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Objective: Barriers can be an effective method for reducing escapement of reservoir sport fish; however, whether the financial benefits of a barrier outweigh the costs of a barrier is unknown. We sought to quantify the costs and benefits associated with constructing barriers to reduce fish escapement while explicitly accounting for variability and uncertainty. Methods: We developed a framework using simulation modeling and discounted cash flow techniques to quantify the costs and benefits of barrier construction on Brushy Creek Lake, Iowa, where a barrier was constructed in 2020 to reduce escapement of stocked Walleye Sander vitreus and Muskellunge Esox masquinongy. We then incorporated this framework into an interactive Shiny application to enable cost–benefit evaluations across a wide range of barrier types, system types, species, and escapement rates. Result: The present value of the parallel‐bar barrier on Brushy Creek Lake, Iowa, over 10 years was US$69,576 (range = $64,484–$73,976), whereas the present value of escaped fish was $316,416 ($253,459–$378,823), indicating a net benefit of $246,840 ($188,975–$304,847) associated with barrier construction. The benefit–cost ratio of barrier construction was 4.55 after 10 years, indicating that for every $1 in present value spent on barrier construction, we saved $4.55 by preventing fish escapement. There was a 99% probability of a positive mean net benefit of the barrier after 3 years. Conclusion: Our results indicate that barriers can be a cost‐effective option to minimize fish escapement, and barrier costs are more predictable compared with the cost of escapement. Quantifying the value of escaped fish and barrier construction on an economic scale enables the use of formal decision‐making tools to address complicated and multifaceted issues associated with reservoir fisheries management. Impact statementWe developed a framework to enable the costs and benefits of barrier construction to minimize reservoir sport fish escapement to be quantified on an economic scale and subsequently applied this framework to a barrier construction project in Iowa. We then integrated this framework into a flexible application to enable the costs and benefits of barrier construction to be assessed across a variety of systems. [ABSTRACT FROM AUTHOR]

The Bigmouth Buffalo Ictiobus cyprinellus is a long‐lived catostomid with ecological and commercial harvest value. Management of Bigmouth Buffalo relies on accurate age data for population dynamic assessments (recruitment, growth, and mortality), but between‐reader precision of nonlethal aging structures compared to otoliths has not been assessed. We analyzed age bias and between‐reader precision of ages estimated from pectoral and dorsal fin rays relative to lapillus otoliths for Bigmouth Buffalo (n = 115) captured from shallow natural lakes in Iowa. Maximum agreed age was 21 years for otoliths, 15 years for pectoral fin rays, and 14 years for dorsal fin rays. Ages estimated from pectoral fin rays were the most precise (CV = 12.6%; average percent error [APE] = 8.9%), followed by dorsal fin rays (CV = 16.1%; APE = 11.4%) and otoliths (CV = 21.5%; APE = 16.5%). Pectoral fin rays also had higher exact agreement between readers (37%) and higher agreement within 1 year (77%) compared to dorsal fin rays (35% exact; 69% within 1 year) and lapillus otoliths (17% exact; 61% within 1 year). Both dorsal fin rays and pectoral fin rays underestimated age relative to otoliths, which resulted in younger population age structures and larger mean length‐at‐age estimates. Our results suggest that biologists can use dorsal and pectoral fin rays as viable nonlethal structures for younger fish (up to 10 years for dorsal fin rays; up to 13 years for pectoral fin rays), whereas otoliths can be difficult to age but are necessary to accurately determine age for older individuals. [ABSTRACT FROM AUTHOR]

Largemouth Bass Micropterus nigricans anglers have mainly adopted catch-and-release practices with limited direct fishing mortality. However, catch-and-release angling could cause delayed mortality and nonlethal effects that could potentially affect population dynamics. For instance, hooking can result in jaw deformities, with unknown subsequent effects on vulnerability to angling, condition, growth, and mortality. Our objectives were to assess the prevalence of Largemouth Bass jaw deformities and test for differences in angling vulnerability, growth, condition, size structure, and mortality of fish with and without jaw deformities. Largemouth Bass were captured by electrofishing and by anglers at 41 tournaments at Brushy Creek Lake, Iowa, between April and August 2015. Jaw deformities were observed in 7.0% of fish caught at tournaments and 3.3% caught while electrofishing (5.8% overall). Angling recapture rates of tagged fish with (78.9%) and without (76.8%) jaw deformities were similar. Condition, growth, size structure, and mortality of fish with and without jaw deformities were also similar. Our results indicate jaw deformities have little effect on Largemouth Bass angling vulnerability, condition, growth, or survival; however, we still recommend careful handling of fish to minimize injuries that may occur during angling. [ABSTRACT FROM AUTHOR]

Common Carp Cyprinus carpio and Bigmouth Buffalo Ictiobus cyprinellus are widespread across the Midwest, where they can achieve high population densities in shallow lakes. Despite their contrasting statuses as invasive and native fishes, these species are commonly managed together due to their capacity to have deleterious effects on water quality. However, intra‐annual sampling variability is poorly understood for both species, making it difficult to track population changes. We compared boat electrofishing CPUE and proportional size distribution (PSD) of Common Carp and Bigmouth Buffalo during May–October 2018–2020 in seven shallow northwestern Iowa lakes. We also estimated sampling effort necessary to reach targets of fish captured (100) and precision (relative standard error < 25%) and to detect 25% and 50% differences in CPUE between samples. Common Carp CPUE peaked in June (29 fish/h), declined across the summer, and was lowest in October (9 fish/h). Bigmouth Buffalo CPUE exhibited bimodal peaks in May (16 fish/h) and October (12 fish/h), with low catches during August (2 fish/h). Common Carp size structure was largest during October (PSD of preferred‐size fish [PSD‐P] = 92) and smallest in July (PSD‐P = 58). Bigmouth Buffalo size structure was smaller in June (PSD‐P = 20) than in all other months (PSD‐P = 34). Our targets for number of fish captured and precision were typically reached within twenty‐five 15‐min electrofishing transects for Common Carp during periods of high catch rates but were not reached after 100 transects for Bigmouth Buffalo in most cases. Our results suggest that timing of sampling is important for reliably and efficiently assessing Common Carp and Bigmouth Buffalo populations. We recommend the sampling of Common Carp with electrofishing during June and the sampling of Bigmouth Buffalo during May in Midwestern shallow lakes to maximize catch rates while minimizing the influence of seasonal sampling variability. [ABSTRACT FROM AUTHOR]

Invasive carp are expanding throughout the upper Mississippi River basin and are of great concern due to their potential economic and ecological impacts. Identification of spawning locations provides critical information on recruitment sources to evaluate potential management strategies. Our objective was to create and validate a spawning habitat suitability model of the Des Moines River, Iowa, during low‐, average‐, and high‐water‐level conditions. Backwater availability, abundance of hardpoints (structures that create turbulence), river gradient and sinuosity, water temperature, and continuously free‐flowing river lengths were used as model parameters. The model was compared to back‐calculated spawning locations from invasive carp eggs collected in 2014–2015. Turbulent hardpoints, river sinuosity, and gradient were not significant predictors of invasive carp spawning locations, and backwater availability in the 25 river kilometers downstream of each reach was inversely correlated with invasive carp spawning locations. Invasive carp eggs were not caught in 2014 despite optimal spawning conditions, revealing that spawning may have high interannual variation. This study suggests that predicting invasive carp reproduction may require variables in addition to those currently proposed. [ABSTRACT FROM AUTHOR]

Tournament mortality of Largemouth Bass Micropterus salmoides can be a major source of population mortality. Tournament captures and mortality may be reduced through restrictive harvest regulations (bag and length limits), but these approaches for mitigating tournament mortality have not been assessed. We assessed the effects of bass tournament angler bag and minimum length limits on the number of bass weighed in, bass tournament weigh‐in probability, and the reduction in tournament mortality. We tagged nearly 4,000 Largemouth Bass during 205 tournaments and electrofishing events at Brushy Creek Lake, Iowa, from 2015 to 2019. We then used a before–after–control–impact analysis to evaluate the effect of tournament regulations (bag limit: either three or five bass; minimum length limit: no minimum or 305, 330, 356, or 381 mm) on bass monthly catch rates and a capture–recapture model to assess tournament weigh‐in probability among regulation types. Number of bass per tournament angler‐hour was similar among a three‐bass, ≥381‐mm length limit and more liberalized regulations (mean = 0.26 bass/angler/h). Length and bag limits had little effect on bass weigh‐in probability. We estimated that reducing the bag limit from five to three bass would have little effect, while a reduction from three to two bass would reduce the number of bass weighed in by 35% and a bag limit of one bass would result in a 62% reduction. Alternatively, a minimum length limit of ≥381 mm could reduce the number of bass weighed in by over 40%. Tournament mortality was greatest in July and August, but low catch rates during these months resulted in little mortality. Although current length and bag limits did not affect bass weigh‐in probability, the number of bass weighed in and associated tournament mortality may be reduced if bag and length limits are very restrictive (≤2 bass/angler or minimum length ≥381 mm). However, restrictive tournament regulations may not be biologically necessary or socially acceptable. [ABSTRACT FROM AUTHOR]

Mercury contamination in aquatic ecosystems is a global concern due to the health risks of consuming contaminated fishes. Fish mercury concentrations are influenced by a range of biotic and abiotic factors that vary among regions, but these complex interactions are difficult to disentangle. We collected bluegill (Lepomis macrochirus), white and black crappie (Pomoxis annularis; P. nigromaculatus), largemouth bass (Micropterus salmoides), walleye (Sander vitreus), muskellunge (Esox masquinongy), and northern pike (E. lucius) from waterbodies throughout Iowa and analyzed them for mercury concentrations. We used land use, water chemistry, and fish characteristics to explain variation in mercury concentrations among and within systems. Mercury concentrations were generally low and undetectable (< 0.05 mg/kg) in 43% of fish analyzed. Detected mercury concentrations were highest in largemouth bass, muskellunge, northern pike, and walleye, lowest in black and white crappie and bluegill, and positively related to fish length and age. Mean lake depth, pH, watershed area to lake area ratio, and percent of watershed as open water were positively related to fish mercury concentrations whereas lake area and percent of watershed as agriculture, developed, forested, and grassland were negatively related to mercury concentrations. Additionally, mercury concentrations were higher in shallow natural lakes compared to other lake types. Our results indicate fish mercury concentrations are lower in Iowa lakes compared to other regions. Models we developed in this study can be used to identify other waterbodies that may have elevated mercury concentrations that can guide fish mercury monitoring programs. [ABSTRACT FROM AUTHOR]

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Many fish species of greatest conservation need (SGCN) in Iowa and Minnesota, USA, have been in decline for decades. A key reason for the decline is the alteration and degradation of naturally flowing streams owing to land use changes resulting from agricultural practices. Populations of several fishes have been adversely affected by widespread stream channelization that has resulted in more homogeneous stream habitats throughout Iowa and Minnesota.The goal of this study was to determine the abiotic and fish assemblage characteristics associated with the presence of these rare fishes. Electrofishing and seining were used to sample fish assemblages and 43 abiotic characteristics were measured at 111 sites in the North Raccoon and Boone River basins in central Iowa and the Rock River and Beaver Creek basins in north‐west Iowa and south‐west Minnesota during 2016 and 2017.Six SGCN, including the federally endangered Topeka shiner (Notropis topeka), were included in statistical modelling to determine habitat and fish assemblage characteristics associated with their presence.Species‐specific nonmetric multidimensional scaling ordinations indicated that abiotic characteristics and fish assemblages often differed between sites where SGCN were present and absent. Random forest and logistic regression models suggested that the presence of four of six SGCN were positively associated with species richness, whereas all other 10 important abiotic and fish assemblage variables were unique to only one or two of the six SGCN.Topeka shiners were present at 36% of sites and were positively associated with orangespotted sunfish (Lepomis humilis) catch per unit effort while being negatively associated with canopy cover and fantail darter (Etheostoma flabellare) catch per unit effort. [ABSTRACT FROM AUTHOR]

Walleye Sander vitreus are commonly introduced to reservoirs and provide valued fisheries. Walleye are lost though harvest and natural mortality in all systems, but escapement may also reduce reservoir populations. However, the effects of harvest, natural mortality, and escapement loss on reservoir Walleye populations are not known. Our objective was to quantify Walleye harvest, natural mortality, and escapement in two Iowa reservoirs (Big Creek Lake and Brushy Creek Lake) to understand how these factors limit populations. We also assessed Walleye behaviors and compared them among escaped, harvested, and in‐lake Walleye to determine if behavior was associated with fate. Walleye were radio‐tagged beginning in October 2016 and tracked through May 2019. Telemetry was used to estimate annual core and home ranges, seasonal depth use, and movement rates. Detection histories were analyzed using a multistate capture–recapture model with environmental covariates to estimate weekly harvest, natural mortality, and escapement. Harvest was greater in Big Creek than Brushy Creek and was higher in April through July compared to other months. Natural mortality was positively related to water temperature but did not differ between systems. No Walleye escaped from Big Creek (fish barrier on spillway), but escapement at Brushy Creek (no fish barrier) was positively related to mean water levels during April. During 2017–2018, annual Walleye escapement ranged from 22% to 47% at Brushy Creek (0% at Big Creek), harvest ranged from 13% to 27%, and natural mortality ranged from 36% to 38%. Depth of habitat occupied by Walleye was shallower during spring and summer when escapement occurred, intermediate in fall, and deepest during winter. Escaped Walleye at Brushy Creek used greater depths and moved less than in‐lake Walleye; however, other behaviors did not differ among Walleye groups. Our results suggest that escapement can have a larger effect than harvest on reservoir Walleye populations in systems without physical barriers, and it should be taken into consideration when managing reservoir Walleye fisheries. [ABSTRACT FROM AUTHOR]

Age‐0 Walleye Sander vitreus are stocked throughout North America to maintain and supplement populations. Predation has been implicated as a factor limiting survival of stocked age‐0 Walleye; however, the timing, duration, and extent of poststocking predation remains uncertain. Our objectives were to estimate the abundance of predators in areas adjacent to stocking locations, estimate temporal variation in the proportion of stocked age‐0 Walleye (98–287 mm) in predator diets, and estimate the total proportion of stocked age‐0 Walleye that were consumed. The diets of Largemouth Bass Micropterus salmoides, Northern Pike Esox lucius, and adult Walleye were examined in East Okoboji and West Okoboji lakes, Iowa, before and after age‐0 Walleye stocking, and bioenergetics models were used to estimate the number of age‐0 Walleye consumed from stocking through ice‐up. During both years, Largemouth Bass had the highest densities in West Okoboji Lake, whereas densities of all other predators were similar in East Okoboji Lake. The highest proportions of age‐0 Walleye in predator diets (up to 1.0) generally occurred within 14 d after the most recent stocking event, with the proportion of age‐0 Walleye in predator diets decreasing thereafter. Northern Pike had the highest proportion of age‐0 Walleye in their diets (mean ± SD = 0.12 ± 0.32 age‐0 Walleye/individual) followed by Largemouth Bass (0.11 ± 0.30 age‐0 Walleye/individual) and adult Walleye (0.04 ± 0.20 age‐0 Walleye/individual). At the end of 2016, the estimated proportion of age‐0 Walleye consumed was 0.15 ± 0.08 (95% CI) in East Okoboji Lake and 0.29 ± 0.13 in West Okoboji Lake. At the end of 2017, the estimated proportion of age‐0 Walleye consumed was 0.47 ± 0.16 in East Okoboji Lake and 0.64 ± 0.02 in West Okoboji Lake. Overall, predators consumed large proportions of stocked Walleye, suggesting that alternative stocking practices should be considered. [ABSTRACT FROM AUTHOR]

Identifying waterbodies where fish methylmercury concentrations are elevated is critical for development of consumption guidelines. However, mercury concentrations vary among waterbodies and fishes due to a suite of environmental conditions and detection of elevated mercury concentrations is imperfect, resulting in inaccurate consumption guidelines. Occupancy models may be a useful approach for addressing these issues but have not been used for these purposes. Our objectives were to use occupancy modeling to (1) estimate number of samples needed to detect mercury levels surpassing >0.30 mg/kg wet weight in fish at a waterbody (2) identify individual fish-level factors associated with detection probability, and (3) identify environmental-level factors linked to elevated mercury levels in fish at a waterbody. Mercury concentrations were estimated from >500 largemouth bass Micropterus salmoides and walleye Sander vitreus from 30 waterbodies throughout Iowa, USA to identify individuals with concentrations > or <0.30 mg/kg. Probability of detecting mercury concentrations >0.30 mg/kg varied between species and increased with fish length; consequently, more samples were needed to detect elevated mercury concentrations in small versus large fish. The probability of a waterbody having fish with elevated mercury levels increased with the percent grassland and declined with percent agriculture in the watershed, providing prioritization metrics for mercury surveillance programs. Our results demonstrate that occupancy models can be a valuable tool for mercury surveillance due to their ability to estimate necessary sample sizes and identify fish sizes and waterbodies with elevated mercury concentrations while accounting for imperfect detection probabilities. [ABSTRACT FROM AUTHOR]

Lakes provide significant ecosystem services that are compromised by human degradation. Watershed and in-lake restoration are used to improve the physical, chemical, and biological condition of lakes, but their success is rarely evaluated. Our objectives were to compare water quality and biological conditions following in-lake, watershed, or a combination of both restoration activities in 20 lakes throughout Iowa, USA compared to reference systems. Lake-specific responses to restoration were variable, making it challenging to detect systematic effects in water quality parameters. Secchi depth generally improved following restoration, particularly in natural in-lake restorations and following sediment removal, fishery renovation, and with the number of restoration practices implemented, but improvements were not sustained. Restoration also tended to reduce nutrient and plankton concentrations and relative abundance of some benthic fishes. Due to the prolonged degradation of eutrophic lakes, it may be unrealistic to expect immediate and long-lasting water quality improvements. In-lake restoration in natural lakes may be the most likely to have detectable effects, but our results also highlight the need for improved restoration documentation and additional research to identify factors associated with restoration success. Our results are useful for guiding lake restoration practices and educating lake users and stakeholders on expected restoration outcomes. [ABSTRACT FROM AUTHOR]

Muskellunge Esox masquinongy is a prized sport fish throughout much of North America. Due to the species' popularity among anglers and limited natural recruitment in reservoirs, Muskellunge are commonly stocked to maintain populations. However, little is known about their poststocking behavior and survival in reservoirs. We used radiotelemetry to evaluate behavior and survival of spring‐stocked yearling Muskellunge in two Iowa reservoirs that differed in habitat availability (Big Creek Lake: limited habitat; Brushy Creek Lake: abundant habitat). Hatchery‐reared Muskellunge were implanted with radio transmitters (n = 15–16 fish·lake−1·year−1; 61 fish total) and stocked in both lakes during May 2017 and 2018; fish were tracked daily for 1 week, every other day for the second week, and then weekly until December. Telemetry data were used to evaluate depth and vegetation use, selection of littoral substrate and coarse woody habitat (CWH) complexities, movement, home ranges, and survival. Muskellunge depth use generally increased with time poststocking and was greater in Brushy Creek Lake than in Big Creek Lake. Movement rates were greatest during the first week poststocking and declined thereafter, with greater rates and home ranges in Big Creek Lake. Muskellunge in both systems selected for fine substrates while avoiding coarse substrates. Muskellunge in Brushy Creek Lake were more commonly associated with CWH and aquatic vegetation compared to those in Big Creek Lake. Muskellunge in Big Creek Lake selected for complex CWH, while those in Brushy Creek Lake used CWH classes in proportion to their availability. Cormack–Jolly–Seber daily apparent survival estimates were lowest for the first 4 d poststocking and ranged from 0.59 to 0.99, after which survival increased from May to September before declining in October and November. Results of this study provide a greater understanding of the poststocking success of yearling Muskellunge and suggest that Muskellunge behavior and survival are dependent on habitat complexity, with weaker habitat selection but higher survival in complex systems. [ABSTRACT FROM AUTHOR]

Walleye Sander vitreus Mitchill have been progressively raised in hatcheries to larger sizes under the paradigm that larger stocked fish have higher survival. However, extended time in hatcheries may result in domestication, with stocked individuals lacking behaviours that promote survival. The objective of this study was to evaluate behaviour and survival of wild versus stocked fingerling (>200 mm) walleye in two Iowa reservoirs. Radio telemetry was used to evaluate walleye movement rates, depth use, home range size, habitat selection and apparent survival. Depth use increased with days since stocking and varied between lake‐years but was similar between walleye groups. Daily movement rates varied by the interaction between group and day, with rates declining through time. Home ranges did not differ between groups but were significantly greater in Big Creek than Brushy Creek. Walleye in both lakes generally used habitat in proportion to availability, with few differences between groups detected. Weekly apparent survival ranged from 0.948 to 1.000, varied across lakes, years and seasons, and was higher for stocked than wild walleye in Big Creek but not Brushy Creek. The results indicate that hatchery‐reared fingerling walleye behave similar to but can have higher survival than wild fish, suggesting that domestication may not be occurring and that stocking autumn fingerling walleye may help supplement year‐class strength. [ABSTRACT FROM AUTHOR]

The success of fish stocking programs is dependent on poststocking survival. However, survival can be influenced by size‐selective mortality, where larger individuals are expected to be less vulnerable to predation. Walleye Sander vitreus is a commonly stocked sport fish, but little is known regarding the role of size‐selective predation on age‐0 Walleye (90–290 mm TL) that are stocked in the presence of various piscivores with different foraging strategies and morphological features. Our objective was to evaluate whether the TL of consumed age‐0 Walleye was related to predator TL, predator gape height, or the probability of predation. We also assessed whether length distributions varied among stocked, recaptured, and consumed age‐0 Walleye. Data for the food habits of Largemouth Bass Micropterus salmoides, Smallmouth Bass M. dolomieu, Northern Pike Esox lucius, adult Walleye, and Muskellunge Esox masquinongy were collected from East Okoboji Lake and West Okoboji Lake, Iowa, USA during fall 2015–2017. Over the course of the study, 301 age‐0 Walleye were recovered from 3,514 predator stomachs. Mean, maximum (85th percentile), and minimum (15th percentile) TL of the consumed age‐0 Walleye were not related to the TL or gape height of the predators (P > 0.05), but the probability of predation decreased by 0.02 for every 10‐mm increase in the TL of the age‐0 Walleye. The length distributions indicated that consumed Walleye were generally smaller, whereas recaptured Walleye tended to be larger than stocked fish were. Our approach to evaluating poststocking size‐selective predation on age‐0 Walleye furthers the current understanding of the importance of size at stocking relative to stocking success and suggests that stocking Walleye > 220 mm is economically advantageous for reducing predation risk. [ABSTRACT FROM AUTHOR]

Grass Carp Ctenopharyngodon idella have been intentionally stocked for aquatic vegetation control across the Midwestern United States for several decades. During the 1970s, escapement of Grass Carp into the Missouri River facilitated their naturalization into much of the Mississippi River basin, including the Upper Mississippi River. Lock and Dam 19 (LD19) in Keokuk, Iowa, is a high-head dam that represents a focal point for naturalized Grass Carp management where populations may differ between upstream and downstream pools as result of limited upstream migration, but potential differences between populations have yet to be evaluated to the best of our knowledge. The objective of this study was to compare the relative abundance, size structure, condition, growth, and recruitment variability of Grass Carp collected upstream and downstream of LD19. We sampled Grass Carp monthly (April–October) during 2014 and 2015 from four locations in the Des Moines River (downstream of LD19) and five locations throughout the Skunk, Iowa, and Cedar rivers (upstream of LD19) using boat electrofishing and trammel net sets. We captured 29 Grass Carp upstream of LD19 compared with 179 individuals captured downstream. Trammel nets only captured Grass Carp downstream of LD19; trammel net catch per unit effort upstream of LD19 was low and ranged from 0.0 to 8.0 fish/net lift (mean ± SE = 0.39 ± 0.13). Electrofishing catch per unit effort ranged from 0.0 to 22.7 fish/h (1.49 ± 0.30) and was higher downstream (2.42 ± 0.30) of LD19 than upstream (0.57 ± 0.07). Grass Carp downstream of LD19 tended to be smaller, younger, of lower body condition, had higher mortality rates, and were slower growing compared with those collected upstream and to populations documented in other systems. Understanding and monitoring adult Grass Carp population characteristics upstream and downstream of LD19 is necessary to determine how they may change in response to ongoing harvest efforts for invasive carps in these river reaches. [ABSTRACT FROM AUTHOR]

Stocking Walleye Sander vitreus is a common management tool to augment populations where natural reproduction is limited. Some hatcheries have progressively raised larger fingerling Walleye to improve poststocking survival; however, little is known about the poststocking survival and behavior of large fingerling Walleye. We sought to evaluate the poststocking daily apparent survival, depth use, dispersal, and home range size of large fingerling Walleye (>200 mm TL) in three Iowa, USA, lakes. Walleye (209–265 mm; n = 15 per lake [45 fish total]) were implanted with radio tags, stocked on October 26–30, 2017, and tracked until May 30, 2018. Cormack–Jolly–Seber recapture models estimated that Walleye apparent survival increased with days poststocking and fish length, resulting in 76% (95% CI = 44–89%) cumulative survival by May. Walleye in Brushy Creek Lake were located in deeper water (mean ± SE = 5.1 ± 0.2 m) than those in Big Creek Lake (3.3 ± 0.2 m) or East Okoboji Lake (1.7 ± 0.1 m), but depth use did not vary with days poststocking. Walleye dispersed an average of 1,355 ± 234 m within 13 d across all lakes, with home range size being larger in Big Creek Lake (mean ± SE = 67.9 ± 21.7 ha) than in Brushy Creek Lake (15.5 ± 15.7 ha) or East Okoboji Lake (31.0 ± 14.0 ha). Our results indicate that Walleye poststocking survival is high overall, with most mortality occurring within 20 d as Walleye are dispersing, suggesting that managers should focus on improving survival during this critical period to improve stocking success. [ABSTRACT FROM AUTHOR]

In the USA, the Topeka shiner (Notropis topeka) is a federally listed endangered species that has been in decline for decades. A key reason for the decline is the alteration of naturally flowing streams and associated oxbow habitats resulting from land‐use changes. The focus of recent conservation efforts for Topeka shiners has been the restoration of oxbow habitats by removing sediment from natural oxbows until a groundwater connection is re‐established. This restoration practice has become common in portions of Iowa and south‐west Minnesota.The goals of this study were to compare the occurrence and abundance of Topeka shiners in restored and unrestored oxbows and to determine the characteristics that influenced their presence in these systems.In 2016–2017, 34 unrestored and 64 restored oxbows in the Boone, Beaver Creek, North Raccoon and Rock River basins in Iowa and Minnesota were sampled for their fish assemblages and abiotic features. Topeka shiners were present more often and with higher average relative abundances in restored oxbows.Nonmetric multidimensional scaling ordinations indicated that fish assemblages found in oxbows where Topeka shiners were present were less variable than assemblages found at oxbows where they were absent, but that abiotic characteristics were similar between oxbow types.Logistic regression models suggested that the presence of Topeka shiners in oxbows was positively associated with species richness, brassy minnow (Hybognathus hankinsoni) catch per unit effort (no. fish/100 m2; CPUE), orangespotted sunfish (Lepomis humilis) CPUE, dissolved oxygen and turbidity, and negatively associated with oxbow wetted length. These results highlight the use of restored oxbows by Topeka shiners while also providing new information to help guide restoration and conservation efforts. [ABSTRACT FROM AUTHOR]

Stocking programs for Muskellunge Esox masquinongy throughout North America rely on the collection of wild adult Muskellunge to acquire gametes for hatchery propagation. The process of collecting, transporting, confining, handling, and spawning broodstock Muskellunge may cause mortality that could alter Muskellunge density, size structure, and population survival rates. We used long‐term Muskellunge capture–recapture data collected from the Iowa Great Lakes and Clear Lake in northern Iowa to estimate the number and proportion of Muskellunge captured annually and the initial mortality rates resulting from broodstock collection. We also evaluated whether Muskellunge apparent survival rates differed between individuals used as broodstock and those that were not captured annually. Finally, we evaluated whether the number of initial mortalities or the number of individuals captured were related to annual population survival estimates. Collectively, 7,010 adult Muskellunge (3,896 males and 3,114 females) captures occurred between 2001 and 2017, and population densities within a system ranged from 0.11 to 0.39 fish/ha. An average of 33% (range = 13–76%) of the population was captured during broodstock operations annually. Between 0 and 28 (0.0000 to 0.0191 fish/ha) Muskellunge died at each hatchery annually, and more males died than females (total of 150 males and 68 females; 3.9% and 2.2% of captured fish, respectively). However, annual mortalities were generally a low proportion of Muskellunge in the lake (<2%; <0.001 fish/ha). There was some evidence of size‐selective mortality, particularly for males, where larger individuals (875–975 mm) were more likely to die, but we found no evidence to suggest that broodstock collection affected annual population survival estimates. Muskellunge broodstock mortality appears to act in a compensatory manner with natural mortality, and other sources of population mortality are more likely to have a greater effect on the population. [ABSTRACT FROM AUTHOR]

Fish mercury concentrations have received considerable attention due to human health implications. Fish mercury concentrations are variable within and among systems due to a suite of biotic and abiotic influences that vary among regions and are difficult to predict. Understanding factors associated with variability in fish mercury concentrations would help guide consumption advisories. Mercury concentrations in channel catfish (Ictalurus punctatus, n = 205), flathead catfish (Pylodictis olivaris, n = 123), northern pike (Esox lucius, n = 60), smallmouth bass (Micropterus dolomieu, n = 176), and walleye (Sander vitreus, n = 176) were assessed in ten Iowa rivers and relationships with land use, water chemistry, and fish characteristics were explored. Mercury concentrations were generally low (mean among all species = 0.17 mg/kg, n = 740) but higher in flathead catfish, northern pike, smallmouth bass, and walleye than channel catfish and were positively related to fish length, age, trophic position, and δ13C signatures. Phosphorus, sulfate, and percent open water and grassland were negatively related to fish mercury concentrations, whereas water hardness, nitrogen-ammonia, Human Threat Index, and percent wetland and forest were positively related to fish mercury concentrations. Fish collected from the Paleozoic Plateau ecoregion in northeast Iowa had higher mercury concentrations than other ecoregions in Iowa. Combined, these factors explained 70% of the variation in fish mercury concentrations. This study provides a comprehensive analysis of abiotic and biotic factors influencing fish mercury concentrations in lotic ecosystems at the individual and system scale that will help guide fish consumption advisories. [ABSTRACT FROM AUTHOR]

Muskellunge Esox masquinongy is a popular species commonly introduced to warm-water reservoirs; however, little is known about seasonal habitat use and movement in these systems which may result in reservoir escapement and reduced Muskellunge abundance. Our objectives were to assess Muskellunge seasonal behaviors and quantify escapement and natural mortality to determine their effects on populations. Muskellunge captured from the lake and spillway were implanted with radio tags in Big Creek (n = 17) and Brushy Creek (n = 30) lakes, Iowa, USA beginning October 2016 and tracked through May 2019. Telemetry data were used to quantify depth at fish locations, movement rates, annual core and home ranges, and proportions of tagged Muskellunge using spillway approach areas. Telemetry encounter data were analyzed using a multi-state model with water temperature and reservoir water level covariates to estimate escapement and natural mortality. Muskellunge in Brushy Creek were located in deeper water than in Big Creek, but depth and movement were similar across seasons and behavior did not differ between fish captured in-lake and the spillway. Big Creek Muskellunge exhibited greater movements in spring, were located in shallow water and moved less in summer, and were found in deeper water during winter. Core and home ranges were similar between lakes and many tagged Muskellunge frequently used spillway approach areas during spring and summer. No escapement occurred from Big Creek (physical barrier on spillway) while weekly escapement probability from Brushy Creek (no barrier) was up to 0.13 and annual escapement ranged from 18 to 54 %. Escapement was greatest from May-August and increased with increasing weekly maximum reservoir level. Natural mortality was similar between systems, ranged from 15 to 18 % annually, and increased with water temperature. Our results suggest escapement can lead to greater loss of Muskellunge from reservoir populations than natural mortality and may be greater in spring and summer. However, escapement does not appear to be associated with fish behaviors. [ABSTRACT FROM AUTHOR]

• Evaluated the effects of number of largemouth bass in a live-well on post-release tournament survival of tournament captured bass. • Used a Cormack-Jolly-Seber model in Program MARK. • Models suggested survival of tournament captured bass was reduced for three days post-release. • The largest effect on post-release tournament survival occurred at high water temperatures but were reduced as water temperatures cooled. • The effect of number of bass in a live-well on tournament survival is likely minimal due to the infrequency of 10 or more bass in a live-well. As live release black bass (Micropterus spp.) tournaments increase in popularity, stress associated with live-well confinement may result in increased mortality rates. Variation in number of bass in tournament angler live-wells is common due to a suite of factors (e.g., regulations, number of anglers per boat, angler success), but the effect on delayed tournament mortality relative to other environmental factors is unknown. Largemouth bass Micropterus salmoides were collected and tagged following tournament weigh-ins (n = 80) and monthly electrofishing events (n = 15) in 2018 and 2019 at Brushy Creek Lake, Iowa, USA. A Cormack-Jolly-Seber model in Program MARK was used to evaluate the duration of reduced post-tournament survival (0–7 day) and the effects of number of bass per live-well (1–15 individuals) compared to environmental covariates (air and water temperature) and bass total length on post-tournament survival. Models indicated bass survival was reduced for three days following tournament capture and was negatively related to water temperature, number of bass in live-well, and number of initial tournament mortalities. Largest effects of all covariates on tournament survival occurred at high water temperatures but were reduced at cooler water temperatures. Daily survival probability ranged from 0.9792 (95 % CI: 0.9757, 0.9822) at 5.71 °C to 0.8927 (95 % CI: 0.8720, 0.9103) at 28.79 °C on day of tournament capture. Survival also decreased from 0.9819 (95 % CI: 0.9592, 0.9921) with one bass in the live-well to 0.9632 (95 % CI: 0.4167, 0.9990) with fifteen bass in the live-well. However, the effect number of bass in a live-well has on overall tournament survival is likely minimal due to the infrequency ten or more bass were confined per live-well. Our study provides information on the effect number of bass in a live-well has on post-release tournament survival while providing management insights to improve post-tournament survival for recreational bass fisheries. [ABSTRACT FROM AUTHOR]

The Topeka shiner Notropis topeka is native to Iowa, Kansas, Minnesota, Missouri, Nebraska, and South Dakota and has been federally listed as endangered since 1998. Our goals were to determine the present distribution and qualitative status of Topeka shiners throughout its current range in Iowa and characterize the extent of decline in relation to its historic distribution. We compared the current (2016–2017) distribution to distributions portrayed in three earlier time periods. In 2016–2017 Topeka shiners were found in 12 of 20 HUC10 watersheds where they occurred historically. Their status was classified as stable in 21% of the HUC10 watersheds, possibly stable in 25%, possibly recovering in 8%, at risk in 33%, and possibly extirpated in 13% of the watersheds. The increasing trend in percent decline evident in earlier time periods reversed, going from 68% in 2010–11 to 40% in the most recent surveys. Following decades of decline, the status of Topeka shiners in Iowa appears to be improving. One potential reason for the reversal in the distributional decline of Topeka shiners in Iowa is the increasing number of oxbow restorations. Until a standardized monitoring program is established for Iowa, periodic status assessments such as this will be necessary to chronicle progress toward conserving this endangered fish species. [ABSTRACT FROM AUTHOR]