Investigating Interactions between Largemouth and Spotted Bass, Lake Norman, North Carolina.
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Date
2009-06-14
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Abstract
Spotted bass Micropterus punctulatus were recently introduced into Lake Norman, which already supported a healthy largemouth bass M. salmoides population. After only ten years, spotted bass now make up about half of the black bass fishery. Because the two species are ecologically similar, and numbers and biomass of largemouth bass have been declining, biologists were concerned that spotted bass were negatively affecting largemouth bass. Additionally, morphological observations suggested the two species were hybridizing. To better understand these issues, hybridization, diet overlap, and habitat use by black bass in Lake Norman were quantified. Genetic analyses confirmed largemouth and spotted bass were hybridizing. Genetic information on individuals was paired with morphological characteristics at juvenile (50 – 100 mm total length, TL; n = 60) and adult (300 – 500 mm TL; n = 78) life stages, and reliable patterns for field identification of spotted bass, largemouth bass, and hybrids were developed (78-88% correct). To understand potential competition between the taxa, juvenile (n = 132) and adult (n = 120) black bass were collected for diet and habitat comparisons. Diet information was collected from juveniles from 31 July – 08 Aug 2007, 29 April 2008, and 10 June 2008 at different spatial scales. Zooplankton and benthic invertebrates were collected to estimate availability. Diet information was collected from adult fish from 29 April – 01 May 2008
and from 12 May – 16 May 2008. Habitat information on substrate and cover use was collected from locations of immobilized fish, and habitat availability of substrate and cover was estimated from 300-m transects (n = 12) throughout the reservoir. Proportion similarity index and Morisita’s index were used to quantify diet overlap by percent by number and percent by occurrence, and 10,000 bootstrap values were generated so that 95% confidence intervals could be estimated. Estimates of habitat selection were calculated with Ivlev’s index of electivity and the Strauss index of selectivity. Diet overlap values were high, and 95 % confidence intervals were typically in the upper half of the range of the indices. Based on prey availability samples, selection of invertebrate prey was largely opportunistic and similar between species. Habitat selection of both substrate and cover was similar with few exceptions. Because largemouth and spotted bass are hybridizing in Lake Norman, and overall, they show high overlap in use of prey items and habitat at both juvenile and adult life stages, they are likely competitors in Lake Norman. Our findings should guide future research and educate managers and anglers about the potential effects of introducing spotted bass or largemouth bass into lakes already containing a healthy black bass fishery.
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competition, habitat, bass, overlap, largemouth, spotted, genetic, hybrid, diet
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Degree
MS
Discipline
Fisheries and Wildlife Sciences
