Gizzard Shad Dorosoma Cepedianum Research Articles

Influence of invasive bigheaded carps on abundance of Gizzard Shad in the Tennessee River

AbstractObjectiveThe Tennessee River basin and its cascade of reservoirs are home to some of the most diverse freshwater fish assemblages in the world. This unique system is threatened by the ongoing invasion of Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis, hereafter referred to together as “bigheaded carps.” Bigheaded carps may directly compete for food resources with native clupeid species such as Gizzard Shad Dorosoma cepedianum, and this potential interaction could have damaging ecological and economic consequences. High relative abundances of Gizzard Shad are crucial to the Tennessee River food web and associated fisheries because of their role as a forage base for piscivorous species.MethodsWe analyzed a collection of annual gillnetting and electrofishing data spanning from 1990 to 2017 to test whether Gizzard Shad relative abundances have changed in Tennessee River reservoirs since the arrival of bigheaded carps.ResultOur analyses indicated that Gizzard Shad abundances have been declining but were already declining prior to the arrival of bigheaded carps in the Tennessee River.ConclusionAt this stage in the invasion, we could not attribute a cause‐and‐effect relationship to the inverse correlation between Gizzard Shad and bigheaded carps, but we advise continued monitoring of indicators of harmful interactions.

Long‐term patterns of fish community structure and decline in native species in a Colorado River reservoir, Arizona and Nevada

AbstractObjectiveThe Colorado River has undergone substantial anthropogenic modifications, and a suite of nonnative species have been introduced since the 1800s; consequently, native fish communities are severely imperiled. We examined temporal patterns in fish community structure in Lake Mohave (i.e., lower Colorado River basin) over 40 years from 1980 to 2020.MethodsWe examined long‐term abundance and richness trends and the trajectory of fish community structure in multivariate space to assess stability and turnover using results from biannual (spring and autumn) trammel‐net monitoring over 40 years from 1980 to 2020.ResultNonnative fishes were established prior to sampling, precluding the ability to determine historical fish community structure. Bonytail Gila elegans and Razorback Sucker Xyrauchen texanus were the only two remaining native fishes, and both declined precipitously in abundance through time. However, a repatriation program initiated in 1991 prevented Razorback Sucker from extirpation, while reintroduction efforts for Bonytail have failed. Both wild populations are gone. Total catch per unit effort showed a negative relationship from 1980 to 2020, whereas total species richness showed no relationship. Long‐term abundance trends at the species level indicated three nonnative species (i.e., Gizzard Shad Dorosoma cepedianum, Yellow Bullhead Ameiurus natalis, and Smallmouth Bass Micropterus dolomieu) increased, nine decreased, and three showed no relationship. Fish community composition exhibited low stability and moderate turnover and shifted directionally through time in multivariate space, with the formation of three clusters, possibly indicating alternative states.ConclusionThe contemporary fish community shows little resemblance to the endemic ichthyofauna that has historically occupied the Colorado River, and the Razorback Sucker is the only remaining native species due to recovery efforts. Continued adaptive management will be required to preserve the most genetically diverse Razorback Sucker population in the Colorado River system, especially while coexisting with an unstable nonnative fish community.

Influence of Electrofishing Boat Operation and Driving Techniques on Reservoir Fish Catches

We compared three methods of boat driving and pedal operation using 600‐s transects: these were the parallel continuous (PC), parallel intermittent (PI), and arc‐intermittent (AI) methods for surveying warmwater fishes in reservoirs. We tested differences in total time and distance per transect, CPUE (fish/h, fish/m), and length frequencies of captured fish among methods. The PC method took the least amount of time, while the AI method took the least amount of distance to complete a transect. The AI method provided slightly higher CPUE (fish/h, fish/m) for Bluegill Lepomis macrochirus and Yellow Bass Morone mississippiensis and higher CPUE (fish/m) for Common Carp Cyprinus carpio, Green Sunfish L. cyanellus, and Largemouth Bass Micropterus salmoides. Each method caught similar size ranges of fish; however, there were slight differences in proportions of sizes for Gizzard Shad Dorosoma cepedianum, Largemouth Bass, and Bluegill. Overall, the AI method performed slightly better for a few species; however, difference in the methods were minor. Any technique should work well for monitoring reservoir fish populations when fish/h is the effort metric.

Can spatial and temporal differences in fish assemblage structure inform conservation of an endangered sucker in a large western reservoir?

AbstractObjectiveConversion of lotic to lentic habitat after river impoundment can lead to habitat loss and threats from introduced species to native aquatic organisms. Some native species can persist in reservoirs despite these alterations. Some of the largest reservoirs in North America were constructed in the Colorado River basin and are used by endangered Razorback Sucker Xyrauchen texanus. This species successfully spawns in several reservoirs and recruits to adulthood in Lake Mead, whereas recruitment in other reservoirs and altered river habitats is limited or nonexistent. Hypothesized mechanisms for the general lack of recruitment include flow and habitat alteration as well as competition and predation from nonnative fishes.MethodsWe analyzed 16 years of netting data from Lake Mead to assess spatial and temporal patterns in fish assemblage structure and the size structure of Razorback Sucker across four sites.ResultThere was a substantial shift in assemblage structure across all sites after the establishment of Gizzard Shad Dorosoma cepedianum in 2010–2011 and an apparent decline in Threadfin Shad D. petenense. Captures of juvenile Razorback Sucker (<450 mm total length in Lake Mead) were higher at sites where overall fish abundance was also higher, suggesting that all fishes might be responding to similar spatial and temporal environmental variation. We identified differences in Razorback Sucker size structure that varied over time and among sites, largely driven by the presence of juvenile Razorback Sucker at some sites in some years.ConclusionRazorback Sucker was among the top‐10 most abundant species at all sites sampled, but assemblages were dominated by abundant nonnative fishes. Razorback Sucker continue to recruit in Lake Mead in the face of abundant and diverse nonnative fishes, but the adult population size remains relatively small (<1000). Further investigation of limiting factors will be necessary to understand which actions might be successful at improving recruitment conditions.

Effects of Ethanol Preservation on Larval and Fingerling Walleye and Gizzard Shad Body Size

Characterizing larval fish dynamics helps identify factors contributing to poor or strong recruitment events and informs stocking practices. Growth is fundamental to fish ontogeny and survival, especially during critical early life stages, which can depend heavily on access to prey. However, obtaining accurate body size measurements of larval fish in the field can be challenging and often means samples must be preserved for later analysis. Importantly, this process can affect fish size. Here, we examined the effects of preservation in 95% ethanol on the total lengths (mm) and wet weights (mg) of larval and fingerling Walleye Sander vitreus and Gizzard Shad Dorosoma cepedianum collected from the field using pushed ichthyoplankton nets. We also estimated the time required for preservation effects to stabilize. Responses to preservation were similar between species, with consistent decreases in wet weights of ~40–70% depending on fish size, which took ~2 months to stabilize. Conversely, the response of total length was variable in direction, with lengths increasing or decreasing up to 5–10%. As a result, the average effect of preservation on total length was minimal (<2.5% decreases). Walleye and Gizzard Shad body size play an important role in understanding their dynamics early in life, and the effects of preservation should be considered to accurately and precisely characterize size metrics.

Consumption of Non-Native Bigheaded Carps by Native Blue Catfish in an Impounded Bay of the Upper Mississippi River

Adult bigheaded carps Hypophthalmichthys spp. have never been observed in the diets of native fishes in the Mississippi River Basin. In addition, blue catfish Ictalurus furcatus diet preference and foraging behavior have never been studied in the presence of non-native bigheaded carps in the Mississippi River system. We examined the gut contents of adult blue catfish (567–1020 mm, n = 65), captured from a Mississippi River backwater using trammel nets. All items in diets were separated and enumerated, and all fish-like diet items were genetically identified to confirm species-level ID. Bigheaded carp ages were determined by sectioning hard structures (pectoral spines, post-cleithra, and vertebrae). Adult silver carp Hypophthalmichthys molitrix (age 3–5, mean = 3.9 years, SE = 0.2; n = 21) had the highest frequency of occurrence (70%) and constituted the greatest percentage by number (58%) and weight (60%) in/of blue catfish diets. Gizzard shad Dorosoma cepedianum ranked second by all three measures (34%, 25%, and 26%). Finally, 50% to 100% of probable age-based sizes of silver carp exceeded gape measurements of blue catfish, suggesting scavenging was the dominant means of predation. More intensive sampling efforts are required to determine the system-wide importance of bigheaded carp in blue catfish diets.

Differences in Population Characteristics and Modeled Response to Harvest Regulations in Reestablished Appalachian Walleye Populations

AbstractHistorically, the Monongahela, Tygart, and Cheat River watersheds in West Virginia were impaired by acidification from acid mine drainage and Walleye Sander vitreus were extirpated from these watersheds by the 1940s. Walleye were reestablished after water quality improvements following passage of environmental legislation and subsequent reintroduction efforts. We compared population characteristics, with emphasis on growth, of Walleye and used modeling to predict the potential effects of harvest regulations in the Monongahela River and two main‐stem reservoirs in the Cheat River and Tygart River watersheds. Statistical comparisons of von Bertalanffy growth curves and relative growth indices indicated that Walleye growth significantly differed across all water bodies. Relative growth index results suggested that Walleye growth was above average in Cheat Lake, average in the Monongahela River, and below average in Tygart Lake relative to other North American populations. Growth was negatively correlated with Walleye relative abundance and positively correlated with estimates of productivity (total phosphorus, chlorophyll a). Walleye diets significantly differed across all water bodies, with diets dominated by Yellow Perch Perca flavescens and Gizzard Shad Dorosoma cepedianum in Cheat Lake, where growth was fastest. Population modeling suggested that effects of exploitation on yield, spawning potential, and size structure were similar under regulations of no length limit and a minimum length limit (381 mm). Models suggested that removing length limits in Tygart Lake could increase angler harvest opportunities and pose minimal threat to the fishery. Models suggested that a protected slot limit could provide increased protection to the spawning potential of Cheat Lake and the Monongahela River populations. Additionally, models predicted that a protected slot limit could increase the number of large (&gt;630‐mm) Walleye in these waters. Our findings demonstrate the different characteristics that Walleye populations can develop after reestablishment based on abiotic and biotic conditions and the need for watershed‐specific management.

Modeled Walleye Regulation Outcomes in a Midwestern Reservoir with Varying Forage and Walleye Density

AbstractIn a put‐grow‐take fishery, management of Walleye Sander vitreus may require length‐based regulation and depends on population dynamics such as growth, which in turn depends on forage. Big Creek Lake, an important Iowa Walleye fishery, underwent forage changes twice within two decades. Concurrently, Walleye density changed due to increased stocking and reduced emigration, resulting in four scenarios: (1) low‐density Walleye with Gizzard Shad Dorosoma cepedianum forage (period A: 1998–2000), (2) low‐density Walleye with centrarchid or percid forage (period B: 2006–2008), (3) high‐density Walleye with centrarchid or percid forage (period C: 2013–2015), and (4) high‐density Walleye with Gizzard Shad forage (period D: 2019). We examined Walleye population dynamics and relative effects of four length‐based regulations during each period. Walleye in Big Creek Lake likely experienced density‐dependent effects when Walleye density was high and Gizzard Shad were absent, resulting in depressed growth, low condition, increased natural mortality, reduced exploitation, and ineffectiveness of regulations. At lower Walleye densities, the centrarchid or percid forage supported Walleye growth and condition equivalent to when Gizzard Shad were present. Fishing regulations for enhancing Walleye size distribution or yield differed over time due to shifting population dynamics and angler exploitation and were notably ineffective during period C. The preferred regulation for the current scenario (high‐density Walleye with Gizzard Shad) depends on angler preferences for higher catch or larger fish. Big Creek Lake’s Walleye fishery provided a useful demonstration of how rapidly a population can respond to changes in density and forage and, therefore, how dynamic fishery management needs to be.

Flow Dynamics Influence Fish Recruitment in Hydrologically Connected River–Reservoir Landscapes

AbstractHydrologic processes are often important determinants of successful recruitment of native fishes. However, water management practices can result in abnormal changes in daily and seasonal hydrology patterns. Rarely has fish recruitment across river–reservoir landscapes been considered in relation to flow management, despite the direct relationship between reservoir water management and the resulting upstream and downstream hydrology. We evaluated the relationships between lotic and lentic hydrology and recruitment of two native broadcast‐spawning fishes, Freshwater Drum Aplodinotus grunniens and Gizzard Shad Dorosoma cepedianum. Four seasonal periods for each species were identified that related to the species’ spawning biology, from which we derived our remaining hydrology variables. Annual hydrology variables were also considered in our analysis. We developed regression models in conjunction with a model‐selection procedure for each species and habitat type based on the catch‐curve residuals from fish populations in hydrologically connected river–reservoir systems in the Ozark Highland and Ouachita Mountain ecoregions, USA. Our results indicated that recruitment of reservoir Freshwater Drum was negatively correlated to annual reservoir retention time. In lotic habitats, Freshwater Drum recruitment was positively correlated with prespawn discharge conditions and negatively correlated with annual flow variability. Similarly, riverine Gizzard Shad recruitment was positively correlated to the frequency of high‐flow pulses during the spawning period. Our results indicate that releasing reservoir water to best mimic relatively natural flow patterns may benefit some broadcast‐spawning species that occupy both lentic and downstream lotic environments, especially during the spring. This information, combined with future efforts on additional spawning guilds, will provide a foundation for developing holistic river–reservoir water‐allocation plans.

Factors affecting the abundance of age‐0 sport fish in four mainstem Missouri River reservoirs

AbstractThe age‐0 abundance of eight sport fish species in the four mainstem Missouri River reservoirs in South Dakota was evaluated to estimate the influence of environmental and biological factors on age‐0 species abundance. Datasets (at least ten consecutive years) from each reservoir were analysed to evaluate the effects of both monthly (i.e. gauge height, temperature and precipitation) and annual (i.e. cooling degree days and heating degree days, minimum, average, and maximum temperature, and average precipitation) environmental and biological factors. Biological factors including age‐0 prey fish abundance (i.e. gizzard shad Dorosoma cepedianum [Leseuer] abundance), age‐0 sport fish abundance and adult sport fish abundance were examined. Factors were included that are known to have impacts on abundance of age‐0 sport fish in other systems. The abundance of all sport fish species was stable or increasing in all reservoirs, except for walleye Sander vitreus (Mitchell) and white bass Morone chrysops (Rafinesque) in Lewis and Clark Lake. Age‐0 white crappie was the most supported model for explaining age‐0 walleye abundance in Lewis and Clark Lake, and adult white crappie abundance was the most supported model parameter for explaining age‐0 white bass abundance in the reservoir. Findings of the current study highlight the need for species‐specific management of both environmental (i.e. flow manipulation) and biological factors (i.e. harvest limits for sport fish) to increase the abundance of age‐0 sport fish. Due to the dynamic nature of aquatic systems, resulting requirements for management agencies are system‐specific evaluations and management approaches.

Estimates of Food Consumption Rates for Invasive Blue Catfish

AbstractAs a prolific invasive species, Blue Catfish Ictalurus furcatus threaten native organisms in numerous estuarine and tidal freshwaters along the Atlantic coast of the United States. However, no published estimates of consumption rates are available for Blue Catfish in the scientific literature. This information is critical for development of bioenergetics models or estimation of population‐level impacts on native species. Using a combination of field and laboratory studies, we provide the first estimates of daily ration, maximum daily ration, and consumption to biomass ratios for Blue Catfish populations. Ad libitum feeding trials conducted in our laboratory reveal that maximum daily ration in Blue Catfish varies by prey type, temperature, and fish size, with maximal feeding occurring in medium‐sized Blue Catfish (500–600 mm total length) and at temperatures ≥15°C. Furthermore, estimates of daily ration were higher for fish prey (Gizzard Shad Dorosoma cepedianum) than for crustacean prey (blue crab Callinectes sapidus). Diel feeding chronologies based on field‐collected diet samples from 1,226 Blue Catfish demonstrated river‐specific variability in daily ration and maximum daily ration. Blue Catfish daily ration ranged between 2.27% and 5.22% bodyweight per 24 h, while maximum daily ration ranges between 8.56% and 9.37% bodyweight per 24 h. Estimates of consumption to biomass ratios varied by river and Blue Catfish size groupings but range between 2.42 and 3.39, which is similar to other benthic omnivores. This research will inform the assessment of predatory impacts of invasive Blue Catfish in the Chesapeake Bay and beyond as it will enable researchers to estimate predatory impacts through the coupling of population models, food habit information, and consumption rate information (current study).

Gizzard Shad Target Strength‐to‐Body Size Equations at Multiple Hydroacoustic Frequencies

AbstractSpecies‐specific target strength (TS)‐to‐length (L) and TS‐to‐weight (W) equations can reduce bias in biomass estimates from hydroacoustic surveys, yet these equations do not exist for most fishes. Equations specific to the Gizzard Shad Dorosoma cepedianum, a wide‐ranging and often highly abundant prey fish in North American reservoirs and rivers, do not exist. Herein, we sought to develop TS–L and TS–W equations for Gizzard Shad by insonifying free‐swimming individuals of known sizes (36–209 mm TL) in a net cage at three transducer frequencies (70, 120, and 200 kHz). We derived TS–size relationships using major‐axis regression (MAR) and least‐squares regression (LSR), comparing our resultant TS–L equations to a commonly used multispecies equation (Love 1971). To determine how our Gizzard Shad‐specific equations affected estimates of prey fish biomass, we conducted mobile hydroacoustic surveys in four small, shallow Midwestern reservoirs and then estimated biomass using each equation. In general, for TS–L equations, MAR produced the highest estimates of biomass, followed by LSR and then the multispecies equation. Similarly, the TS–W equation derived using MAR produced greater biomass estimates than the equation using LSR. Our findings highlight the value of using species‐specific TS–size equations over multispecies equations in ecosystems dominated by a single fish species (e.g., Gizzard Shad in Midwestern reservoirs). They also demonstrate the value of using MAR to develop TS–size equations, owing to its ability to account for fish size measurement error. The use of species‐specific TS–size equations and MAR should lead to robust estimates of biomass in single‐species‐dominated ecosystems, thus benefiting fisheries assessment and decision making.

Use of Gizzard Diameter to Estimate Weight and Length of Partly Digested Gizzard Shad in Piscivore Diets

AbstractIn diet studies, stomach contents from predatory fish may be difficult to identify due to digestion. The Gizzard Shad Dorosoma cepedianum is an important prey species for sport fish; thus, determining the size of ingested shad can assist with evaluating competitive interactions, bioenergetic patterns, and niche partitioning and can add precision to predictive models. The gizzard organ of clupeids appears to be more resistant to digestion compared to other tissues and can often be found in the stomachs of predatory fish after other tissues from Gizzard Shad are digested. If the gizzard diameter is proportional to Gizzard Shad weight or length, it could be a useful structure for estimating the size of partially digested Gizzard Shad when other structures that are traditionally used to estimate weight or length (e.g., backbones) are damaged due to advanced digestion. For this reason, we evaluated the allometry relating gizzard diameter and Gizzard Shad weight and TL. We sampled a total of 936 Gizzard Shad from nine Oklahoma reservoirs. Fish were frozen and later thawed; they were measured for weight (±0.01 g) and TL (±1 mm), and the gizzard was then removed. Gizzard diameter was measured (±0.1 mm) at its widest point using calipers. Eight different equations were evaluated to find the best relationship (lowest Akaike’s information criterion) between gizzard diameter and weight or length. The relationship between gizzard diameter and fish weight was best modeled as a second‐order polynomial, whereas the relationship between gizzard diameter and fish TL was best described by a five‐parameter Richard’s equation. Both relationships explained over 80% of the variation in Gizzard Shad size. The 95% CIs for weight (±4–7%) and TL (±2–7%) indicated good overall precision for mean fish size based on gizzard diameter. Therefore, we recommend using gizzard diameter to determine weight and TL from diet samples when advanced digestion of Gizzard Shad limits the use of more traditional metrics (TL, backbone length, etc.).

Interrelationships among bluegill demographics, predator and competitor abundances and impoundment characteristics

Bluegills Lepomis macrochirus R. provide popular sport fisheries but the quality of these fisheries has declined across much of their range. Factors that may influence bluegill demographics were examined in 18 Midwestern (USA) impoundments which contained largemouth bass Micropterus salmoides L., the main apex predator, as well as varying abundances of gizzard shad Dorosoma cepedianum L. and common carp Cyprinus carpio L., which can negatively influence the quality of bluegill populations. Regression models revealed that the relative abundance (catch-per-unit-effort [CPUE], number per hour of electrofishing) of bluegill was positively associated with largemouth bass CPUE and total phosphorous concentration. The total lengths (TL) and ages of the largest and oldest bluegills were negatively associated with common carp CPUE and total annual mortality of bluegills, and positively associated with the TL and age of bluegills when 50% were sexually mature and largemouth bass CPUE. Total annual mortality negatively influenced the TL and age at sexual maturity. Bluegills matured at larger sizes and older ages in impoundments with clearer water. This study revealed the strong influence of mortality on size and age structure and the onset of sexual maturity of bluegill, and the negative influence of common carp on these populations. Management strategies to improve bluegill populations should involve reducing bluegill mortality and common carp populations.

Diets of double‐crested cormorants in the Lake Winnebago System, Wisconsin

AbstractDouble‐crested cormorant Phalacrocorox auritus Lesson (cormorant) populations have increased throughout the Great Lakes region of North America causing concern related to the impact of cormorant predation on fish communities. A recent decline in yellow perch Perca flavescens (Mitchill) abundance within the Lake Winnebago System, Wisconsin, USA, prompted an assessment of cormorant diets to evaluate potential effects of cormorant predation on the sportfish community. Diets were collected from 883 cormorants (417 from Lake Winnebago and 466 from Lake Butte des Morts) between 2015 and 2017. Cormorant diets on both waterbodies consisted mostly of freshwater drum Aplodinotus grunniens Rafinesque and gizzard shad Dorosoma cepedianum (Lesueur). Yellow perch and walleye Sander vitreus (Mitchill) observations were infrequent and represented &lt; 5% of cormorant diets by weight each year. Under current conditions, cormorant predation likely has minimal impact on the Lake Winnebago sportfish community, but more research is needed to assess potential impacts on Lake Butte des Morts.

Bolstering Piscivore Abundance to Restructure Small Impoundment Fish Communities

AbstractSmall impoundments (hereafter, “lakes”) provide close‐to‐home fishing opportunities for many anglers but do not always provide quality fishing, especially for panfish. Often, these lakes contain populations of slow‐growing Bluegill Lepomis macrochirus and crappies Pomoxis spp. The presence of abundant Gizzard Shad Dorosoma cepedianum and Common Carp Cyprinus carpio is known to negatively influence these populations. Chemical and mechanical removal of these nuisance species requires intensive effort, is costly, and usually results in only short‐term benefits. An alternative approach is to stock piscivores that prey on these species and reduce their abundances. Hybrid Striped Bass (Striped Bass Morone saxatilis × White Bass Morone chrysops) alone or in combination with Flathead Catfish Pylodictis olivaris were stocked into small lakes to consume Gizzard Shad and Common Carp. To evaluate the success of this approach, I determined whether stockings of hybrid Striped Bass and Flathead Catfish were (1) associated with a consequent reduction in abundances and changes in size structure of Common Carp and Gizzard Shad, (2) related to improved growth rates and size structure of Bluegill and crappie populations, and (3) associated with changes in Largemouth Bass Micropterus salmoides demographics and aquatic macrophyte coverage. Nine treatment lakes were each paired with a reference lake, and fish population variables and macrophyte coverage were analyzed with a before–after, control–impact design. With a few exceptions, additions of piscivores were largely unsuccessful in reducing Gizzard Shad and Common Carp abundances and in improving growth of panfishes and the additions had little effect on Largemouth Bass or macrophyte coverage. A multi‐pronged approach combining several methods (e.g., stocking of piscivores, reducing nutrients, and mechanical or chemical removal) may be necessary to effectively reduce the abundances of Gizzard Shad and Common Carp in these small lakes.

Use of Angling Gear to Evaluate the Potential Benefits of Minimum Length Limits on a Highly Mobile Midwestern Blue Catfish Population

AbstractBlue Catfish Ictalurus furcatus provide a popular sport fishery in Mark Twain Lake, Missouri, but little is known about their population demographics or exploitation by anglers. Our objectives were to (1) determine population demographics of Blue Catfish, (2) determine exploitation of Blue Catfish, and (3) determine whether new harvest regulations would improve the quality (e.g., size structure and abundance) of the fishery in Mark Twain Lake. We sampled Blue Catfish by using jug lines baited with pieces of Gizzard Shad Dorosoma cepedianum, the gear used by the majority of anglers in this reservoir. Blue Catfish grew slowly, reaching a preferred size (762 mm TL) in about 12 years. Annual mortality was estimated at 24.8% using a weighted catch curve. Using reward tags, we estimated exploitation to be between 8% and 12%, and we modeled the effects of 508‐, 610‐, and 660‐mm minimum TL limits on yield and size structure of the Blue Catfish population relative to a baseline of 381 mm TL, the smallest fish usually harvested by anglers. All three length limits increased the proportion of larger fish (≥762 mm TL) in the population without reducing yield, except for slight decreases (6% and 10%) under the 610‐ and 660‐mm limits at the highest modeled natural mortality rate. We recommend the 610‐mm limit instead of the 660‐mm limit because it allows more harvest and higher yields with increases in natural mortality and still doubles the proportion of larger fish relative to the 508‐mm limit.

The First Record of Bigscale Logperch and Range Expansions of Smallmouth Buffalo, White Crappie, and Gizzard Shad in Arizona

AbstractBigscale Logperch Percina macrolepida is reported and substantiated for the first time in Arizona. A single specimen was collected during a routine survey of Cow Springs Lake on September 26, 2017, preliminarily identified as Percina sp., preserved, and retained for species identification. We verified the specimen was a Bigscale Logperch through genetic analysis. Review of published literature and the U.S. Geological Survey Nonindigenous Aquatic Species Database suggests that this is the first known occurrence of Bigscale Logperch in Arizona. Further, three additional nonnative species were detected during our sampling events on June 21 and September 26, 2017—Smallmouth Buffalo Ictiobus bubalus, White Crappie Pomoxis annularis, and Gizzard Shad Dorosoma cepedianum—representing the first collection of these species in the Little Colorado River basin that we are aware of. We recommend further evaluation of the ecology, distribution, and abundance of these four nonnative species to better understand their effect on the native fishes of the watershed and the likelihood of establishment in the watershed and elsewhere in Arizona.

Factors Influencing Bluegill Growth in Small Kansas Impoundments

Abstract We evaluated growth of Bluegill Lepomis macrochirus in 24 small Kansas impoundments to understand variability in populations statewide. We assigned ages to 1,323 Bluegill, and when combined, growth parameters using the Ogle–Isermann parameterization of the von Bertalanffy growth model were: L∞ = 228 mm, K = 0.25, and t152 = 3.10 y. Growth was variable among the 24 populations and t152 (time to reach 152 mm total length) ranged from 1.56 to 4.87 y. We selected four representative limnological variables (latitude, maximum depth, total nitrogen, and total phosphorus) and four representative catch variables (catch-per-effort [CPE] of Bluegill, proportional size distribution of 178-mm Bluegill, CPE of stock-length Largemouth Bass Micropterus salmoides, and CPE of Gizzard Shad Dorosoma cepedianum) to elucidate mechanisms that explained t152 in Bluegill populations. We fit all subset candidate models using the eight variables to predict t152. Top candidate models (corrected Akaike's information criterion scores within two units of the most parsimonious model) comprised a confidence model set, and we used model-weighted averaging to calculate parameter estimates with 95% confidence intervals for each independent variable present in the confidence model set to develop a single explanatory model. The final model suggested that Bluegill size structure, latitude, and CPE of stock-length Largemouth Bass affected Bluegill growth, whereas a smaller effect was attributed to CPE of Gizzard Shad. Combined, these variables explained 40% of variation in observed Bluegill growth rate. Results from this study summarize Bluegill growth in Kansas and highlight variation in growth rates across small impoundments. Further, they suggest that Bluegill size structure, latitude, and relative abundance of stock-length Largemouth Bass are important factors regulating Bluegill growth in small Kansas impoundments.

Stock-recruitment dynamics of a freshwater clupeid

The clupeid gizzard shad Dorosoma cepedianum is often the most abundant fish species in North American reservoirs, and this dominance can have cascading trophic effects on entire fish assemblages. Accordingly, a key aspect of managing reservoir fish assemblages involves controlling gizzard shad densities. We used a 33-year time series to evaluate the relative importance of parental stock density, winter temperature, and water regime on recruitment of age-0 gizzard shad in a large reservoir. Recruitment modeled with a Ricker-type curve increased with the size of the adult stock, peaked, and then decreased at high stock densities. This over-compensatory stock-recruitment relationship was made more dynamic by fluctuations in inflow, with recruitment increasing in years of high inflow, however there was no temperature effect at the latitude of the study site. The influence of stock size on recruitment was roughly twice as high as the influence of inflow. This study is the first to report stock-recruitment relationships for a clupeid species in a reservoir and concurs with analyses of marine fishes that have shown that most clupeids exhibit compensatory or over-compensatory patterns in their stock-recruitment relationships.