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Optimal egg size theory implies that female organisms balance between fecundity and individual offspring investment according to their environment. Past interspecific studies suggest that fishes in large marine systems generally produce smaller eggs than those in small freshwater systems. We tested whether intraspecific egg size variation reflected a similar pattern by comparing egg size among yellow perch (Perca flavescens) populations inhabiting a range of system sizes. In 2018, 2019, and 2023, we collected yellow perch egg samples from 12 locations in systems ranging in surface area from 37 to 5,390,492 ha. First, we found that egg diameter significantly increased with maternal total length in five of eight individually tested populations. After accounting for these maternal effects, we found a significant interaction, where females inhabiting larger lakes, such as the main basins of Lakes Erie and Michigan, produced smaller eggs than those in smaller inland lakes, and the greatest differences were demonstrated among females of greater total length. This egg size variation in the largest females is consistent with interspecific egg size comparisons between marine and freshwater fishes. However, by examining a single species across vastly different environments, we were able to support theoretical expectations that maternal investment in offspring should vary with environmental conditions controlling early‐life resource acquisition and competition. [ABSTRACT FROM AUTHOR]

Objective: Fish movements and distributions throughout an ecosystem are important for understanding ecological interactions, conservation, and management. Coarse woody habitat (CWH) additions are a popular habitat enhancement tool that can influence movements and distributions of fishes; however, behavioral responses in relation to CWH additions are understudied. The objectives of our study were to test for changes in habitat use and behavioral responses of Muskellunge Esox masquinongy, Smallmouth Bass Micropterus dolomieu, and Walleye Sander vitreus to CWH additions in a small inland northern lake over 3 years and to evaluate two common forms of fish tracking to estimate daily movement of these fishes. Methods: We used passive integrated transponder tag data collected continuously at 10 littoral sites and radiotelemetry data collected biweekly during the summer-fall months prior (2017) and following (2018-2019) CWH addition to examine movement behaviors and estimate daily probability of movement for the three species among lake habitats using multistate models. Result: Walleye were the most likely to remain near CWH, followed by Smallmouth Bass and Muskellunge. All species were more likely to move away from the modified and unmodified littoral zones and were more likely to remain in the offshore zone. Increased movement of fish may be in response to CWH creating a refuge for forage fish and subsequent increases in prey search times. Conclusion: Our results suggest that CWH additions may alter established species-specific annual movements, distributions, and habitat use to differing degrees in ecosystems, as our results differ from other CWH studies. Methodologically, radio-tagging was most effective for offshore tracking but most labor intensive. Novel passive integrated transponder arrays (less labor intensive once installed) worked well to monitor movement between habitat types in shallow littoral areas. Long-term monitoring of behavioral changes will be essential to assessing the stability changes caused by these habitat alterations. [ABSTRACT FROM AUTHOR]

Harvest in walleye Sander vitreus fisheries is size‐selective and could influence phenotypic traits of spawners; however, contributions of individual spawners to recruitment are unknown. We used parentage analyses using single nucleotide polymorphisms to test whether parental traits were related to the probability of offspring survival in Escanaba Lake, Wisconsin. From 2017 to 2020, 1339 adults and 1138 juveniles were genotyped and 66% of the offspring were assigned to at least one parent. Logistic regression indicated the probability of reproductive success (survival of age‐0 to first fall) was positively (but weakly) related to total length and growth rate in females, but not age. No traits analyzed were related to reproductive success for males. Our analysis identified the model with the predictors' growth rate and year for females and the models with year and age and year for males as the most likely models to explain variation in reproductive success. Our findings indicate that interannual variation (i.e., environmental conditions) likely plays a key role in determining the probability of reproductive success in this population and provide limited support that female age, length, and growth rate influence recruitment. [ABSTRACT FROM AUTHOR]

Discard mortality is an important factor to consider when managing catch‐and‐release fisheries. Even low levels of discard mortality can induce population‐level effects particularly in long‐lived, low‐productivity species like Lake Sturgeon Acipenser fulvescens. Unfortunately, little is known about the effects of catch‐and‐release angling on Lake Sturgeon physiology and probability of discard mortality. We used controlled angling events with standardized gear to capture 96 Lake Sturgeon from August to October 2019 from four regional locations in Wisconsin, USA. We evaluated the physiological effects of angling and activation of the stress response using whole blood concentrations of lactate and glucose as well as assessment of reflex impairment and postcapture monitoring of recovery time. Lactate levels were positively related to fight duration and the fight duration × total length interaction. Glucose level was related to the time a fish spent out of water postangling event. Water temperature had a positive effect on the probability of reflex impairment and the probability that a sturgeon required recovery time. The recovery duration was positively related to the amount of time that the fish was out of water. The movements of a subset of 15 individuals from one location were monitored using acoustic telemetry for approximately 2 weeks postangling. All individuals showed continuous up‐ and downstream movement during the postrelease monitoring period, and there was no evidence of mortality related to the angling events. Managers considering catch‐and‐release fisheries for Lake Sturgeon should consider population‐specific relative abundance and catch rates. They should exercise caution in scenarios when seasonal aggregations may lead populations to be susceptible to high catch rates, during times of elevated water temperatures, or the combination of these factors. The Lake Sturgeon in this study appeared to be robust to angling‐induced stress effects. Nevertheless, caution is still warranted, as low levels of discard mortality have the potential to influence low‐productivity species like Lake Sturgeon. [ABSTRACT FROM AUTHOR]

In response to declines in coarse woody habitat (CWH) and fish productivity in natural lakes and reservoirs, agencies and stakeholders have used woody and artificial habitat enhancements to slow or reverse the effects of habitat loss from aging or shoreline development. Given that natural lakes and reservoirs differ in physical and biological conditions that could influence habitat enhancement outcomes, a framework is needed to guide management expectations for CWH replacement under different ecosystem contexts. We review ecosystem contexts that influence the effects of structural habitat enhancements in natural lakes and reservoirs, use preliminary results from case studies in a natural lake in Wisconsin and two reservoirs in Illinois to illustrate the importance of these contexts, and provide management recommendations for habitat deployments that consider physical and biological ecosystem characteristics. Because of their influence on trophic transfer efficiency, trophic status and turbidity are important contexts for habitat enhancements in natural lakes and reservoirs. Habitat enhancements to large reservoirs must also contend with high nutrient loading, water level fluctuations, and longitudinal gradients in physical and biological conditions. Preliminary results from the Wisconsin experiment illustrated the importance of the recipient fish community, with rates of response to the structural enhancement varying among fish species. The Illinois case studies demonstrated how the magnitude of change (i.e., effect size) after habitat enhancement can differ (1) between CWH additions to an oligotrophic natural lake and a eutrophic, turbid reservoir and (2) by longitudinal position of artificial habitat within a large reservoir. The functions or ecosystem services of CWH targeted for rehabilitation provide guidance as to which ecosystem features will shape the strength, direction, and duration of response. Future whole‐ecosystem manipulations are needed across a wider range of environmental contexts and fish productivity responses, and the strength of productivity increases should be compared to increased harvest efficiency. [ABSTRACT FROM AUTHOR]

Walleye, Sander vitreus (Mitchill), natural recruitment has declined in northern Wisconsin lakes over time. Age‐0 and age‐1 walleye relative abundance (catch per unit effort; CPE) data from northern Wisconsin (1986–2019) were used to test for abiotic (i.e. lake characteristics and temperature variables) and biotic (age‐0 and age‐1 CPE) factors influencing age‐0 to age‐1 walleye mortality. Age‐0 to age‐1 walleye mortality was elevated at high age‐0 CPE and variable at low age‐0 CPE, which indicated strong density‐dependence. Environmental factors such as spawning and ontogenetic phenology (climate change and ice‐off dates), trophic mismatches, and metabolic and consumptive demand influenced age‐0 to age‐1 walleye mortality less strongly. Elevated age‐0 to age‐1 walleye mortality at low age‐0 CPE supports previous findings of depensatory recruitment dynamics in northern Wisconsin walleye populations. Additional research is needed to address elevated juvenile walleye mortality at low adult stock sizes and/or with declining natural recruitment to inform management decisions. [ABSTRACT FROM AUTHOR]

Walleye Sander vitreus natural recruitment has declined in northern Wisconsin lakes over time. Several factors have been implicated to explain Walleye natural recruitment declines in Wisconsin, including climate change, Largemouth Bass Micropterus salmoides interactions, less desirable fish communities, production overharvest, and depensatory effects on recruit survival. Previous research in other systems has suggested that White Crappie Pomoxis annularis negatively influence Walleye recruitment, but interactions between Walleye recruitment and Black Crappie Pomoxis nigromaculatus have not been examined. We evaluated trends between Black Crappie and age‐0 Walleye relative abundance (catch per effort [CPE]) collected in northern Wisconsin during 1991–2017. Specifically, we tested for (1) trends in age‐0 Walleye and Black Crappie CPE over time, (2) a relationship between age‐0 Walleye and Black Crappie CPE, and (3) the influence of several abiotic and biotic covariates (including Black Crappie CPE) on age‐0 Walleye recruitment. Age‐0 Walleye CPE declined and Black Crappie CPE increased significantly during 1991–2017. Within lakes, the relationship between age‐0 Walleye and Black Crappie CPE showed a threshold effect such that age‐0 Walleye CPE was always low when Black Crappie CPE was high. Of the abiotic and biotic covariates tested to explain variability in the age‐0 Walleye and Black Crappie CPE relationship, only Black Crappie CPE was significant. Our results suggest that Black Crappie may negatively influence Walleye natural recruitment; however, we caution that our findings only reveal a pattern and not a mechanistic explanation for negative interactions between the species. Additional research is needed to test for mechanistic interactions between Walleye and Black Crappie and to inform comanagement of these species. [ABSTRACT FROM AUTHOR]

Knowledge of density‐dependent responses of fish populations to exploitation is important for the sustainable management of fisheries and in structuring fish populations to meet angler desires. To better understand the density‐dependent responses of Walleye Sander vitreus to exploitation, we conducted a 10‐year, 50% annual exploitation experiment on Sherman Lake, Wisconsin, during 2007–2016. In the following order, annual exploitation goals were met through liberalized recreational angling regulations, tribal spearfishing, and physical removals (if necessary). Response variables included total and sex‐specific adult density, age‐0 and age‐1 relative abundance, age‐0 to age‐1 survival, length at maturity, individual growth, and population size structure. To control for environmental and interannual influences on adult density and recruitment, unexploited Escanaba Lake, Wisconsin, was used as a reference system. Total and sex‐specific adult density and age‐0 relative abundance did not differ between Sherman and Escanaba lakes. Age‐1 relative abundance was significantly higher and more variable under elevated exploitation compared with the reference lake. Age‐0 to age‐1 survival significantly increased between pretreatment and elevated‐exploitation time periods. Sex‐specific length at maturity significantly declined between pretreatment and elevated‐exploitation time periods. Mean juvenile length at age increased, male asymptotic length declined, and the proportional size distribution of quality‐sized Walleye declined between pretreatment and elevated‐exploitation time periods. Our results suggest that compensatory age‐0 to age‐1 survival and declines in length at maturity interacted to offset elevated‐exploitation effects on adult density. Likewise, density‐dependent growth responses were most evident in juveniles. Although the Sherman Lake Walleye population appeared resilient to elevated exploitation, we caution that this level of long‐term exploitation is likely not sustainable for most Walleye populations due to the findings of previous exploitation studies and observations of depensatory recruitment dynamics in Walleye. [ABSTRACT FROM AUTHOR]

Behavioural responses of fishes to littoral zone habitat enhancements are relatively understudied in diverse fish communities but are critical for understanding overall fish community responses. To advance knowledge on effects of coarse woody habitat (CWH) littoral zone enhancements, we initiated a long‐term study on Sanford Lake, Vilas County, Wisconsin, where 160 trees were added to the littoral zone of the lake in 2018. We tested for short‐term home range responses in muskellunge (Esox masquinongy), smallmouth bass (Micropterus dolomieu) and walleye (Sander vitreus) to this CWH addition. We used radio telemetry data collected premanipulation (2017) and postmanipulation (2018 and 2019) to construct annual home range estimates for each species. Limited kernel density (LKD) estimates, which partially exclude terrestrial areas, were used for estimating 50% and 95% home ranges. Over the course of the three years, average home ranges for each study species increased suggesting a behavioural response to the CWH addition. Muskellunge had the greatest home range estimate increase, followed by smallmouth bass and then walleye. Muskellunge and smallmouth bass had similar home ranges, which were larger than walleye home ranges. Increased home ranges across species could be a searching or deviation from premanipulation equilibrium home range response as a result of the CWH serving as a prey fish refuge, which may make them relatively inaccessible to predators. Our results suggest that fish behavioural responses to CWH additions may be species‐specific and should be taken into consideration prior to implementing littoral habitat enhancements in diverse fish communities. [ABSTRACT FROM AUTHOR]

Sex differentiation in teleost fish is complex and often dictated by genetics, environmental conditions, and population density during critical embryonic/larval development periods. Walleye Sander vitreus have a long propagation and stocking history, and sex ratios of hatchery‐reared Walleye have been variable, typically skewed towards males, and potentially influenced by temperature. In contrast to previous fry and small fingerling Walleye stocking in Wisconsin water bodies, the Wisconsin Walleye Initiative of 2013 focused on the production of extended growth Walleye fingerlings (EGW) stocked out in fall under the assumption of greater survivorship and in response to observed declines in Walleye natural recruitment. Observed sex ratios of adult Walleye in a stocked northern Wisconsin lake chain were suggestive of EGW sex ratios skewed towards females. This lake chain has been under rehabilitation and an aggressive EGW stocking regime due to prolonged Walleye natural recruitment failures. To test whether imbalances in EGW were occurring, we collected 30 EGW from one Wisconsin hatchery in 2019 and about 50 EGW from each of three Wisconsin hatcheries in 2020 to histologically determine sex ratios. In 2019, EGW were about 97% female. In 2020, the percentage of females in hatchery samples ranged from 60% to 100%. Nonfemales in 2019 and 2020 were all undifferentiated. Our results suggest that EGW raised in Wisconsin under similar incubation and rearing protocols may be skewed towards females. If sex ratios of EGW are skewed towards females, the use of EGW may hinder efforts to rehabilitate natural recruitment. A deductive experimental and observational framework will be used to test for mechanism(s) influencing the high percentage of females in the hatchery product to inform protocols to better balance sex ratios. [ABSTRACT FROM AUTHOR]

On June 20, 2021, the Northern Highland Fishery Research Area (NHFRA) celebrated its 75th anniversary of continuous fisheries population monitoring and compulsory angler creel census on five lakes in northern Wisconsin. In 1946, five lakes were designated as experimental fisheries research lakes and all anglers have been required to adhere to the compulsory creel census to record catch information. We review the history of the NHFRA, its role in evaluating experimental regulations, how data derived from the NHFRA were paramount in developing a critical Walleye Sander vitreus management plan for a joint tribal subsistence and recreational angling fishery, discuss the NHFRA as a training ground for early career fisheries professionals, and speculate on its future. By learning from the past and adapting to new challenges and emerging fisheries research needs, the NHFRA is poised to add to its 75‐year legacy of research and training to inform science‐based decision making and to prepare generations of new fisheries professionals. The 75‐year history of the NHFRA exemplifies the importance of adaptation, long‐term data, establishing sentinel lakes for observations of environmental change, field stations, and partnerships for successful fisheries management. [ABSTRACT FROM AUTHOR]

Recruitment declines of walleye, Sander vitreus (Mitchill), observed in some northern Wisconsin lakes have resulted in management actions to evaluate and rehabilitate populations. An effective index for estimating relative abundance of yearling walleye is required. The objectives herein were : (a) to evaluate the relationship between yearling walleye electrofishing CPUE and density in northern Wisconsin lakes; (b) to test for the influence of lake‐specific factors on electrofishing catchability of yearling walleye; and (c) to develop an index whereby electrofishing CPUE can be used to quantify yearling walleye relative abundance. Yearling density was significantly positively related to electrofishing CPUE on a long‐term dataset from Escanaba Lake as well as a dataset including several lakes combined. Electrofishing catchability of yearling walleye was negatively related to lake‐surface area but was not related to other lake‐specific variables. This index can provide an efficient method to continue monitoring natural recruitment and also to evaluate survival of stocked walleye. [ABSTRACT FROM AUTHOR]

Growth information from known‐age Muskellunge Esox masquinongy is relatively rare in the published literature. We tagged all extended‐growth Muskellunge fingerlings stocked into 10 northwestern Wisconsin lakes during 2009–2019 with PIT tags and later recaptured these fish to establish known age and growth. Our objective was to use known age, and length upon recapture of each stocked Muskellunge, to determine sex‐specific asymptotic length (L∞), Brody's growth coefficient (K), and mean length at age using Wang's parameterization of the von Bertalanffy growth function. Our results showed rapid juvenile growth with Muskellunge reaching lengths of about 67 cm by age 3, after which sexually dimorphic growth patterns were displayed and growth rates slowed. For example, the Wisconsin statewide minimum length limit for harvest (102 cm) was not achieved until age 9 for females, with males taking much longer or never achieving this length. Values of L∞ ± SE were 128.5 ± 7.6 cm for females and 102.0 ± 3.3 cm for males. Our study provides a method for managers to collect known age and length data for Muskellunge without sacrificing fish and validates current age and growth of northwestern Wisconsin stocked Muskellunge. [ABSTRACT FROM AUTHOR]

Population size structure and maximum size of managed sportfish populations are dictated by abiotic, biotic, ecosystem, and anthropogenic influences. In their native ranges of northern Wisconsin, muskellunge (Esox masquinongy) and cisco (Coregonus artedi) are co‐adapted cool‐ and cold‐water species where cisco presence may influence population size structure and maximum size of muskellunge. We tested whether muskellunge size structure indices (length‐frequency distributions, proportional size distribution), mean length, and mean maximum length of muskellunge differed when cisco were present or absent in Ceded Territory of Wisconsin (CTWI) lakes during 2015–2018. Cisco presence had a positive influence on size structure and mean length of individual muskellunge within populations. In contrast, cisco presence had no influence on the mean maximum length of muskellunge observed in CTWI populations suggesting that other factors may be better predictors of this metric than cisco presence. In cisco lakes, mean muskellunge length was negatively correlated with mean cisco length suggesting that gape limitation may be a factor influencing population size structure and individual growth rates. Therefore, cisco populations with primarily large individuals may be unavailable to muskellunge as forage. Our results suggest that cisco are an important forage species for some aspects of muskellunge population ecology; however, other factors may also contribute to muskellunge population size structure and maximum size outcomes. As such, conservation of remaining cisco populations in Wisconsin is critical because they influence muskellunge population ecology in lakes where the species coexist. Future research is needed to better understand the interactions of cisco, abiotic and biotic factors, and anthropogenic influences on muskellunge growth dynamics. [ABSTRACT FROM AUTHOR]

Angling for trophy Largemouth Bass Micropterus salmoides and Florida Bass M. salmoides floridanus supports popular fisheries, particularly in the southern United States, where conditions are favorable for growing large fish. Traditional standardized sampling gears, such as electrofishing and creel surveys, often prove ineffective at obtaining sample sizes that are adequate for assessing the quality and temporal trends in trophy fisheries. In this study, we assessed the trophy Florida Bass population in the newly impounded Calling Panther Lake (163 ha), Mississippi, by using a nontraditional, specialized angling technique, and we compared the results with data collected by the more traditional techniques of creel surveys and electrofishing. The specialized angling technique utilized a select few highly skilled and devoted anglers that targeted only the largest bass in the population. The specialized angling technique collected nearly 8 and 24 times more trophy Florida Bass (≥3.6 kg or ≥56 cm TL) than creel surveys and electrofishing, respectively. As a result, this was the only method that reliably collected enough trophy‐sized fish to estimate the population size in Calling Panther Lake. Mark–recapture data were used to estimate an abundance of 150 trophy Florida Bass (95% confidence interval [CI] = 118–206) in 2011 (density = 0.92 fish/ha; 95% CI = 0.73–1.26). The use of data collected by specialized anglers provided vital information for the trophy segment of this bass population, which is often difficult for fisheries managers to obtain with traditional techniques. [ABSTRACT FROM AUTHOR]

Assessment of the Walleye Sander vitreus angling and tribal spearing fisheries in the Ceded Territory of Wisconsin (CTWI) is critical for the sustainability of this resource. Key to these assessments is an understanding of harvest demographics, exploitation, catch and harvest efficiency, and relationships between catch or harvest and adult density. We characterized the size distribution and mean length of harvested Walleyes, harvest, exploitation rate, and catch (angling) or harvest (spearing) rate for both fisheries during 1990–2015. Then, we evaluated catch and harvest rates in relation to adult density and tested for self‐regulation or hyperstability in each fishery. Size distribution and mean length of harvested Walleyes in both fisheries were statistically different but biologically similar. Anglers harvested significantly more Walleyes, and the mean exploitation rate was greater in the angling fishery. Spearfishers had significantly higher mean harvest rates compared with angler catch rates. Catch and harvest rates followed an asymptotic relationship with adult density, with the spear fishery showing more hyperstability than the angling fishery. In the CTWI, naturally reproducing Walleye populations are managed for densities ≥7.4 adults/ha. Our results suggest that maintaining adult Walleye densities near the point of diminishing returns of the asymptotic relationship (10–15 Walleyes/ha) will result in a sustainable fishery that also maximizes tribal harvest and angler catch. However, maintaining adult Walleye densities within this range in the unproductive lakes typical of the CTWI may be unrealistic. Due to the hyperstability observed in each fishery, active management of the spear fishery should continue and monitoring of the angling fishery should also continue given recent declines in natural recruitment and production observed in the CTWI in order to maintain Walleye populations in a "safe operating space." An empirical understanding of CTWI Walleye angler and spearfisher effort dynamics is critically needed to mechanistically explain the observed hyperstability in each fishery. [ABSTRACT FROM AUTHOR]

Abstract: Understanding how fish populations respond to exploitation is critical for sustainable fisheries management. Walleye Sander vitreus have been exploited by tribal spear and angling fisheries in the Ceded Territory of Wisconsin (CTWI) since 1985, and harvest in individual lakes has been regulated using a 35% adult exploitation limit reference point since 1990. We conducted a 35% annual adult Walleye exploitation experiment (1993–1997: baseline exploitation at ~13%; 1998–2008: 35% exploitation) on Big Crooked Lake, Wisconsin, to test for responses in adult, male, female, age‐0, and age‐1 density and sex‐specific mean length at age and proportional size distribution (PSD) indices. Adjacent Wolf Lake was used as the reference system. Adult Walleye density in Big Crooked Lake declined significantly between exploitation periods and was due to the experiment. Adult Walleye density declined from about 16 to 10 fish/ha and was about 7 fish/ha during 2001–2008. Male density declined significantly between exploitation periods, whereas female density did not change. Age‐0 and age‐1 density did not change as a result of the experiment. Male and female mean length at age across several age‐classes increased significantly over time. The PSD indices did not change over time for males, but female PSD‐Quality and PSD‐Preferred increased significantly. Our results suggest that sustained 35% annual exploitation on the Big Crooked Lake Walleye population led to an undesirable adult density (≤7.4/ha) but improved growth. Walleye recruitment did not change in Big Crooked Lake under sustained exploitation; however, we caution that other CTWI populations may respond differently to this level of targeted exploitation. Based on our results, long‐term declines in CTWI Walleye natural recruitment and productivity, and as suggested by other independent studies, we recommend that the limit reference point be lowered to reduce exploitation and be protective of all Walleye populations in the CTWI. [ABSTRACT FROM AUTHOR]

Black bassMicropterusspp. support popular freshwater sport fisheries in North America. Bass anglers commonly adopt catch and release as a conservation practice, and frequently over 75% of angled black bass are released back into the water. If fish survive the angling event, the practice of catch and release as an alternative to harvest reduces direct mortality, but it has the potential to affect the postrelease feeding behavior and survival of the fish. The act of lifting black bass for handling, hook removal, and photograph opportunities may cause stress and injury, and the degree of injury sustained could be influenced by fish size. Holding fish in a tilted grip by the jaw has raised concern among anglers about potential damage to jaw musculature and tendons, as they may not support the fish’s body weight out of water, particularly for trophy bass. We conducted an experiment with Florida Largemouth BassM. salmoides floridanusto evaluate the relative differences in survival, jaw mechanics, and feeding success after the use of three common handling treatments: (1) a vertical hold using a lip-grip device (vertical treatment); (2) a tilted, one-handed grip using only the lower jaw (horizontal treatment); and (3) two-handed support to the lower jaw and body (support treatment). The time taken by fish to regain equilibrium and resume normal swimming behavior after handling differed among the three treatments; the recovery period was shortest for fish in the support treatment (mean ± SD = 7 ± 10 s; vertical treatment: 33 ± 74 s; horizontal treatment: 12 ± 16 s). Minor injuries (e.g., abrasions and sores) and diseases (e.g., tumors and fungus) tended to increase after handling across the entire sample. Results suggested no evidence of handling-specific differences in fish feeding behavior, jaw adjustments, and mortality after release. However, based on our results, we recommend that anglers use two-handed support to handle Florida Largemouth Bass, thus minimizing the mean amount of time for an individual fish to regain equilibrium after an angling event. Received February 22, 2016; accepted October 7, 2016 Published online February 22, 2017 [ABSTRACT FROM AUTHOR]

The relative abundance of the largest size-classes of individuals within a fish population has an important influence on recruitment success. Fishing regulations with a basis in size (e.g., minimum-length limits) can directly impact the abundance of these larger individuals and thus potentially influence recruitment. We analyzed whether recruitment of exploited native Brown TroutSalmo truttapopulations was affected via the extraction of large individuals (>220 mm, i.e., minimum-length limit). The study was replicated temporally (2007–2009) and spatially across seven recreational fishing sections (four exploited and three catch-and-release sections) within the River Tormes located in central Spain. Catch-and-release sections were used as reference points to compare with exploited sections. We tested the hypothesis that minimum-length limit regulations would adversely affect fish recruitment through fishing-induced mortality of large individuals. Spawning stock (measured as fish >220 mm) and young-of-the-year abundances were estimated using multiple-pass depletion methods. We modeled the relationship between spawning stock and subsequent recruitment using a nonparametric approach (generalized additive models) to fit the best stock–recruit relationship. Additionally, von Bertalanffy growth and yield-per-recruit models were generated to evaluate the potential for growth and recruitment overfishing. The restrictive length limits used to regulate harvest in the study area limited both recruitment and adult abundance. The present study provides evidence that the use of minimum-length limit regulations in the management of recreational fisheries has the potential to adversely affect the species’ recruitment. Such adverse impacts could be occurring via both recruitment overfishing and growth overfishing, exemplifying that the removal of the larger size-classes of individuals through recreational fishing could have important consequences for recruitment. Management actions should be directed to protect large individuals (e.g., via harvest slots) rather than promote their removal, thereby reducing the chances of overfishing. Received November 25, 2015; accepted April 18, 2016Published online August 24, 2016 [ABSTRACT FROM AUTHOR]

Fish populations that undergo heavy exploitation and those for which the act of fishing can influence individual brood success are at risk of recruitment effects due to angling. The angling of brood-guarding male black bassMicropterusspp. has been shown to decrease brood success, although there is no evidence that a loss of individual broods has population-level impacts. Therefore, some level of recruitment compensation may influence juvenile bass survival. We sought to measure recruitment compensation and the form of the stock–recruit relationship for a brood-guarding species, the Florida Largemouth BassM. salmoides floridanus(hereafter, Florida Bass). The study was conducted in four north-central Florida lakes during 4 years (2010–2013). We quantified adult stock density by using mark–recapture electrofishing surveys. The estimated broods produced in each spawning season, the number of those broods that were successful, and the age-1 recruit density were quantified via snorkel surveys. We evaluated three models for describing the effects of stock density or successful brood density on recruitment: a proportional (linear; i.e., no compensation) model, a Ricker (dome-shaped) model, and a Beverton–Holt (asymptotic) model. Recruit density was better indicated by the number of successful broods produced than by spawning stock density. Model comparisons indicated that the density-dependent models had the most support, whereas there was no apparent support for the proportional or density-independent model. The Ricker model had the most empirical support overall (estimated parameters:a= 2.2,b= 0.009). Our results indicate that the number of successful broods would have to fall below about 5 broods/ha to generate direct declines in observed average recruitment of Florida Bass. Received August 5, 2015; accepted December 9, 2015 Published online April 14, 2016 [ABSTRACT FROM AUTHOR]

RATIONALE Ammonia (NH3) emissions are a substantial source of nitrogen pollution to sensitive terrestrial, aquatic, and marine ecosystems and dependable quantification of NH3 sources is of growing importance due to recently observed increases in ammonium (NH4+) deposition rates. While determination of the nitrogen isotopic composition of NH3 (δ15N-NH3) can aid in the quantification of NH3 emission sources, existing methods have precluded a comprehensive assessment of δ15N-NH3 values from major emission sources. METHODS We report an approach for the δ15N-NH4+ analysis of low concentration NH4+ samples that couples the bromate oxidation of NH4+ to NO2- and the microbial denitrifier method for δ15N-NO2- analysis. This approach reduces the required sample mass by 50-fold relative to standard elemental analysis (EA) procedures, is capable of high throughput, and eliminates toxic chemicals used in a prior method for the analysis of low concentration samples. Using this approach, we report a comprehensive inventory of δ15N-NH3 values from major emission sources (including livestock operations, marine sources, vehicles, fertilized cornfields) collected using passive sampling devices. RESULTS The δ15N-NH4+ analysis approach developed has a standard deviation of ±0.7‰ and was used to analyze passively collected NH3 emissions with a wide range of ambient NH3 concentrations (0.2 to 165.6 µg/m3). The δ15N-NH3 values reveal that the NH3 emitted from volatilized livestock waste and fertilizer has relatively low δ15N values (-56 to -23‰), allowing it to be differentiated from NH3 emitted from fossil fuel sources that are characterized by relatively high δ15N values (-15 to +2‰). CONCLUSIONS The isotopic source signatures presented in this emission inventory can be used as an additional tool in identifying NH3 emission sources and tracing their transport across localized landscapes and regions. The insight into the transport of NH3 emissions provided by isotopic investigation is an important step in devising strategies to reduce future NH3 emissions, a mounting concern for air quality scientists, epidemiologists, and policy-makers. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We evaluated the influence of sex and reproductive condition on seasonal distribution and movement patterns of Lake Sturgeon Acipenser fulvescens in Namakan Reservoir, Minnesota-Ontario. Blood samples were collected from 133 Lake Sturgeon prior to spawning and plasma concentrations of testosterone and estradiol-17β were analyzed using radioimmunoassay. Steroid concentrations were used to determine sex and the reproductive stage of each sturgeon. A subset of 60 adults were implanted with acoustic transmitters prior to spawning in 2007 and 2008. Movement was monitored using an array of 15 stationary receivers covering U.S. and Canadian waters of Namakan Reservoir and its tributaries. Of the monitored sturgeon, there was no significant difference in the minimum distance traveled between sexes or among seasons. Site residency did not differ between sexes but differed significantly among seasons, and Lake Sturgeon of both sexes had higher residency during winter (mean = 24 d). Five females implanted with transmitters were characterized as presumed reproductive and 14 as nonreproductive based on plasma steroid concentrations. In general, movement patterns (i.e., migration) of presumed reproductive females corresponded positively with availability of spawning habitat in tributaries. Moreover, presumed reproductive females traveled greater distances than nonreproductive females, particularly during prespawn, spawning, and fall time periods. Distance traveled by presumed reproductive females was highest in the fall compared with other seasons and may be linked to increased energy requirements during late oogenesis before spawning in spring. Combining movement data with information on Lake Sturgeon reproductive status and habitat suitability provided a robust approach for understanding their seasonal migration patterns and identifying spawning locations. [ABSTRACT FROM AUTHOR]

Terrestrial and marine photosynthetic organisms emit trace gases, including isoprene and monoterpenes. The resulting emissions can impact the atmosphere through oxidative chemistry and formation of secondary organic aerosol. Large uncertainty exists as to the magnitude of the marine sources of these compounds, their controlling factors, and contribution to marine aerosol. In recent years, the number of relevant studies has increased substantially, necessitating the review of this topic. Isoprene emissions vary with plankton species, chlorophyll concentration, light, and other factors. Remote marine boundary layer isoprene mixing ratios can reach >300 pptv, and extrapolated global ocean fluxes range from <1 to >10 Tg C year-1.Modeling studies using surface chlorophyll concentration as an isoprene emissions proxy suggest variable atmospheric impacts. More information is needed, including emission fluxes of isoprene and monoterpenes from various biogeographical areas, the effects of species and nutrient limitation on emissions, and the aerosol yields via condensation and nucleation, in order to better quantify the atmospheric impacts of marine isoprene and monoterpenes. [ABSTRACT FROM AUTHOR]