Most people think the only purposes of maintaining a healthy fish population in their decorative or recreational pond is either to have them for angling or for having pets. The fact is fish serve a key role in a well-balanced pond ecosystem. Fish are important consumers of energy produced in pond food webs. Through consumption, fish populations directly and indirectly affect algae growth and invertebrate populations which is then reflected in the pond’s appearance and water quality.
In the Denver metro area, the most common fish assemblages are Bluegill and Largemouth Bass. Bluegill will consume zooplankton and benthic invertebrates and Largemouth Bass will quickly become large enough to become the top predator and feed on the Bluegill. Juvenile Bluegill will focus on zooplankton in open water and mature fish will focus on invertebrates. Bluegill spawn during most of the summer months at 2-3 years of age, with females producing multiple clutches per year. When they clear their small, dish shaped nests, the female will lay eggs and leave shortly after while the males stay to guard the nests. Largemouth Bass will begin to spawn when they are about 9-11” in length and like Bluegill will stay to guard the nest, which are usually in slightly deeper water than Bluegill nests. Largemouth Bass will start to feed on insects and zooplankton until they are large enough to begin consuming other fish and larger invertebrates. An ideal ratio for Largemouth Bass to Bluegill is approximately 1:5 by total weight. Higher ratios indicate an overabundance of Bluegill which can interfere with bass spawning success. This can exacerbate the situation and Bluegill growth will begin to stunt. If Bluegills become overcrowded, the pond can be drawn down so protective habitat is reduced and predation increases.
A need for active fisheries management is usually realized either after a sudden fish kill event or from several years of declining angling success. Fisheries management in small ponds in Colorado are usually focused on habitat improvement or adjusting fish species abundance through fish stocking or removal. When examining habitat restoration, the goals should be thought of in terms of achieving optimal areas for spawning, foraging, and shelter. Pond owners can enhance spawning areas by adding sand and pea-gravel to shallow, low gradient areas of the pond. A healthy plant community is also crucial to providing shelter for fish and habitat for invertebrates. Many pond owners are overly concerned with the presence of vegetation, but from an ecological perspective the absence of aquatic vegetation is more of an issue.
The first step to improving fish habitat is understanding the depth contours and the terrain within the resource. Aqua Sierra will conduct a bathymetric survey as a first step in a habitat improvement project. Knowing the abundance and composition of vegetation and structural features within a pond will guide further habitat improvements that will optimize the pond’s fishery. Contact an Aqua Sierra Biologist today to start managing your pond ecologically today!