In the U.S. Gulf of Mexico, Gulf Sturgeon Acipenser oxyrinchus desotoi supported an intense and short-lived commercial fishery in the early twentieth century. Thereafter, it persisted at very low levels until the fishery was closed by individual U.S. states in the Gulf of Mexico region in the mid-1980s. Despite the closure of the fishery, the stock has not recovered and there have been threats to population recovery including the potential effects of the Deepwater Horizon oil spill, storm events, and harmful algal blooms. We developed an age-structured population model for Gulf Sturgeon to examine their population recovery characteristics. We paired this model with simple population reference points to assess the factors that influence the population recovery rate and strategies that resource managers could adopt to promote the recovery of the species. We used the Gulf Sturgeon population in the Apalachicola River as a case history and the date of 2023 that has been identified in Gulf Sturgeon Recovery Plan (GSRP) as the point at which to evaluate recovery, and under current management we predict that (1) age-4+ Gulf Sturgeon (fish 4 years of age and older) will be approaching 50% of current estimated carrying capacity; (2) the dynamic spawning potential ratio is likely >0.3, suggesting a low chance of recruitment overfishing; (3) the population age structure is likely slowly recovering; (4) the recovery of the Gulf Sturgeon population is sensitive to increases in total mortality; and (5) the estimated values for exploitation rate (UMSY) and biomass at maximum sustainable yield (BMSY) are about 0.058 and 1,859 kg (or <200 age-4+ fish per year [age-4 and older fish]), respectively. Our results demonstrate the relative efficacy and influence of various recovery efforts and threats, respectively, and demonstrate that “recovery” is much different when it is based on historic versus currently available habitat. These model results provide reference points for comparing field assessments as part of the planned restoration efforts and upcoming population status reviews for Subject editor: Milo Adkison, University of Alaska–Fairbanks, Juneau *Corresponding author: billpine@ufl.edu Present address: Georgia Department of Natural Resources, Coastal Resources Division, 1 Conservation Way, Brunswick, Georgia 31520, USA. Received April 15, 2019; accepted December 11, 2019 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science 12:33–49, 2020 © 2020 The Authors. Marine and Coastal Fisheries published by Wiley Periodicals, Inc. on behalf of American Fisheries Society. ISSN: 1942-5120 online DOI: 10.1002/mcf2.10105

Stocking of trout to support recreational fisheries is a common practice among state and federal agencies to meet angling and harvest demands. Success of stocking efforts relies upon fish behavior and survival to maximize the availability of fish to anglers. We quantitatively described the movement behavior and survival of stocked Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, and Rainbow Trout Oncorhynchus mykiss in three southern Appalachian Mountain streams in western North Carolina, USA, that were managed under delayed harvest regulations. Hatchery trout were tagged with a combination of PIT tags and radio transmitters (radio tags); stocked into "Delayed Harvest Trout Waters" of the North Toe, East Prong Roaring, and Little rivers; and monitored during the catch-and-release season from October to June. Assessed according to river and species, 19-65% of trout emigrated from the delayed harvest study reaches, while 1-29% died within the reaches. The majority of radio-tagged fish (71%; 59-85% by river) remained within 2 km of the stocking location, whereas 6% migrated over 10 km from the stocking location. Few trout stocked during fall (October and November) were available to anglers the following June due to a combination of migration and mortality. Emigration from delayed harvest study reaches was associated with stocking and high-flow events. Multi-state modeling detailed these observations with weekly estimates of migration and survival rates. River-specific differences in emigration and mortality suggested that emigration was a greater source of trout loss than mortality in all rivers; no pattern related to river size was apparent in emigration, but mortality was greater in small streams. Brook Trout mortality rates were highest among the three species, and large fish of most species showed higher emigration and mortality than catchable-sized trout. Fisheries managers can apply our results to alter stocking regimes so as to enhance the efficiency of stocking and the acclimation of stocked trout to instream environments.

Stream trout fisheries are among the most popular and valuable in the United States, but many are dependent on hatcheries to sustain fishing and harvest. Thus, understanding the ecology of hatchery-reared trout stocked in natural environments is fundamental to management. We evaluated the growth, condition, and trophic relations of Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, and Rainbow Trout Oncorhynchus mykiss that were stocked in southern Appalachian Mountain streams in western North Carolina. Stocked and wild (naturalized) trout were sampled over time (monthly; September 2012-June 2013) to compare condition and diet composition and to evaluate temporal dynamics of trophic position with stable isotope analysis. Relative weights (W-r) of stocked trout were inversely associated with their stream residence time but were consistently higher than those of wild trout. Weight loss of harvested stocked trout was similar among species and sizes, but fish stocked earlier lost more weight. Overall, 40% of 141 stomachs from stocked trout were empty compared to 15% of wild trout stomachs (N = 26). We identified a much higher rate of piscivory in wild trout (18 times that of stocked trout), and wild trout were 4.3 times more likely to consume gastropods relative to stocked trout. Hatchery-reared trout were isotopically similar to co-occurring wild fish for both delta C-13 and delta N-15 values but were less variable than wild trout. Differences in sulfur isotope ratios (delta S-34) between wild and hatchery-reared trout indicated that the diets of wild fish were enriched in delta S-34 relative to the diets of hatchery-reared fish. Although hatchery-reared trout consumed prey items similar to those of wild fish, differences in consumption or behavior (e.g., reduced feeding) may have resulted in lower condition and negative growth. These findings provide critical insight on the trophic dynamics of stocked trout and may assist in developing and enhancing stream trout fisheries.

Abstract Sturgeons (Acipenseridae) are one of the most threatened taxa worldwide, including species in North Carolina and South Carolina. Populations of Atlantic Sturgeon Acipenser oxyrinchus in the Carolinas have been significantly reduced from historical levels by a combination of intense fishing and habitat loss. There is a need for estimates of current abundance, to describe status, and for estimates of historical abundance in order to provide realistic recovery goals. In this study we used N-mixture and distance models with data acquired from side-scan sonar surveys to estimate abundance of sturgeon in six major sturgeon rivers in North Carolina and South Carolina. Estimated abundances of sturgeon greater than 1 m TL in the Carolina distinct population segment (DPS) were 2,031 using the count model and 1,912 via the distance model. The Pee Dee River had the highest overall abundance of any river at 1,944 (count model) or 1,823 (distance model). These estimates do not account for sturgeon less than 1 m TL or occurring in riverine reaches not surveyed or in marine waters. Comparing the two models, the N-mixture model produced similar estimates using less data than the distance model with only a slight reduction of estimated precision.

In 2012, the National Oceanic and Atmospheric Administration (NOAA) declared Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus to be threatened or endangered throughout its range in U.S. waters. Restoration of the subspecies will require much new information, particularly on the location and timing of spawning. We used a combination of acoustic telemetry and sampling with anchored artificial substrates (spawning pads) to detect fall (September-November) spawning in the Roanoke River in North Carolina. This population is included in the Carolina Distinct Population Segment, which was classified by NOAA as endangered. Sampling was done immediately below the first shoals encountered by anadromous fishes, near Weldon. Our collection of 38 eggs during the 21 d that spawning pads were deployed appears to be the first such collection (spring or fall) for wild-spawned Atlantic Sturgeon eggs. Based on egg development stages, estimated spawning dates were September 17-18 and 18-19 at water temperatures from 25.3 degrees C to 24.3 degrees C and river discharge from 55 to 297 m(3)/s. These observations about fall spawning and habitat use should aid in protecting critical habitats and planning research on Atlantic Sturgeon spawning in other rivers.

Abstract Technological advances represent opportunities to enhance and supplement traditional fisheries sampling approaches. One example with growing importance for fisheries research is hydroacoustic technologies such as side-scan sonar. Advantages of side-scan sonar over traditional techniques include the ability to sample large areas efficiently and the potential to survey fish without physical handling-important for species of conservation concern, such as endangered sturgeons. Our objectives were to design an efficient survey methodology for sampling Atlantic Sturgeon Acipenser oxyrinchus by using side-scan sonar and to developmethods for analyzing these data. In North Carolina and South Carolina, we surveyed six rivers thought to contain varying abundances of sturgeon by using a combination of side-scan sonar, telemetry, and video cameras (i.e., to sample jumping sturgeon). Lower reaches of each river near the saltwater-freshwater interface were surveyed on three occasions (generally successive days), and we used occupancy modeling to analyze these data.We were able to detect sturgeon in five of six rivers by using these methods. Side-scan sonar was effective in detecting sturgeon, with estimated gear-specific detection probabilities ranging from 0.2 to 0.5 and river-specific occupancy estimates (per 2-km river segment) ranging from 0.0 to 0.8. Future extensions of this occupancy modeling framework will involve the use of side-scan sonar data to assess sturgeon habitat and abundance in different river systems.

Sturgeons (family Acipenseridae) are a highly threatened taxon worldwide; populations have declined for several reasons, including overfishing and habitat modification. It has been suggested that the widely introduced, highly piscivorous, flathead catfish Pylodictis olivaris is responsible for the decline of certain sturgeon populations in North America. Here we present the first field observation of flathead catfish predation on a sturgeon of any species, an Atlantic sturgeon Acipenser oxyrinchus in the Satilla River, Georgia. Our finding demonstrates a potential impact of flathead catfish predation on sturgeon populations; however, more research is needed to describe the full magnitude of such effects on sturgeon populations.

Molecular kin estimation from eggs in the threatened Gulf sturgeon By E. V. Saarinen*, J. H. Flowers , W. E Pine III, F. Parauka and J. D. Austin Department of Wildlife Ecology & Conservation, University of Florida, Gainesville, FL, USA; School of Forest Resources & Conservation, Program in Fisheries & Aquatic Sciences, University of Florida, Gainesville, FL, USA; Panama City Field Office, U.S. Fish and Wildlife Service, Panama City, FL, USA

Bioenergetics models are commonly used by scientist and managers to describe energy uptake and metabolism of fish species. Much data is needed to inform these models and often species specific data is unavailable or difficult to acquire, such as in the case with Gulf of Mexico sturgeon. This study applied a new method, developed by Walters and Essington (this issue), to estimate bioenergetics parameters using field observations for Gulf sturgeon populations in the Apalachicola and Suwannee Rivers, Florida, U.S.A. Bioenergetics derived growth curves were compared to growth curves developed using traditional direct aging methods. We obtained bioenergetic parameter estimates for both popula- tions and the bioenergetic method was able to accurately simulate annual variability in Gulf sturgeon growth rates. Fur- ther, the bioenergetics growth estimates, which incorporate length-at-age and length-increment data estimated very differ- ent growth trajectories than traditional von Bertalanffy curves that used only length-at-age. This indicates that length-at- age data alone can lead to errors in growth estimates, resulting in erroneous management advice. Using field data to in- form bioenergetic models should be a useful approach for fisheries researchers and managers to describe the growth and energetic characteristics of fish populations.

Bioenergetics models offer a useful framework for assessing the consumptive demand on ecosystems from nonnative fish.Consumption estimates from bioenergetics models can be combined with estimates of population abundance to quantify population-level consumption.This study applies a new bioenergetics modeling framework, developed by Walters and Essington (this volume), to estimate bioenergetics parameters using field data commonly collected from population monitoring programs.We used growth increment and size-at-age data to estimate the parameters of the bioenergetics model described by Walters and Essington (this volume) for an introduced population of Pylodictis olivaris from the Neuse River, North Carolina.The model fit the observed growth data well and predictions of consumption patterns were consistent with observed feeding patterns.The estimated consumption pattern from the general bioenergetics model represents the first characterization of adult flathead catfish consumption.Through use of capture-recapture data, the Walters and Essington bioenergetics model is able to integrate consumption estimates with growth and demographic data.Although further validation of the model is necessary, the modeling framework provides a straightforward approach to assessing the consumptive demand of fish populations.

Rapid human population growth and an associated increase in consumptive water demands within the ecologically diverse Apalachicola-Chattahoochee-Flint (ACF) River basin of the southeastern United States have led to a series of highly publicized water wars, exacerbated by recent drought conditions, between the states of Alabama, Georgia, and Florida. A key issue is how managing riverine flows to meet human water needs will affect the viability of species that are federally listed as threatened or endangered, including the Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi. Our present understanding of Gulf sturgeon ecology within the Apalachicola River basin indicates that altered riverine flow regimes may affect spawning success and possibly the recruitment patterns of the population. Through intensive field work, we documented Gulf sturgeon spawning site selection in the Apalachicola River and then evaluated the relationship between river stage and the available spawning habitat at these sites. We then used an age-structured simulation model to assess the effects of changes in recruitment patterns on population viability using hypothetical scenarios based on changes in flow regime and its effect on available spawning habitat. Over 3 years we were able to collect almost 500 Gulf sturgeon eggs in the Apalachicola River at three different spawning sites. We observed that the depths and flows where eggs were found were similar across years and sites despite varying river conditions. River discharges of less than 142 m(3)/s at Jim Woodruff Lock and Dam significantly reduced the spawning habitat available to Gulf sturgeon at all known spawning sites, potentially affecting recruitment. Gulf sturgeon populations are probably sensitive to changes in recruitment, and if extreme low-flow events occur with increasing frequency owing to water management policy choices or climatic events, population recovery could be impaired and the risk of extirpation could increase. Managers should consider the potential effects on Gulf sturgeon recruitment when determining future flow regime policies within the ACF.

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.