I do not get out to do as much field work as I used to, but I have been able to get out this week and I want to share with you some of the fisheries management activities that are happening in the state. On Monday I drove out to Grand Island to watch the rotenone renovation of the west lake on the Mormon Island State Recreation Area. I say I was there to “watch” because I would not say I did a whole lot to help. There was a newspaper writer who wanted to do a story on the project so I chauffeurred him around and showed him what was happening. Anyway, I can say I was there for at least part of the Mormon Island West 2010 renovation.
Our routine sampling of the fish populations at Mormon Island West had indicated that fishery had become dominated by gizzard shad and common carp, and in just the past few years, submerged aquatic vegetation had virtually disappeared from the pit. Now gizzard shad are an important prey fish in many large Nebraska reservoirs and in those habitats shad are no problem. But in small waters, gizzard shad will ruin panfish fishing because gizzard shad out-compete panfish and other small fish for food. Bluegills in particular suffer in the presence of gizzard shad. Common carp cause major problems as they destroy habitat and reduce water quality through their feeding activities. In addition a high biomass of carp in a body of water means less food, less productivity, for other species of fish. I said all of that to say this–it was time to renovate Mormon Island West.
Now let me tell you that when us pointy-headed fisheries biologists use the word “renovation” we are usually referring to a rotenone renovation. This is a fisheries management to0l that is used to eliminate or control the numbers of unwanted fish. When unwanted species of fish dominate a fishery the most practical and quickest, most efficient way to remedy that situation may be to kill the fish and start over. When that is done a chemical called rotenone is used to kill fish. Unfortunately, it is nearly impossible to selectively eliminate the unwanted fish and leave desirable fish. When a rotenone renovation is done, all fish are elminated. Then we re-stock with desirable species and in a few years produce a fishery that is far more productive than when the unwanted species dominated.
Let me digress by telling you we do no perform a rotenone renovation if there are a lot of desirable fish present. When it is time to renovate there is not much of a desirable sport fishery left. Regardless, folks often want to know if we do anything to salvage or save any of the desirable fish. I always answer that by saying that for the numbers of desirable fish that are left, it is not worth our effort to try to save them; you cannot capture all the fish you would like to save and you have to work hard to get the few that are left. It is a lot easier for us to produce fish in a hatchery than it is to salvage fish from a body of water that is going to be renovated. In addition, where would the salvaged fish go? Yes, there are times when we have waters that could use some additional fish; but waters with established fish populations probably already have as many of those fish as they can support. So, salvage operations are not the great idea that they seem; they mostly are done for good public relations to show that we have made an effort to save some of the desirable fish before we turn around and kill all of them. Prior to the renovation of Mormon Island West, our crews captured some fish on six different days of effort. They salvaged over 950 small bluegills, over 400 small crappies, 70-some channel catfish, 60 yellow perch, less than 4 dozen largemouth bass, 19 white bass and 4 walleyes. Those fish were transferred to the middle lake at Mormon Island, L.E. Ray Lake in Grand Island, and Pit #1 at the Kearney Archway.
Rotenone is a naturally-occurring substance found in certain tropical plants. Years ago Jacques Cousteau did a TV special on the Amazon and on one episode they filmed South American natives pressing the “juices” from certain rain forest plants. They would stomp on the roots and stems of those plants in the water of a stream and the “juices” from those plants would kill the fish in that stream. The natives then picked up the fish and ate them. The plants those natives were using contained rotenone! Rotenone is also used as an insecticide.
Rotenone kills fish by inhibiting the biochemical uptake of oxygen at the cellular level. Rotenone does not coat the gills and suffocate fish, it keeps oxygen from being used by the cells. It prevents the metabolism of oxygen. Rotenone has some toxicity to all oxygen “breathing” animals, but fish are particularly sensitive (different species of fish have different sensitivities to rotenone, but at some concentration all fish will succumb to rotenone). Rotenone will have some impact on other aquatic critters especially zooplankton, but snails and clams and aquatic insects are less sensitive and will survive rotenone concentrations that kill all fish.
The rotenone that we apply is in a liquid form. We have used powdered rotenone but found it to be a lot harder to work with and less effective. Basically we mix the liquid rotenone into the water at a rate of one gallon per acre-foot of water. Using area and depth calculations we can determine the exact volume of water in a water body like Mormon Island West so we know exactly how much rotenone needs to be used and exactly where it needs to be applied. Rotenone is relatively expensive, at least $50 per gallon, so believe me, we do not want to use any more rotenone than we have to. Moromon Island West had 470 acre-feet of water and thus 470 gallons of liquid rotenone were applied; 16, 30-gallon barrels full of rotenone.
A pump is used to pump water from the lake, mix rotenone into that water and then pump it back into the lake. Using valves we are able to meter the mixing of rotenone into the water so that it is thoroughly mixed and evenly dispersed into all of the water. As the pumps are running the boats slowly motor around; GPS units on the boats are very handy in showing boat paths so we can be sure to cover all the water.
As is typical with sandpits there are some portions of Mormon Island West that are relatively deep. Using long hoses and weights we pump rotenone down into that deep water because we do not want carp finding anyplace where they can escape.
The rest of the rotenone is pumped close to the surface. Wind, waves and outboard motors aid in the dispersal and mixing of the rotenone.
Gizzard shad are very sensitive to rotenone; just driving the boat around with a barrel of rotenone makes the shad very nervous.
I told you that we do not perform a rotenone renovation unless a fishery is dominated by undesirables. But I am always amazed when the fish start popping to the surface. Yes, there will always be a few desirable fish, even some big ones, but let me tell you that it is darned few. As the fish were dying at Mormon Island West, while I was there, I saw lots of small bluegills, I saw none that would have been even 7 inches long; there were a few small crappies, a handful of bass, a handful of walleyes, some yellow perch, some 1-3-pound channel catfish and quite a few white bass, BUT BY FAR, most of the fish that were dying were gizzard shad and common carp. We believe many of those undesirables gained access to Mormon Island West when an ice jam caused flooding in the area.
There are always a few surprises that show up when we do a rotenone renovation. Let me tell you about some of those and crawl up on a few of my “soap-boxes” while I am doing it. We have never stocked muskie or tiger muskie in Mormon Island West. Those fish have been stocked in the middle and east Mormon Island lakes in the past, but none in Mormon Island West. Yesterday, surprise, surprise, a couple of muskie/tiger muskie showed up dead in Mormon Island West. Where those fish came from I can only speculate, but I am betting someone transplanted a fish they caught from one of the other Mormon Island lakes–a practice that is illegal! I would say the biggest surprise when fish started popping to the surface was all of the grass carp. While I was there I saw at least a dozen, BIG grass carp come to the surface. All of those fish would have been in excess of 30 pounds, maybe even in excess of 50 pounds–they were HUGE. Grass carp were stocked in Mormon Island West on one occasion back in 1986; 320, 8-10-inch grass carp were stocked at that time. That means that all of those grass carp were 24 years old, and honestly we did not suspect they were in there. I can remember seeing a grass carp in Mormon Island West on one occasion several years ago, but we sure did not expect to see all of those grass carp. I always tell folks to make darned sure they really need or want grass carp stocked in their private waters, because once you have them, they will be extremely difficult to get rid of and they can live a LONG time. I have seen grass carp eliminate aquatic vegetation from many small waters and once that habitat was gone the “cure” was worse than the initial problem.
Not all of the fish that die will float to the surface immediately. By the time I left yesterday, just after noon, there were a lot of dead fish on the shorelines and surface, but there will be more show up in the next few days. Typically we leave those fish to decay when we do a rotenone renovation. All of those decaying fish will recycle nutrients back into that aquatic ecosystem and create a very productive environment for the fish that will be re-stocked. In this case there is a heavily-used camping area at the Mormon Island State Recreation Area and as many fish as possible will be picked up and buried to reduce the odor. We may have some estimates of the actual biomass of fish that were eliminated as those fish are disposed of; stay tuned for that.
Rotenone will detoxify over time. How long it takes for the water to be safe for fish depends on water chemistry and water temperature. Part of the reason the Mormon Island West rotenone renovation was done now was so the water could detoxify and fish could be re-stocked. Largemouth bass, bluegill, channel catfish and black crappie are scheduled for stocking yet this fall. In a couple, three years there will be fishing that is better than ever on Mormon Island West. The middle lake at Mormon Island went through the same rotenone renovation and restocking 5 years ago and there is some excellent fishing there right now.
Oh, while I am rambling, one more news item for the Mormon Island fishery. While we were there, crews were working on a boat ramp for the west lake. The plan is to build an access road and parking area between the middle and west lakes and then have boat ramps off of that parking area into both the middle and west lakes.
And one last thing before I quit; funding for all of this work comes from the sale of fishing permits and from excise taxes collected on the sale of fishing and boating equipment. I hope you will believe me when I say we are trying to be wise stewards of our fisheries resources and of our angler dollars, and I believe this is a good example of that!