Community Responses to Piscivorous Largemouth Bass: A Biomanipulation Experiment

ABSTRACT

To test whether piscivorous largemouth bass (Micropterus salmoides) could be used to biomanipulate a 15-ha water supply reservoir, we assessed the effects of the addition of largemouth bass to the reservoir by monitoring the reservoir during the year before and three years after largemouth bass were stocked. A pilot study conducted in October 1990 indicated that the reservoir was eutrophic and contained a fish community dominated by zooplanktivorous threadfin shad (Dorosoma petenense) and no piscivorous fish. The reservoir was monitored during 1991 prior to stocking of largemouth bass (October 1991) and monitored in 1992, 1993 and 1994 after bass were present. Stocking of largemouth bass was successful and bass spawned in 1992, 1993 and 1994. The effects of bass cascaded down through the food web to the phytoplankton. In 1993 and 1994 the number of threadfin shad decreased, the abundance of cladocerans increased and rotifers decreased. Densities of diatoms and green algae were lower in 1992, 1993 and 1994 than in 1991. Although some phytoplankton densities decreased, blue-green algae, chlorophyll biomass, Secchi transparency, total phosphorus and total nitrogen did not change after stocking of largemouth bass and the biomanipulation was not successful in improving the reservoir's water quality.

Key Words:

• biomanipulation
• trophic cascade
• largemouth bass
• threadfin shad