An Experimental Study of Competition Between the Native Sacramento Perch (Archoplites interruptus) and Introduced Bluegill (Lepomis macrochirus)

The Sacramento perch (Archoplites interruptus), a sunfish (Centrarchidae) native only to the Central Valley of California, has been eliminated from most of its native range. To examine the role of interspecific competition in this decline, a series of experiments were conducted to assess the growth, aggressive behavior, and habitat use of Sacramento perch in the presence of bluegill (Lepomis macrochirus), an introduced centrarchid. The experiments indicate that (1) Sacramento perch gain less weight and show reduced growth when placed with bluegill, but that this interaction only occurs with food limitation, and is not affected by overall fish density; (2) Sacramento perch demonstrate less aggressive behavior than bluegill, but become more aggressive when they are conspicuously larger than bluegill; (3) Sacramento perch shift their habitat use in the presence of bluegill. Overall the results imply that Sacramento perch and bluegill exhibit interspecific competition where the mechanism of interaction is aggressive dominance by bluegill. It is suggested that long term persistence of Sacramento perch may require a habitat that is free of introduced centrarchid fishes, or one controlled by a naturally variable hydrological regime.