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Catostomidae (catostomids) are suckers of the order Cyprinifores and the majority of species are native to North America; however, species in this group are understudied and rarely managed. The popularity in bowfishing and gigging for suckers in the United States has increased concerns related to overfishing. Little information exists about the relative gear effectiveness for sampling catostomids. Our study objective was to evaluate the relative effectiveness of boat electrofishing for sampling Black Redhorse Moxostoma duquesnei, Golden Redhorse M. erythrurum, Northern Hogsucker Hypentelium nigricans, White Sucker, and Spotted Sucker populations in Lake Eucha, OK. We used an information theoretic approach to determine the abiotic variables related to sucker catch per effort (C/f). Our analysis indicated that sucker C/f was highest during night and decreased with increasing water temperature. Sucker size structure was significantly different between daytime and nighttime samples; however, effect size estimates for size structure comparisons indicated size distributions exhibited moderate overlap. Distributional comparisons indicated daytime and nighttime samples were similar for fish >180 mm total length (TL). Effect size estimates also indicated little association between the proportion of each species captured and time of day or water temperature. Night electrofishing in reservoirs at water temperatures from 16-25 ⁰C yielded the most precise C/f estimates, with the highest numbers of suckers collected at water temperatures from 6-15⁰C. Further study of the relationship between abiotic variables and catostomid catchability using various gears would be beneficial to agencies interested in these populations.

Horizontally-oriented echosounders have become more common for sampling pelagic prey species in shallow waterbodies (e.g.

Prey-density data are often used when making management decisions for piscivorous fish species (i.e. stocking rates). Gizzard Shad (Dorosoma cepedianum) are an important prey species in lakes and reservoirs throughout much of the United States. Currently, gill nets are the most common gear used to collect Gizzard Shad data used for deriving population characteristics, but this gear can be time and labor intensive, lacks precision, and may lack accuracy. Horizontally-oriented echosounders may be a better alternative, but accuracy and precision must be measured to determine if this sampling technique produces reliable data. We released Gizzard Shad into a net pen (15-m long × 15-m wide × 4.5-m deep with 6.35-mm square mesh) to produce several different densities of fish. Mean densities were estimated using five passes with a Simrad® EK60 120 kHz split-beam echosounder. Density estimates were acquired by echo-counting and echo-integration. Mean density estimates were then compared to known densities using a linear mixed-effects model and relative standard error (RSE) was calculated for each trial from the five sampling passes. Both echo-counting and echo-integration had slopes not significantly different from one (t = 0.82, d.f. = 13, P = 0.33; t = 3.58, d.f. = 13, P = 0.55) but intercepts that were significantly greater than zero (t = 2.89, d.f. = 88, P

Understanding spatial and temporal fluctuations in animal populations remains a central theme in ecology. Here, we investigated the extent of common carp (Cyprinus carpio) recruitment synchrony across North America in relation to a suite of climatic conditions. Common carp were collected from 21 populations up to a linear distance of 2300 km between the most southern and northern locations. Age-frequency histograms were used to estimate year-class strength, and correlation coefficients were used to evaluate synchrony among populations and environmental variables. We then evaluated relationships between common carp recruitment and winter growing degree-days (GDD), summer GDD, precipitation, wind events, and the El Niño Southern Oscillation Index (ENSO). Common carp recruitment was synchronous up to 756 km but asynchronous at larger scales. Winter and summer GDD, precipitation, and wind were also synchronous among locations up to 1640 km apart. Summer GDD appeared most influential to common carp recruitment but varied across latitudes, with negative effects identified at low latitudes and positive effects identified at higher latitudes. Our results provide new insights into the spatial scale of recruitment synchrony of a non-native freshwater fish and indicate that climatic conditions at local to regional scales likely influence recruitment patterns.

Tandem hoop nets have become the primary gear for sampling channel catfish Ictalurus punctatus, but suffer from high incidences of bycatch, particularly aquatic turtles that usually drown as a result. We sought to determine if bait type, ZOTE© soap and ground cheese logs, would influence catch of channel catfish (CPUE and mean TL) and bycatch of fishes and aquatic turtles. We sampled with tandem hoop nets in 13 Kentucky reservoirs (5–73 ha) using a crossover design and two sampling events. We found no difference in channel catfish catch rates between bait types, but mean sizes of fish caught using ZOTE© soap were approximately 24 mm longer compared to cheese. Fish bycatch was similar between bait types, but tandem hoop nets baited with ZOTE© soap caught up to 61% fewer turtles and mortality of turtles that were captured was up to 12% lower than those baited with cheese. Depth of net set, water temperature, and Secchi depth were environmental factors measured that affected catch and bycatch, but varied among species. Using ZOTE© soap as bait in tandem hoop nets appears to be a fairly simple and straightforward method for maintaining high catch rates of channel catfish while minimizing turtle mortality.

Management of Blue Catfish Ictalurus furcatus and Channel Catfish I. punctatus for trophy production has recently become more common. Typically, trophy management is attempted with length-based regulations that allow for the moderate harvest of small fish but restrict the harvest of larger fish. However, the specific regulations used vary considerably across populations, and no modeling efforts have evaluated their effectiveness. We used simulation modeling to compare total yield, trophy biomass (Btrophy), and sustainability (spawning potential ratio [SPR] > 0.30) of Blue Catfish and Channel Catfish populations under three scenarios: (1) current regulation (typically a length-based trophy regulation), (2) the best-performing minimum length regulation (MLRbest), and (3) the best-performing length-based trophy catfish regulation (LTRbest; “best performing” was defined as the regulation that maximized yield, Btrophy, and sustainability). The Btrophy produced did not differ among the three scenarios. ...

Aquatic vegetation can impact juvenile fishes through multiple pathways. Previous studies have found that dense macrophytes can cause a trade-off of survival for Bluegills Lepomis macrochirus, with decreased foraging efficiency in macrophytes but also decreased predation risk. For juvenile Largemouth Bass Micropterus salmoides, this phenomenon has been proposed but never experimentally tested. In addition, little information exists on the effects of vegetation on juvenile Largemouth Bass prior to the shift to piscivory, a critical period in the recruitment process. Therefore, the objective of this study was to determine if aquatic vegetation reduces the foraging ability of invertivorous (prepiscivorous) juvenile Largemouth Bass. Twenty-four invertivorous juvenile Largemouth Bass were tested individually at each of five stem densities (0, 125, 250, 500, and 1,000 stems/m2) of artificial macrophytes within 20.8-liter aquaria. Five treatments of a simple stem architecture (at all stem densities) and ...

Gill nets are inherently size selective, but selectivity curves can correct this bias. We sampled eight reservoirs with the North American standard gill net to develop a large length-specific data set for six species: Channel Catfish Ictalurus punctatus, hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis), saugeye (Sauger Sander canadensis × Walleye S. vitreus), Walleye, White Bass, and White Crappie Pomoxis annularis. We then used the SELECT (share each lengthclass’s catch total) method to find the best-fit selectivity model to adjust the gill-net catch for contact selectivity. To determine the magnitude of these selectivity corrections, we compared adjusted and unadjusted length frequencies and size indices for each species at each reservoir. The bimodal model was the best fit selectivity model for all species. When selectivity-adjusted length-frequency data were compared with the original data, one-third of hybrid Striped Bass length frequencies and two-thirds of White ...

Previous laboratory studies have demonstrated that turbidity alters prey selection by Largemouth Bass Micropterus salmoides, but this has not been tested in the field. Laboratory studies have also suggested that daily rates of consumption by Largemouth Bass may decline as turbidity increases and that the rate of decline may differ among prey types, possibly providing a mechanism that drives the observed prey selection patterns. We conducted laboratory trials to measure daily consumption rates for Largemouth Bass when foraging on Bluegills Lepomis macrochirus and Gizzard Shad Dorosoma cepedianum; we also collected field data in three reservoir systems (Boomer, Sooner, and Guthrie lakes, Oklahoma) during 2 years to evaluate Largemouth Bass prey selection and consumption rates over a range of turbidity levels. In the laboratory trials, Largemouth Bass daily consumption rates declined with increased turbidity, but the decline was similar between the two prey types. We detected no correlations between ...

State and federal agencies typically introduce aquatic vegetation to increase the recruitment of sport fishes, particularly Largemouth Bass Micropterus salmoides. However, due to frequent turbidity and water-level fluctuations, managers in the southern United States are often left to introduce emergent macrophytes instead of submersed macrophytes. Emergent macrophytes have less underwater structural complexity than most submersed macrophytes and therefore may not be as effective in reducing the predation risk of Largemouth Bass. Therefore, the objective of this study was to determine if American water willow Justicia americana, a common emergent macrophyte species introduced in reservoirs, increases the survival of juvenile Largemouth Bass when exposed to predation. Predator–prey interactions between 10 juvenile and 1 adult Largemouth Bass were observed in tanks with natural densities of American water willow and compared with similar trials in vegetation-free control tanks. Each adult Largemouth ...

Broad-scale niche models are good for examining the potential for invasive species occurrences, but can fall short in providing managers with site-specific locations for monitoring. Using Oklahoma as an example, where invasive bighead carp (Hypophthalmichthys nobilis) are established in certain reservoirs, but predicted to be widely distributed based on broad-scale niche models, we cast bighead carp reproductive ecology in a site-specific geospatial framework to determine their potential establishment in additional reservoirs. Because bighead carp require large, long free-flowing rivers with suitable hydrology for reproduction but can persist in reservoirs, we considered reservoir tributaries with mean annual daily discharge ≥8.5 cubic meters per second (m 3 /s) and quantified the length of their unimpeded portions. In contrast to published broad-scale niche models that identified nearly the entire state as susceptible to invasion, our site-specific models showed that few reservoirs in Oklahoma (N = 9) were suitable for bighead carp establishment. Moreover, this method was rapid and identified sites that could be prioritized for increased study or scrutiny. Our results highlight the importance of considering the environmental characteristics of individual sites, which is often the level at which management efforts are implemented when assessing susceptibility to invasion.

Diel littoral–pelagic migrations by juvenile fish have been suggested as a mechanism that optimizes the trade-off between predation risk and foraging return in open-water habitats. However, previous study designs have not been able to conclusively demonstrate this behavior in the field. We applied a horizontally oriented hydroacoustic transducer, set at the open-water edge of littoral vegetation, to observe diel fish behavior during two summers in Ridge Lake, Illinois, where the fish community is dominated by Largemouth Bass Micropterus salmoides and Bluegills Lepomis macrochirus. Based on acoustically tracked targets, most juvenile fish moved away from vegetated habitat at night and towards vegetation during the day. A greater number of predator-sized fish were observed in the open water during the day than at night and weak acoustic targets, most likely zooplankton, were more abundant in the open-water habitat at night. Therefore, it is likely that the reduced predator abundance and/or activity ...

Gizzard shad, Dorosoma cepedianum (Lesueur), often compose a majority of the prey biomass in southern US reservoirs. Previous studies suggest prey limitation frequently occurs in these systems, suggesting that fisheries managers need tools to evaluate the production potential of the populations they manage. Bioenergetics modelling was used to quantify the abundance of age-0 gizzard shad necessary to sustain multiple piscivore species with diverse growth rates, population sizes, mortality rates and diets. Gizzard shad biomass at the 50th percentile of published values was insufficient to support seven piscivore species in 69% of the simulations, suggesting that above-average prey biomass is required to support multiple piscivore populations at high abundance and growth rates. To help guide management, estimates of the gizzard shad biomass needed to sustain piscivore communities are provided for management situations in which coarse-scale (low, medium or high) growth, population size and percent of shad in diet data are available.

We review the peer-reviewed literature regarding sampling of the three most commonly managed ictalurids: Channel Catfish, Blue Catfish, and Flathead Catfish. For each species, we summarize what is known about data quality (accuracy and precision) and sampling efficiency of the most commonly used gears for surveying these species. We identify research needs and provide information to guide gear selection based on different sampling objectives. To rank gear-specific sampling efficiency (catch/h and catch/person-h), we report median catch rates and the interpolated 25th and 75th percentiles of published means. We also describe the accuracy of relative abundance and size-related metrics for each gear. For Channel Catfish, tandem baited hoop nets provide the most efficient (11–24 fish/net/tandem set, 20–60 fish/person-h) and accurate samples. Low-frequency electrofishing provides the most efficient samples of Blue Catfish (23–373 fish/h, 2.1–11.3 fish/person-h) and Flathead Catfish (19–62 fish/h, 2.1–...

Growing interest in catfish angling, particularly for trophy-sized fish, has resulted in new regulations that limit the harvest of large Blue Catfish Ictalurus furcatus in several states. For these regulations to be effective, released fish must survive to further contribute to the fishery, either through reproduction or subsequent recapture. We investigated the effect of capture depth, hook type, water temperature, and fish size on the delayed hooking mortality of Blue Catfish caught on juglines. Blue Catfish (N = 559) were caught from three Oklahoma reservoirs with either 5/0 circle hooks or J-hooks fished for 24-h sets. One experimental fish (captured via jugline) and one control fish (captured via low-frequency electrofishing) were then placed in field enclosures (N = 25) and monitored for mortality after 72 h. Mean mortality was low at 8.50% (range, 0.00–37.50%; SE, 1.81%). Mortality decreased significantly with decreasing water temperatures (P < 0.01; odds ratio 1.1). Mortality was highest ...

The introduction and spread of invasive species is of great concern to natural resource managers in the United States. To effectively control the spread of these species, managers must be aware of the multitude of dispersal methods used by the organisms. We investigated the potential for survival through the gut of a migrating fish (blue catfish, Ictalurus furcatus) as a dispersal mechanism for two invasive bivalves: zebra mussel (Driessena polymorpha) and Asian clam (Corbicula fluminea). Blue catfish (N = 62) were sampled over several months from Sooner Lake, Oklahoma, transported to a laboratory and held in individual tanks for 48 h. All fecal material was collected and inspected for live mussels. Survival was significantly related to water temperature in the lake at the time of collection, with no mussels surviving above 21.1 C°, whereas 12 % of zebra mussels (N = 939) and 39 % of Asian clams (N = 408) consumed in cooler water survived gut passage. This research demonstrates the potential for blue catfish to serve as a dispersal vector for invasive bivalves at low water temperatures.

For many species of fish, size-specific overwinter mortality is an important factor structuring year-class strength. Protracted spawning by bluegill Lepomis macrochirus leads to extreme variation in individual size going into winter that could result in strong, size-specific overwinter mortality, particularly in locations with limited food resources or long, cold winters. We performed laboratory trials to test the effects of winter temperature (4°C or 9°C) and food availability (food present or no food) on the survival of two size-classes (20–30 or 50–60 mm total length) of young-of-year bluegills. Mortality was strongly size selective and appeared to be related to relative condition, suggesting that energy limitation was the primary mechanism of mortality. Fish of both sizes were less active at colder temperatures, leading to increased survival (presumably via reduced energy expenditure). Bluegills fed heavily in food treatments (wet weight/d consumed was typically 2–4% for both large and small ...

This paper illustrates the use of discrete-choice analysis, a nonmarket valuation technique, for assessing the effect of different management or fishing site quality variables on demand for urban fisheries. The study was carried out in three fishing ponds that are a part of the Close-to-Home Fishing Program in the Oklahoma City metropolitan area. We found that, on average, anglers were willing to pay more for physical infrastructure improvements, such as flush toilets ($3.81/year) and docks ($1.28/year), than for having larger channel catfish Ictalurus punctatus stocked ($0.23/year for a 4-in increase). Willingness to pay for improvements to the ponds was less for minority anglers than for other anglers. Having relative values for potential management changes for a fishery helps to inform fisheries managers about what characteristics are valued most by anglers, allowing managers to better serve the anglers' interest and to justify the costs of implementing these changes.

Current sampling methods for blue catfish Ictalurus furcatus are suspected of being strongly biased against preferred-length fish (≥762 mm in total length [TL]), making it difficult to accurately determine the species' population density and size structure. To understand this potential bias with respect to electrofishing, we conducted seasonal and habitat-specific sampling on three Oklahoma reservoirs using 15-pulse/s DC at the 100–1,000 V setting (the percent of range being adjusted to achieve 4-A output). Temperature, habitat, and reservoir section were analyzed to determine which variables were associated with the highest total catch per unit effort (CPUETotal), the CPUE of preferred-length blue catfish (CPUE762), and the relative stock density of preferred-length fish (RSD762). Total CPUE and CPUE762 were significantly higher when the water temperature was 18°C or more, but the variability increased as the temperature exceeded 28°C. Catch rates were significantly higher in the upper reservoir...

Environmental factors such as turbidity and habitat complexity affect many aspects of aquatic food webs, including predator–prey interactions. We examined the effects of turbidity (0, 5, 10, 20, 40 nephelometric turbidity units [NTU]) and cover (presence or absence) on prey selection by adult smallmouth bass Micropterus dolomieu (mean ± SD = 290 ± 41 mm total length) in laboratory pools. Individual predators were given a choice of five northern crayfish Orconectes virilis, five golden shiners Notemigonus crysoleucas (a pelagic fish), or five round goby Neogobius melanostomus (an invasive benthic fish). Smallmouth bass selected round goby at low turbidities (0 and 5 NTU) and golden shiners at the highest turbidity (40 NTU) in trials without cover. With cover, smallmouth bass increased selectivity for golden shiners, particularly at the turbidity extremes (0, 20, and 40 NTU). Northern crayfish were negatively or neutrally selected in all trials across both turbidity and cover treatments. Turbidity ...

The importance of floodplain lakes to tropical river systems is well established, but little is known about the function of these habitats in temperate river systems. We examined fish diversity, abundance, and reproduction within six oxbow lakes of the Kaskaskia River, Illinois, over 5 years and their relationship to 11 abiotic environmental variables. The lakes were hydrologically dynamic within and among years, varying in the time connected with the main stem (0-22 weeks/year) and the frequency of low (

Turbidity in aquatic systems can change rapidly, affecting the visual ability of predators. Increased turbidity is known to reduce the reactive distance and foraging success of some planktivores and insectivores, leading to decreased growth rates. However, little is known about the effects of turbidity on prey selection by piscivores. We examined the interactions between largemouth bass Micropterus salmoides and their prey in 1.8-m-diameter tanks (58 cm deep) at four turbidity levels (0, 5, 10, and 40 nephelometric turbidity units [NTU]). Prey selectivity was significantly affected by turbidity. At lower turbidity levels (0 and 5 NTU), largemouth bass consumed mostly gizzard shad Dorosoma cepedianum and bluegills Lepomis macrochirus and had negative selectivity for northern crayfish Orconectes virilis. At 10 NTU, all three prey types had similar selectivity, presumably because the largemouth bass had more difficulty in capturing rapidly moving fish prey as their reactive distances decreased. At 4...

Overwinter mortality is an important force structuring year-class strength of many fishes. Conventional wisdom is that overwinter mortality is primarily caused by starvation; however, recent research has demonstrated that piscivores continue to feed during winter and may also contribute to overwinter mortality of their prey populations. We conducted experiments in ten 0.04-ha earthen ponds in central Illinois to assess the effect of predation by largemouth bass Micropterus salmoides on survival of two size-classes (20-30 and 40-65 mm total length [TL]) of age-0 bluegills Lepomis macrochirus. Bluegills (400 fish/size-class) were stocked into each pond at the end of November. Half of the ponds also received five small (90-124 mm TL) and four large (166-192 mm TL) largemouth bass. Survival to the end of the 113-d experiment was higher for large bluegills than for small bluegills in all ponds. For both bluegill size-classes, the predator-present treatment had higher mortality than the predator-free t...

Growth of sympatric populations of three important sport fish species: bluegill Lepomis macrochirus, largemouth bass Micropterus salmoides and channel catfish Ictalurus punctatus ,i n 14 Illinois reservoirs was assessed in an attempt to relate size-specific growth to environmental conditions. Multiple regression relationships for most species and size classes explained a large percentage of the variation in growth. Growth of small bluegill (50 mm total length, LT) showed a strong negative relationship with bluegill catch per unit effort (cpue), per cent littoral area and pH. Large bluegill (150 mm LT) growth was negatively related to Daphnia spp. and benthic macroinvertebrate abundance and lake volume, and positively related to bluegill cpue. Growth of small (100 mm LT) and large (250 mm LT) largemouth bass was not well explained by any of the measured variables. Growth of both small (300 mm LT) and large (450 mm LT) channel catfish was strongly positively related to forage fishes and ichthyoplankton abundance, and per cent littoral area while negatively related to benthic macroinvertebrates. By identifying environmental conditions associated with increased growth rates, these models provide direction for managing fish populations and suggest testable hypotheses for future study of the complex interactions between environmental conditions and growth. # 2007 The Authors Journal compilation # 2007 The Fisheries Society of the British Isles

Bluegill Lepomis macrochirus, gizzard shad Dorosoma cepedianum, and largemouth bass Micropterus salmoides are common lentic species that may compete for invertebrate prey resources, and interactions among these species can have important consequences for aquatic community structure. Differential foraging behavior of bluegills and gizzard shad as juveniles, for example, may structure zooplankton and benthos communities and influence the growth of juvenile largemouth bass. We conducted a mesocosm experiment (1.6-m-diameter circular tanks) in which we allowed high and low densities of juvenile bluegills (70–100 mm total length [TL]) and gizzard shad (135–155 mm TL) to forage on established zooplankton and benthos communities for 6 weeks. After this period, we added juvenile largemouth bass (50–80 mm TL) to each tank for 4 weeks to examine growth and diets. Although foraging by bluegill and gizzard shad had limited effects on the total population densities of invertebrates, important taxon-specific e...

Understanding sampling effectiveness is critical to gear selection and the determination of larval fish dynamics. We evaluated bow-mounted push nets for collecting larval fish across reservoirs and habitats and compared them with traditional tow nets. By means of a pushed 0.5-m-diameter conical net and towed 0.5-m-diameter and 0.75-m-diameter conical nets, ichthyoplankton samples were taken during daylight hours from May to July on 21 reservoirs that varied in morphological and environmental characteristics. The push net had higher catches than the same-diameter tow net. However, the push net was not as efficient as the larger-sized tow net in July, when larvae are larger. For pelagic habitats, bow-mounted push nets or large tow nets will sample the larval fish community more efficiently than traditional 0.5-m-diameter conical tow nets. We also assessed push nets for sampling nearshore littoral habitats (

We used three different sizes of trap nets (small, medium, and large sizes of both mesh and throats) sampled at 6-h intervals to determine peak activity time(s) for fish along the deep vegetation line in Sandy Lake, Portage County, Ohio. Over 90% of the total catch comprised bluegill Lepomis macrochirus, largemouth bass Micropterus salmoides, pumpkinseed L. gibbosus, and black crappie Pomoxis nigromaculatus. All four species had their lowest catch per unit effort (CPUE) at night (2200–0400 hours). Different length-classes of pumpkinseeds and black crappies had peak CPUE during different times of the day. Smaller length-classes of all species (i.e., those captured in small and medium trap nets) had peak CPUE during either dawn (0400–1000 hours) or midday (1000–1600 hours), whereas the only piscivores captured in high abundance (black crappies 150–303 mm total length captured in large trap nets) had higher CPUE at dusk (1600–2200 hours) than during any other time of the day. It is possible that the...

Trap nets of varying design are commonly used to assess fish populations, but the effect of the design on gear selectivity is not well known. In particular, it may be advantageous to use multiple net designs with different mesh and throat sizes to maximize the catch of specific length-classes and to minimize the risk of predation on small fish by larger fish. We compared the species composition, catch rate, and length distribution of fishes caught by three trap net designs with dimensions differing only in mesh size and throat size (0.6-cm delta mesh and 3.8-cm × 3.8-cm square throats, 1.3-cm square mesh and 7.6-cm × 7.6-cm square throats, or 2.5-cm square mesh and 12.7-cm × 12.7-cm square throats). A total of 3,473 fish of 18 species were captured from Sandy Lake, Portage County, Ohio, during 24 sample dates from June to August 1999. The large net design had a significantly higher average number of species captured (mean = 11) than the medium or small net design (means = 9 and 8, respectively). ...

Little is known about nocturnal habitat selection by fishes under the risk of predation. Using a photoperiod of 15 h light : 9 h dark, we quantified the diel use of artificial macrophytes and open water by two size-classes of bluegill Lepomis macrochirus when the open water was empty (control), contained food, or contained both a caged predator and food. Small bluegills (6.2–7.7 cm total length) spent significantly more time in macrophytes in the predator and food treatment than in the control, followed by the food-only treatment. In addition, small bluegills spent significantly more time in macrophytes during the day than at night in all treatments. The frequency with which small bluegills were found in the same location in subsequent observations was significantly higher in the predator and food treatment during the day than in any other treatment and light combination. Large bluegills (10.2–13.0 cm total length) showed no difference in habitat use among treatments but spent significantly less ...

The functions of an organism‘s morphological structures indicatethe organism‘s potential resource use (fundamental niche). Whilethis information often is also used to predict differences inactual resource use (realized niche) among individuals or species,such predictions may not be accurate because the maximum abilitiesmay not be useful to the organism under specific conditions or inspecific environments. We investigated the importance of sixpreviously studied morphologically based performanceabilities/constraints in structuring the diet of Menidiaberyllina (inland silverside) and Lepomis megalotis (longearsunfish) in Lake Texoma, a reservoir in the Red River basin(Oklahoma-Texas, USA). Of the six morphological characteristicsmeasured (number of gill rakers, length of gill rakers, spacebetween gill rakers, eye lens diameter, mouth size, mouthprotrusibility), only one characteristic for M. beryllina(mouth size) and three for L. megalotis (space betweenrakers, mouth size, and raker length) correlated with the gutcontents as predicted by previous functional morphology studies.This indicates that caution should be exercised when makinguntested predictions about the ecology of an organism based on itsfunctional morphology.

Spatialstructuringinreservoirfishpopulationscanexistbecauseofenvironmentalgradients,species-specific behaviour or even localised fishing effort. The present study investigated whether white crappie exhibited evidence of improved population structure where the northern more productive half of a lake is closed to fishing to provide waterfowl hunting opportunities. Population response to angling was modelled for each substock of white crappie (north (protected) and south (unprotected) areas), the entire lake (single-stock model) and by combining simulations of the two independent substock models (additive model). White crappie in the protected area were more abundant, consisting of larger, older individuals,andexhibitedalowertotalannualmortalityratethanintheunprotectedarea.Populationmodellingfoundthat fishing mortality rates between 0.1 and 0.3 resulted in sustainable populations (spawning potential ratios (SPR) .0.30). The population in the unprotected area appeared to be more resilient (SPR.0.30) at the higher fishing intensities (0.35-0.55). Considered additively, the whole-lake fishery appeared more resilient than when modelled as a single- panmictic stock. These results provided evidence of spatial structuring in reservoir fish populations, and we recommend model assessments used to guide management decisions should consider those spatial differences in other populations where they exist. Additional keywords: aquatic protected areas, environmental gradients, population dynamics, population model, spatial complexity, sustainability, yield.