Fecundity of Atlantic sturgeon (Acipenser oxyrinchus Mitchill, 1815) captured by the commercial fishery in the Saint John River,New Brunswick,Canada

Knowledge of fecundity in fishes is important for understanding life history, modeling population dynamics, developing fisheries management and determining conservation status. Sturgeon species are known for their high fecundity but to date only two populations of Atlantic sturgeon (Acipenser oxyrinchus Mitchill, 1815) have been examined for this aspect of their biology. The species is protected in most regions of eastern North America but the Saint John River, New Brunswick supports one of the two remaining commercial fisheries in Canada. Sixty females selected by this fishery were sampled for total length, weight, age, gonad weight and egg number. Absolute fecundity ranged from 153,630 to 1,306,626 eggs, with a mean fecundity of 582,832 ± 261,806 eggs. Absolute fecundity exhibited a significant positive relationship to increasing body weight but not to total length or age. Relative fecundity ranged from 129 to 216 eggs/g gonad weight and although it declined with both increasing body size and age the relationships were not significant. The Gonadosomatic Index (GSI) ranged from 1.3% to 27.0% with a mean of 7.8% ± 4.94 SD. Relative fecundity found in this study was higher and mean GSI lower than reported for other Atlantic sturgeon populations and other sturgeon species. Differences were probably due to location of the fishery downstream from spawning sites and selection of pre-spawning females by the commercial fishery.     

The annual marine feeding aggregation of Atlantic sturgeon Acipenser oxyrinchus in the inner Bay of Fundy: population characteristics and movement

Atlantic sturgeon Acipenser oxyrinchus aggregate to feed from May to October in Minas Basin (45° N; 64° W), a large, cul‐de‐sac embayment of the inner Bay of Fundy. The aggregation consists mainly of migrants from the Saint John, NB and Kennebec Rivers, ME (99%). During 2004–2015, 4393 A. oxyrinchus were taken as by‐catch by commercial fish trawlers or at intertidal fishing weirs, and 1453 were marked and/or sampled and released. Fork length (L_F) ranged from 458 to 2670 mm, but 72·5% were <1500 mm. Mass (M) ranged from 0·5 to 58·0 kg. The mass‐length relationship for fish ≤50 kg was log₁₀M = 3·32log₁₀L_F ? 5·71. Observed growth of unsexed A. oxyrinchus recaptured after 1–8 years indicated fish of 90–179 cm L_F grew c. 2–4 cm a year. Ages obtained from pectoral spines were from 4 to 54 years. The Von Bertalanffy growth model predicted K = 0·01 and L_∞ = 5209 mm L_F. Estimated annual mortality was 9·5–10·9%. Aggregation sizes in 2008 and 2013 were 8804 and 9244 individuals, respectively. Fish exhibited high fidelity for yearly return to Minas Basin and population estimates indicated the total at‐sea number utilizing the Basin increased from c. 10 700 in 2010 to c. 37 500 in 2015. Abundance in the Basin was greatest along the north shore in spring and along the south shore in summer, suggesting clockwise movement following the residual current structure. Marked individuals were recaptured in other bays of the inner Bay of Fundy, north to Gaspé, Quebec, and south to New Jersey, U.S.A., with 26 recoveries from the Saint John River, NB, spawning run. Fish marked at other Canadian and U.S. sites were also recovered in Minas Basin. Since all A. oxyrinchus migrate into and out of the Basin annually they will be at risk of mortality if planned tidal power turbines are installed in Minas Passage.     

Microsatellite DNA variation in Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and cross-species amplification in the Acipenseridae

Overharvest and habitat alteration have led toa collapse of most commercial Atlantic sturgeon(Acipenser oxyrinchus oxyrinchus)fisheries while pushing the species to rarityor extirpation in most of its historical range. A biologically sound conservation program forthis species requires knowledge of its geneticdiversity and of the evolutionary relationshipsamong geographic populations. To address theseresearch needs, six microsatellite loci wereisolated from A. o. oxyrinchus. Pedigreeanalysis suggested that all are inherited in acodominant Mendelian pattern. The six lociwere tested in ten additional sturgeon speciesfrom three genera and three apparent ploidylevels (4n, 8n, 16n). Approximately 70% ofsuccessful locus-species amplifications werepolymorphic. Polysomy was observed most oftenin 8n and 16n species. Genetic diversity andpopulation structure of A. o. oxyrinchuswere assayed using three polymorphic Aoxmarkers and four markers developed from lakesturgeon (A. fulvescens). A. o.oxyrinchus were sampled from the AltamahaRiver, Georgia, USA north to the St. LawrenceRiver, Quebec, Canada. Gulf sturgeon, A.o. desotoi, were sampled from the SuwanneeRiver, Florida, USA, to assess differentiationbetween the subspecies. Seventy-seven alleleswere observed to segregate into uniquemultilocus genotypes for each of the 392individuals assayed. Mean diversity wasgreatest in the Chesapeake Bay (9.7 alleles perlocus) and Delaware River (7.4 alleles perlocus) collections, and lowest in the St.Lawrence River (4.6 alleles per locus). Meanheterozygosity across seven loci ranged from44.3% (St. Lawrence River) to 62.6% (Altamaha River). Significant allelic heterogeneity wasobserved in 82% of pairwise comparisons aswell as a global test (p < 0.0001) for A.o. oxyrinchus collections. Genetic distancesuggests the presence of at least sixsubpopulations in A. o. oxyrinchus: St.Lawrence River, St. John River, Hudson River,Delaware River, Albemarle Sound, and AltamahaRiver. Genetic and geographic distances werepositively correlated (r = 0.57, p < 0.03) amongA. o. oxyrinchus, suggesting isolation bydistance and philopatry. Hierarchical genediversity analysis indicated significantgenetic population structure at every level. Maximum likelihood assignment tests correctlyassigned individual fish to collection with ahigh rate of success (mean = 87.5%); this andother lines of evidence indicated that theChesapeake Bay collection represents a mixedpopulation of sub-adult sturgeon from northernand southern Atlantic coast populations. Population structure was correlated with thatsuggested by earlier mitochondrial (mt) DNAanalyses. Significant diversity was observedbetween two Canadian populations from whichonly a single mtDNA haplotype has beenreported.     

Dual Annual Spawning Races in Atlantic Sturgeon

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus, Acipenseridae) populations in the United States were listed as either endangered or threatened under the Endangered Species Act in 2012. Because of the endangered/threatened status, a better understanding of Atlantic sturgeon life-history behavior and habitat use is important for effective management. It has been widely documented that Atlantic sturgeon reproduction occurs from late winter to early summer, varying clinally with latitude. However, recent data show Atlantic sturgeon also spawn later in the year. The group that spawns later in the year seems to be completely separate from the spring spawning run. Recognition of the later spawning season has drastically modified estimates of the population status of Atlantic sturgeon in Virginia. With the combination of new telemetry data and historical documentation we describe a dual spawning strategy that likely occurs in various degrees along most, if not all, of the Atlantic sturgeon''s range. Using new data combined with historical sources, a new spawning strategy emerges which managers and researchers should note when determining the status of Atlantic sturgeon populations and implementing conservation measures.     

Atlantic sturgeon presence in a designated marine hydrokinetic test site prior to turbine deployment: A baseline study

In 2009, the Fundy Ocean Research Centre for Energy (FORCE) developed a 1.6 x 1.0 km Crown Lease Area (CLA) to test Marine Hydrokinetic devices (MHKs) in Minas Passage (MP), a strait that connects the Bay of Fundy to Minas Basin (MB), Nova Scotia. Minas Basin is an important summer feeding aggregation site for numerous fishes including Atlantic sturgeon (Acipenser oxyrinchus Mitchill, 1815) stocks from Canada and the US. In this study, acoustic tagging technology was used to describe sturgeon presence in the CLA, as well as an adjacent site proposed for MHKs deployment. During 2018 and 2019, 33.9% (n = 19/56 Atlantic sturgeon tagged) and 29.9% (n = 23/77 Atlantic sturgeon tagged) respectively, of sturgeon acoustically tagged in MB during 2014–2019 were detected in these two FORCE sites. Binomial General Linear Models (GLMs) were fit to determine if environmental parameters influenced the presence, or depth of Atlantic sturgeon in the FORCE sites. The only significant predictor of Atlantic sturgeon depth and presence at the FORCE sites was tide type. Atlantic sturgeon was found to have a higher likelihood of being detected during ebb tide (12%) as opposed to flood tide (3%). Apparent decline in the presence of sturgeon during flood tide was probably due to poor signal reception caused by turbulence from higher current speeds. Tagged sturgeon travelled through the FORCE sites pelagically at similar depths (27.5 ± 14.57 m) to those proposed for seabed mounted MHKs (~30 m), travelling deeper during flood tide than ebb, suggesting they may be at risk of spatial overlap with MHKs. While this study indicated that the duration Atlantic sturgeon utilized the FORCE sites throughout the summer appeared to be low, sturgeon from both endangered and threatened stocks migrated through this region during their yearly entry and exit to MB and were present for approximately 12% of the days assessed in this study.     

Oceanic Distribution,Behaviour, and a Winter Aggregation Area of Adult Atlantic Sturgeon,Acipenser oxyrinchus oxyrinchus,in the Bay of Fundy,Canada

Seasonal distribution of adult Atlantic sturgeon was examined using pop-up satellite archival tags (PSATs) and ultrasonic transmitters deployed in the Saint John River, New Brunswick, Canada. Seven MK10 PSATs programmed for release in June 2012 and seven MiniPAT PSATs programmed for release in February and April 2013 were deployed in August 2011 and 2012, respectively. Eleven of 14 PSATs surfaced and transmitted depth and temperature data archived for the duration of their deployment (121–302 days). Among these eleven PSATs, five were recovered and 15-sec archival data was downloaded. Following exit from the Saint John River in the fall, tagged fish occupied a mean monthly depth of 76.3–81.6 m at temperatures as low as 4.9˚C throughout the winter before returning to shallower areas in the spring. The majority of ultrasonic detections occurred in the Bay of Fundy, but fish were detected as far as Riviere Saint-Jean, Quebec, approximately 1500 km from the Bay of Fundy (representing long-distance migratory rates of up to 44 km/day). All PSATs were first detected in the Bay of Fundy. Tags that released in February and April were found 5–21 km offshore of the Saint John Harbour, while tags that released in June were first detected in near shore areas throughout the Bay of Fundy. The substrate at winter tag release locations (estimated from backward numerical particle-tracking experiments) consisted primarily of moraines and postglacial mud substrate with low backscatter strength, indicative of soft or smooth seabed. Based on the proximity of winter tag release locations, the consistent depths observed between fish, and previous research, it is suspected that a winter aggregation exists in the Bay of Fundy. This study expands the understanding of the marine distribution and range of Atlantic sturgeon on the east coast of Canada.     

Seasonal variation in the diet of juvenile lake sturgeon,Acipenser fulvescens,Rafinesque, 1817, in the Winnipeg River,Manitoba, Canada

The lake sturgeon, Acipenser fulvescens, is a threatened species across most of its range. To understand any potential shifts in diet across season or habitat, stomach contents were examined from juvenile lake sturgeon caught in the Winnipeg River, Manitoba, Canada. This information will aid in assessment of environmental impacts and conservation initiatives for this threatened species. From 2006 to 2008 gut contents were collected from juvenile lake sturgeon using a non‐lethal gastric lavage methodology. Juvenile lake sturgeon were sampled from four discrete deep water habitat types (13.7–27.4 m depths), during the months of May, June, July and October. In total, 13 066 prey items belonging to 14 prey groups were collected from 345 juvenile lake sturgeon (251–835 mm TL). Overall, juvenile lake sturgeon consumed a low diversity of organisms; insect larvae from three invertebrate orders, Trichoptera, Diptera and Ephemeroptera, accounted for 97.4% of the total numeric abundance of prey items recovered. A relationship between size of juvenile lake sturgeon and prey quantity or type was not observed. Diet of juvenile lake sturgeon varied in relation to season, with Diptera (77.6%) being the most abundant prey in May, Trichoptera the most abundant in June (n = 3,056, 60.4%) and July (n = 2,055, 52.6%). During October, 96% of stomachs examined were empty. In terms of habitat type, the standardized abundance of invertebrate prey items was highest in deep water habitats characterized by medium water velocity (depths > 13.7 m) and coarse substrate (particle sizes > 0.063 mm) in May and June when compared to deep water habitats characterized by low water velocity (<0.2 m.s^?1) and fine substrate (particle sizes < 0.063 mm). However, in July, the opposite was observed and prey abundance in juvenile lake sturgeon stomachs decreased with increasing particle size. Results suggest a high degree of dietary overlap among juvenile lake sturgeon from multiple size/age classes occupying deep‐water habitats of the Winnipeg River.     

First documented occurrences of the shortnose sturgeon (Acipenser brevirostrum,Lesueur, 1818) in the Saco River,Maine, USA

During sampling efforts to study the more abundant Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus, between May of 2009 and November of 2011, four shortnose sturgeon were captured in gill nets near the mouth of the Saco River, Maine. Two of these individuals were tagged with acoustic transmitters to monitor their movement within the Saco River. Additionally, six shortnose sturgeon that had been tagged with acoustic transmitters in the Merrimack River, Massachusetts were detected on the acoustic array deployed within the Saco River and its estuary over this time period. These incidences represent the first verified documentation of shortnose sturgeon within this estuary.     

Atlantic sturgeon Acipenser oxyrinchus Mitchill, 1815 seasonal marine depth and temperature occupancy and movement in the Bay of Fundy

Pop‐up satellite archival tags were used to collect fisheries‐independent data that characterized the seasonal habitat occupancy and movement of Atlantic sturgeon Acipenser oxyrinchus Mitchill, 1815 in the Bay of Fundy (BoF). Atlantic sturgeon from Canadian and United States stocks aggregate annually for feeding in Minas Basin, inner BoF (45.28N, 64.18W), during May to September but depart to other locations from October to April. Sixteen PSAT tags were applied to sturgeon ranging from 152 to 203 cm total length captured and released in Minas Basin during May to August. Ten of the tags were reported after 1 year at large and provided pop‐off locations. Seven were recovered with archived data, or provided transmitted data sets, which were analyzed for depth and temperature occupancy from June 2011 to August 2013. During June to August while in the Minas Basin the sturgeon spent >90% of time at depths <10 m and temperatures of 16–22°C. Departure from Minas Basin through the Minas Passage was in September and October, when depth occupancy varied from <10 to 120 m. From November to April sturgeon were in the outer BoF, where mean depth occupancies ranged from 40 to 100 m at mean temperatures of 3–14°C. Deepest mean depth occupancy of 60 to 90 m was recorded during December 2011 and 2012, and coldest mean temperature occupancy of 0–4°C in March 2011 and 2012. During April and May mean depth and temperature occupancy ranges shallowed from 40 to <10 m and increased from 4 to 15°C, respectively. Tag pop‐off locations indicated that sturgeon spent the winter season in the outer BoF but by June had either migrated back to the Minas Basin or off the mouth of the Saint John River, a known spawning location.     

Critical thermal maxima and hematology for juvenile Atlantic (Acipenser oxyrinchus Mitchill 1815) and shortnose (Acipenser brevirostrum Lesueur, 1818) sturgeons

The critical thermal maximum (CTmax) and the associated hematological response of juvenile (~145 g, n = 8 for both species) Atlantic Acipenser oxyrinchus and shortnose Acipenser brevirostrum sturgeons acclimated to 15°C were determined using a heating rate of 8°C h^?1. The critical thermal maximum averaged 30.8°C and 31.6°C for Atlantic and shortnose sturgeon, respectively, and values fell within the range noted for other sturgeon species. Oxygen‐carrying capacity (hemoglobin and hematocrit) measures were generally unaffected by thermal stress. Plasma lactate levels increased from 0.5 mm to 4 mm following temperature stress in both species. Both plasma glucose and potassium levels increased following CTmax, however, these levels were about double in the shortnose sturgeon. Lastly, plasma sodium and chloride levels were significantly depressed (by more than 10%) following thermal stress in shortnose sturgeon, whereas only chloride levels decreased in Atlantic sturgeon. Taken together, while CTmax values were similar, thermal stress resulted in different hematological profiles; these differences are consistent when compared to other stressors, and may be related to the phylogenetic position and thus could reflect the evolutionary history of these two species.     

Stock composition of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) encountered in marine and estuarine environments on the U.S. Atlantic Coast

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) is a large, anadromous fish native to the Atlantic Coast of North America. Although this species once supported important fisheries, centuries of exploitation and habitat degradation have resulted in dramatic declines, presumed extirpation in some rivers, and ultimately listing under the U.S. Endangered Species Act (ESA). Under the ESA, Atlantic sturgeon are listed as five separate Distinct Population Segments (DPSs), which form the basis for federal management. Despite state and federal protections Atlantic sturgeon still face significant threats to their recovery, including fisheries bycatch mortality, marine construction, dredging, dams, and vessel strikes. However, because subadult and adult Atlantic sturgeon migrate extensively across estuarine and marine environments and frequently form mixed-stock aggregations in non-natal habitats, it can be difficult to determine how these threats impact specific populations and DPSs. To better understand ontogenetic shifts in habitat use and stock-specific exposure to anthropogenic threats, we performed a mixed-stock analysis of 1704 Atlantic sturgeon encountered across the U.S. Atlantic Coast. Collections made north of Cape Cod, MA and south of Cape Hatteras, NC were dominated by individuals from regional stocks; however, we found extensive stock mixing in the mid-Atlantic region, particularly in coastal environments where individuals from all five DPSs were commonly observed. Subadults and adults that were encountered in offshore environments had moved, on average, 277 km from their natal source; however, 23% were sampled over 500 km from their natal river suggesting long-distance movements are relatively common in these age classes. Overall, our work highlights that Atlantic sturgeon populations are vulnerable to threats over vast areas and emphasizes the need for continued genetic monitoring to track recovery progress.

     

Laboratory study of the susceptibility of hatchery reared Atlantic sturgeon (Acipenser oxyrinchus Mitchill, 1815) larvae to predation

The aim of the study was to determine the susceptibility to predation of Atlantic sturgeon larvae (Acipenser oxyrinchus) reared under traditional hatchery conditions. Experiments were conducted to determine whether predators would prey on Atlantic sturgeon if alternative prey was available and if the presence of substrate on the tank bottom impacted the number of Atlantic sturgeon consumed. European perch (Perca fluviatilis) was used as the predator, and the alternative prey were three‐spined stickleback (Gasterosteus aculeatus) or gudgeon (Gobio gobio). The predators and alternative prey were obtained from the wild. The mortality of sturgeon (n = 10) and alternative prey (n = 10) caused by four predators was recorded during 15 min trials. Trials with three‐spined stickleback and gudgeon as alternative prey were performed separately. Each experimental trial was repeated five times. The predators consumed significantly more Atlantic sturgeon than alternative prey in both the experimental setups when the bottom of the tank was covered with gravel and stone substrate and when there was no substrate. In trials with three‐spined stickleback the mortality of Atlantic sturgeon in both experimental setups was 94 ± 8.94%, while that of three‐spined stickleback in the setup with substrate was 20 ± 19.23%, and without substrate it was 22 ± 10.00%. European perch also consumed more Atlantic sturgeon than they did gudgeon, and the mean Atlantic sturgeon mortality in the experimental setup with substrate was 94 ± 5.48%, while for gudgeon it was 48 ± 8.37%. In the experimental setup without substrate the predators also consumed substantially more Atlantic sturgeon than gudgeon, with a mean Atlantic sturgeon mortality of 94 ± 8.94%, while for gudgeon it was 76 ± 5.48%. The study indicated that hatchery reared Atlantic sturgeon larvae are susceptible to predation by European perch. Predation could impact the survival of juvenile Atlantic sturgeon in the natural environment, and it could be one of the factors that is impeding the restoration of this species in the Baltic Sea basin.     

Shifting Distributions of Adult Atlantic Sturgeon Amidst Post-Industrialization and Future Impacts in the Delaware River: a Maximum Entropy Approach

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) experienced severe declines due to habitat destruction and overfishing beginning in the late 19^th century. Subsequent to the boom and bust period of exploitation, there has been minimal fishing pressure and improving habitats. However, lack of recovery led to the 2012 listing of Atlantic sturgeon under the Endangered Species Act. Although habitats may be improving, the availability of high quality spawning habitat, essential for the survival and development of eggs and larvae may still be a limiting factor in the recovery of Atlantic sturgeon. To estimate adult Atlantic sturgeon spatial distributions during riverine occupancy in the Delaware River, we utilized a maximum entropy (MaxEnt) approach along with passive biotelemetry during the likely spawning season. We found that substrate composition and distance from the salt front significantly influenced the locations of adult Atlantic sturgeon in the Delaware River. To broaden the scope of this study we projected our model onto four scenarios depicting varying locations of the salt front in the Delaware River: the contemporary location of the salt front during the likely spawning season, the location of the salt front during the historic fishery in the late 19^th century, an estimated shift in the salt front by the year 2100 due to climate change, and an extreme drought scenario, similar to that which occurred in the 1960’s. The movement of the salt front upstream as a result of dredging and climate change likely eliminated historic spawning habitats and currently threatens areas where Atlantic sturgeon spawning may be taking place. Identifying where suitable spawning substrate and water chemistry intersect with the likely occurrence of adult Atlantic sturgeon in the Delaware River highlights essential spawning habitats, enhancing recovery prospects for this imperiled species.     

Exploring epidermal mucus protease activity as an indicator of stress in Atlantic sturgeon (Acipenser oxyrinchus oxyrhinchus)

Atlantic sturgeon are anadromous fish that spend much of their life in near-shore environments. They are designated as “threatened” by the Committee on the Status of Endangered Wildlife in Canada and listed by the IUCN as “near threatened.” In Canada, Atlantic sturgeon support small commercial fisheries in the Saint John River, New Brunswick, and the St. Lawrence River, Quebec. While occupying the marine environment, the species is susceptible to various anthropogenic stressors, including by-catch in trawl fisheries and through interactions with coastal engineering projects such as tidal power development. Atlantic sturgeon are also susceptible to implantation of acoustic tags used by researchers to study their movement ecology. These stressors can cause physiological and behavioural changes in the fish that can negatively impact their viability. Because the species are commercially important, and are also of conservation concern, it is important to understand stress responses of Atlantic sturgeon to better mitigate the effects of increased industrial activity in the coastal zone. This study used proteomics to identify and characterize protease activity and identify putative novel protein biomarkers in the epidermal mucus of Atlantic sturgeon. Changes in protein profiles in Atlantic sturgeon epidermal mucus as a result of by-catch and surgery stress were investigated using one-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis and mass spectrometry. Proteolytic activity was identified and characterized using inhibition zymography, which provided information on the classes of proteases that are associated with stress. Samples were collected from Atlantic sturgeon on the Minas Basin, Nova Scotia, Canada, after capture by brush weir and otter trawl, and after surgical implantation of a V16-69 kHz VEMCO acoustic tag. Significant proteins found in the epidermal mucus include various inflammatory proteins, with calmodulin and complement 9 found ubiquitously, and more rarely lysosome C, identified in a brush weir capture sample. Serum albumin, a blood plasma protein, was another ubiquitous protein and verifies how the sample collection method provides a picture of the internal systems. Protease activity was dominantly exhibited by matrix metalloproteases and serine proteases in all sample collections, with serine proteases more active in otter trawl captures than in brush weir captures. By identifying potential protein biomarkers of stress, this study is an example of a non-invasive method for measuring stress in Atlantic sturgeon. Understanding the defence mechanism and release of non-specific biomarkers can be used to improve conservation regulations, as well as to contribute to the limited scientific knowledge on the stress response of Atlantic sturgeon.     

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.     

Comparison of karyotypes of <Emphasis Type="Italic">Acipenser oxyrinchus</Emphasis> and <Emphasis Type="Italic">A. sturio</Emphasis> by chromosome banding and fluorescent in situ hybridization

A highly debated problem in Acipenseridae taxonomy is whether Acipenser oxyrinchus (North American Atlantic sturgeon) and A. sturio (European Atlantic sturgeon) are true species: a detailed comparison of their karyotypes could provide relevant information. Here we describe for the first time the karyotype of A. oxyrinchus (2n = 121 ± 3), and its features, among which the constitutive heterochromatin, revealed by C-banding technique, the distribution of telomeric regions, and the 5S rRNA genes, detected by FISH. The results reveal that A. oxyrinchus and A. sturio karyotypes and features are quite similar. Moreover, comparing the results obtained through hybridization by FISH with HindIII and PstI satellite DNA in these and in other sturgeon species, no hybridization signals are detected in A. sturio and A. oxyrinchus, while A. stellatus and A. gueldenstaedtii show hybridization. Thus A. sturio and A. oxyrinchus appear very similar from a cytogenetic point of view: these and molecular data repeatedly point out that A. sturio and A. oxyrinchus represent a sister clade in comparison to all other sturgeon species up to now studied.     

First archaeozoological identification of Atlantic sturgeon (Acipenser oxyrinchus Mitchill 1815) in France

To this day, the only sturgeon to be listed on the French vertebrate inventory is the European sturgeon (Acipenser sturio Linnaeus, 1758). The recent study of sturgeon remains on various French archaeological sites shows the presence of another species: the Atlantic sturgeon (A. oxyrinchus Mitchill 1815). This species already existed in the French Atlantic region at the end of the Neolithic Age 5000 years ago and was still to be found 3000 years later. Thus the A. oxyrinchus determined in several Baltic medieval sites are neither the only nor the first sturgeons to have inhabited European waters. Sturgeon restoration projects in European rivers necessitate a precise determination of the native species. In the case of relict or extinct species, the bone remains found on archaeological sites represent the most reliable source of information. This discovery will also be the starting point of palaeogenetical research (mitochondrial and cellular aDNA) and will give information about the genetic diversity of these threatened or recently extinct populations.     

Characteristics of lake sturgeon Acipenser fulvescens Rafinesque, 1817 in a tributary of Lake Michigan,USA: Status of the Muskegon River population

The overall goal of this study was to characterize the age, growth, condition, and total catch of lake sturgeon Acipenser fulvescens in a remnant population associated with a Lake Michigan, USA tributary. Lake sturgeon were captured (2008–2013) using large‐mesh (25.4 and 30.5 cm) and small‐mesh (6.4 and 7.6 cm) gill netting in Muskegon Lake (which connects the Muskegon River to Lake Michigan), and adults were captured with boat electrofishing in the Muskegon River. A total of 268 unique lake sturgeon (24.8–191.0 cm total length; <0.1–59.5 kg weight) were captured. Of these, 180 fish were aged using pectoral fin rays, representing 27 age cohorts and a mean age of 7.6 years. The weight–length relationship for lake sturgeon was log₁₀ (W) = 3.446·log₁₀ (L) ? 6.163 and the von Bertalanffy growth model was L = 180.719 [1?e^{?0.093(t + 0.902)}], where W was wet weight (kg), L was total length (cm), and t was age (years). Mean growth rate of juveniles (ages 3–6) recaptured in successive years was 8.6 cm/year and 558 g/year. Annual catch of adults during the spawning migration suggested that the number of spawners each year was low (i.e., probably <50 individuals in most years). Natural reproduction appeared to be occurring given the catch of juvenile lake sturgeon in Muskegon Lake. However, recovery of this remnant population is uncertain given the population age structure and low rate of adult recruitment during the study.     

The Holocene occurrence of Acipenser spp. in the southern North Sea: the archaeological record

Archaeological sturgeon remains from the southern North Sea basin used to be automatically attributed to Acipenser sturio, since this was the only acipenserid species believed to occur there. These species identifications, however, were in need of revision after a growing number of indications were found for the historical presence of Acipenser oxyrinchus in western Europe. In this study, morphological and genetic data on sturgeon remains from archaeological sites along the southern North Sea are revised. A large number of Dutch, Belgian, British and some French archaeological sturgeon remains, dating from the Mesolithic up to Late Modern times, are morphologically examined and fish sizes are reconstructed. This study of >7000 acipenserid bones proves the sympatric occurrence of European sturgeon A. sturio and Atlantic sturgeon A. oxyrinchus in the southern North Sea at least since the Neolithic (fourth millennium BC onwards), with A. oxyrinchus remains always outnumbering those of A. sturio. Human influence is documented by the decrease in finds through time, but no clear evidence was found for a diachronic change in fish lengths that could possibly be related to fishing pressure.