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We collected annual gill-net samples of yellow perch Perca flavescens in six South Dakota lakes over 4-5 years. We also simulated the effects of reductions in daily creel limits for yellow perch (i.e., from 25 fish/angler to 5, 10, or 15 fish/angler) and use of minimum total length limits (229 and 254 mm). Population indices varied widely among lakes and among years within lakes to the extent that indices from any individual year were largely uninformative. Creel surveys indicated that few anglers typically achieved a daily creel limit of 25 yellow perch. Except in Waubay Lake, lowering the creel limit from 25 to 5 fish/angler would be necessary to achieve harvest reductions of 25% or more within most of the fisheries we examined. Minimum length limits were projected to improve size and age structure, but harvest reductions often exceeded 50% and yield declined or only slightly increased (by 13%). Yellow perch in these lakes had achieved much of their full growth potential by the time they reached 229 and 254 mm. Consequently, although length limits were predicted to increase age and size structures, asymptotic growth prevented yellow perch from attaining substantially larger sizes. Length limits were predicted to be most beneficial when fishing mortality represented most of the total mortality in each population and when growth occurred at median or fast rates. A 229-mm length limit was predicted to improve size and age structures with less-severe reductions in harvest or yield than a 254-mm limit. Population dynamics and the harvest-oriented nature of yellow perch anglers may dictate that yield maximization is still a reasonable management goal for many South Dakota yellow perch fisheries. Increasing the number of yellow perch that attain 229 mm is possible for certain fisheries if angler harvest represents the dominant source of mortality.

North American black bullhead, Ameiurus melas, which were introduced to Europe in the nineteenth and twentieth centuries, have received relatively little study. With focus on growth and reproduction, this extensive review, which includes new European data, aims to inform the risk analysis process concerning this non-native species in Europe. Surprisingly, the new data for Europe were more comprehensive than for native populations, with data available mainly from Oklahoma, and North and South Dakota (USA). In terms of relative growth, juvenile A. melas were found to have a relatively uniform body shape regardless of the population's origin, whereas adults developed different phenotypes depending upon location. Overall growth trajectory was significantly faster for native than for non-native populations.Growth index values decreased significantly with increasing latitude in non-native but not native populations-the latter decreasing weakly with increasing altitude in the populations located at latitudes \40°. Mean general condition (slope 'b'), mean sex ratio and mean egg diameter did not differ significantly between native and non-native populations. Absolute fecundity was slightly (but not significantly) higher in non-native than native populations. GSI data, which were very scarce for native populations, suggest gonad production may be slightly higher in native than in non-native populations. Precise data on age at maturity (AaM) are lacking for the native range, where 2-5 years is reported. Whereas, in the introduced range the greatest AaM was 3.5 years, and AaM decreases with increasing juvenile growth (TL at age 3). The populations with fastest juvenile growth tended to be from warmer water bodies where they are considered to be invasive. The great growth and life-history plasticity of black bullhead affords the species great potential to invade and establish viable populations in new areas.

We evaluated harvest patterns, exploitation, size selectivity, and angler catch preferences associated with winter fisheries for yellow perch Perca flavescens (i.e., ice fishing) on South Dakota lakes. Seasonal trends in the percentage of anglers targeting yellow perch and in yellow perch harvest were apparent in creel surveys on seven lakes; trends varied among lakes. Exploitation of yellow perch was estimated on two lakes through tag-return studies. Nonreporting rates estimated from surrogate postcards varied between angler groups (19-52%). On East 81 Slough, where the relative stock density (RSD) of yellow perch of 254 mm or longer (RSD-254) was low (RSD-254 ϭ 10), exploitation was only 7% during the winter of 2000-2001; much of the total annual mortality (48%) in the population was attributed to natural causes (40%). Conversely, the estimated exploitation rate on Pelican Lake, where size structure was dominated by larger fish (RSD-254 ϭ 92), was 61% from December to June. Anglers on East 81 Slough demonstrated size-selective harvest of yellow perch, harvesting higher proportions of older, larger fish than were observed in trap-net samples. High percentages of anglers on both lakes reported preferences for catching or harvesting fewer, larger yellow perch rather than catching or harvesting more, but smaller, fish. Variation in the size structure of the yellow perch available to anglers will probably result in variable exploitation rates both among populations and among years within a single population. Angler catch preferences and size selectivity suggest that future management strategies should be designed to provide reasonable numbers of large yellow perch to meet angler desires.

The American Fisheries Society (AFS) has recommended standard gears and methods for collecting North American freshwater fish data, but selectivity of these gears, including gill nets, is poorly described for most species. We calculated contact selectivity for species commonly collected with AFS standard gill nets in lakes and reservoirs of North America, including Black Bullhead Ameiurus melas, Channel Catfish Ictalurus punctatus, Walleye Sander vitreus, and Yellow Perch Perca flavescens. The normal selectivity curve provided the best fit to empirical catch data for all species. Inclusion of a tangle factor improved model fit for Black Bullhead, Channel Catfish, and Walleye, indicating that tangling is an important means of capture for these species. Channel Catfish were more susceptible to tangling than the closely related Black Bullhead, likely because larger Channel Catfish are more vulnerable to tangling by spines in the smallest meshes, whereas Black Bullhead in the same meshes were wedged. Failure to include a tangle factor for Channel Catfish and Walleye would have underestimated peak length of captured fish by 80 and 40 mm, respectively. Tangling was not an important factor in Yellow Perch capture. Total selectivity curves for each species captured with the AFS standard gill net were calculated, and relative selectivity values are provided as correction factors for size-selectivity bias. Our correction factors and modeled selectivity curves for Channel Catfish, Walleye, and Yellow Perch corroborate previous studies that modeled selectivity of the AFS standard gill net for Channel Catfish, Walleye, and Yellow Perch, but our study provided novel information on Black Bullhead. Improved selectivity information for the AFS standard gill net may help to promote further voluntary adoption of AFS standard gears and methods.

The influence of water levels on population characteristics of yellow perch, Perca flavescens (Mitchill), and walleye, Sander vitreus (Mitchill), was evaluated across a range of glacial lakes in north‐eastern South Dakota, USA. Results showed that natural variation in water levels had an important influence on frequently measured fish population characteristics. Yellow perch abundance was significantly (P < 0.10) greater during elevated water levels. Yellow perch size structure, as indexed by the proportional size distribution of quality‐ and preferred‐length fish (PSD and PSD‐P), was significantly greater during low‐water years, as was walleye PSD. Mean relative weight of walleye increased significantly during high‐water periods. The dynamic and unpredictable nature of water‐level fluctuations in glacial lakes ultimately adds complexity to management of these systems.

Saugeyes, a purposeful hybrid between walleye Stizostedion vitreum and sauger S. canadense, were introduced into 336‐ha Richmond Lake, South Dakota, with a management objective of improving the size structure of the population of black crappies Pomoxis nigromaculatus. The objectives of this study were to determine (1) the influence of stocking size on the relative survival of saugeyes, (2) changes in the black crappie population that were potentially associated with the saugeye introduction, and (3) the incidence of black crappies in the diet of saugeyes. Saugeyes were stocked at a total length of 3–4 cm in 1992 and 1993; survival was low. Larger, 14–25‐cm saugeyes were stocked annually from 1994 to 1998, and survival was significantly greater. The larger fingerlings were able to survive and establish a population in the face of predation by and competition with black crappies. Black crappie growth rates increased significantly after the saugeye population was established. Before the saugeye introduction program, a 20‐cm black crappie typically grew less than 25 mm over a year, but by 1999 this had increased to 70 mm. As a result, black crappie size structure increased significantly. Before the saugeye introduction, few black crappies exceeded 25 cm total length, whereas 25‐cm and longer fish were common by 1998 and 1999. Saugeye food habits were monitored seasonally at Richmond Lake during 1998. Saugeyes in all length‐groups consumed age‐0 black crappies during all sampling periods except in early spring, when age‐0 fishes were not yet available. Larger (>20 cm) black crappies were not observed in saugeye stomachs during our study. Thus, the saugeyes in Richmond Lake probably reduced the abundance and intraspecific competition of small black crappies, which resulted in increased growth and improved size structure for crappies.

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