Theses and Dissertations

Title: Manipulating Gizzard Shad Dorosoma cepedianum Populations to Manage for Their Sport Fish Predators: Potential of Selective Poisoning and Predatory Control

Name: Irwin, Brian James

Degree: MS

Chair: Dennis R. DeVries


University: Auburn University

Location: Auburn, Alabama

Date: 2001

Pages: 170

Keywords: gizzard shad,largemouth bass,reservoir management,population management


I quantified system responses to gizzard shad Dorosoma cepedianum recovery during the third (1998) and fourth (1999) years following their reduction in Walker County State Fishing Lake (WCL). Data for the first (1996) and second (1997) years following the selective shad reduction in WCL are included from a previous study (Kim 1998: Kim and DeVries 2000). Larval gizzard shad appeared early and persisted in samples during 1997, and this abundant larval production led to density-dependent growth of age-0 gizzard shad and an eventual increase in total gizzard shad biomass. Zooplankton abundance had declined during the second year following the selective removal (1997), and was even lower during 1998 and 1999 relative to both 1996 and 1997. Despite dramatic reduction of large bodied zooplankton, such as Daphnia spp., compensatory replacement by smaller taxa was not realized, and chlorophyll-a concentrations did not indicate a strong zooplankton-phytoplankton linkage. During 1996 and 1999 (years of low larval gizzard shad density), larval white crappie Pomoxis annularis appeared first in larval fish collections and achieved relatively high densities during both years. Consistent, strong production of larvae by sunfishes may have limited negative impacts of abundant gizzard shad on sunfishes. Catch-per-effort of juvenile bluegill Lepomis macrochirus in inshore seine hauls was higher during 1998 and 1999 than during 1996 and 1997. Gizzard shad appeared capable of returning to pre-treatment conditions within two years. However, strong negative impacts on adult sport fishes were still not detected as late as the fourth year following the selective gizzard shad reduction. When gizzard shad spawn late and produce low densities of larvae (relative to sport fishes), negative impacts of abundant gizzard shad on the sport fishery may be reduced. In addition, high consumptive demands of picivores may limit the survival of the relatively lower densities of age- 0 gizzard shad. To quantify this possibility, I conducted bioenergetics simulations on three size groups of largemouth bass at three levels of predator density and two levels of predator mortality using diet and prey density data from 6 experimental ponds. Simulations using two sets of diet data suggested that largemouth bass populations in these ponds at intermediate and high densities could annually consume between 50 and 186 kg/ha of gizzard shad. Relative comparison of an estimated range of age-0 gizzard shad abundances and these bioenergetics estimates of predator consumption, indicated that largemouth bass predation could potentially regulate survival of age-0 gizzard shad in small ponds.

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