The influence of habitat on introgression and condition of largemouth bass in Louisiana

Florida largemouth bass (Micropterus salmoides floridanus) have been stocked in Louisiana since 1982, but little is known about the factors regulating genetic introgression.  We collected habitat data and largemouth bass samples from 12 stocked reservoirs to examine the relationships between reservoir characteristics, genetic identity, relative weight (W_r), liver somatic index (LSI), and back-calculated length-at-age.  Principle component analysis was used to classify the reservoirs into habitat types.  We used analysis of variance to assess whether W_r, LSI, or length-at-age were influenced by genetic strain or habitat type, and logistic regression to determine whether habitat type influenced the relative abundance of northern (M. s.salmoides), Florida, or hybrid largemouth bass in the reservoirs.  Although similar across bass strains, W_r, LSI, and length-at-age varied by lake (all P<0.0001).  Shallow, nutrient rich lakes with high chlorophyll a concentrations and large littoral zones appeared to promote high W_r and non-native largemouth bass.  Conversely, northern largemouth bass were more prevalent, and W_r was lower, in lakes with dense vegetation.  Aquatic macrophytes may reduce foraging efficiency of larger, piscivorous fish while increasing survival of young-of-the-year largemouth bass.  Reservoirs with little vegetative cover may reduce natural recruitment of resident largemouth bass allowing rapid genetic introgression.