Search

In business, benchmarking is a widely used practice of comparing your own business processes to those of other comparable companies and incorporating identified best practices to improve performance. Biologists and resource managers designing and conducting monitoring programs for fish in large river systems tend to focus on single river basins or segments of large rivers, missing opportunities to learn from those conducting fish monitoring in other rivers. We briefly examine five long-term fish monitoring programs in large rivers in the United States (Colorado, Columbia, Mississippi, Illinois, and Tallapoosa rivers) and identify opportunities for learning across programs by detailing best monitoring practices and why these practices were chosen. Although monitoring objectives, methods, and program maturity differ between each river system, examples from these five case studies illustrate the important role that long-term monitoring programs play in interpreting temporal and spatial shifts in fish populat...

Eastern oysters have been acknowledged for their important contribution to human well-being by providing goods and services including nitrogen removal from water bodies. In this study, we integrated daily environmental data (2008–2016) and filtration rate model parameter uncertainty to estimate nitrogen removal from denitrification and nitrogen burial services provided by the current extent of oyster (Crassostrea virginica) reefs in Mobile Bay, Alabama. Oyster landing data (2008–2016) in the Bay were also used to estimate nitrogen removal through oyster harvest. A replacement cost method using an engineering solution from wastewater treatment plants was implemented to quantify the economic benefit of the nitrogen removal. The estimated total nitrogen removal services provided by oyster reefs in Mobile Bay was 34,911 ± 5,032 kg N yr−1 (mean ± 1sd), in which 22,095 ± 3,305 kg N yr−1 from denitrification, 11,047 ± 1,652 kg N yr−1 from burial of nitrogen into sediments and 1,769 ± 876 kg N yr−1 by oyster harvest. The mean economic benefit was $76,455 ± 11,020 yr−1 which was estimated as $73.2 ± 11.5 ha−1 yr−1. This method could be used for any time period to estimate the nitrogen removal service in Mobile Bay. With proper modification of model parameters, this method could also be used elsewhere to estimate nitrogen removal services provided by oysters.

Quantifying ecosystem services can provide information to justify conservation and restoration decisions so as to allocate limited resources effectively. Consequently, decision makers and public typically ask for simple and understandable information with confidence regarding the availability of the services and the probable economic value. Here, we compiled published information on density enhancement and species life-history information to quantify fish and crustacean production and its uncertainty associated with the current extent of oyster (Crassostrea virginica) reefs in Mobile Bay, Alabama. We applied Alabama fishing size limits as a cutoff to exclude the production of non-harvestable size individuals. Fishery landing (2005–2015) and Willingness-To-Pay information were used to quantify the economic benefit of the harvestable production enhancement (commercial and recreational production). Sixteen species were found to be production-enhanced in the bay with a mean of 354 ± 182 g m−2 year−1, of which 170 ± 112 g m−2 year−1 was economically quantifiable based on their harvestable production and landing information. The mean economic value was $509,000 year−1 in direct economic value for commercial fishers and $19.59 million year−1 estimated by the willingnesstopay value from recreational anglers. The results demonstrated a substantial positive economic benefit of ecosystem services from oyster reefs associated with fishery production in Mobile Bay, Alabama. The method could be applied elsewhere to estimate the economic return from the investment of conserving and restoring of similar structured habitats.

Understanding trends in the diverse resources provided by large rivers will help balance tradeoffs among stakeholders and inform strategies to mitigate the effects of landscape scale stressors such as climate change and invasive species. Absent a cohesive coordinated effort to assess trends in important large river resources, a logical starting point is to assess our ability to draw inferences from existing efforts. In this paper, we use a common analytical framework to analyze data from five disparate fish monitoring programs to better understand the nature of spatial and temporal trends in large river fish assemblages. We evaluated data from programs that monitor fishes in the Colorado, Columbia, Illinois, Mississippi, and Tallapoosa rivers using non-metric dimensional scaling ordinations and associated tests to evaluate trends in fish assemblage structure and native fish biodiversity. Our results indicate that fish assemblages exhibited significant spatial and temporal trends in all five of the rivers. We also document native species diversity trends that were variable within and between rivers and generally more evident in rivers with higher species richness and programs of longer duration. We discuss shared and basin-specific landscape level stressors. Having a basic understanding of the nature and extent of trends in fish assemblages is a necessary first step towards understanding factors affecting biodiversity and fisheries in large rivers.

We designed a digital underwater video camera system to monitor nesting centrarchid behavior in the Tallapoosa River, Alabama, 20 km below a peaking hydropower dam with a highly variable flow regime. Major components of the system included a digital video recorder, multiple underwater cameras, and specially fabricated substrate stakes. The innovative design of the substrate stakes allowed us to effectively observe nesting redbreast sunfish Lepomis auritus in a highly regulated river. Substrate stakes, which were constructed for the specific substratum complex (i.e., sand, gravel, and cobble) identified at our study site, were able to withstand a discharge level of approximately 300 m3/s and allowed us to simultaneously record 10 active nests before and during water releases from the dam. We believe our technique will be valuable for other researchers that work in regulated rivers to quantify behavior of aquatic fauna in response to a discharge disturbance.

Modifications to stream hydrologic regimes can have a profound influence on the dynamics of their fish populations. Using hierarchical linear models, we examined the relations between flow regime and young-of-year fish density using fish sampling and discharge data from three different warmwater streams in Illinois, Alabama, and Georgia. We used an information theoretic approach to evaluate the relative support for models describing hypothesized influences of five flow regime components representing: short-term high and low flows; short-term flow stability; and long-term mean flows and flow stability on fish reproductive success during fish spawning and rearing periods. We also evaluated the influence of ten fish species traits on fish reproductive success. Species traits included spawning duration, reproductive strategy, egg incubation rate, swimming locomotion morphology, general habitat preference, and food habits. Model selection results indicated that young-of-year fish density was positively related to short-term high flows during the spawning period and negatively related to flow variability during the rearing period. However, the effect of the flow regime components varied substantially among species, but was related to species traits. The effect of short-term high flows on the reproductive success was lower for species that broadcast their eggs during spawning. Species with cruiser swimming locomotion morphologies (e.g., Micropterus) also were more vulnerable to variable flows during the rearing period. Our models provide insight into the conditions and timing of flows that influence the reproductive success of warmwater stream fishes and may guide decisions related to stream regulation and management.

We developed stochastic matrix models to evaluate the effects of hydrologic alteration and variable mortality on the population dynamics of a lotic fish in a regulated river system. Models were applied to a representative lotic fish species, the flathead catfish (Pylodictis olivaris), for which two populations were examined: a native population from a regulated reach of the Coosa River (Alabama, USA) and an introduced population from an unregulated section of the Ocmulgee River (Georgia, USA). Size-classified matrix models were constructed for both populations, and residuals from catch-curve regressions were used as indices of year class strength (i.e., recruitment). A multiple regression model indicated that recruitment of flathead catfish in the Coosa River was positively related to the frequency of spring pulses between 283 and 566 m3/s. For the Ocmulgee River population, multiple regression models indicated that year class strength was negatively related to mean March discharge and positively related to June low flow. When the Coosa population was modeled to experience five consecutive years of favorable hydrologic conditions during a 50-year projection period, it exhibited a substantial spike in size and increased at an overall 0.2% annual rate. When modeled to experience five years of unfavorable hydrologic conditions, the Coosa population initially exhibited a decrease in size but later stabilized and increased at a 0.4% annual rate following the decline. When the Ocmulgee River population was modeled to experience five years of favorable conditions, it exhibited a substantial spike in size and increased at an overall 0.4% annual rate. After the Ocmulgee population experienced five years of unfavorable conditions, a sharp decline in population size was predicted. However, the population quickly recovered, with population size increasing at a 0.3% annual rate following the decline. In general, stochastic population growth in the Ocmulgee River was more erratic and variable than population growth in the Coosa River. We encourage ecologists to develop similar models for other lotic species, particularly in regulated river systems. Successful management of fish populations in regulated systems requires that we are able to predict how hydrology affects recruitment and will ultimately influence the population dynamics of fishes.

We used an information-theoretic approach to examine the variation in detection probabilities for 87 Piedmont and Coastal Plain fishes in relation to instream gravel mining in four Alabama streams of the Mobile River drainage. Biotic and abiotic variables were also included in candidate models. Detection probabilities were heterogeneous across species and varied with habitat type, stream, season, and water quality. Instream gravel mining influenced the variation in detection probabilities for 38% of the species collected, probably because it led to habitat loss and increased sedimentation. Higher detection probabilities were apparent at unmined sites than at mined sites for 78% of the species for which gravel mining was shown to influence detection probabilities, indicating potential negative impacts to these species. Physical and chemical attributes also explained the variation in detection probabilities for many species. These results indicate that anthropogenic impacts can affect detection pro...

We developed and validated methods for estimating the daily age of age-0 channel catfish Ictalurus punctatus. Two clutches of channel catfish eggs were hatched in the laboratory; subsequently, one was stocked in a 186-m2 earthen nursery pond and the other in a 757-L outdoor circular tank. Before stocking, subsamples of fish were collected at swim-up and 3 d after swim-up to evaluate early ring formation. Fish were sampled from the pond and tank on eight occasions ranging from 30 to 119 d posthatch. Distinct differences in early ring formation were found between yolk sac and free-swimming larval stages. Mean ring count and known age were closely related for tank- and pond-raised fish, indicating that daily ring deposition occurred in the otoliths of age-0 channel catfish up to 119 d posthatch. The accuracy of daily age estimation was similar between tank and pond samples, and daily ring counts were considerably accurate up to 60 d posthatch. Pond-raised fish were more difficult to age than tank-ra...

We compared growth of flathead catfish Pylodictis olivaris from two native populations in Alabama (Coosa and Tallapoosa rivers) and two introduced populations in Georgia (Ocmulgee and Satilla rivers). We also compared mortality rates and potential outcomes of various management regimes (minimum length limits [MLLs]) among the populations. Total length–log10(age) regression slopes for introduced fish were higher than those for native fish, and von Bertalanffy growth coefficients (K) were greater for introduced fish (Ocmulgee: 0.195; Satilla: 0.201) than for native individuals (Coosa: 0.057; Tallapoosa: 0.059). Therefore, introduced flathead catfish grew more rapidly than those in their native range. Mortality (instantaneous mortality rate, Z) was higher in the Satilla River population (Z = −0.602) than in the Ocmulgee River (Z = −0.227) and Coosa River (Z = −0.156) populations. However, fish in the Satilla River population had been introduced for only 10 years and presumably did not reach their th...

White crappie Pomoxis annularis and black crappie P. nigromaculatus are among the principle species sought by anglers in the midwestern and southeastern United States. The focus of management activ...

Conserving river biota will require innovative approaches that foster and utilize scientific under- standing of ecosystem responses to alternative river-management scenarios. We describe ecological and soci- etal issues involved in flow management of a section of the Tallapoosa River (Alabama, U.S.A.) in which a species-rich native fauna is adversely affected by flow alteration by an upstream hydropower dam. We hy- pothesize that depleted low flows, flow instability, and thermal alteration resulting from pulsed flow releases at the hydropower dam are most responsible for changes in the Tallapoosa River biota. However, existing data are insufficient to prescribe with certainty minimum flow levels or the frequency and duration of stable flow periods that would be necessary or sufficient to protect riverine biotic integrity. Rather than negotiate a specific change in the flow regime, we propose that stakeholders—including management agencies, the power utility, and river advocates—engage in a process of adaptive-flow management. This process would require that stakeholders (1) develop and agree to management objectives; (2) model hypothesized relations between dam operations and management objectives; (3) implement a change in dam operations; and (4) evaluate biological responses and other stakeholder benefits through an externally reviewed monitoring program. Models would be updated with monitoring data and stakeholders would agree to further modify flow regimes as necessary to achieve management objectives. A primary obstacle to adaptive management will be a per- ceived uncertainty of future costs for the power utility and other stakeholders. However, an adaptive, itera- tive approach offers the best opportunity for improving flow regimes for native biota while gaining informa- tion critical to guiding management decisions in other flow-regulated rivers.

Basal recess and articulating process sections of pectoral spines are often used to estimate the age of channel catfish Ictalurus punctatus. However, identification of annuli in pectoral spine sections can be difficult. We developed and validated a method for estimating the age of channel catfish by using sagittal otoliths. We also validated a new method using pectoral spines in which a single cut is made through the dorsal and anterior processes (hereafter termed cut spines) and annuli are enhanced with side illumination. Age estimates from otoliths and cut spines were compared with age estimates from traditional articulating process sections of pectoral spines for channel catfish of known ages (1–4). Age estimates by the three methods were correct for more than 90% of fish after two experienced readers independently estimated ages and resolved disagreements by mutual examination. Otoliths were more accurate and less variable in estimating age. Otolith age estimates were always within 1 year and...

During population dynamic and reproductive biology research on three species of Lepisosteidae (i.e., alligator gar Lepisosteus spatula (also known as Atractosteus spatula), longnose gar L. osseus, and spotted gar L. oculatus), we determined that misidentification of sex through gross examination of the gonads was probable. During gross examination of the gonads of all three species, postspawning and juvenile ovaries frequently resembled testes due to the envelopment of the ovaries by fatty tissue. We examined the gonads and gamete release pathways of 598 individuals and found that gamete release pathways (i.e., oviduct in females and vasa efferentia in males) were differentiable and can be used reliably in all seasons for all reproductive stages of the three species. Misidentification of sex can lead to inaccurate estimation of sex ratios and sex-dependent mortality and growth rates. Accurate estimates of Lepisosteidae population structure and vital rates are needed for successful conservation an...

The toxicity of an acid mine drainage (AMD) mixing zone was investigated by placing bluegill (Lepomis macrochirus) at the confluence of a stream contaminated by AMD and a stream having neutral pH. A mixing channel receiving water from both streams was assembled in the field, during July and October 1996, to determine the toxicity of freshly mixed and aged water (2.9-7.5 min). The AMD stream had elevated concentrations of Al and Fe, which precipitated upon mixing, and of Mn, which did not precipitate in the mixing zone. Fish exposed to freshly mixed water had higher mortality than fish exposed to water after aging. Precipitating Al, but not Fe, accumulated on the gills of bluegill, and accumulation was more rapid early during the mixing process than after aging. Fish exposed for 3.5 h to freshly mixed water had hypertrophy and hyperplasia of gill filament and lamellar epithelial cells. Similar lesions were observed after 6.0 h in fish exposed to water aged after mixing. Results demonstrated that Al was the predominant metal accumulating on the gills of fish in this AMD mixing zone, and that mixing zones can be more toxic than AMD streams in equilibrium.

Conserving biological resources native to large river systems increasingly depends on how flow-regulated segments of these rivers are managed. Improving management will require a better understanding of linkages between river biota and temporal variability of flow and instream habitat. However, few studies have quantified responses of native fish populations to multiyear (>2 yr) patterns of hydrologic or habitat variability in flow-regulated systems. To provide these data, we quantified young-of-year (YOY) fish abundance during four years in relation to hydrologic and habitat variability in two segments of the Tallapoosa River in the southeastern United States. One segment had an unregulated flow regime, whereas the other was flow-regulated by a peak-load generating hydropower dam. We sampled fishes annually and explored how continuously recorded flow data and physical habitat simulation models (PHABSIM) for spring (April–June) and summer (July–August) preceding each sample explained fish abundances. Patt...

The toxicity of an acid mixing zone produced at the confluence of a stream that was contaminated by acid mine drainage (AMD) and a pH-neutral stream was investigated in toxicity tests with juvenile bluegill Lepomis macrochirus and largemouth bass Micropterus salmoides. Fish mortalities in instream cages located in the mixing zone, below the mixing zone, and upstream in both tributaries were compared to determine relative toxicity at each site. In all tests and for both species, significantly higher mortality was observed in the mixing zone than at any other location, including the acid stream, which had lower pH (2.9–4.3). The mixing zone was defined chemically by rapid precipitation of dissolved aluminum and iron, which arrived from the low-pH stream, and by the presence of white precipitates, which were attached to the substratum and which extended below the confluence. Possible seasonal changes in mixing zone toxicity were investigated by conducting field tests with bluegill in June, July, and...

Relations between landscape features and the littoral distribution of young largemouth bass Micropterus salmoides were determined for 43 contiguous sections along the entire 8-km shoreline of an unvegetated embayment in B. E. Jordan Lake, North Carolina. Night shoreline electrofishing was conducted in July and October 1991–1992 and individual capture points of age-0 largemouth bass were recorded. Significant correlations among and between years in catch rate per section of shoreline indicated consistency in distribution. Habitat was characterized in 35 sections in July–August and 22 sections in October to quantify the relation between abundance and landscape components. Stepwise multiple regression indicated that distribution was strongly and positively related to landscape features, specifically bottom slope and gravel substrata. Correlations of catch rates with cover components were negative for July but positive for October. These data indicate that cover may be limiting late in the year, coin...

Latitudinal trends in reproductive characteristics are evident for some species of Clupeidae. However, selection for life history styles may operate at the population level. The reproductive cycles of alewifeAlosa pseudoharengus and threadfin shadDorosoma petenense in Dale Hollow Reservoir, Tennessee, were monitored over two spawning seasons on the basis of a gonadosomatic index (GSI). Inshore movements normally associated with spawning migrations were monitored using gill nets in spring 1989. GSI values peaked for both species at least one month earlier in 1989 than in 1988 due to warmer water temperatures earlier in the year. Highest GSI values for female alewife occurred each year when surface water temperatures were about 20° C; threadfin shad GSI values peaked at temperatures of 22°–26° C. Trends in male GSI values in both species were similar to those in females. Alewives were not abundant in warm (> 22° C), shallow water after 1 May 1989, but alewife GSI values remained high after this date, suggesting that elevated inshore temperatures limited alewife reproduction. All aspects of alewife reproduction were comparable to other populations of alewife but did not follow latitudinal trends. Threadfin shad reproductive characteristics were similar to other published accounts. We suggest that thermal regimes and reservoir trophic status are important factors for clupeid reproduction and population-level analysis is suggested when considering reproductive styles. Further, our ability to predict the ecology of introduced species in freshwater systems is impaired when species considered have not coevolved or evolved in marine environments.

Channel catfish Ictalurus punctatus (280–379 mm, total length) were tagged with soft visual implant alphanumeric tags and Floy t-bar anchor tags to evaluate long-term tag retention (270 d). Visual implant tags were not considered to be a viable method of tagging channel catfish; tag loss was 100% at 172 d after tagging. Retention of anchor tags was 100% at 97 d; however, tag retention had decreased to 71% at 270 d after tagging.

We describe age structure, growth, and fecundity of Hiodon tergisus (Mooneye) from the lower Tallapoosa River, AL. Mooneye (N = 49, 214–316 mm total length, 79–284 g) were aged using otoliths, and a von Bertalanffy growth model was derived for the species (L∞ = 316, K = 0.285, to = −0.7). Growth rates of Mooneye differed between the Tallapoosa River population and a previously studied population from the northern extent of the species' range (Assiniboine River, MB, Canada). In addition, fecundity of Mooneye from the Tallapoosa River was similar to the northern population, ranging from 5321 to 7432 eggs per female. Because the species is declining throughout its range in Alabama, we recommend that managers use our findings in conservation efforts. Future studies should investigate how hydrology influences the spawning success and early growth and development of Mooneye in regulated systems. More information about this species is needed regarding their early life history, including early growth, survival, and habitat use.

An electronic bacterial colony counter was used to count eggs of two clupeid species. Accuracy was evaluated by using regression techniques to model the relation between actual number of eggs and average machine count. When the data were log10 transformed, both models were significant (P < 0.001; r 2 ≥ 0.94). The method is accurate and fast.