Too Many Fish?

By Rex Johnson June, 2005

“Too many fish? How could a lake have too many fish?” That is exactly what I asked myself the first time someone told me that some lakes have too many fish. To me, it seemed impossible; it would be like having too much money. Well, as it is with most things in life, I did not understand the whole situation.

Let me explain. We all know that fish need food to survive and grow. For any lake, there is only a finite amount of food available and the lake can only support a certain number of healthy fish. Perhaps you have been to a lake that has way too many fish. They are stunted, very skinny and snake like. Why? Because they are starving! In addition, the other life-forms in these lakes that are important to a healthy aquatic environment are either being eaten totally or find their food sources affected by the fish that are devouring everything they can find. Scientific studies have shown that when there are too many fish in a lake, not only the fish but the entire aquatic balance of the lake suffers.

A typical stunted trout

In fact, every lake can be viewed as a controlled environmental experiment where the fish are an indicator of the balance between food sources and prey.If the fish are healthy, so is the lake as a whole. If the fish are not doing well, neither is the overall lake ecology. Many fishermen avoid lakes with stunted fish because who wants to catch or eat sickly looking stunted fish? In Washington, stunted fish typically occur in lakes that have over reproducing brook or cutthroat trout. Using the joint Hi-Laker/Trail Blazer data base, we have been able to identify approximately 100 high mountain lakes that have over-populated stunted fish. This is about 6% of all the fish bearing lakes in the Washington mountains! This is not an insignificant number.

OK, now some people may say, “Thanks for the information, but who cares if there are a few lakes with too many fish?” Well, there are lots of people who care, including responsible fishermen. Remember, most lakes in Washington had no fish in them naturally; fish were placed in these lakes by man. And in so doing, we have altered the lake environment and changed the natural balance, especially in those cases where the fish populations are excessive. Too many fish in a lake forces the fish to eat things they normally would not, basically everything that’s available. That is how we end up with the entire aquatic environment of a lake being out of balance. The awareness of this problem has been growing, and responsible citizens and land managers are now looking for long term solutions. The North Cascades National Park is such an example. The park is considering removing the fish entirely from their overpopulated lakes, and limiting or even stopping fish stocking. I am sure that no fisherman wants other land managers to follow the lead of the North Cascades National Park and reduce or eliminate fish stocking. It sure looks to me that we have gotten into the present situation by having a fisheries management plan that allowed the stocking of fish into lakes where they over reproduce, with no active program in place to resolve the overpopulated lake problem if it occurred.

A nice rainbow

What can be done about these existing overpopulated lakes, so that we can restore a healthy, balanced aquatic system? There are several approaches used today: fishing pressure, piscicides, gill netting, and predator fish. Each has good and bad points, and a role in improving lake habitat and quality fishery management. In lakes that have adequate fishing pressure, enough fish are removed from the lake annually that the lake never becomes over populated. Since we now have a list of over-populated lakes, the State could and should have special regulations for these lakes. Fish limits should either be higher than the present 5 fish limit or there should be no limit at all, and it should be required that any fish caught must be kept. Unfortunately, many of the over populated lakes are remote, difficult to get to, and some have no trail access at all. Changing the fishing rules will not help on these remote lakes.

Piscicides (fish poisons) are quite effective, but the safe use of these chemicals requires considerable planning, permits, and manpower to implement, and therefore it is expensive. Furthermore, for lakes with a strong outlet, there are concerns about downstream impacts. Also chemical solutions often elicit a strong negative public response. Therefore use of piscicides is generally limited. Gill netting has also been used to remove fish from lakes including a few mountain lakes. This technique is very labor intensive. For example, to remove all of the 66 brook trout from a small 1.2 acre lake in Mt Rainier National Park, researchers had to gill net the lake several times a year for 5 years, from 1993 to 1998. Although this technique has been tried on larger lakes with more complicated structure, it is doubtful that all the offending trout could ever be removed. Without removing all the problem fish, their reproducing habits soon results in the same over populated situation. This and its high cost limits gill netting to only a few mountain lakes.

Fish biologists with gill nets

Predator fish attempts have been used to control fish populations here in Washington. These experiments used lake trout or other predator fish that were not significantly more voracious than the target fish. The results have been mixed, from either no observable change to a slow improvement over decades.

A more effective, voracious predator does exist which could provide faster and better results: the tiger muskie. The tiger muskie is a hybrid created by crossing a male northern pike with a female muskellunge. The crossbreeding makes tiger muskies sterile. They can live for up to 25 years and in the right environment, they can grow to 20 inches in the first year! Tiger muskies are also well known for their voracious appetite and aggressive behavior. They are capable of eating other fish up to 2/3 their own body length. The best part is that they work 24 hours a day, 7 days a week, including holidays at no extra pay. There are presently over 17 states that stock them. In a well documented study in Idaho, tiger muskies were stocked in two mountain lakes to control brook trout. The results were very positive. In Ice lake, three years after the tiger muskie were introduced, and with some additional help from hand electro-shock fishing, all the brook trout in the lake were removed! In the other lake, the population of brook trout was reduced and the mean size of the remaining trout increased. Based on these very positive results, Idaho is now stocking tiger muskies in other lakes to control runaway overpopulations of trout.

A 12" tiger muskie in a mountain lake

Since Washington State already grows tiger muskies for its warm water program, they are readily available here and in fact Idaho has purchased its tiger muskies from Washington. With volunteer organizations like the Hi-Lakers and the Trail Blazers, mountain lakes can be surveyed and tiger muskies can be stocked in these lakes at almost no cost to the state. The introduction of predator fish like the tiger muskie appears to be an effective approach for improving overpopulated lakes. There are experiments in progress now in Washington to test the effectiveness of using tiger muskies to control overpopulated lakes.

A well fed tiger muskie

“Are there any concerns about the tigers leaving the lake and heading downstream eating everything?” When I asked fish biologists this question, they told me that they feel this is of little or no concern, because tigers are not a fish that would do well in a fast moving mountain stream. It is not their nature to live in fast moving water and their feeding habits are not suited to this environment. The consensus opinion was that they doubted tigers would want to leave the lake and if any did they would not survive.

“Well, that sounds good but what will happen to the tigers after they eat all the brookies in these lakes? Does the lake end up being infested with a few stunted tigers instead of a lot of stunted brookies?” Good question! As of now only a few mountain lakes have been stocked with tiger muskies, so there is not a lot of data, but based on the limited number of experiments, it is not expected that the tigers will be able to eradicate all the overpopulated fish, unless humans help by electro-shocking those that can successfully hide from the tigers.

In the Idaho test lake, they did electro-shock the remaining brook trout and then the tigers died (no food). Fish biologists then restocked this lake with non-reproducing trout. In the other lake, the tigers grew and got fat, and the remaining brookies got larger too, since there was more food for the remaining brook trout.

In about 25 years, the tigers will die off (they cannot reproduce) and then the brookies will again over reproduce and become stunted. Some people might say that nothing was accomplished, but this is hardly the case. There would be 25 years of quality fishing, and after that period more tigers could easily be stocked in the lake to keep the brookie population healthy. The cost to do this would be almost zero. Stocking tigers once every 20-25 years is no different than the stocking of the many high lakes that we presently do every 1 to 5 years with non-reproducing trout. As long as the lake has normal, non-stunted fish, then the lake ecology is in much better balance than with a lake that has stunted fish. Stunted fish clearly indicate that there are more mouths eating than there is food available, and we end up with the lake biota being totally out of balance. It is on this basis that people have been able to successfully force land managers to remove stunted fish populations, which is typically done by chemical means. Once this has been done (at tremendous cost) some land managers are hesitant to allow any fish to be restocked in those lakes. So by ignoring this problem of overpopulated lakes, we could easily end up with fewer and fewer lakes that have fish.

If we want avoid further intervention and possible curtailment of fish stocking in mountain lakes, all stocking needs to be done in a responsible manner based on scientific studies. These studies have shown that fish stocked at low densities have no discernable effect on the overall aquatic balance. Furthermore, we need to aggressively find solutions for the lakes that have runaway populations of reproducing fish. These problem lakes could become the Achilles heel of the fish stocking program. All of the approaches mentioned above can and should be used to resolve these problem lakes. Amended regulations and use of predator fish are especially important. As responsible fishermen and members of this society, I ask you to lend your support in encouraging the State to have an active program for addressing over-populated mountain lakes- lakes with too many fish!