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Objective: In a changing climate, the effects of air temperature, precipitation, and groundwater on water temperature and thermal habitat suitability for Gulf Sturgeon Acipenser desotoi, listed as threatened under the U.S. Endangered Species Act, are not well understood. Hence, we incorporated these factors into thermal habitat models to forecast how Gulf Sturgeon may be affected by wide‐ranging climate change scenarios in 2024–2074. Methods: Using data from the Choctawhatchee River, Florida, we developed precipitation‐ and groundwater‐corrected air–water temperature models, compared their accuracy with that of conventional air–water temperature models used in fisheries management, and projected future Gulf Sturgeon thermal habitat suitability for normal physiological functioning and fieldwork (i.e., population sampling and telemetry surgeries) in summer (May–August) under 16 climate change scenarios. Result: Precipitation‐ and groundwater‐corrected models were more accurate than conventional air–water temperature models (mean improvement in adjusted R2 = +0.45; range = +0.09 to +0.75). Water temperature was projected to warm at widely variable rates across climate change scenarios encompassing different air temperature, precipitation, and groundwater regimes. Importantly, Gulf Sturgeon summer aggregation areas were cooler and influenced more by precipitation and groundwater and less by air temperature than were non‐aggregation areas. If precipitation and groundwater—as drivers of cooling—become warm in a changing climate, summer aggregation areas were projected to exhibit thermal habitat degradation equivalent to or greater than that of non‐aggregation areas. Conclusion: Our results add hydrological context to the premise that aggregation areas provide cool water and energetic savings for Gulf Sturgeon during summer, underscoring the importance of protecting these habitats through groundwater conservation, water quality monitoring, and riparian/watershed habitat management. Our findings indicate that identifying thermally appropriate times for fieldwork activities will be increasingly important and time‐restricted as climate change intensifies. However, our research provides managers with a portfolio of water temperature models and an accurate, cost‐effective, management‐relevant approach to forecasting thermal habitat conditions for Gulf Sturgeon and other species in a changing climate. Impact StatementWater temperature models with precipitation and groundwater are accurate and useful, allowing managers to locate key thermal habitats, forecast temperatures, and decide when and where to safely target, capture, tag, and monitor Gulf Sturgeon and other species amid climate change. [ABSTRACT FROM AUTHOR]

Objective: Acoustic telemetry was used to examine the spatial‐temporal distribution and anadromous migration pattern of juvenile Gulf Sturgeon Acipenser desotoi within the Pearl River and associated coastal estuaries of Louisiana and Mississippi. Methods: Acoustic transmitters were surgically implanted in 52 juvenile Gulf Sturgeon (<890 mm fork length) from the Pearl River between 2016 and 2019. Sturgeon were monitored on 247 acoustic receivers in the lower Pearl River and adjacent estuaries across numerous partnering arrays. Result: Juveniles were detected on receivers from Lake Pontchartrain, Louisiana, east to Bay St. Louis, and Biloxi Bay, Mississippi. The 3‐year study found that juvenile Gulf Sturgeon migration in the Pearl River occurred on cycles similar to those reported from other populations. Juveniles were rarely observed in the estuary and nearshore marine environments from May through mid‐October of each year, during which time most sturgeon inhabited the Pearl River. Conversely, most of the juveniles inhabited coastal estuaries from December through February of each year and were rarely observed in freshwater environments during this period. Migration from the river into the estuary occurred during late‐October through November, and migration from the estuary into the river occurred in March and April. Distribution patterns varied spatially within the river and estuary ecosystems during each phase of migration. Tagged juveniles occupied the lowest 40 km of the Pearl River while in freshwater, and they occupied the northeastern shoreline of Lake Pontchartrain and Bay St. Louis while in the estuary. Interestingly, juveniles seemed to target specific areas in the estuary during winter that were farther away from the mouth of natal rivers than has been previously reported. Conclusion: This study provides a new assessment of juvenile Gulf Sturgeon migration and seasonal distribution for the Pearl River and provides important information for designing and assessing the potential benefits and challenges of habitat restoration for Gulf Sturgeon. Impact statementThis research increased our understanding of juvenile Gulf Sturgeon spatial and temporal distribution by providing novel information regarding the timing, duration, and geographic extent for the Pearl River population that will guide ongoing recovery efforts for this threatened species. [ABSTRACT FROM AUTHOR]

Coastal restoration projects often require sediment resources borrowed from estuarine or marine ecosystems. A generalized additive modeling (GAM) framework was used to characterize fish-habitat relationships and predict spatiotemporal and ontogenetic shifts of Gulf sturgeon distribution within an impacted estuary in the northern Gulf of Mexico, Lake Pontchartrain. Habitat use and movement of Gulf sturgeon (n = 103) was monitored using an array of acoustic receivers (n = 81) from 2016 to 2019. Telemetry data was paired with environmental conditions hindcast from a high-resolution hydrodynamic model to develop GAMs for three life stages of Gulf sturgeon: juvenile, sub-adult, and adult. Model results demonstrated clear spatial, temporal, and ontogenetic shifts in habitat use for Gulf sturgeon in the Lake Pontchartrain estuary. The importance of spatial and temporal variables in the final models of all life stages suggests that distribution of Gulf sturgeon within the estuary is more likely driven by biology (prey distribution) rather than environment. Interestingly, dependence of Gulf sturgeon on the estuary for overwintering habitat declined with ontogeny. The northeastern shoreline of Lake Pontchartrain was identified as potential nursery habitat for overwintering juvenile sturgeon from the Pearl River, while eastern portions of the estuary and associated channels provide critical staging habitat and corridors of connectivity for migrating sub-adult and adult sturgeon. Given the clear need to prioritize conservation of Gulf sturgeon while restoring coastal marshes, findings from this study provide needed information to shape future coastal restoration and inform the siting and timing of future dredging operations in Lake Pontchartrain.

Objective: Gulf Sturgeon Acipenser oxyrinchus desotoi populations have undergone substantial declines since the start of the 20th century due to overfishing and habitat loss. A predicted increase in the frequency of major hurricanes, driven by climate change, presents an additional but poorly characterized threat to Gulf Sturgeon populations. In October 2018, category 5 Hurricane Michael made landfall 40 km west of the Apalachicola River, causing a hypoxic event and an ensuing fish kill that included Gulf Sturgeon. Methods: We used acoustic telemetry, mark–recapture, and side‐scan sonar data to examine migration behavior and estimate Gulf Sturgeon abundance, mortality, and annual recruitment in the system before and after the storm. Result: Within 2 days of landfall, we observed an early and rapid emigration response among tagged adults residing in lower portions of the river system, coinciding with declining dissolved oxygen levels; migration behavior returned to normal by the subsequent spring. The hurricane caused an acute mass mortality event: mortality of Gulf Sturgeon in October 2018 was four to five times greater than that in previous years. Several other independent metrics also indicate a major decline in Gulf Sturgeon abundance after the hurricane. Juvenile recruitment to age 1 after the storm was >5 of the previous 6 years, indicating the hurricane did not cause a year‐class failure. Conclusion: These findings suggest that major hurricanes can impact the structure and abundance of Gulf Sturgeon populations, yet elements of resiliency, including survival (facilitated by early emigration and refugia) and enhanced recruitment, may aid in population recovery following such disturbances. [ABSTRACT FROM AUTHOR]

Abstract Gulf Sturgeon, Acipenser oxyrinchus desotoi , is listed as threatened, with critical habitat designated throughout the northern Gulf of Mexico (GOM) to protect, in part, areas where feeding occurs. Because not all critical habitat appears to provide equivalent foraging value, reliably identifying areas of relatively high vs. low prey density coupled with appropriate sediment composition may provide important management considerations. Examination of existing benthic datasets (1980-2006) across the Gulf Sturgeon's range revealed potential prey assemblages differed geographically, with a dominance of amphipods on the northwest coast of Florida, lower overall potential prey densities in the north-central GOM, and relatively high gastropod and bivalve densities in Louisiana. Within sites, high prey densities frequently occurred where high Gulf Sturgeon activity levels previously were identified in telemetry studies, suggesting the historical benthic data sets provide information relevant to foraging habitat. Gulf Sturgeon prey assemblages were correlated with physical parameters at 11 of 14 sites examined and physical parameters included in these correlations differed between eastern and western regions. Gulf Sturgeon prey assemblages were typically correlated with depth and % sand where sand content was high, such as the eastern portion of the sturgeon's range, as well as parts of both Mississippi Sound and Chandeleur Sound. In contrast, depth, % TOC, and DO were associated with prey assemblages in areas with low sand content in Louisiana and Alabama. These regional results indicate that management approaches on spatial scales smaller than the northern GOM should be considered. [ABSTRACT FROM AUTHOR]

In order to reduce wave energy associated with tropical storms and hurricanes in the western Mississippi Sound, the Mississippi Coastal Improvements Program will close a 5.6 km breach (i.e. Camille Cut) separating East and West Ship Island, Mississippi, and restore sediments to the southern shoreline of East Ship Island. As part of this program, federally designated critical Gulf Sturgeon habitat associated with Ship Island was monitored to establish baseline patterns of use prior to island restoration using a passive acoustic array during overwintering periods from 2011 to 2014. Gulf Sturgeon of both western and eastern populations occupied the passes, cuts, and ends of Ship Island over the study period, but no difference in occupancy was observed among four initially established zones. However, when comparing the new most eastern zone, Dog Keys Pass, to the four initial zones, occupancy was four times greater in this zone than any other monitored zone, indicative of foraging behavior associated with high abundance of benthic resources. Reconnecting East and West Ship Island through filling Camille Cut proper may increase Gulf Sturgeon occupancy in Dog Keys Pass and other areas near the ends and passes of the barrier islands. The loss of Camille Cut proper as critical habitat may be partially augmented by "new" nearshore habitat north and south of Camille Cut; however, it is uncertain whether filling in Camille Cut will alter the physical components of the habitat, causing a shift in benthic prey availability and, thus, quality of forage habitat. [ABSTRACT FROM AUTHOR]

Trace element and 87Sr/86Sr isotope analyses of fish pectoral fin rays offer non-destructive methods for determining habitat use. In this study, water and fin ray samples were analyzed for Gulf Sturgeon Acipenser oxyrinchus desotoi from the Choctawhatchee River Basin (FL and AL, USA) and compared with reference samples from Atlantic Sturgeon A. o. oxyrinchus held at controlled salinities (0, 10, 33 ppt). Samples were analyzed using inductively coupled plasma mass spectrometry, with a multi-collector for 87Sr/86Sr. In water, Sr, Ba, Mn and Zn differed between freshwater and saline habitats, with increases in Sr and decreases in Ba, Mn and Zn. 87Sr/86Sr decreased upstream to downstream with lowest values in saline habitats. In the reference study, water trace element concentrations and 87Sr/86Sr corresponded to those in pectoral fin rays. 87Sr/86Sr was higher in pectoral fin ray than water, due to influence of diet, which differed with salinity. In wild fish, trace elements in pectoral fin rays indicated freshwater emigration to saline habitats primarily occurred in the second to third growth zone with some heterogeneity in the population (4% <0.3 years, 39% 0.5-1.3 years, 39% 1.5-2.3 years, 17% 2.5-3.3 years). Analyses of 87Sr/86Sr indicated initial locations of Gulf Sturgeon were in the middle river, with few fish in the upper or lower river. Most (74%) juvenile Gulf Sturgeon utilized more than one river region prior to freshwater emigration and 48% moved upstream temporarily based on increased 87Sr/86Sr. After initial freshwater emigration, fish utilized lower-river to saline habitats. Collectively, these studies demonstrate the usefulness of trace element and 87Sr/86Sr analyses in sturgeon pectoral fin rays. [ABSTRACT FROM AUTHOR]

The Gulf Sturgeon, Acipenser oxyrinchus desotoi, is an anadromous species of Acipenseridae and native to North America. It currently inhabits and spawns in the upper reaches of seven natal rivers along the northern coast of the Gulf of Mexico from the Suwannee River, Florida, to the Pearl River, Louisiana, during spring to autumn. Next to the Alligator Gar (Atractosteus spatula), the Gulf Sturgeon is currently the largest fish species occurring in U.S. Gulf Coast rivers, attaining a length of 2.35 m and weights exceeding 135 kg, but historically attained a substantially larger size. Historically, the spawning populations existed in additional rivers from which the species has been wholly or nearly extirpated, such as the Mobile and Ochlockonee rivers, and possibly the Rio Grande River. Most Gulf Sturgeon populations were decimated by unrestricted commercial fishing between 1895-1910. Subsequently most populations remained unrecovered or extirpated due to continued harvest until the 1970s-1980s, and the construction of dams blocking access to ancestral upriver spawning grounds. Late 20th Century harvest bans and net bans enacted by the several Gulf Coast states have stabilized several populations and enabled the Suwannee River population to rebound substantially and naturally. Hatchery supplementation has not been necessary in this regard to date. Sturgeon are resilient and adaptable fishes with a geological history of 150 million years. Research undertaken since the 1970s has addressed many aspects of Gulf Sturgeon life history, reproduction, migration, population biology, habitat requirements, and other aspects of species biology. However, many knowledge gaps remain, prominently including the life history of early developmental stages in the first year of life. Natural population recovery is evident for the Suwannee River population, but seems promising as well for at least four other populations. The Pascagoula and Pearl River populations face a challenging future due a combination of natural and anthropogenic factors. These two populations, and perhaps the Escambia River population, are particularly vulnerable to periodic mass mortality due to major stochastic events including hurricanes, flooding, hypoxia, and toxic spills. The present manuscript provides a comprehensive synthesis of knowledge regarding the Gulf Sturgeon at the organismal and population levels, identifying knowledge gaps as priorities for future research. Topics not treated in the present synthesis include morphology, internal biology, physiology, and endocrinology. Topics only briefly treated include parasites and diseases, contaminants, and sturgeon aquaculture. [ABSTRACT FROM AUTHOR]

Accurate estimates of age and growth of fishes are important in the management and conservation of species and for the development of modeling approaches. Assessments of endangered or rare species typically are limited by poor or inadequate data owing to low abundance, unrepresentative sampling, and/or restrictions on sampling. Atlantic SturgeonAcipenser oxyrinchus oxyrinchus, which occurs along the east coast of North America, has five distinct population segments (DPSs) listed under the U.S. Endangered Species Act. The New York Bight (NYB) DPS is listed as endangered and represents the largest DPS in the United States. Coastal trawl surveys from 2005 to 2012 were used to evaluate the current age structure of the NYB DPS. A total of 21 year-classes (mean age = 8.89 years,n= 742 fish) were observed. Age data for the NYB DPS were combined with other available age estimates from multiple research laboratories and sources (n= 2,774) in the Hudson River and Delaware River as well from the coastal regions of New York, New Jersey, and Delaware from 1975 to 2012. Collectively, the combined data set captured much of the age range of the species, minimizing age biases and resulting in improved von Bertalanffy parameter estimates (L∞= 278.87,K= 0.057,t0= −1.27) with high overall model fit (r2= 0.87). We assessed the effects of individual data sets through a series of leave-one-out bootstrap routines that evaluated the influence of each data set on growth parameter estimates. The parameter estimates of the von Bertalanffy growth function were influenced by sampling location and/or researcher effects. Despite these differences, the combined data set approach used here represents the most comprehensive study on the age-and-growth relationship of Atlantic Sturgeon and provides parameter estimates for the development of population dynamics models and valuable information for future management. Received February 23, 2015; accepted September 24, 2015 [ABSTRACT FROM AUTHOR]

Environmental cues that are associated with individual movement of threatened Gulf Sturgeon from upriver areas to nearshore and offshore winter feeding areas have been described throughout much of their range in the Gulf of Mexico. In this study, we focus on small-scale movement of Gulf Sturgeon between summer 'holding' areas and the fall staging area in the Pascagoula River system (Mississippi, USA). We evaluated a set of logistic regression models using Akaike's Information Criterion and found that relative changes in barometric pressure, time of day, and water temperature were cues for small-scale Gulf Sturgeon movements during fall outmigration. Numerous environmental cues appear to drive the activity of Gulf Sturgeon in staging areas, indicating the complexity of abiotic factors affecting the observed staging patterns during emigration. The identification of the environmental drivers that are associated with Gulf Sturgeon movement is particularly important if these known saline transition zones change spatially annually with variable rainfall or due to water withdrawals and are used by Gulf Sturgeon making osmotic adjustments while moving downriver. [ABSTRACT FROM AUTHOR]

We determined that the average gastrointestinal tract length of 8–11-month-old Gulf of Mexico SturgeonAcipenser oxyrinchus desotoi, a subspecies of Atlantic SturgeonA. oxyrinchus, was approximately 82% of its fork length. The time required for digesta to pass through the digestive tract was approximately 32 h. Defecation was initiated between 8 and 16 h after feeding. The main site for digestion and absorption of energy, dry matter, and crude protein was the spiral valve region of the intestine, as determined by apparent digestibility coefficients. By the time digesta had reached the lower spiral valve most of the energy, dry matter, and crude protein had been absorbed. Morphological examination of the intestine, including the spiral valve region, revealed a highly developed mucosal surface area, which is essential for efficient nutrient digestion and absorption during the extended period required for the digesta to move through the digestive tract. Received November 19, 2014; accepted January 25, 2015 [ABSTRACT FROM PUBLISHER]

An experimental release of 1192 hatchery-reared, individually PIT tagged, 220 days old (296-337 mm TL) Gulf sturgeon, Acipenser oxyrinchus desotoi, was undertaken in 1992 in the Suwannee River, Florida. The original objectives of the 1992 release experiment were to: (1) evaluate survival rate of cultured Gulf sturgeon in the wild vs survival rate of their wild 1992 cohort counterparts, (2) determine the differential effect of release site within the river upon long-term survival, and (3) evaluate comparative growth rates of recaptured hatchery vs captured wild 1992 cohort Gulf sturgeon. The present investigation addressed those original objectives, plus an additional fourth objective: (4) evaluation of hatchery fish recapture rate change over the 19-year experiment. The primary objective was to determine efficacy of potential conservation aquaculture for this species in terms of long-term survival in the wild. Follow-up 1993-2011 gill net sampling in freshwater reaches (rkm 4-237) and the estuarine river mouth (rkm −6 to 4) yielded recaptures representing 13.0% of the total released. Mean annual hatchery fish mortality (including emigration) rate estimated for the 19-year period (1993-2011) was more than twice that for same cohort wild fish. Mark-recapture survival probability (phi) for hatchery fish, 1993-2011, was substantially lower (0.733) than for their wild counterparts (0.888). Mean annual hatchery fish recapture rate, as a percentage of all 1992 cohort fish recaptures, declined significantly after age-7, coinciding with age of onset of migration into the open Gulf of Mexico. Hypothesized causal factors may be differentially lower fitness in the marine habitat or permanent outmigration due to natal river imprinting failure. Hatchery fish recapture rates varied significantly for fish from the ten release sites, being highest near the river mouth, and lowest for the furthest upriver sites in the Suwannee River and its Santa Fe River tributary. Hatchery fish also displayed a significantly lower growth rate than their wild counterparts through age 3000 days. Cumulative hatchery fish mortality of 99.87% over 19 years predicts <3 individuals would have survived through 2011. From the results of the 1992 release experiment, hatchery supplementation as a Gulf sturgeon conservation measure does not appear to be an effective option. [ABSTRACT FROM AUTHOR]

The Gulf sturgeon, Acipenser oxyrinchus desotoi Mitchill 1815, is an anadromous fish native to the Gulf of Mexico ( GOM). This threatened species ascend northern GOM rivers ranging from the Pearl River, Louisiana to the Suwannee River, Florida. The drainage fidelity seen within this species coupled with the complex migration patterns create many unknowns concerning the functionality between drainages and size classes. Being a threatened species that cannot be sacrificed, morphometric measurements are difficult to acquire due to minimized handling times and non-lethal data collection methods. Seven morphometric measurements of Gulf sturgeon were compared between western and eastern GOM rivers and multiple size classes (juvenile, sub-adult, and adult). Principal Component, Discriminant Function, and Maximum Chance Criterion analyses were conducted and identified differentiating morphometrics and classified groupings among size classes and rivers of Gulf sturgeon. This morphometric approach has the potential to be used in parallel with molecular findings and should allow managers to identify sub-populations for a variety of threatened and endangered species. [ABSTRACT FROM AUTHOR]

Understanding mortality rates and movement patterns across a species' distribution can provide key insight necessary for developing effective conservation, recovery, and management plans. We directly estimated site fidelity and natural mortality rates for the threatened Gulf sturgeon ( Acipenser oxyrinchus desotoi) across a large portion of their range in the northern Gulf of Mexico using acoustic telemetry methods and a simulation-tested, multistate mark-recapture model. Our results suggest that fidelity rates to riverine habitats used during spring and summer are high, but natural mortality rates vary widely. Our results are highly relevant for managing this species. The high fidelity rates, coupled with supporting genetic analyses, suggest that management of individual riverine populations of Gulf sturgeon should be considered. The need for individual river-based management is exacerbated by the variation in natural mortality rates among rivers. The reasons for these differences in mortality are unclear, but are an important area of future research because higher mortality rates may impede recovery of some Gulf sturgeon populations to stated management targets. [ABSTRACT FROM AUTHOR]

To determine the most suitable aging structure for sturgeons, band counts of transverse sections of otoliths and the pectoral-, dorsal-, pelvic-, and anal-fin rays of Gulf sturgeon (Acipenser oxyrinchus desotoi) were compared. The otoliths and dorsal-, pelvic- and anal-fin rays produced inconsistent band patterns, but bands formed in the first (fin spine) and second marginal pectoral- fin rays were easily read and the most consistent. The index of average percent error and the coefficient of variation between final ages from the fin spines and the second marginal fin ray were 0.75% and 1.06%, respectfully. Percent agreement between the assigned age of the fin spine and second marginal fin ray was high. The fin spine is commonly used to age sturgeon species; however, removal of the fin spine was considered potentially deleterious, especially to larger sturgeon. Sampling the second marginal fin ray appeared to be less harmful. Annual band formation in the second marginal fin ray for 3 Gulf sturgeon was validated with the use of oxytetracycline. We propose the second marginal pectoral-fin ray as an acceptable and less harmful alternative structure to the fin spine for aging Gulf sturgeon and recommend its use for other threatened and endangered sturgeon species. An extraction method of minimal invasiveness is presented here for field removal of the second marginal pectoral-fin ray from live sturgeon. [ABSTRACT FROM AUTHOR]

A large feeding aggregation of Atlantic sturgeon occupies the inner Bay of Fundy during summer, presumably to forage on the intertidal mudflats. The feeding habits of Atlantic sturgeon were examined during summer 2011 in Minas Basin as description of diet is important for identifying critical foraging areas. Atlantic sturgeon demonstrated an overall preference for sandy tube-dwelling polychaetes (Index of Relative Importance ( IRI) = 99.7%). Major prey taxa included Maldanidae ( Clymanella sp., 52.5%) and Spionidae, primarily the species Spiophanes bombyx (41.6%). Other prey items consumed included Phyllodocidae ( Eteone sp., 2.1%), Nephtyidae (2.2%), Nereididae (0.7%), and Glyceridae including Glycera dibranchiata (0.6%). Seventeen additional taxa were identified in trace amounts (mean IRI = 0.02%), including Corophidae and Mysidae. There was no significant difference in the number of prey items consumed and the fork length of the fish. Analysis of gut fullness with respect to tidal state indicated no significant difference between gut fullness on the flood or ebb tide. An overall preference for sandy tube-dwelling polychaetes may indicate that particular areas of the Minas Basin intertidal region are more important than others to these foraging fish. Considerable baitworm harvesting occurs during summer months in Minas Basin and could potentially create impacts with sturgeon consumers, both directly through competition for prey items and indirectly through change in sediment and benthic community composition. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Stable C, N, and S isotopes were analyzed to define the feeding habitats of Acipenser oxyrinchus desotoi in the Suwannee and Yellow River populations . For the majority (93.9%) of Suwannee subadults and adults, C and S signatures indicate use of nearshore marine waters as primary winter feeding habitat, probably due to the limiting size of the Suwannee Sound estuary. In the Yellow River population, C isotope signatures indicate that adults remain primarily within Pensacola Bay estuary to feed in winter, rather than emigrating to the open Gulf of Mexico. A minor Suwannee River subset (6% of samples), comprised of juveniles and subadults, displayed C signatures indicating continued feeding in freshwater during the spring immigration and fall emigration periods. This cannot be interpreted as incidental feeding since it resulted in a 20.5% turnover in tissue δC signatures over a 1-3 month period. Cessation of feeding in the general population does not coincide with high river water temperatures. The hypothesis of reduced feeding in freshwater due to localized prey depletion as a result of spatial activity restriction is not supported by the present study. Instead, Suwannee River A. o. desotoi appear to follow two trophic alternatives; 1) complete cessation of feeding immediately upon immigration in spring, continuing through emigration 8-9 months later (the predominant alternative); 2) continued intensive feeding for 1-3 months following immigration, switching to freshwater prey, selected primarily from high trophic levels (i.e., large prey). Stable δS data verifies that recently immigrated, fully-anadromous A. o. desotoi adults had fed in nearshore marine waters, not offshore waters. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to characterize distribution of Gulf of Mexico sturgeon in nearshore Gulf of Mexico (GOM) and compare distributions prior to and after hurricane activity, 187 Gulf sturgeon ( Acipenser oxyrinchus desotoi) were tagged with acoustic transmitters in Ochlockonee, Apalachicola, Brothers, Choctawhatchee, Yellow, Blackwater and Escambia rivers to monitor marine movement along the GOM coastline from Florida (FL) to Alabama (AL). Nine juveniles (79-86 cm fork length, 3.4-5.2 kg), 22 sub-adults (91-126 cm fork length, 4.5-17.1 kg) and 156 adults (130-210 cm fork length, 14.9-75.2 kg) were tagged between 2003 and 2005 and acoustically monitored each year between January and April, 2004-2008. Of the 187 tagged Gulf sturgeon, 72 adults, one sub-adult and no juveniles were relocated in the GOM throughout the entire duration of monitoring between 2004 and 2008. Fish were relocated on average 1.5 km from shore in two very important foraging and over wintering areas, one of which is not currently protected under the critical habitat designation: Site A located geographically between Pensacola, FL and Gulf Shores, AL and Site B located between Mexico Beach, FL and Panama City Beach, FL. Sediment studies conducted concluded that substrate at Site A consisted of fine sand, shell and areas of silty mud and substrate at Site B consisted of shell hash and fine sand. Macro invertebrates, such as polychaetes: Hobsonia florida and Mediomastus ambiseta and mollusk: Ervillia concentric, all typical to the Gulf sturgeon diet, were present at both sites. Forty-three tagged adult Gulf sturgeon were relocated at Site A and 27 adults and one sub-adult were relocated at Site B, with two additional fish located in other areas. Individual fish movement in one direction ranged from 10 to 315 km each year. Several fish exited one river, over wintered in the GOM, and entered a different river. Identification of new, frequently used Gulf sturgeon habitat ( Site A), outside of federally protected critical habitat, provided vital information that will aid in the future protection of coastal areas that support Gulf sturgeon during the winter and help with recovery efforts of the species. [ABSTRACT FROM AUTHOR]

Temporal and spatial distributions of Gulf of Mexico (Gulf) sturgeon Acipenser oxyrinchus desotoi were assessed in the Pensacola bay system, Florida, using stationary ultrasonic telemetry. Fifty-eight Gulf sturgeon were tagged within the Escambia (n = 26), Yellow (n = 8), Blackwater (n = 12) and Choctawhatchee Rivers (n = 12) in June, July, September and October, 2005. Fifty-four Gulf sturgeon were detected at least once during the study. Migration of sturgeon occurred throughout the bay system in fall, to various winter habitats in the Gulf of Mexico and Santa Rosa Sound. In spring, tagged sturgeon migrated back through the bay system to summer habitats in rivers. Based on the duration and number of detections, Gulf sturgeon primarily used the upper portions of East and Escambia Bays as migration routes in and out of all rivers during spring and summer and inhabited the lower portion of Pensacola Bay for longer durations in fall and winter. Specific areas within the Pensacola bay system were used in summer and winter that were not previously documented as essential sturgeon habitat. Areas in southeastern Pensacola Bay were heavily used during winter by a large portion of the population. Gulf sturgeon also exhibited long-term winter residency in Santa Rosa Sound for two consecutive years. An area in northeastern Escambia Bay supported Gulf sturgeon during the summer, which was unexpected and can not be explained by the data from this study. However, the discovery that Gulf sturgeon remain in the bay during the summer has important ecological and management implications that need further investigation. [ABSTRACT FROM AUTHOR]

Three automated listening post-telemetry studies were undertaken in the Suwannee and Apalachicola estuaries to gain knowledge of habitats use by juvenile Gulf Sturgeons ( Acipenser oxyrinchus desotoi) on winter feeding grounds. A simple and reliable method for external attachment of small acoustic tags to the dorsal fin base was developed using shrink-tubing. Suspending receivers on masts below anchored buoys improved reception and facilitated downloading; a detection range of 500–2500 m was realized. In the Apalachicola estuary, juvenile GS stayed in shallow water (< 2 m) within the estuarine transition zone all winter in the vicinity of the Apalachicola River mouth. Juvenile GS high-use areas did not coincide with high density benthic macrofauna areas from the most recent (1999) benthos survey. In the Suwannee estuary, juveniles ranged widely and individually throughout oligohaline to mesohaline subareas of the estuary, preferentially using mesohaline subareas seaward of Suwannee Reef (52% of acoustic detections). The river mouth subarea was important only in early and late winter, during the times of adult Gulf Sturgeon migrations (41% of detections). Preferred winter feeding subareas coincided spatially with known areas of dense macrofaunal benthos concentrations. Following a dramatic drop in air and water temperatures, juvenile GS left the river mouth and estuary, subsequently being detected 8 km offshore in polyhaline open Gulf of Mexico waters, before returning to the estuary. Cold-event offshore excursions demonstrate that they can tolerate full-salinity polyhaline waters in the open Gulf of Mexico, for at least several days at a time. For juvenile sturgeons, the stress and metabolic cost of enduring high salinity ( Jarvis et al., 2001 ; McKenzie et al., 2001 ; Singer and Ballantyne, 2002 ) for short periods in deep offshore waters seems adaptively advantageous relative to the risk of cold-event mortality in shallow inshore waters of lower salinity. Thus, while juveniles can tolerate high salinities for days to weeks to escape cold events, they appear to make only infrequent use of open polyhaline waters. Throughout the winter foraging period, juvenile GS stayed primarily within the core area of Suwannee River mouth influence, extending about 12 km north and south of the river mouth, and somewhat seaward of Suwannee Reef (< 5 km offshore). None were detected departing the core area past either of the northern or southern acoustic gates, located 66 and 52 km distant from the river mouth, respectively. [ABSTRACT FROM AUTHOR]

Gulf sturgeon are anadromous, spawning in freshwater and returning to the marine environment to feed. Herein, we document the marine distribution and timing of movement in and out of the marine environment of Gulf sturgeon natal to the Pascagoula and Pearl rivers (MS and LA). From 1999 to 2004, we attached sonic transmitters to 194 fish averaging 151 (MS) to 160 (LA) cm in fork length. We located 56 different Gulf sturgeon in the estuarine or marine environments, some multiple times. Fish were distributed nonrandomly, being found primarily in shallow water (mean=3.9 m) in barrier island passes. Benthic samples taken at Gulf sturgeon telemetry location sites were dominated by Florida lancelets, sand dollars, annelids, haustoriid amphipods, and mollusks-all documented prey of Gulf sturgeon. Movement into salt water consistently occurred in October and November; movement back into rivers or low salinity estuaries was complete by the end of March. [ABSTRACT FROM AUTHOR]

A study of the seasonal movements of Gulf' sturgeon Acipenser oxyrinchus desotoi was conducted in the Pearl River system and the Mississippi Sound from 2000 through 2003. We captured or recaptured, marked, and released 503 Gulf sturgeon, 98 adults being tagged with internal or external telemetry tags. Movement chronologies were generally similar to those reported in other studies. Summer habitats were found in the Pearl and Bogue Chitto rivers (Louisiana-Mississippi), and these habitats were occupied from April through November. Adults and subadults were spatially separated, the adults being concentrated in the Bogue Chitto River and the subadults in the Pearl River. Tagged adults began to leave the summer habitat during September and to arrive at the mouth of the Pearl River and the Rigolets Pass. The last departure from this location was in late November. Wintering habitat between Cat, Ship, Horn, and Petit Bois islands in the Mississippi Sound was used between November and early March. Gulf sturgeon returned to the Rigolets Pass from March through June. Despite extensive sampling and the use of multiple collection gears, no eggs, larvae, or age-0 fish were captured and Gulf sturgeon spawning sites within this system remain unknown. The identification of summer and wintering habitats is essential for critical habitat designation for this species, which is federally listed as threatened. [ABSTRACT FROM AUTHOR]

Apparent digestibility coefficients (ADCs) of dry matter, energy, and crude protein in the diet of Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi were determined by two methods, dissection and hand stripping of feces from the lower spiral valve-rectal area of the digestive tract. Hand stripping resulted in ADC values of 58, 69, and 85% and the dissection method resulted in values of 54, 64, and 78% for dietary dry matter, energy, and crude protein, respectively. No significant differences in the ADC values obtained between the two methods were observed. Gulf of Mexico sturgeon are protected in the Gulf Coast region of the United States and listed as a threatened species under the U.S. Endangered Species Act. The hand stripping method is recommended over dissection for Gulf of Mexico sturgeon since it is an accurate and reliable procedure that does not require killing the fish. [ABSTRACT FROM AUTHOR]

Sturgeons were fed on commercially available diets for hybrid bass, catfish or trout. The impact of these diets on the quality of the smoked fillets was investigated through determination of proximate com- position, fatty acid profiles and sensory characteristics. Sensory analysis showed significant differences in moistness, saltiness and acceptability. No significant differences were detected in fattiness and smoked flavor intensity. Proximate analysis revealed an approximate 10% decrease in moisture content together with an estimated 3% salt uptake due to brining and smoking. Results showed that smoking did not adversely affect the fatty acid profile of the fillets. The commercial fish diets tested had no detrimental impact on the composition of the smoked product. Trout and bass diet provided higher levels of EPA and DHA in sturgeon fillets than the catfish diet. Consequently, ratios of ω3-ω6 fatty acids determined for the smoked fillets of sturgeon fed on either bass or trout diet were twice the value determined for the smoked fillets of sturgeon fed on catfish diet. [ABSTRACT FROM AUTHOR]

Post-release survival and upstream movement of Gulf of Mexico sturgeon ( Acipenser oxyrinchus desotoi) in the Suwannee River, Florida, were examined following induced spawning using carp pituitary extract (CPE). Six mature females (one CPE-treated and five control) and 12 mature males (five CPE-treated and seven control) were implanted with ultrasonic tags in March 2001 during their ingress into the Suwannee River. All CPE-treated sturgeon and 10 of the 12 control fish were relocated using ultrasonic telemetry during 4 months following their release, resulting in 100% survival of treated fish and 83% known survival of control fish. Two control fish (one female and one male) could not be relocated after 2 weeks post-release. CPE treatment did not result in mortality but did affect upstream movement behavior, with CPE-treated males moving upstream at a significantly slower rate than control males and females. Similarly, the maximum observed distance that the fish moved upstream differed among control fish (males and females) and treated males, with control fish moving further upstream than CPE-treated males. The rate of upstream movement for the single CPE-treated female was similar to the control females and the maximum upstream distance that this female was located was near a putative spawning area. In general, the environmental parameters of temperature, dissolved oxygen, and conductivity differed over the course of the study but did not differ between treatments and sexes. Treating sturgeon with CPE to induce spawning therefore did not cause mortality but did appear to slow the rate of upstream movement and maximum distance moved in male Gulf sturgeon. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Our objectives were to determine processing yields of Gulf sturgeon fillets based on whole fish weight and to measure their proximate composition. Fifty fish, in five weight groups were studied. Fillets yields increased with fish weight. Gulf sturgeon should weigh at least 2.5 kg to provide 60% headed and gutted yields. Dressed fillet yields were between 19-23% of live weight. Fillets from three similar fish were subdivided into three chunks: `tail,' `middle' and `head.' Each proximate analysis was replicated using left and right fillets. Results show small differences in the protein and moisture content of these sections. [ABSTRACT FROM AUTHOR]

Two species of freshwater stenohaline fish (channel catfish, Ictalurus punctatus; and goldfish, Carassius auratus) and four species of euryhaline fish (rainbow trout, Oncorhynchus mykiss; brown trout, Salmo trutta; striped bass, Morone saxatilis; and Gulf sturgeon, Acipenser oxyrinchus desotoi) were raised in salinities from 0‰ to 9‰, and then their resting ammonia and urea excretion were compared. The ammonia excretion of channel catfish, goldfish, rainbow trout, and brown trout was higher in 9.0‰ salinity than in the other tested salinities, but ammonia excretion by Gulf sturgeon and striped bass was lowest in 9.0‰ salinity. The urea excretion of goldfish and channel catfish increased with increasing salinity, while that of Gulf sturgeon did not change and that of all other species decreased. In the higher salinities, excretion of urea-N as a percentage of the total nitrogen excretion (ammonia-N plus urea-N) increased for channel catfish, goldfish, and Gulf sturgeon but decreased for the other species. Overall, the effects of salinity were similar for two stenohaline species, while the euryhaline species were more variable. [Copyright &y& Elsevier]

The anadromous Gulf sturgeon occurs along the north central coast of the Gulf of Mexico and is federally listed as threatened. We analyzed fine-scale patterns of Gulf sturgeon population structure, focusing on the Pascagoula River drainage of Mississippi, in reference to movement patterns as determined via telemetry and capture data. We genotyped 361 Gulf sturgeon using eight microsatellite loci including samples from the Pascagoula, Pearl, Escambia, Yellow, Choctawhatchee, and Apalachicola river drainages. Pairwise FST estimates indicated that genetic structure occurs at least at the drainage level. The Pascagoula and Pearl rivers form a western group, demonstrating 100% bootstrap support for a division with drainages to the east. Assignment tests detected non-natal genotypes occurring in all drainages. According to assignment tests, the Pascagoula supports an admixture of individuals, containing minimal influence from drainages to the east (2%) and substantial interaction with the Pearl River (14.1%). The occurrence of Pascagoula River fish in the Pearl was non-reciprocal, observed at 1.1%. After accounting for non-natal genetic diversity within the Pascagoula, there remained a disparity between a pooled Pascagoula group and the only documented spawning site within the drainage located in the Bouie River. We interpret this as an indication of a second genetic stock within the Pascagoula River drainage. Radio telemetry data suggest that spawning likely occurs in the Chickasawhay River, in areas isolated from the Bouie River spawning site by about 350 river kilometers. We emphasize the utility of integrating field and molecular approaches when delineating fine-scale patterns of population structure in anadromous fishes. [ABSTRACT FROM AUTHOR]

Growth and survival of fingerling Atlantic sturgeon, Acipenser oxyrinchus, were examined at three different feed rates. Sturgeon (mean initial weight ±SD of 28±12 g) were offered a closed-formula, commercially-available sturgeon diet (48.5% protein, 16.2% fat, 9.9% moisture, 7.6% ash, 0.5% fiber and 17.4% nitrogen free extract) via 24-hour, time-controlled feeders at rates of 1.5, 3.0, and 4.5% body weight per day (BW/day). Mean water temperature was 16.8°C. After 49 days of feeding, final length, final weight and feed conversion were all significantly affected by feeding rate (P ὄ 0.05). Peak feed conversion occurred at a ration of 1.5%, while maximum increase of both length and weight occurred at approximately 3.0%. No mortality occurred during the seven-week trial. The choice of feeding rates will ultimately depend upon production requirements and the culturist. Offering diet at a rate of 3.0% BW/day will result in significantly greater growth accompanied by high survival. Delivering diet at a rate of 1.5% BW/day will result in equally high survival and require approximately 50% less diet. It will, however, yield lower growth rates. [ABSTRACT FROM PUBLISHER]

We observed Suwannee River Gulf sturgeon, Acipenser oxyrinchus desotoi, in the laboratory and found free embryos (first interval after hatching) hid under rocks and did not migrate. Thus, wild embryos should be at the spawning area. Larvae (first interval feeding exogenously) initiated a slow downstream migration, and some juveniles (interval with adult features) continued to migrate slowly for at least 5 months, e.g., a 1-step long larva-juvenile migration. No other population of sturgeon yet studied has this migration style. A conceptual model using this result suggests wild year-0 sturgeon have a variable downstream migration style with short-duration (short distance) migrants and long-duration (long distance) migrants. This migration style should widely disperse wild fish. The model is supported by field studies that found year-0 juveniles are widely dispersed in fresh water to river km 10. Thus, laboratory and field data agree that the entire freshwater reach of river downstream of spawning is nursery habitat. Foraging position of larvae and early juveniles was mostly on the bottom, but fish also spent hours holding position in the water column, an unusual feeding location for sturgeons. The holding position of fish above the bottom suggests benthic forage in the river is scarce and fish have evolved drift feeding. The unusual migration and foraging styles may be adaptations to rear in a river at the southern limit of the species range with poor rearing habitat (low abundance of benthic forage and high summer water temperatures). Suwannee River Gulf sturgeon and Hudson River Atlantic sturgeon, A. o. oxyrinchus, are similar for initiation of migration, early habitat preference, and diel migration. The two subspecies differ greatly for migration and foraging styles, which is likely related to major differences in the quality of rearing habitat. The differences between Atlantic sturgeon populations show the need for geographical studies to represent the behavior of an entire species. [ABSTRACT FROM AUTHOR]

Summary The Gulf sturgeon (Acipenser oxyrinchus desotoi ) was listed as a threatened species in 1991 because of declines in abundance throughout the Gulf of Mexico. One recommendation of the recovery plan for Gulf sturgeon was to characterize critical habitats. In this study, radio telemetry was used to determine summer (June–August) distribution and habitat use of Gulf sturgeon in the Choctawhatchee River, Florida–Alabama. Ranging from 74 to 222 cm total length, 63 radio-tagged fish were located 398 times during weekly or biweekly searches in June–August of 1994–1997. A 10-km section of the lower Choctawhatchee River (river km 40–49.9) accounted for 38% of the summer locations of immature fish (less than 1.3 m fork length) and 73% for mature fish. Fish were typically located at sites that were 2–5 m in depth, with water temperatures of 25–28°C and a sand substrate. Spring discharges account for up to one-third of the mainstem river flow in this reach, but water temperatures at fish locations were similar to temperatures at fish locations in all other sections of the river. Efforts to monitor and improve habitat quality should be focussed on this river reach, given that a high percentage of the total Choctawhatchee River population occurs there during summer. [ABSTRACT FROM AUTHOR]

Summary Gulf sturgeon (Acipenser oxyrinchus desotoi ), as well as many other sturgeons, frequently jump out of the water. It is not known why they jump and expend energy during their non-feeding residency in freshwater rivers, but many explanations have been proposed. In the present study, it is hypothesized that jumping is a form of group communication that serves to maintain group cohesion. Information was collected on seasonal and diurnal temporal patterns of jumping at a known sturgeon aggregation ‘holding’ area; jumping sounds were recorded and analyzed to test this hypothesis. Jumping was found to vary seasonally, with number of jumps every 0.5 h much higher in June than during other months in which observations were made (April, May, August, and September in 2000 and 2001). Over 1000 jumps per day were recorded in a short (0.8 km) stretch (at river kilometer 61) of the Suwannee River in northwestern Florida. Jumping activity peaked near dawn and to a lesser degree near sunset in months other than June. The June jumping rate (jumps per 0.5 h) did not show a distinct dawn peak, although it was lowest during midday. Jumping sounds were recorded on a digital video/audio recorder attached to a hydrophone. Video images of sturgeon jumps were used to register specific sounds with specific components of the jumping action. Sonograms of sturgeon jumping sounds were compared and found to be distinct and different from sounds of other fish jumping or from objects dropped into the water for comparative purposes. These results are consistent with the hypothesis (but not to the exclusion of other hypotheses) that jumping is a form of communication. [ABSTRACT FROM AUTHOR]

A juvenile Acipenser oxyrinchus desotoi (Gulf Sturgeon) was collected from the Santa Fe River, a major tributary of the Suwannee River, FL, on 6 December 2006. The Suwannee River is believed to contain the largest existing population of Gulf Sturgeon; however, our specimen is only the third Gulf Sturgeon collected from the Santa Fe River. Based on these observations, we believe that the Santa Fe River should be studied further to determine its importance as Gulf Sturgeon habitat, especially in the face of future management plans that may alter the hydrology of the system. [ABSTRACT FROM AUTHOR]