Search

Conservation of sport fisheries and populations of several native fishes in the western United States is dependent on sustained success of removal programs targeting invasive Lake Trout Salvelinus namaycush. Gill-netting of spawning adults is one strategy used to decrease spawning success; however, additional complementary methods are needed to disrupt Lake Trout reproduction where bycatch in gill nets is unacceptable. We developed and tested two portable electrode arrays designed to increase Lake Trout embryo mortality in known spawning areas. Both arrays were powered by existing commercial electrofishing equipment. However, one array was moved across the substrate to simulate being towed behind a boat (i.e., towed array), while the other array was lowered from a boat and energized when sedentary (i.e., sedentary array). The arrays were tested on embryos placed within substrates of known spawning areas. Both arrays increased mortality of embryos (>90%) at the surface of substrates, but only the s...

The efficacy of various sampling gears for age-0 Mountain Whitefish Prosopium williamsoni is largely unknown, which makes it difficult to investigate recruitment and early life history dynamics for the species. We compared four gears: seine, backpack electrofisher, minnow trap, and lighted minnow trap. Gears were tested in backwaters, large channels, and small channels in the Madison River, Montana. No age-0 Mountain Whitefish were captured in minnow traps or lighted minnow traps. Mean CPUE of age-0 Mountain Whitefish was higher for seining (0.18 fish/m2; SD, 0.39) than for electrofishing (0.01 fish/m2; SD, 0.03), and the CV was lower for seining. A broader length distribution was sampled by seining (17–41 mm) than with electrofishing (21–36 mm). Age-0 Mountain Whitefish CPUE in seines was highest in backwaters. In channel sites, Mountain Whitefish presence was associated with areas of still or slow water ≥2 m2. Relative to the other sampling gears we evaluated, seining was the most efficient gear...

There is an urgent need to consider more aggressive and direct interventions for the conservation of freshwater fishes that are threatened by invasive species, habitat loss, and climate change. Conservation introduction (moving a species outside its indigenous range to other areas where conditions are predicted to be more suitable) is one type of translocation strategy that fisheries managers can use to establish new conservation populations in areas of refugia. To date, however, there are few examples of successful conservation-based introductions. Many attempts fail to establish new populations—in part because environmental factors that might influence success are inadequately evaluated before the translocation is implemented. We developed a framework to assess the feasibility of rescuing threatened fish populations through translocation into historically unoccupied stream and lake habitats. The suitability of potential introduction sites was evaluated based on four major components: the recipie...

Given the large amount of resources required for long-term control or eradication projects, it is important to assess strategies and associated costs and outcomes before a particular plan is implemented. We developed a population model to assess the cost-effectiveness of mechanical removal strategies for suppressing long-term abundance of nonnative Lake Trout Salvelinus namaycush in Swan Lake, Montana. We examined the efficacy of targeting life stages (i.e., juveniles or adults) using temporally pulsed fishing effort for reducing abundance and program cost. Exploitation rates were high (0.80 for juveniles and 0.68 for adults) compared with other lakes in the western USA with Lake Trout suppression programs. Harvesting juveniles every year caused the population to decline, whereas harvesting only adults caused the population to increase above carrying capacity. Simultaneous harvest of juveniles and adults was required to cause the population to collapse (i.e., 95% reduction relative to unharvested...

The detrimental impacts of nonnative lake trout Salvelinus namaycush in the western USA have prompted natural resource management agencies in several states to implement lake trout suppression programs. Currently, these programs rely on mechanical removal methods (i.e., gill nets, trap nets, and angling) to capture subadult and adult lake trout. We conducted a study to explore the potential for using high-intensity sound from a relatively small (655.5 cm3 [40 in3]) seismic air gun to reduce survival of lake trout embryos. Lake trout embryos at multiple stages of development were exposed to a single discharge of the seismic air gun at two depths (5 and 15 m) and at two distances from the air gun (0.1 and 2.7 m). Control groups for each developmental stage, distance, and depth were treated identically except that the air gun was not discharged. Mortality in lake trout embryos treated at 0.1 m from the air gun was 100% at 74 daily temperature units in degrees Celsius (TU°C) at both depths. Median mo...

We evaluated the distribution and population characteristics of nonnative lake trout Salvelinus namaycush in Lake McDonald, Glacier National Park, Montana, to provide biological data in support of a potential suppression program. Using ultrasonic telemetry, we identified spatial and temporal distribution patterns by tracking 36 adult lake trout (1,137 relocations). Lake trout rarely occupied depths greater than 30 m and were commonly located in the upper hypolimnion directly below the metalimnion during thermal stratification. After breakdown of the metalimnion in the fall, lake trout primarily aggregated at two spawning sites. Lake trout population characteristics were similar to those of populations within the species’ native range. However, lake trout in Lake McDonald exhibited lower total annual mortality (13.2%), later maturity (age 12 for males, age 15 for females), lower body condition, and slower growth than are typically observed in the southern extent of their range. These results will ...

Few studies have assessed catch-and-release mortality of salmonids at water temperatures of 23°C or above, despite predictions of warming stream temperatures due to climate change. The primary objective of this study was to measure the catch-and-release mortality of rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, and mountain whitefish Prosopium williamsoni in three water temperature treatments, namely, when daily maximum water temperatures were cool (

Pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon S. platorynchus are commonly sampled using drifting trammel nets in the Missouri and Mississippi river basins. Despite the fact that drifting trammel nets have been used for decades to sample these species, little is known about the capture efficiency of this gear. We estimated conditional capture probability for drifting trammel nets over known locations of pallid sturgeon and shovelnose sturgeon. In addition, we examined several variables that were predicted to influence the success of capturing a pallid sturgeon or shovelnose sturgeon in a drifting trammel net. Conditional capture probability (the conditioning factor was known presence) varied from 0.37 on the first attempt to 0.51 on the second attempt. None of the variables measured were useful in explaining the success of sampling a fish in a drifting trammel net. Drifting trammel nets are relatively efficient, and we suggest that they continue to be used to sample pallid sturgeon...

The vectors involved in the spread of whirling disease, which is caused by Myxobolus cerebralis, are only partly understood. However, the parasite has rapidly become established in many regions, suggesting that it is easily disseminated. We gained insight into transport vectors by examining the surface porosity of common wading equipment materials and the adherence of M. cerebralis myxospores to them. Interstitial spaces within rubber, felt, lightweight nylon, and neoprene were measured on scanning electron microscope images. Myxospores were applied to each material, the material was rinsed, and the myxospores recovered to assess adherence. The mean interstitial space size of rubber was the smallest (2.0 μm), whereas that of felt was the largest (31.3 μm). The highest recovery rates were from rubber and the glass control. Percent myxospore recovery varied by material, the recovery from felt being lower than that from all other materials. The potential for felt to carry even small numbers of myxos...

Natural recruitment of pallid sturgeon Scaphirhynchus albus has not been observed in the Missouri River above Fort Peck Reservoir, Montana, for at least 20 years. To augment the population, age-1 hatchery-reared juvenile pallid sturgeon were released in 1998. The objective of this study was to evaluate the habitat use of these fish and compare it with that of indigenous shovelnose sturgeon S. platorynchus. Twenty-nine juvenile pallid sturgeon and 21 indigenous shovelnose sturgeon were implanted with radio transmitters in 2003 and 2004. The two species showed no differences in habitat use in terms of mean depth, cross-sectional relative depth, longitudinal relative depth, column velocity, bottom velocity, and channel width. However, there were seasonal differences within both species for cross-sectional relative depth, column velocity, and channel width. Both shovelnose sturgeon and juvenile pallid sturgeon were primarily associated with silt and sand substrate. However, shovelnose sturgeon were a...

After the introduction of hybrid striped bass (white bass Morone chrysops × striped bass M. saxatilis) into Harlan County Reservoir, Nebraska, gill-net catch per unit effort (CPUE) of walleyes Sander vitreus appeared to decline while that of white bass remained stable. This result prompted the question of whether these three species can be managed collectively in reservoir ecosystems. However, despite the frequency with which these three popular sport fishes coexist in Great Plains reservoirs, we are unaware of any studies that evaluate resource overlap among them. Therefore, we compared their diets, diet overlap, isotopic composition, vertical distribution, and vertical overlap in Harlan County Reservoir from June to September 2002 and 2003. All three species consumed similar prey (i.e., gizzard shad Dorosoma cepedianum and Chironomidae), and diet overlap was high (i.e., Pianka's index > 40) during all months. On no occasion did all three predators consume the same sizes of gizzard shad. Hybrid ...

American water willow Justicia americana has been planted in reservoirs to provide important littoral habitat for fish because of its ability to form dense stands, spread along shorelines, grow in water up to 1.2 m deep, and withstand harsh conditions. The response of water willow to periods of inundation or desiccation has not previously been quantified and is critical for evaluating its potential success in reservoirs. We tested the inundation response of plants at depths of 0.75, 1.50, and 2.25 m for 2, 4, 6, and 8 weeks. Response to desiccation was investigated using drying durations of 2, 4, 6, and 8 weeks. In addition, 2- and 4-week drying periods were tested separately in June, July, and August. Number of leaves, total height, and total dry weight were measured as indicators of plant condition. Condition rapidly declined after inundation for 4 weeks at all experimental depths and plants did not recover by the end of the experiment. A significant decrease in height and increase in leaf numb...

Using backpack electrofishing in three Kansas reservoirs, we investigated the need for block nets when estimating density (fish/ha) and species diversity and determined whether time of sampling affected catch rates (fish/h) of age-0 largemouth bass Micropterus salmoides and age-0 Lepomis spp. and species diversity. Block nets were used to enclose or buoys were used to mark the boundaries of 149 m2 of reservoir surface area. Species richness, diversity, and density of age-0 largemouth bass and Lepomis spp. did not differ significantly between areas enclosed with block nets and areas marked with buoys, but species richness, diversity, and catch rates differed significantly between day and night sampling. Age-0 largemouth bass and Lepomis spp. catch rates, species richness, and species diversity were all significantly higher during night sampling. Our results indicate that use of block nets may not be necessary to estimate age-0 largemouth bass and Lepomis spp. densities, species richness, or divers...

Age structure, total annual mortality, and mortality caps (maximum mortality thresholds established by managers) were investigated for walleye Sander vitreus (formerly Stizostedion vitreum) populations sampled from eight Kansas reservoirs during 1991–1999. We assessed age structure by examining the relative frequency of different ages in the population; total annual mortality of age-2 and older walleyes was estimated by use of a weighted catch curve. To evaluate the utility of mortality caps, we modeled threshold values of mortality by varying growth rates and management objectives. Estimated mortality thresholds were then compared with observed growth and mortality rates. The maximum age of walleyes varied from 5 to 11 years across reservoirs. Age structure was dominated (≥72%) by walleyes age 3 and younger in all reservoirs, corresponding to ages that were not yet vulnerable to harvest. Total annual mortality rates varied from 40.7% to 59.5% across reservoirs and averaged 51.1% overall (SE = 2....

Although biotelemetry has been widely used in fisheries science, the standardization of methods is uncommon. Researchers often use more than one time interval (frequency of recording locations) in a study, and different researchers frequently use different time intervals. There is a paucity of information describing the relationship between time interval used and movement observed or the proportion of time associated with habitat type. The objectives of this study were to evaluate the effects of varying time intervals on fine-scale (i.e., minutes-to-hours) diel movement and habitat use by spotted bass Micropterus punctulatus. To evaluate such effects, we tracked spotted bass (n = 11) every 15 min for a 24-h period. Using these data we simulated tracking at 30-min, 1-h, and 2-h intervals. The mean percent error of time interval simulations for total daily movement varied from 24.3% to 64.3% for 30-min and 2-h intervals, respectively. Loss of movement information (i.e., detecting less movement with...

We compared the growth of walleyes Stizostedion vitreum in Kansas to that of other populations throughout North America and determined the effects of the abundance of gizzard shad Dorosoma cepedianum and temperature on the growth of walleyes in Kansas reservoirs. Age was estimated from scales and otoliths collected from walleyes (N = 2,072) sampled with gill nets from eight Kansas reservoirs during fall in 1991-1999. Age-0 gizzard shad abundance was indexed based on summer seining information, and temperature data were obtained from the National Oceanic and Atmospheric Administration. Parameter estimates of von Bertalanffy growth models indicated that the growth of walleyes in Kansas was more similar to that of southern latitude populations (e.g., Mississippi and Texas) than to that of northern (e.g., Manitoba, Minnesota and South Dakota) or middle latitude (e.g., Colorado and Iowa) populations. Northern and middle latitude populations had lower mean back-calculated lengths at age 1, lower growth...

We evaluated the effects of reservoir hydrology (April/May inflow (m3/s) and April/May storage ratio (reservoir volume at conservation pool/monthly discharge)) and catch per unit effort (CPUE) of gizzard shad Dorosoma cepedianum less than 18 cm long on the CPUE of age-0 white bass Morone chrysops in 16 Kansas reservoirs from 1981 to 2000. Hydrological data were collected from U.S. Geological Survey gauging stations and the U.S. Army Corps of Engineers. Data on gizzard shad CPUE were from summer seine hauls and fall gill-net samples. The recruitment of white bass was indexed using the CPUE of age-0 white bass from fall gill-net samples. The CPUE of age-0 white bass was positively correlated with that of gizzard shad for 44% of the reservoirs, and spring inflow was a positive correlate for 19% of the reservoirs. Variation in the CPUE of age-0 white bass was best explained by a two-variable model (gizzard shad CPUE and April inflow) for only one reservoir. There was no relationship between the CPUE ...

The collapse of the European and Asian caviar industry has raised concern about the overexploitation of shovelnose sturgeon Scaphirhynchus platorynchus in the Missouri River. Unfortunately, little is known about the potential effects of harvest on the population dynamics of this species. Therefore, this study was conducted to describe the population characteristics (e.g., growth, longevity, and mortality) and to determine the influence of exploitation and harvest regulations (minimum length limits) on the yield, size structure, and egg production of shovelnose sturgeon from three sites in the Missouri River using a Beverton–Holt equilibrium model. Despite differences in the population characteristics (e.g., growth and longevity) of shovelnose sturgeon among sites, all populations responded similarly to harvest at the conditional natural mortality rates (death rate in the absence of harvest) used in our simulations (i.e., 5% and 20%). Our simulations of yield indicated that growth overfishing (i.e...

Knowledge of the early life history of sport fish is important for understanding recruitment and population dynamics. Unfortunately, little is known about the early life history of the white bass Morone chrysops. Therefore, this study was conducted to describe the spatial and temporal distribution, age structure, growth, mortality, and food habits of larval white bass in a Kansas reservoir. Larval white bass and zooplankton were sampled weekly from March to July 1999 in Glen Elder Reservoir; 92% of these fish were sampled from the upper reservoir. The larval white bass varied in age from 3 to 35 d and grew approximately 0.32 mm/d. Cohort-specific instantaneous mortality rates varied from 0.02 to 0.15. Differential mortality among early- and late-spawned fish was not apparent. The white bass first hatched during late April and continued hatching until late May. We estimated that most fish spawned during early and mid-May and that spawning activity was closely related to high reservoir inflows (10–...

White bass Morone chrysops were sampled monthly from March 1996 to August 1997 in Fall River Reservoir, Kansas, to document the temporal variation in gonad development, growth, and condition. Both females and males reached sexual maturity at age 2. Mean egg diameter varied temporally, with the largest egg diameters occurring from March through May. Age structure was skewed toward younger ages, with 91% of the females and 94% of the males sampled being less than age 5. Growth in length and weight varied between sexes; females grew faster in both length and weight than males. Mean length and weight varied temporally by sex and year-class. The highest specific growth in length and weight occurred during the summer and fall. During late winter and spring, fish lost up to 7% of the growth in weight from the previous year. The variation in the gonadosomatic index (GSI) for females paralleled that in egg diameter, with the highest GSI values occurring in spring. The decline in weight during late winter ...

Relative weight (W r) is one of several condition indices used to assess the general health of fishes. Standard weight (W s) equations are required to calculate W r, but are unavailable for many nongame and riverine fish species. Therefore, we developed W s equations for the following taxa: longnose gar Lepisosteus osseus, spotted gar L. oculatus, common carp Cyprinus carpio, bigmouth buffalo Ictiobus cyprinellus, river carpsucker Carpiodes carpio, shorthead redhorse Moxostoma macrolepidotum, smallmouth buffalo I. bubalus, white sucker Catostomus commersoni, black bullhead Ameiurus melas, brown bullhead A. nebulosus, flathead catfish Pylodictis olivaris, white catfish A. catus, yellow bullhead A. natalis, white perch Morone americana, yellow bass M. mississippiensis, green sunfish Lepomis cyanellus, rock bass Ambloplites rupestris, and warmouth L. gulosus. These W s equations were evaluated with statistical validation approaches similar to previously defined regression-line-percentile equations. ...

Several studies have indicated that use of scales to age river carpsuckers Carpiodes carpio is difficult. Thus, an alternative body structure may reduce variability in aging this species and provide more accurate estimates of the growth history and age structure of river carpsucker populations. We compared the precision of age determinations and means of back-calculated lengths at age of river carpsuckers between two readers and between the use of scales and dorsal fin ray sections from 172 individual fish collected in the Missouri River. Age agreement between the two readers was 71% for both scales and fin rays. Similarly, age agreement between scales and fin rays within readers was 68% and 72%. Precision of age determination by both readers declined after age-5 for both structures. Generally, more annuli were detected on fin rays than scales as fish age exceeded 5 years. Means of back-calculated lengths for ages 1–4 were significantly greater (P < 0.05) for fin rays than scales. Excluding ages ...

A telephone survey was conducted regarding tournaments for largemouth bass Micropterus salmoides in Kansas reservoirs. A total of 297 Kansas licensed anglers were contacted and asked to be interviewed; these anglers were also respondents to the 1995 Kansas Licensed Angler Use and Preference Survey. Anglers were grouped into three categories: largemouth bass anglers in a sporting club (club), largemouth bass anglers not in a sporting club (nonclub), and nonlargemouth bass anglers not in a sporting club (general). Response rates for angler categories were 77% for club, 88% for nonclub, and 89% for general. More club anglers participated in fishing tournaments in Kansas than nonclub or general anglers. The majority of anglers in all angler categories either agreed or strongly agreed that fishing tournaments should be held on Kansas reservoirs. The majority of anglers in all angler categories disagreed or strongly disagreed with the statement “Fishing tournaments for largemouth bass in Kansas that re...

Weight–length data were compiled from 32 populations of shovelnose sturgeon Scaphirhynchus platorynchus (N = 11,820) from nine states within the geographic distribution of the species. We used the regression-line-percentile technique, which provides a 75th-percentile standard, to develop the standard weight (Ws ) equation. The proposed equation in metric units is log10 Ws = −6.287 + 3.330 log10FL; Ws is weight in grams and FL is fork length in millimeters. The equivalent equation in English units is log10 Ws = −4.266 + 3.330 log10FL; Ws is weight in pounds and FL is fork length in inches. These equations are proposed for use with shovelnose sturgeon between 120 mm (5 in) and 1,050 mm (41 in). Values for relative weight (Wr ) calculated with the Ws equation did not consistently increase or decrease with increasing fish length, indicating absence of length bias. We propose the following length categories for calculation of proportional stock density (PSD) and relative stock densities (RSDs): stock,...

Spotted bass Micropterus punctulatus are popular sport fish in streams and reservoirs throughout the southeastern United States. Despite their popularity, there is a paucity of information on population characteristics and habitat requirements of spotted bass in streams. The purpose of this study was to document the factors that influence spotted bass populations in Kansas streams. Study sites were selected throughout the native range of spotted bass in Kansas. Spotted bass were sampled by electrofishing, and 31 habitat variables were measured at 16 study sites. Linear regression analyses (single and multiple) were used to determine relationships between habitat variables and spotted bass density (number/ha), biomass (kg/ha), catch per effort (CPE; number per minute of electrofishing), relative weight (Wr ), and growth. Variability in density of spotted bass 180 mm or longer was best explained by rootwad area (m2/ha). However, variability in biomass and CPE of spotted bass 180 mm or longer was be...

Paddlefish Polyodon spathula were tagged with 1.25-mm-long coded wire tags (CWTs) to determine rate of tag loss and identify a suitable tagging location. Tag loss was 77% for paddlefish held 51 d in rectangular fiberglass tanks (tank study), and 3% for fish held 96 d in ponds (pond study). We believe the difference in tag loss between the two studies was related to fish behavior. In intensive culture operations, a paddlefish tends to injure the tip of its rostrum by striking i1 against the walls of the tank; thus, it is likely that high tag loss is a result of rostra being continually scraped. Mortality rate of tagged fish in tanks was 4% and not influenced by tagging procedures. In the pond study, paddlefish with tags implanted 5 mm into the distal end of the rostrum, slightly off the center axis, had significantly lower tag loss (0%) than those implanted 2 mm into the center of the ventral side (3%) or 2 mm into the distal end, slightly off the central axis, (3%). However, we recommend implanti...

White crappies Pomoxis annularis were collected from 13 Kansas reservoirs with trap nets and horizontal gill nets. Ten of the reservoirs were sampled concurrently for two or more years. Our objective was to determine if catch per unit effort (CPUE)—the number of stock-length (≥13-cm) white crappies captured per trap-net-night or per gill-net-complement-night—and size structure—indexed by measures of stock density—differed between trap nets and gill nets. We found no significant relation between trap-net and gill-net log10(CPUE). Conversely, size structure of white crappies was similar between gears. Proportional stock density (PSD) and relative stock density of preferred-length fish were positively correlated between gears. Relative stock densities by length category were also significantly correlated between gears. These data indicate that the two gears likely would give similar information about changes in white crappie population size structure, but disparate information about the species' rel...

We collected juvenile striped bass Morone saxatilis and white bass M. chrysops with various gears to evaluate size selectivity and the precision of mean catch per unit effort (CPUE). We used four types of trawls, horizontal and vertical gill nets, conventional electrofishing and electrofishing with a push net, cove rotenone, and bag seine. Trawling was ineffective for sampling juvenile striped bass (

We sampled 22 populations of black crappie Pomoxis nigromaculatus from three ecosystem types (large impoundments, >40 ha; small impoundments, ≤40 ha; natural lakes) to determine the factors that influence population characteristics (recruitment, growth, size structure, and condition) in South Dakota. Recruitment variability was best correlated with the log10 of the shoreline development index (r = 0.63, df = 16) and the log10 of the watershed : lake area ratio (r = 0.89, df = 12). Mean back-calculated length at age was highly variable among ecosystems and was inversely correlated with the log10 of the catch per unit effort (CPUE; r = –0.35 to –0.69). Mean back-calculated length for all ages was positively correlated with mean relative weight (r = 0.48–0.78, df = 18-21). Proportional stock density and relative stock density of preferred-length fish were inversely correlated with log10 CPUE (Spearman correlation, rs = –0.31 to –0.83, df = 21) and were positively correlated with growth of black crap...