Effects of Electrofishing on fish & nymphs?

[HCR]

Colorado division of Wildlife had two rafts on the Rio Grande at the Coller public access (between Creede and South Fork) this morning.

The crews were shocking up fish that were then netted and put on board in live wells. Guys with the net missed about a third of the fish they tried to catch.

Three questions:

(1) What is the effect of the shocks on the nymphs in the water? I was standing on the bank and one of the crew guys advised me to keep my dog out of the water (I wasn't about to let her get in).

(2) After the fish are shocked, do they make their way back to the holding lies from which they were taken? The rafts moved about 1/2 mile downstream before beaching (I assume to measure and return fish to river).

(3) What is the mortality rate of the fish that are shocked? I saw a couple of fish that were netted pronounced "dead" and tossed up on the bank (perhaps they were aready dead--I don't know)?

[JohnScott]

HCR -

Can't give you any scientific answers, and don't know the answer to your first question about nymphs.

Having said that, I was fortunate several years ago to work as a volunteer with the Idaho Fish and Game electroshocking and surveying trout on a two plus mile stretch of the Henry's Fork. My comments are based on that experience.

The shocking temporarily disrupts the fishies' motor control. Not being able to swim, they float up to the surface. Once netted and brought to the boat, they were placed in a holding tank with an anesthetic which kept them calm. After being measured and tagged ( a one hole punch in the tail ), they were transferred to another fresh water tank to "wake up" before they were returned to the river.

The effects of shocking are temporary. It is evident that the fish on the very perimeters of the shocked area are stunned, but they just swim away unaffected. The larger the fish, it seemed, the less affected they were by the shocking process - that is, large fish on the perimeters had less loss of control than the smaller fish. Also, in my case, where I was the guy netting the fishies, we probably boated about 20% of the fish that came to the surface. The others were capable of swimming off on their own, unaffected, shortly after they floated out of the shocked area.

I don't recall ANY mortality during this process. We had two boats. Each boat floated the two plus miles one time each on each side of the river. On each pass, as I recall, each boat accounted for something like 200 fish - rainbows, cutts, browns, and mountain whitefish - boated, tagged and measured, and released. Again, that was probably 20%, maybe a bit more, of the fish that we saw.

If you saw dead fish, they were likely fish that were weaker than normal that couldn't take the minimal effects of shocking and the handling involved in the process. Dead fish would not come to the surface during the shocking, and believe me, it is very unlikely the guy handling the net would try to net any dead fish around the shocked area. It is hard work trying to use a large net to catch 3 or 4 or 5 or 6 trouts and whitefish in one scoop and then lift them into the boat and put them in the holding tank. No way anyone would waste time netting a dead fish during that process, although it could happen accidentally.

One of the intriguing things was how the fish school up, how they really are in the holes, whatever that means on a given river. We would go along with the electroshock at full charge for a little way with no fish, then all of a sudden, there would be 20 or 30 or 40 fish coming to the surface. Net all you can and keep going. Drift another 25 yards and a fish or two would pop. A little further along, maybe a dozen. On a bit further, maybe another hole where 20 to 40 fish would come up. Two plus miles of that kind of action.

As a side note - I was so focussed on trying to net fish and get them into the holding tank that I never knew where we were on the river. So I couldn't go back and fish the hot spots if I wanted to. Another thing - even knowing that there are something like 4000 trout per mile in that stretch of the river, and having seen a LOT of them during that survey outing, I very seldom fish there because it is not a stretch of water that I like to be on.

Maybe someone will come along with more scientific answers / observations and broader based experience to fill in the blanks.

John

P.S. Did I mention SUCKERS. Golly, there were bunches of those in that stretch of river. And being huge, they seemed unaffected by the electroshocking process. They seemed to be aware of it, but stayed down near the bottom and swam off readily.

[Gigante]

How it affects the insect life but seeing as how those things produce in such high numbers and live very short lives anyway, I can't see how it would have much of an averse affect. I am speaking very generally about insect lifespan of course.

On a related note. Does anyone know about the "natural" method for doing this? I remember my grandfather doing it when I was very young. When he wanted a fish fry he crushed something organic into socks or panty hose or something and threw it out in the water or tied it to a tree in the water and fish just floated up as if shocked only were not nearly as ready to swim again. It seems like I've been told it's not very health and possibly illegal. Just curious.

[HCR]

Organic dynamite?

[FISHN50]

Organic dynamite?

That's a "DuPont" Fly.......

[James Smith]

I seem to recall that the flower Pyrethrum which is in the daisy flower family contains the same chemical as used in Rotenone, a chemical commonly used to kill off fish populations. I believe that Rotenone actually binds up the O2 in the water, causing the fish to suffocate.

I also remember reading somewhere that the American Indians used to crush the dried flower heads and sprinkle the dust into the water in small streams to harvest fish.

Jim Smith

[bugman]

How it affects the insect life but seeing as how those things produce in such high numbers and live very short lives anyway, I can't see how it would have much of an averse affect. I am speaking very generally about insect lifespan of course.

On a related note. Does anyone know about the "natural" method for doing this? I remember my grandfather doing it when I was very young. When he wanted a fish fry he crushed something organic into socks or panty hose or something and threw it out in the water or tied it to a tree in the water and fish just floated up as if shocked only were not nearly as ready to swim again. It seems like I've been told it's not very health and possibly illegal. Just curious.

Broken up black wallnuts... We used to take them & breakem up, put them in a burlap bag and then drop in in a lake... a few minutes later fish would float up... Its illegal now but we did it years ago... How it works is that the wallnuts takes away the oxygen out of the water around where the bag was dropped so any fish remaining in that area would float a few minutes later... That doesnt work in moving water like rivers or streams, only lakes or ponds...

[HCR]

Thanks John Scott for your very informative reply. Helpful, per usual.

As for you other guys--Wow!. I had no idea. Have heard of Rotenone, of course, but flowers and walnuts--come on now, you're not pulling my leg are you?

[DG]

I don't have the references for mortality and such, but I can get them if you want. After vacation. *S*

From personal experience, I can tell you that I have caught fish in the lines where the shocking boats have floated, within minutes of the boat's passage. Remember too that the boat shockers are only doing one line down the river, not the whole river (unless it is a small river, but even on tiny water you miss a lot of fish). I used to get annoyed when the shocking boats went by in MT, but got over it real fast after catching some toads behind the boat. Guess the tickling wakes them up *S*. My problem with the DOW shocking is more the guy trying to run over me with the boat while I am throwing to rising trout.

The effect of the electricity is a function of the length/surface area of the fish, so bigger fish feel the effects differently from smaller fish. The math on that is beyond me tonight. If the shocker is set to shock small fish (say, to check for whirling disease in young of the year fish) and a 20-inch brown gets hit, it can hurt.

Sometimes I see fish with spinal deformities on rivers that they have shocked. While this may be a sign of WD, it is also a side effect of the shocking process if the settings are not just right. Then again if I can catch the fish, it must still be a functioning fish.

As for the bugs, no idea, but as small as they are, they may not receive too much of a shock.

If I get time tomorrow, I will ask the fish squeezers.

Dennis

[JohnScott]

Just a couple follow up points.

DG made one of them already - that only a small portion of a large river is effected. The diameter of the shock zone was probably not more than ten to fifteen feet, centered out front of a drift boat. The Henry's Fork is well over one hundred feet wide on the section we surveyed. So even two boats doing two passes each shocked maybe only 30% of the width of the river, probably less.

My experience does seem to contradict DG's comments about how the shock effects fish of different sizes. My recollection is that the smaller fish ( roughly 10" to 14" ) were much more effected that the larger fish ( roughly 16" up into the low 20 inches, not including the suckers ). Maybe all those fish fall on the upper end of the spectrum compared to the small fish which would be checked for whirling disease ??

When it comes to the aquatic insects, remember that on a large river only a small portion of the total area is being covered. In the Henry's Fork example, probably less than 30%. Even if there were some damage to aquatic insects within the effected zone, there would still be a huge mass of life to takes its place.

John