Adult Atlantic Sturgeon Research Articles

Non-natal Adult Atlantic Sturgeon Are Common in the Altamaha River Estuary, Georgia, USA

Non-natal Adult Atlantic Sturgeon Are Common in the Altamaha River Estuary, Georgia, USA

Spatiotemporal patterns in habitat use of natal and non-natal adult Atlantic sturgeon in two spawning rivers

BackgroundMonitoring movement across an organism’s ontogeny is often challenging, particularly for long-lived or wide-ranging species. When empirical data are unavailable, general knowledge about species’ ecology may be used to make assumptions about habitat use across space or time. However, inferences about habitat use based on population-level ecology may overlook important eco-evolutionary contributions from individuals with heterogenous ethologies and could diminish the efficacy of conservation and management.MethodsWe analyzed over a decade of acoustic telemetry data to understand individual differences in habitat use of federally endangered adult Atlantic sturgeon (Acipenser o. oxyrinchus) in the Delaware and Hudson rivers during spawning season. In particular, we sought to understand whether sex or natal origin could predict patterns in habitat use, as there is a long-held assumption that adult Atlantic sturgeon seldom stray into non-natal rivers.ResultsIn both rivers, migration timing, spawning habitat occupancy, and maximum upstream migration distance were similar between natal and non-natal individuals. While non-natal individuals represented only 13% of fish detected in the Hudson River, nearly half of all tagged fish detected in the Delaware River were non-natal and generally occupied freshwater habitats longer than natal individuals. In both systems males had more heterogenous patterns of habitat use and longer duration of occupancy than did females.ConclusionsThis study demonstrates the importance of non-natal rivers for fulfilling ontogenetic habitat requirements in Atlantic sturgeon. Our results may also highlight an opportunity to improve conservation and management by extending habitat designations to account for more heterogenous patterns in individual habitat use in non-natal freshwater environments.

Spawning Intervals, Timing, and Riverine Habitat Use of Adult Atlantic Sturgeon in the Hudson River

AbstractThe Hudson River currently supports the largest population of Atlantic Sturgeon Acipenser oxyrinchus in the United States despite currently supporting less than 1% of historic abundance. Federally listed as endangered throughout much of their range, Atlantic Sturgeon are still impacted by multiple threats, resulting in habitat destruction or direct mortality that has inhibited the rebuilding of populations despite more than 20 years without direct fishing pressure. To assist in management and reduction in anthropogenic impacts to adult Atlantic Sturgeon in the Hudson River, we have examined sex‐specific patterns related to spawning. Utilizing hundreds of adult Atlantic Sturgeon telemetered along the Atlantic coast and an extensive passive acoustic array from 2010 to 2016, we were able to estimate arrival, departure, and duration of occupancy for four segments of the Hudson River for male, female, and unknown‐sex individuals. Male Atlantic Sturgeon arrived above river kilometer (RKM; RKM 0 = Battery Park, New York) 100 at an average date of May 27, 12 d prior to females on June 8. While there were only a few significant differences in the timing of departure, the average date from RKM 100 was July 11 for males, June 29 for females, and July 23 for unknown‐sex individuals, as such occupancy was significantly longer for male Atlantic Sturgeon. This study shows that female Atlantic Sturgeon often spawned in consecutive years and had much shorter mean intervals between spawning appearances (females 1.66 years, males 1.28 years) than the historical literature suggests. While the timing of spawning is consistent with the historic record, we provide a timeline with finer resolution and much greater detail for adults in the Hudson River, as well as update the historic estimate of spawning return rates. Conservation measures to reduce direct impacts to spawning habitat and mature Atlantic Sturgeon would likely provide the most benefit if conducted between mid‐May through the end of July.

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.

Dredging activity and associated sound have negligible effects on adult Atlantic sturgeon migration to spawning habitat in a large coastal river.

Dredging is considered a major threat/impedance to anadromous fish migrating to spawning habitat. Due to the perceived threat caused by dredging, environmental windows that restrict dredge operations are enforced within many rivers along the east coast. However, it is generally unknown how anadromous fish react to encountering an active dredge during spawning migrations. Atlantic sturgeon (ATS) are an endangered, anadromous species along the Atlantic slope of North America. To determine if and how an active dredge may affect ATS spawning migration, a Vemco Positioning System array was deployed around an active hydraulic-cutterhead dredge that adult ATS must traverse to reach spawning habitat in the James River, VA. Telemetry data showed that all ATS that entered the study area survived. ATS that migrated upstream during dredge operations (N = 103) traversed the dredge area and continued upstream to spawning habitat. Many ATS made multiple trips through the study area during dredge operations. There was no noticeable difference in swim behavior regardless of whether the dredge was absent or working within the study area. We suggest that dredging in the lower James River does not create a barrier for adult ATS migrating to spawning habitat or cause adults to significantly modify swim behavior. This is the first study to utilize fine-scale telemetry data to describe how an organism moves in relation to an active dredge. This methodology could be used to describe dredge-sturgeon interactions on different life stages and in other locations and could be expanded to other aquatic organisms of concern.

Comparing abundance estimates from closed population mark-recapture models of endangered adult Atlantic sturgeon

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 39:63-76 (2019) - DOI: https://doi.org/10.3354/esr00957 Comparing abundance estimates from closed population mark-recapture models of endangered adult Atlantic sturgeon J. E. Kahn1,2,*, C. Hager3, J. C. Watterson4, N. Mathies3, K. J. Hartman2 1National Marine Fisheries Service, Office of Protected Resources, Silver Spring, Maryland 20910, USA 2Division of Forestry and Natural Resources, West Virginia University, Morgantown, West Virginia 26506-6125, USA 3Chesapeake Scientific, Williamsburg, Virginia 23185, USA 4U.S. Department of the Navy, Naval Facilities Engineering Command, Atlantic Norfolk, Virginia 23508, USA *Corresponding author: jason.kahn@noaa.gov ABSTRACT: Atlantic sturgeon Acipenser oxyrinchus oxyrinchus were listed as 5 distinct population segments under the US Endangered Species Act in 2012. At that time, only 2 abundance estimates of the Atlantic sturgeon population were available: one from commercial fisheries landings in the Hudson River ending in 1995 and one from mark-recapture research in the Altamaha River, Georgia, in 2004 and 2005. In 2013, we verified spawning in the York River, Virginia, system and initiated a multiple-year mark-recapture study focusing on spawning-run abundance. We used a Schumacher-Eschmeyer model and Program CAPTURE to produce estimates of annual spawning abundances from 2013 to 2018. The Schumacher-Eschmeyer estimates of spawning-run abundance with 95% confidence intervals from 2013 to 2018 were 75 (31-190), 157 (115-244), 184 (150-238), 222 (137-576), 212 (157-328), and 145 (89-381), respectively. Because Atlantic sturgeon do not spawn every year, the trends in estimates do not suggest a recovering or declining population, but rather variability in proportions of the adult population that return to spawn each year. The estimates produced in Program CAPTURE using M0 (null), Mt (Chao Mt and Darroch), Mh (Chao Mh and Jackknife), and Mth (Chao Mth) models all produced similarly reliable estimates. The models that consider a behavioral response to initial capture (Mb, Mbh, and Mtb) failed to produce reliable estimates for this data, likely because as an endangered species, the dataset for Atlantic sturgeon was sparse. The Jackknife equation (model Mh) was the most precise every year with reliable accuracy and therefore is recommended. KEY WORDS: Anadromous · Conservation · Endangered species · Fish · Mark-recapture · Monitoring · Native fish · Population ecology · Population modeling Full text in pdf format Supplementary material PreviousNextCite this article as: Kahn JE, Hager C, Watterson JC, Mathies N, Hartman KJ (2019) Comparing abundance estimates from closed population mark-recapture models of endangered adult Atlantic sturgeon. Endang Species Res 39:63-76. https://doi.org/10.3354/esr00957 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 39. Online publication date: June 06, 2019 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2019 Inter-Research.

Environmental Drivers of Adult Atlantic Sturgeon Movement and Residency in the Delaware Bay

AbstractAnimals utilize various habitats throughout their life to optimize growth, fitness, and survival. Identifying environmental conditions and locations where animals exhibit different movement behaviors can be used to infer the relative importance of habitat types. In the case of threatened and endangered species, such as the Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus, critical habitat designations are a tool used to promote conservation and recovery. We utilized an extensive passive acoustic telemetry array, observed atmospheric conditions and river flow, modeled seawater conditions, and used generalized additive mixed modeling to determine environmental predictors of Atlantic Sturgeon movement and residency in the Delaware Bay on the U.S. East Coast. Our results suggested that shallower waters, warmer bottom temperatures, and areas toward the eastern portion of the Delaware Bay were predictive of residency, while movement was predicted by increased depth, cooler bottom temperatures, and areas toward the western portion of the bay. Our findings add to a growing body of evidence highlighting habitats at the Delaware Bay mouth, where Atlantic Sturgeon occur at heightened concentrations from late spring through fall. The Delaware River estuary once supported the largest population of Atlantic Sturgeon in North America, but that population is now critically imperiled (or endangered). Atlantic Sturgeon spend the vast majority of their life in marine, polyhaline waters, and without enhanced protection for these habitats, their recovery may never be realized.

Genetic differentiation of spring-spawning and fall-spawning male Atlantic sturgeon in the James River, Virginia.

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus, Acipenseridae) populations are currently at severely depleted levels due to historic overfishing, habitat loss, and pollution. The importance of biologically correct stock structure for effective conservation and management efforts is well known. Recent improvements in our understanding of Atlantic sturgeon migrations, movement, and the occurrence of putative dual spawning groups leads to questions regarding the true stock structure of this endangered species. In the James River, VA specifically, captures of spawning Atlantic sturgeon and accompanying telemetry data suggest there are two discrete spawning groups of Atlantic sturgeon. The two putative spawning groups were genetically evaluated using a powerful microsatellite marker suite to determine if they are genetically distinct. Specifically, this study evaluates the genetic structure, characterizes the genetic diversity, estimates effective population size, and measures inbreeding of Atlantic sturgeon in the James River. The results indicate that fall and spring spawning James River Atlantic sturgeon groups are genetically distinct (overall FST = 0.048, F’ST = 0.181) with little admixture between the groups. The observed levels of genetic diversity and effective population sizes along with the lack of detected inbreeding all indicated that the James River has two genetically healthy populations of Atlantic sturgeon. The study also demonstrates that samples from adult Atlantic sturgeon, with proper sample selection criteria, can be informative when creating reference population databases. The presence of two genetically-distinct spawning groups of Atlantic sturgeon within the James River raises concerns about the current genetic assignment used by managers. Other nearby rivers may also have dual spawning groups that either are not accounted for or are pooled in reference databases. Our results represent the second documentation of genetically distinct dual spawning groups of Atlantic sturgeon in river systems along the U.S. Atlantic coast, suggesting that current reference population database should be updated to incorporate both new samples and our increased understanding of Atlantic sturgeon life history.

Population Characteristics of Adult Atlantic Sturgeon Captured by the Commercial Fishery in the Saint John River Estuary, New Brunswick

AbstractThe commercial fishery for Atlantic Sturgeon Acipenser oxyrinchus in the Saint John River, New Brunswick, began in 1880. The early fishery was unregulated, and the adult stock was depleted by 1886 after landings of 712 metric tons. After a 10‐year closure the fishery was reopened in 1897 with management regulations, and landings varied from 6 to 20 metric tons/year until 2010. In 2011 an annual quota of 350 adults was established and landings are now stable at 11.3 ± 1.7 (mean ± SD) metric tons/year. Since 2009, fishers have collected biological statistics from adults taken in the fishery and 14–60% of captured individuals have been marked and released each year. During 2009–2015, annual mean values of total length and dressed weight of landed adults were stable, the male : female sex ratio was 1.2:1.0, and mean age of males and females was 27.2 and 34.0 years, respectively. Estimates of instantaneous total mortality ranged from 0.08 to 0.11, and mean annual survival was 90.9%. Of 1,396 marked adults released, 147 were recaptured in the estuary in subsequent years. Tag returns indicated that the modal spawning periodicity of males was 2 years and that of females was 4 years. Valid, modified Schnabel and Jolly–Seber mean annual population estimates for 2013–2015 were 18,179 and 20,798 adults, respectively. The quota in relation to these estimated adult populations represented annual exploitation rates of 1.9% and 1.7%, which are below F50 and would maintain present stock size. The virgin adult population was determined using 1880–1886 total landings and a mean weight range for adults of 50–30 kg. Estimated range of the 1880 virgin population size was 14,240–23,733 adults. These data suggest that the fishery is sustainable at its current annual yield and that the population is near the carrying capacity of the Saint John River.Received July 12, 2016; accepted November 17, 2016 Published online February 21, 2017

Timing and Location of Spawning Based on Larval Capture and Ultrasonic Telemetry of Atlantic Sturgeon in the Saint John River, New Brunswick

AbstractThe timing and location of spawning of Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus were investigated using larval sampling and ultrasonic telemetry in 2010–2014 in the lower Saint John River, New Brunswick, Canada. Larval sampling was conducted to identify potential spawning areas using anchored D‐frame drift nets and towed bongo nets. Forty‐four adult Atlantic Sturgeon (138–213 cm) were ultrasonically tagged and passively tracked using hydrophone receivers located throughout the river. Spawning was confirmed with the first capture of Atlantic Sturgeon larvae in the river. Four Atlantic Sturgeon yolk sac larvae (13.44–14.43 mm) were captured on July 23, 2011, and one exogenous feeding larva (22.6 mm) on July 25, 2011, at river kilometer (rkm) 106 near Burton, New Brunswick. Spawning time was estimated using larval growth models and is likely to have occurred July 6–13, 2011, above rkm 106. Eleven tagged fish returned to the river in May and June after a minimum of 2 years at large: nine males, one female, and one unknown sex. Seven of the 11 returning fish migrated to potential spawning areas above rkm 100. Based on the upstream occupancy observed, annual variability in spawning time is likely. The other four fish that returned remained below the salt–fresh interface with brief upstream migrations below rkm 100, suggesting that some fish are not spawning during summer migration. The majority of fish migrated from the river in August and September. This study provides the first description of the location and timing of Atlantic Sturgeon spawning and migratory patterns in the Saint John River.Received April 3, 2016; accepted November 17, 2016 Published online February 1, 2017

Atlantic Sturgeon Spatial and Temporal Distribution in Minas Passage, Nova Scotia, Canada, a Region of Future Tidal Energy Extraction.

In the Bay of Fundy, Atlantic sturgeon from endangered and threatened populations in the USA and Canada migrate through Minas Passage to enter and leave Minas Basin. A total of 132 sub-adult and adult Atlantic sturgeon were tagged in Minas Basin during the summers of 2010–2014 using pressure measuring, uniquely coded, acoustic transmitters with a four or eight year life span. The aim of this study was to examine spatial and seasonal distribution of sturgeon in Minas Passage during 2010–2014 and test the hypothesis that, when present, Atlantic sturgeon were evenly distributed from north to south across Minas Passage. This information is important as tidal energy extraction using in-stream, hydrokinetic turbines is planned for only the northern portion of Minas Passage. Electronic tracking data from a total of 740 sturgeon days over four years demonstrated that Atlantic sturgeon used the southern portion of Minas Passage significantly more than the northern portion. Sturgeon moved through Minas Passage at depths mostly between 15 and 45 m (n = 10,116; mean = 31.47 m; SD = 14.88). Sturgeon mean swimming depth was not significantly related to bottom depth and in deeper regions they swam pelagically. Sturgeon predominately migrated inward through Minas Passage during spring, and outward during late summer-autumn. Sturgeon were not observed in Minas Passage during winter 2012–2013 when monitoring receivers were present. This information will enable the estimation of encounters of Atlantic sturgeon with in-stream hydrokinetic turbines.

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.

Annual Spawning Migrations of Adult Atlantic Sturgeon in the Altamaha River, Georgia

AbstractThe Atlantic Sturgeon Acipenser oxyrinchus has declined throughout its range, and the species is now protected under the U.S. Endangered Species Act. Information on the timing and extent of spawning migrations is essential for the development and implementation of effective management and recovery strategies, yet this information is lacking for most populations. The objectives of this study were to document and identify temporal and spatial patterns in the seasonal movements and spawning migrations of Atlantic Sturgeon in the South Atlantic distinct population segment. A stationary array of acoustic receivers was used to monitor the movements of 45 adults in the Altamaha River system, Georgia, from April 2011 through March 2014. Telemetry data revealed that putative adult spawners exhibited two distinct patterns of upriver migration: a spring two‐step migration and a fall one‐step migration. During the spring two‐step migration, the adults appeared to stage in the upper Altamaha during the spring and early summer, before migrating to suspected spawning habitats in the Ocmulgee and Oconee tributaries during the fall. During the fall one‐step migration, fish entered the system in late summer and migrated directly upriver to suspected spawning habitats in the Ocmulgee and Oconee tributaries. Regardless of which pattern was used during the upstream migration, all fish returned downstream and left the system by early January. Although direct evidence of spawning has not yet been obtained, the telemetry and environmental data provide strong circumstantial evidence that Atlantic Sturgeon spawning in the Altamaha population occurs only during the fall months when water temperatures are less than 25°C. These findings further illustrate the clinal variation in the life history of Atlantic Sturgeon and highlight the need to manage the species as distinct population segments with regionally specific recovery goals.Received March 23, 2016; accepted September 25, 2016

Capture and Brief Invasive Procedures Using Electronarcosis Does Not Appear to Affect Postrelease Habits in Male Atlantic Sturgeon During the Spawning Season

AbstractWith advances in technology and demand for life history information, researchers are increasingly conducting invasive procedures on fish that require an anesthetic. This study examined the effectiveness of electronarcosis as a field anesthetic on Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus during the spawning season in the James River, Virginia. Concerns about sampling Atlantic Sturgeon during spawning runs prompted our examining whether movements after capture, narcosis, and tagging were noticeably modified. An electronarcosis system, which consisted of a power supply, fiberglass tank, and hardware cloth, were set up both on land and on a sampling boat. During the spawning season Atlantic Sturgeon were caught and implanted with Vemco V16 telemetry tags using electronarcosis as an anesthetic. Anesthesia induction, surgery, and recovery averaged 5 min. Telemetry data from the tagging year was compared with returning fish tagged in previous years. This showed movements during the spawning season and spawning exit dates were similar between the two groups, suggesting that electronarcosis was effective and time‐efficient for conducting invasive procedures. Capturing and implanting transmitters in Atlantic Sturgeon during spawning runs does not appear to modify spawning movements. Managers may benefit from targeting adult Atlantic Sturgeon and other iteroparous anadromous fishes in rivers during spawning periods, which is typically very efficient due to high densities of fish during that period.Received February 21, 2014; accepted December 31, 2014

Estimated Survival of Subadult and Adult Atlantic Sturgeon in Four River Basins in the Southeastern United States

AbstractPrompted by concerns about the status of Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus, in 2012 the National Oceanic and Atmospheric Administration listed one distinct population segment (DPS) as threatened (Gulf of Maine) and listed the remaining four DPSs as endangered (New York Bight, Chesapeake Bay, Carolina, and South Atlantic). To provide information for recovery planning, we estimated the survival of subadult and adult Atlantic Sturgeon in two river basins within the Carolina DPS (Roanoke and Cape Fear rivers, North Carolina) and two basins within the South Atlantic DPS (Ashepoo–Combahee–Edisto rivers [ACE], South Carolina; Altamaha River, Georgia). Estimated detection probability varied strongly by season but was similar among river basins, likely reflecting a winter migration into marine waters with minimal receiver coverage. Apparent monthly survival was very high and precisely estimated for the Roanoke River (0.985; 95% credible interval [CI] = 0.970–0.995), Cape Fear River (0.979; 95% CI = 0.971–0.986), ACE (0.989; 95% CI = 0.979–0.993), and Altamaha River (0.985; 95% CI = 0.973–0.994) basins. A pooled estimate for 87 adults from all four basins was 0.988 (95% CI = 0.982–0.992). The monthly rates implied annual apparent survival rates of 0.839 (Roanoke River basin), 0.778 (Cape Fear River basin), 0.871 (ACE basin), and 0.842 (Altamaha River basin); the pooled estimate for adults was 0.860. Our estimated survival rates were similar to other recent estimates for Atlantic Sturgeon but lower than recent estimates for several populations of Gulf Sturgeon A. oxyrinchus desotoi. Recovery of Atlantic Sturgeon in these southeastern rivers will occur more quickly if survival can be increased to a level that is consistent with published estimates of true natural mortality (0.03–0.07; annual survival ≥ 0.93).Received March 18, 2015; accepted August 26, 2015

Atlantic Sturgeon Annual Spawning Run Estimate in the Pamunkey River, Virginia

AbstractOn February 6, 2012, the National Marine Fisheries Service listed five distinct population segments (DPSs) of Atlantic Sturgeon Acipenser oxyrinchus encompassing their entire U.S. range, including one DPS in Chesapeake Bay, as either threatened or endangered under the Endangered Species Act. Designation of DPSs is a management tool that identifies significant, discrete, geographically defined portions of a species’ range, which can be listed as unique management units. At the time of listing, all DPSs except the Chesapeake Bay DPS comprised several rivers with known reproduction. After the Chesapeake Bay DPS was established, an additional spawning population was confirmed in the Pamunkey River, which is part of the York River system. We used the Schumacher–Eschmeyer formula for multiple census to estimate the number of adult Atlantic Sturgeon that spawned in the Pamunkey River during 2013. Gill nets were placed between river kilometers 27 and 67 in the upper Pamunkey River for 10 weeks during spawning season. The Schumacher–Eschmeyer model gave an estimate of 75 adult Atlantic Sturgeon (95% confidence interval = 17–168 adults) for the 2013 spawning population. This study represents the first estimate of annual spawning population abundance for any river in the Chesapeake Bay DPS and is only the third estimate of Atlantic Sturgeon abundance rangewide.Received March 24, 2014; accepted July 14, 2014

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 19th 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 19th 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.

Stock Origins of Subadult and Adult Atlantic Sturgeon, Acipenser oxyrinchus, in a Non-natal Estuary, Long Island Sound

The anadromous acipenserid Atlantic sturgeon Acipenser oxyrinchus was listed in 2012 under the U.S. Endangered Species Act as having four endangered and one threatened distinct population segment (DPS) in American waters. Anthropogenic activities outside of natal estuaries, particularly bycatch, may hinder the abilities of some populations to rebuild. Most Atlantic sturgeon are residential for their first 2–6 years within their natal estuaries, whereas older subadults and adults may migrate to non-natal estuaries and coastal locations. Previous studies demonstrated that subadults and adults aggregate during summer at locations in Long Island Sound (LIS) and its tributary, the Connecticut River; however, the population origin of these fish is unknown. Because of its geographic proximity and relatively robust population, we hypothesized that the LIS and Connecticut River aggregations were almost solely derived from the Hudson River. We used microsatellite nuclear DNA analysis at 11 loci and mitochondrial DNA control region sequence analyses to estimate the relative contributions of nine Atlantic sturgeon populations and the five DPS to these aggregations using individual-based assignment tests and mixed-stock analysis. From 64 to 73 % of specimens from LIS were estimated to be of Hudson origin. Similarly, 66–76 % of specimens from the Connecticut River were of Hudson origin. However, moderate numbers of specimens were detected from distant spawning populations in the southeastern DPS and from two populations once thought to be extirpated or nearly so, the James River (6–7.3 %), and the Delaware River (7.6–12 %). Additionally, specimens were detected from all five DPS in both the LIS and Connecticut River collections. These results highlight the difficulty of evaluating the status of individual Atlantic sturgeon populations because of the propensity of subadults and adults to migrate for extended duration to distant sites where they may be vulnerable to anthropogenic disturbances.

The Potential for Vessel Interactions with Adult Atlantic Sturgeon in the James River, Virginia

AbstractIn 2012, all populations of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus were listed as either threatened or endangered under the U.S. Endangered Species Act. During 2007–2010, researchers documented 31 carcasses of adult Atlantic sturgeon in the tidal freshwater portion of the James River, Virginia. Twenty‐six of the carcasses had gashes from vessel propellers, and the remaining five carcasses were too decomposed to allow determination of the cause of death. The types of vessels responsible for these mortalities were not explicitly demonstrated. Most (84%) of the carcasses were found in a relatively narrow reach that was modified to increase shipping efficiency. To explore the number of Atlantic sturgeon being hit and their horizontal and depth distributions in relation to vessel draft, we conducted telemetry experiments on three living fish (all males) and six dead specimens. While staging (holding in an area from hours to days, with minimal upstream or downstream movements), the adult male Atlantic sturgeon spent most (62%) of the time within 1 m of the river bottom. Assuming that behavior is not modified by vessel noise, adult male Atlantic sturgeon in the James River would rarely encounter small recreational boats or tugboats with shallow drafts; instead, mortalities are likely caused by deep‐draft ocean cargo ships, which have drafts that coincide with the distribution of the tracked adult males. Dead specimens (n = 6) drifted with the current for several hours to almost 4 d before beaching at distances ranging from 0.5 to over 50 river kilometers from the point of release. We estimated that current monitoring in the James River documents less than one‐third of vessel strike mortalities. A better understanding of Atlantic sturgeon behavior in the presence of vessels will aid in restoring this federally endangered species.Received February 20, 2012; accepted July 19, 2012

Empirical Evidence of Fall Spawning by Atlantic Sturgeon in the James River, Virginia

AbstractDue to overfishing and habitat alteration, the anadromous Atlantic sturgeon Acipenser oxyrinchus oxyrinchus is severely depleted across its historic range. The James and York rivers in Virginia are the two rivers comprising the Chesapeake Bay distinct population segment, where Atlantic sturgeon reproduction has been confirmed. It is widely recognized that Atlantic sturgeon spawn in the spring throughout their range; however, there is debate over whether they also spawn in the fall. To determine if Atlantic sturgeon spawn in the fall, independent of the spring spawn, large‐mesh gill netting in the freshwater portion of the James River (above river kilometer 108) was conducted in the spring (April–June) and fall (August–October) for 3 years (2009–2011), resulting in the capture of 125 adult Atlantic sturgeon (three were recaptures) during the fall sampling, but none were captured during the spring. Field examination for sex and stage of maturity identified 106 mature males and one postspawned female. Sex was not determined for four fish, and due to time constraints, 11 were not examined. Forty mature males were externally tagged with Vemco© ultrasonic passives tags and movements were monitored with a Vemco© VR2W passive receiver array. Collection and tracking data showed that mature Atlantic sturgeon aggregate in the freshwater portion of the James River during the fall season, entering during August and out‐migrating by the end of November. No tagged fish were detected in the freshwater area of the river during the subsequent spring months. Though James River Atlantic sturgeon may spawn in the spring, we suggest there is strong evidence for an independent fall spawn, which should be considered in future management and recovery actions.