Scaphirhynchus Species Research Articles

Ontogenetic development of pallid sturgeon (Scaphirhynchus albus) and shovelnose sturgeon (Scaphirhynchus platorynchus) from hatch through yolk absorption

AbstractSturgeons have a complex free‐embryo period extending from hatch to the initiation of exogenous feeding. Although available for some sturgeon species of the genus Acipenser, descriptions of the developmental stages of free embryos of the genus Scaphirhynchus are lacking. We characterised the ontogenetic development of pallid sturgeon (Scaphirhynchus albus) and shovelnose sturgeon (S. platorynchus) free embryos from hatch through melanin plug expulsion. The rate of development was similar between Scaphirhynchus species among free embryos from 4 pallid sturgeon and 7 shovelnose sturgeon crosses reared separately in the laboratory at a mean temperature of 17.8°C. Free embryos required a mean of 18.2 days postfertilisation (DPF; 323.5 cumulative thermal units; CTU) to reach melanin plug expulsion for pallid sturgeon and 17.9 DPF (318.3 CTU) for shovelnose sturgeon. Free embryos of both species showed overlap in lengths among developmental stages indicating that length of free embryos alone is insufficient to estimate age. Description of pallid sturgeon and shovelnose sturgeon free‐embryo development provides a template to develop more sophisticated models incorporating length and stage to estimate the age of field‐collected specimens. Improved estimates of free‐embryo developmental stage and age may aid in the identification of timing and location of spawning and better inform flow manipulation and habitat management actions tailored to increase survival of early life‐stage pallid sturgeon.

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 cautiously for juvenile and adult Pallid Sturgeon, especially in highly variable conditions.Received December 4, 2014; accepted March 19, 2015

Trotline efficiencies and catch rates in a large river

AbstractTrotlines have proved to be an effective collection method for riverine fish species, but an understanding of the interaction between fish and gear post‐deployment is lacking. The objectives of this study were to use trotlines rigged with hook timers that record the time when fish are hooked to determine the activation rate of hook timers, to determine the retention rate of fish on trot lines, to document hourly catch rates and to document whether hooking duration causes stress or mortality. Four thousand hook timers were deployed in an 80.5 rkm reach of the Missouri River during April 2011, resulting in a mean catch rate of 14.6 fish per line, while 3.1 timers per line were activated but did not capture a fish. Over half of all fish were captured within 4 h post‐deployment. Stress and mortality associated with trotlines did not appear to be related to hooking duration. This study showed that hourly catch rates and retention rates can be ascertained from the use of trotlines rigged with hook timers. Information gathered from this study and further investigation with hook timers could aid in targeting specific time of day and set duration to collect river fish more efficiently, especially sturgeons, Scaphirhynchus species.

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

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.

Comparative neuromorphology of the telencephalon of sturgeon of the genera Acipenser, Huso and Scaphirhynchus (Actinopterygii; Acipenseridae)

Summary Brain anatomy and structure, composition of the neurons, and cytoarchitectural maps were compared between five species of Acipenser, one species of Huso and two species of Scaphirhynchus. Morphological differences in the forebrain structure between species and genera were apparent. The evolutionary history of the Acipenseridae has been marked by an extensive mosaic radiation in the evolutionary development of the inner structure of their brains. Members of Scaphirhynchus have a very simple telencephalon structure differing significantly from that of Huso and Acipenser. It is clear that neuromorphological variation of sturgeon species will serve as an additional data useful in understanding the evolutionary processes and history associated with the speciation in Acipenseridae.

Molecular systematics of Scaphirhynchinae: an assessment of North American and Central Asian Freshwater Sturgeon Species

Summary The sturgeon subfamily Scaphirhynchinae contains two genera of obligate freshwater sturgeon: Scaphirhynchus and Pseudoscaphirhynchus, from North America and Central Asia, respectively. Both genera contain morphologically variable species. A novel data set containing multiple individuals representing four diagnosable morphological variants for two species of Pseudoscaphirhynchus, P. hermanni and P. kaufmanni, was generated. These data were used to test taxonomic hypotheses of monophyly for the subfamily Scaphirhynchinae, monophyly of both Scaphirhynchus and Pseudoscaphirhynchus, monophyly of P. hermanni and P. kaufmanni, and monophyly of the recognized morphological variants. Monophyly of the subfamily Scaphirhynchinae is consistently rejected by all phylogenetic reconstruction methodologies with the molecular character set while monophyly of both river sturgeon genera is robustly supported. The molecular data set also rejects hypotheses of monophyly for sampled species of Pseudoscaphirhynchus as well as monophyly for the recognized intraspecific morphological variants. Interestingly both Scaphirhynchus and Pseudoscaphirhynchus demonstrate the same general pattern in reconstructed topologies; a lack of phylogenetic structure in the clade with respect to recognized diversity. Despite rejection of monophyly for the subfamily Scaphirhynchinae with molecular data, reconstructed hypotheses from morphological character sets consistently support monophyly for this subfamily. Disparities among the data sets, as well as reasons for rejection of monophyly for Scaphirhynchinae and species of Scaphirhynchus and Pseudoscaphirhynchus with molecular characters are examined and a decreased rate of molecular evolution is found to be most consistent with the data.

Morphologic comparisons of hatchery-reared specimens of Scaphirhynchus albus, Scaphirhynchus platorynchus, and S. albus�נS. platorynchus hybrids (Acipenseriformes: Acipenseridae)

Summary Extensive habitat modifications within the Mississippi and Missouri rivers have presumably interfered with the reproductive isolating mechanisms between the endangered pallid sturgeon, Scaphirhynchus albus, and the sympatric shovelnose sturgeon, Scaphirhynchus platorynchus, causing hybridization between these two species. Several character indices were developed to assist fisheries biologists in identifying specimens of S. albus, S. platorynchus, and their putative hybrids. The indices have numerous assumptions, including that pure strains of both parental species are within the sample analyzed and that hybrids are morphologically intermediate relative to their parents. If these indices have produced inaccurate identifications, then previous work on Scaphirhynchus studies in the Mississippi and Missouri rivers are questionable, including status surveys, captive propagation efforts, or the harvesting of tissues for genetic studies. In this study we tested indices by examining progeny of known pallid, shovelnose, and hybrid sturgeon propagated, raised, and preserved at hatcheries. These 60 specimens [78–600 mm standard length (SL)] were propagated with breeding stock from the upper Missouri River drainage, where hybridization between these two species presumably does not occur. Existing indices did not correctly identify small ( 250 mm SL) sizes of S. albus, S. platorynchus, and their hybrids. Indices worked fairly well in identifying large S. platorynchus, but not in differentiating large S. albus from hybrids. We used principal components analysis (PCA) as an alternative approach to character indices. No a priori knowledge of the identity of the specimen is required with this multivariate technique, which avoids potential circular reasoning present in indices. We were able to completely or almost completely separate both sturgeon species and their hybrids by extracting principal components from a correlation matrix of 13 meristic characters in a standard PCA and extracting size-corrected principal components from a covariance matrix of 51 morphometric variables using a sheared PCA. Additionally, we demonstrated that first generation hybrids were intermediate with respect to their parental species. Multivariate analyses with a reduced character set of six meristic and 12 morphometric variables also led to accurate and reliable specimen identification. Head spines and numerous qualitative characters are also extremely useful in differentiating between Scaphirhynchus species and their hybrids. In addition to all morphometric characters, some meristic characters and the degree of head spine fusion vary significantly with SL of sturgeons. Recording appropriate data from released specimens, including photovouchers, and making this information available is essential for researchers to have any scientific or legal basis for genetic or any other studies involving these sturgeons.

Phylogenetics ofScaphirhynchusBased on Mitochondrial DNA Sequences

Species delineation and taxonomy within the sturgeon genus Scaphirhynchus is controversial. This issue is made more complex by political issues regarding the Alabama sturgeon S. suttkusi and potential hybridization between sympatric shovelnose sturgeon S. platorynchus and pallid sturgeon S. albus. We investigated phylogenetic relationships among species of Scaphirhynchus based on nucleotide sequences for two mitochondrial loci, cytochrome b and the control region (D-loop). White sturgeon Acipenser transmontanus and green sturgeon A. medirostris were used as outgroups. Phylogenetic analyses did not recover monophyletic shovelnose or pallid sturgeon; however, some populations of pallid sturgeon were resolved as sister to the Alabama sturgeon, and one specimen of shovelnose sturgeon was consistently resolved as the sister to all other ingroup taxa. The hierarchical pattern of relationships produced by analysis of mitochondrial DNA is not consistent with that produced by morphological data. It is consistent with the hypothesis of a low rate of evolution of these genes in Scaphirhynchus and reflects recent hybridization between shovelnose and pallid sturgeon, probably due to habitat degradation.

Microsatellite Analysis of Genetic Variation in Sturgeon: New Primer Sequences forScaphirhynchusandAcipenser

Low levels of genetic variation at traditional molecular markers have hampered genetic research within the family Acipenseridae. In an effort to develop a large set of polymorphic genetic markers, 172 clones were sequenced from three subgenomic libraries of shovelnose sturgeon Scaphirhynchus platorynchus; the libraries were enriched for two dinucleotide and one tetranucleotide microsatellite motifs (CA, GA, and TAGA). Primers were designed for 113 of the sequences and tested against shovelnose sturgeon, pallid sturgeon S. albus, white sturgeon Acipenser transmontanus, lake sturgeon A. fulvescens, and green sturgeon A. medirostris. Of the 113 primer sets tested, 96% amplified in one or more species (58 dimeric and 50 tetrameric). In Scaphirhynchus species, 93% of all loci amplified, and 76% were polymorphic. Within the individual Acipenser species, 65–80% of loci amplified, with 42–58% being polymorphic. Polymorphic systems for Scaphirhynchus species predominately displayed simple, disomic banding patterns, while those for Acipenser species typically displayed banding patterns characteristic of tetraploid or higher polyploid levels. These new microsatellite loci provide a group of genetic markers that are detectable with noninvasive sampling and that should prove useful in the preservation of threatened and endangered sturgeon species worldwide.

Phylogenetic Relationships of the North American Sturgeons (Order Acipenseriformes) Based on Mitochondrial DNA Sequences

The evolutionary relationships of the extant species within the order Acipenseriformes are not well understood. Nucleotide sequences of four mitochondrial genes (12S rRNA, COII, tRNAPhe, and tRNAAsp genes) in North American sturgeon and paddlefish were examined to reconstruct a phylogeny. Analysis of the combined gene sequences suggests a basal placement of the paddlefish with regard to the sturgeons. Nucleotide sequences of all four genes for the three Scaphirhynchus species were identical. The position of Scaphirhynchus based on our data was uncertain. Within the genus Acipenser, the two Acipenser oxyrinchus subspecies were very similar in sequence and found to be basal to the remaining Acipenser species examined. Based on our data, Acipenser transmontanus and Acipenser medirostris were sister taxa, as were Acipenser fulvescens and Acipenser brevirostrum. Comparisonof our results with hypotheses of sturgeon relationships proposed by previous authors is presented. The sequence data presented here are phylogeneticallyuseful and provide a solid foundation of genetic information for the North American Acipenseriformes that can be expanded to include Eurasian species to provide a global picture of sturgeon evolution.

Genetic distinction of pallid, shovelnose, and Alabama sturgeon: emerging species and the US Endangered Species Act

The sturgeon genus Scaphirhynchus consists of threerecognized species. Pallid and shovelnose sturgeon (S. albusand S. platorynchus, respectively) are sympatric in theMissouri and lower Mississippi Rivers of the central United States. TheAlabama sturgeon (S. suttkusi) is endemic to the nearby MobileRiver drainage and is isolated geographically from the other twospecies. Pallid sturgeon and the extremely rare Alabama sturgeon arelisted as endangered under the US Endangered Species Act (ESA).In contrast, shovelnose sturgeon are relatively common and are notlisted. Despite these taxonomies and morphological evidence, somebiologists have questioned the genetic and taxonomic distinctions of thethree species, thus raising doubts concerning the validity of protectingpallid and Alabama sturgeon under the ESA. To investigate thesequestions, we compared a 436 base-pair sequence of the mitochondrial DNA(mtDNA) control region among the three species. We observed 16 mtDNAhaplotypes defined by 27 single base-pair substitutions (transitions)and one single base-pair insertion/deletion (indel) among 78individuals examined. The maximum sequence divergence among thosehaplotypes (2.06%) was less than values usually observed betweenfish species. However, Alabama sturgeon (n = 3) weredistinguished from the other two taxa (n = 75) by aunique base-pair substitution and haplotype, and pallid and shovelnosesturgeon at their northern range of natural sympatry (upper MissouriRiver) did not share any haplotypes. On the other hand, only frequencydifferences among shared haplotypes distinguished (P < 0.01)pallid and shovelnose sturgeon at their southern range of naturalsympatry (Atchafalaya River), and genetic distances between northern andsouthern localities for each species were nearly as large as thedistances between species. These latter results are consistent withseveral hypotheses, including reports (based on morphology) of putativenatural hybrids in the Atchafalaya River but not in the upper MissouriRiver. Overall, these mtDNA results indicate significant reproductiveisolation between pallid and shovelnose sturgeon in areas of naturalsympatry, and recent evolutionary divergence of Alabama sturgeon. ThesemtDNA results provide the first molecular genetic evidence fordistinguishing the three Scaphirhynchus species and, coupledwith morphological and biogeographic data, indicate that pallid andAlabama sturgeon should be evaluated as distinct species under theESA.

Genetic variation at microsatellite loci in sturgeon: primer sequence homology inAcipenserandScaphirhynchus

Eleven tri- and tetra-meric motif microsatellite loci were identified in a lake sturgeon genomic library and were tested against the six North American species of Acipenser (lake sturgeon, A. fulvescens; shortnose sturgeon, A. brevirostrum; white sturgeon, A. transmontanus; green sturgeon, A. medirostris; Atlantic sturgeon, A. oxyrhynchus oxyrhynchus; gulf sturgeon, A. o. desotoi) and the two species of Scaphirhynchus (pallid sturgeon, S. albus; shovelnose sturgeon, S. platorhynchus) using four to six individuals of each species. Eight loci were amplified equally well in all eight species, and the remaining three loci were amplified in two, four, and seven species, respectively. Of the eight loci that worked in all species, one was monomorphic in all species, while the other seven were polymorphic in three to eight species. Single repeat differences in these tri- and tetra-meric repeat motifs can be readily scored on 4% Metaphor agarose gels stained with ethidium bromide. In addition, dosage for those loci exhibiting four gene doses can also be readily scored with this technique. These loci provide a much needed group of genetic markers, detectable with non-invasive sampling (blood, barbel, or fin), that should work well in threatened and endangered species of sturgeon worldwide.