Assessing the Genetic Status and Factors Leading to the Decline of the Roanoke Bass (Ambloplites Cavifrons)

Although numerous factors have led to the staggering declines in freshwater biodiversity throughout the United States and the world, habitat alteration and introduced species pose some of the greatest challenges to conservation efforts. Learning more about how these two factors lead to the decline of an endemic organism could help prevent the future loss of unique species and the premature conclusion of evolutionary trajectories. Roanoke bass (Ambloplites cavifrons) is a sport fish endemic to portions of the Roanoke, Chowan, Tar, and Neuse river basins of North Carolina and Virginia. This species has been in decline for many years, and it is believed that their continued existence is threatened by competition, and potentially hybridization and introgression with their introduced relative, the rock bass (Ambloplites rupestris). In addition to interactions with this invasive species, significant alteration of habitat is likely also a contributing factor in the decline of A. cavifrons. This study seeks to evaluate the relative contributions of these various factors to the decline of A. cavifrons. I utilized a combination of nuclear markers and mitochondrial sequence data to address the question of whether or not the two species are hybridizing in areas of syntopy, and furthermore to determine whether hybrids are fertile and able to breed back with the parental species. In addition, I identified extant populations of A. cavifrons throughout their historic range, and evaluated the genetic diversity of these populations and correlated these values with changes to the landscape in the form of alterations to watershed land use and the construction of impoundments. My results indicate large portions of the historic range of A. cavifrons no longer contain the species, and that remaining populations occur at the stream level and exist in isolation from one another. Obtaining this information allows for a better understanding of the current state of this unique species, provides information that may help managers prevent its disappearance from its native range, and affords insight into the interactions of an introduced and a native species in a landscape that has been heavily altered by human activity

Hybridization and Replacement of Roanoke Bass (\u3cem\u3eAmbloplites cavifrons\u3c/em\u3e) with Invasive Rock Bass (\u3cem\u3eA. rupestris\u3c/em\u3e) in Virginia: How Big is the Problem?

The Roanoke bass (Ambloplites cavifrons) is a sport fish endemic to the Roanoke, Chowan, Tar, and Neuse drainages in Virginia and North Carolina. Virginia populations of this species are threatened by competition and hybridization with rock bass (A. rupestris), an invasive congener introduced from the Gulf slope throughout the early 20th century. Displacement and hybridization were reported as early as the 1950’s, but the current status of this invasion and its impacts on A. cavifrons populations are unknown. Eleven nuclear DNA microsatellite markers were developed to discriminate between A. cavifrons, A. rupestris, and their hybrids, and in doing so to assess the current distribution of A. cavifrons in Virginia. The panel of markers provided a high degree of resolution among these groups, further allowing us to separate F1 hybrids from backcrossed individuals. Our results suggest a complex mosaic of invasion, displacement, and introgression patterns across the range of A. cavifrons in Virginia. A. cavifrons persists in only 4 of the 8 watersheds we examined, but has been mostly to completely replaced by A. rupestris in 3 others. In the Pigg watershed, an ongoing invasion is apparent: A. rupestris and hybrids were distributed throughout this system. Most extant A. cavifrons populations are geographically small, and all are vulnerable to invasion. This highlights the importance of educational campaigns that discourage anglers from transplanting “redeyes” to new waterways and potentially the need to establish new refuge populations of A. cavifrons

Novel Polymorphic Microsatellite Loci for Distinguishing Rock Bass (\u3cem\u3eAmbloplites rupestris\u3c/em\u3e), Roanoke Bass (\u3cem\u3eAmbloplites cavifrons\u3c/em\u3e), and Their Hybrids

The rock bass (Ambloplites rupestris) is a popular sport-fish native to the Mississippi and Great Lakes basins of North America. The species has been widely introduced outside its native range, including into Atlantic-slope streams of Virginia where it may hybridize with an imperiled, similar-looking congener, the Roanoke bass (Ambloplites cavifrons). In this study, we identified and evaluated novel molecular markers to facilitate identification of these species and study the extent of hybridization. Using molecular libraries developed from A. rupestris, we identified a suite of candidate nuclear microsatellite loci, synthesized primer sets, and tested these markers for amplification and polymorphism in populations of both species. We then calculated standard diversity statistics within and differentiation statistics between species, the latter providing an indication of marker power for distinguishing the species and their hybrids. Additionally, we evaluated our efficiency for identifying hybrids by classifying simulated genotypes of known ancestry. Eleven loci were polymorphic (2-22 alleles per locus) and reliably amplified in both species. Multilocus genetic differentiation between A. cavifrons and A. rupestris was quite high (F ST = 0.66; D LR = 19.3), indicating the high statistical power of this marker set for species and hybrid identification. Analyses of simulated data suggested these markers reliably distinguish between hybrids and non-hybrids, as well as between F1 hybrids and backcrossed individuals. This panel of 11 loci should prove useful for understanding patterns of hybridization between A. rupestris and A. cavifrons. As the first microsatellite markers developed for Ambloplites, these markers also should prove broadly useful for population genetic studies of this genus

Hybridization and Replacement of Roanoke Bass (\u3cem\u3eAmbloplites cavifrons\u3c/em\u3e) with Invasive Rock Bass (\u3cem\u3eA. rupestris\u3c/em\u3e) in Virginia: A Genetic Assessment of the Scope of the Problem

The Roanoke Bass (Ambloplites cavifrons) is a sport fish endemic to the Roanoke, Chowan, Tar, and Neuse drainages in Virginia and North Carolina. Virginia populations of this species have declined over time, presumably in part due to competition and hybridization with Rock Bass (A. rupestris), an invasive congener introduced from the Gulf slope throughout the early 20th century. Displacement and hybridization were reported as early as the 1950s, but the current status of this invasion and its impacts on A. cavifrons populations are unknown. Eleven nuclear DNA microsatellite markers were developed to discriminate between A. cavifrons, A. rupestris, and their hybrids, and in doing so to assess the current distribution of A. cavifrons in Virginia. The panel of markers provided a high degree of resolution among these groups, further allowing us to separate F1 hybrids from backcrossed individuals. Our results suggest a complex mosaic of invasion, displacement, and introgression patterns across the range of A. cavifrons in Virginia. In some populations all individuals appear to remain genetically A. cavifrons, whereas in other populations A. cavifrons has been partially or completely replaced by A. rupestris and/or hybrids. In the Pigg watershed, an ongoing invasion is apparent, with A. rupestris dispersing upstream and hybridizing with A. cavifrons, whereas in another watershed upstream invasion is prevented for now by a small dam. Of eight Virginia watersheds that historically contained A. cavifrons, only five now contain predominantly A. cavifrons, and three of these are susceptible to future invasion. This research helps to identify intact A. cavifrons populations that could be targeted for habitat restoration efforts, as well as vulnerable populations that could be targeted for programs seeking to prevent the spread of A. rupestris from adjacent waterways

Hybridization and Replacement of Roanoke Bass with Invasive Rock Bass in Virginia: A Genetic Analysis of the Problem

The Roanoke bass is a sport fish endemic to several drainages in Virginia and North Carolina. Virginia populations are threatened by competition and introgressive hybridization with rock bass, an invasive congener introduced to many waterways between the 1890s and 1950s. The current status of this invasion and its impacts on Roanoke bass populations are unknown. Eleven microsatellite markers were developed to discriminate between Roanoke bass, rock bass, and their hybrids, and in doing so to assess the current distribution of Roanoke bass in Virginia. The panel of markers provided a high degree of resolution, allowing us to discern F1 hybrids and backcrossed individuals. Our results suggest a mosaic of invasion, displacement, and introgression patterns across the range of Roanoke bass in Virginia. Roanoke bass persist in 4 of the 8 watersheds examined, but have been mostly to completely replaced by Rock bass in 3 others. In the Pigg watershed, an ongoing invasion is apparent: rock bass and hybrids were distributed throughout this system. All extant Roanoke bass populations are vulnerable to future invasion. This highlights the importance of educational campaigns that discourage anglers from transplanting rock bass to new waterways

Counting the Parts to Understand the Whole: Rethinking Monitoring of Steelhead in California’s Central Valley

Steelhead (Oncorhynchus mykiss expressing an anadromous life history) in the Sacramento and San Joaquin rivers and their tributaries in California’s Central Valley (CCV) belong to a Distinct Population Segment (DPS) that is listed as threatened under the US Endangered Species Act. Although contemporary management and recovery plans include numerous planned and ongoing efforts seeking to aid in DPS recovery—such as gravel augmentation, manipulation of spring flows, and restoration of rearing and spawning habitat—a paucity of data precludes the possibility of evaluating the effect of these actions on populations of Steelhead in CCV streams. Knowledge gaps relating to historic and current abundance, population-specific ratios of resident and anadromous life-history expression, and the influence of hatchery-reared fish remain largely unaddressed. This is partly a result of aspects of Steelhead biology that make them difficult to monitor, including the multitude of factors that contribute to the expression of anadromy, polymorphic populations, and migration periods that coincide with challenging field conditions. However, these gaps in understanding are also partly the result of an institutional focus on Chinook Salmon (Oncorhynchus tshawytscha) and a pervasive notion that actions benefiting Chinook populations will also benefit Steelhead populations. To evaluate these gaps and to suggest approaches for assessing DPS recovery actions, we review available data and existing monitoring efforts, and consider the actions necessary to inform the development of targeted O. mykiss monitoring programs. Current management and recovery goals focus on abundance estimates of Steelhead only, yet current monitoring is insufficient for reliable estimates. We argue that a reallocation of monitoring resources to better understand the interaction between resident O. mykiss and Steelhead would provide better data to estimate the vital rates needed to evaluate the effects of recovery actions

Dispersal and Survival of Captive-Reared Threatened Fishes in a Tonle Sap Lake Reserve

The Tonle Sap Lake in Cambodia supports several species of threatened megafish and contains one of the largest networks of freshwater fish reserves in the world. Despite these traits, this system remains understudied in terms of its utility for endangered fish conservation and restoration. This study was the first of a series of planned fish releases designed to test the effectiveness of conservation supplementation programs in the Tonle Sap Lake. In March 2022 (during the dry season), 1582 captive-reared fishes, including 1538 striped catfish Pangasianodon hypopthalmus, 42 giant barb Catlocarpio siamensis, and two Mekong giant catfish Pangasianodon gigas, were tagged and released into a 986-hectare fish reserve to assess post-release dispersal and survival. Brightly colored external tags with unique identification numbers were used to facilitate tag returns. A high-profile release event was held to raise awareness about the activity, bringing attention to the importance of fish reserves and endangered species conservation, and disseminating information about the research and tag return and reward program. This, in concert with other efforts, served to be an important education and outreach tool and increased tag return rates. We found that mortality from fishing was rapid and very high. Nineteen percent of released fishes were recaptured in the first 2 days after the fish release, and 46% were recaptured by day 83 after the release, indicating intense fishing pressure on the Tonle Sap Lake fisheries. Eighty percent of recaptured fishes were caught in stationary gill nets, most within 10 km of the release site. Fishing mortality rates were independent of fish size or source (pond-reared or cage-reared). Environmental DNA (eDNA) was found to be capable of detecting each of these species’ presence in the water at the release site and could prove to be a useful tool for endangered species monitoring and restoration. Future research should explore alternative release timing, release location, and other methods of increasing post-release survival. Ultimately, underlying sources of mortality, especially fishing, will need to be addressed for conservation supplementation programs to succeed in the Tonle Sap Lake. Conservation supplementation should not be viewed as a substitute for more fundamental conservation measures, such as maintenance of environmental flows, preservation of ecological connectivity, and science-based fisheries management