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Objective: Understanding recruitment dynamics is necessary to predict population‐level responses to exploitation, management actions, or anthropogenic influences. Fecundity is commonly used as a metric of recruitment dynamics and can guide successful management of fisheries. However, an individual female's fecundity is not constant over time; females resorb ovarian follicles to regulate fecundity as they approach spawning. This suggests that sampling for fecundity too early may produce inaccurate estimates of relative fecundity. In Yellowstone National Park, suppression of invasive Lake Trout Salvelinus namaycush reduced the abundance of mature fish by 92% between 2012 and 2022. The continued efficacy of this suppression effort requires accurate assessments of reproductive potential of the population that remains. Methods: We sought to determine whether the timing of ovarian follicle collection affected estimates of mean relative fecundity. We collected ovarian follicles from female Lake Trout, which are autumn spawners, between mid‐August and early October in 2021 and 2022. The number of ovarian follicles per sample was counted to obtain estimates of relative fecundity for each female. Result: We observed a 13% decline in estimated mean relative fecundity between individuals that were sampled before mid‐September and those that were sampled after mid‐September. Conclusion: Our data support strategic timing of fecundity sampling to best capture the true reproductive capability of a population, which is a key metric used in models that guide adaptive management of fishes. Impact statementFemale Lake Trout undergo fecundity reduction through follicular atresia, reducing the number of ovarian follicles that may be spawned, which suggests that fecundity estimates based on fish that are sampled too early in the reproductive cycle will be inaccurate. [ABSTRACT FROM AUTHOR]

Objective: Conservation propagation facilities in the upper basin of the Missouri River are currently experiencing inconsistent survival of first‐feeding larval Pallid Sturgeon Scaphirhynchus albus among genetic families (i.e., distinct male–female pairings). The inconsistent survival can have unintended negative consequences for genetic representation of Pallid Sturgeon that are returned to the Missouri and Yellowstone rivers. We conducted a laboratory study designed to determine whether a live diet improves survival and growth of first‐feeding larval Pallid Sturgeon. Methods: First‐feeding larval Pallid Sturgeon from three distinct genetic families were assigned to one of the following diets: live first instar brine shrimp (Artemia franciscana) nauplii, an Otohime dry diet, a 50–50% combination of Otohime and live first instar brine shrimp nauplii, or food restricted (no food). Mortality was evaluated at the end of each day and at the end of the trial (21 days after the onset of exogenous feeding), and individual weight (g) was measured at the end of the trial. Result: Pallid Sturgeon larvae that received a live diet (either solely live first instar brine shrimp nauplii or the combined diet) experienced higher survival than larvae that were fed solely Otohime. Furthermore, there was statistical evidence that larvae receiving solely live first instar brine shrimp nauplii were heavier at 21 days postexogenous feeding than larvae that were fed either solely Otohime or the combined diet. Conclusion: Our results suggest that a live diet can improve survival and growth of first‐feeding larval Pallid Sturgeon at conservation propagation facilities. Impact statementLive diets improved the survival and weight of first‐feeding larval Pallid Sturgeon and can be incorporated into feeding regimens at conservation propagation hatcheries. [ABSTRACT FROM AUTHOR]

Abiotic conditions and demographic factors can influence the timing of spawning. Behavioral plasticity allows females to select spawning conditions that are conducive to offspring development; however, reproductive costs associated with delaying spawning are not well understood. In this study, factors influencing timing of female spawning, residence time (RT), and reproductive success (RS) during two seasons were determined, and plasma testosterone concentrations were used to quantify atretic rates in a wild, lake sturgeon (Acipenser fulvescens) population. For the 123 females monitored, RT ranged from 1 to 23 days and was influenced by arrival date, temperature, discharge, and male number, with the latter having the largest influence. RS varied due to arrival date, temperature, discharge, male number, male length, and operational sex ratio. Two females had testosterone levels indicative of atresia and RS estimates lower than yearly means; however, most females had normal ovaries, suggesting little reproductive costs of plasticity in spawning ground residency time. Results demonstrate the multitude of factors influencing female reproductive behavior and RS, highlighting the importance of abiotic and demographic conditions to recruitment in wild populations. Des conditions abiotiques et des facteurs demographiques peuvent influencer le moment du frai. Si la plasticite comportementale permet aux femelles de choisir des conditions de frai favorables au developpement de leur progeniture, les couts de reproduction qu'entraine le fait de retarder le frai ne sont pas bien compris. Nous avons determine les facteurs qui influencent le moment du frai, le temps de residence (TR) et le succes de reproduction (SR) de femelles durant deux saisons, et les concentrations plasmatiques de testosterone ont ete utilisees pour quantifier les taux d'atresie dans une population sauvage d'esturgeons jaunes (Acipenserfulvescens). Pour les 123 femelles suivies, le TR allait de 1 a 23 jours et etait influence par la date d'arrivee, la temperature, le debit et le nombre de males, ce dernier facteur exercant la plus grande influence. Le SR variait selon la date d'arrivee, la temperature, le debit, le nombre de males, la longueur des males et le rapport des sexes operationnel. Si deux femelles presentaient des concentrations de testosterone temoignant d'une atresie et des SR estimes plus faibles que les moyennes annuelles, la plupart des femelles avaient des ovaires normaux qui indiqueraient de faibles couts de reproduction associes a la plasticite du temps de residence dans le lieu de frai. Les resultats demontrent qu'une multitude de facteurs influencent le comportement et le succes de reproduction des femelles, soulignant l'importance de conditions abiotiques et demographiques pour le recrutement dans des populations sauvages., Introduction Identifying factors influencing timing of reproduction, residency time on spawning grounds (RT), and reproductive success (RS) are essential for understanding the biological requirements and selective pressures acting on wild [...]

Significant progress has been achieved during the past several years in understanding endocrine control of reproduction in white sturgeon, Acipenser transmontanus (Moberg et al., 1995; Doroshov et al., 1997), however the regulation of prespawning oocyte development and the effects of environmental factors on this phase have been inadequately studied. Field and experimental observations suggest that the thermal regime of rivers plays a pivotal role in environmental control of tinal ovarian maturation (FOM) and spawning of wild sturgeon (Dettlaff et al., 1993), and constant, elevated temperatures have been found to result in decreased plasma sex steroid concentrations, a high incidence of ovarian atresia, and spawning failure in cultured sturgeon (Webb et al., 1999). Chapter l reviews our current knowledge of sturgeon reproductive endocrinology and the effects of environmental factors, specifically temperature, on the late phase of oogenesis.The effects of environmental temperature, ultimately mediated y brain-pituitary secretions, can be tested at the level of the ovary by observations on sex steroid secretion correlated with oocyte development. The objectives of this project were l) to determine baseline steroidogenic profiles in prespawning female sturgeon exposed to seasonal temperature, 2) to identify native steroid hormones involved in oocyte maturation, and 3) to examine and compare ovarian development, acquisition of maturational competence, and plasma sex steroid profiles in gravid females reared in warm water and transferred to cold water in the late fall or early spring.Chapter 2 characterizes the baseline plasma steroid profile and in vitro ovarian steroid secretion in two females held at seasonal temperatures throughout FOM and ovulation. Ovarian follicles were incubated with or without pregnenolone (P5), and concentrations of testosterone (T), 11-ketotestosterone (KT), estradiol (E2), and 17a, 208-dihydroxy-4-pregnen-3-one (17, 208-P) were measured by radioimmunoassay in the incubation media. The follicles of both females reached maturational competence (the ability to undergo germinal vesicle breakdown, GVBD, in response to a progestin in vitro), and ovulation was induced by hormonal treatment. Female 1 responded with oocyte maturation (GVBD), but did not ovulate. Female 2 underwent the normal sequence of oocyte maturation and ovulation. Lower in vitro production of T, KT, and 17, 208-P and elevated E2 were detected in Female 1 compared to Female 2. A surge in plasma 17, 20B-P was found in Female 2 at the onset of oocyte maturation before ovulation. No such surge was detected in the plasma of Female 1. High performance liquid chromatography (HPLC) analysis of plasma at the actual or expected time of ovulation revealed several C21 steroids present in the plasma of Female 2 that were absent in Female 1 These results suggest that it may be possible to assess follicular health during FOM through plasma steroid concentrations or follicular steroidogenesis as a means to select females for hormonal induction of ovulation or estimate the spawning potential of wild females.The ovarian follicles collected from Females 1 and 2 after a priming injection with pituitary extracts were used to determine the putative maturation-inducing steroid (MIS) involved in GVBD (Chapter 3). Follicles were incubated in the presence of a radiolabelled precursor eH-P5). Steroids were extracted from media and intact follicles, and the extracts were analyzed and fractionated by HPLC. The fractions were used in a bioassay to determine the potency of the endogenous steroid products. The results revealed production of C 19 and C2l steroids by the ovarian follicles of primed females, and several of these steroids were found to be physiologically active in the induction of GVBD in oocytes collected from ripe sturgeon females. However, only two fractions, containing a steroid with the same isopolarity as the authentic steroid 11-deoxycortisol (S) on HPLC and a steroid positively identified as 17, 208-P (HPLC and gas chromatography-mass spectrometry), were found to stimulate the resumption of meiosis at the shortest time of oocyte incubation. These steroids, produced in large quantities in vitro by the follicles undergoing GVBD, may be potential putative MISs in white sturgeon.The in vitro effects of steroids on oocyte maturation in sturgeon were further investigated using synthetic hormones matching native C19 and C21 steroids produced in vitro during GVBD (Chapter 4). Ovarian follicles from four mature sturgeon females were incubated with the synthetic steroids at different concentrations and exposure times. At the highest concentration (>1 J.Lg/rnl), all of the C21 steroids tested (progesterone, P4; 17a­ hydroxyprogesterone, 170HP; 17a, 20B, 21-trihydroxy-4-pregnen-3-one, 20B-S; cortisol, F; 17, 20B-P, and S) and T induced maturation at 14 and 22 hrs. At 6 hrs, only P4 and 17, 20B-P induced maturation at the highest concentration. At 14 and 22 hrs, S was the most potent steroidal inducer of GVBD followed closely by P4 and 170HP. The C21 steroids induced oocyte maturation at lower concentrations compared to the C19 steroid T. Calculation of the mean effective concentration that induced 50% GVBD (EC50) revealed the following order of potencies: S > P4 > 170HP > 17, 20B-P > 20B-S >> F > T. These results, together with previous findings on the in vitro production of native steroids, indicate that more than one steroid has a biological role in the resumption of meiosis in sturgeon follicles and provides empirical evidence for S, 17. 20B-P, P4, and 170HP as the most potent steroid inducers of GVBD.The objective of Chapter 5 was to examine and compare ovarian development, acquisition of maturational competence, and plasma sex steroid profiles in gravid sturgeon females reared in warm water and transferred to cold water in the late fall or early spring. Eighteen gravid females that had been raised under natural photoperiod at water temperatures of 16-20°C were randomly assigned to two groups (n=6 in Group 1 and n=12 in Group 2). Group 1 was transferred from warm water to cold water (12±1°C) in November 1997, while Group 2 was held in ambient water temperatures (10-19°C). Both groups were sampled in March 1998. Half of the fish in Group 2 had regressed ovaries, but the remaining females (n=6) had intact ovarian follicles and were transported to the cold water one week after the sampling. Ovarian follicles and blood were collected from October 1997 to November 1998, and the reproductive development was monitored until each female reached the stage of spawning readiness (oocyte polarization index s 0.10 and ovarian follicles had acquired maturational competence in vitro) or until atretic follicles were detected. Chonic exposure of gravid sturgeon females to elevated water temperature from October to March led to a decrease in plasma sex steroids and a high incidence of ovarian atresia in 50% of the females. It appears that the temperature-sensitive phase in ovarian development occurs during the transition from vitellogenic growth to FOM. The degree and timing of sensitivity to environmental temperature in the broodstock population are dependent on the female endogenous rhythms. Normal ovarian development occurred in the majority (83%) of females with intact follicles transferred to cold water in the fall or early spring. Though holding gravid females in cold water has extended the spawning season, the majority of females in our study reached the stage of spawning readiness by June. Several females, however, did retain maturational competence until early fall. A decrease in plasma T and KT was evident five weeks to several months prior to visual signs of atresia indicating that aquaculturists and conservationists may be able to screen potential sturgeon spawners based on androgen concentrations.Understanding ovarian steroidogenesis during FOM and ovulation elucidates the hormonal regulation of late oogenesis in sturgeon and provides useful information for environmental studies in aquaculture and in the wild. For example, baseline plasma steroid data may be used in the analysis of normal and abnormal gonad function of fish exposed to adverse environmental conditions during spawning migrations or holding in captivity. Characterization of the temperature-sensitive stage in late oogenesis of sturgeon enables aquaculturists and conservationists to determine the best timing of exposure of maturing females to cool water and ensure that environmental temperature is not a limiting factor influencing follicular development and spawning of sturgeon.

Green sturgeon (Acipenser medirostris) and white sturgeon (A. transmontanus) are closely related, sympatric species that inhabit the San Francisco estuary. Green sturgeon have a more marine life history but both species spawn in the Sacramento River and reside for some duration in San Francisco Bay. These sturgeons are of conservation concern, yet little is known about their dietary competition when they overlap in space and time. To examine evidence of dietary differentiation, we collected whole blood and blood plasma from 26 green sturgeon and 35 white sturgeon in San Francisco Bay. Using carbon and nitrogen stable isotope analyses, we compared their relative trophic levels and foraging locations along the freshwater to marine gradient. Sampling blood plasma and whole blood allowed comparison of dietary integration over shorter and longer time scales, respectively. Plasma and whole blood δ13C values confirmed green sturgeon had more marine dietary sources than white sturgeon. Plasma δ15N values revealed white sturgeon fed at lower trophic levels than green sturgeon recently, however, whole blood δ15N values demonstrated the two species fed at the same trophic level over longer time scales. Larger individuals of both species had higher δ13C values than smaller individuals, reflecting more marine food sources in adulthood. Length did not affect δ15N values of either species. Isotope analyses supported the more marine life history of green than white sturgeon and potentially highlight a temporary trophic differentiation of diet between species during and preceding the overlapping life stage in San Francisco Bay. [ABSTRACT FROM AUTHOR]

The Amur River is one of the longest free-flowing rivers in the world, extending some 4,400 kilometers (2,700 miles) from the mountains of Mongolia to the Sea of Okhotsk (Figure [...]

This study sought to determine whether wild white sturgeon from the Columbia River (Oregon) were exhibiting signs of reproductive endocrine disruption. Fish were sampled in the free-flowing portion of the [...]

Research on seed survival of the Astrocaryum mexicanum palm shows a causal network between low buried-seed recovery rates of ignorant foragers and palm seedling recruitment. Ignorant foragers are rodents which have not buried seeds in caches for future consumption, as opposed to scatter hoarding foragers which do.

Hatchery‐origin white sturgeon Acipenser transmontanus in the lower Columbia River, Canada are approaching puberty, and describing the reproductive structure of the population is critical to determine if they are capable of contributing to spawning events in the wild, a key management uncertainty. Few studies have compared the accuracy of available tools (histology, ultrasound, endoscopy, and plasma sex steroids) used to assign sex and stage of maturity within the same population of prepubertal and post‐pubertal sturgeon. Population reproductive structure was described using these tools in 332 hatchery‐origin and 75 wild individuals over 2 years (2017 and 2018). True sex was determined using histological analysis of gonadal tissue, which is 100% accurate at assigning sex and stage of maturity in fish when germ cells are present in the biopsy. All hatchery‐origin fish assessed had not reached puberty and were pre‐meiotic males (n = 158) or pre‐vitellogenic females (n = 174). Assignment of true sex using histology was 97% in hatchery‐origin and 94% in wild fish as several biopsies did not contain germ cells. Fish with gonadal biopsies that did not contain germ cells and intersex fish (n = 3) were not included in further analyses of other tools. Accuracy in assigning sex to both the hatchery‐origin (98%) and wild (100%) fish was highest using endoscopy (an otoscope). The other tools evaluated were less accurate, with 69% accuracy in hatchery‐origin and 74% accuracy in wild fish for plasma sex steroids and 57% accuracy in hatchery‐origin and 70% accuracy in wild fish for ultrasonography. Based on these results, endoscopy was the most reliable tool for assigning sex in both prepubertal and post‐pubertal fish and can be easily complimented with histology when determining stage of maturity or describing population reproductive structure. [ABSTRACT FROM AUTHOR]