Shovelnose Sturgeon Research Articles

Observations on the Identification of Larval and JuvenileScaphirhynchusspp. in the Lower Mississippi River

Abstract Scaphirhynchus albus (Pallid Sturgeon) and S. platorynchus (Shovelnose Sturgeon) are sympatric and not uncommon in the lower Mississippi River from the confluence of the Ohio River to the Gulf of Mexico, and in its distributary, the Atchafalaya River. Reports of sturgeon larvae have been rare in the Mississippi River but have been increasing with more effective collection methods. A suite of characters identified in hatchery-reared larval Pallid Sturgeon and Shovelnose Sturgeon from the Yellowstone and upper Missouri rivers has been used to distinguish larval Scaphirhynchus spp. In the Mississippi River; however, a large proportion of wild Scaphirhynchus spp. larvae are intermediate in these characters and have been identified by some as hybridized Pallid Sturgeon and Shovelnose Sturgeon. We applied three diagnostic characters developed from Missouri River sturgeon larvae to hatchery-reared progeny of Atchafalaya River Pallid Sturgeon and found them inadequate to identify most of the known Pallid...

Shovelnose sturgeon exhibit predator avoidance behaviour in the presence of a hungry predator

An experiment was designed to test whether age-0 shovelnose sturgeon (Scaphirhynchus platorynchus) exhibited predator avoidance behaviour in response to a channel catfish (Ictalurus punctatus) predator. It was hypothesized that shovelnose sturgeon would not exhibit any innate predator avoidance behaviour because previous reports have shown a congener of the shovelnose sturgeon, the pallid sturgeon (S. albus), to be an unfavourable prey item for channel catfish. The results, however, indicated that shovelnose sturgeon generally avoided space occupied by the catfish predator and spent a greater proportion of time in the predator avoidance zone within the experimental tank. Bitten fish, in particular, spent a greater period of time in the predator avoidance zone. Of all sturgeon used in this experiment (N = 30), 73% swam within the fork length (350 mm) of the catfish predator. The results seem to indicate that shovelnose sturgeon were initially oblivious to the risk of predation by the catfish predator, but after interaction (e.g. being chased or bitten) appeared to display predator avoidance behaviour. Predator avoidance behaviour in shovelnose sturgeon may thus be suggested as a learned rather than an innate behaviour.

Blood Chemistry Values for Shovelnose and Lake Sturgeon

Blood chemistry panels are commonly used for assessing the general health of vertebrate animals. Here, we present novel blood chemistry data for two North American sturgeon species, shovelnose sturgeon Scaphirhynchus platorynchus and lake sturgeon Acipenser fulvescens. Measurements were done using a portable chemistry analyzer (VetScan Analyzer; Abaxis). Among the plasma values measured (mean ± SD for shovelnose and lake sturgeon, respectively) were total proteins (3.7 ± 0.9 and 2.8 ± 0.4 g/dL), albumin (2.0 ± 0.5 and 1.1 ± 0.2 g/dL), globulin (1.7 ± 0.7 and 1.7 ± 0.3 g/dL), glucose (107 ± 46 and 62 ± 9.7 mg/dL), sodium (Na(+); 132 ± 3.6 and 150 ± 14 mEq/L), potassium (K(+); 3.5 ± 0.2 and 2.8 ± 1.7 mEq/L), phosphorus (10.4 ± 1.9 and 11.6 ± 3.6 mg/dL), and aspartate aminotransferase (AST; 676 ± 433 and 634 ± 234 IU/L). Higher values for total proteins, albumin, glucose, and Na(+) in shovelnose sturgeon than in lake sturgeon probably are the result of handling stress. In addition, the plasma of male shovelnose sturgeon had higher concentrations of AST, glucose, and globulin than did that of females, whereas the plasma of females had higher concentrations of albumin and K(+) than that of males. This study is the first to report blood chemistry data for shovelnose sturgeon. Robust blood chemistry databases can be used by aquaculturists and fish managers for monitoring sturgeon health.

SHOVELNOSE STURGEON SPAWNING IN RELATION TO VARYING DISCHARGE TREATMENTS IN A MISSOURI RIVER TRIBUTARY

ABSTRACTMany lotic fish species use natural patterns of variation in discharge and temperature as spawning cues, and these natural patterns are often altered by river regulation. The effects of spring discharge and water temperature variation on the spawning of shovelnose sturgeon Scaphirhynchus platorynchus have not been well documented. From 2006 through 2009, we had the opportunity to study the effects of experimental discharge levels on shovelnose sturgeon spawning in the lower Marias River, a regulated tributary to the Missouri River in Montana. In 2006, shovelnose sturgeon spawned in the Marias River in conjunction with the ascending, peak (134 m3/s) and descending portions of the spring hydrograph and water temperatures from 16 °C to 19 °C. In 2008, shovelnose sturgeon spawned in conjunction with the peak (118 m3/s) and descending portions of the spring hydrograph and during a prolonged period of increased discharge (28–39 m3/s), coupled with water temperatures from 11 °C to 23 °C in the lower Marias River. No evidence of shovelnose sturgeon spawning was documented in the lower Marias River in 2007 or 2009 when discharge remained low (14 and 20 m3/s) despite water temperatures suitable and optimal (12 °C−24 °C) for shovelnose sturgeon embryo development. A similar relationship between shovelnose sturgeon spawning and discharge was observed in the Teton River. These data suggest that discharge must reach a threshold level (28 m3/s) and should be coupled with water temperatures suitable (12 °C−24 °C) or optimal (16 °C−20 °C) for shovelnose sturgeon embryo development to provide a spawning cue for shovelnose sturgeon in the lower Marias River. Copyright © 2012 John Wiley & Sons, Ltd.

Tag Retention of T‐Bar Anchor Tags and Passive Integrated Transponder Tags in Shovelnose Sturgeon

AbstractCapture–recapture methods are commonly used to estimate population parameters when the necessary assumptions are met. One of the broadest assumptions of capture–recapture models is that tags are not lost. Therefore, one must understand tag retention to be able to adjust estimates if tag loss occurs. Our objectives were to (1) determine retention rates of T‐bar anchor tags and passive integrated transponder (PIT) tags injected into the dorsal musculature of shovelnose sturgeon Scaphirhynchus platorynchus and (2) determine whether using an alternative PIT‐tagging location (the operculum) and a new tagging procedure (cyanoacrylate [i.e., superglue] to seal the tag insertion point) provided higher retention. The T‐bar tags had a retention rate of 100%; PIT tag retention, however, was more variable. Injection of PIT tags along the dorsal fin resulted in a retention rate of 73%, and tag loss was observed throughout the 98‐d experiment. The application of cyanoacrylate did not appear to deter PIT tag loss; retention rates before and after cyanoacrylate was applied were 73% and 77%, respectively. Further, we observed a similar trend of continual PIT tag loss throughout the experiment. The operculum location resulted in a 92% PIT tag retention rate and showed no trend in cumulative loss through time. The high retention rate of PIT tags placed in the operculum suggests that this location is a reliable alternative to inserting PIT tags along the dorsal fin of adult Scaphirhynchus species. In addition, the excellent retention of T‐bar tags makes them a viable option for use in Scaphirhynchus studies.Received October 8, 2011; accepted March 1, 2012

Heterogeneous detection probabilities for imperiled Missouri River fishes: implications for large-river monitoring programs

Occupancy modeling was used to determine (1) if detection probabilities (p) for 7 regionally imperiled Missouri River fishes (Scaphirhynchus albus, Scaphirhynchus platorynchus, Cycleptus elongatus, Sander canadensis, Macrhybopsis aestivalis, Macrhybopsis gelida, and Macrhybopsis meeki) differed among gear types (i.e. stationary gill nets, drifted trammel nets, and otter trawls), and (2) how detection probabilities were affected by habitat (i.e. pool, bar, and open water), longitudinal position (five 189 to 367 rkm long segments), sampling year (2003 to 2006), and season (July 1 to October 30 and October 31 to June 30). Adult, large-bodied fishes were best detected with gill nets (p: 0.02-0.74), but most juvenile large-bodied and all small-bodied species were best detected with otter trawls (p: 0.02-0.58). Trammel nets may be a redundant sampling gear for imperiled fishes in the lower Missouri River because most species had greater detection probabilities with gill nets or otter trawls. Detection probabilities varied with river segment for S. platorynchus, C. elongatus, and all small-bodied fishes, suggesting that changes in habitat influ- enced gear efficiency or abundance changes among river segments. Detection probabilities var- ied by habitat for adult S. albus and S. canadensis, year for juvenile S. albus, C. elongatus, and S. canadensis, and season for adult S. albus. Concentrating sampling effort on gears with the great- est detection probabilities may increase species detections to better monitor a population's response to environmental change and the effects of management actions on large-river fishes.

Habitat for Age‐0 Shovelnose Sturgeon and Pallid Sturgeon in a Large River: Interactions among Abiotic Factors, Food, and Energy Intake

AbstractThe main stems of large rivers throughout the world have been highly modified with little consideration for effects on fishes that rely on these areas to complete their life histories. Particularly important is the ability of riverine habitats to provide foraging opportunities for young fish. We explored how temperature, flow, and food availability influenced diet content, prey selection (Strauss's linear selectivity index), and energy condition of age‐0 shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus in major habitat areas (e.g., islands, channel borders, wing dikes, and side channels) of the middle Mississippi River during spring (March–May) and summer (June–August) 2008. Standardized diet mass (dry mass standardized for fish body mass) of the age‐0 sturgeon peaked at about 19°C and at a flow velocity of 0.5 m/s. Although potential prey taxa were diverse, the diets for age‐0 sturgeon of all sizes were dominated by mayflies (Ephemeroptera) and midge larvae (Chironomidae) across all habitats. As age‐0 sturgeon grew, the relative energy return per habitat appeared to diverge; island tips upstream of the main channel and channel border areas behind wing dikes provided higher gains in standardized diet mass than other habitats. No differences in energy condition (kJ/g) occurred among habitats, although large (51–200 mm total length [TL]) age‐0 sturgeon had higher energy densities than their small (≤50 mm TL) counterparts. Enhancement of areas with flow and substrates that facilitate the production and availability of midges and mayflies (e.g., instream island complexes) is critical for the recruitment of age‐0 Scaphirhynchus sturgeon in large rivers.Received August 2, 2011; accepted October 6, 2011

Hybridization between pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon Scaphirhynchus platorynchus

This study found that introgressive hybridization of the pallid sturgeon Scaphirhynchus albus with the common shovelnose sturgeon Scaphirhynchus platorynchus has probably occurred across the range of S. albus. Bayesian clustering found evidence of hybridization in all management units of S. albus. Some individuals were intermediate at both genetic and morphological characters, and some had discordant results. The results support introgressive hybridization throughout much of the range of S. albus, yet individuals consistent with being pure members of each species were detected in all management units. Simulations demonstrated that it would be very difficult to distinguish introgressed individuals from pure specimens after multiple generations of backcrossing with these microsatellite markers. Using hybrid or backcross fish as broodstock could artificially accelerate the loss of unique genetic variation in S. albus. Additional microsatellite loci or additional genetic markers, along with morphological data may be required to ensure that hybrid or backcross fish are not used. Introgressive hybridization requires at least two generations and generation lengths of S. albus are long, perhaps as long as 30 years. The proportion of individuals consistent with introgressive hybrid origins indicates that hybridization between S. albus and S. platorynchus probably has occurred for several generations and is not a recent phenomenon.

Larval Surveys Indicate Low Levels of Endangered Pallid Sturgeon Reproduction in the Middle Mississippi River

AbstractThe pallid sturgeon Scaphirhynchus albus is an endangered riverine species that is less abundant than the sympatric shovelnose sturgeon S. platorynchus with which it hybridizes. The two species are morphologically similar, and due to morphological variation within species, allometry, and the occurrence of morphological intermediates, morphological identification of specimens can be problematic. When the pallid sturgeon was listed under the U.S. Endangered Species Act in 1990, perceived threats included habitat loss due to habitat alteration (dams and channelization), hybridization, and commercial harvest. Previous studies estimated the ratio of adult pallid sturgeon to adult shovelnose sturgeon to be approximately 1:77 in the middle Mississippi River (MMR; the reach between the Missouri River confluence and the Ohio River confluence). One study using morphological identification estimated that 8–26% of Scaphirhynchus larvae collected in the MMR during May and June were pallid sturgeon. Given that larval pallid sturgeon, shovelnose sturgeon, and their hybrids have overlapping morphologies, DNA markers may provide more accurate species identification. The present study aimed to estimate relative larval abundances of pallid sturgeon, shovelnose sturgeon, and hybrids in the MMR. We genotyped 583 Scaphirhynchus larvae collected from the MMR at 16 DNA microsatellite loci and determined that 581 larvae were shovelnose sturgeon, one was a hybrid, and one was a pallid sturgeon. This study is the first to provide genetically verified larval abundance estimates of Scaphirhynchus species in the MMR. The present data indicate that the rate of pallid sturgeon reproduction relative to shovelnose sturgeon reproduction is an order of magnitude lower than expectations based on adult ratios and that hybrid sturgeon larvae are as common as pure pallid sturgeon.

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

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 differ from that of fish that did not (542.4 mm). Overall, 43% of the hook timers were activated within the first 2 h of deployment and an additional 19% in the next 2-h period; 54% of the fish were collected prior to sunset. Our study shows that hook timers can be a valuable tool that will aid in the interpretation of trotline catches. Received March 16, 2011; accepted June 14, 2011

Habitats of Age‐0 Sturgeon in the Lower Missouri River

AbstractLittle is known about the habitats of young pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon S. platorynchus. Therefore, we compared the distribution and abundance of age‐0 fish of these species collected in benthic trawls among most of the mesoscale habitats comprising the channelized lower Missouri River (i.e., rock‐dike channel modifying structures, large‐channel sandbar, bankline, tributary, floodplain, and wooded island) from 2007 through 2009. Most age‐0 sturgeon were less than 110 mm (fork length) by the end of the growing season. Age‐0 fish were most frequently collected in areas with a relatively fast bottom velocity (0.5–0.7 m/s) associated with channel sandbars, rootless‐dikes, and wing‐dikes and were rarely found at L‐dikes, along banklines, or in tributaries where bottom velocity was slower (≤0.2 m/s). Age‐0 sturgeon habitat use in the lower Missouri River supports the hypothesis that main‐channel areas are important habitats throughout the life cycle of some fluvial specialist species. In light of existing literature on habitat use by wild age‐0 sturgeon, our results highlight their complex ecology in contemporary large rivers throughout their range. Therefore, we do not predict the response of pallid sturgeon to contemporary habitat restoration goals but discuss current knowledge gaps important to characterizing the early life history of Scaphirhynchus spp. Habitat restoration design on the Missouri River should consider the impact on ecosystem structure and the response by early life stages of these species.

Nymphal Cicadas (Hemiptera: Cicadidae) as a Prey Item of Shovelnose Sturgeon (Scaphirhynchus platorynchus) in the Lower Mississippi River

Stomach contents of 3 Scaphirhynchus platorynchus (Shovelnose Sturgeon) collected in the Lower Mississippi River in January 2010 yielded 44 specimens of cicada nymphs, Diceroprocta sp. The fish were collected during a sudden rise in water level. The floodplain-dwelling cicada were likely washed out of their terrestrial habitat and into the river, where opportunistic sturgeon were foraging.

Olfactory projections in the white sturgeon, Acipenser transmontanus: An experimental study

Telencephalic evolution in ray-finned fishes shows increasing complexity from polypteriform fishes through sturgeons to teleosts. Telencephalic organization in sturgeons is thus critical to our understanding of ray-finned fish evolution, but it is poorly understood, particularly as regards the roof or pallium. Two major hypotheses exist regarding the medial part of area dorsalis (Dm): that Dm is extended; and that Dm is restricted. The extent and topography of secondary olfactory projections to the pallium are critical in evaluating these hypotheses, but there is little agreement regarding these projections. Olfactory projections in the white sturgeon were therefore examined by using the carbocyanine probe DiI, biocytin, and biotinylated dextrin amine (BDA). Both DiI and BDA revealed primary olfactory projections to the olfactory bulb and primary extrabulbar projections widely in the telencephalon and to more restricted regions of the diencephalon. Myelinated secondary olfactory fibers caused DiI to be less effective in labeling secondary olfactory projections, which terminate in all subpallial nuclei and in the pallium: sparsely in the medial pallial division (Dm); heavily in the posterior pallial division (Dp); and more lightly in the lateral pallial division (Dl). In the diencephalon, substantial secondary olfactory projections were seen to the habenular nuclei, the rostral pole of the inferior lobe, and several nuclei of the posterior tubercle. All secondary olfactory projections were bilateral but heavier ipsilaterally. Bulbopetal neurons were located in both pallial and subpallial centers and were more numerous ipsilaterally. These results corroborate an earlier experimental study on the shovelnose sturgeon and indicate a restricted Dm in sturgeons.

Seasonal Diet Composition of Adult Shovelnose Sturgeon in the Middle Mississippi River

Because the shovelnose sturgeon (Scaphirhynchus platorynchus) population in the Middle Mississippi River (MMR) between Cairo, IL and St. Louis, MO (RKM 0–320) appears to be declining, we must understand dietary needs to help assess its conservation status. Diet is linked to growth, condition and reproduction and reflects population state. Thus, we quantified diets of adult shovelnose sturgeon monthly using gill nets (5.08-cm bar mesh) during Jan. 2005 through Nov. 2005 at three sites on the MMR (RKM: 201-198; 191-188, and RKM 127-124). Stomachs were removed from adult shovelnose sturgeon (winter n = 71; spring n = 163; summer n = 149; fall n = 179; fork length mean = 617 mm; standard deviation = 64.57). Overall, prey items occurred in less than 30% (n = 170) of shovelnose sturgeon stomachs. Dominant prey items throughout all seasons (winter, spring, summer and fall) were Chironomidae, Hydropsychidae, Ephemeridae and Corophiidae respectively. Corophiidae is an exotic amphipod that has not previously been documented in the MMR. The total abundance of diet items was high during winter through spring and low during summer through fall. Ephemeridae dominated in winter. Hydropsychidae was the most important prey item during spring through summer. Corophiidae dominated diets in the fall. Temperature and perhaps low river discharge appeared to affect prey consumed, with high temperatures and low discharge during summer through fall causing low energy intake, lowered condition and likely poor growth. Conservation efforts that provide flow refugia may improve energy intake and likely enhance shovelnose sturgeon populations in the MMR.

Discrete choice modeling of shovelnose sturgeon habitat selection in the Lower Missouri River

Summary Substantive changes to physical habitat in the Lower Missouri River, resulting from intensive management, have been implicated in the decline of pallid (Scaphirhynchus albus) and shovelnose (S. platorynchus) sturgeon. To aid in habitat rehabilitation efforts, we evaluated habitat selection of gravid, female shovelnose sturgeon during the spawning season in two sections (lower and upper) of the Lower Missouri River in 2005 and in the upper section in 2007. We fit discrete choice models within an information theoretic framework to identify selection of means and variability in three components of physical habitat. Characterizing habitat within divisions around fish better explained selection than habitat values at the fish locations. In general, female shovelnose sturgeon were negatively associated with mean velocity between them and the bank and positively associated with variability in surrounding depths. For example, in the upper section in 2005, a 0.5 m s−1 decrease in velocity within 10 m in the bank direction increased the relative probability of selection 70%. In the upper section fish also selected sites with surrounding structure in depth (e.g., change in relief). Differences in models between sections and years, which are reinforced by validation rates, suggest that changes in habitat due to geomorphology, hydrology, and their interactions over time need to be addressed when evaluating habitat selection. Because of the importance of variability in surrounding depths, these results support an emphasis on restoring channel complexity as an objective of habitat restoration for shovelnose sturgeon in the Lower Missouri River.

Diet composition and feeding patterns of adult shovelnose sturgeon (Scaphirhynchus platorynchus) in the lower Platte River, Nebraska, USA

Two-hundred and seven adult shovelnose sturgeon ranging from 450 to 718 mm in length were sampled from June to October 2001 and May to July 2002 to determine diet composition and feeding patterns in the lower Platte River. Shovelnose sturgeon fed primarily upon aquatic insect larvae and nymphs (>99% composition by number). Diptera of the family Chironomidae were the dominant prey items in both years and composed 98.1% of the shovelnose sturgeon diet in 2001 and 96.8% in 2002. Chironomidae were primarily represented by the four genera Paracladopelma, Chernovskiia, Saetheria and Robackia accounting for 90.2% of the ingested prey items in 2001 and 83.6% in 2002. In addition, shovelnose sturgeon showed in both years a generalized feeding pattern towards Ephemeroptera of the families Isonychiidae and Caenidae, as well as Trichoptera of the family Hydropsychidae. Other aquatic insects, terrestrial invertebrates and fishes were found infrequently and in low numbers in shovelnose sturgeon diets. The four most abundant Chironomidae genera are often found on sand and the high abundance of these taxa in the diet suggests that shovelnose sturgeon feed primarily near or on this substrate type. This highlights the importance of habitats that provide sand substrate for shovelnose sturgeon foraging in the lower Platte River.

Characterization of environmental cues for initiation of reproductive cycling and spawning in shovelnose sturgeon Scaphirhynchus platorynchus in the Lower Missouri River, USA

Summary We presume that the shovelnose sturgeon (Scaphirhynchus platorynchus) has evolved to spawn in the springtime when environmental conditions are at some optimum, but this state has not yet been defined. In this study physiological readiness to spawn in shovelnose sturgeon was examined to define more closely when spawning could occur and thus identify and evaluate prevailing environmental conditions that could cue spawning during that period. Reproductive assessments of Lower Missouri River shovelnose during 4 years (2005–2008) and at two locations (Gavins Point Dam, South Dakota and Boonville, Missouri) were used to identify shovelnose sturgeon spawning periods. Initiation of the spawning period, as defined by the presence of reproductively ready fish, was a highly predictable yearly event and extended over several weeks at each reach. The spawning period occurred earlier in the lower reach than in the upper reach and environmental conditions during the periods varied between locations and among years. Shovelnose sturgeon collected during the presumed spawning periods were at varying degrees of readiness to spawn as indicated by oocyte polarization index and blood reproductive hormones. Evaluation of the influence of environmental factors on readiness to spawn using stepwise multiple regression analysis indicated photoperiod followed by temperature were the best candidate variables overall to explain the trend. However, within geographically distinct populations gravid females are not all reproductively synchronized. Assuming that this apparent asynchrony in readiness is normal and not an artifact of the disturbed Missouri River system, we infer that individual sturgeon can persist in a reproductively ready state until conditions appropriate for spawning occur. Taken together, our results lead us to hypothesize that gravid females early in the reproductive cycle (post-vitellogenesis) respond to day length, a reliable annual cue, become increasingly more ready to spawn in response to temperature, and that another set of cues, short-term and specific for localized environmental conditions or events, serve to signal ovulation and release of gametes.

Evaluating spawning migration patterns and predicting spawning success of shovelnose sturgeon in the Lower Missouri River

Approaches using telemetry, precise reproductive assessments, and surgically implanted data storage tags (DSTs) were used in combination with novel applications of analytical techniques for fish movement studies to describe patterns in migratory behavior and predict spawning success of gravid shovelnose sturgeon. From 2004 to 2007, over 300 gravid female shovelnose sturgeon (Scaphirhynchus platorynchus) from the Lower Missouri River, that were expected to spawn in the year they were collected, were surgically implanted with transmitters and archival DSTs. Functional cluster modeling of telemetry data from the spawning season suggested two common migration patterns of gravid female shovelnose sturgeon. Fish implanted from 958 to 1181 river kilometer (rkm) from the mouth of the Missouri River (or northern portion of the Lower Missouri River within 354 rkm of the lowest Missouri River dam at rkm 1305) had one migration pattern. Of fish implanted from 209 to 402 rkm from the mouth of the Missouri River (or southern portion of the Lower Missouri River), half demonstrated a movement pattern similar to the northern fish while the other half demonstrated a migration pattern that covered more of the river. There was no apparent difference in migration patterns between successful and unsuccessful spawners. Multiple hypotheses exist to explain differences in migratory patterns among fish from different river reaches. Additional work is required to determine if observed differences are due to multiple adapted strategies, environmental alteration, and/or initial tagging date. Hierarchical Bayesian modeling of DST data indicated that variation in depth usage patterns was consistently different between successful and unsuccessful spawners, as indicated by differences in likelihood of switching between high and low variability states. Analyses of DST data, and data collected at capture, were sufficient to predict 8 of 10 non-spawners/incomplete spawners and all 30 spawners in the absence of telemetry location data. Together, the results of these two separate analyses suggest that caution is necessary in extrapolating spawning success from broad-scale movement data alone. More direct measures of spawning success may be necessary to precisely determine spawning success and to evaluate the effects of management actions.

Critical swimming speeds of adult shovelnose sturgeon in rectilinear and boundary-layer flow

Summary Critical swimming speeds of sturgeon are presumably lower in vertically uniform, rectilinear flow than in heterogeneous boundary-layer flow. Movement in rectilinear flow of the water column necessitates frequent high-energy free-swimming, while movement in boundary-layers near the bottom of the river permits a variety of lower energy behaviours, and presumably, negotiation of greater mid-column water velocities. Comparative studies of sturgeon swimming performance in rectilinear and boundary layer flows, however, are lacking. Using a 1200-l laboratory swim tunnel, swimming performance was measured for 12 adult shovelnose sturgeon (Scaphirhynchus platorynchus), 494–705 mm standard length. Tests were conducted at 20–25� C in rectilinear (N = 4) and boundary-layer flows (N = 8). Fifteen minute critical swimming speeds ranged from 89.3 to 112.6 cm s )1 in rectilinear flow, 129.5–172.1 cm s )1 in boundary-layer flow. Higher critical swimming speeds observed in boundary-layer flows was a combination of behavioural adaptations (body appression to flat, horizontal substrate) and availability of a low velocity refugium (water velocities at bottom of tank 21– 65 cm s )1 slower than those in mid and upper levels of tank). Results support the idea that sturgeon exploit boundary-layers to effectively move or hold position in fast-flowing rivers. Data may be applied to man-made river structures to facilitate fish passage and to reduce risk of sturgeon entrainment.

Identifying structural elements needed for development of a predictive life-history model for pallid and shovelnose sturgeons

Summary Intensive management of the Missouri and Mississippi Rivers has resulted in dramatic changes to the river systems and their biota. These changes have been implicated in the decline of the pallid sturgeon (Scaphirhynchus albus), which has been listed as a United States federal endangered species. The sympatric shovelnose sturgeon (S. platorynchus) is more common and widespread but has also been in decline. The decline of pallid sturgeon is considered symptomatic of poor reproductive success and low or no recruitment. In order to organize information about these species and provide a basis for future development of a predictive model to help guide recovery efforts, we present an expert-vetted, conceptual life-history framework that incorporates the factors that affect reproduction, growth, and survival of shovelnose and pallid sturgeons.