Spatial structure within populations promotes population stability and resilience through asynchronous responses among population subcomponents (i.e., portfolio effect). In fishes, spatial structure frequently develops via early-life partial migration, leading to diversified nursery use. However, the portfolio effect depends on how adult recruitment from different nurseries exhibits asynchronous dynamics in response to climate variables, and whether nursery experiences carry over to adult demographics. For a three-decade span, we tested adult nursery recruitment and carryover effects associated with early-life partial migration in Hudson River striped bass. Early-life partial migration led to structured utilization of freshwater, brackish, and coastal nurseries, all of which recruited to the adult population. Adult recruitment from brackish nurseries increased with freshwater flow, while coastal nurseries produced more adults during severe winter years. First-year nursery experiences carried over to influence adult sex, but not growth. Most adult females utilized brackish nurseries in their first year, while adult males recruited from freshwater and brackish nurseries. Early-life partial migration led to diversified nursery use and influenced adult demographics, which buffered populations against perturbations.

ObjectiveOnce thought to be extirpated from the Chesapeake Bay, fall spawning runs of Atlantic Sturgeon Acipenser oxyrinchus have been rediscovered in the Marshyhope Creek (MC)-Nanticoke River (NR) system of Maryland, United States. High recapture rates in past telemetry surveys suggested a small population in the two connected tributaries. This study aims to generate estimates of abundance and understand within system connectivity for spawning runs in 2020 and 2021.MethodsData from mobile side-scan sonar surveys and detections of acoustically tagged adults on stationary telemetry receivers were analyzed in an integrated model to estimate spawning season abundance and examine run timing and system connectivity for this population. An array of acoustic receivers was deployed throughout the MC-NR system to monitor the movement of tagged fish during the spawning run period from mid-August to late October. Side-scan sonar surveys were conducted weekly in September in an area of high spawner aggregation to generate count data on spawning run abundance.ResultIn 2020 and 2021, 32 (95% credible interval [CRI] = 23-47) and 70 (95% CRI = 49-105) Atlantic Sturgeon, respectively, used the MC-NR system. The lower estimate for 2020 coincided with an earlier end to the spawning run related to cooler September temperatures in that year.ConclusionIn both years, high spawning run connectivity between MC and the upper NR was observed. Overall, run estimates supported previous hypotheses that the MC-NR system supports a very small population and that both MC and the upper NR serve as important areas for spawning activity. Sturgeon recovery plans require estimates of population abundance. For a small Atlantic Sturgeon population (Chesapeake Bay), this study integrated side-scan sonar counts with telemetry data to develop spawning run estimates that were quite low: 32 and 70.

Partial migration is a widespread phenomenon in animals, whereby multiple groups follow different migration behaviors (i.e. contingents) within a single population. Fishes exhibit particularly high diversity in their early dispersal behaviors; however, whether these represent conditional partial migration behaviors remains unclear. We combined otolith microstructure and chemistry to assess the influence of early life conditions and environmental drivers on juvenile-stage partial migration of anadromous striped bass Morone saxatilis in the Hudson River (USA) in 2 consecutive years with contrasting hydrologic conditions. Time series clustering on otolith strontium (Sr) and barium (Ba) profiles revealed 4 dominant early migration contingents in both years: freshwater residents, oligohaline migrants, small mesohaline migrants, and large mesohaline migrants. In both years, juvenile partial migration appeared to be a conditional strategy linked to a growth-mediated threshold. The propensity to migrate early was related to slower larval growth, whereas freshwater residency and delayed migration were associated with faster larval growth. Differences in hatch dates may have indirectly affected migration contingents by exposing larvae to varying environmental conditions. In the dry year, dispersal timing to mesohaline habitats coincided with high freshwater flow and tidal currents, but not so in the higher-flow year. Recruitment to coastal nurseries outside the Hudson River occurred primarily during the juvenile phase. Early migration contingents could carry over to population dynamics, whereby diverse estuarine nursery habitats contribute differently to recruitment.

The flyway construct was developed in the 1930s to protect networks of bird stopover habitats along annual migration circuits. Here flyway is conceived as a quantifiable vector, a construct of the seasonal velocity and the geographic route taken among networked habitats, generalizable among marine migratory animals, and a way forward in assessing regional offshore wind (OW) development impacts. OW development in the South and East China Sea, North Sea, and US Mid-Atlantic Bight will result in thousands of offshore wind turbines that transect coastal and shelf flyways, not only for birds but also for fishes, sea turtles, and marine mammals. With increased capacity to fully measure the extent and dynamics of migrations through electronic tracking and observing systems, avian-like behaviors are apparent for whales, turtles, and fishes, such as stopover behaviors, migration synchrony, and partial migration. Modeled northwest Atlantic flyways (migration vectors) for northern gannets, striped bass, and North Atlantic right whale quantified seasonal speed, persistence, and variance during seasonal migration phases. From these flyway models, a series of flyway metrics are proposed that lend themselves to hypothesis-testing, dynamic habitat models, and before-after impact assessment. The flyway approach represents a departure from current impact designs, which are dominated by local OW farm studies and, at regional dimensions, survey-based (Eulerian) data structures (overlap models). As a next step, we encourage colleagues to develop flyway databases and test flyway hypotheses for model species.

Offshore wind energy development, including along the US Atlantic coast, frequently occurs within important multispecies migration corridors; however, assessing the regional factors influencing the local Eulerian occurrence of these species poses a significant challenge. We used generalized models incorporating lagged variables and hierarchical formulations to account for temporal dependencies and hierarchical structure that occur outside the narrower frame of a sampled project area. Acoustically tagged striped bass, the most frequently detected species regionally, were sampled using a gridded acoustic telemetry array in the Maryland Wind Energy Area of the US Mid-Atlantic Bight. The daily occurrence of striped bass was better explained by broad-scale sea surface temperature warming patterns than by local concurrent environmental conditions, demonstrating the importance of drivers that occur across the wider spatial scales of migration. Weekly residency patterns were similar between tagging origin groups, suggesting that Chesapeake Bay, Hudson River, Delaware Bay, and other Northwest Atlantic populations migrate synchronously through the Southern Mid-Atlantic Bight and are similarly influenced by sea surface temperature. Our study demonstrates that adapting an Eulerian approach to include lagged variables can improve regional assessments of fish on the move until richer Lagrangian insights become possible through future coordination of telemetry arrays throughout the Mid-Atlantic flyway.

In this study, we examined whether otolith microconstituents are deposited seasonally in a manner similar to optical annulus formation and thereby can be used to validate age interpretations. In temperate species, seasonal temperature changes drive the formation of optical annuli, and we hypothesized that they similarly caused oscillations in microconstituent deposition. Using laser ablation inductively coupled plasma mass spectrometry analysis, we tested for periodicity in the deposition of barium (Ba), calcium, copper, magnesium (Mg), manganese (Mn), phosphorus (P), strontium, and zinc in otoliths and compared that periodicity to the periodicity of the annulus zonation (optical opaque and translucent zones). For this investiga-tion of chemical annulus periodicity, we used black sea bass (Centropristis striata), a species with yearly optical annulus formation that has been val-idated. Periodicities in elemental pro -files in otoliths from black sea bass were detected by using Lomb-Scargle periodogram analyses. Optical annulus formation aligned with Mg profiles, but periodicity in annular deposition of other elements-Ba, Mn, and P- was observed only after the first optical annulus, an outcome that is indicative of ontogenetic changes in habitat (from coastal to near- shelf waters) known to occur during the juvenile life stage of this species. Certain elements, such as Mg, identified through this otolith analysis and the periodogram analyses could be applied to species for which no validated aging procedure exists.

Abstract Vertical movements can expose individuals to rapid changes in physical and trophic environments—for aquatic fauna, dive profiles from biotelemetry data can be used to quantify and categorize vertical movements. Inferences on classes of vertical movement profiles typically rely on subjective summaries of parameters or statistical clustering techniques that utilize Euclidean matching of vertical movement profiles with vertical observation points. These approaches are prone to subjectivity, error, and bias. We used machine learning approaches on a large dataset of vertical time series (N = 28,217 dives) for 31 post‐nesting leatherback turtles (Dermochelys coriacea). We applied dynamic time warp (DTW) clustering to group vertical movement (dive) time series by their metrics (depth and duration) into an optimal number of clusters. We then identified environmental covariates associated with each cluster using a generalized additive mixed‐effects model (GAMM). A convolutional neural network (CNN) model, trained on standard dive shape types from the literature, was used to classify dives within each DTW cluster by their shape. Two clusters were identified with the DTW approach—these varied in their spatial and temporal distributions, with dependence on environmental covariates, sea surface temperature, bathymetry, sea surface height anomaly, and time‐lagged surface chlorophyll a concentrations. CNN classification accuracy of the five standard dive profiles was 95%. Subsequent analyses revealed that the two clusters differed in their composition of standard dive shapes, with each cluster dominated by shapes indicative of distinct behaviors (pelagic foraging and exploration, respectively). The use of these two machine learning approaches allowed for discrete behaviors to be identified from vertical time series data, first by clustering vertical movements by their movement metrics (DTW) and second by classifying dive profiles within each cluster by their shapes (CNN). Statistical inference for the identified clusters found distinct relationships with environmental covariates, supporting hypotheses of vertical niche switching and vertically structured foraging behavior. This approach could be similarly applied to the time series of other animals utilizing the vertical dimension in their movements, including aerial, arboreal, and other aquatic species, to efficiently identify different movement behaviors and inform habitat models.

Stable isotopes are an important tool to uncover animal migration. Geographic natal assignments often require categorizing the spatial domain through a nominal approach, which can introduce bias given the continuous nature of these tracers. Stable isotopes predicted over a spatial gradient (i.e., isoscapes) allow a probabilistic and continuous assignment of origin across space, although applications to marine organisms remain limited. We present a new framework that integrates nominal and continuous assignment approaches by (1) developing a machine-learning multi-model ensemble classifier using Bayesian model averaging (nominal); and (2) integrating nominal predictions with continuous isoscapes to estimate the probability of origin across the spatial domain (continuous). We applied this integrated framework to predict the geographic origin of the Northwest Atlantic mackerel (Scomber scombrus), a migratory pelagic fish comprised of northern and southern components that have distinct spawning sites off Canada (northern contingent) and the US (southern contingent), and seasonally overlap in the US fished regions. The nominal approach based on otolith carbon and oxygen stable isotopes (δ13C/δ18O) yielded high contingent classification accuracy (84.9%). Contingent assignment of unknown-origin samples revealed prevalent, yet highly varied contingent mixing levels (12.5-83.7%) within the US waters over four decades (1975-2019). Nominal predictions were integrated into mackerel-specific otolith oxygen isoscapes developed independently for Canadian and US waters. The combined approach identified geographic nursery hotspots in known spawning sites, but also detected geographic shifts over multi-decadal time scales. This framework can be applied to other marine species to understand migration and connectivity at a high spatial resolution, relevant to management of unit stocks in fisheries and other conservation assessments.

Rising coastal flood risk and recent disasters are driving interest in the construction of gated storm surge barriers worldwide, with current studies recommending barriers for at least 11 estuaries in the United States alone. Surge barriers partially block estuary-ocean exchange with infrastructure across an estuary or its inlet and include gated areas that are closed only during flood events. They can alter the stratification and salt intrusion, change sedimentary systems, and curtail animal migration and ecosystem connectivity, with impacts growing larger with increasing gate closures. Existing barriers are being used with increasing frequency due to sea level rise. New barrier proposals typically come with maximum closure frequency recommendations, yet the future adherence to them is uncertain. Given that the broader environmental effects and coupled-human dynamics of surge barriers are not well-understood, we present an interdisciplinary research agenda for this increasingly prevalent modification to our coastal zone.

Biotelemetry of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus has exposed spawning behaviors in ever-smaller estuaries, surprising for the NW Atlantic's largest anadromous species. Small estuary - the Nanticoke River and Marshyhope Creek (Chesapeake Bay) - spawning-run adults and their habitat affinities are described based upon direct sampling and biotelemetry for the period 2014-2018. High rates of recapture over this period indicate a very small adult population size. Genetics revealed a very small effective population size (N-e = 12.2, 95% CI = 6.7-21.9). Most returns occurred during September at 20-27 degrees C. All fish departed as fall temperatures declined below 20 degrees C. Multi-beam sonar identified small-dispersed areas of sand-cobble and cobble, which could support adhesive embryo attachment. Movements of adults were higher during nighttime than daytime, with habitat preference for hard bottom habitats. Genetic evidence indicates that the sudden discovery of this population was unrelated to a hatchery release of several thousand juvenile sturgeon (Hudson River progeny) in 1997. The newly discovered population in the Nanticoke River exhibits a degree of resilience including multiple spawning regions and suitable spawning habitat. Still, critical vulnerabilities persist including curtailed habitat, continued agricultural and maritime development, invasive blue catfish, and a very small apparent population size. Supplemental data for this article is available online at https://doi.org/10.1080/23308249.2021.1924617

Background The detection efficiency of ultrasonic transmitters is seasonally variable, requiring long-term studies to evaluate key environmental features that mask, alter speed, bend, or reflect transmissions. The US Southern Mid-Atlantic Bight shelf is characterized by a strong summer thermocline capping remnant winter water, known as the Cold Pool, and a well-mixed water column in other seasons. To investigate the effects of interactions between temperature stratification and storm-induced noise on transmission detectability, we conducted a year-long range test of 69-kHz acoustic transmitters in the bottom waters of the US Southern Mid-Atlantic Bight. We used generalized additive models and cross-validation to develop and evaluate a predictive model of detection efficiency and visualize variability in detection distance throughout the year of deployment. Results The most-predictive model contained the effects of temperature stratification and ambient noise, predicting that stratification results in a 33% increase in detectability and 56% increase in detection distance. The model had an overall error rate of 17.1% and an 18.7% error at a distance of 800 m, predicting 17% detectability at median ambient noise when the water column was not stratified and > 50% when the difference between surface and bottom temperatures was greater than 4.2 °C. The distance at 50% detectability increased with the formation of the Cold Pool during spring, increasing by nearly 300 m over 3 days. All seasons were associated with storm-induced reductions in overall detectability and distance at 50% detectability. Conclusion Thermal stratification within the Southern Mid-Atlantic Bight increases bottom water ultrasonic transmitter detection distance and reduces the impact of surface noise. This effect leads to a seasonal increase in detection distance from the late-spring through the summer. To our knowledge, this study is the first to report and quantify an increase in detection range as a result of temperature stratification, likely due to placing transmitters and receivers on the same side of a strong thermocline.

Accurate estimates of growth and mortality are needed to understand drivers of production and cohort success. Existing methods for estimating mortality rates, such as catch-curves, require large sample sizes, as they work by grouping individuals into age-bins to determine a frequency distribution. Yet, sampling enough larvae is often not possible at fine scales within the constraints of research projects, due to low density of larvae in pelagic environments. Here, we develop a novel method to simultaneously estimate growth and mortality rates of fish larvae as a continuous function of size using theory of size-structured populations, eliminating the need to group data into age-bins. We compare the effectiveness of our model to existing methods by generating data from a known distribution. This comparison demonstrates that while all models recover correct parameter values under ideal circumstances, our new method performs better than existing methods when sample sizes are low. Additionally, our method can accommodate non-linear growth and mortality functions, while also allowing growth and mortality to vary as functions of environmental co-variates. This increased accuracy and flexibility of our method should improve our ability to relate variability in larval production to environmental fluctuations at finer spatial scales.

Abstract Fishes commonly exhibit diel rhythms in movements with consequences to feeding, reproduction, predator evasion, and resting. Such behaviors are conceived as plastic, persisting for phases (days to weeks), and then becoming disrupted, masked, and altered by changed environmental or ecological conditions. In telemetered black sea bass Centropristis striata (family Serranidae), we documented a remarkable 4‐month record of persistent diurnal vertical movements. Within the U.S. Mid‐Atlantic Bight June–October 2019 setting, biotelemetry data of 31 fish were examined through time series analysis and generalized additive modeling. Sun altitude played a dominant role throughout the series, where movements were diurnal. Thermal conditions were uniform until a September hurricane caused a 10°C rise in inhabited waters within the span of six hours, the result of water column mixing. This and other storms caused short‐term disruptions (<2 d) to diel rhythmicity. Daytime vessel traffic, but not dolphin presence, caused ≤1 h refuge‐seeking excursions. The discovery of pelagic behaviors (up to 15 m off the seabed) requires revision to the species’ natural history, which was previously conceived as exclusively demersal. Spring‐autumn movement functions included reef recruitment and evacuation, courtship and spawning, and seasonal changes in feeding ecology and predator fields. Throughout these phases, the cycle of daytime movement and nighttime inactivity persisted. We hypothesize that during the nocturnal period these visual specialists become immobile and thus evade predation and mobilize energy toward growth, reproduction, and storage. Because this function does not change from spring through autumn, we speculate that nocturnal quiescence serves as the proximate control for the diurnal activity cycle.

In many coastal ecosystems, habitat compression is caused by seasonal combinations of hypoxia and supraoptimal temperatures. These conditions commonly induce avoidance behaviours in mobile species, resulting in the concentrated use of marginal habitats. Using 3 years of acoustic telemetry and high-resolution water quality data recorded throughout Chesapeake Bay, we measured the seasonal movements and exposure of striped bass (Morone saxatilis) to oxy-thermal habitat compression. Striped bass moved to tidal freshwaters in spring (March–May), mesohaline waters in summer (June–August) and fall (September–November), and mesohaline and polyhaline waters in winter (December–February): seasonal patterns consistent with known spawning, foraging, and overwintering migrations. Analyses of habitat selection suggest that during conditions of prevalent sub-pycnocline hypoxia (June–September), striped bass appeared to select surface waters (i.e. they may avoid bottom hypoxic waters). Striped bass detections indicated tolerance of a wide range of surface water temperatures, including those >25°C, which regional regulatory bodies stipulate are stressful for this species. Still, during summer and fall striped bass selected the lowest-available temperature and avoided water temperature >27°C, demonstrating that Chesapeake Bay striped bass can encounter habitat compressions due to the behavioural avoidance of bottom hypoxia and high temperatures.

Temperate eels are well known for partial migration where contingents may remain settled in marine habitats or move between seawater and brackish and freshwater habitats during their sub-adult life. This behaviour is less described in tropical Anguillid eels, particularly as it relates to salinity preference, habitat selection, and growth. In this study, glass eels Anguilla marmorata were collected from an estuary near the Cagayan River, northern Philippines, and observed for their behaviour and growth response in freshwater, brackish water, and seawater. A. marmorata glass eels spent most of their time in freshwater and brackish water and the least amount of time in seawater throughout the 30-min trial. Some individuals showed switching behaviour between salinity choices, but freshwater was the final selection. Growth-in-length was moderately and significantly lower for seawater-reared glass eels than those reared in freshwater and brackish water. Glass eels reared in freshwater had the highest survival, followed by those reared in brackish water and seawater. Habitat choice, growth, and survival trials all indicated that A. marmorata glass eels found in the Cagayan River have a major preference for freshwater and brackish water over seawater. These findings raise concerns with regard to the increased fishing pressure of eels, water pollution, and quarrying which is concentrated in freshwater habitats.

The Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic is comprised of northern and southern components that have distinct spawning sites off Canada (northern contingent) and the US (southern contingent), and seasonally overlap in US fished regions. Thus, assessment and management of this population can be sensitive to levels of mixing between contingents, which remain unknown. Multi-decadal trends in contingent mixing levels within the US fisheries region were assessed, and the contingent composition across seasons, locations, ages, and size classes were characterized using archived otoliths and developing a classification baseline based on juvenile otolith carbon and oxygen stable isotopes (δ13C/δ18O values). Classification of age ≥ 2 adults demonstrated that northern contingent mixing was prevalent within the US continental shelf waters during the past 2 decades (2000–2019), providing an important seasonal subsidy to the US winter fishery despite substantial depletion in spawning stock biomass of the dominant northern contingent. While the majority of older fish were of the northern contingent during the early 2000s, the southern contingent contribution increased with age/size class during the recent period (2013–2019). Spatial mixing was most prevalent during February and March when the northern contingent occurred as far south as the Delmarva Peninsula, but were mostly absent from US waters in May. A positive relationship (albeit not significant; r = 0.60, p = 0.07) occurred between northern contingent mixing and US fisheries landings, which could imply that higher contingent mixing levels might be associated with greater landings for the US winter mackerel fishery. The yield of the Northwest Atlantic mackerel depends upon the status of the northern contingent, with the southern contingent possibly more prone to depletion. Spatially explicit stock assessment models are recommended to conserve both productivity and stability in this two-component population.

A targeted commercial fishery for Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus once operated in the New York Bight, where it was assumed that most harvested Atlantic Sturgeon were natal to the Hudson River population. However, more recent evidence suggests that the fishery may have been targeting a mixed-stock aggregation, in which case harvested Atlantic Sturgeon could have been comprised of individuals from multiple populations throughout the species' range. Although there is now a moratorium on Atlantic Sturgeon harvest in the New York Bight, modern molecular approaches provide an opportunity to use archived tissues to perform a retrospective mixed-stock analysis on the fishery. Genomic DNA extracted from archived fin spines from 80 Atlantic Sturgeon collected nearly 30 years ago suggests that the fishery primarily harvested individuals from the Hudson River population. However, based on individual-based assignment tests, our results indicate that the fishery also harvested individuals from at least eight other populations located throughout the species' range. This study highlights how archival hard parts that were previously used for age and growth analyses can be employed for retrospective genetic analyses. Further, because the New York Bight harbors relatively high concentrations of Atlantic Sturgeon, the study shows how localized management decisions can influence Atlantic Sturgeon conservation at rangewide scales. When integrated with more recent knowledge of species ecology, these analyses can be used to evaluate the efficacy of previous management strategies and understand the effects of historical processes on contemporary demography.

Multiple spawning run contingents within the same population can experience varying demographic fates that stabilize populations through the portfolio effect. Multiple spawning run contingents (aka run timing groups) are reported here for the first time for striped bass, an economically important coastal species, which is well known for plastic estuarine and shelf migration behaviors. Adult Hudson River Estuary striped bass (n = 66) were tagged and tracked with acoustic transmitters from two known spawning reaches separated by 90 km. Biotelemetry recaptures for two years demonstrated that each river reach was associated with separate contingents. Time series of individual spawning phenologies were examined via nonparametric dynamic time warping and revealed two dominant time series centroids, each associated with a separate spawning reach. The lower spawning reach contingent occurred earlier than the higher reach contingent in 2017 but not in 2018. The majority (89%) of returning adults in 2018 showed the same contingent behaviors exhibited in 2017. Spawning contingents may have been cued differently by temperatures, where warming lagged 1-week at the higher reach in comparison to the lower reach. The two contingents exhibited similar Atlantic shelf migration patterns with strong summer fidelity to Massachusetts Bay and winter migrations to the southern US Mid-Atlantic Bight. Still, in 2017, differing times of departure into nearby shelf waters likely caused the early lower reach contingent to experience substantially higher mortality than the later upper reach contingent. Anecdotal evidence suggests that higher fishing effort is exerted on the early-departing individuals as they first enter shelf fisheries. Thus, as in salmon, multiple spawning units can lead to differential demographic outcomes, potentially stabilizing overall population dynamics.