Massachusetts Series Eastern Region

New Hampshire Series Western Region

by Kenneth J. Wagner, Ph.D., CLM. ENSR Corporation, Willington, CT.

Lake management embodies a wide range of activities aimed at meeting what should be clearly specified goals. Improving or maintaining water quality, controlling invasive species, optimizing plant community features, and maximizing fish production are common activities that relate to those goals, but not all goals are completely compatible. It is not necessary to choose one goal over another in most cases, but rather to balance the goals to sustain all appropriate uses and manage accordingly. Boating and fishery interests often present potential conflicts with uses such as swimming and water supply, but it is often possible to obtain a balance of uses if the ecological basis for potential conflicts is understood and the lake management plan incorporates planning for all uses. Since fishing is the primary interest of those reading this guide, fishery needs to be considered in lake management will be addressed here.

For the most part, controlling pollution is in the best interest of all lake users, human and non-human. Certainly there is wide agreement on the desirability of efforts to minimize the discharge of toxic pollutants, increase oxygen levels, lower sediment inputs, and stabilize features like temperature and pH within an appropriate range for each waterbody, no matter what the range and priority of uses of a given lake might be. There is also wide recognition of the problems caused by over-fertilization, many of which are linked to the other issues just mentioned. However, while the lowest possible fertility may have benefits for uses such as water supply and swimming, it poses challenges for fish production, which depends largely on the production of food within the lake, which in turn is related to its level of fertility.

The fundamental conflict between fish production and high water clarity has been described in a number of NALMS publications previously (Wagner and Oglesby 1984, Jones 2001). As algae decrease, a goal of most lake water quality management programs, water clarity rises but fish yield declines. The clearest possible water is desired for swimming or water supply, as clarity confers aesthetic, safety and economic benefits. However, greater fertility is desired for fish production, and usually results in lower water clarity. Some decision about what use has the highest priority may be needed. For the most part, water quality managers and fishery managers should all be pulling in the same direction. Yet it is possible to make a lake “too clean” from the perspective of fishery management, and water quality managers need to be aware of this.

It is also true, however, that a highly fertile lake may have problems that hurt fish and fishing. There are overfertilized lakes where fishkills limit fish biomass and fishery value, and others where there are so many panfish that anglers can’t keep them off the hook long enough to catch gamefish. Would you rather fish in “pea soup” conditions and catch 6-inch panfish with every cast with a long-shot chance at a trophy-sized gamefish, or spend your day on a lake where you might only catch a few fish, but where they are likely to be of better quality and size and where the sights, smells and swimming potential are much more favorable? This is a legitimate question, and each set of conditions has its supporters. It points out the importance of rational management goals. Management decisions that affect water quality and fish should depend upon clearly stated goals and the priority of water uses, which in turn require knowledge of user needs and ecological constraints.

Where fish production may be significantly reduced by a water quality project, consideration should be given to the changes that are expected. Will fish be of more desirable types, quality or size as a result of the change, or is there no benefit to offset the expected productivity loss? For example, higher clarity after nutrient controls may allow predators to better find prey species, favorably changing the size distribution of both over time. Are fish impacted by a loss of nutrients or some other change that might be mitigated? For example, dredging to eliminate contaminants may remove key structural features of fish habitat, including woody debris and plants that could be replaced or otherwise compensated. Is overall fish production reduced, or just production in part of the lake or by certain species? For example, an aeration project may reduce fertility and increase clarity in shallow waters while greatly enhancing deeper water fish habitat. In any of these examples, one must ask if the expected changes are consistent with management goals and priorities, which should balance the various uses to the extent practical.

Where reduction of nutrients does represent a loss of valued fish production, one might ask how the goal of increased water clarity might be achieved without such a major reduction in nutrients and overall fertility. Projects that remove planktivores (most panfish) and/or stock piscivores (most gamefish) are indeed possible, and can improve water clarity. These approaches may not eliminate the need for nutrient controls, but may better support the fish community than drastic reductions in nutrient supply.

Changing the plant community represents an area of frequent conflict between management for fishing and for swimming or many forms of boating. The amount of vegetation needed to properly support a fishery depends on the type of fish and tends to have a wide range even for one species. There is room for multi-use management as long as the swimmers understand that a lake is not a swimming pool, the powerboaters are willing to stay out of shallow water, and the anglers recognize a desirable limit on plant density. Management can get complicated, however, when invasive plant species are involved. Prevention of invasions and rapid response to new infestations should pose little conflict, but major plant control projects on a lakewide basis have limited probability of eliminating the invader and often damage non-target plants or animals. These lakewide projects should be planned with consideration of all uses and associated biological elements.

Some of the more serious conflicts between anglers and plant managers have occurred in relation to constructed reservoirs where there is no native flora and invasive species represent most of the vegetation available to support a fishery. While consideration must be given to the impact of inadequate control, complete eradication is often unlikely and control to some intermediate level that supports the range of uses may be the most practical approach. Such situations require careful planning on a case by case basis, capitalizing on experience elsewhere but not assuming that because an approach worked or did not work in Lake A that it is or is not appropriate for Lake B. Interested parties need to do their homework before getting involved in the permitting process for lake management projects.

Stocking programs have generated a lot of discussion among both fishery professionals and lake managers in recent years. Decades of genetic research and gradual recognition of the value of native communities have fostered a shift in fishery management emphasis. There are major programs to remove competing or predatory species to restore native fish communities in many areas, and fishermen at many lakes are either prohibited from using live bait or discouraged from releasing unused baitfish. Yet stocking is still a mainstay of fishery management, given much higher demand than supply in some areas. But to what degree should the support of stocked fish communities dictate lake management? The answer would again appear to lie with a clear statement of goals and a management plan that seeks balance among them.

Not all management plans can accommodate all desired uses in a balanced fashion; sometimes a yes-or-no answer is required, and decisions on which uses will have priority over other uses are necessary. Water supply for human consumption is not likely to yield to desires for greatly enhanced fertility to support better fishing; even access to the water supply for fisherman may be prevented based on multiple risk factors. In New England, the desire to restore historic runs of alewife (Alosa pseudoharengus) from the sea to lakes in which they can spawn threatens water clarity through loss of large zooplankton grazers that are eaten by the young before departing downstream to the sea. Yet such restored runs are a benefit to coastal ecology. However, the establishment of landlocked alewife populations to support stocked gamefish has sparked a major controversy. Such a forage base will support excellent gamefish growth, but will decimate the zooplankton and limit recruitment of many fish species, drastically altering lake ecology, limiting algal control, and favoring algal blooms. Not all lakes can support all uses.

In developing lake management plans, all interests should be considered, and the best plans will balance those interests to the extent possible, while clearly justifying actions that appear to favor one use over another. There is indeed a need to incorporate fishery considerations in lake quality projects, but these are not the only considerations in lake management. Ultimately, it is up to competent lake managers to work with user groups and to understand the ecological opportunities and constraints presented by each lake when crafting management plans.   

References:
Jones, W.I. 2001. Chapter 2. Ecological Concepts. Pp 9-48 in Holdren, C., W. Jones and J. Taggart. Managing Lakes and Reservoirs. NALMS, Terrene Inst. and USEPA, Madison, WI.
Wagner, K.J. and R.T. Oglesby. 1984. Incompatibility of common lake management objectives. Pp 97-100 in Lake and Reservoir Management. USEPA 440/5/84-001.

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