The worth of reclamation as a fishery management tool has been demonstrated well in many cold- and warm-water habitats in recent decades. The art of reclamation, however, is still in an early stage of development. Because the removal of undesirable fishes from a pond, lake, or stream with toxicants is a complex process, frequently including impacts on human welfare and ecology, a discussion of recommendations and research needs is in order.
A fish toxicant should be specific to target species, easy to apply, harmless to non=target animals and plants, safe to human handlers, subject to rapid and complete degradation or detoxification, and non-persistent in animals, plants, or the environment. Although cost of a toxicant is important, it must be a secondary criterion rather than a governing one. Also, a fishery manager using a toxicant should be provided with adequate information on the relationships between duration of exposure and concentration to yield a killing dose. This information must include any limitations inherent in the performance of the toxicant due to environmental factors such as water quality, water temperature, turbidity, or presence of abundant plant life. The fishery manager must be advised on methods for distributing the toxicant to secure optimum results with minimum quantities. Moreover, he must have field-type analytical means to determine the quantity of toxicant present in water at a given time and to detect when it has degraded to non-toxic levels. He must know how and when to detoxify the chemical, if necessary, to protect competing users of the water.
Few of the fish toxicants discussed in this review meet most of the above criteria. Thus, some chemicals such as endrin, toxaphene, Guthion, parathions, and cyanide compounds have been banned or restricted as fish toxicants in Federal waters in the United States. Many more specific toxicants such as TFM, Fintrol, and Squoxin are needed, but the research necessary to find and develop them is long and expensive.
The matter of formulating fish toxicants has received too little attention in the past. The fact that a body of water is a three-dimensional system, perhaps complicated by thermal stratification, is often ignored. A toxicant applied at the surface of the water may fail to penetrate into depths unless it has been properly formulated to do so. For example, liquid toxicants sprayed from aircraft onto the surface of a lake stand little chance of penetrating to preferred depths. The volatile solvent of the toxicant may evaporate in the aircraft wash, leaving particles of the insoluble toxicant to fall and remain on the surface film. Through research, non-repellent formulations of toxicants must be designed to reach target fishes at their preferred depths. The most desirable formulations would release the toxicants only in the certain strata of water target fishes dwell.
The many possibilities of integrated controls deserve attention from investigators. For example, attractants possibly would be used to concentrate target fishes, or electrical gear to herd them into bays where they could be confined by nets and killed with toxicants. Mechanical or electrical barriers could be refined and employed more often to prevent re-invasion of reclaimed waters by undesirable fishes. A harmless repellent in tributary waters might keep target fishes restricted to waters under treatment with a toxicant. An irritant might force bullheads out of bottom sediments and into more effective contact with a toxicant. Water levels in impoundments might be manipulated to force undesirable fish into situations where they could be controlled with toxicants. Hopefully, integrated controls can be developed that will meet objectives, but result in smaller quantities of toxicants applied to waters or a reduction in the number of re-treatments necessary to maintain control.
Much study is needed on the means and methods for valid and meaningful assessment of reclamations, especially on large, wild waters. The results of a reclamation must be weighed honestly against the short- and long-term improvements in a fishery and benefits to the public. Greater use of statistically sound and computerized sampling may aid in assessing reclamations.
Knowledge of the biology of undesirable fishes is a primary requisite to effective control. The weakest link in the life cycle may be the only logical target for toxicants or other control measures. The larval stage of the sea lamprey in streams is an example. Or, attacking spawning congregations of problem fishes may provide a degree of control where poisoning of an entire body of water is impractical or impossible. Furthermore, an understanding of the life history of an undesirable fish might lead to biological or other controls less drastic than poisoning.
It is important, too, that we learn more about the environments in which problem fish exist and the factors which contribute to the development of problems. In some situations, the problems with undesirable species may be avoided or solved by manipulating environmental factors instead of by poisoning.
In any case, the correction of undesirable fish problems with toxicants should be the last resort of a fishery manager. All alternatives to the use of a toxicant should be considered or tested. Then, in instances where the need for control can be well demonstrated, the recommendation to treat a body of water of public interest should be referred to an impartial panel of experts for a decision on whether to employ a toxicant or not. It is apparent that fish control activities with toxicants will incur increasing scrutiny by the public and regulatory agencies in the years ahead. Research can provide the means and methods for achieving control of problem fishes without undue hazard to the environment.
We also recommend that professional societies and conservation agencies adopt ecologically sound policies governing all vertebrate animal control, including fish. Supervising echelons should refer recommendations for lake or stream reclamations to impartial advisors for review of the demonstrated need, of the definition of target species, of the candidate toxicants and formulations, of the scope of pre- and post-treatment surveys, and of plans for subsequent management and evaluation. Provision should be made that the same reviewers have an opportunity to study the results of each reclamation and to make changes as necessary in the guidelines pertaining to reclamations within their purview. Moreover, we recommend that fishery personnel engaged in reclamations have or receive formal training in control methodology in academic or in-service schools. Considering the public concern over pesticides and the quality of the environment, it is imcumbent on the fishery profession to ensure that the poisoning of waters to control fish is executed only by competent, well-trained biologists.
Some countries face certain problems in fishery management that do not exist in North America, in addition to problems of universal nature. An attempt will be made to cover both types of problems with emphasis on the first.
More fish culture is carried on than ever before, and the need for more research on toxicants and collecting aids has been recognized. When fish are intensively cultured, it is necessary to eliminate predators and competitors of the desired species. However, the more desirable specific toxicants, such as rotenone and antimycin, are not always available in countries which need them. For example, New Guinea has a problem with tilapia that burrow into the mud to escape exposure to toxicants. Powerful insecticides were readily available and used with serious results to the streams and ponds. Rotenone also was available, but not in the most effective formulation until recently. Rhodesia has expressed concern about tilapia in ponds, but as yet has not obtained a selective toxicant. The United Kingdom also needs a suitable selective toxicant which will eliminate all fishes except the trouts. Ceylon has a problem with marine animals and needs a solution. The Philippines need a toxicant that is inexpensive, non-toxic to other life, and readily available. Endrin is used at present, but the means to monitor its degradation are lacking there. The Philippines also desire a toxicant that will rid oyster beds of predators without harming the oysters. Netherlands would like a selective toxicant that would control fish which are not localized in one place. They also are looking for surfacing agents which are more or less harmless to the fish.
Improvements in application methods are greatly needed. Methods must be found to reach fish burrowed into mud or remaining in shallow, marshy, or weedy areas. Ireland encounters the latter problem with northern pike in trout waters. The vegetation intercepts the spray, or the toxicant breaks down before it reaches target fishes. Better methods also are needed to ensure proper dispersion of toxicants in all types of waters. Perhaps, improved equipment might permit treatment of areas which were heretofore unreachable.
Steps should be taken to ensure that adequate pre-treatment surveys are made. Little, if any, survey is carried on by some countries. Ireland provides an example of what should be done. Contour surveys are made with echo sounders; inflowing drains or streams are located, identified, and treated to prevent re-infestation; deep areas are marked with buoys; and the outflow volume and dilution are recorded. Large lakes are spot-treated when the fish are spawning. No mention was made, however, of chemical and biological surveys, or use of on-site bioassays. New Guinea and the Philippines use wire screens to prevent re=infestation by problem species, and New Guinea computes the water volume to determine the necessary quantity of toxicant. The United Kingdom and Denmark require a survey of fish species present, and soundings to determine the volume of water to be treated.
Post-reclamation surveys also are needed in greater detail. Ireland sets nets and traps a few weeks after treatment to detect if any undesirable fish are present. If the treatment was successful, caged trout are placed in the lake 2 months after the treatment for a week to ensure that the water is not toxic. Then trout are stocked. The United Kingdom tests the suitability of treated waters for restocking by exposing fish in live=boxes. Other countries such as Sweden, Finland, and Yugoslavia have studied the effects of rotenone on the flora and fauna in treated waters.
A lack of management follow-up also is evident. Ireland stated a policy that is followed. Each season after treatment, test netting is done to see if the water still is free of unwanted fish. If not, netting and trapping are practiced to suppress the undesirable fishes. The water is not treated again with a toxicant until these populations get out of hand. This usually occurs every 5 to 10 years. New Guinea finds that ponds have to be drained and dug out every 2 years to eliminate burrowing fishes.
There are problems which result from the selection of a toxicant. The cost of a toxicant may be weighted too heavily in comparison with the expected benefits of a reclamation. Thus, cheaper but more hazardous toxicants are selected and used more often than they should be. This may lead to environmental contamination that proves more costly in the long run.
Much more research and an increased emphasis on policy development are needed in reclaiming waters for fish management. At least we have a beginning.
