smell’ like all of the water [that’s] dammed off. There have even been American shad in the tailrace [the water channel below the dam] of the Rio reservoir on the Mongaup River. Besides their innate sense to swim upstream, why would they be there? I can’t help but wonder if it might be something about how that water ‘smells’ to the fish. It wants to go home in a sense,” she said.

The last thing she mentioned about human impacts to fish populations was the introduction of invasive species to the river. Over time we have introduced a number of non-native fish to the Delaware River, most of which have become naturalized since their introduction. Some of those fish species are now vitally important to the economy of the Delaware River, but they have unfortunately also become one more predatory species to our native species.

“And that’s just from the fish side of things. Now that I’m learning more about all of the other devastating aquatic invasive species that can completely ruin an entire river and its aquatic ecosystems, I hope that we make smarter decisions. Something simple that everyone should do is be more mindful of cleaning their equipment, shoes, boats, etc. before they enter a water body. Just because it’s not the world we live in, doesn’t mean it’s okay to ruin it for another organism.”

Check out our annual Fish supplement in this week’s paper.

Protecting the river against invasive species

New York State Department of Environmental Conservation regulations prohibit the launching of undrained boats (or boats and trailers with visible plant and animal material attached to them) at any DEC boat launch facility. Additional county or town ordinances prohibiting the transport of aquatic invasive species are in place in many areas. Please make sure that your boat and trailer is cleaned of attached plants and animals prior to leaving your home. This ensures that your boat does not spread aquatic invasive species and is in compliance with these laws and regulations. All water-holding compartments should also be completely drained.


The Main Stem of the Delaware River is the longest un-dammed, free-flowing river east of the Mississippi, extending 330 miles from Hancock, NY to the mouth of the Delaware Bay where it meets the Atlantic Ocean. The river is fed by 216 tributaries. Its main tributaries in New York are the Mongaup and Neversink rivers and Callicoon Creek. From Pennsylvania, the major tributaries are the Lackawaxen, Lehigh and Schuylkill rivers.

Tributaries that are dammed include the river’s East Branch to form the Pepacton Reservoir, the river’s West Branch to form the Cannonsville Reservior and the Neversink River, which forms the Neversink Reservoir. New York City gets roughly half of its drinking water from these three reservoirs, which together impound 270 billion gallons of water. Over 13 million people, including about five million in the New York City area and northern New Jersey, rely on the waters of the Delaware River Basin for drinking and industrial use. The Delaware River directly supplies drinking water to the cities of Trenton, NJ and Philadelphia, PA

For a map of the reservoirs listed above, see:



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