4 Things You Should Know About Electrofishing

Anytime I talk to someone about the research we’re conducting, I get a nearly identical response almost every time I start talking about electrofishing. Whether it’s someone in my family, one of my friends back home in Pittsburgh, or just some random person who’s curious as to why we’re trudging through the backwoods with all kinds of weird equipment, their reaction to hearing about “electrofishing” usually sounds something like this:

“You electrocute the fish?!”

Either that or they call it cheating, if they’re fishing enthusiasts. Well, it’s not as simple as that – there’s actually a lot to understand about electrofishing. Of course, a month ago I didn’t know anything about electrofishing, and I would have probably reacted the exact same way if I had heard someone talking about it. So, just like yesterday’s post on fracking, I thought it might be helpful to explain a thing or two about electrofishing and how it works.

4. It doesn’t kill the fish

This has to be the most important thing to understand about electrofishing – when done correctly, the process does not kill the fish. Electrofishing is a very common technique used by biologists to survey populations of freshwater fish. This is accomplished by using the equipment to temporarily stun the fish so that they can be collected. There are a few different kinds of electrofishers, but what the Grant Lab uses is a Smith Root backpack model.

Jacob wearing the electrofishing equipment

Jacob wearing the electrofishing equipment

Backpack models can be powered by either a battery or a generator (we use a battery). The backpack sends a pulsed electrical current into the water, which is delivered by two electrodes – an anode (the positive electrode) and a cathode (the negative electrode). On our model, the anode is the diamond-shaped metal ring at the end of the pole, and the cathode is the braided metal cable which is meant to drag behind the person who is electrofishing. Current travels from the anode, through the water, then back through the cathode. The final result is that fish around the anode end up getting stunned (but not killed).

3. It’s not as easy as it sounds

What I’d like to address next are the people who believe electrofishing to be an excessively easy means of catching fish. Obviously we’re not doing this for sport – we can’t sit around all day with fishing rods, trying to catch enough fish so that we have an adequate amount of data; we have to be efficient. That being said, electrofishing is actually much more difficult than it sounds.

photo (6)

You see, with the right amount of current, the fish will go into taxis – an involuntary muscle response that makes the fish swim towards the anode. As the fish get closer to the anode, they will eventually go into narcosis and float belly up, stunned (this doesn’t just happen with fish, actually: we sometimes come across stunned frogs, salamanders, and even snakes). However, narcosis only lasts a few seconds, at the most; if we’re operating at a low voltage, the fish might only be stunned for a split second. After the stun has worn off, the fish do everything in their power to get as far away from us as possible. This is what makes electrofishing challenging, because we only have a short window of time to try to net the fish before they escape under a rock, stump, or upstream. It can be difficult, but it’s also kind of fun.

2. The entire body of water does not become a blanket of electricity

Another important thing to understand about electrofishing with a backpack unit is that it only works in a limited range; it’s not like we stick the electrodes in the water and flip a switch and suddenly everything in the stream is stunned. What happens is that a transformer actually makes the current pulse out into the water, in waves, in the shape of the anode – so, in our case, a diamond. All the water within a meter or so of the anode will be shocked, but beyond that, the current is no longer strong enough to do anything.

photo (2)

A stunned brook trout

But still, we have to be careful, because if we touch the water near the electrofisher, we could also be shocked. Thanks to the thick rubber waders that we wear in the water, we won’t get shocked while walking around the stream. We don’t generate enough current to seriously hurt a fish, let alone a human, but just to be sure there are plenty of safety precautions built into the equipment to make sure that no one gets shocked – including audible beeping that lets everyone know when the electrofisher is on, and a failsafe that turns off the electricity if the backpack becomes submerged or is tilted more than 45 degrees. There is also an on/off switch on the anode pole that is operated by whoever is wearing the equipment.

1.  The majority of fish are released back into the stream

As we stun and net fish, we place them into a bucket full of water to await processing. Once an adequate stretch of the stream has been electrofished (or if we’re running out of room in the bucket), then we can start processing the fish. While we keep track of the number of each fish species we catch, we’re mostly interested in trout. Any brook trout or brown trout that we catch are measured and their length and weight are recorded. Sometimes getting this data can be difficult, especially if the fish is being particularly uncooperative.

Me processing fish with Devin and Jen

After all the fish have been processed, we release them back into different parts of the stream. For the Marcellus & Mercury project, we do keep several brook trout per stream to analyze various tissues for mercury concentration, take morphemetric measurements, and determine age and food sources.

Hopefully that clears up electrofishing a little better for everyone. Who knows, maybe you learned something today! Feel free to post a comment if you have any questions.

– John Dubensky

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5 thoughts on “4 Things You Should Know About Electrofishing

    • Hi Jack,
      Thanks for the question. If the cathode and anode get too close or touch, there is an automatic shutoff to protect the unit from getting damaged.
      Chris

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