On a rainy August morning, three men dressed in dark-shaded green chest waders and rain jackets slowly make their way upstream, through the chilly waters of the Rock River in Alger County.

Two of the men carry long white poles with rectangular boxed ends in one rubber-gloved hand and a fishing net at the end of a wooden pole in the other.

From each of the two men, a thick yellow electrical cord runs downstream to a blue or red equipment box in a small aluminum boat, which is being pulled up the river by the third man.

As the men move the ends of the white poles under the stream banks, and the wet alder trees overhanging the water, large and small brook trout begin to appear, floating sideways or upside down in the creek.

Quickly, the fish are netted and moved to a plastic bin filled with water that’s sitting in the bottom of the boat. The men pull the boat to the muddy shore and they begin measuring the fish and collecting information on each of them.

They work quickly because it won’t be long before the fish have revived and are once again darting under the banks of the stream, looking for places to hide. 

This process is called electrofishing, and it’s been around for quite a while. The men and women who perform this task for the state are fisheries biologists and technicians with the Michigan Department of Natural Resources.

Within the DNR, the Fisheries Division is responsible for managing fish populations within the state’s streams, protecting and preserving these valuable resources for the public and posterity.

Because every stream is unique, each one requires attention to factors that may, or may not, have an impact on the fish community.

In every case, fisheries managers are trying to gather more data on fish populations to help guide management recommendations.

How it works

Electrofishing in Michigan got its start at the Hunt Creek Research Station in Montmorency County during the summer of 1942.

A stream shocker is made up of a small generator and a control box that can alter the amount of current being produced by the generator. The electric current flows from a positive to negative charged direction.

These components are put into a small boat or barge. There can be two or three anode (positive) electrodes on the boat (the red and blue boxes), allowing several people to “shock” the stream at the same time. These electrodes are often connected with cord reels, allowing the technicians to be able to move away from the boat to get to different areas of the stream. The boat acts as the other electrode (negative) or “cathode,” completing the electrical circuit in the water.

The final, and largest, electrofishing tool is the boom shocker. These tools are used on large rivers and lakes. They usually consist of a 16- to 20-foot, flat-bottomed boat equipped with large booms, a generator and a control box. The booms act as the anode (positive) electrode, and the boat serves as the cathode (negative) electrode. 

All three types of electrofishing gear options serve the same purpose. They produce an electric current in the water which temporarily stuns the fish, firing their muscles involuntarily, allowing technicians to collect the fish and collect biological samples.

The fish are netted and placed in temporary holding tanks to be sampled and then released back into the water of the stream or lake being surveyed.

Uses of the technology

For decades, fisheries managers have used electrofishing gear to grow their knowledge about the fish community that lives in each stream or lake.

The many uses for electrofishing gear, illustrating why it is a critical tool for fisheries managers, include:

• Aiding in estimating the number and type of species living within fish communities.
• Collecting wild fish for egg gathering. The eggs are taken to fish hatcheries and hatched. The fish produced from these eggs are used for stocking streams and lakes.
• Providing data to help judge the effectiveness of fisheries management actions.
• Monitoring important fish species or non-native, invasive species that can harm fish populations, water quality, recreation or economic concerns.

In the early 2000s, the DNR’s Fisheries Division developed a standard process for stream sampling to compare fish populations between different streams with similar habitat types. Electrofishing gear is used to collect information from the populations in these streams.

Typically, information fisheries biologists, technicians and managers are looking for includes length, fish species type and age. They often will take scale or spine samples to help determine age.

Examples

Under a rotation plan – three years of stream sampling, three years without – the Rock River in Alger County, is sampled using the established standard method. The stream contains a wild population of brook trout.

By sampling within a 1,000-foot length of stream, a population estimate for brook trout is calculated from each sampling effort. From the information gathered, trends in brook trout abundance, mortality and growth can be identified, which are key components to fisheries management.

Every year during spring runoff, rivers rise, swollen with snowmelt. In Newaygo County, the DNR’s Fisheries Division organizes a fleet of electrofishing boats to head to the Muskegon River, below Croton Dam, in search of walleye.

The Muskegon River serves as one of two locations in Michigan where wild walleye brood stock (eggs used to grow fish populations) is collected. The second is Little Bay de Noc in Delta County.

Because of the high and fast water conditions of the Muskegon River during the spring spawning run, electrofishing boats are very effective at successfully capturing spawning walleye. This provides the number of eggs needed to meet targets for production at the Wolf Lake State Fish Hatchery in Van Buren County.

Additionally, about one month later, on the east side of Michigan, electrofishing boats search the Detroit River for muskellunge during their spawning period. Great Lakes, or “spotted,” muskellunge have been the primary focus for DNR Fisheries Division production since 2010.

Until inland brood-stock lakes become well-established with an acceptable population level of Great Lakes muskellunge, the DNR will rely entirely on the Detroit River to collect eggs for its statewide muskellunge stocking program.

In the early stage of this muskellunge program, efforts with other gear types were unsuccessful on this massive waterbody. Today the sole method for collection is with electrofishing boats.

Many times, anglers visiting a stream wonder, “Why does this stream have a different fish size limit than another stream just down the road?”

To answer this question, fisheries managers typically reply with some data, biological reasoning and information that may seem like it just came out of nowhere.

However, that information was most likely learned from data collected during electrofishing, which supported a need for a fish size restriction on one stream and not another.

Similarly, when a dam is removed after being in place for years, fisheries managers will want to know what effects the removal has had on the stream. Electrofishing gear most likely would be used to help evaluate the changes in the fish communities, upstream and downstream of the dam site.

Another instance to consider is invasive fish species and how the DNR and other entities identifies their occurrence or status. Invasive species awareness has been of the utmost importance in recent years and on the radar of every fisheries manager across the nation.

When someone reports seeing an invasive species to the DNR, field staffers often conduct electrofishing surveys to determine the presence or absence, and location, of the invasive species.

Responses to invasive species reports are relatively fast using electrofishing gear, since all the components of the tools typically are found within one unit, not requiring any significant amount of setup time.