Electrofishing seems to be a myth to some pondmeisters. Those are the folks who don't know much about it, why to do it, or when it should be done. Plus, it ain't cheap.
Full-blown electrofishing surveys can cost $750 up to $3-4,000, depending on whom you choose and the circumstances for the survey.
First, electrofishing is the most common method fisheries biologists use to get as close to a "random" sample as possible in freshwater lakes and ponds.
The gist of electrofishing revolves around a scientific research boat equipped with an onboard generator that sends electricity to a unit that converts the electricity into a form that will temporarily stun fish. The device, typically made by specialized companies that manufacture them specifically for that purpose, rectifies alternating current into direct current and has a rheostat knob that allows the operator to adjust the amperage.
Water, by itself, doesn't conduct electricity. It's the metals and minerals dissolved in water that conduct the current. As you might imagine, each pond or lake has its own "conductivity," so electrofishing equipment must be adjustable.
It takes from 3 to 10 amps for fish to be affected enough to go into what's called electrotaxis or galvanotaxis. When the proper amount of electricity hits a fish, it stops and loses its balance, and netters on the bow of the boat can capture the fish and put them into a large live well where it takes only a few minutes for the fish to recover to normal. When using direct current (DC), the electric field causes fish to turn toward it and swim into the area where they become stunned.
The rheostat switch allows the operator to adjust the amperage by sending voltage through a transformer to either increase or decrease the volts, allowing the amps to hit the best window for effectiveness.
The electrofishing boat has a cathode and an anode that essentially work similarly to welding principles. The boat is creating a direct arc under water. When the boat is underway, the electrofishing unit has an emergency switch engaged by the boat's captain to allow a redundant footswitch, usually on the bow, to be pressed to begin electrofishing. Safety is huge. Water and electricity are a risky mix, but with proper safety equipment, it's truly safe.
Just don't put your hand in the pond water when switches are engaged. You'll get a tingle.
Now that we know the principles behind electrofishing equipment, the next concept is why?
The reason for electrofishing is to get an idea of the status of a fishery at that point in time. Look at it similar to an underwater snapshot of the fish population. There are limitations, however. The electrical field can only go down about six feet deep and maybe twelve to fifteen feet wide in front of the boat, tapered toward the back of the boat. If fish are eight feet deep, the boat won't stun them. Plus, when fish begin to feel the tingle of the electricity, they often bolt and run. That's why most electrofishing is done in the cooler months of spring and fall.
Speaking of those seasons, if a fishery is sampled in the spring, we get an idea of what's missing and what needs to be done to keep the fishery on a positive track for the upcoming seasons. Fall electrofishing surveys are conducted to see how the fish population fared over the last few months and to decide what, if anything, needs to be done to keep the fish healthy coming into the coldest months.
Each biologist or lake management company has its strategy for collecting fish and handling the data. The primary data to collect are the lengths and weights of critical species, such as largemouth bass, and it is vital to get an accurate idea of the different species of fish that make up the population. Plus, it's wise to understand the ratios of size classes within each species.
Lengths and weights of fish allow a comparison of your fish to what we call "standard" weights for a given length. The best companies and biologists plot your fish lengths and weights into a spreadsheet to compare to the "standard" curve. "Normal" fish are within 5-8% of "Standard." Their relative weight often depends on the time of year or season. For example, female bass are overweight before spawning, but when those eggs are deposited into nests, their weight drops considerably, which is normal. When males finish their spawning cycles of sitting on nests for many days at a time, they also lose a considerable amount of weight.
It's common to find certain size classes of game fish or sunfish species, such as bluegills, to be underweight. That happens because fish in that size class are overcrowded and overeating the food chain of prey specifically for their size. The electrofishing survey gives solid data to help make decisions such as slot limits and culling fish. Or, you may harvest some predator fish, ramp up a feeding program for their prey, and stock more forage fish.
While electrofishing is the primary "go-to" sampling technique for evaluating a freshwater fishery, it does have several biases. For example, you can't depend on data strictly from angling because catching fish is seriously biased based on your ability, baits used, and catch rates of aggressive fish...often hungry fish. It gives zero idea of all the size ranges of fish, how well the population has reproduced, or a random dataset of non-target species.
But angling, coupled with electrofishing and some seine pulls in shallow water, can offer more clues toward the true status of your fishery.
Recently, I participated in an electrofishing survey of a nice-sized lake trending toward overcrowded bass in the 12-15" size class. But, some finesse angling by experienced fishermen produced several bass in the 4-8-pound size class. They were caught in water seven to ten feet deep, beyond the range of the electrofishing boat. Although we had some clues that big bass exist in that lake due to the numbers and sizes of smaller bass and the associated food chain, we couldn't prove it without seeing some.
Is an electrofishing survey for you? Maybe so, maybe not. It depends on your goals, budget, and desire to keep the fishery on an upward trend.
If a primary goal is to grow trophy-sized fish, electrofishing is much more critical than if you simply want the grandkids to catch some big bluegills off the dock.
Here's one vital thing to remember. If big fish is a goal, the more meals they miss and the longer they stay stuck in the slot, the more their top-end growth potential declines. If a fish misses a meal for several days in a row, it can't make it up. That bass with an aggressive nature and the genetic propensity for massive growth but denied the opportunity due to lack of food may not even make it to double-digits...especially if it stays at 12-14 inches for six weeks or, six months...or a year.
Here's the bottom line. If you have a lot of money invested in building your pond, stocking it with fish, and an aggressive management strategy, electrofishing is worth it.
If you are just having fun and the fishery is more of a play toy, the juice may not be worth the squeeze.
You get to make that call.
Reprinted with permission from Pond Boss Magazine
