K. D. Steffensen

Assessment of Hatchery-Reared Pallid Sturgeon Survival in the Lower Missouri River

Abstract The population of pallid sturgeon Scaphirhynchus albus in the lower Missouri River between Gavins Point Dam (river kilometer [rkm] 1,305.2) and the confluence with the Mississippi River (rkm 0.0) remains imperiled, little to no natural recruitment occurring. Artificial propagation and subsequent population augmentation (i.e., stocking) may be the only viable option for maintaining pallid sturgeon populations in the lower Missouri River in the near term. Because relatively little is known about the ability of hatchery-reared pallid sturgeon to survive, the objective of this study was to quantify survival estimates for hatchery-reared pallid sturgeon stocked into the lower Missouri River. We used stock–recapture data collected from 1994 to 2008 to derive survival estimates based on the Cormack–Jolly–Seber model within program MARK. Since 1994, a total of 78,244 hatchery-reared pallid sturgeon have been released and 1% of these have been recaptured. Recapture numbers by size at stocking were as foll...

Population Size of Hatchery-Reared and Wild Pallid Sturgeon in the Lower Missouri River

Abstract The population size of pallid sturgeon Scaphirhynchus albus is currently unknown throughout much of the Missouri River. Listed as federally endangered in 1990, the pallid sturgeon remains one of the rarest fishes in the Missouri and Mississippi River basins, and little to no natural recruitment occurs. Artificial population supplementation via a hatchery propagation program was initiated, necessitating the collection of sexually mature pallid sturgeon. Therefore, the Nebraska Game and Parks Commission maintained an intensive broodstock collection and mark–recapture effort from 2008 to 2010 to capture reproductively ready adults for the propagation program. Coordinated crews fished baited trotlines from the confluence of the Platte and Missouri rivers at river kilometer (rkm) 957.6 to a point about 80.5 rkm downstream. A total of 438 pallid sturgeon were captured, which amounts to a 7.8% recapture rate. The objectives of the study were to (1) use these data to estimate the annual population sizes ...

Fish community response to floodplain inundation in a regulated river

Floodplain connectivity has been identified as an important element of river ecosystem function for enhancing biological productivity, yet most of the worlds large rivers have been managed to reduce river–floodplain connectivity to protect human interests. Flow events in the Missouri River basin during the summers of 2010 and 2011 offered a unique opportunity to investigate the influence of floodplain connectivity on fish communities. The floods created aquatic habitats not generally available on the main stem and the magnitude and duration of the 2011 event have not occurred since the main-stem dams were closed. Therefore, the objectives were to: (1) document species use on available floodplain habitats and assess age-0 fish presence, (2) compare spatial and temporal distribution of fish species, and (3) evaluate fish community responses at different discharges. Age-0 fish dominated the fish community during the 2010 and 2011 floods, representing 90% and 94% of all fish collected each year. Species composition during the 2011 flood was different above and below the Platte and Missouri rivers confluence (ANOSIM; r = 0.211; p < 0.001) and between individual sites (r = 0.667; p < 0.001) but did not change temporally (r = 0.086; p = 0.244). Comparison of the age-0 fish community response to varying water levels also differed (r = 0.619; p = 0.038) annually. The effects of this flood on the fish community of the Missouri River initially appear to have been beneficial for the native fish community; however, continued research and evaluation will verify the floods effects.

Comparison of Green and White Mesh Trammel Nets and Gill Nets to Assess the Fish Community in a Large River

Abstract Standardized monitoring programs in great rivers need to identify and minimize the bias in the estimates of fish population characteristics to enable fishery managers to make informed decisions. We compared the effectiveness of green and white mesh in drifted trammel and anchored gill nets in capturing fish in the Missouri River from downstream of Fort Randall Dam, South Dakota, to the mouth of the river near St. Louis, Missouri. Sampling occurred from March to November 2006 and from April to May 2007. Paired green and white trammel net drifts (N = 383) caught 28 fish species from 12 families. Pairs of anchored gill nets set overnight (N = 193) caught 24 fish species from 12 families. Chi-square tests indicated that for most species there were no significant differences in occurrence between mesh colors in both the trammel and gill nets. However, occurrence was significantly higher in white mesh nets for goldeye Hiodon alosoides and blue sucker Cycleptus elongatus in trammel nets and for river ca...

Variability in Age Estimation Results in Ambiguity and False Understanding of Population Persistence

AbstractMortality, growth, and recruitment are the primary dynamic rate functions that regulate fish populations. Age data obtained from calcified structures can provide direct and indirect information needed for calculations of these metrics; therefore, knowledge of the fish population age structure is often coveted information. Unfortunately, potential sources of error exist in the form of subjectivity in interpretation of growth increments, inconsistent deposition of growth increments, and lack of validation in age-estimation processes. However, many sources of error are either not known or simply ignored, particularly for long-lived fishes. Therefore, we included a level of uncertainty in our age estimates of a periodic life history strategist, the Shovelnose Sturgeon Scaphirhynchus platorynchus, by incorporating variability in reader assignment of age. We used a bootstrapping procedure to generate a matrix of new age distributions and demonstrated how calculations of mortality varied as a result of r...

Using Lindgren–Pitman Hook Timers to Understand the Dynamics of Trotline Catches in a Large River

Abstract Trotlines have historically been used by commercial fishers to target ictalurids and have recently been shown to be effective for collecting sturgeons Scaphirhynchus spp. However, little is known about the gear–fish interaction after trotlines are deployed. Therefore, the objectives of this study were to determine whether trotlines equipped with Lindgren-Pitman (LP) hook timers could withstand harsh riverine conditions and whether catch rates, retention rates of hooked fish, capture times of targeted species, and bycatch would be affected. Our results showed no difference between standardized trotlines and trotlines with hook timers and indicated that 31% of pulled hook timers resulted in no fish being collected. Hook timers were activated by 69% of all the fish collected. The majority of fish collected were shovelnose sturgeon S. platorynchus (77%), of which 70% activated the timer. The fork length of the shovelnose sturgeon that did activate the timer (571.0 ± 60.1 mm [mean ± SE]) did not diffe...

Assessment of pallid sturgeon relative condition in the upper channelized Missouri River

ABSTRACT During the spring 2015 sampling efforts on the Missouri River, several adult pallid sturgeon (Scaphirhynchus albus) were captured in a visually emaciated condition. As pallid sturgeon recovery efforts continue throughout the Missouri River, this may negatively impact the local population and hamper recovery. Therefore, the objectives were to (1) assess the annual variation in pallid sturgeon condition, (2) determine how condition varies amongst gender and reproductive status and if condition affects fecundity, (3) determine the annual proportion of reproductive female pallid sturgeon, and (4) test several hypothesized factors which may contribute to variations in pallid sturgeon condition. Overall, the relative condition of pallid sturgeon has significantly declined over the past 12 years, except for the large adult-sized fish (> 840 mm fork length). Pallid sturgeon condition began to decline in 2013 then rapidly declined in 2014 and even more in 2015. The mean annual pallid sturgeon condition reached record lows in 2015. Females had a higher overall Kn compared to males and sexually reproductive fish had a significantly higher Kn for both genders. Overall, 28% of the females captured have been in reproductive condition; however, that frequency appears to be declining with condition. Also, relative condition was not correlated with the number of eggs released by reproductively ready females. Correlation between pallid sturgeon condition and hypothesized variables did not result in any statistically significant relationships that would explain the variations in pallid sturgeon condition. As pallid sturgeon recovery continues throughout the lower Missouri River, concern arises over whether or not the current habitat available and river management can support a viable pallid sturgeon population.

Conditional Capture Probability of Pallid Sturgeon in Benthic Trawls

AbstractLong-term population monitoring assumes that relative abundance reflects trends in the population. Sampling efficiency and capture probability are assumed to be consistent so samples can be temporally and spatially compared. Benthic otter trawls are being used for a long-term monitoring project on the Missouri River. To estimate the capture probability of Pallid Sturgeon Scaphirhynchus albus, we used acoustic telemetry to locate and target tagged sturgeon with benthic otter trawls. Conditional capture probability (pi*) of a fish in a known location was only 0.08 on the first pass, increased slightly (pi* = 0.18) on the second pass, and again on the third pass (pi* = 0.26). Individual habitat parameters or their interactions did not explain when Pallid Sturgeon were successfully or unsuccessfully captured. Our study suggests that otter trawls are a highly inefficient gear for capturing Scaphirhynchus species. Therefore, relative abundance indices based on otter trawl captures need to be assessed ca...

A comparison of fish catch rate with two different benthic trawls in the Missouri River.

ABSTRACT Trawling is commonly used to assess abundance, distribution, and diversity of fish assemblages as well as to commercially harvest various species of fish. We compared fish community structure and total catch of a 4.9-m otter trawl (OT16; 19-mm bar mesh body with a 6-mm mesh cod end) with a smaller mesh trawl of similar physical dimensions (OT01; composed entirely of 4-mm bar mesh). Total catch from both trawls revealed a trend toward the capture of smaller-sized individuals in the OTO1 and larger individuals in the OT16; however, both trawls provided a high degree of overlap in species richness and diversity. Shannons index values (H′) were 2.47 and 2.40 for the OT16 and the OT01, respectively, signifying that both of these trawls caught a diverse assortment of fishes, regardless of mesh size. An analysis of similarity test resulted in strong similarities in fish assemblage composition between both trawls, corroborating diversity indices. Our results indicate that 19-mm and 4-mm bar mesh are both effective mesh sizes to collect a variety of benthic fish species of various size classes in the Missouri River.

Population Characteristics of Northern Pike in a Southern Kansas Impoundment

Northern pike, Esox lucius, were historically stocked throughout Kansas; however, lack of suitable habitat generally led to the senescence of these populations. Currently, Kingman State Fishing Lake (SFL) is the only public fishery in Kansas that still supports a self-sustaining northern pike population. Due to the extreme habitat conditions on the far southern edge of the northern pikes range, traditional sampling methods (e.g., fall trap nets and gill nets, spring electrofishmg) generally cause excessive mortality or are not effective at capturing northern pike. As such, data regarding the only Kansas northern pike fishery are lacking. Northern pike were sampled with trap nets during February and March 2011, to estimate population charactensties such as recruitment, growth, mortality, and population size. Kingman SFL northern pike grew quickly, generally lived less than 10 years, and exhibited annual recruitment. Total annual mortality was 44%. Population estimates obtained from mark-recapture data suggest the population density is approximately four to nine adult northern pike per surface hectare.