Juvenile Atlantic Sturgeon Research Articles

Salinity effects on Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus Mitchill, 1815) growth and osmoregulation

Summary The Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus Mitchill, 1815) is an anadromous sturgeon species, yet little is known with regard to its osmoregulatory ability and habitat use at early life stages. In order to examine whether salinity poses a physiological challenge to juvenile Atlantic sturgeon near the sizes where they may begin to move into saline habitats, growth and osmoregulatory ability were tested. Juvenile Atlantic sturgeon (mean initial weight: 440 g) were acclimated to one of three salinity conditions (0, 10, or 33 ppt) representing the range of salinities they would be expected to encounter. Growth was measured over a 6-month period, and osmoregulatory ability (i.e. blood plasma osmolality and ionic concentrations) was measured after 4 months. Mean weight and length increased in all treatments, but fish in 0 and 10 ppt grew more than fish in 33 ppt. Blood plasma osmolality was regulated at similar levels regardless of salinity. Therefore, juvenile Atlantic sturgeon have the physiological capability to move between salinity habitats, but grow faster in low salinities.

Genetic diversity and effective size of Atlantic sturgeon, Acipenser oxyrhinchus oxyrhinchus river spawning populations estimated from the microsatellite genotypes of marine-captured juveniles

Juvenile Atlantic sturgeon (Acipenser oxyrhinchus oxyrhinchus) forming aggregations at coastal sites in the mid-Atlantic Bight were subjected to a mixed stock analysis (MSA) and individual-based assignment using twelve microsatellite loci. We confirmed earlier findings from an analysis of mitochondrial DNA that three river spawning populations (Hudson, James and Delaware Rivers) are the primary sources of these particular marine aggregations. Of the 460 individuals sampled 322, 36 and 47 were assigned to the Hudson, James and Delaware Rivers, respectively. MSA estimated that the New York Bight Distinct Population Segment (Hudson River and Delaware River) contributed 83–90 % of individuals to the marine aggregations and the Chesapeake (James River) and Southeast Distinct Population Segments contributed 5.5–11 %. Mean M-ratios were lower than expected at equilibrium in all three rivers (Delaware = 0.726, Hudson = 0.748, James = 0.664), indicative of genetic bottlenecks affecting all three spawning populations. Further, there were low but detectable levels of inbreeding in all three rivers populations. Effective population size (Ne) was estimated for three populations: Hudson River (172–230 individuals), James River (40–100 individuals) and Delaware River (75–186 individuals). Despite these issues, simulations based on life-history information and the Ne estimates suggest that if ongoing management measures are effective, contemporary levels of population genetic diversity are likely to be retained over the next century.

Potential for Electropositive Metal to Reduce the Interactions of Atlantic Sturgeon with Fishing Gear

Atlantic sturgeon (Acipenser oxyrhynchus) populations have been declared either endangered or threatened under the U.S. Endangered Species Act. Effective measures to repel sturgeon from fishing gear would be beneficial to both fish and fishers because they could reduce both fishery-associated mortality and the need for seasonal and area closures of specific fisheries. Some chondrostean fishes (e.g., sturgeons and paddlefishes) can detect weak electric field gradients (possibly as low as 5 Μv/cm) due to arrays of electroreceptors (ampullae of Lorenzini) on their snout and gill covers. Weak electric fields, such as those produced by electropositive metals (typically mixtures of the lanthanide elements), could therefore potentially be used as a deterrent. To test this idea, we recorded the behavioral responses of juvenile Atlantic sturgeon (31-43 cm fork length) to electropositive metal (primarily a mixture of the lanthanide elements neodymium and praseodymium) both in the presence and absence of food stimuli. Trials were conducted in an approximately 2.5 m diameter × 0.3 m deep tank, and fish behaviors were recorded with an overhead digital video camera. Video records were subsequently digitized (x, y coordinate system), the distance between the fish and the electropositive metal calculated, and data summarized by compiling frequency distributions with 5-cm bins. Juvenile sturgeon showed clear avoidance of electropositive metal but only when food was present. On the basis of our results, we conclude that the electropositive metals, or other sources of weak electric fields, may eventually be used to reduce the interactions of Atlantic sturgeon with fishing gear, but further investigation is needed.

Comparison of MS‐222 and Electronarcosis as Anesthetics on Cortisol Levels in Juvenile Atlantic Sturgeon

AbstractInvasive surgical procedures on sturgeon (family Acipenseridae) are sometimes conducted without anesthesia. We examined plasma cortisol concentrations in Atlantic Sturgeon Acipenser oxyrinchus exposed to the anesthetic MS‐222 (tricaine methanesulfonate), electronarcosis, or no anesthetic 1 and 24 h after a small incision mimicking an invasive procedure (tag implantation or laparoscopy). We also determined the feasibility of using electronarcosis in the field and the effect of salinity on electronarcosis. One hour after surgery under electronarcosis or MS‐222 anesthesia, cortisol concentrations did not differ significantly from those in untreated controls but all three were significantly lower than the no‐anesthetic group. There were no significant changes between 1‐ and 24‐h blood cortisol concentrations. We recommend electronarcosis as a method to minimize stress in fish studies involving surgical procedures because it avoids the use of toxic chemicals and because induction and recovery are virtually instantaneous.

Experimental Examination of Surgical Procedures for Implanting Sonic Transmitters in Juvenile Shortnose Sturgeon and Atlantic Sturgeon

Abstract Acoustic telemetry has become a leading tool for monitoring the movements of and habitat use by many sturgeon species worldwide; however, procedures for internal tagging of small juvenile sturgeon (<55 cm TL) are lacking. We examined effects of implantation technique on growth, tag retention, and survival of juvenile (<55 cm) Shortnose Sturgeon Acipenser brevirostrum and Atlantic Sturgeon A. oxyrinchus by using dummy acoustic tags. Two implantation techniques were used: (1) anchoring the tag to the wall of the peritoneal cavity and (2) no internal anchoring of the tag. These treatment groups were compared with two control groups: fish that received anesthetic only and fish that received anesthetic and an incision. Retention rate was significantly higher for anchored tags (88%) than for nonanchored tags (25%) in Shortnose Sturgeon juveniles, while Atlantic Sturgeon juveniles retained 100% of tags regardless of treatment. Nonanchored tags that were lost during the second week were expelled through ...

Effect of chloride on nitrite‐induced methaemoglobinemia in Atlantic sturgeon,Acipenser oxyrinchus oxyrinchus(Mitchill)

We evaluated the effects of chloride concentration on the clinical pathology in juvenile Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus (Mitchill), following semi-static exposures to 1 mg L(-1) nitrite for 96 h. In spring water naturally low in chloride (5 mg L(-1)), plasma nitrite concentrated to more than 40× environmental levels resulting in a severe methaemoglobinemia characterized by torpid behaviour, 30-fold increase in methaemoglobin fraction, anaemia, leucopenia and hyperkalaemia. Loss of intracellular water and potassium to extracellular space may have resulted in hyperkalaemia and haemodilution. Fish survived nitrite exposure, but 60% of torpid fish died following capture and tissue sampling. Fish acclimated to 10-fold higher chloride content (55 mg L(-1)) did not concentrate nitrite in the plasma above environmental levels or develop methaemoglobinemia, but did exhibit similar haematology and plasma chemistry changes. Plasma nitrite returned to preexposure levels by 14 days following nitrite exposures, but severity of clinical pathology changes persisted or increased, suggesting that Atlantic sturgeon have reduced capacity to recover from methaemoglobinemia. Fish that survive methaemoglobinemia may be susceptible to mortality from the cumulative effects of intoxication, handling and other stresses for two or more weeks following nitrite remediation. Chloride buffering in aquaculture systems reduces the toxic effects of nitrite accumulation.

Age and Growth of Atlantic Sturgeon in the James River, Virginia, 1997–2011

AbstractHistorically the Chesapeake Bay supported a large population of Atlantic sturgeonAcipenser oxyrinchus, but loss of suitable spawning habitat and overfishing coincided with dramatic in‐system declines throughout the 20th century. Atlantic sturgeon harvest moratoriums were implemented in 1974 for Virginia waters and were expanded coastwide in 1998. In 1997, researchers became aware that commercial fishers in the James River, a tributary of the Chesapeake Bay, were catching juvenile and subadult Atlantic sturgeon as bycatch in various fisheries. Genetic studies showed that the Chesapeake Bay population has maintained genetic integrity and qualifies as a distinct population segment. Between 2007 and 2011, almost 150 adults have been caught in the tidal–freshwater portion of the James River during putative spawning runs. Pectoral fin spines from juveniles and subadults collected in the Burwell Bay (rkm 40) and Cobham Bay (rkm 60) areas and mature adult samples from vessel strikes in freshwater around or above rkm 120 were analyzed to create a length‐at‐age curve for Atlantic sturgeon in the James River. Five models were used to analyze the data, and the double von Bertalanffy (k1= 0.054,k2= 0.097,t1= −2.85,t2= 1.09,tp= 6.03 years,L∞= 2241 mm) provided the best fit to the observed data. We estimated an increase in growth coefficient attp, which could be an artifact of low sample size or due to ontogenetic changes in habitat use as older fish spend more time in oceanic waters than younger fish. Atlantic sturgeon in the 6–9 year age range are rarely encountered in the James River compared with younger and older age‐classes, so a more in‐depth analysis of the increased growth coefficient would require ocean sampling.

Using energy dispersive x-ray fluorescence microchemistry to infer migratory life history of Atlantic sturgeon

Atlantic sturgeon migrate between ocean and freshwater habitats to spawn, and juveniles spend several years in fresh/brackish water before returning to the ocean. Because strontium/calcium (Sr/Ca) ratios are diagnostic for freshwater and marine environments, we examined the utility of energy-dispersive x-ray fluorescence (EDXRF) to quantify Sr/Ca ratios of Atlantic sturgeon pectoral fin spines. Atlantic sturgeon spines from wild adults and experimental juveniles were analyzed along a linear transect from the primordium to the outermost point. To verify the technique hatchery juvenile Atlantic sturgeon were held in experimental tanks at <0.5, 13–15, or 33–35‰ and sampled after 5 months. Sr/Ca ratios of experimental hatchery fish increased with salinity, and Sr/Ca ratios in wild adults varied predictably along the measurement transect. However, the ratio decreased in the outermost region of the spine in mature fish collected during a return to freshwater for spawning. Therefore EDXRF is a useful tool to track individual movements of Atlantic sturgeons and other diadromous fish.

Evaluation of tricaine methanesulfonate (MS-222) as a surgical anesthetic for Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus

Summary Dose-response experiments were conducted at 14 and 24°C to evaluate the efficacy and physiological effects of tricaine methanesulfonate (MS-222) to induce and maintain surgical anesthesia in juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus). Anesthetic induction time, duration of hyperactivity, recovery time and total handling time of fish were inversely related to MS-222 concentration and water temperature. Minimum effective concentration of MS-222 to maintain anesthesia with fewest signs of stress was 85 mg L−1. Sensitivity to stimuli and body movements progressively increased when fish were exposed to a lower maintenance concentration (70 mg L−1) of MS-222, resulting in reduced biopsy success rates and traumatic injury to internal organs during laparoscopy as fish regained consciousness. Anesthesia with MS-222 resulted in bradychardia, near medullary collapse, elevated signs of stress (plasma cortisol and reddening of the skin) and a generalized hemo-concentration consisting of erythrocyte swelling and increased protein and monovalent ion concentrations. Magnitude of hematologic changes and stress indicators increased with decreasing MS-222 concentration and increased water temperature while plasma chemistry changes increased in magnitude with decreasing MS-222 concentration. This study demonstrates that rapid induction of surgical anesthesia with a relatively high concentration of MS-222 results in reduced signs of physiological stress, and that empirical evaluation of maintenance dosage is important to achieve the best balance between safety, efficacy and stressful side effects for invasive surgical procedures.

Feeding of hatchery-reared juvenile Atlantic sturgeon, Acipenser oxyrinchus Mitchill, released into the Drwęca River

Atlantic sturgeon, Acipenser oxyrinchus Mitchill was once one of the largest European freshwater fish, and it was common in the Vistula River drainage. Since 2006, juvenile Atlantic sturgeon obtained by artificially reproducing wild spawners caught in the St. John River in Canada have been stocked into several rivers in Poland. The current study to assess the feeding of Atlantic sturgeon in the Drweca River in Poland is part of a larger project to restore the species to this region. Hatchery-reared eleven-month-old Atlantic sturgeon were recaptured 2 to 10 days after their release into the river. This study provides the first data on the diet of A. oxyrinchus in the fresh waters of Europe. In June 2008, the stomach contents of the juvenile Atlantic sturgeon that had been recaptured were collected using gastric lavage. Of the 70 sturgeon the Drweca River which were subjected to gastric lavage, 67% of them had empty stomachs. The diet of juvenile Atlantic sturgeon consisted of nine taxa of prey. Primarily, sturgeon eat small, soft-bodied larval Oligochaetae and Chironomidae.

Atlantic sturgeon, Acipenser oxyrinchus Mitchill, infected by the parasitic leech, Caspiobdella fadejewi (Epshtein) (Hirudinea; Piscicolidae), in the Drwęca River

This study presents the parasitic relationship between the leech, Caspiobdella fadejewi, and the juvenile Atlantic sturgeon, Acipenser oxyrinchus. The aim was to determine leech invasion intensity and extensity and describe parasite feeding location preferences on the ventral side of the snout and gill cavities. The prevalence of C. fadejewi occurrence was 37.3%, at an intensity of one to eight leeches. It was confirmed that the intensity of leech occurrence was positively correlated with sturgeon total length (r=0.545, P<0.05, N=15). The host-searching mechanism is most probably based on positive phototaxis. This is the first record of C. fadajewi from A. oxyrinchus. The leech was first observed during routine examinations of sturgeon collected in June 2008. The leeches were usually attached to the inside lower portion of opercula near the isthmus.

Distribution and growth of juvenile Atlantic sturgeon released into the Drwęca and Wisłoka rivers (Poland)

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Impact of higher stocking density of juvenile Atlantic sturgeon, Acipenser oxyrinchus Mitchill, on fish growth, oxygen consumption, and ammonia excretion

The impact of stocking density on the growth, feed conversion, oxygen consumption, and ammonia excretion of juvenile Atlantic sturgeon (Acipenser oxyrinchus Mitchill) was studied. Three initial stocking densities were used in the experiment: 1.27, 2.49, and 3.80 kg m -2 . The length of the experiment was 64 days. The mean water temperature was 15.0C. The fish were fed commercial feed Nutra T 1.9 (Trouv, France). Atlantic sturgeon body weight growth was the highest in the group stocked at the lowest density. The fish from this group attained a final body weight of 130.1 g, which was statistically significantly higher than that of the groups stocked at densities of 2.49 kg m -2 (P 0.01). Stocking density had a substantial impact on the value of the feed conversion ratio (FCR) in the different groups. The lowest FCR was noted at the density of 1.27 kg m -2 at 0.67. This value differed statistically significantly from group 2.49 kg m -2 ,i n which it was 0.74 (P < 0.05), and it differed highly statistically significantly from group 3.80 kg m -2 at 0.83 (P < 0.001). The differences in the FCR value between groups 2.49 and 3.80 kg m -2 were also highly statistically significant. Stocking density was not noted to impact oxygen consumption or ammonia excretion. Mean daily ammonia excretion fluctuated from 2.09 to 2.39 mg kg -1 h -1 , and oxygen consumption ranged from 90.5 to 93.8 mg O2 kg -1 h -1 .

Movement and habitat use of juvenile Atlantic sturgeon in the Wisłoka River (southern Poland)

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Abundance and Recruitment of Juvenile Atlantic Sturgeon in the Altamaha River, Georgia

AbstractJuvenile Atlantic sturgeon Acipenser oxyrinchus remain in natal rivers for several years prior to out‐migrating to marine environments during later portions of their life history. Data regarding river‐resident juvenile population dynamics are unknown. During the summers of 2004–2007, we performed mark–recapture of juvenile Atlantic sturgeon in the Altamaha River to assess age‐specific abundance, apparent survival, per capita recruitment, and factors influencing recruitment. Estimates indicated that juvenile abundance ranged from 1,072 to 2,033 individuals, and age‐1 and age‐2 individuals comprised greater than 87% of the juvenile population, while age‐3 or older individuals constituted less than 13% of the population. Estimates of apparent survival and per capita recruitment from Pradel models indicated that the juvenile population experienced high annual turnover: apparent survival rates were low (&lt;33%), and per capita recruitment was high (0.82–1.38). Fall discharge, which had a positive relationship with recruitment, was the only factor assessed that significantly explained time variation in per capita recruitment. The findings of this study suggest that juvenile populations at the southern extreme of the Atlantic sturgeon's range may remain in natal rivers for less time than northern counterparts. This is further evidence of life history differences between northern and southern populations of Atlantic sturgeon. Potential findings of density dependence could have major implications for both population recovery and management of this species.

Assessment of Prerelease Diet Regimes on Growth of Juvenile Atlantic Sturgeon

AbstractTo determine whether the growth rates of juvenile Atlantic sturgeon Acipenser oxyrinchus would be improved if the fish were weaned to natural food before being released into a simulated natural environment, 60 sturgeon from the 2006 and 2007 year‐classes (ages 2 and 1, respectively) were subjected to two prerelease diet regimes (n = 30 per treatment, 120 total). Each year‐class was divided into two groups, a control group that was fed a commercial diet for 10 d until stocking into a 0.2‐ha earthen pond in June 2008 and a treatment group that was weaned to natural food over a 10‐d period before stocking. Final sampling (84 d poststocking) showed that year‐class had an effect on the specific growth rate (% weight gain/d) but that treatment did not. The survival rates were 77% and 80% among the controls from the 2007 and 2006 year‐classes and 87% and 90% among the treatment fish. This study shows that weaning to natural food before release into a natural environment does not significantly affect the specific growth or survival rates of Atlantic sturgeon.

Dissolved oxygen, temperature and salinity effects on the ecophysiology and survival of juvenile Atlantic sturgeon in estuarine waters: II. Model development and testing

Hypoxia–temperature interactions can have major effects upon fish physiology and energetics. In estuarine species, such effects can be also modified by natural salinity gradients leading to a three-way habitat contraction under extreme conditions. In this paper we use Fry's paradigm to propose an explanatory framework and to expand traditional mass balance bioenergetic models, incorporating dissolved oxygen and salinity effects. Water temperature was modeled as the controlling factor that establishes maximum potential rates and minimum oxygen demand; dissolved oxygen was considered to constrain physiological responses whenever oxygen demands exceed oxygen delivery rates; salinity was incorporated as a masking (loading) factor, demanding both energy and oxygen for osmoregulation processes. This general framework was expressed as a set of algorithms, with a total of 30 parameters, which were estimated using results from a large set of laboratory experiments conducted on young-of-the-year and yearling Atlantic sturgeons, as well as from other published studies. Compared to an empirical quadratic fit of these laboratory data, the model was more informative (lower AIC), suggesting that measured responses followed theoretical expectations. The model was tested in mesocosm trials, where strong correlations were observed between predicted and observed monthly and seasonal growth rates but modest to poor correlations were observed for predicted daily instantaneous growth rate. Sensitivity tests showed that uncertainty in activity cost and food consumption ratio parameters contributed most to model error.

Dissolved oxygen, temperature and salinity effects on the ecophysiology and survival of juvenile Atlantic sturgeon in estuarine waters: I. Laboratory results

Dissolved oxygen and salinity are relevant structuring factors which should be incorporated into habitat and bioenergetic models for estuarine fishes. We measured growth, food consumption, routine and postprandial metabolism, egestion and survival responses of juvenile Atlantic sturgeon (young-of-the-year: YOY, 6–48 g) in an incomplete factorial array of temperature, salinity and dissolved oxygen levels. Complementary measures were also conducted on yearlings (1 year-old, 70–300 g) to evaluate size and age effects upon food consumption and growth. All three factors had a significant effect on major bioenergetic responses, as well as several of their first order interactions. Maximum growth and food consumption rates were observed above 70% dissolved oxygen saturation, at 20 °C, and between salinities of 8 and 15. Postprandial metabolism was reduced and egestion increased under hypoxia (50% DO saturation), suggesting compensatory mechanisms aimed to reduce assimilation rates. A significant shift in growth responses with age indicated higher tolerance to salinity in yearlings than in YOY. No other size dependent changes were significant, either for hypoxia or for temperature effects. Survival tended to increase with dissolved oxygen saturation, and decreased at the highest temperature and salinity levels. Our results indicated both additive and synergistic effects of tested environmental factors upon ecophysiological responses and highlighted the need to consider these in new bioenergetic models.

Juvenile Atlantic Sturgeon Habitat Use in Newburgh and Haverstraw Bays of the Hudson River: Implications for Population Monitoring

AbstractPopulations of Atlantic sturgeon Acipenser oxyrinchus are at historically low levels along the Atlantic coast of North America. Atlantic sturgeon is a long‐lived species with a complex life history, making population assessment difficult. The purpose of this study was to determine seasonal habitat use by juvenile Atlantic sturgeon in the Hudson River estuary and provide recommendations for future population monitoring. Our study focused on Newburgh and Haverstraw bays in the Hudson River, as these are areas of known juvenile sturgeon concentrations. The habitat within each bay was coarsely stratified according to substrate (hard versus soft) and depth (deep versus shallow). Sampling occurred during fall 2003, spring and fall 2004, and spring and fall 2005. Fall sampling occurred from October through November and spring sampling occurred from March through April. We used anchored gill nets of 76‐, 102‐, and 127‐mm stretch mesh fished together at a sampling site. A total of 562 individual juvenile Atlantic sturgeon were captured during the course of this study (14 were captured more than once), the majority (90%) coming from Haverstraw Bay. Soft and deep habitat comprised only 25% of the available habitat in Haverstraw Bay but yielded the greatest frequency of catches, the highest mean catch per unit effort (CPUE), and lowest variance of CPUE. Catch per unit effort was highest during spring seasons in soft–deep areas of Haverstraw Bay. These results suggest that future population monitoring should focus sampling effort in soft–deep areas of Haverstraw Bay to have the greatest statistical power in detecting population trends.

Modeling spatial and temporal variation of suitable nursery habitats for Atlantic sturgeon in the Chesapeake Bay

For rare and endangered species, bioenergetics modeling can represent a valuable approach for understanding issues of habitat value and connectivity among potential habitats within nurseries in restoration programs. We used multivariable bioenergetics and survival models for Atlantic sturgeon to generate spatially explicit maps of potential production in the Chesapeake Bay. For the period 1993–2002, spatial and temporal patterns in water quality effects (temperature, dissolved oxygen [DO] and salinity) on potential production were evaluated. In addition, two forecasted scenarios were modeled: one implementing newly revised U.S. Environmental Protection Agency (EPA) DO-criteria for the Chesapeake Bay, and the other assuming a bay-wide increase of 1 °C due to an underlying trend in regional climate. Atlantic sturgeon's low (survival/growth) tolerance to temperatures >28 °C was a critical constraint during their first 1–2 summers of life. Hatched in freshwater (spring to mid-summer), young-of-the-year were predicted to occupy cooler (deeper) areas as temperature approached sub-lethal levels. While most thermal refuges were located down-estuary, a large fraction of potential refuges were unsuitable due to persistent hypoxia and/or salinity levels beyond the limited osmoregulatory capabilities of early juvenile Atlantic sturgeon. As a result, suitable summer habitats for juvenile Atlantic sturgeons in the Chesapeake Bay were predicted to be spatially restricted and variable between years, ranging from 0 to 35% of the modeled bay surface area. In critical (drought) years, almost no summer habitat was predicted to be available for juvenile Atlantic sturgeon. Value and size of nursery habitat was highly sensitive to climatic oscillations and anthropogenic interventions affecting freshwater inflow, water temperature and/or DO. Achieving EPA DO-criteria for the Chesapeake Bay was predicted to increase total suitable habitat by 13% for an average year, while increasing water temperature by just 1 °C bay-wide would reduce suitable habitat by 65%.