Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—Prey selection and diet are highly plastic and can vary with temporal and spatial differences in competition or prey availability. This study investigated the possibility that the trophic position of Smallmouth Bass <em> Micropterus dolomieu </em>might change in response to systematic, hierarchical variation in community structure in stream networks. We hypothesized that a shift toward increased insectivory and decreased piscivory would be observed in smaller streams, resulting in a lower trophic position of Smallmouth Bass and reflecting differences in community structure and prey availability. We applied a combination of diet analyses and stable isotope methods to compare prey selection and trophic position of Smallmouth Bass across a range of stream sizes. Stable isotope analyses indicated that Smallmouth Bass trophic position was slightly elevated in smaller watersheds, contradicting our initial hypothesis. However, differences in average trophic position in watershed size categories were small (ranging from 3.6 to 3.8) and of limited ecological significance. Isotopic niche width did not vary among stream size categories, and gut content analyses revealed no differences in frequency of occurrence of fish, crayfish, or insects (larvae and adults). Collectively these results indicate that trophic position, and perhaps trophic niche, of Smallmouth Bass are consistent across hierarchical variation in stream size and habitat.

Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—We reexamined a local population of Guadalupe Bass <em>Micropterus treculii </em>after cessation of a stocking program that significantly reduced the number of individuals that were hybridized with Smallmouth Bass <em>M. dolomie</em> u. Analysis of five years of post-stocking fish collection data show that the percentage of hybrids has increased in all four study sections of the upper Guadalupe River since stocking stopped. We found that hybridization had increased from 0.0% to 9.9% in Johnson Creek, 19.8% to 28.8% in North Fork Guadalupe River, 5.6% to 12.0% in South Fork Guadalupe River, and 24.2% to 26.5% in Guadalupe River main stem sections. This represents an average increase of 6.8% for all streams combined (range = 2.2–9.9%) from the last year of stocking. We also examined hybridization levels in individual stream fragments created by instream barriers (<em>n </em>= 76) to assess spatial variability along tributary and main stem corridors. Although hybridization appears to be increasing on a stream-wide basis, finer scale analysis show that hybrid distribution was spatially complex and there was a substantial portion of the study area with little or no hybridization. There were gradients of decreasing hybridization in an upstream direction in each of the tributaries and marked break points upstream of which hybridization was considerably lower (<10%). We also found that hybridization was highly variable among individual stream fragments (range 0%–71.4%) including those immediately adjacent to one another. These findings suggest that instream barriers may restrict genetic mixing throughout the system and contribute to partial isolation of populations within stream fragments. As such, further targeted intervention efforts are likely necessary to further reduce hybridization in fragments that still contain high proportions of hybrids. The patchy distribution that we observed may be a critical component to consider in assessment and restoration efforts; not only for Guadalupe Bass but also in other endemic black basses threatened by hybridization.

Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—Coastal rivers provide important fishing opportunities throughout the southeastern United States. Black bass <em> Micropterus </em>spp. are major components of these fisheries and are highly valued by anglers, especially in northwest Florida, where few impoundments exist. In the Escambia and Yellow rivers, as in most other rivers on the northern Gulf Coast, salinity is low in the upper segments but may exceed 13‰ in the lower, mesohaline sections. Both rivers are located within the natural intergrade zone between Largemouth Bass <em> M. salmoides </em>and Florida Bass <em> M. floridanus</em>, and the age and size structure of fish inhabiting riverine reaches differ considerably from those in salt marsh habitats. We collected tissue samples from fish in both the riverine and salt marsh habitats in the Escambia and Yellow rivers and conducted genetic analyses to determine whether individuals from the two habitat types exist as a single randomly mating (panmictic) population in each system. Analysis of 15 microsatellite loci identified significant differences in the allele frequency distributions of samples collected from riverine versus salt marsh habitats in each river. Both rivers were found to be inhabited by intergrade populations that included pure Largemouth Bass and hybrids between Largemouth Bass and Florida Bass. Fish in the salt marsh habitats tended to have more Largemouth Bass alleles than fish in riverine habitats in both systems. Together, these findings indicate fish in the salt marsh and river habitats do not exist in panmixia and have different genetic compositions. Environmental differences between the riverine and estuarine habitats may have led to divergent selection and limited mating between subpopulations within the same river system. Largemouth Bass alleles may confer greater fitness than Florida Bass alleles in estuarine environments of the northern Gulf Coast, which could explain the greater frequencies of Largemouth Bass alleles in these unique habitats.

Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—Angler harvest and population characteristics of Smallmouth Bass <em> Micropterus dolomieu </em>were assessed through electrofishing surveys and tagging 3,027 fish with reward tags at six sites on five Ozark streams. Growth, exploitation, and mortality were estimated for each site. Predicted population responses to higher length limits were simulated using Fishery Analysis and Modeling Simulator software. Tag return rates ranged between 37% and 64%, angler release rates ranged between 63% and 94%, and annual exploitation ranged between 5% and 26%. The median time at-large for tags returned within one year of tagging ranged from 22 to 47 d of the tagging date. Growth rates were relatively slow, as mean time to reach 305 mm was 4.9 years and mean time to reach 381 mm was 7.8 years. Total annual mortality estimates ranged from 37% to 55%. Annual natural mortality estimates ranged from 13% to 33%. Predicted responses to higher length limits varied considerably by site because of differences in estimated rate functions. Although simulations predicted small increases (0.54–2.73 fish/100 recruits >381 mm) in the number of larger fish with the 381-mm length limit at five of six sites, predicted increases were substantial (17 fish/100 recruits >381 mm) and yield increased 6% at the Current River-Powder Mill site. Individuals in the Current River-Powder Mill site were not reaching their full growth potential due to growth overfishing, while simulations of the remaining five populations indicated no growth overfishing under current conditions and regulations. The combined effects of natural mortality and slow growth limited the effectiveness of higher length limits. Under most conditions, the statewide length limit of 305 mm was adequate to balance the desire of quality fishing and harvest opportunities on most Ozark streams. Our study indicates that fisheries at select stream reaches may be improved by higher length limits where exploitation is high, growth is adequate, and natural mortality is low.

Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—The Ozark Plateau is located at the southern extent of native Smallmouth Bass <em>Micropterus dolomieu </em>range and water temperature and drought conditions during summer months may potentially affect growth of Smallmouth Bass in this region. Groundwater streams in the region do not warm to the same extent as runoff streams during summer months and could provide a thermal refuge habitat for Smallmouth Bass from high summer temperatures and drought conditions. Our study objective was to examine differences in body condition and diet of Smallmouth Bass through summer months between groundwater and runoff streams. We sampled Smallmouth Bass from eight streams across two flow regimes monthly from June–September from 2014 to 2016 in the Ozark Plateau of Arkansas and Missouri. Relative weights were calculated and diet contents were examined for each fish. Linear mixed model analyses indicated that relative weights declined in both stream types in 2014 and 2015, but not in 2016. Surprisingly, there was no significant difference in change in relative weights between runoff and groundwater streams in any year. No diet shifts over the course of the summer were noted in any year, and no differences were seen between stream types. Our results suggest that further work should investigate the refuge qualities of groundwater streams for Smallmouth Bass in this region as Smallmouth Bass from both stream types may currently respond similarly to summer conditions.

Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—Unique genetic lineages of <em> Micropterus </em>species are increasingly recognized; however, little effort has been devoted to identifying their ecological relationships despite recognition of their conservation value by management agencies. Our study objectives were to determine young-of-year, first-summer survival, and examine overall channel-unit habitat use by the Neosho subspecies of Smallmouth Bass <em> Micropterus dolomieu velox </em>from two Ozark streams (Spring and Buffalo creeks). We completed snorkel surveys approximately every 2 weeks from June–September 2013. As anticipated, young-of-year mortality was high during the first 2 weeks of the sampling period (85% in Buffalo Creek and 99% in Spring Creek). Mortality stabilized by the end of July in both streams and was similar over subsequent 2-week periods (95% CI: 0.13%–2.38% and 0.72%–3.48%, in Spring Creek and Buffalo Creek, respectively). In Spring Creek, backwater habitats were unavailable, and young-of-year fish used both pool and run habitats throughout the study duration. However, we observed different habitat-use patterns in Buffalo Creek: young-of-year fish used pools and backwaters throughout the season, use of run habitats increased by late July, and increased use of backwater habitats followed an increase in late summer discharge. In general, there was substantial habitat use variability both within and between streams. Considering both stream reaches combined, young-of-year fish densities in riffle habitat were statistically lower than other channel units. We show that young-of-year Neosho Smallmouth Bass mortality is high during the first few weeks following swim up, and that backwater habitats may be important to early life stages under certain environmental conditions.

Managing Centrarchid Fisheries in Rivers and Streams

<em> Abstract.</em>—Identifying abiotic variables that influence fish recruitment patterns is crucial to understanding, assessing, and managing populations. Smallmouth Bass <em> Micropterus dolomieu </em>have been sampled from five streams in southwestern Wisconsin since 1989 with the goals of explaining variation and describing patterns of annual age-0 relative abundance. Summer water temperature and stream stage data have been collected annually since 2010 and United States Geological Survey modeled stream temperature and stage data were acquired from 1990–2009. Catch-per-unit-effort (CPUE) of age-0 fish was highly variable within and among streams and ranged from 0 to 48.54 fish/100 m across all streams. Random forest models with stepwise variable selection processes were used to determine the relative importance of stream temperature and stream stage variables in describing variation in CPUE from 2010–2016. July mean water temperature and maximum summer temperature explained 69.7% of the variation in CPUE of age-0 Smallmouth Bass. July mean temperature and maximum summer temperature were positively related with CPUE of age-0 fish from 2010–2016; however, modeled July mean water temperatures and modeled maximum summer temperatures were not significantly correlated with CPUE from 1990–2008. We conclude that caution must be taken when using models to predict CPUE of age-0 Smallmouth Bass from temperature or flow variables, as variability in both recruitment patterns and climatic conditions may reduce model application over longer time frames.

Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—Fish assemblages in Atlantic coastal rivers have undergone extensive ecological change in the last two and a half centuries due to human influence, including extirpation of many migratory fish species, such as river herring <em> Alosa </em>spp. and introduction of nonnative piscivores, notably Smallmouth Bass <em> Micropterus dolomieu</em>. Recently, dam removals and fish passage improvements in the Penobscot River, Maine, have allowed river herring to return to reaches of the river that have been inaccessible since the late 19th century. Alosine populations have increased and this trend is anticipated to continue. This may increase forage in the system which could potentially increase growth for Smallmouth Bass, the dominant piscivore. We examined the diet and growth of Smallmouth Bass collected from areas of the Penobscot River watershed with and without access to river herring as prey. We collected 765 Smallmouth Bass throughout 2015, examined the stomach contents of 573 individuals, and found notable differences in diet among three river reaches with common seasonal trends. Juvenile river herring composed an average of 19% (SE = ±6%) of stomach contents by mass from Smallmouth Bass collected in the freshwater tidal area but were rarely observed in the diets upstream. We used estimates from von Bertalanffy growth models to examine differences in growth among reaches and found that asymptotic length was the longest (425 mm TL) in the Tidal reach where access to river herring was unrestricted. We then used these data to predict changes to growth associated with increased access to juvenile river herring prey with bioenergetics models. Results indicated that substituting juvenile river herring for less energy-dense prey (e.g., invertebrates) may lead to increases in seasonal growth throughout the watershed as river herring populations continue to rebound in response to dam removal. Our results provide insight into the diet and growth of Smallmouth Bass in a large New England river, and provide a foundation for future work investigating unfolding changes to these characteristics following recent dam removals.

Managing Centrarchid Fisheries in Rivers and Streams

<em>Abstract.</em>—Shoal Bass <em> Micropterus cataractae </em>are fluvial specialists endemic to the Apalachicola-Chattahoochee-Flint River Basin that are considered to be in decline throughout their native range. Effective conservation requires a comprehensive understanding of the migratory behavior and multi-scale habitat associations of Shoal Bass with riverine shoals, the critical mesohabitat upon which the species depends. We assessed movement patterns and habitat use of Shoal Bass using radio telemetry in the lower 24 km of Ichawaynochaway Creek, a 6th-order tributary of the Flint River and one of the few relatively undisturbed streams inhabited by this species. In general, Shoal Bass exhibited relatively low movement rates with increased movement in the spring, and no tagged Shoal Bass migrated from the creek into the Flint River during the study period. Most study fish preferred moderate depths (<2 m) and swift velocities during the year, and higher velocities in the winter, potentially reflecting seasonal changes in flow. These conditions were routinely satisfied through occupation of a 9-km reach with a network of large shoal complexes. Shoal Bass exhibited a distinct preference for close proximity to large shoals, and an affinity for greater depth variability associated with edge and boundary conditions within discrete shoal complexes. Despite previous studies that have documented high movement of this species in other systems, these findings suggest that the Ichawaynochaway Creek Shoal Bass population may be relatively sedentary and associate to specific areas that provide suitable habitat. This may have implications for assessing the integrity, distribution, and abundance of suitable Shoal Bass habitat in small karst limestone streams, designing projects for restoration or enhancement of existing habitat, and gauging the species vulnerability to threats such as habitat loss, introgression, and hybridization.