Growth, Size Structure, and Condition Effects of an Experimental Reduction of Largemouth Bass Biomass from a Bass-Crowded Tropical Reservoir

Largemouth Bass Micropterus salmoides floridanus were stocked in Cerrillos Reservoir in 1997. Within three years, relative weight declined from above 100 to about 80 and the population displayed size structure characteristic of overcrowding, with much of the population composed of fish ≤ 350mm. A protected slot limit (356-508mm) was implemented in 2003; however, limited effort and angler attitudes towards harvest of small bass maintained the bass crowded situation in the reservoir.  To examine the effect of population reduction on growth, size structure, and condition, experimental removals of bass from the crowded size classes (200-380 mm) were conducted in 2012 and 2013. In these two years, we removed and relocated 2,333 and 1,993 Largemouth Bass equaling 26% and 27% of the crowded biomass and 20% and 22% of the total biomass, respectively.  Following the experimental removals, mean condition of largemouth bass increased from 81 to 87 (F=294.7, P<0.0001). Although mean daily growth rate (mm/d) did not significantly increase, length distributions shifted towards larger size classes (D=0.094, P<0.0001). We concluded that the removals were successful at partially restructuring the Largemouth Bass population, but continued removals or increased angler harvest will be necessary to maintain observed improvements or to further the fishery.