Influence of Trophic State on Spotted Bass and Largemouth Bass Spawning Time and Age-0 Population Characteristics in Alabama Reservoirs

Abstract

We described and compared spawning periodicity, abundance, and growth of age-0 largemouth bass Micropterus salmoides and spotted bass M. punctulatus from six Alabama reservoirs in 1993 and 1994 that displayed a wide range of limnological and morphological characteristics. One reservoir was divided into three distinct areas based on limnological conditions and thus, eight reservoir study areas were examined. Reservoirs fell along a continuum from deep, long-retention reservoirs with fluctuating water levels and low phytoplankton biomass to shallower, short-retention reservoirs with minimum water level fluctuations and generally high phytoplankton biomass. Fish were collected with rotenone in 0.02-ha enclosed shoreline areas. Daily rings on sagittal otoliths were counted to determine growth rates and to back-calculate spawning times. Trophic states included oligotrophic (chlorophyll a, <3 mg/m³; N = 1), mesotrophic (chlorophyll a, 3–7 mg/m³; N = 4), and eutrophic (chlorophyll a, >8 mg/m³; N = 3) systems. Spotted bass swim-up was slightly earlier than largemouth bass in the two least productive reservoirs in 1993 and 1994. In all other comparisons, spotted bass and largemouth bass spawned at similar times, except in one mesotrophic reservoir where largemouth bass spawned earlier than spotted bass. Spawning duration was slightly longer for largemouth bass. Density and biomass of age-0 largemouth bass varied by an order of magnitude and were higher in the most productive reservoirs. However, age-0 spotted bass biomass was only about twice as great in eutrophic reservoirs compared with the lowest productivity system. Age-0 largemouth bass density exceeded spotted bass density in eutrophic reservoirs, but largemouth bass density and biomass were lower than spotted bass in mesotrophic and oligotrophic reservoirs. Both species grew faster in eutrophic reservoirs, but spotted bass grew faster than largemouth bass in the oligotrophic water body. Although chlorophyll a was correlated to other reservoir features, oligotrophication could favor young spotted bass while eutrophication of low-productivity water bodies may select for largemouth bass.