What is a Balanced Fish Community?

Fishery management is very challenging. It involves physical, chemical and biological factors, plus the interactions between them. There are multiple life stages for each species, multiple species, and multiple trophic levels. The community is in constant flux, so stability is not a very applicable term. Instead, we tend to think in terms of a balanced fish community, one in which the various components are found in relative proportions that minimize fluctuations in year class strength, overall biomass, and energy flow. There is no one “right” combination, but a balanced fish community will have predator and prey species at a ratio that prevents either from being dominant. A balanced fish community will sometimes have strong temporal variations, such as when young of the year are produced and there are suddenly many small fish present, but predation is expected to foster an annual cycle of increase and decrease that maintains balance.

Range of species and sizes.

Lakes provide a variety of fish habitats and food resources, but not all lakes are created equal and some are better suited for some species than others. A deep lake with a cold bottom layer with adequate oxygen through the summer will support trout much better than a shallow lake with only a warmer upper layer during summer. Species such as pickerel and pike are “sit and wait” predators, doing best in lakes with ample submerged vegetation where they can hide until prey come near, while others such as walleye tend to prowl open water chasing schools of smaller fish. Largemouth and smallmouth bass are intermediate in predator tactics, with slightly different temperature and cover preferences. Prey species have similarly variable preferences, including yellow and white perch, multiple sunfish species, and a suite of minnows. And larger specimens of many prey species become predators of smaller fish. So there are many considerations in managing a fishery, and achieving balance can be elusive, but similarity of the results of successive surveys over 3 to 5 year intervals is a good indication of balance.

Overabundant and stunted sunfish.

In theory, stocking fish can help maintain balance if it compensates for weak year classes of key species, or adds species that occupy habitats and/or consume food resources that are otherwise not fully utilized, but that is not typically how stocking is used in New England states. Rather, gamefish are stocked to support fishing where natural production is inadequate. Prey species are stocked to support gamefish growth, but usually this involves species that overlap with existing species and destabilize the fish community.  Landlocked alewife represent a controversial example; they provide an impressive forage base but out-compete other fish by efficient filtering of all but the smallest zooplankton from the water column. Good fishing is usually the key goal of fish stocking programs, which is not mutually exclusive with community balance, but the two often do not go hand in hand.

Top Down vs. Bottom Up Control of Algae

A lot of research over about two decades led to the conclusion that algal abundance may be strongly influenced by cascading influences from the top of the food web. Certainly low nutrient availability will minimize algae biomass, but just because nutrients are abundant does not always translate into high algae biomass. The reason appears to be that a favorable biological structure can result in rapid consumption of algae as they are produced, preventing the build-up of algal biomass. Having abundant large predatory fish reduces the number of small fish, which in turn reduces predation on zooplankton, allowing greater grazing pressure on algae. Not just any zooplankton will depress algae, however, and the forms that generate the greatest grazing pressure (large bodied herbivores, especially Daphnia) are also the preferred food of many small fish. But a greater biomass of big grazing zooplankton will increase consumption of algae, resulting in the lowest biomass of algae for whatever level of fertility is present.

Small (Chydorus) cladoceran zooplankton

So can the most favorable biological structure possible achieve algae control when nutrients are abundant? The answer appears to be “no”. At phosphorus levels in excess of about 80 ug/L, research in Europe has found that no amount of zooplankton can prevent algae blooms. As blooms are probable at phosphorus levels above about 25 ug/L, there is an intermediate zone where biological structure can make a major difference, but nutrient controls may be necessary to prevent blooms. And since some cyanobacteria grow to large particle sizes at the sediment-water interface before rising in the water column, presenting zooplankton with a difficult challenge for consumption, even low nutrients in the water column and an elevated biomass of large bodied zooplankton may not be able to control cyanobacteria.

Large (Daphnia) cladoceran zooplankton

Creating a favorable biological structure provides benefits and is strongly encouraged. Nutrient control is clearly a critical part of algae management. But there is not much reason for a debate over the relative value of bottom up vs. top down controls; we need every tool we can get to keep our lakes in desirable condition!

Evaluating Risk Associated with Cyanobacteria

Cyanobacteria have taken center stage in many newscasts in the last couple of years, and have gotten more attention from the USEPA and state environmental agencies in the last 3 years or so than in the two decades before that. Cyanobacteria are not new; they are among the oldest organisms on the face of the earth, and are adapted to life under a wide range of conditions. But they do best in warm, freshwater with elevated phosphorus levels and a low ratio of nitrogen to phosphorus. Urbanization and agricultural use of land tends to create conditions that favor cyanobacteria, and the warmer temperatures related to climate change are fostering increases in blooms. All of this has been well documented in scientific literature with minimal bias; all political wrangling aside, we understand why cyanobacteria are becoming a more common problem and recognize the risks associated with these organisms.

But how is that risk assessed? New England states have a range of systems in place, but most fall short of addressing the issue to the extent necessary to allow appropriate response. The World Health Organization came up with thresholds of 20,000 and 100,000 cells/mL for low, moderate, and high risk, but cell counts are approximate and do not directly translate into toxin concentrations, which is where the risk really lies. Most states adopted a compromise concentration of 70,000 cells/mL, but it is certainly not true that 69,999 cells/mL is acceptable while 70,001 cells/mL represents extreme hazard. Thresholds create hard boundaries along a gradient with a lot of important variation. Some states now encourage toxin testing, but the ability to economically and rapidly test for the range of known toxins is very limited. Consequently, lakes get posted with warnings to avoid contact when cyanobacteria levels are elevated without actual confirmation of a hazard. Warnings do not legally prevent lake use, but rational people usually take those warnings seriously.

So what is the actual risk? This is a tough question. There is no doubt that some cyanobacteria produce toxins, including liver, nerve and skin toxins, but many species do not produce toxins. We know which species potentially produce toxins, and have identified the genes that allow toxin production, but because a species can produce toxins does not mean that it will. Many very dense blooms contain no toxins. Major die off of a bloom of toxin-producing cyanobacteria can result in elevated toxins in the water without a high cell concentration, although rarely for more than a few days. Risk is a matter of toxicity and exposure, and we don’t know enough about either to make definitive statements in many cases. Posting a lake for elevated cyanobacteria can help control exposure, but failure to follow up on toxicity leaves open questions and impairs our future ability to predict risk. We still have a lot of work to do to characterize cyanobacterial risk.

Managing in a Regulatory Climate

Many years ago when someone or a group felt that something about a lake was not right, they organized and changed it. Lake level was lowered, sediment was scraped, herbicides were applied, shorelines were bulkheaded, and so on. Many of these actions were appropriate, but many were not and most have impacts to other aspects of lake ecology that were not being considered or mitigated. In some cases the results were disastrous, not curing the targeted problem and making things worse in other ways. The dawn of ecological thinking and the incorporation of such thought into government resulted in many environmental laws, starting in the 1960s and peaking in the 1970s, with follow up ever since. Many environmental agencies were created, some completely new (the federal EPA) and others altered to redirect their mission (the federal USACE). State agencies underwent similar formation or transformation. The basic premise was that we needed to regulate how we treated the environment to avoid catastrophes while “fixing” perceived problems.

It is good that we have such agencies and the laws and regulations that guide them, but like most institutions over time, the mission is sometimes perverted or focus is lost. Incremental adjustments to regulations or changes in definitions create unforeseen consequences for legitimate activities. People use the system as a weapon instead of a tool. Agendas get created, processes become more complicated, and it becomes harder to manage. Lake management is suffering from just such a progression.

The fundamental problem with permitting systems is that they are managed by regulatory agencies with little or no obligation to solve a problem. Permits are not applied for because it is a fun thing to do; we request permits because we want to solve a problem. It is rare to have a regulatory staffer say “Oh, I see your problem. And I understand why you want to do what you have laid out in this application. There are a few issues we have to address, but let me see if I can find a way to make this work…” Instead, the regulator views his/her job as preventing environmental damage, not solving an existing environmental problem. If, after a frustrating process of submission, hearings, delays, and revisions,  you give up trying to solve the problem, that is just as good as the agency issuing a denial. The permit system has been upheld. The potential risks from the proposed action have been averted. It doesn’t matter to the regulator that the problem has not been solved.

If someone is advancing a clearly detrimental request, say asking to fill a cove of a public lake full of endangered species to build a supermarket accessible by boat, all to make a few bucks, it is pretty easy to rule that out. But most requests have merit and raise management issues that need attention. What happens when the request is to control an invasive species known to reduce biodiversity, one that will impact some of the endangered species in that same lake, but the options for control may do some temporary harm to the lake? This is a balancing act, but one in which the actual problem may be given very limited consideration. After all, no state in New England (or anywhere for that matter) has a law saying that if an invasive species is found it must be addressed, but most states do have a law that says you can’t harm a protected species or damage wetlands, of which lakes are usually considered to be a category.

Any action that reduces the invasive species may be rejected under current regulatory systems if it is perceived as being harmful to some interest of an applicable law, such as taking individuals of an endangered species, and the burden of proof is on the applicant. The regulatory agency is under no obligation to properly justify its assumptions at that stage (you would have to go to court for that) and can require all sorts of studies of the applicant before rendering a final decision, which may still be unfavorable. And if the applicant gives up and the invasive species eliminates some endangered species in the lake? Apparently that is acceptable, as opposed to losing some of the endangered population in the process of eliminating and invasive species and saving the endangered species in the long run!

The problem is twofold: 1) Lack of big picture thinking by agency staffers, partly attributable to having limited background in aquatic ecology and lake management, and 2) Vesting authority in a regulatory process without any obligation to solve the problems that result in requests for permits. Both of these are solvable, but appear to require political intervention; scientific logic and economic sense are just not getting the job done these days.

Zebra mussels killed this mollusk