A MODEL OF BLUEGILL LARGEMOUTH BASS INTERACTIONS IN RELATION TO AQUATIC VEGETATION AND ITS MANAGEMENT

Dense, slow growing populations of bluegill sunfish are common in lake s where heavy vegetation prevents thinning of bluegill numbers by thei r primary predator, the largemouth bass. Since bass can effectively pr ey on bluegill only along the periphery of dense macrophyte beds, mowi ng vegetation to create additional edge may improve growth rates and s ize structure of both species. While this concept is straightforward, determining the optimal vegetation configuration for the two species i s difficult because mechanisms such as feeding, competition, and morta lity together determine the population response and may interact in co mplex ways. This paper describes a model that simulates the interactio ns of bluegill, largemouth bass and their invertebrate prey in the con text of vegetation structure. The model is calibrated to data from a h eavily vegetated temperate lake and is used to examine the fish respon se to additional edge created by mowing channels through plant beds, B ass growth rates and numbers increased after most simulated vegetation removals because their access to prey increased, Bluegill grew fastes t when about 30% of the vegetation was cut, but responded negatively t o mowing more than about half the plants. Bluegill responded to the ma nipulations more by changing growth rates, while bass responded more b y increasing numbers. Moderate plant removals accomplished by mowing m any narrow channels are most likely to simultaneously benefit both spe cies. The model synthesizes current understanding of the relationship between macrophytes, bluegill and largemouth bass, and suggests which vegetation manipulations are most informative to test in large scale e xperiments. (C) 1997 Elsevier Science B.V.