Achieving Good Fishing
Fish are important consumers of energy produced in pond food webs. The abundance and body condition of particular species often provide a good indication both of pond habitat quality and of influences exerted by other fish species. As consumers, fish can also deplete their food sources, directly or indirectly affecting algae and benthic invertebrates.
The two most common species in warmwater fish assemblages of this region are bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides), forming a relationship in which the bluegill consume zooplankton and benthic invertebrates, and the bass rather quickly become large enough to consume bluegill.
Bluegill sunfish are common not only in ponds but also pools and backwaters of local streams. Spawning takes place during much of the growing season, with larger females producing multiple clutches each year. Bluegill sunfish typically become mature at ages 2-3 at this latitude. Nests are dish-like cleared out areas, in shallow water on sand or gravel, and are guarded by the male. Young-of-the-year and smaller juveniles feed predominantly on zooplankton in open water, while larger fish feed on benthic invertebrate prey in amongst plants in shallower parts of the pond.
Largemouth bass, like bluegill, are widespread in both streams and ponds of southeast Pennsylvania, and share similar spawning habits. Spawning typically occurs at lengths of 9-10" (ages 3-4), with the male guarding a dish-shaped nest in somewhat deeper water than is typical of the bluegill. The fry begin life as plankton feeders, but soon switch to consuming larger invertebrate prey and fish (largemouth bass can eat bluegill up to 1/3 their size). A wide variety of other fish species may also be considered. Be careful, however, before adding goldfish or carp, however, as they may tend to stir up bottom sediments or consumer aquatic plants.
Concerns about fisheries management normally arise over several years of perceived declines in fishing success, or more suddenly from a fish kill. Management approaches usually focus either on 1) habitat restoration, or 2) fish removal and/or stocking to change the relative abundances of fish species.
Habitat restoration should seek to enhance portions of the pond needed for spawning, foraging and shelter. Spawning areas, for example, can be enhanced by adding sand to areas with shallow gradients. A healthy plant community can provide critical food as well as shelter, and the survival of smaller fish can be greatly enhanced by retention of plant beds in parts of the pond. Although too many plants may sometimes interfere with fishing, their absence is therefore usually of greater concern.
Careful attention to the bathymetry (depth contouring) of a pond provides the best means of providing both shallow areas that can be colonized successfully by plants, and deeper, open water needed by larger fish. Logs and other structures providing cover, and deep holes can likewise improve physical habitat for fish. One benefit of dredging can be the planning of specific areas within a pond as fish habitat.
Guidelines for manipulating the relative densities of largemouth bass and bluegill are provided by the PA Fish and Boat Commission. An ideal ratio of bluegills/bass is considered to be approximately 5:1 by total weight. Higher ratios (e.g., 8:1) indicate an excess of bluegills. Overcrowding of the bluegill population can lead to interference with bass nesting success, further reducing bass population numbers, and causes stunting of the bluegills (undersized fish) which must compete more heavily with each other for limited food. Drawdowns are sometimes used to remove protective cover for the bluegills, making them easier prey for the bass and thereby helping to create more optimal ratios of prey/predators.
In extreme cases of last resort, rotenone may be used to completely remove the fish community, and start over by restocking. Rotenone is a plant extract that interferes with oxygen consumption by gill-breathers. A permit is required from the Commonwealth of Pennsylvania for rotenone application. A month after fish are removed, desired species can be restocked.
Don't be surprised if a highly productive fish pond is also a magnet for Great Blue Herons. Based on homeowner observations, the herons may often "case out" ponds while flying over, returning later when they can be undisturbed for a little quiet fishing.