Population genetics of shortnose sturgeon Acipenser brevirostrum based on mitochondrial DNA control region sequences

Shortnose sturgeon is an anadromous North American acipenserid that since 1973 has been designated as federally endangered in US waters. Historically, shortnose sturgeon occurred in as many as 19 rivers from the St. John River, NB, to the St. Johns River, FL, and these populations ranged in census size from 10(1) to 10(4), but little is known of their population structure or levels of gene flow. We used the polymerase chain reaction (PCR) and direct sequence analysis of a 440 bp portion of the mitochondrial DNA (mtDNA) control region to address these issues and to compare haplotype diversity with population size. Twenty-nine mtDNA nucleotide-substitution haplotypes were revealed among 275 specimens from 11 rivers and estuaries. Additionally, mtDNA length variation (6 haplotypes) and heteroplasmy (2-5 haplotypes for some individuals) were found. Significant genetic differentiation (P < 0.05) of mtDNA nucleotide-substitution haplotypes and length-variant haplotypes was observed among populations from all rivers and estuaries surveyed with the exception of the Delaware River and Chesapeake Bay collections. Significant haplotype differentiation was even observed between samples from two rivers (Kennebec and Androscoggin) within the Kennebec River drainage. The absence of haplotype frequency differences between samples from the Delaware River and Chesapeake Bay reflects a probable current absence of spawning within the Chesapeake Bay system and immigration of fish from the adjoining Delaware River. Haplotypic diversity indices ranged between 0.817 and 0.641; no relationship (P > 0.05) was found between haplotype diversity and census size. Gene flow estimates among populations were often low (< 2.0), but were generally higher at the latitudinal extremes of their distribution. A moderate level of haplotype diversity and a high percentage (37.9%) of haplotypes unique to the northern, once-glaciated region suggests that northern populations survived the Pleistocene in a northern refugium. Analysis of molecular variance best supported a five-region hierarchical grouping of populations, but our results indicate that in almost all cases populations of shortnose sturgeon should be managed as separate units.     

Distribution of mitochondrial DNA variation in lake sturgeon (Adpenser fulvescens) from the Moose River basin, Ontario, Canada

We analysed mitochondrial DNA (mtDNA) variation of lake sturgeon ( Adpenser fulvescens ) from the Moose River basin. Our objective was to address various proximate and ultimate factors which may influence the distribution of lake sturgeon mtDNA haplotype lineages in this watershed. The lake sturgeon sampled were characterized by only two mtDNA hapiotypes based on a restriction fragment length polymorphism analysis with 40 restriction endonucleases and direct sequencing of 275 nucleotides in the mtDNA control region. We detected no heterogeneity in the mtDNA haplotype frequencies of lake sturgeon captured from different sites within rivers including those separated by major hydroelectric installations. However, lake sturgeon from one tributary had significantly different haplotype frequencies than those from other tributaries suggesting that they composed a discrete genetic stock. These results suggest that gene flow among most sites is significant and is an important factor affecting the distribution of mtDNA variation in this species. The genetic structuring and diversity are discussed in relation to lake sturgeon management and conservation.     

Intraspecific DNA sequence variation of the mitochondrial control region of white sturgeon (Acipenser transmontanus)

Intraspecific sequence variation in the D-loop region of mtDNA in white sturgeon (Acipenser transmontanus), a relict North American fish species, was examined in 27 individuals from populations of the Columbia and Fraser rivers. Thirty-three varied nucleotide positions were present in a 462-nucleotide D-loop sequence, amplified using the polymerase chain reaction. Bootstrapped neighbor-joining and maximum- parsimony trees of sequences from 19 haplotypes suggest that the two populations have recently diverged. This is consistent with the hypothesis that the Columbia River, a Pleistocene refugium habitat, was the source of founders for the Fraser River after the last glacial recession. On the basis of a divergence time of 10-12 thousand years ago, the estimated substitution rate of the white sturgeon D-loop region is 1.1-1.3 x 10(-7) nucleotides/site/year, which is comparable to rates for hypervariable sequences in the human D-loop region. Furthermore, the ratio of mean percent nucleotide differences in the D- loop (2.27%) to that in whole mtDNA (0.54%, as estimated from restriction-enzyme data) is 4.3, which is similar to the fourfold-to- fivefold-higher substitution rate estimated for the human D-loop. The high nucleotide substitution rate of the hypervariable region indicates that the vertebrate D-loop has potential as a genetic marker in molecular population studies.      

Assessment of the seasonal usage of the lower Pascagoula River estuary by Gulf sturgeon (Acipenser oxyrinchus desotoi)

The Pascagoula watershed likely offers the greatest possibility for the survival of the Gulf sturgeon, Acipenser oxyrinchus desotoi, within Mississippi. Thus, understanding and preserving the connectivity between distant habitats in this region plays a major role in protecting and managing such anadromous fish populations. The focus of this project was to determine the within‐river routes Gulf sturgeon take through the lower Pascagoula River downstream of the point where it splits (river kilometer 23) into two distinct distributaries. Sixty days were sampled throughout a two‐year period with a total effort of 81 947 net‐meter‐hours and eight Gulf sturgeon were captured, ranging from 74 to 189 cm FL and weighing from 3.6 to 52.6 kg. Using an array of automated telemetry receivers, acoustically tagged Gulf sturgeon movements were monitored within the lower river and associated estuary. Estimated residence times (days) suggest Gulf sturgeon appear to prefer the eastern distributary upriver from Bayou Chemise as the primary travel corridor between freshwater habitats and marine feeding grounds. The western distributary mouth was more highly used by Gulf sturgeon during both seasonal migrations between upriver and offshore habitats. Thus, the western distributary appears to represent the main entrance point utilized by Gulf sturgeon to the Pascagoula River watershed and should be protected as the eastern distributary mouth has been altered from a natural marsh edge to one of hardened surfaces.     

Delineation of discrete population segments of shortnose sturgeon <Emphasis Type="Italic">Acipenser brevirostrum</Emphasis> based on mitochondrial DNA control region sequence analysis

Shortnose sturgeon Acipenser brevirostrum is federally listed as ‘‘an endangered species threatened with extinction’’ in the U.S. but its listing status is currently under review. As part of this process, the U.S. National Marine Fisheries Service will determine if shortnose sturgeon are divided into Distinct Population Segments (DPS) across its distribution. In this regard, we sought to determine if shortnose sturgeon occur in genetically “discrete population segments,” and if so, the boundaries of each. We used mitochondrial DNA (mtDNA) control region sequence analysis to assess the genetic discreteness of 14 of 19 river populations that were recommended as DPS in the 1998 Final Recovery Plan for Shortnose Sturgeon. Nine of the 14 proposed DPS proved significantly discrete (P < 0.05 after Bonferoni correction) from both of their bracketing populations, the exceptions being those in the Penobscot River, Chesapeake Bay, Cooper River, and Ogeechee River (our sample from the Cape Fear River was insufficient to statistically analyze). Haplotype frequencies in the newly “rediscovered” Penobscot River collection were almost identical to those in the proximal Kennebec River system. Genetic data in combination with tagging results suggest that shortnose sturgeon in the Penobscot River are probably migrants from the Kennebec. Likewise, shortnose sturgeon found today within the Chesapeake Bay appear to be migrants from the Delaware River. While haplotype frequencies in the remnant Santee River population in Lake Marion differed significantly from those in nearby Winyah Bay, they did not differ significantly from those in the Cooper River. This suggests that the Cooper River harbors descendants of the Santee River population that are unable to access their historical spawning locales. The Ogeechee River collection was not genetically distinct from that in the nearby Savannah River, suggesting that it may host descendants of hatchery-reared individuals of Savannah River ancestry. Our genetic results indicate that most, but not all, rivers with shortnose sturgeon host genetically discrete populations, constituting important information in the consideration of DPS designations. However, shortnose sturgeon migrations through coastal waters to proximal rivers and release of hatchery-reared fish may confound results from genetic studies such as ours and lead to the possible misidentification of discrete population segments.     

Gulf sturgeon summer habitat use and fall migration in the Pascagoula River, Mississippi, USA

The locations and habitat features of freshwater holding areas and the timing of fall migration are undocumented for Gulf sturgeon in the Pascagoula River drainage, Mississippi. Our objectives were to identify and characterize holding areas for Gulf sturgeon (Acipenser oxyrinchus desotoi), document their summer and fall movement patterns, and determine migration cues. To do this we captured, radio‐tagged, and monitored movement of Gulf sturgeon in the Pascagoula River drainage and analyzed these data using geographic information systems. From May to November Gulf sturgeon congregate in a holding area in the lower portion of the Pascagoula River and Big Black Creek [river kilometers (rkm) 57–68] and near Cumbest Bluff (rkm 40), before they return to the Gulf of Mexico. While in the holding area, Gulf sturgeon were typically found in deep locations, either in or downstream from river bends. As found in other rivers, Gulf sturgeon in the Pascagoula River showed little movement within the holding area and often stayed within a single river bend; although we observed local movements by some individuals (under 10 rkm). In the Pascagoula River, Gulf sturgeon initiated their migration out of fresh water from late‐September to mid‐October, coincident with shorter day length, falling water temperature (mean = 23.7°C, range 21–26°C), and elevated river flow. Our work demonstrates that the lower Pascagoula River serves as a vital area for Gulf sturgeon.     

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.     

Evidence of autumn spawning in Suwannee River Gulf sturgeon,Acipenser oxyrinchus desotoi (Vladykov, 1955)

Evidence of autumn spawning of Gulf sturgeon Acipenser oxyrinchus desotoi in the Suwannee River, Florida, was compiled from multiple investigations between 1986 and 2008. Gulf sturgeon are known from egg collections to spawn in the springtime months following immigration into rivers. Evidence of autumn spawning includes multiple captures of sturgeon in September through early November that were ripe (late‐development ova; motile sperm) or exhibited just‐spawned characteristics, telemetry of fish that made >175 river kilometer upstream excursions to the spawning grounds in September–October, and the capture of a 9.3 cm TL age‐0 Gulf sturgeon on 29 November 2000 (which would have been spawned in late September 2000). Analysis of age‐at‐length data indicates that ca. 20% of the Suwannee River Gulf sturgeon population may be attributable to autumn spawning. However, with the very low sampling effort expended, eggs or early life stages have not yet been captured in the autumn, which would be the conclusive proof of autumn spawning. More sampling, and sampling at previously unknown sites frequented by acoustic telemetry fish, would be required to find eggs.     

Geographic variation within a tandemly repeated mitochondrial DNA D-loop region of a North American freshwater fish, Pylodictis olivaris

The present study reports the distribution of a 35-bp mitochondrial DNA (mtDNA) D-loop tandemly repeated sequence in the populations of a North American freshwater catfish, Pylodictis olivaris, and the important role of a past geological event in the phylogeographic pattern of this species. A total of 330 individuals of flathead catfish, representing 34 drainages throughout the species' native range in the United States, were collected. While more than 70% of individuals sampled from the Southeastern Gulf Coast drainages were characterized by the presence of a 35-bp mtDNA D-loop tandem repeat proximal to the 5′ end, more than 95% of samples from the Mississippi River and its tributaries, as well as from the drainages of the Southwest Gulf Coast region, lack this tandem repeat. Concomitantly, phylogenetic analyses revealed the existence of two distinct matrilineal lineages (lineage I and II) of P. olivaris, which were estimated to have diverged from a common ancestor sometime between 0.70 and 2.05 myr ago. While one lineage is comprised of samples from the Mississippi River and its tributaries and rivers draining to the Southwest Gulf Coast, the other lineage is comprised of samples from the Southeastern Gulf Coast drainages. Each lineage also has two sub-lineages, which also showed geographic specificity.     

Mitochondrial DNA Length Variation and Heteroplasmy in Populations of White Sturgeon (Acipenser Transmontanus)

Southern blot analysis was used to quantify the extent of mtDNA D-loop length variation in two populations of white sturgeon, Acipenser transmontanus. Over 42% of individuals were heteroplasmic for up to six different mtDNA length variants attributable to varying copy numbers of an 82-bp repeat sequence. Chi-square analyses revealed that the frequencies of length genotypes and the incidence of heteroplasmy were significantly different between Fraser and Columbia River sturgeon populations but not between restriction site haplotypes. Heteroplasmic fish have, on average, higher copy number than homoplasmic fish. Forty-five of 101 homoplasmic individuals carry only a single copy of the repeat, while none of the 73 heteroplasmic fish has the single repeat as the predominant variant. On the basis of differences in frequency distributions of copy number within and between fish, we suggest that (1) heteroplasmy is maintained by high recurrent mutation of multiple copy genomes, favoring increased copy number and (2) the mutation pressure toward higher copy number heteroplasmy is partially offset by selection to reduced genome size and segregation to the homoplasmic condition.     

Ontogenetic patterns in prey use by pallid sturgeon in the Missouri River, South Dakota and Nebraska

The pallid sturgeon ( Scaphirhynchus albus ) is an endangered species native to the Missouri and Mississippi rivers. To date, recovery efforts have focused on stocking juvenile fish, but little is known about ontogenetic changes in diet composition. Although diet composition for pallid sturgeon is believed to change from macroinvertebrates to fish, it is unclear at what size and/or age these ontogenetic diet shifts occur. To evaluate diet composition, 29 hatchery-stocked pallid sturgeon (range 356–720 mm fork length [FL]; mean = 549; SE = 23) were collected from the Missouri River downstream of Fort Randall Dam, South Dakota and Nebraska during summer 2006. The majority of pallid sturgeon (72%) were captured within a large delta region formed by the Niobrara River in the headwaters of Lewis and Clark Lake. Predominant prey of pallid sturgeon based on percent occurrence was Ceratopogonidae (81%), Isonychiidae (67%), Chironomidae (52%), and fishes (24%). Percent composition by wet weight showed that diets were composed of fishes (68%), Ephemeroptera (23%), Decapoda (6%), and Diptera (3%). Graphical analysis of combined data showed that mayflies, particularly Isonychiidae, were an important component of pallid sturgeon diets. Nonetheless, the percent composition of fishes in the diet increased with pallid sturgeon body size; for fish > 600 mm FL (5–7 years of age) diets were composed primarily of fish prey (66%, mostly johnny darters Etheostoma nigrum ). These findings highlight the importance of ontogenetic changes in diet composition for pallid sturgeon. Moreover, the unique habitat formed in the delta region is characterized by higher fish and invertebrate densities that may enhance foraging opportunities and thus improve recovery efforts for stocked pallid sturgeon.     

An evaluation of introgression of Atlantic coast striped bass mitochondrial DNA in a Gulf of Mexico population using formalin-preserved museum collections

Striped bass Morone saxatilis populations in drainages along the Gulf of Mexico coast (Gulf) were depleted in the 1950s and 1960s, probably because of anthropogenic influences. It is believed that only the Apalachicola-Chattahoochee-Flint (A-C-F) river system continually supported a naturally reproducing population of Gulf lineage. Striped bass juveniles of Atlantic coast (Atlantic) ancestry were introduced to restore population abundances in the A-C-F from the late 1960s to the mid 1970s and in many other Gulf rivers from the 1960s to the present. We previously identified mtDNA polymorphisms that were unique to ? 60% of striped bass from the A-C-F and which confirmed the continued successful natural reproduction of striped bass of Gulf maternal ancestry within the system. However, the genetic relatedness of the extant A-C-F population to ‘pure’ Gulf striped bass was not addressed. In this study, we determined the frequency of a diagnostic mtDNA XbaI polymorphism in samples of ‘pure’ Gulf striped bass that were collected from the A-C-F prior to the introduction of Atlantic fish, that were obtained from museum collections, and that were originally preserved in formalin. PCR primers were developed that allowed for amplification of a 191-bp mtDNA fragment that contained the diagnostic XbaI restriction site. Using RFLP and direct sequence analyses of the PCR amplicons, we found no significant differences in mtDNA XbaI genotype frequencies between the archived samples and extant A-C-F samples collected over a 15-year period. This indicates that significant maternally mediated introgression of Atlantic mtDNA genomes into the A-C-F gene pool has not occurred. Additionally, we found no evidence of the unique Gulf mtDNA genotype in striped bass from extant populations in Texas, Louisiana and the Mississippi River. These results highlight the importance of the A-C-F as a repository of striped bass to restore extirpated Gulf populations and the potential use of museum collections in retrospective population studies.     

Mitochondrial DNA variation and population genetic structure of the northern redbelly dace (Phoxinus eos)

Two sections of the control region and the genes coding for NADH dehydrogenase sub-units 5 and 6 (ND-5/6) of mitochondrial DNA (mtDNA) were amplified from Phoxinus eos with the polymerase chain reaction. Both sections of the control region were sequenced directly while the ND-5/6 fragment was sequenced in from each end only. Additionally, the entire ND-5/6 fragment was examined for sequence variation using RFLP analysis. No sequence variation was detected in the control region among 70 individuals sampled from 18 populations across three Ontario regions (Spanish River, Madawaska R. and Cataraqui R.). To examine ND-5/6 variation, a total of 75 individuals were sampled from five populations representing two of the three regions (Madawaska River and Cataraqui R.). Six haplotypes were detected by direct sequencing and four by RFLP analysis. Estimates of population subdivision from RFLP data, sequence analysis, and the two data sets combined for the ND-5/6 fragment, suggest that gene flow is restricted within and between regions. However, estimates of sequence divergence for both sequence and RFLP analysis of this fragment suggested that populations were either founded by already differentiated populations or that populations were founded by a single stock and divergence between regions occurred prior to isolation of populations within regions. These estimates of population structure are much greater than those obtained from allozyme analysis. Additionally, high levels of heterozygosity in nuclear DNA, but low mtDNA diversity suggests that populations have experienced reductions in population size sufficient to reduce only mtDNA variation. Random lineage extinction and limited time for the accumulation of new mutations are likely responsible for low levels of mtDNA variation in ND-5/6 and the control region, while functional constraints may limit variation more than expected in the control region in dace and other fishes.     

Experimental passage of adult male Gulf sturgeon around Jim Woodruff Lock and Dam on the Apalachicola River,Florida

Dams can impede access to habitats that are required for the completion of life history phases of many migratory fish species, including anadromous sturgeons. Various forms of fish passage have been developed to permit migratory fishes to move above dams, but many dams still lack such structures. Translocation of ripe, mature fish above dams has been used as a first step to determine the efficacy of potential fish passage systems. The anadromous Gulf sturgeon, Acipenser oxyrinchus desotoi, inhabits the Gulf of Mexico and coastal rivers from Florida to Louisiana, and requires upriver spawning habitats to complete its life cycle. Historic overfishing and other anthropogenic threats, including dam construction, led to species declines and subsequent listing as threatened under the Endangered Species Act. In the Apalachicola River, FL, the 1957 completion of Jim Woodruff Lock and Dam (JWLD) created Lake Seminole and blocked Gulf Sturgeon from accessing 78% of historic riverine habitat—including potential spawning habitat—in the Apalachicola-Chattahoochee-Flint River Basin. The objective of this pilot study was to determine the efficacy of passage around JWLD through the trap-and-transport of 10 male Gulf sturgeon from the Apalachicola River to the reservoir above the dam. Through the use of acoustic telemetry, we were able to assess the ability of these fish to navigate Lake Seminole, access potentially suitable spawning habitat in the Flint and River, and complete their seasonal outmigration to the Gulf of Mexico. In this study, 2 translocated sturgeon moved 69 km upstream into potential spawning habitat in the Flint River, but 6 fish fell back through the lock/spill gates at JWLD within days of translocation. Four sturgeon appeared to remain trapped in the reservoir, and their long-term survival was deemed unlikely. Given our low sample size, and examination of male fish only, we cannot conclude that a trap-and-transport program would ultimately fail to restore spawning above JWLD, but our findings suggest that the risk of adult mortality is nontrivial. Alternatively, we suggest future studies examine the population level trade-offs associated with translocation of adults or consider alternatives such as a head-start program to rear and release juvenile sturgeon above JWLD to study viability of their passage in addition to effects on overall recruitment in the population.     

Length Variation, Heteroplasmy and Sequence Divergence in the Mitochondrial DNA of Four Species of Sturgeon (Acipenser)

The extent of mtDNA length variation and heteroplasmy as well as DNA sequences of the control region and two tRNA genes were determined for four North American sturgeon species: Acipenser transmontanus, A. medirostris, A. fulvescens and A. oxyrhnychus. Across the Continental Divide, a division in the occurrence of length variation and heteroplasmy was observed that was concordant with species biogeography as well as with phylogenies inferred from restriction fragment length polymorphisms (RFLP) of whole mtDNA and pairwise comparisons of unique sequences of the control region. In all species, mtDNA length variation was due to repeated arrays of 78-82-bp sequences each containing a D-loop strand synthesis termination associated sequence (TAS). Individual repeats showed greater sequence conservation within individuals and species rather than between species, which is suggestive of concerted evolution. Differences in the frequencies of multiple copy genomes and heteroplasmy among the four species may be ascribed to differences in the rates of recurrent mutation. A mechanism that may offset the high rate of mutation for increased copy number is suggested on the basis that an increase in the number of functional TAS motifs might reduce the frequency of successfully initiated H-strand replications.     

POPULATION STRUCTURE OF THE BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) AS DETERMINED BY RESTRICTION ENDONUCLEASE ANALYSIS OF MITOCHONDRIAL DNA

Abstract: Restriction fragment length polymorphisms of mitochondrial DNA (mtDNA) were used to test for population subdivision in the bottlenose dolphin (Tursiops truncatus). Atlantic and Pacific dolphin mtDNA samples exhibited distinctly different haplotypes (approximately 2.4% sequence divergence), indicating a lack of gene exchange. Within the Atlantic Ocean, mtDNA samples from the Gulf of Mexico and the Atlantic Coast were also found to be distinct, with a sequence divergence of approximately 0.6%. The Atlantic Coast–Gulf of Mexico dichotomy is consistent with patterns of genetic variation from other marine and coastal organisms from this region, and supports the hypothesized role of bio-geographic events in promoting the divergence of these and other forms. Regional differentiation was identified along the Atlantic Coast, whereas low sequence divergences among haplotypes and consistent haplotype frequencies across populations suggested considerable gene exchange among Gulf of Mexico populations. A highly divergent haplotype found in two individuals from two localities in the Gulf of Mexico is best explained by dispersal from either a distinct offshore Gulf stock or an unsampled Atlantic Coast stock. Additional samples are required to test for the existence of a distinct offshore race and, if it exists, to identify its distribution and contribution to population structure.     

Genetic diversity of Garra rufa Heckel, 1843 (Teleostei: Cyprinidae) in Anatolia

In the present study, mitochondrial DNA polymerase chain reaction-restriction-fragment length polymorphism (PCR-RFLP) and nuclear DNA inter-simple sequence repeat (ISSR) assays were used to assess the phylogenetic and phylogeographic relationships among Garra rufa samples from Anatolia. The complete mtDNA NADH 3/4 dehydrogenase (ND-3/4) gene amplified by PCR was digested with eight restriction enzymes. These enzymes produced 20 composite haplotypes for G. rufa populations. All the mtDNA haplotypes detected were highly diverged from each other and each lineage had a unique genetic profile. The evaluation of mtDNA PCR-RFLP data coupled with geological history of Anatolia indicated a deep genetic divergence among the mtDNA haplotypes of G. rufa populations from drainages of the Mediterranean and Persian Gulf, suggesting an early isolation of Tigris-Euphrates with Orontes river and other rivers draining into the Mediterranean Sea. In general, data from both mtDNA and nDNA were congruent.     

Monitoring demographics of a commercially exploited population of shovelnose sturgeon in the Wabash River,Illinois/Indiana,USA

Shovelnose sturgeon (Scaphirhynchus platorynchus, Rafinesque, 1820) in the Wabash River, Illinois/Indiana, USA, provide an important recreational sport and commercial caviar fishery. In fact, it is one of the last commercially viable populations for sturgeon roe harvest. Due to increased demand in the caviar trade and endangered species legislation that protect shovelnose sturgeon in only a portion of their range, efforts of the roe harvest market may continue to divert toward unprotected populations like the shovelnose sturgeon in the Wabash River. Previous studies have shown that increased harvest pressure in this species can affect the age‐at‐maturation and result in recruitment overfishing. Therefore, it is important to closely and continuously monitor commercially exploited populations. Over the past decade (2007–2016), 13,170 shovelnose sturgeon were sampled with boat electroshocking, hoop nets, drift nets, trotlines, and benthic electrified trawls. Captured fish ranged from 61 to 910 mm fork length (FL; mean = 668 mm), with very few fish less than 550 mm FL. Although fish were found to be in a healthy condition (mean relative weight = 87), there was a decrease in the mean condition over time. In addition, we saw declines in mean FL, weight of roe‐per‐fish, and size‐at‐maturity for female fish directly impacted by harvest. The decline of these population parameters, coupled with an increase in total annual mortality and a truncated age frequency distribution, suggest that harvest is negatively impacting the demographics and recruitment of shovelnose sturgeon in the Wabash River. Considering the downward trajectory of population dynamics and high estimates of mortality, their resiliency to continued harvest and environmental changes will be limited.     

Age and growth of pallid sturgeon in the free-flowing Mississippi River

Trotlines were used to capture pallid sturgeon in the free‐flowing Mississippi River, which extends from the Gulf of Mexico to the mouth of the Missouri River. Trotlines were baited with worms, and set overnight usually along the channel border. The pectoral fin rays of 165 pallid sturgeon caught in the Mississippi River were aged; 118 were from the lower Mississippi River (LMR) between the Gulf and mouth of the Ohio River, and 47 were from the middle Mississippi River (MMR) between the mouths of the Ohio and Missouri rivers. Initial agreement within ±1 year between two readers ranged from 53% for the LMR specimens, which were read first, to 84% for the MMR. Final age was agreed upon by both readers. For LMR pallid sturgeon, final age estimates ranged from 3 to 21 years with a mean (±SD) of 11.0 ± 4.7. For MMR pallid sturgeon, final age estimates ranged from 5 to 14 years with a mean of 9.5 ± 2.1. Seven pallid sturgeon marked with coded wire tags (CWT), indicating hatchery origin, were collected in the MMR. Age estimates for CWT fish were 7–8 years representing 1997 stocked fish, and 11–12 years representing 1992 progeny stocked in 1994. Von Bertalanffy growth equations for length indicated that pallid sturgeon in the MMR had higher growth rates for a given age than pallid sturgeon in the LMR. However, there were no significant differences (anova , P > 0.5) in the length–weight relationships between reaches. In the LMR, pallid sturgeon fully recruited to trotlines at age 11 and instantaneous total mortality (Z; slope of catch curve) was estimated at −0.12 (n = 10 year classes, r² = 0.55, P = 0.01). Of the 118 sectioned rays from the LMR, 28 could not be reliably aged (only one section from the MMR could not be aged). Therefore, age was predicted from length using the von Bertalanffy equation. The catch curve was re‐calculated using the predicted ages of the 28 pallid sturgeon in the LMR resulting in Z = −0.07. In the MMR, pallid sturgeon fully recruited to trotlines at age 9 and Z was estimated at −0.36 (n = 6 year classes, r² = 0.67, P = 0.04), which was significantly higher (anova , P = 0.04) than the LMR estimate. Higher mortality in the MMR may be due to habitat limitations compared to a larger, more diverse channel in the LMR, and incidental take of larger, older individuals during commercial harvesting of shovelnose sturgeon. Commercial take of shovelnose does not occur in the LMR except in the northern portion of the reach. Considering the presence of pallid sturgeon with CWT, recruitment of older individuals in the MMR may have been influenced by stocking a decade earlier. Management strategies for this endangered species should consider the differences in mortality rates among reaches, the impacts of commercial fishing on recovery of pallid sturgeon in the MMR, and the long‐term effects of hatchery fish now recruiting into the free‐flowing Mississippi River.     

Endemic sturgeons of the Amur River: kaluga, Huso dauricus, and Amur sturgeon, Acipenser schrenckii

General biological characteristics and the contemporary status of the kaluga, Huso dauricus, and Amur sturgeon, Acipenser schrenckii, are described. Both inhabit the Amur River basin. Kaluga is the largest freshwater fish in this river system reaching more than 5.6 m in length and more than 1000 kg in weight. We recognize four populations of kaluga: the first is from the estuary of the Amur River and coastal brackish waters of the Sea of Okhotsk and Sea of Japan, the second is from the lower Amur River, the third is from the middle-Amur, and the fourth occurs in lower reaches of the Zeya and Bureya rivers. Freshwater and brackish water morphs exist in the estuary population, with the freshwater morph predominating in number. The number of individuals in the lower Amur River population at age 2 or greater was recently estimated to be 40 000, and in the middle Amur, 30 000. The population will continue to decline because of rampant overfishing. The Amur sturgeon is represented in the Amur River basin by two morphs: brown and gray. Brown morphs occur in the middle and lower parts of the Amur River; they grow more slowly than the gray ones. Today, the lower Amur River population of Amur sturgeon is made up of 95 000 fish at age 2 or greater and is approximately half as large as the population in the middle Amur River. Populations of kaluga and Amur sturgeon in the Zeya and Bureya rivers are extremely small and on the verge of extinction.