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Assessing the status of several migratory fishes in the Mobile River Basin, Alabama, has been complicated due to a general lack of historical data on their life history, habitat requirements, and distributions. Whether distributions were restricted by natural or man‐made barriers to migration is difficult to answer because few scientific collections were made before dams were built, and the earliest dams were built at the largest biogeographic barrier in the basin: the geological fall line. Therefore, we used what information was available, including anecdotal information, primarily records from archived newspapers and government reports, to describe the ranges of six migratory species prior to the construction of dams in the Mobile Basin. We describe the complicated history of Alabama Shad Alosa alabamae and show that range declines may have been masked by the stocking of American Shad Alosa sapidissima in the late 19th century. We show that Gulf Sturgeon Acipenser oxyrinchus desotoi probably migrated well above the fall line in the Coosa River, and may have been sympatric with Lake Sturgeon Acipenser fulvescens. We found no records of Alabama Sturgeon Scaphirhynchus suttkusi above the fall line. American Eel Anguilla rostrata migrated above the fall line in every Mobile Basin river before dams were built. Finally, Paddlefish Polyodon spathula may have once occurred above the fall line in at least two rivers, but they persist today in impounded reaches in the coastal plain, unlike some other species. We hope that future work will continue to consider archival sources of information to re‐trace the histories of imperilled species. [ABSTRACT FROM AUTHOR]

Objective: Reducing Largemouth Bass Micropterus salmoides recruitment and therefore population density could benefit recreational fisheries in small impoundments by improving individual growth rates and increasing the average size and condition of Largemouth Bass. To achieve these effects, methods of controlling Largemouth Bass recruitment should avoid reducing the productivity of their primary prey species, the Bluegill Lepomis macrochirus. Methods: We tested this hypothesis by evaluating the effects of shoreline rotenone application on the density of Bluegill and the density, growth, and survival of age‐0 and age‐1 Largemouth Bass in 15 Alabama small impoundments. Result: After treatment, Largemouth Bass age‐0 densities declined and mean age‐1 length increased, whereas Bluegill populations were not significantly reduced. Conclusion: Our study indicates that shoreline rotenone application may be a valuable method for reducing Largemouth Bass recruitment and increasing the growth of age‐1 Largemouth Bass in small impoundments. However, further research is needed to understand the effects of treatment on nontarget fishes and to better assess the effects of factors such as impoundment surface area and treatment frequency and duration on the ultimate utility of the approach. Impact statementSmall impoundment management could benefit from reducing Largemouth Bass recruitment. We found that shoreline rotenone application improved age‐1 Largemouth Bass growth rates while Bluegill densities were unaffected. Shoreline rotenone application appears to immediately enhance Largemouth Bass populations in impoundments ≤11 ha. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are undergoing rapid thermal shifts, making it increasingly important to understand species-specific responses to these changes. Traditional techniques for determining a species' thermal tolerance are often lethal and time consuming. Using the enzyme activity associated with the electron transport system (ETS; hereafter referred to as enzyme assay) may provide a non-lethal, rapid, and efficient alternative to traditional techniques for some species. We used largemouth bass Micropterus salmoides (Lacepede, 1802) to test the efficacy of using an enzyme assay to determine thermal tolerance and respiratory exploitation in response to variable acclimation temperatures. Three tissue types were dissected from fish acclimated to 20, 25, or 30 °C and used in ETS assays at temperatures ranging from 7.5 to 40 °C. While there were significant differences among tissue types and acclimation temperatures, maximal enzyme activity occurred from 25.23 to 31.91 °C. Fish lost equilibrium at 39–42 °C in traditional CTmax trials, significantly higher than the upper optimum range determined via enzyme assays. The ratio of enzyme activity to measured whole organism respiration rate decreased with increasing water temperature, with the largest changes occurring at the upper optimum thermal range determined by enzyme assays. Our results indicate that ETS analysis may prove useful for obtaining biologically relevant thermal tolerances. [ABSTRACT FROM AUTHOR]

Objective: Movement of fish past dams can be facilitated by dedicated fish passage structures, navigational locks, and crested spillways, with the efficacy of a passage structure depending strongly on the nature of the system (height of the dam, flow rate, etc.) and the fish's behavior and swimming capability. However, once the fish have passed a dam, whether by using a mitigation structure or due to active translocation, they encounter a different habitat upstream versus in the tailrace, potentially affecting their ability to continue their upstream migration. Methods: Here, we had two objectives. First, we determined whether Paddlefish Polyodon spathula that successfully passed a structure continued their upstream migration in the Alabama River. Because assuring passage by tagged fish required that we move the fish past the dam, our second objective was to determine whether translocated fish exhibited fallback behavior (downstream drift or movement postrelease that would compromise their continued migration). We used both active and passive telemetry methods to quantify the postpassage movements of tagged and translocated Paddlefish. Result: Fish that were translocated above Claiborne Lock and Dam (CLD) exhibited upriver movements once translocated, and they exhibited no fallback (i.e., downstream movement with delayed or no continuation upstream). Timing of movement relative to spawning periods did not influence initial fish movement or the likelihood of reaching the next upstream dam (Millers Ferry Lock and Dam [MFLD]; ~100 river kilometers upstream) within the first 30 days of observation, but more fish that were tagged and released during the early prespawn period made it to within 4.83 km of MFLD (the location of our closest receiver below MFLD) relative to fish from the prespawn or spawning period. Fish that were released above CLD had a lower probability of being subsequently detected downstream of their release sites compared to fish that were released below CLD. Conclusion: Our findings support that Paddlefish will continue their upstream migration once they have passed a structure, despite changes in habitat. Impact statementDams represent barriers to fish movement in rivers, but the question remains whether fish will continue an upstream migration once they pass a dam given that the upstream habitat differs from the habitat below the dam. We tracked tagged fish that were moved from downstream to upstream of a lock‐and‐dam structure and found that they did continue their upstream migration. [ABSTRACT FROM AUTHOR]

Objective: We used two approaches, fish hard‐part microchemistry and genetics, to quantify effects of low‐use lock‐and‐dam structures on riverine fish movement. Each approach varied in temporal scope, with microchemistry addressing effects within a lifetime and genetics addressing effects across generations. Methods: Water samples and individuals of two species (Paddlefish Polyodon spathula and Smallmouth Buffalo Ictiobus bubalus) were collected from four river sections that were separated by three low‐use lock‐and‐dam structures on the Alabama River. Quarterly water samples were collected from 15 sites during 2017–2018, and concentrations of Sr, Ba, Mn, Mg, and Ca were quantified using mass spectrometry. Result: Water elemental signatures were spatially variable but temporally consistent. The Sr:Ca ratios in fish hard parts differed significantly among river sections for both species. Additionally, discriminant function analyses classified fish to their river capture section with accuracy between 55% and 74% for Paddlefish (errors nearly always assigned individuals to adjacent river sections) and 37–47% for Smallmouth Buffalo. Population genetic analyses included fish from each river section, as well as from Alabama River tributaries and a neighboring watershed. Genotyping‐by‐sequence techniques identified 1,889 and 3,737 single nucleotide polymorphisms postfiltering in Paddlefish and Smallmouth Buffalo, respectively, which we used to estimate population diversity indices and conduct differentiation analyses. Analysis of molecular variance, discriminant analysis of principal components, Bayesian clustering, and pairwise comparisons of FST values indicated no strong evidence for genetic divergence in either species among river sections. Conclusion: Within‐lifespan results based on hard‐part microchemistry suggested a potential for population isolation. However, longer‐term genetic effects were not apparent, possibly because the life span of these large and relatively long‐lived species means that few generations have passed since dam construction, and there could be sufficient mixing or population connectivity to prevent genetic divergence across river sections, particularly at the most downstream structure. Impact StatementPaddlefish and Smallmouth Buffalo showed evidence of population separation by Alabama River lock‐and‐dams via a within‐generation measure (chemical composition of fish jaw bones and ear stones) but not with a longer‐term metric (genetic isolation). Both species are long lived relative to the age of the dams; effects may be more apparent in shorter‐lived species. [ABSTRACT FROM AUTHOR]

Objective: Altered temperature and dissolved oxygen (DO) regimes in the tailwaters below dams can cause stress to fish. Despite their widespread distribution in rivers across North America, Freshwater Drum Aplodinotus grunniens have received little attention relative to the effects of these potential stressors. Quantifying fish swimming performance and kinematics in simulated tailwater conditions can help to determine how riverine species are affected by dam water releases, with the ultimate goal of identifying improved management strategies for these systems. Methods: We quantified Freshwater Drum swimming performance and kinematics by measuring critical swimming speed (in both relative [RUcrit; body lengths/s] and absolute [AUcrit; cm/s] units), tailbeat frequency, tailbeat amplitude, and Strouhal's number under all combinations of low‐DO (4 mg/L), normoxic (9 mg/L), and high‐DO (14 mg/L) conditions at low (10°C), intermediate (20°C), and warm (30°C) water temperatures using both 90‐ and 850‐L swim flumes. Result: Dissolved oxygen at these concentrations did not affect swimming performance. The effect of temperature on swimming performance depended on fish size; RUcrit, AUcrit, and tailbeat frequency decreased with fish length but increased with temperature. In contrast, tailbeat amplitude increased with fish length but did not differ across temperatures. Conclusion: These results suggest that acute low‐ and high‐DO exposure within the tested range may not affect swimming performance or kinematics. However, the influence of temperature on Freshwater Drum swimming performance suggests that the ability of fish to hold position in a tailrace or to successfully pass upstream of a dam may vary seasonally and may depend on the depth from which water is released from a reservoir, as release depth determines the water temperature. Impact statementDams are a globally pervasive feature of moving waters that can provide benefits but also negatively affect aquatic ecosystems, including alteration of temperature and dissolved oxygen. Such alterations could affect the swimming ability of fishes experiencing those alterations. We found that temperature effects on Freshwater Drum swimming performance and kinematics were size‐dependent, while dissolved oxygen concentrations within the ranges we tested did not affect swimming performance or kinematics. The influence of temperature suggests that fish ability to hold position may vary seasonally, and potentially depend on temperatures of water releases from dams. [ABSTRACT FROM AUTHOR]

Management of fish populations for conservation in thermally variable systems requires an understanding of the fish's underlying physiology and responses to thermal stress. Physiological research at the organismal level provides information on the overall effects of stressors such as extreme temperature fluctuations. While experiments with whole organisms provide information as to the overall effects of temperature fluctuations, biochemical assays of thermal stress provide direct results of exposure that are both sensitive and specific. Electron transport system (ETS; Complex III) assays quantify a rate‐limiting step of respiratory enzymes. Parameters that can be estimated via this approach include optimum thermal temperature (Topt) and optimal breadth of thermal performance (Tbreadth), which can both be related to organismal‐level temperature thresholds. We exposed enzymes of seven fish species (native fish chosen to represent a typical community in Alabama streams) to temperatures in the range 11–44°C. The resultant enzymatic thermal performance curves showed that Topt, the lower temperature for enzyme optimal thermal performance (Tlow), the upper temperature for enzyme optimal thermal performance (Tup), and Tbreadth differed among species. Relationships between enzymatic activity and temperature for all fish followed a pattern of steadily increasing enzyme activity to Topt before gradually decreasing with increasing temperature. A comparison of our enzyme optimum and upper‐temperature limit results versus published critical thermal maxima values supports that ETS Complex III assays may be useful for assessing organismal‐level thermal tolerance. Highlights: Relationships between Complex III enzyme activity and temperature for all fish followed a pattern of steadily increasing enzyme activity to an optimal temperature before gradually decreasing with increasing temperature.The temperature at the upper limit of the optimum thermal range was close to published CTmax values for five of the seven fish species. [ABSTRACT FROM AUTHOR]

Some freshwater fishes occur regularly in estuarine areas that experience spatial and seasonal variation in marine influence. These dynamic abiotic and biotic conditions potentially influence food consumption and growth. We found that effects of an estuarine environment on the growth of largemouth bass (Micropterus salmoides) in Alabama's Mobile-Tensaw River Delta depended on body size, distance from the marine source, and amount of freshwater inflow. Incremental growth analyses demonstrated that young largemouth bass ( Certains poissons dulcaquicoles sont regulierement presents en zones estuariennes dans lesquelles l'influence de la mer varie dans l'espace et en fonction de la saison. Ces conditions abiotiques et biotiques dynamiques peuvent avoir une incidence sur la consommation d'aliments et la croissance. Nous avons constate que les effets d'un milieu estuarien sur la croissance de l'achigan a grande bouche (Micropterus salmoides) dans le delta des rivieres Mobile et Tensaw, en Alabama, dependaient de la taille du corps, de la proximite de la source marine et de l'ampleur de l'apport en eau douce. Des analyses de la croissance differentielle ont demontre que la croissance des jeunes achigans a grande bouche (, Introduction Estuaries are composed of a mosaic of abiotic conditions that occur along a generally predictable spatial gradient (upstream to downstream), serving as an initial physiological template influencing the spatial [...]

Estuaries are productive, heterogeneous, and dynamic systems that support a diverse array of fishes. However, our understanding of how presumably stenohaline fishes persist in such transitional systems is limited, particularly for most fishes in tidal freshwater areas. We conducted a laboratory experiment and field investigation along an upstream--downstream salinity gradient in the Mobile--Tensaw River Delta, Alabama, USA, to test the hypothesis that age-0 largemouth bass (Micropterus salmoides), an economically and ecologically important freshwater species that uses low-salinity habitats in many North American estuaries, move to avoid seasonal salinity increases. To do so, we quantified changes in otolith microchemistry (e.g., Sr to Ca ratios) along the major growth axis of otoliths in both field-collected and laboratory-reared individuals. Our experiment revealed a 21-day lag time between initial salinity changes and [Sr:Ca.sub.otolith] saturation but that [Sr:Ca.sub.otolith] in field-collected fish reflect changes in ambient salinity. Further, contrary to our expectation, otolith microchemical analyses from spring- and fall-collected age-0 largemouth bass indicate no avoidance of increased salinity, which has potential implications for their growth and recruitment in these systems. Resume: Les estuaires sont des systemes productifs, heterogenes et dynamiques qui contiennent un ensemble diversifie de poissons. Nous comprenons mal, cependant, comment des poissons supposement stenohalins persistent dans de tels syste mes de transition, particulierement dans le cas de la plupart des poissons qui habitent les regions d'eau douce de la zone des marees. Nous avons fait une experience de laboratoire ainsi qu'une recherche sur le terrain le long d'un gradient de salinite amont--aval dans le delta des rivieres Mobile--Tensaw en Alabama, E.-U., afin de tester l'hypothese selon laquelle les achigans a grande bouche (Micropterus salmoides) d'age 0, des poissons d'importance economique et ecologique qui utilisent les habitats de faible salinite dans plusieurs estuaires nord-americains, se deplacent afin d'eviter les augmentations saisonnieres de salinite. Pour ce faire, nous avons dose les changements microchimiques des otolithes (par ex., les rapports Sr sur Ca) le long de l'axe principal de croissance des otolithes, tant chez des individus recoltes en nature qu'eleves au laboratoire. Notre experience revele l'existence d'un temps de latence de 21 jours entre les changements initiaux de salinite et la saturation de [Sr:Ca.sub.otolithes]; cependant, chez les poissons recoltes en nature, [Sr:Ca.sub.otolithes] represente les changements de salinite ambiante. De plus, contrairement a nos attentes, les analyses microchimiques des otolithes des achigans a grande bouche d'age 0 recoltes au printemps et en automne n'indiquent aucun evitement de la salinite accrue, ce qui a des consequences potentielles sur leur croissance et leur recrutement dans ces systemes. [Traduit par la Redaction], Introduction Estuaries serve as an interface among marine, freshwater, and terrestrial environments and are characterized by heterogeneous physical habitats (e.g., seagrass, emergent vegetation, and oyster reefs) that are structured along [...]

Gizzard shad [Dorosoma cepedianum) population characteristics vary with lake productivity, competing with and providing prey for sport fishes. Because age-0 gizzard shad (>30 mm total length) are facultative detritivores. they can link benthic energy, carbon, and nutrients to pelagic food webs. To determine how age-0 gizzard shad success varies along a detritus-quality gradient, we completed a 15-day laboratory experiment in which age-0 gizzard shad fed lake sediment and starved gizzard shad both suffered high mortality, whereas fish fed zooplankton grew and survived well. This suggested that detritus alone is insufficient to ensure gizzard shad growth and survival. When sediment quality was high in outdoor mesocosms, density-dependent factors led to rapid growth only at low fish density and high-quality sediments: however, survival generally increased with sediment quality, regardless of gizzard shad density. In four small reservoirs, annual growth of gizzard shad increased with sediment quality. Collectively, our findings suggest that detritus quality ultimately can contribute to regulation of community and ecosystem productivity, mediated by its influence on gizzard shad biomass available for trophic transfer to gape-limited predators (i.e., piscivorous fish). This role of gizzard shad can link higher trophic levels in aquatic food webs to allochthonous detritus subsidies from the surrounding watershed. Les caracieristiques des populations d'aloses a gesier (Dorosoma cepedianum) varienl en fonction de la productivite des lacs dans lesquels elles font competition avec les poissons sportifs et leur servent de proies. Parce que les aloses a gesier d'age 0 (>30 mm de longueur tolale) sont des detritivores facultatifs, ils peuvenl servir de lien entre l'energie benthique. le carbone et les nutriments, d'une part, et les reseaux alimentaires pelagiques, d'autre part. Afin de determiner le succes d'aloses a gesier d'age 0 dans un gradient de qualite de detritus, nous avons mene une experience de laboratoire de 15 jours durant laquelle des aloses a gesier d'age 0 nourries de sediments lacustres et des aloses maintenues a jeun ont toutes connu une forte mortalite, alors que les aloses nourries de zooplancton ont eu une bonne croissance et une bonne survie. Cela indique que le detritus seul ne suffit pas a assurer la croissance et la survie chez les aloses a gesier. Lorsque la qualite des sediments est elevee dans des mesocosmes a l'exterieur, les facteurs dependant de la densite permettent une croissance rapide seulement si la densite des poissons est faible et les sediments sont de haute qualite; cependant, la survie augmente generalement en fonction de la qualite des sediments, independamment de la densite des aloses a gesier. Dans quatre petits reservoirs, la croissance annuelle des aloses a gesier augmente en fonction de la qualite des sediments. Dans leur ensemble, nos resultats indiquen! qu'en fin de compte, la qualite du detritus peut contribuer a la regulation de la productivite de la communaute et de l'ecosysteme, par le biais de son influence sur la biomasse des aloses a gesier disponible pour transferi trophique vers les predateurs a ouverture de bouche limitee (c'est-a-dire, les poissons piscivores). Ce role des aloses a gesier peut relier les niveaux trophiques superieurs des reseaux alimentaires aquatiques aux apports de detritus allochtone provenant du bassin versan! environnant. [Traduit par la Redaction], Introduction The flow of material and energy across aquatic habitats influences ecosystem productivity. Although phytoplankton primary production is a principal carbon source for higher trophic levels, a fraction of this [...]

Abstract: Although critical periods often explain first-year growth and recruitment patterns of young fishes, isolated subpopulations in spatially heterogeneous environments can be influenced by distinct factors, preventing critical periods from [...]

Impacts of low‐head, run‐of‐the‐river dams on migratory fish movements depend on the structure of the dam, river hydrology, and the ability of fish to navigate the tailrace environment. Here, we present results from a 3‐year movement study in which telemetered Paddlefish Polyodon spathula and Smallmouth Buffalo Ictiobus bubalus were tracked as they approached and sometimes migrated past Claiborne Lock and Dam (CLD), a low‐use low‐head lock‐and‐dam structure on the Alabama River. A spillway portion of the dam is periodically inundated during early spring, dependent on precipitation and releases from the next upstream dam. Our goals were to (1) quantify dam passage rates for both species, (2) assess the importance of factors affecting passage success, and (3) quantify space use patterns in the tailrace. Both species exhibited annual upstream migrations during the study period. Correlation of daily average river position versus the CLD hydrograph showed that movements by both species appeared to be related to flow variation. Passage efficiency (range = 10.7–30.2%) varied between species and among years, with tailrace gauge height being the most important factor affecting passage success for both species. Using an acoustic positioning system in the tailrace, we quantified space use by individuals of both species. Time spent in the tailrace (mean = 3.9 continuous days; range = 0–94 continuous days) did not differ between individuals that passed and those that did not pass. Fine‐scale position estimates showed that space use differed between species, across gauge heights, and between individuals that passed and those that did not pass. Differential space use may be due to the species' habitat preferences or swimming abilities. Our findings provide information to inform potential design of mitigation structures, and they also identify the need for additional work required to more fully understand the mechanisms of passage success versus failure for these and other native potamodromous species. [ABSTRACT FROM AUTHOR]

Roberts CM, DeVries DR, Wright RA. 2018. Introduced yellow perch in two Southeastern US reservoirs: ecological interactions with resident fishes. Lake Reserv Manage. 34:141—153. Yellow perch (Perca flavescens) has been introduced into Southeastern US drainages outside its native range; unfortunately, the effects of these introductions at the edge of their distribution on resident fishes have not been well documented. To determine the potential interactions between introduced yellow perch and resident fishes, we quantified diets of multiple life stages over 2 yr in 2 Alabama reservoirs. Temporal and spatial co-occurrence between larval yellow perch and native fishes was limited, and diet overlap was generally low at all life stages. Juvenile yellow perch were consumed by Micropterus spp. in both lakes during spring, suggesting some potential benefit for native piscivores. We suggest minimal negative effects of yellow perch on native fishes in these Southeastern US systems due to their generalist diet, early spawning period, and cool water temperature requirements. In addition, yellow perch may represent an alternative prey resource for piscivores. [ABSTRACT FROM AUTHOR]

Many applications of otolith chemistry use the ratios of strontium (Sr) and barium (Ba) to calcium (Ca) as indicators of salinity exposure, because typically, as salinity increases, Sr concentration increases and Ba concentration decreases. However, these relationships are nonlinear, can be confounded by temperature, and investigations of salinity and temperature effects on otolith chemistry produce varied results. To determine the relationships of temperature and salinity on Sr:Ca and Ba:Ca in otoliths, we used free ranging Gulf Killifish (Fundulus grandis) in the northern Gulf of Mexico. This species is ideal because it is euryhaline and exhibits limited movements. Otolith edge Sr:Ca and Ba:Ca ratios were related to the previous 30-day mean salinity and temperature experienced by fish. The best model to describe otolith Sr:Ca was one that included a positive asymptotic relationship for both salinity and temperature. However, the salinity asymptotic maximum was reached at 10 psu and changes in otolith Sr:Ca above 10 psu were indicative of temperature changes. Otolith Ba:Ca exhibited an exponential decreasing relationship with salinity, and an exponential increasing relationship with temperature, and these two models combined best explained otolith Ba:Ca. Above 10 psu, the modeled Ba:Ca ratio continued to decrease demonstrating that this ratio may be indicative of salinity changes beyond this value. Therefore, using both Sr:Ca and Ba:Ca could be beneficial in reconstructing fish environmental histories. Temperature effects on otolith element ratios could confound past salinity reconstructions as well and must be a result of endogenous processes, given that no relationship between temperature and water chemistry existed. [ABSTRACT FROM AUTHOR]