Ministry of Natural Resources
Black crappie: Their distribution and potential impact on fisheries in northwestern Ontario Scott Parker The invasion of Canadian freshwaters by non-native species is potentially the greatest threat to the ecological integrity and sustainability of native fisheries (see Schindler 2001). There is relatively little information as to why an introduced species succeeds or fails in its new habitat (Kerr and Grant 2000). Similarly, the ecological consequences of introduced species is generally poorly understood and equally poorly documented. Difficulties associated with examining interactions of introduced species with native species include the lack of pre-invasion data and the effect of other stressors, such as exploitation and climate change. Rarely is the introduction of a non-native species beneficial or at best benign to its new environment. The introduction of a non-native fish will have some impact on the recipient ecosystem and immediate effects are not necessarily indicative of the long-term result (Kerr and Grant 2000). In northwestern Ontario, black crappie (Pomoxis nigromaculatus) is a valued sport fish where it occurs. Black crappie have been so widely introduced intentionally, accidentally, and illegally, that the extent of their native range is unclear. The introduction of black crappie into new waterbodies is often an attempt to provide additional angling opportunities. Historically, the distribution for black crappie is believed to have been restricted to the eastern and midwestern United States, and southeastern Canada (Scott and Crossman 1973). In Ontario, black crappie are native only to portions of southern Ontario, but their distribution has dramatically increased provincewide. In northwestern Ontario, they were first introduced into Rainy Lake by the state of Minnesota in the 1920s (Kerr and Grant 2000), and similarly into Lake of the Woods at approximately the same time (Mosindy 1995). However, most populations of black crappie in northwestern Ontario are the result of intentional but unauthorized transfers (Krishka et al. 1996) and subsequent natural dispersal through connected waterbodies. In recent years, questions have arisen regarding the affects that the introductions may have on aquatic ecosystems. Historically, black crappie were believed to be relatively sedentary. However, unlike other sunfish, they travel in small schools throughout the year (Kerr and Grant 2000) and exhibit daily vertical and horizontal movements between resting and feeding areas (McNeil 1992). Once introduced into a waterbody,
Aquatic Update 2011-4
their movement between interconnected lakes can be extensive (Parsons and Reed 2005). In a chain of lakes in central Minnesota, annual emigration of black crappie into adjacent connected lakes was as high as 92 percent (Parsons and Reed 2005). If there are no barriers, once a fish species is introduced they will eventually colonize connected waterbodies in both an upstream and downstream direction. Establishment of black crappie populations is ultimately dependant on lake characteristics and habitat availability (Krishka et al. 1996, Schiavone 1985). Black crappie prefer relatively shallow productive lakes, bays, and rivers with extensive areas of aquatic macrophytes (Kerr and Grant 2000, Scott and Crossman 1973). Crappie are generally associated with abundant cover, particularly aquatic plants found in deeper nearshore areas (McNeil 1992). They are found most often in clear, calm water and prefer summer water temperatures of 20 to 25 C (Scott and Crossman 1973, McNeil 1992). They also tolerate prolonged winter temperatures and lower dissolved oxygen levels than other members of the sunfish family (Kerr and Grant 2000). Black crappie occupy nearshore areas like other centrarchids, but they are also open-water predators (McNeil 1992). Their flexibility in habitat and omnivorous diet enable crappie to utilize a variety of physical and environmental conditions and exploit habitats similar to walleye and yellow perch (Keast 1968). Black crappie are nest builders and spawn in late spring and early summer when water temperatures reach 13 to 20 C (Scott and Crossman 1973, Kerr and Grant 2000, Holm et al. 2009). They mature at two to four years of age and may live to be eight to 10 years old (Scott and Crossman 1973) or older. Black crappie up to 14 years old have been consistently sampled in Rainy Lake in northwestern Ontario (MNR, unpublished data). Black crappie are prolific breeders with mature females producing an average of 30,000 to 137,000 eggs annually. Deposited eggs hatch in three to five days (Scott and Crossman 1973, McNeil 1992). Young are initially pelagic and are distributed horizontally near the surface in open water (Krishka et al. 1996, Kerr and Grant 2000). As they grow, fry move into vegetated littoral areas to feed on a greater variety of prey (Kerr and Grant 2000).