Search

Harvest regulations are important tools that fisheries professionals use to impact fish abundance, alter population size structure, and improve fishing opportunities. Fisheries professionals often assume that specialized harvest regulations will have specific effects on target fish populations, but these predictions are not always realized because theory and practice do not always match (literature indicates that predictions are not met in about half of the cases). To identify trends that can improve the future success of harvest regulations, we reviewed a representative sample of harvest regulation evaluations for inland sport fish (i.e., 62 evaluations from 41 studies). Our review revealed gaps related to quantitative predictions, evaluation duration, statistical design, researcher–manager collaboration, and data standardization. Fisheries professionals can benefit from shared and thoughtful data collection designs and protocol standardizations. These designs can transform assessment sampling into empirical regulation evaluations that provide generality across locations and time periods with similar effort and cost.

Background: Restocking by introducing hatchery-reared fish into wild habitats aids in the restoration of fishery aquatic ecosystems and reefs to increase the abundance of fish resources, restore the ecological balance of water bodies, and enhance ecosystem functioning. Accurately, rapidly, and effectively evaluating the success of restocking using chemical markers (e.g., strontium [Sr]) remains challenging for fisheries management. Consequently, for non-lethal fish sampling, hard tissues, such as fin rays, have received increasing attention as a target for marking method. However, data on the differences in marking different types of fin rays remain limited. Therefore, we exposed juvenile blunt snout bream individuals (Megalobrama amblycephala) to 0 (control group) or 800 mg/L of SrCl2·6H2O (marked group) for 5 days and transferred them into normal aerated water for post-immersion culture. We sampled their pectoral, dorsal, ventral, anal, and caudal fin rays. The Sr marks among the fin types were sampled at 0 and 20 days post-immersion and evaluated using an electron probe micro-analyzer (EPMA) for the five-day Sr/Ca ratios, along with line transect and Sr mapping analyses. Results: Sr marking signatures were observed in all fin types in the marked group, with a success rate of up to 100%. Although marking efficiency varied among the different fin ray types, the highest Sr/Ca ratios were most often detected in the dorsal fin. Cross-sectional Sr concentration maps of all fin rays sampled showed high-Sr domains in the marked group; in contrast, the entire cross-sections of the control group displayed low Sr contents, indicating successful marking efficiency. Conclusions: Fin ray Sr marking is a successful method for juvenile M. amblycephala, with the advantages of non-lethality and negligible sampling injuries, facilitating the rapid and effective evaluation of Sr marking in restocking M. amblycephala.

Channel Catfish Ictalurus punctatuswere collected during 2018 and 2019 from the Monongahela River in West Virginia using hoop nets to estimate population dynamics. Length, weight, sex, fecundity, and age data were obtained from collected individuals. Population characteristics (e.g., relative abundance, size structure, age structure, growth, etc.) were modeled under three proposed length limits of 300, 375, and 450 mm. Simulation results indicated that growth overfishing may occur when exploitation rates reach 36% under a 300‐mm minimum length limit. Furthermore, recruitment overfishing began to occur at 40% exploitation under a 300‐mm minimum length limit. Additionally, simulations suggest that no recruitment or growth overfishing occur at minimum length limits of 375 mm or 450 mm until extremely high exploitation levels (>90%) are reached. Thus, future consideration should be given for implementation of a 375‐mm minimum length limit of Channel Catfish in the Monongahela River to prevent growth and recruitment overfishing while also ensuring anglers are still able to harvest Channel Catfish.

The addition of limestone sand directly to streams is an effective method for treating chemical and biological issues associated with acid precipitation, a common concern in many Appalachian watersheds. The unique water chemistry created by limestone remediation potentially creates a “mark” in fish hard parts (e.g., otoliths and fin rays) that can be used to identify fish from remediated habitats, even after fish disperse into the surrounding riverscape. We tested whether elevated concentrations of calcium from a limestone‐treated stream could be identified by microchemistry in the otoliths of Brook Trout Salvelinus fontinalisand whether the concentrations could distinguish fish among treated and untreated habitats within the upper Shavers Fork watershed in West Virginia. Calcium concentrations in water were similar between the treated headwater stream and the control stream. Multivariate ANOVA and Bonferroni post hoc analyses indicated that calcium and strontium concentrations were significantly higher in Brook Trout otoliths from the treatment stream than in those from the control stream. Our results suggest that hard‐part microchemistry is a promising tool for identifying locally produced fish from limestone‐remediated streams in the surrounding riverscape.

In temperate waters, growth and mortality of bony fishes are frequently estimated from age information derived from the examination of annular rings on hard structures (e.g., otoliths). However, determining ages from hard structures can be time consuming, often requires sacrificing fish, and has associated costs for supplies and personnel time in processing or reading structures. Subsampling based on a target number of fish per length bin is commonly used to reduce time and costs but may introduce biases into the estimation of population characteristics. We wanted to understand how interactive effects of bin width, gear selectivity, and length‐at‐age variability influence the estimation of growth parameters, total instantaneous mortality (Z), and age frequency. We developed a simulation model to generate populations under the assumption that growth followed the von Bertalanffy growth model; we then sampled from those populations for age analysis based on no gear selectivity, dome‐shaped selectivity, and logistic selectivity. Furthermore, we wanted to determine whether observed biases could be corrected by using a weighting procedure during growth model fitting. Fifteen subsampling schemes were evaluated, with five different length bin widths and three target subsample sizes for each bin (subsampling levels). Gear selectivity, variability in length at age, and estimation procedures had a greater and more predictable influence on growth parameters than bin widths for size‐based subsampling. Dome‐shaped gear selectivity was associated with biases in growth parameter and Zestimation. Weighted regression based on weighting factors calculated from the original sample's length frequency generally improved the consistency of growth parameter estimates among subsampling schemes but did not always improve accuracy. No bin widths or subsample sizes were clearly superior across modeled scenarios. Consequently, alteration of bin widths seems less useful in reducing biases than using alternative estimation methods for population characteristics of interest and considering other external factors.

The Ozark streams of Missouri provide anglers with unique Smallmouth Bass Micropterus dolomieufishing opportunities. To ensure the sustainability and potential of these fisheries, we sampled five streams in the Ozark highland ecoregion of southern Missouri via recreational angling methods. From our samples, we developed estimates of recruitment, growth, and mortality, and assessed current regulations for Smallmouth Bass. To accomplish these objectives, we aged otoliths from 75 legal (305‐mm) fish on each stream. Back‐calculated length‐at‐age estimates were formed for sublegal lengths, and were paired with electrofishing length distributions on each stream using an age‐length key. These data were used to develop estimates of dynamic rate functions and models of yield, spawning potential, and number of memorable fish for each study population. We found that recruitment was stable on each stream, but growth and mortality varied among streams. We also found that models of yield, spawning potential, and number of memorable fish varied greatly among streams. Our results showed that the current 305‐mm statewide minimum length limit is applicable for some of our study streams, but yield, spawning potential, and trophy potential could increase with more restrictive length limits on some of our study streams. More spatially explicit length limits can help these Smallmouth Bass populations reach their growth potential. This information can help inform stream management in Missouri and across the Ozark region of the Midwest.

Large‐river fishes (e.g., sturgeons [Acipenseridae] and Paddlefish Polyodon spathula) that inhabit reservoir systems are potentially unable to sense environmental cues that elicit typical life history behaviors. These cues can be masked by altered hydrology and temperature regimes. In many reservoirs throughout North America, Paddlefish populations are potentially affected by these unnatural conditions. In an attempt to understand and identify the potential mechanisms that limit Paddlefish reproduction in reservoir systems, we selected Harry S. Truman Reservoir (Truman Lake), Missouri, as our study area of focus. This population is supplemented by stocking, and although anecdotal evidence of potential natural reproduction exists, spawning has never been documented. We implanted ultrasonic transmitters into 113 reproductively mature Paddlefish, and the movements of these fish were tracked over 2 years. Paddlefish migratory behavior was significantly related to water temperature and gauge height, and differences in movement behaviors existed between sexes. Spring aggregations were located in the riverine portion of the Osage River, and embryos and larvae were sampled in 2015 and 2016 near said aggregations. Using acoustic telemetry and egg mats, we acquired evidence suggesting that the Truman Lake Paddlefish are spawning. Our technique can likely be applied to determine spawning locations for Paddlefish inhabiting other large reservoirs.

Paddlefish Polyodon spathulaand three sturgeon species are present in the upper Mississippi River; of these four species, two are commercially and recreationally important (Paddlefish and Shovelnose Sturgeon Scaphirhynchus platorynchus), and two are protected under federal or state endangered species laws (Pallid Sturgeon S. albusand Lake Sturgeon Acipenser fulvescens). Before management strategies can be implemented, quantification of movement patterns is necessary to determine the appropriate spatial scale for management. To increase the available relevant information, we investigated broad‐scale movement patterns of the above species in the upper Mississippi River by using telemetry. All four species were capable of long‐range (>300‐km) movements, and these movements were cued by the changing river stages and water temperature. Ultimately, our data suggest that sturgeon and Paddlefish movement patterns are highly variable, with fish moving freely among rivers (e.g., the Mississippi, Missouri, Illinois, Ohio, and Des Moines rivers) across many political boundaries and encompassing multiple regulatory agencies. This migratory nature can lead to portions of the population being subject to harvest in multiple management units, affecting population dynamics, biology, harvest, and management/recovery in both the natal area and in the harvest areas. To effectively manage or recover these highly mobile fish populations, interjurisdictional collaboration will be necessary.

Recruitment of many fish populations is inherently highly variable interannually. However, this variability can be synchronous at broad geographic scales due to fish dispersal and climatic conditions. Herein, we investigated recruitment synchrony of Silver Carp Hypophthalmichthys molitrixacross the Mississippi River basin. Year‐class strength (YCS) and synchrony of nine populations (maximum linear distance = 806.4 km) were indexed using catch‐curve residuals correlated between sites and related to local and regional climatic conditions. Overall, Silver Carp YCSwas not synchronous among populations, suggesting that local environmental factors are more important determinants of YCSthan large‐scale environmental factors. Variation in Silver Carp YCSwas influenced by river base flow and discharge variability at each site, indicating that extended periods of static local discharge benefit YCS. Furthermore, river discharge and air temperature were correlated and synchronized among sites, but only similarities in river discharge were correlated with Silver Carp population synchrony, indicating that similarities in discharge (i.e., major flood) among sites can positively synchronize Silver Carp YCS. The positive correlation between Silver Carp YCSand river discharge synchrony suggests that regional flood regimes are an important force determining the degree of population synchrony among Mississippi River Silver Carp populations.

Lake of the Ozarks, Harry S. Truman Reservoir, and Table Rock Lake in Missouri contain important recreational fisheries for trophy Paddlefish Polyodon spathula. These three reservoirs were created by damming major rivers. Because of river modifications, Paddlefish natural reproduction is thought to be limited; subsequently, populations have been maintained through supplementation and harvest regulations. However, these fisheries have not been thoroughly assessed, and the applicability of management actions (e.g., supplementation and minimum length limits) has not been fully evaluated. Population simulations indicated that changes in the amount of trophy‐sized Paddlefish and broodstock remaining were similar among the three reservoirs, with larger minimum length limits resulting in a greater proportion of mature and trophy‐sized individuals. However, the number of Paddlefish that could be harvested at Harry S. Truman Reservoir and Lake of the Ozarks was much greater than at Table Rock Lake. These disparities are likely attributable to the amount of supplementation occurring at each reservoir. Based on unmarked fish from each reservoir, the percentage of sampled fish that were considered wild suggested that natural reproduction is occurring in Lake of the Ozarks (51.5%), Harry S. Truman Reservoir (83.9%), and Table Rock Lake (13.7%). Considering the Missouri Department of Conservation's desired management goals for maintaining trophy fisheries, a minimum length limit of at least 864 mm is suggested. If supplementation, natural reproduction, and harvest regulations are inadequate, reductions in Paddlefish abundance, size structure, harvest, and popularity could occur. One motivator for anglers to participate in trophy fisheries is the opportunity to catch a rare, unique, and large fish. Declines in a trophy fishery could cause economic losses to local areas and state agencies; thus, having an adaptive management plan in place to manage trophy fisheries is imperative.

Research In Action--Anecdotal reports suggest barge traffic may increase angler success on rivers, but no scientific studies had been done to verify this phenomenon. The Missouri Department of Conservation evaluated [...]

Management of migratory fishes is a difficult task for fishery managers because fish cross jurisdictional boundaries and encounter differing regulations. States within the Mississippi River basin have differing commercial and recreational regulations for riverine Paddlefish Polyodon spathulapopulations, and the current population dynamics have not been evaluated on a system-wide basis. The objective of this study was to simulate the current reproductive potential of the population using various harvest scenarios. At the current exploitation rate of all locations pooled (u = 14.8%), the population may experience recruitment overfishing at a 610 mm minimum length limit and has the potential to experience recruitment overfishing at a 710 mm length limit (u = ~20%). Any added stressors (e.g., Asian carp) may cause further mortality; thus, adopting a precautionary approach is necessary to maintain sustainable Paddlefish fisheries. At an 810 mm length limit, the population would not realistically experience recruitment overfishing. Implementing a basin-wide minimum length limit of at least 810 mm on riverine Paddlefish fisheries is suggested. Given the migratory nature of Paddlefish, developing a form of governance to ensure management strategies are complementary, and a sustainable source of funding is available is imperative to ensure sustainability. To accomplish this, developing a Mississippi River Basin Interstate Fishery Commission may be beneficial. El manejo de peces migratorios es un reto importante para los administradores de recursos ya que los peces cruzan fronteras jurisdiccionales y se exponen a diferentes regímenes de regulación. Los estados que comparten la cuenca del Río Mississippi, poseen diferentes esquemas de regulaciones recreativas y comerciales para el manejo de las poblaciones del pez espátula, Polyodon spathula, y aun no se ha evaluado la dinámica poblacional vigente a escala de cuenca. El objetivo de este estudio fue simular el potencial reproductivo actual de la población bajo distintos escenarios de captura. Aplicando la tasa de explotación vigente a todas las localidades muestreadas (u = 14.8%), la población pudiera experimentar una sobrepesca en el reclutamiento, usando una talla mínima de captura de 610 mm, y existe el potencial de que ocurra sobrepesca en el reclutamiento incluso a una talla mínima de captura de 710 mm (u = ~20%). Cualquier factor adicional que genere estrés (e.g. la carpa asiática) puede causar una mayor mortalidad; por consiguiente es necesario adoptar un enfoque precautorio con el fin de mantener sana la pesquería del pez espátula. En términos reales, una talla límite de 810 mm sería suficiente como para evitar una sobrepesca en el reclutamiento. De aquí se recomienda implementar en la pesquería del pez espátula, una talla mínima de captura de por lo menos 810 mm en toda la cuenca. En virtud de la naturaleza migratoria del pez espátula, es necesario desarrollar un plan de manejo a nivel cuenca para asegurar la sustentabilidad del recurso. Para lograr esto, pudiera ser útil desarrollar un Comisión de Pesca Interestatal de la cuenca del Río Mississippi. La gestion des poissons migratoires constitue une tâche complexe pour les gestionnaires de pêcheries, car le poisson traverse les frontières juridictionnelles et est donc soumis à différentes règlementations. Les états qui bordent le bassin du fleuve Mississippi appliquent différentes règlementations en matière de pêche commerciale et récréative pour les populations de poissons spatulaire (Polyodon spathula), et les dynamiques de populations actuelles n'ont pas été évaluées sur tout le système. L'objectif de cette étude consistait à simuler le potentiel de reproduction actuel des populations en appliquant différents scénarios de pêches. Au rythme d'exploitation actuel de tous les sites sondés (u = 14.8 %), la population peut s'attendre à une surpêche des recrues à une limite de longueur de 610 mm minimum et a le potentiel pour subir une surpêche des recrues à une limite de longueur de 710 mm (u = ~20 %). Tout facteur de pression supplémentaire (comme la carpe asiatique) peut entraîner une mortalité supérieure; il est donc nécessaire d'adopter une approche précautionneuse pour maintenir des pêcheries de paddlefish (poisson spatule) durables. A une longueur limite de 810 mm, la population pourrait ne pas subir de surpêche des recrues. L'application d'une limite de longueur d'au moins 810 mm sur l'ensemble du bassin sur les pêcheries de paddlefish fluvial est suggérée. En raison de la nature migratoire du paddlefish, il est impératif de mettre en œuvre un plan de gestion sur tout le bassin, et d'unifier les stratégies de gestion de l'espèce, pour en assurer la durabilité. Pour cela, il est conseillé de mettre en place une Commission inter-état du bassin du fleuve Mississippi.

Natural resource professionals have frequently criticized universities for poorly preparing graduates to succeed in their jobs. We surveyed members of the American Fisheries Society to determine which job skills and knowledge of academic topics employers, students, and university faculty members deemed most important to early-career success of fisheries professionals. Respondents also rated proficiency of recently hired, entry-level professionals (employers) on how well their programs prepared them for career success (students and faculty) in those same job skills and academic topics. Critical thinking and written and oral communication skills topped the list of important skills and academic topics. Employers perceived recent entry-level hires to be less well-prepared to succeed in their careers than either university faculty or students. Entry-level hires with post-graduate degrees rated higher in proficiency for highly important skills and knowledge than those with bachelor's degrees. We conclude that although universities have the primary responsibility for developing critical thinking and basic communication skills of students, employers have equal or greater responsibility for enhancing skills of employees in teamwork, field techniques, and communicating with stakeholders. The American Fisheries Society can significantly contribute to the preparation of young fisheries professionals by providing opportunities for continuing education and networking with peers at professional conferences.

More Field Science--Black crappies often have a protracted spawning window and may spawn over several weeks. Spawning usually begins when spring temperatures reach 55°F to 60°F. Fish in Florida may [...]

Mortality is a key parameter in understanding the dynamics of any fish population. We examined three methods to evaluate Shovelnose Sturgeon Scaphirhynchus platorynchusmortality (e.g., ratio of first year recruits to all recruits [Heincke's method], a linearized weighted catch curve, and an open system mark–recapture mortality approach). The Mississippi River was sampled in two distinct but connected geomorphic sections: upper Mississippi River (UMR; river kilometer 323–587) and the middle Mississippi River (MMR; river kilometer 0–322). All analyses were pooled across these areas due to potential emigration or immigration throughout both study reaches. Heincke's method estimated annual mortality at 16.9% for the full range of ages (9–23 years) with generally increasing estimates with decreasing age ranges considered (10–23, 11–23, 12–23, and so on). A linearized weighted catch curve that considered increasing estimates of mortality for the shorter age ranges generated an annual mortality estimate of 29.0%.d Four mark–recapture models were considered using the program MARK. The model with the greatest support was the model that provided estimates of annual mortality for each year and a single recapture probability. The annual mortality estimates from this model varied from 2.7% to 70.7% after correcting for tag loss. The best fit model with a single estimate of annual mortality was the one that estimated annual recapture probabilities for each year and had a mortality estimate of 34.6% (after correcting for tag loss, but not for immigration, emigration, or sampling effort). The three methods provided varying results, and our data indicated that a single method to estimate Shovlenose Sturgeon mortality rate may not be appropriate. As such, biologists must recognize that disparities in Shovelnose Sturgeon mortality rates may exist using various methods and should use caution when choosing which method will be employed to estimate sturgeon mortality. Received August 1, 2012; accepted May 16, 2013

To combat the potential deleterious effects that Silver Carp Hypophthalmichthys molitrixhave on native populations, management of this species is essential. Before developing population-level models, a determination of which aging structure for estimating the age of Silver Carp is needed. To our knowledge, no consensus has been reached on which structure should be used for estimating Silver Carp ages. We collected 120 Silver Carp from the Illinois, Mississippi, Missouri, and Ohio rivers via electrofishing to evaluate aging structures. Removal time, processing time, and discernible annuli were evaluated for scales, opercles, vertebrae, pectoral fin rays, postcleithra, and asterisci and lapilli otoliths. Asteriscus otolith, opercle and scale annuli were difficult to discern and not evaluated further. Total processing times for postcleithra (246.1 s) and lapilli (251.2 s) were the most time-efficient; pectoral fin rays and vertebrae were more time intensive. Between-reader precision and agreement rates resulted in lapilli being the most precise, followed by postcleithra, pectoral fin rays, and vertebrae. Comparisons of structures with lapilli revealed that pectoral fin rays exhibited 78% agreement, 49% agreement with postcleithra, and 53% agreement for vertebrae. In terms of agreement ±1 year to lapilli, pectoral fin ray, postcleithrum, and vertebra resulted in high agreement (>85%). Age bias plots revealed that these discrepancies consistently underestimated ages compared with lapilli. Discrepancies may be attributed to erosion of the central lumen of fin rays and postcleithra, while locating the first annulus on vertebrae may have led to this disparity. Based on previous studies, evaluation of overall processing times, assessment of between-reader precision, between-reader agreement rates, and bias that may be involved with alternative structures, we recommend lapilli otoliths be used for estimating age of Silver Carp. Future efforts should focus on validating accuracy of lapilli for estimating Silver Carp ages. Received March 1, 2013; accepted June 5, 2013

Asian carp (Cyprinidae) are among the most invasive fishes in North America, but assessment tools for evaluating stock structure have not been established. Thus, we used data from national and international published reports or manuscripts to develop standard length categories for four species of Asian carp. Due to the similarities in maximum reported size for Bighead Carp Hypophthalmichthys nobilisand Grass Carp Ctenopharyngodon idella, we propose the following standardized length categories for those two species: stock = 30 cm, quality = 54 cm, preferred = 68 cm, memorable = 89 cm, and trophy = 111 cm. Proposed Black Carp Mylopharyngodon piceuslength categories are stock = 40 cm, quality = 72 cm, preferred = 90 cm, memorable = 118 cm, and trophy = 148 cm. Finally, we propose the following length categories for Silver Carp H. molitrix: stock = 25 cm, quality = 45 cm, preferred = 56 cm, memorable = 74 cm, and trophy = 93 cm. We then used existing data collected in the Illinois River and Mississippi River from 2003 to 2011 to evaluate Silver Carp proportional size distribution (PSD). Incremental PSD provided a temporal index of Silver Carp size structure in the Illinois River and strong cohorts could be followed through the incremental PSD values over time. Traditional PSD provided a quantifiable, comparative index of Silver Carp size structure among two locations in the Mississippi River and one location in the Illinois River. We believe this index provides an additional tool for fisheries managers to evaluate size structure of Asian carp and help assess overall population status. Received September 19, 2012; accepted December 12, 2012

The main stems of large rivers throughout the world have been highly modified with little consideration for effects on fishes that rely on these areas to complete their life histories. Particularly important is the ability of riverine habitats to provide foraging opportunities for young fish. We explored how temperature, flow, and food availability influenced diet content, prey selection (Strauss's linear selectivity index), and energy condition of age-0 shovelnose sturgeon Scaphirhynchus platorynchusand pallid sturgeon S. albusin major habitat areas (e.g., islands, channel borders, wing dikes, and side channels) of the middle Mississippi River during spring (March–May) and summer (June–August) 2008. Standardized diet mass (dry mass standardized for fish body mass) of the age-0 sturgeon peaked at about 19°C and at a flow velocity of 0.5 m/s. Although potential prey taxa were diverse, the diets for age-0 sturgeon of all sizes were dominated by mayflies (Ephemeroptera) and midge larvae (Chironomidae) across all habitats. As age-0 sturgeon grew, the relative energy return per habitat appeared to diverge; island tips upstream of the main channel and channel border areas behind wing dikes provided higher gains in standardized diet mass than other habitats. No differences in energy condition (kJ/g) occurred among habitats, although large (51–200 mm total length [TL]) age-0 sturgeon had higher energy densities than their small (=50 mm TL) counterparts. Enhancement of areas with flow and substrates that facilitate the production and availability of midges and mayflies (e.g., instream island complexes) is critical for the recruitment of age-0 Scaphirhynchussturgeon in large rivers. Received August 2, 2011; accepted October 6, 2011

The pallid sturgeon Scaphirhynchus albusis a U.S. federally endangered species that occurs in the 320-km middle Mississippi River (MMR). Historic in-channel island habitat has vanished, and the extent of the population's range within the MMR is unknown. We surgically implanted ultrasonic transmitters in 88 adult pallid sturgeon (>600 mm fork length; mean = 791 mm) during 2002–2005 and used boat-mounted hydrophones to quantify their seasonal use of major MMR habitat features (wing dikes, side channels, island side channel tips, tributaries, and main channel; total of 8,629 river kilometers monitored). Distance from habitat features (gravel bars, wing dikes, and island side channels) was quantified during spring, a period considered to be critical for many fish species. We quantified maximum seasonal movement of each fish in the entire MMR with stationary data-logging hydrophones during 2004–2006. Combining data across years and seasons, we found that pallid sturgeon selected the tips of wing dikes over other habitat features. However, during spring pallid sturgeon moved from the tips of wing dikes to within about 100 m of known gravel bars. Maximum distance moved by pallid sturgeon varied the most in spring relative to other seasons. One pallid sturgeon moved through the entire study reach, and a few individuals left the MMR for the Missouri River or the lower Mississippi River. Unique flow and substrate characteristics of wing dikes probably emulated missing habitat complexity (i.e., in-channel islands, deep scour holes, and sand bars). Other habitats such as gravel bars may be important during spring, although their contributions to reproduction, foraging, and survival of pallid sturgeon are unknown. The range of this pallid sturgeon population extends beyond the entire stretch of the MMR into other river basins; thus, the population requires rangewide management.

Mark–recapture studies require knowledge of tag retention rates specific to the tag types, fish species and size, and study duration. We determined the probability of tag loss for passive integrated transponder (PIT) tags implanted into dorsal musculature, T-bar anchor tags attached to dorsal pterygiophores, and both tags in relation to years posttagging for double-marked adult muskellunge Esox masquinongyover a 10-year period. We also used PIT tags as a benchmark to assess the interactive effects of fish length at tagging, sex, and years posttagging on T-bar anchor tag loss rates. Only five instances of PIT tag loss were identified; the calculated probability of a fish's losing its PIT tag was consistently less than 1.0% for up to 10 years posttagging. The probability of T-bar anchor tag loss by muskellunge was related to both the number of years posttagging and the total length (TL) of the fish at tagging. The T-bar anchor tag loss rate 1 year after tagging was 6.5%. Individuals of less than 750 mm TL at tagging had anchor tag loss rates less than 10% for up to 6 years after tagging. However, the proportion of fish losing T-bar anchor tags steadily increased with increasing years posttagging (~30% after 6 years) for larger muskellunge. Fish gender did not influence the probability of T-bar anchor tag loss. Our results indicate that T-bar anchor tags are best suited for short-term applications (=1 year) involving adult muskellunge. We recommend use of PIT tags for longer-term tagging studies, particularly for muskellunge larger than 750 mm TL. Received November 19, 2010; accepted March 28, 2011

Habitat use by wild age-0 shovelnose sturgeon Scaphirhynchus platorynchusand pallid sturgeon S. albuswas quantified by trawling macrohabitats (i.e., main channel, main-channel border, island, and artificial structures [e.g., wing dams]) in the middle Mississippi River during 1998–2007 (1,702 trawls; n= 1,507 age-0 sturgeon captured). Age-0 sturgeon catch rates were highest around artificial structures and island areas, while main-channel habitat provided the lowest catch rates. Moreover, size-selective macrohabitat analyses indicated that small age-0 sturgeon (i.e., majority < 50 mm total length) were located in channel-border dike and island side-channel macrohabitats, while all other macrohabitats were occupied by small and large age-0 sturgeon. Furthermore, our analyses indicated that age-0 sturgeon mesohabitat use within macrohabitats was influenced by depth, substrate, and bottom velocity. Low velocity (i.e., ~0.1 m/s), moderate depths (i.e., 2–5 m), and sand substrate were positively related to age-0 sturgeon relative abundance. As such, instream habitat modifications that provide the correct combination of macrohabitats with suitable mesohabitats may hold high densities of age-0 shovelnose sturgeon and pallid sturgeon and may improve recruitment success.

Several studies have investigated the demographics of shovelnose sturgeon Scaphirhynchus platorynchusand pallid sturgeon S. albusin the Mississippi River through assessment of adult populations; however, comparatively few studies have examined the early life history of these species. Here, we describe a comprehensive 4-year study that examined the effects of water temperature and river stage on the mortality, abundance, hatch timing, and growth rates of age-0 Scaphirhynchusspp. sturgeon in the middle Mississippi River. We trawled island areas every 7–10 d from April to August 2004–2007. We captured 1,256 individuals ranging from 10 to 193 mm total length over the 4-year study. Mean age-0 sturgeon growth rates ranged from 1.42 to 1.50 mm/d over the 4 years; however, growth rates did not differ among years. Individuals hatched over a 25–65-d period, and peak hatch dates were between 10 and 20 May in all years. Moreover, hatch timing possibly coincided with optimum spawning temperatures of 17–20°C and an increase in river stage. Abundance appeared to be regulated by river stage; longer durations of high water were related to higher relative abundance. Furthermore, mortality increased with the number of days on which water temperature exceeded 28°C. Based on these data, management strategies may need to ensure sturgeon hatching success and subsequent survival through optimizing hydrologic and thermal regimes that occur during the early life stage.

Sagittal otoliths and the articulating process of the pectoral spine have both been validated as accurate techniques for estimating the age of channel catfish Ictalurus punctatus(=age 4). However, there is limited information on the relative precision of estimates from these two structures. Thus, we analyzed the precision of age estimates derived from otoliths and the articulating process of the pectoral spine and compared the dynamic processes (recruitment, growth, and mortality) resulting from those estimates. Aging structures were removed from 110 channel catfish captured from the Wabash River (river kilometers 550–9.6) via day–time electrofishing. The age estimation methodologies were similar to those described in previous studies. Agreement between the ages derived from the two structures was high; the average percent error was 8.4%, the coefficient of variation was 11.4, and the slope of the age bias plots did not differ from 1, indicating similar age assignments between structures. The corresponding recruitment patterns, von Bertalanffy growth models, and mortality rates did not differ between the aging structures. We conclude that the articulating process of the pectoral spine provides age assignments similar to those of otoliths and that the dynamic processes do not differ between structures. Further, based on the results of this study, the articulating process of the pectoral spine provides a suitable alternative to otoliths and has the advantage that channel catfish do not have to be sacrificed.

We evaluated the efficacy of three gears commonly used to sample shovelnose sturgeon Scaphirhynchus platorynchus, pallid sturgeon S. albus, and lake sturgeon Acipenser fulvescensin large rivers. We stratified habitats and randomly sampled sites with trawls, gill nets, and trotlines in the middle Mississippi River from June 2003 through May 2005 (N= 3,476 samples). A total of 3,523 shovelnose sturgeon, 31 pallid sturgeon, and 13 lake sturgeon were captured. When sample sizes were adequate (based on power analysis), we used a mixed analysis of variance (ANOVA) procedure to determine the relative impact of season and gear type on sturgeon catch per unit effort (CPUE). Kolmogorov–Smirnov tests were used to determine whether the length frequency distributions for each species differed among gears. Overall, the power analyses indicated that there were adequate sample sizes for comparing standardized CPUE for shovelnose sturgeon among seasons; however, too few pallid or lake sturgeon were collected to make statistical comparisons. Shovelnose sturgeon catch rates varied among gears and seasons; season and gear type interacted in the ANOVA model. Among gear types, 5.08-cm gill nets produced the highest standardized CPUE, and catch rates were highest during spring. The length frequency distributions of shovelnose sturgeon depended on gear type. Shovelnose sturgeon can be sampled in large rivers using stratified random sampling with this combination of gear. However, pallid sturgeon and lake sturgeon may be too rare to sample with this approach.

Shovelnose sturgeon Scaphirhynchus platorynchusin the middle Mississippi River provide one of the last commercially viable sturgeon fisheries in the world, yet their maturation and reproduction have not been linked. During 2005 and 2006, we sampled adult and age-0 shovelnose sturgeon to link age at maturation, the timing and periodicity of spawning, age-0 sturgeon production, and the resulting age-0 growth rates. Age at maturity was later than previous estimates, the minimum age of first maturation being 8 years for males and 9 years for females. Total egg count was slightly lower than previously reported (mean = 29,573 per female; SE = 2,472). Males and females typically spawned every 2 and 3 years, respectively. Peaks in mature fish coincided with rising river stages and water temperatures at which shovelnose sturgeon probably spawn. Peaks in spent adults followed. Age-0 shovelnose sturgeon occurred during June and July 2005 and May and June 2006, confirming successful spawning. Age-0 sturgeon grew between 0.69 and 1.69 mm total length/d; four distinct weekly cohorts occurred each year. During fall 2006, females contained ripe eggs, males were milting, and a single age-0 sturgeon (total length = 55 mm) was captured, suggesting that shovelnose sturgeon spawn during fall as well as spring. Management must consider the protracted nature of spawning within seasons as well as differences in spawning activity between seasons.

Ten nest colonies of black crappie Pomoxis nigromaculatus were visually located and verified by angling in Campus Lake, a small urban impoundment in southern Illinois. Habitat characteristics were measured at these nest sites and compared to habitat measurements obtained from 45 unused sites. Seven habitat characteristics (substrate firmness, temperature, dissolved oxygen, distance to deep water [3.8-m depth contour], substrate type, vegetation height, and vegetation density) were significantly different between nest sites and unused sites. Although temperature and dissolved oxygen were significantly different between nest sites and unused sites, all values were within the suitable range for black crappie spawning to occur. Black crappies selected nest sites close to deep water with firm substrates and low vegetation height and density. Our results present insight on habitat characteristics of black crappie spawning locations in a small urban impoundment. Interestingly, we located several black crappie nesting colonies with more than 10 individual nests in close proximity to one another; colonial nesting by black crappies has not previously been reported in the literature. Furthermore, we suggest that degree of shoreline modification and other anthropogenic influences in and adjacent to Campus Lake did not affect black crappie nest site selection. Black crappie nest sites in Campus Lake were always located near deep water (3.8 m), in low-density, short vegetation, and on firm clay or sand substrate; because nest site selection can influence earlylife survival and recruitment of black crappie, the availability of these habitat characteristics may regulate black crappie population demographics in Campus Lake. Efforts to limit sediment inputs will be important for maintaining suitable black crappie spawning habitat in Campus Lake and other small impoundments.

Climatic variation and dispersal are two primary factors thought to induce recruitment synchrony in fish populations. We hypothesized that climate factors correlated across a broad geographical scale (i.e., the Moran effect) would induce synchrony in recruitment for common carp Cyprinus carpioamong 18 glacial lakes across a 175-km2area in eastern South Dakota. Cross-correlation analysis indicated that common carp population fluctuations were highly synchronous among lakes. To evaluate the influence of the Moran effect on recruitment, we examined several candidate models using an information-theoretic approach. The model with the most support included the interaction of temperature, precipitation, and wind during the open-water period. This model indicated that the effects of any one of these climate variables on recruitment strength depended on the level of each of the other variables in any given year. Our results suggest that common carp populations in the Midwestern United States exhibit synchronous recruitment across regionwide geographic areas as a result of climatic variability.

Various gear types have been used to sample populations of channel catfish Ictalurus punctatus in lotic systems. However, these gears produce different population characteristics (i.e., recruitment, growth, and mortality). We compared the population demographics of channel catfish in the Wabash River, Indiana, sampled with baited 25- and 32-mm-bar mesh hoop nets and three-phase alternating current (AC) electrofishing. Based on catch per unit effort, the relative abundance of channel catfish sampled with 32-mm hoop nets was lower than that of fish sampled with 25-mm hoop nets and AC electrofishing. Each gear type also resulted in a different length frequency, mean length increasing progressively in sampling with 25-mm hoop nets, 32-mm hoop nets, and AC electrofishing. Similarly, age-frequency distributions differed among gears. The 25-mm hoop nets biased the age structure toward younger individuals (mean age = 2.5), whereas both 32-mm hoop nets (mean age = 4.0) and AC electrofishing (mean age = 5.8) included older fish. Catch-curve analysis generated different mortality rates for the three gear types, the mortality rate being highest (50%) in fish sampled with 25-mm hoop nets. Gear-specific size and age structures led to differences in von Bertalanffy statistics among the 25-mm hoop nets and AC electrofishing, while the results for 32-mm hoop nets were uninterpretable. Because the different gears led to conflicting parameter estimates, management practices based on sampling with single gears may be contradictory. Given the differences in gear selectivity, biologists need to approach management cautiously until calibration to the true size and age structure is conducted.

Mean stomach fullness provides a useful index for quantifying fish diets. However, estimating stomach fullness for planktivorous fishes can be time-consuming and prone to error because of small prey and unidentifiable remains. In this study we developed a predictive equation for estimating the stomach volume of yellow perch Perca flavescens as a function of total length (TL). We then used an optical plankton counter (OPC) to estimate the biovolume of invertebrate prey consumed. The OPC quickly estimated the digital size and abundance of zooplankton prey, which can then be converted to estimates of prey biovolume. Stomach volume (V (mm3)) for yellow perch (113–279 mm TL) was significantly related to body size (L (mm)) and was estimated as V = 3 × 10-7· L2.96. Using the OPC, yellow perch stomach contents (99% Daphnia pulex) were converted to prey biovolume (mm3) and then divided by stomach volume (mm3) to estimate stomach fullness (%). This approach provided reasonable estimates of stomach fullness ranging from 3% to 85% (mean = 21%). Although the initial cost for the OPC equipment is relatively high, this method provided substantial time and labor savings compared with traditional approaches for quantifying zooplankton abundance and biomass (e.g., microscopic identification and enumeration and length–mass conversions). Similarly, the OPC can be used to estimate the abundance and biomass of freshwater zooplankton, thus reducing the time and costs associated with traditional plankton analyses. The approach is limited, however, in cases where very small prey (<250 µm) are a dominant proportion of the sample because of the potential errors involved in detecting and estimating the biovolumes of small particles.

Otoliths (asteriscus) have been validated as an accurate structure for estimating age of common carp Cyprinus carpio. However, extraction and processing of common carp otoliths are time consuming and require sacrifice of fish. Therefore, we analyzed age estimation precision of four alternative structures relative to otolith age for 139 common carp collected from five eastern South Dakota lakes. All common carp were collected using daytime electrofishing. Each fish was assigned an identification number and measured to the nearest millimeter total length, after which aging structures were removed. Age was estimated from scales, vertebrae, opercles, pectoral fin rays, and asteriscus otoliths by methods similar to those recommended by previous researchers. Relative to otolith age, average percent error was 6.8% for scales, 15.4% for vertebrae, 9.9% for opercles, and 1.2% for pectoral fin rays. Compared with all other structures, ages from pectoral fin ray sections were nearly as precise as otoliths through age 13 (lowest average percent error); however, fin rays consistently underestimated the ages of fish older than 13 years. In most cases, pectoral fin ray ages matched otolith ages, thereby providing similar age estimates. We conclude that pectoral fin rays provide a precise, economical, and nonlethal alternative for estimating common carp age structure. Accuracy of common carp ages estimated from pectoral fin rays still requires evaluation.

The invasion of non-native fishes has caused a great detriment to many of our native fishes. Since the introduction of invasive carps, such as Silver, Bighead, Common and Grass Carp, managers and researcher have been struggling to remove these species while also hypothesizing the detriment of further invasion. This study developed a food web model of four locations on the Mississippi River and used those models to assess the impacts of two scenarios: carp removal and carp invasion. In the Middle Mississippi River where these invasive carps are already present, the models found that it would take a sustained exploitation of up to 30% of initial biomass over an extended period to remove Grass Carp and up to 90% removal of initial biomass to remove Silver and Bighead Carp. In the locations where Silver, Bighead, and Grass Carp are not yet established (i.e., Pools 4,8, and 13) the invasion of these species could cause declines from 10 to 30% in initial biomass of native fishes as well as already established nonnative invasive species.