Experimental Population Reduction of Largemouth Bass from an Overpopulated Tropical Reservoir: Impacts on Predators and Prey

Behavioral shifts by bass (Micropterus spp.) anglers toward catch and release practices has severely decreased the ability of managers to control predator-prey dynamics and reduced effectiveness of harvest as a management tool. Lack of harvest reduces managers’ ability to use harvest regulations to influence bass growth and can result in slower growth and poor condition due to excessive predator abundance and reduced prey availability. This scenario appears to have developed in a tropical reservoir where angler harvest has been limited. Largemouth bass (M. nigricans) were experimentally removed from Cerrillos Reservoir, Puerto Rico, to test if targeted population reduction could improve prey availability and condition of largemouth bass in tropical systems. Specific objectives were to 1) assess the response of prey species abundance and size distributions to reduced predator abundance, and 2) determine the response of largemouth bass size structure and relative weight to experimental population reductions. The experimental removals resulted in increased abundance and decreased mean size of sunfish (Lepomis spp.) and tilapia (Coptodon and Oreochromis spp.) as recruitment of prey species increased. Abundance of threadfin shad (Dorosoma petenense) also increased. Largemouth bass Wr increased, indicating improvement in prey availability and improved predatory success. However, recruitment of largemouth bass also increased, highlighting the need for harvest, either by anglers or managers, to maintain population abundance necessary to maintain improvements in size-structure and condition.