Effects of Mechanical Harvesting of Eurasian Watermilfoil on Largemouth Bass and Bluegill Populations in Fish Lake, Wisconsin

Abstract

We examined changes in populations of largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus associated with mechanical plant harvesting in a lake heavily infested with Eurasian watermilfoil Myriophyllum spicatum. In Aug 1994, 18% of the total plant biomass in Fish Lake, Dane County, Wisconsin, was removed in a radial pattern of 2‐m‐wide channels. Largemouth bass and bluegill abundance, survival, growth, and length frequency were compared between pretreatment (1992–1993) and posttreatment (1995–1996) years. Following vegetation removal, mean abundance of largemouth bass and bluegill did not change significantly, but growth increased for age‐2–4 largemouth bass and declined for age‐5 largemouth bass and age‐4–5 bluegills. Survival increased for age‐2, −3, and −5 largemouth bass and age‐4–6 bluegills. Population size structure increased for both species. We conclude that removal of Eurasian watermilfoil may increase growth and survival of some age‐groups of centrarchid populations without altering the abundance of either species. However, this study lacked replication and control that is needed to separate effects of plant harvesting from effects of other biotic and abiotic factors.

Size‐specific growth of bluegill, largemouth bass and channel catfish in relation to prey availability and limnological variables

“…Therefore, bluegill in reservoirs with high per cent littoral volume may experience lower growth rates as a result of increased foraging in this habitat. This finding is consistent with Unmuth et al (1999) who found increased bluegill growth rates after manual vegetation removal. Bluegill typically avoid habitats with pH ≥ 9·5 (Serafy & Harrell, 1993) but are tolerant of habitats with pH as low as 5·0 (Rahel, 1984).…”

“…These models include some variables that managers can attempt to manipulate to enhance growth. For example, managers can manipulate prey populations (Noble, 1981) or alter the per cent of littoral area (Unmuth et al , 1999). Other variables, however, may not be easily manipulated ( e.g.…”

Changes in Diet and Food Consumption of Largemouth Bass Following Large-scale Hydrilla Reduction in Lake Seminole, Georgia

“…This decline in feeding efficiency has resulted in decreased growth and condition of largemouth bass in heavily vegetated systems (Colle & Shireman, 1980;Hayse & Wissing, 1996;Miranda & Pugh, 1997;Cailteux et al, 1998). When SAV is reduced, largemouth bass growth and condition increase, presumably because they have improved access to prey (Bettoli et al, 1992;Wrenn et al, 1996;Pothoven et al, 1999;Unmuth et al, 1999). Declines in SAV can result in a diet shift to prey with greater energy densities, which also leads to higher growth (Bettoli et al, 1992;Miranda & Pugh, 1997;Cailteux et al, 1998;Unmuth et al, 1999).…”

“…When SAV is reduced, largemouth bass growth and condition increase, presumably because they have improved access to prey (Bettoli et al, 1992;Wrenn et al, 1996;Pothoven et al, 1999;Unmuth et al, 1999). Declines in SAV can result in a diet shift to prey with greater energy densities, which also leads to higher growth (Bettoli et al, 1992;Miranda & Pugh, 1997;Cailteux et al, 1998;Unmuth et al, 1999).…”

“…Also, large shifts in SAV density can affect recruitment of phytophilic species, leading to changes in prey population composition (Anderson, 1984;Bettoli et al, 1991Bettoli et al, , 1993. The combination of these two factors can lead to large diet shifts in largemouth bass when SAV suddenly increases or decreases (Bettoli et al, 1992;Miranda & Pugh, 1997;Cailteux et al, 1998;Unmuth et al, 1999). Changes in diet can also affect fish growth, if food consumption and/or diet energetic content differs (Adams et al, 1982;Anderson, 1984;Bettoli et al, 1992).…”