Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—Historic reports and museum records describe a distinct spatial distribution pattern and habitat partitioning between Largemouth Bass <em> Micropertus salmoides salmoides </em>and Spotted Bass <em> Micropterus punctulatus</em>. However, beginning in the mid-20th Century, the literature describes more co-occurrences and less species specificity among habitats and distributions. Herein, we conducted a retrospective analysis of recently collected data (2005–2014) to assess: (1) how current distributional patterns of Spotted Bass and Largemouth Bass compare with historic distributions in Louisiana; (2) evidence of species-specific habitat associations based on abundance and habitat data collected; and (3) whether the Florida Largemouth Bass <em> M. salmoides floridanus </em>stocking program has affected Spotted Bass populations in adjacent river systems. Analyses of 68 wadeable streams and rivers indicated that current spatial distributions matched historic descriptions for 6 of 9 major drainages, with evidence still supporting distinct habitat associations for each species. Importantly, Spotted Bass did appear to be negatively influenced by widespread Largemouth Bass stocking. Further, construction of reservoirs across the state and landscape conversion from wet prairie and forest to intensive agriculture may have negatively impacted both species. Overall, habitat alteration and loss was the most widespread explanation for declines in Spotted Bass, with Largemouth Bass stocking of secondary and more localized importance.

Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—The Choctaw Bass <em> Micropterus cf. punctulatus </em>is an undescribed black bass found in coastal river systems of northwest Florida and southern Alabama. The Choctaw Bass is morphologically similar to the Spotted Bass <em> M. punctulatus</em>. Prior to this study, there was no published life history information specific to this black bass. The need to address these information gaps was further influenced by the popularity of black bass fishing and potential statewide black bass regulation changes in Florida. Our research examined relative abundance, age, mortality, growth, and diet of Choctaw Bass collected from the Choctawhatchee River, Florida and Holmes Creek, a major tributary of the Choctawhatchee River in fall 2012 and 2013. Choctaw Bass were compared to sympatric Largemouth Bass <em> M. salmoides </em>× Florida Bass <em> M. floridanus </em>intergrades. Relative abundance was lower for Choctaw Bass than Largemouth Bass in both the Choctawhatchee River and Holmes Creek. The oldest Choctaw Bass from the Choctawhatchee River was age-5 and the oldest Choctaw Bass from Holmes Creek was age-11. Total instantaneous mortality of Choctaw Bass was statistically similar between the study areas. Total instantaneous mortality for Choctaw Bass from Holmes Creek was also similar to sympatric Largemouth Bass. Growth differed for Choctawhatchee River and Holmes Creek Choctaw Bass. Diets of Choctaw Bass collected from the Choctawhatchee River consisted primarily of fish while diets of Choctaw Bass and Largemouth Bass collected from Holmes Creek consisted primarily of crayfish. The observed restricted distribution, limited abundance relative to Largemouth Bass, limited number of Choctaw Bass collected greater than 406 mm TL, and the lack of Choctaw Bass older than age-5 in the Choctawhatchee River led to the recommendation that Choctaw Bass be managed separately from Largemouth Bass.

Black Bass Diversity: Multidisciplinary Science for Conservation

<em>Abstract</em>.—Following reports of invasive Spotted Bass <em>Micropterus punctulatus</em> in the Chipola River, Florida, we initiated a microsatellite DNA survey of black basses in that system to assess genetic risks to the native population of Shoal Bass <em>M. cataractae</em>. Nonnative Spotted Bass and naturally occurring Largemouth Bass <em>M. salmoides</em> × Florida Bass <em>M. floridanus</em> intergrades were sampled from the Apalachicola and lower Chipola rivers to serve as reference specimens. In 2007, we identified five Shoal Bass hybrids among 45 specimens of <em>Micropterus</em>. Two of the hybrid specimens had introgressant alleles from Spotted Bass and another two had introgressant alleles from Largemouth Bass × Florida Bass intergrades. The introgressing taxon for the remaining hybrid was not immediately identifiable and was later determined to be an undescribed species of <em>Micropterus</em> (provisionally named Choctaw Bass), which inhabits the coastal plain rivers of the eastern Gulf of Mexico. From 2008 to 2010, an additional 217 specimens from the system were genotyped, resulting in the identification of 36 hybrids. Overall, 15.9% of the unknown specimens were heterospecific; the overall genomic proportion of introgressant alleles was 4.0%. The largest fraction of introgressant alleles (3.0%) originated from Choctaw Bass, most likely carried by emigrants from the nearby Choctawhatchee River system. Largemouth Bass × Florida Bass intergrades contributed the next highest introgressant proportion (0.6%), followed by Spotted Bass (0.4%). One genetically pure Spotted Bass was detected among the upper Chipola River specimens. Point estimates of genetic effective size for the Chipola River Shoal Bass population ranged from 110.4 to 131.4 (95% confidence interval [CI] = 79.1 to 195.9); values of this magnitude could signal an increased susceptibility to hybrid-swarm formation and reduced efficacy of purifying selection. While this population harbors a nontrivial amount of introgressant alleles, the majority of interbreeding appears to originate via natural processes. Nonetheless, if nonnative Spotted Bass become further established in the Chipola River and increase their interactions with Shoal Bass, the genetic integrity of the endemic population could deteriorate rapidly.

Black Bass Diversity: Multidisciplinary Science for Conservation

<em>Abstract</em>.—Shoal bass <em>Micropterus cataractae</em> are endemic to the Apalachicola drainage, including the Chattahoochee (Alabama and Georgia), Flint (Georgia), and Chipola (Florida) River systems. Habitat modification, including extensive dam construction, has reduced population sizes in many areas of their native range and, in some cases, has led to local population extinctions. The most abundant Shoal Bass populations reside in the Flint River, but even there they are suspected to be hybridizing with the invasive Spotted Bass <em>M. punctulatus</em>, which have become established in the system. To assess the threat that hybridization poses to the genetic integrity of Shoal Bass in the Flint River, tissue samples were collected from presumptive Shoal Bass, nonnative congeners, and their potential hybrids. Fish were collected from multiple locations above and below the Flint River Dam and from Ichawaynochaway Creek, a southern tributary. These were genotyped using 17 polymorphic microsatellite loci and a subset was sequenced for the mitochondrial DNA (mtDNA) 16S ribosomal RNA gene. Above the Flint River Dam, 12% of the specimens carried nonnative alleles; however, genomic proportions of these alleles were low (1%). Below the Flint River Dam, the percentage of hybrid specimens ranged from 17% to 43% and sample genomic proportions increased to 6–7%. In Ichawaynochaway Creek, the percentage of hybrid specimens was 27% and the sample genomic proportion was 7%. Pure spotted bass were collected below the Flint River Dam; most F₁ hybrids were collected in Ichawaynochaway Creek. The mtDNA of hybrids indicated that Shoal Bass males cross with Spotted Bass females more frequently than the converse. Hybridization was bidirectional (i.e., hybrids were found to backcross to both Spotted Bass and Shoal Bass). Because introgressive hybridization occurs, the flux of nonnative alleles in this system should be monitored and all broodfish in stocking programs should be screened. Studies should be implemented to determine if natural genetic mechanisms (e.g., disruptive selection) will be sufficient to maintain the integrity of the species boundaries.