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.