White Perch in Small North Carolina Reservoirs: What Explains Variation in Population Structure?

White Perch Morone americana have been introduced into many inland systems throughout the United States. To determine factors affecting White Perch abundance and size structure, we compared White Perch growth, timing of maturity, and trophic level; the abundance of a predator (Largemouth Bass Micropterus salmoides); the abundance of an ecologically significant mid-level omnivore (Gizzard Shad Dorosoma cepedianum); prey availability (chironomid and zooplankton abundances); and environmental variables (specific conductivity, Secchi depth, dissolved oxygen concentration, and temperature) among four reservoirs (two with high White Perch abundance and two with low abundance). White Perch size structure was closely tied to abundance, with truncated size structure as abundance increased. Among the other variables we tested, only Largemouth Bass abundance had a significant (negative) relationship with White Perch abundance. White Perch size structure appeared to be highly density dependent, and variables that commonly explain variation in abundance of introduced fishes did not explain differences in the four White Perch populations we studied. Further study of the competitive and predatory interactions of White Perch and Largemouth Bass over ontogeny could shed light on the mechanism(s) potentially shaping population structure of the two species where they coexist. Introductions of White Perch Morone americana have been problematic for freshwater fisheries managers (Madenjian et al. 2000; Gosch et al. 2010b). Since the 1950s, White Perch have been intentionally and unintentionally moved from their native range (i.e., North America’s Atlantic coastal estuaries and river tributaries) into freshwater lakes, inland rivers, and reservoirs of the eastern and central United States (Scott and Christie 1963; Irons et al. 2002; Harris 2006). Studies in these areas have indicated detrimental impacts of White Perch on native species, primarily through competition (Schaeffer and Margraf 1986; Parrish and Margraf 1990, 1994; Prout et al. 1990) and egg *Corresponding author: [email protected] 1Present address: Minnesota Department of Natural Resources, 5351 North Shore Drive, Duluth, Minnesota 55805, USA. Received June 28, 2013; accepted July 24, 2013 predation (Schaeffer and Margraf 1987; Hartman and Margraf 1992; Madenjian et al. 2000). White Perch are excellent competitors and invaders due to a variety of life history traits, including their tolerance of a wide range of environmental conditions (Stanley and Danie 1983; Johnson and Evans 1990); their role as omnivorous, opportunistic feeders (Reid 1972; Hines 1981; Schaeffer and Margraf 1987; Hurley 1992; St-Hilaire et al. 2002; Couture and Watzin 2008; Gosch et al. 2010b); and their reproductive flexibility, with maturation occurring as early as age 1 or as late as age 3 (Sheri and Power 1968; Bur 1986; Schaeffer and Margraf 1986; Chizinski 2007; Feiner et al. 2012). Population dynamics of native and introduced White Perch have been linked to a variety of abiotic and biotic factors (Feiner et al. 2012, 2013), such as turbidity, dissolved solids, and specific conductivity (Hawes and Parrish 2003; North and Houde 2003) as well as predation (Ward and Neumann 1998; Margulies 1990; Vrtiska et al. 2003; Gosch et al. 2010a) and competition with other fish (Hawes and Parrish 2003). Finally, intraspecific competition in high-density White Perch populations may structure those populations through density-dependent mechanisms (Sheri and Power 1972; Schaeffer and Margraf 1986; Hurley 1992). White Perch are widely distributed in North Carolina reservoirs, and the population abundance and size structure of White Perch vary among these systems (Wong 2002; Feiner et al. 2012). Anecdotal evidence indicates that White Perch attain a large adult body size in some reservoirs. Conversely, White Perch can also dominate reservoir fish communities via high densities of small individuals. A better understanding of the mechanisms driving this variability in abundance and size structure is important for managing present and future introductions of White Perch. Thus, we quantified the abundance and size structure of White Perch in four small North Carolina reservoirs 77 D ow nl oa de d by [ N or th C ar ol in a St at e U ni ve rs ity ] at 0 9: 32 1 1 D ec em be r 20 13