Atlantic and shortnose sturgeons of the Hudson River: common and divergent life history attributes

The Hudson River estuary supports substantial number of Atlantic sturgeon, Acipenser oxyrinchus, and shortnose sturgeon, Acipenser brevirostrum. Both species have complex life cycles that have been studied sporadically in the past 50 years. The life cycle of the shortnose sturgeon may be divided into four life intervals: non-spawning adults, spawning adults, eggs and larvae, and juveniles. The life cycle of the Atlantic sturgeon is reviewed in six intervals: non-spawning adults, female spawners, male spawners, eggs and larvae, early juveniles, and late juveniles. Both species are long-lived, mature at advanced age, have rapid and similar growth during the first few years of life, feed on generally similar taxa, use deep channel habitats for all life intervals, and have complex migratory patterns with distinct, seasonal, concentration areas. Atlantic and shortnose sturgeons differ, however, in ages and sizes at maturity, maximum size, timing and location of spawning, migratory behaviors, and management. Use of marine habitats and long-distance coastal migrations are restricted to Atlantic sturgeon, but some evidence indicates that large Atlantic sturgeon juveniles reside in riverine habitats along the Atlantic coast during warm months. Movements and habitat use by both sturgeons in the Hudson River estuary contrasts with the spatial segregation of the species reported in other river systems. Juvenile shortnose sturgeon and early juvenile Atlantic sturgeon have almost the same distributions in the Hudson River estuary during all seasons. During this period of co-occurrence, both species are very similar in size, grow at about the same rate, feed on similar foods, and share deep, channel habitats. Adult shortnose sturgeon distribution overlaps with the distribution of juvenile Atlantic sturgeon, and the latter commence river emigration at a size comparable to co-occurring adult shortnose sturgeon. Life history information on the Hudson River sturgeons substantiates the need to carefully conserve these species because of vulnerability to exploitation and habitat disruption.     

Ontogenetic Behavior and Migration of Atlantic Sturgeon, Acipenser oxyrinchus oxyrinchus, and Shortnose Sturgeon, A. brevirostrum, with Notes on Social Behavior

Ontogenetic behavior of Hudson River Atlantic sturgeon and Connecticut River shortnose sturgeon early life intervals were similar during laboratory observations. After hatching, free embryos were photonegative and sought cover. When embryos developed into larvae, fish left cover, were photopositive, and initiated downstream migration. Free embryos may remain at the spawning site instead of migrating downstream because the risk of predation at spawning sites is low. The two species are sympatric, but not closely related, so the similarities in innate behaviors suggest common adaptations, not phylogenetic relationship. Atlantic sturgeon migrated downstream for 12 days (peak, first 6 days), shortnose sturgeon migrated for 3 days, and year-0 juveniles of both species did not resume downstream migration. Short or long migrations of larvae may reflect different styles related to the total migratory distance from spawning sites to juvenile rearing areas. Atlantic sturgeon need to move a short distance to reach rearing areas and they had a long 1-step migration of 6–12 days. In contrast, shortnose sturgeon need to move a long distance to reach all rearing areas. This may be accomplished by a 2-step migration, of which the brief migration of larvae is only the first step. Early migrant Atlantic sturgeon were nocturnal, while late migrants were diurnal, and shortnose sturgeon were diurnal. These diel differences may also be adaptations for long (Atlantic sturgeon) or short (shortnose sturgeon) migrations. Cultured shortnose sturgeon, and possibly Atlantic sturgeon, have a dominance hierarchy with large fish dominant when competing for limited foraging space. Social behavior may be more important in the life history of wild sturgeons than is generally recognized.     

Effects of Temperature on the Early Development, Growth, and Survival of Shortnose Sturgeon, Acipenser brevirostrum, and Atlantic Sturgeon, Acipenser oxyrhynchus, Yolk-Sac Larvae

We reared shortnose and Atlantic sturgeons at different temperatures after hatch and measured yolk utilization rate and efficiency (YUE), maximum standard length, survival and development of escape response. Newly hatched Atlantic sturgeon, were smaller in size, more efficient at utilizing yolk (incorporating yolk to body tissue) and reached developmental stages sooner than shortnose sturgeon reared at the same temperatures (13–15°C). Within each species, decreasing temperature delayed yolk absorption, escape initiation, time to reach maximum size, and time to 100% mortality. However, YUEs and the size of the larvae at these 'stages' were independent of rearing temperature for both species. These results suggest that even as temperature drives metabolic processes to speed up development, these two species are still extremely efficient at transferring yolk energy to body tissues. The lower efficiencies experienced by larval shortnose may reflect difference in yolk quality between the two species and/or the Atlantic sturgeon's higher conversion efficiency. The ability of these two sturgeon species to develop successfully and efficiently under a wide range in temperatures may provide a competitive advantage over more stenothermic species and explain their persistence through evolutionary time.     

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

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

几种鲟鱼基因组大小、倍体的特性及鲟形目细胞进化的探讨

采用Ｆｅｕｌｇｅｎ－显微分光光度计方法,以鸡红细胞为标准ＤＮＡ（３．２２ｐｇ／２Ｃ）测定了长江白鲟、达氏鲟、中华鲟、史氏鲟和北美匙吻鲟的体细胞基因组大小（ＤＮＡ含量）。结果表明,上述五种鲟鱼ＤＮＡ含量分别为４．１１、８．２６、９．０７、６．０７和３．９６ｐｇ。长江白鲟和北美匙吻鲟均属于四倍体鱼类,分布在长江水系的中华鲟和达氏鲟两种鲟属鱼类为八倍体类型。史氏鲟初步判断为八倍体,据分析可能存在四倍体的     

Viability and fertilizing capacity of cryopreserved sperm from three North American acipenseriform species: a retrospective study

Populations of sturgeon across the globe are threatened due to unregulated harvest and habitat loss, and the status varies among species across North America. Ready access to viable and functional sperm would contribute to recovery programmes for these species. In this study, we examined the motility, viability (cell membrane integrity) of cryopreserved sperm from three North American acipenseriform species and fertilizing capacity. Milt samples were collected from captive shortnose sturgeon (Acipenser brevirostrum), wild paddlefish (Polyodon spathula) and pallid sturgeon (Scaphirhynchus albus) and cryopreserved using combinations of Modified Tsvetkova’s (MT) extender, Original Tsvetkova’s extender, and modified Hanks’ balanced salt solution, along with the cryoprotectants methanol (MeOH) or dimethyl sulfoxide (DMSO). A dual‐staining technique using the fluorescent stains SYBR‐14 and propidium iodide was employed with flow cytometry to determine the percentages of spermatozoa that were viable by virtue of having intact membranes. The percentage of viable spermatozoa ranged from 5% to 12% in shortnose sturgeon, 30–59% in paddlefish, and 44–58% in pallid sturgeon. In the first experiment with shortnose sturgeon sperm, methanol allowed for higher values for dependent variables than did DMSO, and sperm viability generally correlated with post‐thaw motility. However, fertilization rate, neurulation, or hatching rates were independent from these factors. In the second experiment with shortnose sturgeon, 5% MeOH combined with MT yielded higher values for all parameters tested than the other combinations: viability was correlated with motility, fertilization rate, and hatching rate. Overall, viability and post‐thaw motility was not affected by the use of hyperosmotic extenders (OT) or cryoprotectants (DMSO), but their use decreased fertilization percentages. For paddlefish sperm (experiment 3), MT combined with 10% MeOH was clearly a good choice for cryopreservation; viability and motility results were correlated, but independent of fertilization. For pallid sturgeon sperm (experiment 4), MT with 5–10% MeOH showed significantly higher sperm quality and fertilization parameters. Membrane integrity can be used as a predictor of fertilization by cryopreserved sperm, however additional sperm quality parameters, supplementary to motility and membrane integrity, would be useful in the refining and optimizing cryopreservation protocols with acipenseriform sperm.     

Phylogenetic relationships of the North American sturgeons (order Acipenseriformes) based on mitochondrial DNA sequences

The evolutionary relationships of the extant species within the order Acipenseriformes are not well understood. Nucleotide sequences of four mitochondrial genes (12S rRNA, COII, tRNA(Phe), and tRNA(Asp) genes) in North American sturgeon and paddlefish were examined to reconstruct a phylogeny. Analysis of the combined gene sequences suggests a basal placement of the paddlefish with regard to the sturgeons. Nucleotide sequences of all four genes for the three Scaphirhynchus species were identical. The position of Scaphirhynchus based on our data was uncertain. Within the genus Acipenser, the two Acipenser oxyrinchus subspecies were very similar in sequence and found to be basal to the remaining Acipenser species examined. Based on our data, Acipenser transmontanus and Acipenser medirostris were sister taxa, as were Acipenser fulvescens and Acipenser brevirostrum. Comparison of our results with hypotheses of sturgeon relationships proposed by previous authors is presented. The sequence data presented here are phylogenetically useful and provide a solid foundation of genetic information for the North American Acipenseriformes that can be expanded to include Eurasian species to provide a global picture of sturgeon evolution.     

Haematology of juvenile Acipenser oxyrinchus and Acipenser brevirostrum at rest and following forced activity

In vivo experiments were conducted to examine the haematology of juveniles from two relic bony fishes, Atlantic sturgeon Acipenser oxyrhinchus and shortnose sturgeon Acipenser brevirostrum . Oxygen transport characteristics (haematocrit, haemoglobin and mean erythrocytic haemoglobin concentration), ionic composition (Na⁺, Cl⁻, K⁺ and osmolality), metabolite concentration (lactate, cortisol and glucose) and protein content in blood were measured or calculated at rest and during recovery from forced activity. Under resting conditions, plasma osmolality and concentrations of Na⁺, Cl⁻, lactate, cortisol and total protein were significantly different between Atlantic and shortnose sturgeon. All other resting variables were not different between species. Following forced activity, plasma lactate levels were significantly higher in both species than at rest. Plasma cortisol levels in both species were only significantly higher 1 h following forced activity compared to resting values. Plasma lactate levels were significantly higher in Atlantic sturgeon than in shortnose sturgeon, but these levels returned to resting levels by 1 h in both species. Cortisol increases were greater in shortnose sturgeon than in Atlantic sturgeon. In general, oxygen transport characteristics, blood glucose, plasma protein and plasma osmolality were not altered by forced activity in either sturgeon species. Overall, both species had reduced responses ( i.e . the magnitude of changes in measured variables) to forced activity compared with teleosts.     

A Noninvasive Technique for Determining Sex of Live Adult North American Sturgeons

We have developed a noninvasive technique to determine the sex of adult North American sturgeon by examination of the external morphology of live individuals. We analyzed four sturgeon species taken by commercial and scientific harvest: white Acipenser transmontanus, green A. medirostris, Atlantic A. oxyrinchus and shortnose A. brevirostrum. Males have a urogenital opening in the shape of a letter Y, while the opening of females is in the shape of the letter O. We accurately sexed 26 of 36 sturgeon using this criterion. Accuracy was highest in live fish (82%), and significantly lower in dead fish (29%). Dead sturgeon usually have the rectum prolapsed so that the urogenital opening is protruded, and thus making the sexes indistinguishable.     

Morphology and ecology of Pacific sturgeons

The six North Pacific members of the genus Acipenser have generally similar environmental requirements and share several specific morphological features. This Pacific group consists of green sturgeon, Acipenser medirostris, Sakhalin sturgeon, A. mikadoi, white sturgeon, A. transmontanus, Chinese sturgeon, A. sinensis, Dabry’s sturgeon, A. dabryanus and Amur sturgeon, A. schrenkii. A qualitative morphological examination of these species revealed synapomorphic characters that suggest close phyolgenetic relationships resulting from common ancestry of eastern and western species within the Pacific Rim. An evolutionary taxonomic approach, considering a reduction of characters from east to west, would suggest an Asian ancestry for all Pacific sturgeons. In contrast however, a phylogenetic approach using derived character states suggests a North American ancestry. Besides a common ancestry for Chinese and American sturgeons, the taxonomic status of A. mikadoi is discussed.     

Migration patterns and survival of stocked Atlantic sturgeon (Acipenser oxyrinchus Mitchill, 1815) in Nemunas Basin,Baltic Sea

The restoration of the Atlantic sturgeon Acipenser oxyrinchus in Lithuania started in 2011. Two rivers (Neris and ?ventoji) were chosen for reintroduction in the Nemunas river basin based on historical data and ecological conditions. Since 2011, more than 116 thousand of sturgeon juveniles have been stocked in Lithuania. In order to achieve successful population restoration, it is vital to evaluate the efficiency of performed artificial stocking. Analysis of post‐stocking survival, migration patterns, predation pressure, fisheries‐related mortality and possible aggregation zones are all important to understand the main threats and prepare possible mitigation measures necessary for population establishment during the initial phase of restoration. Therefore, conventional and radio tagging studies were performed during the initial restoration phase in Lithuania. Atlantic sturgeon downstream migration was divergent in summer and appeared to have no significant associations with fish size, river quality or hydrophysical parameters, but in autumn migration speed and even survival in small rivers seemed to depend on flow velocity and water discharge. The distribution of recaptured tagged juveniles coincided with dominant currents in the Curonian Lagoon and Baltic Sea. Some tagged specimens migrated long distances, with two sturgeons from Lithuania being caught in Estonian and Finnish territorial waters at up to 800 km from their release site. Tag recapture analysis and mortality rate of tagged fish clearly indicate that annual fisheries‐related mortality exceeds the required threshold of 5% for population establishment. High survival in rivers indicates that the main threat for a successful sturgeon reintroduction program is commercial fishing in the Curonian Lagoon and Baltic Sea coastal zone.     

Unusual intraindividual variation of the nuclear 18S rRNA gene is widespread within the Acipenseridae

Significant intraindividual variation in the sequence of the 18S rRNA gene is unusual in animal genomes. In a previous study, multiple 18S rRNA gene sequences were observed within individuals of eight species of sturgeon from North America but not in the North American paddlefish, Polyodon spathula, in two species of Polypterus (Polypterus delhezi and Polypterus senegalus), in other primitive fishes (Erpetoichthys calabaricus, Lepisosteus osseus, Amia calva) or in a lungfish (Protopterus sp.). These observations led to the hypothesis that this unusual genetic characteristic arose within the Acipenseriformes after the presumed divergence of the sturgeon and paddlefish families. In the present study, a survey of nearly all Eurasian acipenseriform species was conducted to examine 18S rDNA variation. Intraindividual variation was not found in the polyodontid species, the Chinese paddlefish, Psephurus gladius, but variation was detected in all Eurasian acipenserid species. The comparison of sequences from two major segments of the 18S rRNA gene and identification of sites where insertion/deletion events have occurred are placed in the context of evolutionary relationships within the Acipenseriformes and the evolution of rDNA variation in this group.     

Assessing water quality suitability for shortnose sturgeon in the Roanoke River,North Carolina,USA with an in situ bioassay approach

The aim of this study was to determine the suitability of water quality in the Roanoke River of North Carolina for supporting shortnose sturgeon Acipenser brevirostrum, an endangered species in the United States. Fathead minnows Pimephales promelas were also evaluated alongside the sturgeon as a comparative species to measure potential differences in fish survival, growth, contaminant accumulation, and histopathology in a 28‐day in situ toxicity test. Captively propagated juvenile shortnose sturgeon (total length 49 ± 8 mm, mean ± SD) and fathead minnows (total length 39 ± 3 mm, mean ± SD) were used in the test and their outcomes were compared to simultaneous measurements of water quality (temperature, dissolved oxygen, pH, conductivity, total ammonia nitrogen, hardness, alkalinity, turbidity) and contaminant chemistry (metals, polycyclic aromatic hydrocarbons, organochlorine pesticides, current use pesticides, polychlorinated biphenyls) in river water and sediment. In the in situ test, there were three non‐riverine control sites and eight riverine test sites with three replicate cages (25 × 15‐cm (OD) clear plexiglass with 200‐μm tear‐resistant Nitex^® screen over each end) of 20 shortnose sturgeon per cage at each site. There was a single cage of fathead minnows also deployed at each site alongside the sturgeon cages. Survival of caged shortnose sturgeon among the riverine sites averaged 9% (range 1.7–25%) on day 22 of the 28‐day study, whereas sturgeon survival at the non‐riverine control sites averaged 64% (range 33–98%). In contrast to sturgeon, only one riverine deployed fathead minnow died (average 99.4% survival) over the 28‐day test period and none of the control fathead minnows died. Although chemical analyses revealed the presence of retene (7‐isopropyl‐1‐methylphenanthrene), a pulp and paper mill derived compound with known dioxin‐like toxicity to early life stages of fish, in significant quantities in the water (251–603 ng L^?1) and sediment (up to 5000 ng g^?1 dry weight) at several river sites, no correlation was detected of adverse water quality conditions or measured contaminant concentrations to the poor survival of sturgeon among riverine test sites. Histopathology analysis determined that the mortality of the river deployed shortnose sturgeon was likely due to liver and kidney lesions from an unknown agent(s). Given the poor survival of shortnose sturgeon (9%) and high survival of fathead minnows (99.4%) at the riverine test sites, our study indicates that conditions in the Roanoke River are incongruous with the needs of juvenile shortnose sturgeon and that fathead minnows, commonly used standard toxicity test organisms, do not adequately predict the sensitivity of shortnose sturgeon. Therefore, additional research is needed to help identify specific limiting factors and management actions for the enhancement and recovery of this imperiled fish species.     

Population viability analysis of the Danube sturgeon populations in a Vortex simulation model

Populations of six sturgeon species in the Danube River (beluga, Russian sturgeon, stellate sturgeon, sterlet, ship sturgeon and Atlantic sturgeon) have experienced severe decline during the last several decades, mostly due to the unsustainable fishery, river fragmentation and water pollution. Present lack of knowledge on basic sturgeon demography, life history and relative effects of different negative factors is further hindering implementation of efficient policy and management measures. In the present study, population viability analysis in a Vortex simulation model has been conducted in order to assess the state of the six Danube sturgeon species, their future risk of extinction and to determine the most suitable conservation and management measures. Population viability analysis has revealed a large sensitivity of the Danube sturgeon populations to changes in the natural mortality, fecundity, age at maturity and spawning frequency. It was also confirmed that the sturgeons are highly susceptible to even moderate levels of commercial fishery, and that their recovery is a multi-decadal affair. Stocking with adult individuals was shown to produce considerably greater effect on population persistence than stocking with juveniles, but the latter approach is probably still preferable since it avoids many inherent problems of aquaculture cultivation. This study represents the first population viability analysis of the Danube sturgeons.     

A Nuclear DNA Perspective on Delineating Evolutionarily Significant Lineages in Polyploids: The Case of the Endangered Shortnose Sturgeon (Acipenser brevirostrum)

The shortnose sturgeon, Acipenser brevirostrum, oft considered a phylogenetic relic, is listed as an “endangered species threatened with extinction” in the US and “Vulnerable” on the IUCN Red List. Effective conservation of A. brevirostrum depends on understanding its diversity and evolutionary processes, yet challenges associated with the polyploid nature of its nuclear genome have heretofore limited population genetic analysis to maternally inherited haploid characters. We developed a suite of polysomic microsatellite DNA markers and characterized a sample of 561 shortnose sturgeon collected from major extant populations along the North American Atlantic coast. The 181 alleles observed at 11 loci were scored as binary loci and the data were subjected to multivariate ordination, Bayesian clustering, hierarchical partitioning of variance, and among-population distance metric tests. The methods uncovered moderately high levels of gene diversity suggesting population structuring across and within three metapopulations (Northeast, Mid-Atlantic, and Southeast) that encompass seven demographically discrete and evolutionarily distinct lineages. The predicted groups are consistent with previously described behavioral patterns, especially dispersal and migration, supporting the interpretation that A. brevirostrum exhibit adaptive differences based on watershed. Combined with results of prior genetic (mitochondrial DNA) and behavioral studies, the current work suggests that dispersal is an important factor in maintaining genetic diversity in A. brevirostrum and that the basic unit for conservation management is arguably the local population.     

Juvenile atlantic and shortnose sturgeons (family: Acipenseridae) have different hematological responses to acute environmental hypoxia

Experiments were conducted to determine the behavioral and physiological responses to acute hypoxic challenges in Atlantic (Acipenser oxyrinchus) and shortnose (Acipenser brevirostrum) sturgeons. We measured the ventilatory rate following a 45-mmHg hypoxic challenge, as well as a variety of hematological parameters, including O2 transport and hormonal, ionic, and metabolic variables, following a 1-h exposure to either 75- or 30-mmHg hypoxic challenges. Compared to fish in normoxic conditions (Pwo2 150 mmHg), juveniles of both species increased their ventilatory rate by approximately 40% when exposed to a 1-h challenge at 45 mmHg Pwo2. Hematological variables (e.g., hematocrit, hemoglobin, and Na+ and Cl- levels) did not change substantially following a 1-h challenge at 75 mmHg Pwo2. Conversely, a severe hypoxic challenge of 30 mmHg caused changes in several hematological variables (e.g., whole blood glucose and plasma cortisol and lactate levels). Most of these hematological parameters returned to prehypoxic levels within 2 h. Severe environmental hypoxia elicited the same basic pattern of response in both species; however, maximal plasma lactate levels were higher in Atlantic sturgeons, and maximal cortisol levels were higher in shortnose sturgeons. Whether these species differences are related to dissimilar hypoxia-tolerance, ecological, and/or endocrinological characteristics between these two species is not entirely clear.     

Use of Washington Estuaries by Subadult and Adult Green Sturgeon

Green sturgeon, Acipenser medirostris, are the most marine-oriented of North American sturgeons. However, their estuarine/marine distribution and the seasonality of estuarine use are largely unknown. We used acoustic telemetry to document the timing of green sturgeon use of Washington estuaries. In the summers of 2003 and 2004, uniquely coded acoustic transmitters were surgically implanted in green sturgeon captured using commercial gillnets. All sturgeon tagged were greater than 1.2 m total length. They were caught, tagged, and released in both Willapa Bay (n = 49) and Columbia River (n = 11) estuaries. We deployed an array of four fixed- site acoustic receivers in Willapa Bay to detect the estuarine entry and exit of these and any of over 100 additional green sturgeon tagged in other systems during 2003 and 2004. Green sturgeon occurred in Willapa Bay in summer when estuarine water temperatures exceeded coastal water temperatures by at least 2°C. They exhibited rapid and extensive intra- and inter- estuary movements and green sturgeon from all known spawning populations were detected in Willapa Bay. We hypothesize that green sturgeon optimize their growth potential in summer by foraging in the relatively warm, saline waters of Willapa Bay and we caution that altering the quality of estuarine habitats could negatively affect this species throughout its range.     

A split decision: the impact of substrate type on the swimming behaviour,substrate preference and UCrit of juvenile shortnose sturgeon (<Emphasis Type="Italic">Acipenser brevirostrum</Emphasis>)

Critical swimming speed (UCrit) is a standard test to measure sustained swimming capabilities of fish species, however, much of this research is focused on pelagic fish or popular game fish. Recently, more research is emerging on the swimming capabilities of sturgeons, mainly due to their conservation status. Substrate preference has been examined in sturgeons, however, few studies have investigated whether sturgeon would select for a particular substrate (smooth or pebble) when provided a choice under high-flow conditions, as irregular shaped bottom substrates may provide an energetic advantage. Critical swimming tests were performed in a linear flume to evaluate whether substrate (smooth, pebble, pebble on the left side of the flume/smooth on the right side of the flume, and pebble on the right side of the flume/smooth on the left side of the flume) would affect UCrit of juvenile shortnose sturgeon (Acipenser brevirostrum), and if the sturgeon would select for a particular substrate at different speeds. All swimming experiments were video recorded and subsequently reviewed to determine the amount of time individual sturgeon spent in particular sections of the flume. Overall, there was no clear preference for a particular substrate and substrate configuration did not affect UCrit. These results may be attributed to small sample sizes, and the small pebble sizes used in relation to the sturgeon’s body size may not elicit an energetic advantage.