HURRICANE IMPACTS ON THE LITTORAL FISH COMMUNITY AT LAKE OKEECHOBEE, FLORIDA
Mark Rogers and Micheal S. Allen Dept. of Fisheries and Aquatic Sciences University of Florida Gainesville, FL
Aquatic habitat abundance and complexity influence fish community interactions, species diversity, and abundance (Benson and Magnuson 1992). Natural disturbances can result in changes to aquatic habitats that disrupt ecological processes and those changes may be magnified by anthropogenic modifications. In Florida, aquatic vegetation is a principle component of available habitat to littoral fish communities and interactions between natural disturbances and human modifications may result in large changes in aquatic habitats and fish communities. Lake Okeechobee, Florida, was impacted by catastrophic hurricanes during 2004-2005 that resulted in lake-wide changes to littoral habitats.
We sampled the littoral fish community at Lake Okeechobee during the summers of 2003 and 2004 (i.e., pre-hurricane) and again in summer 2006 (i.e., post-hurricane). Sampling was conducted in the northwest area of the lake and fish were collected using 10m x 10m (total area = 0.01 ha) block nets treated with rotenone (3 mg/L). Sample sites were selected to represent available habitat types (e.g., emergent vegetation, submerged vegetation) and sampling occurred in the same areas during each time period. Fish were collected by 4 individuals within each blocknet using dipnets. Collected fish were placed on ice and returned to the laboratory for
Total lengths (nearest mm) and weights (nearest g)
subsamples of 50 fish per species and total catch biomass for each species in
blocknet. each net.
were measured from used to extrapolate the
We evaluated the following fish community metrics for each time period: total species richness, species diversity, species evenness, and total fish biomass. We also evaluated total biomass between time periods for species groups that are associated with littoral vegetation and/or open water habitats. Species groups were omnivore/obligate planktivores (i.e., brook silversides Labidesthes sicculus, inland silversides Menidia beryllina, gizzard shad Dorosoma cepedianum, and threadfin shad D. petenense), centrarchids (i.e., bluegill Lepomis macrochirus, dollar sunfish L. marginatus, warmouth L. gulosus, redear sunfish L. microlophus, redbreast sunfish L. auritus, spotted sunfish L. punctatus, bluespotted sunfish Enneacanthus gloriosus, black crappie Pomoxis nigromaculatus, and largemouth bass Micropterus salmoides). Community and family group metrics were estimated for each net during each period and bootstrap resampling was used to recreate expected distributions of average metric values for each period.
We found decreased species diversity, species richness, total biomass, and centrarchid biomass after hurricanes relative to pre-hurricane conditions. These decreases were likely due to
loss of littoral
vegetated habitats and the forage
resources and predation refuges vegetated littoral habitats also
they provide resulted in
for many increased
Session 3 – Page 2