River alteration and niche overlap among three native minnows (Cyprinidae) in the Missouri River hydrosystem

The influence of physical and hydrologic stabilization on habitat niche overlap among three native cyprinid species: flathead chub Platygobio gracilis , sicklefin chub Macrhybopsis meeki and sturgeon chub Macrhybopsis gelida , in riverine segments of the Missouri and Yellowstone Rivers in western North Dakota and eastern Montana, was evaluated. Collectively the three species exhibited higher niche overlap in quasi‐natural river segments than in segments highly altered by a mainstem dam based on relatively high percentages of individuals in quasi‐natural river segments that were classified correctly, according to species, in discriminant function analyses of resource use, compared to lower percentages of individuals classified correctly in the altered river segments. The lower niche overlap in altered river segments resulted primarily from the lower overlap between flathead chub and the remaining species; this appears to be related to a decline in the diversity of natural habitats and conditions that provided a wide range of habitat conditions suitable for all three species. Results from this study suggest that selective segregation and habitat changes, rather than interactive segregation and competition, is probably the mechanism responsible for the pattern of habitat use and niche overlap among the three species in the altered segments.     

Reproductive strategy,spawning induction,spawning temperatures and early life history of captive sicklefin chub Macrhybopsis meeki

Macrhybopsis reproduction and propagule traits were studied in the laboratory using two temperature regimes and three hormone treatments to determine which methods produced the most spawns. Only sicklefin chub Macrhybopsis meeki spawned successfully although sturgeon chub Macrhybopsis gelida released unfertilized eggs. All temperature and hormone treatments produced M. meeki spawns, but two treatments had similar success rates at 44 and 43%, consisting of a constant daily temperature with no hormone added, or daily temperature fluctuations with hormone added to the water. Spawns consisted of multiple successful demersal circular swimming spawning embraces interspersed with circular swims without embraces. The most spawns observed for one female was four and on average, 327 eggs were collected after each spawn. The water‐hardened eggs were semi‐buoyant and non‐adhesive, the first confirmation of this type of reproductive guild in the Missouri River Macrhybopsis sp. From spawn, larvae swam vertically until 123 accumulated degree days (° D) and 167° D for consumption of first food. Using average water speed and laboratory development time, the predicted drift distance for eggs and larvae could be 468–592 km in the lower Missouri River. Results from this study determined the reproductive biology and early life history of Macrhybopsis spp. and provided insight into their population dynamics in the Missouri River.     

Introgression Between Lahontan and Endangered Owens Tui Uhubs,and Apparent Discovery of a New Tui Chub in the Owens Valley,California

Owens tui chubs (Siphateles bicolor snyderi [Miller]) have become extirpated throughout most of their range by introgression with introduced Lahontan tui chubs. The remaining non-introgressed Owens tui chub populations persist in a small number of fragmented habitats. These survivors are listed as “endangered” under both the state and federal endangered species acts. This study employs six microsatellite DNA loci to assess degrees of genetic difference within and among populations of Owens and Lahontan tui chubs and their putative hybrids. It reveals four distinct groups of tui chubs: Owens, Lahontan, hybrid Owens × Lahontan, and Cabin Bar. Patterns of microsatellite DNA variation confirm that tui chubs in the Owens River and its tributaries, and Mono Lake tributaries comprise a hybrid swarm. The overall degree of introgression between Lahontan and Owens tui chubs is approximately 40%, while the remaining 60% derives from Owens tui chub’s original genetic composition. Unexpectedly, Owens tui chubs are more genetically similar to Lahontan tui chubs than to Cabin Bar tui chubs, although they share the same river basin with the latter. Cabin Bar tui chubs possess a 3 bp deletion in the flanking region of microsatellite locus Gbi-G79. We give the Cabin Bar tui chub a common name “toikona tui chub” to distinguish it from the Owens tui chub, and recommend independent protection and recovery efforts. Management practices should prevent any future genetic mixing of non-introgressed Owens, toikona, or Lahontan tui chubs with each other, or with the hybrid swarm. Habitats of Owens and toikona tui chubs should remain isolated from the Owens River. Toikona tui chubs should be established in multiple sites.     

Characterization of Pallid Sturgeon (Scaphirhynchus albus) Spawning Habitat in the Lower Missouri River

Acipenseriformes (sturgeons and paddlefish) globally have declined throughout their range due to river fragmentation, habitat loss, overfishing, and degradation of water quality. In North America, pallid sturgeon (Scaphirhynchus albus) populations have experienced poor to no recruitment, or substantial levels of hybridization with the closely related shovelnose sturgeon (S. platorynchus). The Lower Missouri River is the only portion of the species’ range where successful reproduction and recruitment of genetically pure pallid sturgeon have been documented. This paper documents spawning habitat and behavior on the Lower Missouri River, which comprises over 1,300 km of unfragmented river habitat. The objective of this study was to determine spawning locations and describe habitat characteristics and environmental conditions (depth, water velocity, substrate, discharge, temperature, and turbidity) on the Lower Missouri River. We measured habitat characteristics for spawning events of ten telemetry-tagged female pallid sturgeon from 2008–2013 that occurred in discrete reaches distributed over hundreds of kilometers. These results show pallid sturgeon select deep and fast areas in or near the navigation channel along outside revetted banks for spawning. These habitats are deeper and faster than nearby river habitats within the surrounding river reach. Spawning patches have a mean depth of 6.6 m and a mean depth-averaged water-column velocity of 1.4 m per second. Substrates in spawning patches consist of coarse bank revetment, gravel, sand, and bedrock. Results indicate habitat used by pallid sturgeon for spawning is more common and widespread in the present-day channelized Lower Missouri River relative to the sparse and disperse coarse substrates available prior to channelization. Understanding the spawning habitats currently utilized on the Lower Missouri River and if they are functioning properly is important for improving habitat remediation measures aimed at increasing reproductive success. Recovery efforts for pallid sturgeon on the Missouri River, if successful, can provide guidance to sturgeon recovery on other river systems; particularly large, regulated, and channelized rivers.     

Documentation of lake sturgeon (Acipenser fulvescens Rafinesque, 1817) recovery and spawning success from a restored population in the Mississippi River,Missouri, USA

Lake sturgeon Acipenser fulvescens are considered rare and were nearly extirpated in the Mississippi River in Missouri by 1931 as a result of overfishing and habitat fragmentation. Propagation efforts have been implemented by the Missouri Department of Conservation since 1984 as means to restore the lake sturgeon population. Although recent population increases have been observed, a formalized evaluation to determine if lake sturgeon are self‐sustaining in the Missouri portion of the Mississippi River has not been completed. Therefore, the objectives of this study were to: (i) determine the proportion of reproductive individuals, (ii) evaluate seasonal movement patterns of adults, and (iii) validate purported spawning locations within the Mississippi River in Missouri. Lake sturgeon catch data indicated that approximately 11 percent of the population are reproductively mature. Additionally, telemetry data confirms that the greatest movement by adult lake sturgeon occurs during spring, which suggests spawning behavior. Finally, it was possible to document lake sturgeon embryos and emergent fry larvae below Melvin Price Locks and Dam 26 in the Upper Mississippi River near St. Louis, Missouri. Water velocity, depth, and substrate size were measured at this location and embryos were collected and hatched in the laboratory. River gage data suggest that spawning behavior may have been elicited by a large influx of water during a drawdown period of water above the dam. This study represents the first documented spawning of A. fulvescens in the Mississippi River and highlights the success of recovery efforts in Missouri.     

Natural growth and diet of known‐age pallid sturgeon (Scaphirhynchus albus) early life stages in the upper Missouri River basin,Montana and North Dakota

Prior to anthropogenic modifications, the historic Missouri River provided ecological conditions suitable for reproduction, growth, and survival of pallid sturgeon Scaphirhynchus albus. However, little information is available to discern whether altered conditions in the contemporary Missouri River are suitable for feeding, growth and survival of endangered pallid sturgeon during the early life stages. In 2004 and 2007, nearly 600 000 pallid sturgeon free embryos and larvae were released in the upper Missouri River and survivors from these releases were collected during 2004–2010 to quantify natural growth rates and diet composition. Based on genetic analysis and known‐age at release (1–17 days post‐hatch, dph), age at capture (dph, years) could be determined for each survivor. Totals of 23 and 28 survivors from the 2004 and 2007 releases, respectively, were sampled. Growth of pallid sturgeon was rapid (1.91 mm day^?1) during the initial 13–48 dph, then slowed as fish approached maximum length (120–140 mm) towards the end of the first growing season. The diet of young‐of‐year pallid sturgeon was comprised of Diptera larvae, Diptera pupae, and Ephemeroptera nymphs. Growth of pallid sturgeon from ages 1–6 years was about 48.0 mm year^?1. This study provides the first assessment of natural growth and diet of young pallid sturgeon in the wild. Results depict pallid sturgeon growth trajectories that may be expected for naturally produced wild stocks under contemporary habitat conditions in the Missouri River and Yellowstone River.     

Range‐wide assessment of pallid sturgeon Scaphirhynchus albus (Forbes & Richardson, 1905) relative condition

Pallid sturgeon Scaphirhynchus albus relative condition has been observed to be declining along the Nebraska reach (rkm 1212.6–801.3) of the Missouri River over the past several years; therefore, pallid sturgeon capture data was synthesized from the entire Missouri and Middle Mississippi rivers to document and compare how pallid sturgeon condition varies spatially and temporally throughout much of their current range. The study area was subdivided into four river reaches based on a priori statistical differences for pallid sturgeon catches from 2003 to 2015. Pallid sturgeon in the Middle Mississippi River (Alton Dam [rkm 321.9]) to the confluence of the Ohio River (rkm 0.0) were in the best condition while pallid sturgeon in the Middle Missouri River (Fort Randall Dam [rkm 1416.2]) to the Grand River confluence (rkm 402.3) were in the poorest condition. Furthermore, pallid sturgeon condition in the Upper Missouri River (Fort Peck Dam [rkm 2850.9] to the headwaters of Lake Sakakawea [rkm 2523.5] and lower Yellowstone River) and the Lower Missouri River (Grand River confluence to the Mississippi River confluence [rkm 0.0]) were significantly less than in the Middle Mississippi River but significantly higher than the Middle Missouri River. Temporally, pallid sturgeon condition was highly variable. Relative condition in the Middle Mississippi River was consistently above average (Kn = 1.1). Comparatively, Kn throughout the Missouri River rarely exceeded “normal” (Kn = 1.0), with Kn in the middle and lower reaches of the Missouri River having declined to the lowest observed. As pallid sturgeon recovery efforts continue, understanding the range‐wide differences and effects on condition could be critical, as poor condition may cause maturation delays, reproductive senescence or even mortality, which affects the likelihood of natural reproduction and recruitment.     

Differences in Species Composition and Feeding Ecology of Catostomid Fishes in Two Distinct Segments of the Missouri River, North Dakota, U.S.A.

In 1997 and 1998, we sampled the Missouri River, North Dakota to determine if anthropogenic disturbances had influenced catostomid species composition and feeding ecology. We compared two distinct river segments, the Missouri River between the mouth of the Yellowstone River and Lake Sakakawea (the Yellowstone–Sakakawea segment (YSS)), a moderately altered segment and the Missouri River between Garrison Dam and Lake Oahe (the Garrison–Oahe segment (GOS)), a highly altered segment. The segments exhibited greatly different sucker communities. Bigmouth buffalo, Ictiobus cyprinellus, smallmouth buffalo, Ictiobus bubalus, and river carpsucker, Carpiodes carpio, represented 94% of the sucker catch in the YSS, whereas in the GOS, white sucker, Catostomus commersoni, and longnose sucker, Catostomus catostomus, constituted 98% of the sucker catch. In the YSS, high zooplankton densities led to greater sucker zooplanktivory and food niche overlap than in the GOS. Intense anthropogenic disturbances to the GOS are associated with the differences in sucker species composition, prey density and composition, and sucker feeding ecology between the two segments.     

Genetic relationships of tui chub populations in the northwestern Great Basin and conservation implications for the Cow Head Tui Chub

The Cow Head Tui Chub, Siphateles thalassinus vaccaceps, is restricted to the small Cow Head basin in far northeastern California and northwestern Nevada. Using microsatellite DNA loci, we found extensive genetic variation among tui chub populations in the Cow Head and surrounding basins of the northwestern Great Basin. Our data support the systematic conclusions of earlier authors, while showing distinct intraspecific differences between populations in most subbasins within the pluvial basins examined. The Cow Head Tui Chub forms a distinctive population within S. thalassinus with greatest affinity to the tui chub in the Warner Valley into which the Cow Head Lake drains. Tui chubs from the Goose Lake and Pit River basins are genetically very similar. Warner, Abert, Summer Lake, Catlow and Guano basin tui chubs appear distinct, both from each other and from tui chubs in the other basins. However, genetic proximity and some overlap between populations in presumably isolated hydrologic basins (i.e. Summer–Goose–Warner) suggest the possibility of unrecognized hydrologic connections or anthropogenic transport across barriers. Current genetic diversity in the Cow Head Tui Chub population is similar to that of stream-associated populations. We suggest that the Cow Head Tui Chub should remain a species of conservation concern due to its highly restricted distribution in an arid environment. Successful conservation of this unique fish will depend on stewardship of its limited habitat and maintenance of connectivity between subpopulations in a manner that ensures its long-term viability.     

Identity of Squalius (Actinopterygii, Cyprinidae) from Istra Peninsula in Croatia (Adriatic Sea basin)

A chub of previously ambiguous identity from the Boljunscica and Pazincica rivers (south-eastern Istra Peninsula) was studied and compared with geographically close Squalius squalus, Squalius zrmanja, and Squalius janae recently described from the Dragonja River drainage in the Adriatic Sea basin in Slovenia. It was shown that the chub from the south-eastern Istra Peninsula differs from all know species of Squalius but one: Squalius janae. Three samples examined from Boljunscica and Pazincica rivers and Squalius janae from its type locality, Dragonja River, show the following characters typical for the latter species: a long head (the head length 27–32% SL); a pointed conical snout with a clearly projecting upper jaw; a long straight mouth cleft, the lower jaw length (39–45% HL) exceeding the caudal peduncle depth; a large eye; commonly 9? branched anal-fin rays; commonly 44 total vertebrae (24+20 or 25+19); bright silvery colouration, scales easily lost; iris, pectoral, pelvic and anal fin pigmentation with yellow shades. The data on the distribution of Squalius chubs in the northern Adriatic basin support the assumption that the range of Squalius janae is determined by the geology of the Trieste Flysch Basin and the Pazin Flysch Basin forming the base of the Istra Peninsula. The distribution pattern of this species does not support a simple model of fish dispersal and a complete connectivity within the whole Palaeo-Po historical drainage. Indeed, it indicates a disrupted surface palaeohydrography that was heavily fragmented by karstification in the whole Dinaric area.     

Adult paddlefish migrations in relation to spring river conditions of the Yellowstone and Missouri rivers, Montana and North Dakota, USA

Migrations and movements of paddlefish (Polyodon spathula) into the regulated Missouri River and the largely unregulated Yellowstone River, North Dakota and Montana, USA were monitored with radio‐telemetry to assess if (i) differential discharge between the Yellowstone River and the Missouri River influenced river selection, (ii) river conditions influenced directional movements in the Yellowstone River and (iii) inter‐annual and sex‐related migration patterns existed. In 2003 and 2004, telemetered upriver migrants selected the Yellowstone River rather than the Missouri River above its confluence with the Yellowstone River 34 of 54 times (63%). Fish typically ascended the river with flows that were increasing at a greater rate or decreasing at a lesser rate than the other river. Most (70%) upriver movements occurred when discharge and suspended sediment were increasing. Most (80%) downriver movements occurred when flows and suspended sediment were decreasing. Total migration distance was greater in 2004 than in 2003 for both sexes despite greater peak discharge in 2003. Movement of pre‐spawn paddlefish into the Missouri River above its confluence with the Yellowstone River in response to attraction flows may have implications towards this stock’s reproductive success. Accordingly, these implications should be taken into account when regulating spring Missouri River discharge levels upriver at Fort Peck Dam.     

Juvenile white sturgeon (Acipenser transmontanus) habitat and distribution in the Lower Fraser River, downstream of Hope, BC, Canada

The primary objective of this study was to identify and characterize juvenile white sturgeon (Acipenser transmontanus) habitat in the Lower Fraser River downstream of Hope, BC, Canada. A secondary objective was to estimate the juvenile white sturgeon population in the Lower Fraser River. A total of 1867 white sturgeon was captured with gill nets at 26 sites in the Lower Fraser River. The greatest numbers of sturgeon were caught in three sloughs; all but three sturgeon were captured in the June to August period. These three sloughs all had water deeper than 5 m and current that was multidirectional. Turbidity ranged greatly from 1.5 NTU (Nephelometric Units) to 67.0 NTU and the substrate of most sites was fine sediments, fine sand, silt and clay. Stomach contents were mysid shrimp (Mysidacea), midge larvae (Chironomidae) and peamouth chub (Mylocheilus caurinus). We identified three of 26 sites with appreciable numbers of juvenile sturgeon, identified water quality parameters of these sites, identified any incidental species that might be prey and also determined that between 1985 and 1993 the juvenile white sturgeon population had declined.     

Resource selection by juvenile pallid sturgeon Scaphirhynchus albus (Forbes and Richardson, 1905) in the channelized Missouri River,Nebraska, USA

Habitat selection has been quantified for age‐0 and adult pallid sturgeon Scaphirhynchus albus Bull. Illinois State Lab. Nat. Hist., 7, 1905, 37, but little is known regarding habitat use of the juvenile fish. The objective of this study was to quantify habitat use and selection of juvenile pallid sturgeon in the Missouri River, Nebraska, USA. Thirty‐seven age‐4 pallid sturgeon with transmitters were released in July of 2014, plus an additional 21 in September, with habitat monitored using biotelemetry. Age‐1 and age‐4 hatchery reared pallid sturgeon were found to avoid areas associated with the outside bend and thalweg habitats that were characterized by rapid water velocity (>1 ms^?1), which accounted for 50% of the area in the channelized Missouri River. Age‐1 pallid sturgeon selected an off‐channel habitat and inside bend habitat while age‐4 pallid sturgeon selected an off‐channel and inside bend channel border habitat. Juvenile pallid sturgeon in unaltered rivers have been shown to associate with island tips and sand bars, habitat that is largely absent in the channelized Missouri River. This study indicates that juvenile pallid sturgeon in the Missouri River, Nebraska are selecting habitats with shallow water and slow water velocity, similar to those associated with island tips and sand bars in unaltered reaches.     

Migrations and swimming capabilities of endangered pallid sturgeon (Scaphirhynchus albus) to guide passage designs in the fragmented Yellowstone River

Fragmentation of the Yellowstone River is hypothesized to preclude recruitment of endangered Scaphirhynchus albus (pallid sturgeon) by impeding upstream spawning migrations and access to upstream spawning areas, thereby limiting the length of free‐flowing river required for survival of early life stages. Building on this hypothesis, the reach of the Yellowstone River affected by Intake Diversion Dam (IDD) is targeted for modification. Structures including a rock ramp and by‐pass channel have been proposed as restoration alternatives to facilitate passage. Limited information on migrations and swimming capabilities of pallid sturgeon is available to guide engineering design specifications for the proposed structures. Migration behavior, pathways (channel routes used during migrations), and swimming capabilities of free‐ranging wild adult pallid sturgeon were examined using radiotelemetry, and complemented with hydraulic data obtained along the migration pathways. Migrations of 12–26% of the telemetered pallid sturgeon population persisted to IDD, but upstream passage over the dam was not detected. Observed migration pathways occurred primarily through main channel habitats; however, migrations through side channels up to 3.9 km in length were documented. The majority of pallid sturgeon used depths of 2.2–3.4 m and mean water velocities of 0.89–1.83 m/s while migrating. Results provide inferences on depths, velocities, and habitat heterogeneity of reaches successfully negotiated by pallid sturgeon that may be used to guide designs for structures facilitating passage at IDD. Passage will provide connectivity to potential upstream spawning areas on the Yellowstone River, thereby increasing the likelihood of recruitment for this endangered species.     

Asymmetric introgression between fishes in the Red River basin of Texas is associated with variation in water quality

When ecologically divergent taxa encounter one another, hybrid zones can form when reproductive isolation is incomplete. The location of such hybrid zones can be influenced by environmental variables, and an ecological context can provide unique insights into the mechanisms by which species diverge and are maintained. Two ecologically differentiated species of small benthic fishes, the endemic and imperiled prairie chub, Macrhybopsis australis, and the shoal chub, Macrhybopsis hyostoma, are locally sympatric within the upper Red River Basin of Texas. We integrated population genomic data and environmental data to investigate species divergence and the maintenance of species boundaries in these two species. We found evidence of advanced‐generation asymmetric hybridization and introgression, with shoal chub alleles introgressing more frequently into prairie chubs than the reciprocal. Using a Bayesian Genomic Cline framework, patterns of genomic introgression were revealed to be quite heterogeneous, yet shoal chub alleles were found to have likely selectively introgressed across species boundaries significantly more often than prairie chub alleles, potentially explaining some of the observed asymmetry in hybridization. These patterns were remarkably consistent across two sampled geographic regions of hybridization. Several environmental variables were found to significantly predict individual admixture, suggesting ecological isolation might maintain species boundaries.     

Comparison of electrofishing and trammel netting variability for sampling native fishes

The variability in size structure and relative abundance (CPUE; number of fish ≥200 mm total length, L_T, collected per hour of electrofishing or trammel netting) of three native Colorado River fishes, the endangered humpback chub Gila cypha, flannelmouth sucker Catostomus latipinnus and bluehead sucker Catostomus discobolus, collected from electrofishing and trammel nets was assessed to determine which gear was most appropriate to detect trends in relative abundance of adult fishes. Coefficient of variation (CV) of CPUE ranged from 210 to 566 for electrofishing and 128 to 575 for trammel netting, depending on season, diel period and species. Mean CV was lowest for trammel nets for humpback chub (P = 0·004) and tended to be lower for flannelmouth sucker (P = 0·12), regardless of season or diel period. Only one bluehead sucker >200 mm was collected with electrofishing. Electrofishing and trammel netting CPUE were not related for humpback chub (r = ?0·32, P = 0·43) or flannelmouth sucker (r = ?0·27, P = 0·46) in samples from the same date, location and hour set. Electrofishing collected a higher proportion of smaller (<200 mm L_T) humpback chub (P < 0·001), flannelmouth suckers (P < 0·001) and bluehead suckers (P < 0·001) than trammel netting, suggesting that conclusions derived from one gear may not be the same as from the other gear. This is probably because these gears fished different habitats, which are occupied by different fish life stages. To detect a 25% change in CPUE at a power of 0·9, at least 473 trammel net sets or 1918 electrofishing samples would be needed in this 8 km reach. This unattainable amount of samples for both trammel netting and electrofishing indicates that detecting annual changes in CPUE may not be practical and analysis of long‐term data or stock assessment models using mark‐recapture methods may be needed to assess trends in abundance of Colorado River native fishes, and probably other rare fishes as well.     

Distribution, relative abundance and movements of pallid sturgeon in the free-flowing Mississippi River

A multiyear study of pallid sturgeon distribution and relative abundance was conducted in the lower and middle Mississippi river (LMR and MMR, respectively). The LMR and MMR comprise the free‐flowing Mississippi River extending 1857 river kilometers (rkm) from its mouth at the Gulf of Mexico upstream to the mouth of the Missouri River. A total of 219 pallid sturgeon and 6018 shovelnose sturgeon was collected during the periods 1996–1997 and 2000–2006. Trotlines baited with worms were the primary collecting gear. The smallest pallid sturgeon captured on trotlines was 405 mm FL and the largest was 995 mm FL. Mean size of pallid sturgeon was statistically smaller in the Mississippi River below the Atchafalaya River near Baton Rouge, LA (621 mm FL). Mean abundance (catch per trotline night) of pallid sturgeon was highest at water temperatures around 10°C. There was a latitudinal trend in mean abundance of pallid and shovelnose sturgeon, but the pattern differed between species. Pallid sturgeon abundance was statistically (P < 0.05) higher (0.3 fish per trotline night) in the lower reach between the Atchafalaya River and New Orleans (rkm 154–507), and at the Chain of Rocks (COR), a low water dam near the mouth of the Missouri River. Pallid sturgeon abundance between these two locations was statistically the same (0.12–0.23). Shovelnose sturgeon abundance increased going upstream, but was disproportionally higher at the COR (22 fish per line compared with <6 fish per line in other reaches). Overall, the ratio between pallid and shovelnose sturgeon varied from a high of 1 : 6 at the lower reach, and gradually decreased upstream to a low of 1 : 77 at the COR. Based on differences in sturgeon abundance, size and habitat characteristics, the free‐flowing Mississippi River can be divided into two reaches in the MMR (i.e. COR is a separate location), and four reaches (i.e., including the Atchafalaya River) in the LMR where management goals may differ.     

Characterization of 16 highly variable tetranucleotide microsatellite loci for Oregon chub (Oregonichthys crameri) and cross amplification in Umpqua chub (O. kalawatseti)

We describe the isolation and development of 16 polymorphic tetranucleotide microsatellite loci for the endangered Oregon chub (Oregonichthys crameri). Two loci appear to be duplicated. For the remaining 14 loci, we observed between three and 19 alleles per locus in a sample of 42 fish. Thirteen of these loci were also polymorphic in the closely related Umpqua chub (O. kalawatseti). These loci will aid in our understanding of the molecular ecology and conservation of these two species.     

Life history and status of the shovelnose sturgeon, Scaphirhynchus platorynchus

The shovelnose sturgeon, Scaphirhynchus platorynchus, is a freshwater sturgeon of the Mississippi and Missouri rivers and their tributaries. It is one of the smaller North American sturgeons, seldom weighing more than 2.5 kg over most of its range except in the upper Missouri River, where individuals of over 7 kg have been found. Spawning occurs in spring at temperatures between 17 and 21 °C over rock or gravel substrate downstream from dams, near rock structures, or in tributaries. most males reach sexual maturity at 5 years, most females at 7 years. Adults do not spawn every year. Shovelnose sturgeon are found in large, turbid rivers and frequently concentrate in areas downstream from dams or at the mouths of tributaries. Population densities range up to 2500 fish per km. They are commonly found in areas of current over sandy bottoms or near rocky points or bars, where they feed primarily on aquatic invertebrates. The shovelnose sturgeon is classified as a sport species in 12 of 24 states where it occurs. Commercial harvest is allowed in seven states, where fresh shovelnose sturgeon sell for 55 to 88 cents per kg, smoked shovelnose for about $5.75 per kg, and roe from 33 to 110 dollars per kg. About 25 tons of shovelnose sturgeon are harvested commercially each year. Shovelnose sturgeon are considered extirpated in three states, fully protected in four states, and rare, threatened, or of special concern in eight states. Populations are considered stable throughout most of the upper Mississippi, lower Missouri, Red, and Atchafalaya rivers. Three states, Wyoming, West Virginia, and New Mexico, have developed plans to reintroduce the species into rivers where it has been extirpated.     

Morphometric variation among river sturgeons (Scaphirhynchus spp.) of the Middle and Lower Mississippi River

Pallid sturgeon (Scaphirhynchus albus) captured in the Middle and Lower Mississippi River (i.e. below St. Louis, MO, USA) are morphologically very similar to shovelnose sturgeon (Scaphirhynchus platorynchus). Available empirical data are limited to a few studies based on low sample sizes from disjointed populations. Geneticists are currently searching for markers that will differentiate the two species, but the need for unequivocal species‐specific field characters remains. Continuation of commercial fishing for shovelnose sturgeon in some states necessitates an immediate means for accurate field identifications. Previous studies of lower basin river sturgeon classified individuals with simple morphometric character indices and interpreted intermediacy as interspecific hybridization. In this study, morphometric variation among Scaphirhynchus specimens from the Middle and Lower Mississippi River is examined for evidence of hybridization. Data are compared for large (>250‐mm standard length) hatchery‐reared and wild pallid specimens and wild shovelnose specimens. Specimens are compared using two morphometric character indices, two morphometric/meristic character indices and principal components analysis. Results indicate substantial morphological variation among pallid sturgeon below the mouth of the Missouri River. The amount of variation appears to decrease downstream in the Mississippi River. Sheared principal components analysis of morphometric data shows complete separation of shovelnose and pallid sturgeon specimens, whereas character indices indicate overlap. Both character indices and sheared principal components analysis demonstrate that pallid sturgeon in the Lower Mississippi River are morphologically more similar to shovelnose sturgeon than are pallids from the Upper Missouri River. This similarity, explained in previous studies as hybridization, may be the result of latitudinal morphometric variation and length‐at‐age differences between populations of the upper and lower extremes of the range.