ElectroshockingBy Judy Nugent - November 1, 2006
The southwest corner of the state boasts a large concentration of trout streams and the fish populations keep getting better. But it wasn't always this way. Back in the 1930's water quality and erosion were so bad that carp and suckers were showing up in the warm shallow streams. Thanks to land management practices and watershed initiatives, brown trout are well established and brook trout are making a comeback.
Electroshocking is an integral part of watching and maintaining these populations. Other methods of trapping fish, like seining, are not practical because of make up of the streams. Seining is more appropriate for larger bodies of water with shallow shorelines. Electorshocking allows the biologists to probe the Lunker structures that extend far beneath the banks as well as catch the fish in the center of the stream. DNR crews are able to capture 65% to 85% of the fish in the stream. This provides them with plenty of data to get an accurate picture of the health of the watershed.
How is it done?
Electroshocking begins with three DNR personnel in the water wearing chest waders. They are connected to a boat with ropes on spring loaded reels. This gives them the flexibility to walk upstream away from the boat. The generator on the boat is capable of delivering 240 volts or 6 amps into the water through the probes carried by the workers. (??? How powerful is 6 amps?) Hard water carries electrical current better, so in southwestern Wisconsin 3 amps is enough to conduct the shocking. (Sand counties in the north need more amps.) The probes emit a positive charge to stun the fish and underneath the boat is a rod with the negative charge that grounds the system. When the system is on, the electrical current extends 3 to 4 feet in all directions around the boat. The workers in the water have to wear rubber waders to insure that they don't feel the electricity.
To start the shocking, one member of the team stands right next to the boat. This person is responsible for towing the boat and operating the kill switch in case of emergency. The other members of the crew carry the probes and walk upstream. The tip of the probe is maneuvered through the water in a sweeping motion. The nearby trout are drawn to the DC current, much like a person who grabs an electric fence and can't let go. The worker brings the probe towards the net and quickly captures the fish. The workers then pass the fish from net to net back to the tub in the boat. When shocking a lunker structure, one worker goes to the top of the structure (upstream) and the second worker is at the bottom. They work together sticking the probe under the structure and netting all of the fish that come to the surface. When large boom shocking equipment is used on larger bodies of water, the whole structure can be shocked at once.
What do they look for?
Usually the DNR picks 1,000 consecutive feet of stream in which to do their survey. In this area the DNR team evaluates many things. They test the temperature, pH, conductivity, stream flow, and turbidity of the water. They take notes on all of the different species of aquatic vegetation as well as the type and concentration of invertebrates. Then they do a survey of all fish caught. This includes: species, size, weight, and year class. Fish collected through electroshocking on these trout streams can include 6 pound monster brown trout to 2 inch Stickleback. To keep the fish calm during the process, carbon dioxide is placed into the holding tank. This allows the team to get accurate readings on size and weight. With out this additive, the fish would be jumping out of the tank or off the scales. When the survey is complete and the data documented, a copy is sent to the regional director of the DNR. The regional director will then assess if stocking and/or if reclassification is warranted.
There are three types of classification that indicate the health of the trout population. Class 3 streams are basically put and take waters. The DNR stocks these streams because there is little to no natural reproduction found during electroshocking. Examples would be: few young of the year indicating poor reproduction or several young of the year but no survival to a subsequent year class. Class 2 streams have some reproduction but not enough to sustain the population. Class 1 streams have good natural reproduction to the point where many no longer need to be stocked. It is important to evaluate the results over time and by year class. Shocking this spring has revealed that many young of the year did not survive because the floods came when the trout were in the redds. This will show up in the future as a poor year class. (i.e., next year there will be few 4-6 inch fish.)
When the report becomes available we will discuss in detail what was found during the electroshocking. But until then, check out your local DNR office and see if you can attend an electroshocking demonstration. You might think you are a good fisherman now, but when you see all of the fish that surface during an electroshocking, you might think twice. Just be sure to bring your rod. Once you see the size and numbers of trout, you'll want to wet a line before going home.