Non-native fish have invaded and altered freshwater ecosystems around the world. Many of these species are popular gamefish that have been purposefully introduced beyond their native range to enhance local fishing opportunities. However, the long-term impacts of these introductions are often detrimental to native fishes. Once introduced, non-native species can quickly outcompete native species for food and habitat.
White perch (Morone americana; Figure 1) are a widespread invasive species in freshwater habitats throughout North America. Perch are native to brackish and tidal freshwater rivers along the East Coast and are commonly targeted by anglers for their tablefare. Because of their opportunistic appetite and ability to adapt to a wide range of habitats, white perch can quickly dominate the native fish community.
Though native to rivers that flow into the Albemarle and Pamlico Sounds, white perch have become established and invasive in inland lakes and reservoirs in the Piedmont region of North Carolina. The diets of these landlocked populations of white perch have been found to overlap with gamefish such as bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides). Black crappie (Pomoxis nigromaculatus; Figure 2) are another popular species of gamefish native to lakes in North Carolina. In the mid-2000s, recreational anglers targeting crappie began reporting reduced catch rates in many North Carolina reservoirs. Around this time, white perch were also increasing in abundance.
Dr. Zach Feiner, Dr. Marybeth Brey and Caroline Burgett from North Carolina State University led a study to examine the potential dietary overlap between white perch and black crappie. The study took place in two large reservoirs in the Piedmont: Lake Norman and Jordan Lake (Figure 3). Crappie and perch were collected from four study sites in each reservoir during the spring, summer and fall by nighttime electrofishing and gillnetting. Additional crappies were collected in Lake Norman by purse seining, where a school of fish is encircled by a wall of netting. The fish were categorized into three size classes that represented their life history stage: small (young-of-the-year or age-1 if caught early in the spring), medium (primarily juveniles) and large (primarily adults). To analyze their diets, the stomachs were removed, and the contents were identified visually. A molecular technique known as stable isotope analysis was also used to look at long-term dietary patterns by examining the ratios of nitrogen and carbon in the fish’s tissues.
The results indicate that there is considerable overlap between the diets of black crappie and invasive white perch. The overlap was most prominent between black crappie early in their development and all sizes of white perch. Black crappie and white perch primarily feed on invertebrates at smaller sizes. By examining gut contents, the researchers found that zooplankton and free-swimming insect larvae were consumed readily by both species in spring but by fall, the fish fed heavily on benthic macroinvertebrates. The stomach contents of white perch and black crappie indicate that both fishes have similar dietary preferences that change with the season. The overlap in diet suggests that these two species are competitors for food, which may hinder the growth and survival of young black crappie.
As crappie and perch grow larger, they become more piscivorous, feeding on smaller forage fish. Larger white perch have a broader diet than black crappie, feeding on fish eggs and larvae, invertebrates, and detritus (decaying organic matter). This flexibility in their diet can be beneficial to white perch if their preferred prey decreases in abundance.
Invasive species can quickly alter the aquatic food web, increasing the level of competition with native species. As white perch become more abundant in inland lakes and reservoirs, it is important to understand how they may compete with native species. Controlling the spread of white perch may be needed to help restore black crappie populations.
Feiner, Z.S., M.K. Brey, and C. Burgett. 2019. Consistently high trophic overlap between invasive white perch and native black crappies in southeastern reservoirs. North American Journal of Fisheries Management 39(1): 135-149.