by | Apr 18, 2011 | 0 comments

This explanation of Electrofishing is straight from Montana FWP.  For years, myself and many others,  have been  against electrofishing and after sitting through detailed lectures given by biologists I still feel the same way.  Do we really need it?  Does the public really care how many trout are in Montana’s rivers?  Would you still come out if you didn’t know there were 2800 rainbows and 569 browns per mile in the Craig stretch of the Missouri River?  I bet you would.  Could the money and the energy be spent for studying habitat and stream improvements to better the fisheries….I think so.   Through the grape vine I hear that FWP is compiling all the electrofishing studies on the Madison to see if there are any obivious trends that stick out and need attention.  I hope they do complete this and have it available to everyone to read.    Not much has been done since FWP quit stocking the Madison in the early 70’s.   Which was a really big deal and shoud not be forgotten.  Sure, there have been some changes with catch and release practices, but the Madison just kind of takes care of itself…..if it allowed to that is.  Stream flows play a very important roll in how the Madison works, every trout stream is dependent on stable flows for that matter.  Especially in the spring time.  I think that FWP should take another look at the Madison get to know her a little better.  There are some new folks in Region 3 who haven’t really spent all that much time on the Madison.   They have been on the Big Horn or the Smith, but the Madison is a different beast.  

 After the Hebgen Dam incident in August of 2008, the river just hasn’t seemed like herself.  Was there too much disturbance in the river bottom for the fish to get comfy by the time spawning season rolled around?  Will the warm water coming in from Hebgen Lake effect things this summer with warmer river temps?  What about all that rock which came tumbling down in 1959?  Will the river try to find it’s original pathway some day?    Why hasn’t the main channel below Quake Lake moved around like it used to do prior to 1993?  Never fished that stretch prior to 1993?  Ask those who did and make sure you pay attention to their words. 


Electrofishing in our rivers is done to obtain fisheries information that is used to determine trends in fish populations. This information is used in setting fishing regulations that affect fish populations such as creel limits, harvest restrictions (such as catch and release or a slot limits), and angling seasons to enhance or maintain the quality of our fisheries. It is also integral to assessing and implementing habitat improvement, restoration, and conservation measures such as improving flows during critical periods or overall watershed health. In rivers, electrofishing is the most effective means of catching fish and obtaining these data. Many factors like river temperature, flow, turbidity and weather, which vary each time we are on the river, affect how well we catch fish. Because of our relatively low catch rates and our variable efficiency, we use a mark-recapture study design to obtain population estimates in many trend sections. To get population estimates with this method, fish must be marked then released back into the population to mix with fish that were not captured and marked. At a later date, another electrofishing run is taken through the section and the total population size is statistically computed based on comparing the proportion of marked fish to those that were not marked. Therefore, this methodology requires two electrofishing runs through a section to obtain a population estimate. Another method used to obtain fisheries population trends is a single pass through a section. However, because the factors mentioned above can often have a big influence on how many fish and what sizes we catch, this approach is not appropriate in some sections such as Fish and Game on the Beaverhead River. In other sections, such as the Maloney on the Ruby River and Hildreth on the Beaverhead River, where we are rigorously assessing the response of fish populations to controlled dam releases this approach provides inadequate data. However, in other sections such as Anderson Lane on the Beaverhead River and Silver Springs on the Ruby River a single pass sample is adequate to inform our present management direction.  On the Beaverhead River we presently sample three trend sections. The Hildreth section is located between the High Bridge and Henneberry and is 1.2 miles in length, the Fish and Game Section is located between Tash Bridge and Poindexter Slough and is 1.7 miles in length, and the Anderson Lane section is between Anderson Lane and the Malesich Ranch and is 3.1 miles long. Two sections are sampled on the Ruby River; the Maloney section is between the Vigilante FAS and the Anderson Ranch and is 0.9 miles long and the Silver Springs section is located on the Barnosky Ranch just upstream of Silver Springs Bridge and is 1.9 miles long. We sample two trend section on the Red Rock River; the Martinell section is on the Martinell Ranch near Dell and is 0.8 miles long and the Roe Section runs about 3 miles from Roe Lane to the headwaters of Clark Canyon Reservoir. We sample one trend section on the Poindexter Slough FAS. 

One of the most frequent questions we receive about our electrofishing surveys is what are the effects on the fish with respect to injury and mortality. Many studies have been done to refine electrofishing techniques to reduce injury and mortality. When we electrofish, we only use smooth DC current, which significantly reduces injury to fish. Contrary to what most folks think, electrofishing does not generally “stun” fish. Rather, as the electrical current is placed into the water, it causes the fish in close proximity (within 5-15 ft) of the small metal ring anode to swim uncontrollably. The fish are drawn toward the anode, which is on the end of 30 ft cord, and when it is brought close to the boat the fish are scooped up and put into a tank of water in the boat. Most fish are not stunned at all and are immediately swimming around inside the tank. Those that do get stunned because they were in very close contact to the anode are generally swimming around the tank within a few minutes. Interestingly, whitefish for reasons we do not fully understand, are much more susceptible to electricity than the trout and they commonly are stunned and seem to take longer before regaining their equilibrium. After capturing the fish, they are weighed and measured. To reduce stress to captured fish, anesthetic is placed in their water before they are handled. Once fish are weighed and measured they are placed in a net cage in the river to revive from the anesthetic. Once they are revived, they are released. Any mortality is recorded. Immediate mortality of trout is rare when we are electrofishing, generally less than 1%. Studies involving holding fish overnight or implanting radio transmitters and following fish movements for up to several years indicate that long term mortality related to electrofishing is similarly low. Mortality rates are greatest with smaller fish (i.e,<  10 inches). As temperature increases, mortality increases, which is why we sample early in the spring and later in the fall. We also record electrofishing injury to fish, which usually is usually evidenced by a deformity in the spine caused by compressed vertebrae (it is actually caused by the fish’s mussels contracting so hard they cause injury). These injuries are most common in rainbow trout, and much less common in brown trout for unknown reasons. Recorded rainbow injury rates that appear to be related to electrofishing run between 1 and 5% and less than 1% for brown trout. When handling fish, we also keep track of hooking injury from anglers and they range between 5 and 10% for rainbow, and 1 and 5% for browns. 

 There have been some questions that our sampling is affecting invertebrate populations and salmonflies in particular. Many studies have been done on electrofishing effects on macroinvertebrates. The major conclusion of these studies is that electrofishing increases drifting rates (i.e., invertebrates are affected by the electricity and momentarily let go of the rocks and drift in the current), but as soon as the electrical current is removed, they recover and swim back to the bottom. I am not aware of any studies that have shown long-term impacts to any invertebrate species or populations, including salmonflies, as a result of electrofishing. Further, given that we only sample less than 20% of the river, it is unlikely that our sampling would have population level effects on invertebrates.

Electrofishing is an integral part of the fisheries management of our rivers. The information we gather helps us better manage the fish and their habitat. We recognize that our sampling sometimes is an inconvenience for angling and outfitting, but the data collected is essential to the management of our wild trout fisheries. Wild fish management rather than hatchery based management has its roots in electrofishing monitoring data. The information also helps anglers because the counts are shared with the public which helps them plan their trips. We also are questioned frequently by angling publications about fish counts and fish trends on or local rivers. The effects of various flow regimes on fish populations and the benefits of securing minimum instream flows during critical periods are also gleaned through these surveys. This information would not be available if these surveys were not conducted. It would be difficult to argue for winter flows on the Beaverhead River or for more water in the lower Big Hole, if we could not show how these improvements benefit the fishery. 

Thanks and please let me know if you have questions.

Matt Jaeger

 Fisheries Management Biologist

 Montana Fish, Wildlife&  Parks

730 1/2 N. Montana

Dillon, MT 59725

 (406) 683-9310