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, 2.1–2.5 fish/person‐h) and the most accurate samples of Blue Catfish. No accuracy studies exist for Flathead Catfish. Other gears examined for each species may also be useful for some sampling objectives; however, most are inefficient or lack accuracy.

Turbidity in aquatic systems can change rapidly, affecting the visual ability of predators.

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 Bass length frequencies were significantly different (unadjusted distributions underestimated smaller length classes). Roughly one‐third of the proportional size distributions (PSDs) from all species analyzed showed meaningful changes (≥5 PSD units) after selectivity adjustments were made (unadjusted PSDs were too large). By correcting for contact selectivity the data are improved, and at times the adjustments can be large enough to alter management decisions. Therefore, we recommend that selectivity adjustments should become a part of routine data analysis for the design of the North American standardized gill net as this will improve data for fisheries management. Received September 1, 2015; accepted December 21, 2015 Published online May 16, 2016

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 had a greater effect than cover on prey consumption rate, which decreased as turbidity increased. Our results suggest that turbidity and cover, two important environmental variables, can influence prey selectivity by smallmouth bass.

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 section for all length‐groups, and no differences in CPUETotal were detected among habitats (channels, points, or flats). Both CPUE762 and RSD762 were highest in channel habitats, but the high variability and low catch rates of these larger fish limit the utility of habitat‐specific sampling based on these findings. Additionally, we evaluated the capture efficiency of electrofishing by creating a population with a known length‐frequency distribution. This population was sampled on three separate dates to determine which length‐groups were more vulnerable to electrofishing. No significant differences in catch rate were detected among the length‐groups, and the mean total catch from each sample was always less than 10% of the total population. Our results indicate that low‐frequency electrofishing is not size selective and provides representative samples of blue catfish between 200 and 1,000 mm TL. We recommend that sampling be conducted at temperatures between 18°C and 28°C and that standard sampling protocols adopt a stratified design that incorporates reservoir section.

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. For each fishery, the MLRbest and LTRbest produced greater yield (>22% more) than the current regulation and maintained sustainability at higher finite exploitation rates (>0.30) than the current regulation. The MLRbest and LTRbest produced similar yields and SPRs for Channel Catfish and similar yields for Blue Catfish; however, the MLRbest for Blue Catfish produced more resilient fisheries (higher SPR) than the LTRbest. Overall, the variation in yield, Btrophy, and SPR among populations was greater than the variation among regulations applied to any given population, suggesting that population‐specific regulations may be preferable to regulations applied to geographic regions. We conclude that LTRs are useful for improving catfish yield and maintaining sustainability without overly restricting harvest but are not effective at increasing the Btrophy of catfish. Received February 1, 2016; accepted June 16, 2016

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 time in macrophytes at night than during the day. There was no difference in the frequency with which large bluegills were found in the same location in subsequent observations among treatments or light levels. This suggests the potential for a diel littoral−pelagic habitat change by juvenile bluegills that would have important implications for the role of bluegills in lake food webs, including the possibility of nutrient translocation that could generate alternate stable states in lakes.

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 ϫ 3.8cm square throats, 1.3-cm square mesh and 7.6-cm ϫ 7.6-cm square throats, or 2.5-cm square mesh and 12.7-cm ϫ 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 ϭ 11) than the medium or small net design (means ϭ 9 and 8, respectively). Whereas nets with larger mesh and throat size combinations typically caught larger fish for the six most commonly captured species, only rarely did nets capture fish as large or as small as possible based on their physical dimensions. Specific length-classes of some species were not captured in the nets or were very net design specific, indicating a possible difference in trap net vulnerability of different ontogenetic stages. We conclude that data from trap nets with different mesh and throat sizes should not be directly compared with each other, and that multiple net mesh and throat sizes (or even multiple gear types) should be used when a more complete picture of fish length and abundance is desired.