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Silver carp (Hypophthalmichthys molitrix Valenciennes, 1844) have been invading North American rivers for decades, often altering zooplankton community structure and impacting native fishes. Silver carp invaded eastern South Dakota tributaries of the Missouri River in the early 2000s. Changes in dynamic rate functions can occur as invasive populations move to the latter stages of the invasion curve, but direct temporal assessments of silver carp populations are limited. Our objectives were to compare current growth of silver carp 1) between the Big Sioux and James rivers in South Dakota and 2) with previous growth recorded from the early stages of invasion (2009-2012) in these rivers. We collected silver carp in May and June of 2020-2022 using boat electrofishing and cast netting. We extracted lapilli otoliths for consensus aging from 99 and 82 silver carp from the Big Sioux and James rivers, respectively. We evaluated growth for each population using Bayesian von Bertalanffy models and compared posterior mean length at ages 2-5 to determine the probabilities of differences between rivers and with estimates from the introduction stage. Posterior estimated mean L8 values were similar between the Big Sioux (714 mm) and James rivers (709 mm); however, the probability that the posterior mean K estimate was greater for silver carp in the James River (0.271) than the Big Sioux River (0.248) was >99.9%. Estimated mean lengths at age 2 were larger in the Big Sioux and James samples than during the introduction stage, but mean lengths at ages 3-5 were smaller. Changes in growth characteristics indicate that growth has slowed in the current establishment stage of invasion from the earlier introduction stage. [ABSTRACT FROM AUTHOR]

We used a long‐term data set (2000–2016) of larval, age‐0 (juvenile), and age‐2 Yellow Perch Perca flavescens catches from nine glacial lakes in eastern South Dakota to track multiple cohorts through time to determine whether year‐class strength (measured as gill‐net CPUE of age‐2 fish) could be indexed at the larval or juvenile stage. We observed a strong relationship between larval and juvenile abundance (r = 0.78), but neither were related to abundance of the same cohort at age 2. Furthermore, categorical analyses suggested that some of the strongest age‐2 year‐classes corresponded with the lowest larval and juvenile catches and vice versa. Our assessment suggests that Yellow Perch year‐class strength in eastern South Dakota glacial lakes may not be fixed until some point after the juvenile (i.e., fall age 0) stage and correspondingly that values for larval and juvenile CPUE are of limited utility as early indices of year‐class strength for Yellow Perch. Before using abundance estimates at early life stages as measures of recruitment, researchers and managers should confirm that these estimates provide a meaningful index of abundance at adulthood or the point of recruitment to the fishery. [ABSTRACT FROM AUTHOR]

Localized hypoxia can reduce available habitat, restrict movement and limit the abundance of aquatic invertebrates. Although cultural eutrophication, coupled with the effects of climate change, is likely to increase the frequency and extent of hypoxia in aquatic ecosystems, little is known about how oxygen gradients in small reservoirs influence spatial distribution and abundance of aquatic invertebrates. The present study evaluated the effects of environmental and biological attributes on seasonal and spatial variation of macroinvertebrates and explored how hypoxic conditions influenced littoral, benthic and pelagic macroinvertebrate communities in Lake Alvin, South Dakota. Data on reservoir conditions, in conjunction with macroinvertebrate sampling from May to October 2009–2011, were applied in an information theoretic approach to evaluate factors affecting invertebrate abundance. Hypoxic conditions were present from May to September in the lacustrine zone impacting 10%–39% of the water column. Benthic invertebrates were typically absent from the lacustrine zone during periods of severe hypoxia and were most abundant in the shallow, well‐oxygenated riverine zone. Littoral invertebrates were negatively related to the per cent of the hypoxic water column, suggesting fish, confined to shallow waters by hypoxia, may be consuming a larger portion of littoral invertebrates in their diets. Cladocera and Copepoda densities were influenced primarily by water depth and monthly precipitation. The larger size of Daphnia found in the hypoxic‐prone transitional and lacustrine zones suggested low oxygen concentrations may provide a refuge from fish predation. The results of the present study demonstrated spatial variations in near‐bottom oxygen concentrations were important predictors of macroinvertebrate and zooplankton abundance and size structure in Lake Alvin and that macroinvertebrates, particularly benthic and littoral invertebrates, could benefit from measures taken to reduce summer hypoxia. [ABSTRACT FROM AUTHOR]

Catfish are popular with anglers fishing southeastern South Dakota rivers, and a group of anglers has expressed concern about the perceived overharvest of trophy‐size catfish. However, existing data are insufficient for determining whether Flathead Catfish Pylodictis olivaris and Channel Catfish Ictalurus punctatus are being overharvested. Our objective was to determine the population dynamics of Flathead and Channel catfish and model potential outcomes of length‐based trophy regulations (one fish and no fish harvested over 610 mm) in the lower James River, South Dakota. Multiple gears were used to collect Flathead Catfish (low‐frequency electrofishing and trotlines) and Channel Catfish (baited hoop nets and low‐frequency electrofishing) during 2018, and samples were augmented with angler‐caught catfish collected from three angling tournaments. Pectoral spines were removed from a subsample of fish for age estimation; 305‐mm and larger fish received a Carlin dangler tag with a reward value of US$0, $10, or $100. Growth rates were slow to moderate for Flathead Catfish and moderate for Channel Catfish. Trophy‐size Flathead Catfish (TL ≥ 1,020 mm) were sampled, but few of the collected Channel Catfish exceeded preferred length (TL ≥ 610 mm). Total annual mortality was estimated at 25.7% for Flathead Catfish and 25.2% for Channel Catfish. Exploitation estimated from angler reward tag returns was less than 1% for each species. Yield‐per‐recruit models indicated that a regulation specifying one fish over 610 mm would slightly reduce yield for both species but would only increase the number of memorable‐length Flathead Catfish (860 mm) and Channel Catfish (710 mm) by less than 1%. A no‐harvest regulation would substantially reduce yield of Flathead Catfish and would increase the number of memorable‐length Flathead Catfish by approximately 2% and Channel Catfish by less than 1%. Information obtained during this study suggests that current Flathead and Channel Catfish populations have limited trophy potential and that length‐based trophy regulations would have limited impact on the abundance of large catfish in the lower James River. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 = 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 = 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. [ABSTRACT FROM AUTHOR]

Age-0 white bass Morone c so s were sampled during late summer-earlyfall from 1984 to 1993 in Enemy Swim and Pickerel lakes, South Dakota, with a bottom trawl. Age-0 white bass catch per unit effort (CPUE)among years was correlated (r=0.69; P=0.027) between these two natural lakes, indicating that environmental factors were likely affectingwhite bass recruitment similarly in the two water bodies. Therefore,we assessed climatological variables to help explain variability in abundance of age-0 white bass among years. Age-0 white bass abundancewas positively correlated with mean daily air temperature during June in both Enemy Swim (r=0.63; P=0.051) and Pickerel (r=0.62; P=0.056)lakes. In addition, multiple regression analysis indicated that precipitation and temperature jointly and positively influenced age-0 white bass abundance in both lakes. Although these are not necessarily cause-and-effect relations, they do provide insight into the importance of environmental conditions for successful recruitment of white bass in South Dakota natural lakes. [ABSTRACT FROM AUTHOR]