Can a Fish Climb a Ladder?


Wilsons Mill Fish Ladder, Deer Creek, MD | © Jessie Thomas-Blate

Jim Thompson (MD DNR) cleans out the top of a blocked fish ladder at Wilson’s Mill Dam on Deer Creek, MD | © Jessie Thomas-Blate

As part of our celebration leading up to World Fish Migration Day on May 24, 2014, today we are talking about fish ladders!

First things first— what is a fish ladder? The image conjured up in my mind is a little fish hopping from one side of its tail to the other up the rungs of a ladder, and holding on to the sides with its little pectoral fins. Of course, this is not what we are talking about with a fish ladder.

Many fish, such as shad and river herring, feel compelled to swim upstream to find the best habitat for spawning their young. Basically, a fish ladder is a structure that helps fish move upstream around a barrier in the river, such as a dam. Fish swim through fish ladders, which are theoretically designed to maintain enough water flow to attract fish, yet slow the flow enough to allow the fish to swim up the structure to the river above the barrier. If it sounds like a complicated balance, believe me it is.

To get an idea of what it might be like to be a fish travelling up a fish ladder, check out this video provided by Jim Thompson, with the Maryland Department of Natural Resources:

Now that you’re really “in the ladder” and “feeling fishy,” we can talk about the problems that are encountered when using fish ladders to aid in the migration of fish. First, as a fish, you have to find the opening of the fish ladder. OY! You will likely run into the dam a number of times before you happen upon the opening of the fish ladder because they are usually only a couple of feet wide.

Next, you have to swim your little fishy heart out to ascend the ladder. Some ladders have rest areas, but others do not. Some ladders also have twists and turns, so don’t get lost! Also, hopefully the top isn’t blocked off with debris from trees and plants floating down the river. People try to maintain a flow in the ladder that will allow you to keep swimming, while trying to avoid exhaustion as you make your climb. I can’t lie— it will probably be one of your hardest workouts.

But then… you reach the top of the ladder and you are ready to keep swimming up the river to your spawning grounds. I’m sure your honey is waiting for you there.

For some more insight into the trials and tribulations of fish laddering, check out this next video:

As you have gathered by now, there are many challenges that must be overcome to establish an effective fish ladder. In fact, some researchers have determined that some fish ladders just don’t work.  While the most ideal choice might be removal of a barrier, in some cases that is just not practical, as Jim describes in the video above. Consequently, we must continue to strive to improve the science and engineering of fish passage structures to give the fish the best chance of reaching their spawning grounds to ensure sustainable populations in the future.