Monday, July 24, 2023

Episode 660 (7-24-23): Fish Sampling Explores the Underwater World

CLICK HERE to listen to episode audio (5:58).

Sections below are the following:
Transcript of Audio
Audio Notes and Acknowledgments
Extra Information

Related Water Radio Episodes
For Virginia Teachers (Relevant SOLs, etc.).

Unless otherwise noted, all Web addresses mentioned were functional as of 7-21-23.


From the Cumberland Gap to the Atlantic Ocean, this is Virginia Water Radio for the weeks of July 24 and July 31, 2023.  This is a revised version of an episode from July 2013.

SOUND – ~7 sec

That underwater sound, recorded by a kayaker on Virginia’s Appomattox River, opens an episode about how scientists and resource managers learn about the finned creatures that live underwater.  We start with some mystery sounds.  Have a listen for about 30 seconds, and see if you can guess what’s going on with this beeping and splashing.  And here’s a hint:  If a finned creature detects this signal, it might soon have a stunning experience.

SOUNDS AND VOICES – ~27 sec – “Everybody’s hands out of the water?”  Beeping and splashing.  “Ok, whenever you all are ready, you can pull it.... One, two, three...”

If you guessed fish sampling, you’re right!  Those were sounds from an electrofishing demonstration, during a May 2013 Virginia Master Naturalist field trip about fish in streams and rivers.  The demonstration was led by Jamie Roberts, who at the time was a Virginia Tech research scientist and as of 2023 is an associate professor of fisheries at Georgia Southern University.  Participants learned about fish-assessment techniques commonly used by fishery managers and by fish scientists, known as ichthyologists.  For some more details on fish sampling in streams, let’s listen to a two-minute excerpt from Dr. Roberts’ session.

GUEST VOICE - ~2 min./2 sec.

“So one of the things I want us to notice as we’re sampling is what we catch with different types of gears, with different types of methods, and then what we catch in different types of habitats.

“So there’s really, essentially three different types of habitats that we have here [in a stream].  You have that shallow, turbulent stuff [that] we in the stream ecology world tend to call riffles; you have these, sort of, deep, deeper still somewhat high velocity areas called runs; and you have still waters, which we call pools.  And the three gear types that I wanna play with are...electrofishing with a dip net, which we’ll do in pools; electrofishing into a stationary seine—so this is a seine net; and then sweeping a seine around like crazy and just seeing what we can get, like an old-time ichthyologist.  We’ll do some sampling that is more like the golden days of ichthyology, before we had $10,000 electrofishers.

“Icthyologists often rely on electrofishers of one type or another to catch fish, because it sort of brings fish out of the woodwork.  Fish are in this environment that’s very difficult for us to access and see through and everything, and electricity is sort of the equalizer; it makes fish a lot easier to catch.  There are electrofishers that are mounted on boats; there are electrofishers that are barges that you tow around; and this is called a backpack electrofisher.  It’s powered by a DC battery that looks a lot like a motorcycle battery.  And it produces electricity that this fancy box turns into the correct frequency and wavelength and pulse type to momentarily stun fish, and while they’re stunned, we net ‘em; and as soon as they get out of the electrical field, if we’ve done everything like we’re supposed to, they just immediately come back.  So if we throw them in a bucket, they should immediately regain normal composure.”

As Jamie Roberts noted, fish live in an environment largely hidden from unaided human vision or hearing.  So scientists and resource managers combine ancient technologies—like nets—with modern electronics to get the information needed to understand and properly manage fish and the aquatic areas that sustain them.

Thanks to Dr. Roberts and the New River Valley Master Naturalist chapter for permission to record the fish-sampling session.  Thanks also to Raven Harris for the Appomattox River sounds.  We close with a musical selection whose title describes the water world of many fish.  Here’s about 25 seconds of “The Deep Blue Green,” by Andrew VanNostrand.

MUSIC - ~27 sec – instrumental.


Virginia Water Radio is produced by the Virginia Water Resources Research Center, part of Virginia Tech’s College of Natural Resources and Environment.  For more Virginia water sounds, music, or information, visit us online at, or call the Water Center at (540) 231-5624.  Thanks to Stewart Scales for his banjo version of “Cripple Creek” to open and close this episode.  In Blacksburg, I’m Alan Raflo, thanking you for listening, and wishing you health, wisdom, and good water.


This Virginia Water Radio episode revises and replaces Episode 172, 7-29-13.

The Appomattox River sounds were recorded by Raven Harris on the Appomattox River in Petersburg, Va., on April 18, 2014; used with permission.

The fish sampling sounds and talk by Dr. Jamie Roberts were May 13, 2013, along Toms Creek in Montgomery County, Virginia, at a class of the New River Valley Chapter of the Virginia Master Naturalists Program.  Thanks to Jamie Roberts and to participants in that Master Naturalist class for permission to record the session.

“The Deep Blue Green,” from the 2019 album “That We Could Find a Way to Be,” is copyright by Andrew VanNorstrand, used with permission.  More information about Andrew VanNorstrand is available online at  This music was used previously by Virginia Water Radio most recently in Episode 632, 7-18-22.

Click here if you’d like to hear the full version (1 min./11 sec.) of the “Cripple Creek” arrangement/performance by Stewart Scales that opens and closes this episode.  More information about Mr. Scales and the group New Standard, with which Mr. Scales plays, is available online at


Virginia Department of Game and Inland Fisheries (now Department of Wildlife Resources) personnel giving a backpack electrofishing demonstration to the Virginia Master Naturalists/New River Valley Chapter at Toms Creek in Montgomery County on May 6, 2013.  Photo by Bill Sydor, courtesy of New River Valley Master Naturalists Chapter.

Virginia Department of Game and Inland Fisheries (now Department of Wildlife Resources) personnel leading a seining demonstration to the Virginia Master Naturalists/New River Valley Chapter at Toms Creek in Montgomery County on May 6, 2013.  Photo by Shannon Ritter, courtesy of New River Valley Master Naturalists Chapter.

Jess Jones (left), co-director of the Freshwater Mollusk Conservation Center at Virginia Tech, examining the settings on a backpack electrofishing device, in the North Fork Holston River in Saltville, Va. (Smyth County), June 19, 2018.  Photo by Virginia Water Radio.


The following information on electrofishing is quoted from the Virginia Department of Wildlife Resources blog, Alex McCrickard, “Not Too Shocking: Your Electrofishing Questions Answered,” by Alex McCrickard, November 9, 2020, online at, accessed July 17, 2023.

“Have you watched some of the videos from aquatic biologists at the Department of Wildlife Resources (DWR) and seen a boat outfitted with long, wand-like poles with dangling cables?  Have you ever showed up to a river or stream and witnessed a crew of biologists with large backpacks and long rods extending into the water?  This unusual-looking activity is called electrofishing, and it’s modern science in action.

“As Virginia’s state fish and wildlife agency, DWR is responsible for the management of our fish and wildlife resources for the benefit of the public.  Our agency staff work hard to conserve and protect our freshwater fisheries across the Commonwealth.  The best way to monitor the health of fish populations is to catch a number of fish from one area at one time.  While our aquatics biologists are all excellent anglers, there is a more efficient, safe, and effective way to catch the fish!  Electrofishing is a common method used in fisheries science; this type of biomonitoring is truly one of the most effective ways to monitor our fisheries.

“Fish can really help tell the story of the health of a certain waterbody.  They are in the water 24/7 and are constantly exposed to the elements.  Some species are more tolerant to pollution than others.  The make-up and diversity of a water body’s fish population can help tell the story of water quality and inform our agency’s biologists.  In turn, all of this influences sound management decisions that can improve habitat, water quality, and fish health, which benefits the general public and anglers who cherish Virginia’s freshwater resources.

“So, you now might be wondering what exactly happens during electrofishing?  What’s going on behind the scenes during these surveys?  Our electrofishing FAQs below cover these basics.

“What is electrofishing?

“Electrofishing is a technique used in fisheries science to sample fish populations.  Sampling is when biologists study a number of fish from a certain area, measuring and examining them and recording the statistics.  When biologists electrofish, a generator or battery gives off an electrical current that runs through the water.  Volts, amps, and frequency can be adjusted based on water temperature, conductivity, and other variables.  Electrofishing can take place on foot with a backpack unit on a small stream or river.  For larger rivers and lakes, electrofishing typically takes place from a boat or barge.

“From a boat, the anodes enter the water from a long boom off the bow.  Electrical current travels from anode cables back to the cathode(s)–in many cases, the metal hull of the boat acts as the cathode.  The electrical field typically expands 5 to 7 feet in circumference from each anode and down about 6 to 7 feet.  The size of the electrical field can vary depending on conductivity, voltage, and frequency of electrical current.

“Fish are temporarily stunned as the electrical current causes their muscles to contract.  The fish then float towards the surface where they can be easily netted.

“Is electrofishing harmful to fish?

“Electrofishing has the potential to be harmful if not used properly; however, biologists have the training and experience to operate the equipment safely and effectively while minimizing impacts to fish.  Prior to any sampling, biologists adjust and monitor electrofishing settings to the target species in a particular habit. In some cases, electroshocking is avoided during spawning periods and habitats of certain rare and endangered species to eliminate even the perception of harm.

“Does electrofishing affect different species of fish differently?

“Yes, the frequency of the electromagnetic current can affect species differently.  For example, low frequency electrofishing tends to only affect catfish species.  When we sample tidal rivers to assess the catfish populations, we solely use low frequency.  High frequency sampling is often used for standard community assessment of multiple species.  Because of their larger surface area, big fish such as bass and muskie are more susceptible to electroshocking than small fish such as minnows and darters.

“Electrofishing is only efficient in shallow water, so sampling is usually conducted when all species and sizes of interest are likely to be vulnerable to this technique.

“Why do DWR biologists electrofish?  What’s the goal for sampling and what do DWR biologists do with the fish during electrofishing?

“Electrofishing is an effective method to assess the health of a fishery in a non-lethal manner.  It allows biologists to evaluate the health, variety, size distribution, and abundance of fish species on a given body of water and how that population can change over time.  Length and weight measurements further allow biologists to assess overall fishery health.  This type of sampling allows DWR to look at interactions within a fish population.  Furthermore, we can track status of endangered and threatened species or the status of spread of any invasive species.  All of this information influences sound management decisions that benefit the public who recreate on these resources.

“Is electrofishing safe for the DWR biologists?

“Yes, because of their training and experience, DWR biologists are safe when electrofishing.  Our biologists wear non-breathable waders that keep them from being shocked while using backpack electrofishing units.  For electrofishing boats, numerous electric cut-offs are in place to prevent accidents, and the boat is grounded.  All DWR biologists wear personal flotation devices while sampling on boats.  DWR biologists have also had formal training in electrofishing principles and techniques (for example the U.S. Fish and Wildlife Service electrofishing course), which contributes to the safe operation of electrofishing gear.

“In what kinds of waters do you electrofish?

“Electrofishing takes place in freshwater and tidal freshwater rivers and streams.  Because of the high conductivity of saltwater, it is not conducive to electrofishing.

“Can anglers use electrofishing equipment to catch fish?

“No, it is unlawful for the general public to use electrofishing equipment to catch fish.”


Used for Audio

Alex McCrickard, “Not Too Shocking: Your Electrofishing Questions Answered,” Virginia Department of Wildlife Resources, November 9, 2020, online at

Stephen R. Moulton II, Jonathan G. Kennen, Robert M. Goldstein, and Julie A. Hambrook, “Revised Protocols for Sampling Algal, Invertebrate, and Fish Communities as Part of the National Water-Quality Assessment Program,” U.S. Geological Survey Open-File Report 02-150, online at

National Park Service, “What Lies Beneath: How Electrofishing and Environmental DNA Is Being Used to Monitor and Conserve Fish Species in Great Smoky Mountain National Park,” April 8, 2021, online at

Jordanna Sheermohamed, “Sea Science: Why is the ocean blue, green and everything in between?  The Triton, April 24, 2019.

Virginia Master Naturalists Program, online at  The organization is at 460 Stagecoach Road, Charlottesville, Virginia, 22902; phone (434) 872-4587.

U.S. Geological Survey, “Water Science School/Water Color,” online at

For More Information about Fish or Fishing in Virginia or Elsewhere

American Fisheries Society, online at

University of Michigan Museum of Zoology, “Animal Diversity Web,” online at

U.S. Fish and Wildlife Service, “Assessment and Monitoring,” online at  This site has a collection of articles on techniques for monitoring fish populations.

Virginia Department of Wildlife Resources (formerly Department of Game and Inland Fisheries):
“Fish and Wildlife Information Service,” online at;
“Fishing,” online at;
“List of Native and Naturalized Fauna in Virginia, August 2022,” online (as a PDF) at

Virginia Marine Resources Commission, online at  See particularly the following:
“Commercial Fishing,” online at;
“Recreational Fishing,” online at


All Water Radio episodes are listed by category at the Index link above (  See particularly the “Fish” and “Recreation” subject categories.

Following are links to some other episodes on fishing or fisheries.

Fishing-line recycling – Episode 590, 8-16-21.
Freshwater mussel restoration work involving electrofishing – Episode 433, 8-13-18.
Spring signals to fish and anglers – Episode 571, 4-5-21.
Stream access law in Virginia – Episode 76, 8-22-11.
River stewardship – Episode 383, 8-28-17.


Following are some Virginia Standards of Learning (SOLs) that may be supported by this episode’s audio/transcript, sources, or other information included in this post.

2020 Music SOLs

SOLs at various grade levels that call for “examining the relationship of music to the other fine arts and other fields of knowledge.”

2018 Science SOLs

Grades K-5: Earth Resources
4.8 – Virginia has important natural resources.

Grade 6
6.9 – Humans impact the environment and individuals can influence public policy decisions related to energy and the environment.

Life Science
LS.8 – Change occurs in ecosystems, communities, populations, and organisms over time.
LS.9 – Relationships exist between ecosystem dynamics and human activity.

BIO.7 – Populations change through time.
BIO.8 – Dynamic equilibria exist within populations, communities, and ecosystems.

Virginia’s SOLs are available from the Virginia Department of Education, online at

Following are links to Water Radio episodes (various topics) designed especially for certain K-12 grade levels.

Episode 250, 1-26-15 – on boiling, for kindergarten through 3rd grade.
Episode 255, 3-2-15
– on density, for 5th and 6th grade.
Episode 282, 9-21-15
– on living vs. non-living, for kindergarten.
Episode 309, 3-28-16
– on temperature regulation in animals, for kindergarten through 12th grade.
Episode 333, 9-12-16
– on dissolved gases, especially dissolved oxygen in aquatic habitats, for 5th grade.
Episode 404, 1-22-18 – on ice on ponds and lakes, for 4th through 8th grade.
Episode 407, 2-12-18 – on snow chemistry and physics, for high school.
Episode 483, 7-29-19 – on buoyancy and drag, for middle school and high school.
Episode 524, 5-11-20 – on sounds by water-related animals, for elementary school through high school. Episode 531, 6-29-20 – on various ways that animals get water, for 3rd and 4th grade.
Episode 539, 8-24-20 – on basic numbers and facts about Virginia’s water resources, for 4th and 6th grade.
Episode 606, 12-6-21 – on freezing and ice, for kindergarten through 3rd grade.