Chinook salmon depth distributions on the continental shelf are shaped by interactions between location, season, and individual condition

BACKGROUND

Ecological and physical conditions vary with depth in aquatic ecosystems, resulting in gradients of habitat suitability. Although variation in vertical distributions among individuals provides evidence of habitat selection, it has been challenging to disentangle how processes at multiple spatio-temporal scales shape behaviour.

METHODS

We collected thousands of observations of depth from > 300 acoustically tagged adult Chinook salmon Oncorhynchus tshawytscha, spanning multiple seasons and years. We used these data to parameterize a machine-learning model to disentangle the influence of spatial, temporal, and dynamic oceanographic variables while accounting for differences in individual condition and maturation stage.

RESULTS

The top performing machine learning model used bathymetric depth ratio (i.e., individual depth relative to seafloor depth) as a response. We found that bathymetry, season, maturation stage, and spatial location most strongly influenced Chinook salmon depth. Chinook salmon bathymetric depth ratios were deepest in shallow water, during winter, and for immature individuals. We also identified non-linear interactions among covariates, resulting in spatially-varying effects of zooplankton concentration, lunar cycle, temperature and oxygen concentration.

CONCLUSIONS

Our results suggest Chinook salmon vertical habitat use is a function of ecological interactions, not physiological constraints. Temporal and spatial variation in depth distributions could be used to guide management decisions intended to reduce fishery impacts on Chinook salmon. More generally, our findings demonstrate how complex interactions among bathymetry, seasonality, location, and life history stage regulate vertical habitat selection.

Where does floating Sargassum in the East China Sea come from?

Floating macroalgae of Sargassum horneri (S. horneri) in the East China Sea (ECS) has increased in recent years, with ocean warming being one of the driving factors. Yet their possible origins, based on a literature review, are unclear. Here, using multi-sensor high-resolution remote sensing data and numerical experiments for the period of 2015-2023, we show two possible origins of the ECS floating S. horneri, one being local near the Zhejiang coast with initiation in January-February and the other being remote (> 800 km from the first) in the Bohai Sea with initiation in June-November. While their drifting pathways are revealed in the sequential remote sensing imagery, numerical experiments suggest that S. horneri from the remote origin (Bohai Sea) can hardly meander through the strong Yangtze River frontal zone, which may serve as a "wall" to prevent trespassing of surface floating seaweed to the south of the frontal zone, where S. horneri has a local origin. PLAIN LANGUAGE SUMMARY: Sargassum horneri (S. horneri) is a brown macroalgae (seaweed) abundant in surface waters of the East China Sea (ECS), which can serve as a moving habitat, but can also cause major beaching events and environmental problems. Knowledge of its origins is important to help implement mitigation strategies and understand possible ecological impacts along its drifting pathways. Using high-resolution remote sensing images and numerical experiments, we track floating S. horneri in space and time between 2015 and 2023. Two possible origins are identified, one being far away from the ECS and the other being local, both of which are known to have benthic S. horneri. The study also reveals how S. horneri are transported from their source regions resulting in large-scale distributions previously observed in medium-resolution satellite imagery.

Transport of the Tumen River water to the Far Eastern Marine Reserve (Posyet Bay) based on in situ, satellite data and Lagrangian modeling using ROMS current velocity output

We study physical mechanisms of the Tumen River water transport in the area of the Posyet Bay (Peter the Great Bay, Sea of Japan). This study is based on the satellite and in situ measurements, and numerical simulation of advection of river water by the current velocity simulated by Regional Ocean Model System (ROMS). The importance of this study is in identification of the reasons of the transport of pollutants into the area of the Far Eastern Marine Reserve. The results of the study showed that such reasons are wind currents and mesoscale cyclonic eddies. These eddies were originally detected on satellite imagery and CTD and bio-optical measurements. The anomalies in the form of spots of the chlorophyll a (CHL) increased concentration were detected on satellite images in fall 2009. The oceanographic sections of CTD and bio-optical measurements through the anomalies show that they are cyclonic eddies. These eddies consist of two cores - upper and lower. The upper core is filled with river waters with low salinity, high values of CHL and colored dissolved organic matter content (CDOM). The lower core is filled with cold saline waters. The ROMS results show that eddies are generated as a result of symmetrical and centrifugal instabilities.

Multiscale hydrodynamics modeling reveals the temperature moderating role of the Northern Red Sea Islands

A growing interest in the hydrodynamics of the Red Sea has been observed since the beginning of the 21st century. However, the interaction between the Gulf of Suez (GOS) and the Red Sea along with possible natural mitigation mechanisms of heat stress on its southern coral reef zones have not been adequately investigated. This study evaluated different Regional Ocean Modeling System (ROMS) simulations of the Red Sea using a nesting approach in the southern parts of the GOS to elucidate the three-dimensional nature of thermal variability. The developed regional ROMS model simulated the general circulation patterns and sea surface temperature on the TSUBAME 3.0 supercomputer operated by the Tokyo Institute of Technology. Ultimately, remotely sensed satellite data of Sea Surface Temperature (SST) spanning the period 2016-2020 were used to validate the regional model results. A further challenge posed by the scarcity of distributed depth-varying temperature data on the northern islands' region was overcome by using an offline nesting approach (i.e., incorporating boundary conditions from the parent domain) to simulate the local 3-D thermal regimes. Intriguingly, the results of the nested model scenarios confirmed unique northern islands-enhanced thermal moderating mechanisms where islands act as barriers to the impacts of the relatively warmer water originating from the eastern boundary current. Additionally, this study introduces a new approach to applying higher-resolution models to the precise spatial and temporal representation of thermal indices in a way that surpasses the widely adopted remote sensing approaches. In short, multiscale modeling provides a valuable approach for assessing the thermal regimes around one of the most precious marine ecosystems in the world.

Assessing a model of Pacific Northwest harmful algal bloom transport as a decision-support tool

In the Pacific Northwest, blooms of the diatom Pseudo-nitzschia (PN) sometimes produce domoic acid, a neurotoxin that causes amnesic shellfish poisoning, leading to a Harmful Algal Bloom (HAB) event. The Pacific Northwest (PNW) HAB Bulletin project, a partnership between academic, government, and tribal stakeholders, uses a combination of beach and offshore monitoring data and ocean forecast modeling to better understand the formation, evolution, and transport of HABs in this region. This project produces periodic Bulletins to inform local stakeholders of current and forecasted conditions. The goal of this study was to help improve how the forecast model is used in the Bulletin's preparation through a retrospective particle-tracking experiment. Using past observations of beach PN cell counts, events were identified that likely originated in the Juan de Fuca eddy, a known PN hotspot, and then particle tracks were used in the model to simulate these events. A variety of "beaching definitions" were tested, based on both water depth and distance offshore, to define when a particle in the model was close enough to the coast that it was likely to correspond to cells appearing in the intertidal zone and in shellfish diets, as well as a variety of observed PN cell thresholds to determine what cell count should be used to describe an event that would warrant further action. The skill of these criteria was assessed by determining the fraction of true positives, true negatives, false positives, and false negatives within the model in comparison with observations, as well as a variety of derived model performance metrics. This analysis suggested that for our stakeholders' purposes, the most useful beaching definition is the 30 m isobath and the most useful PN cell threshold for coincident field-based sample PN density estimates is 10,000 PN cells/L. Lastly, the performance of a medium-resolution (1.5 km horizontal resolution) version of the model was compared with that of a high-resolution (0.5 km horizontal resolution) version, the latter currently used in forecasting for the PNW HAB Bulletin project. This analysis includes a direct comparison of the two model resolutions for one overlapping year (2017). These results suggested that a narrower, more realistic beaching definition is most useful in a high-resolution model, while a wider beaching definition is more appropriate in a lower resolution model like the medium-resolution version used in this analysis. Overall, this analysis demonstrated the importance of incorporating stakeholder needs into the statistical approach in order to generate the most effective decision-support information from oceanographic modeling.

Fate of river-derived microplastics from the South China Sea: Sources to surrounding seas, shores, and abysses

Microplastics (MPs) in the ocean have been widely recognized as causing global marine environmental problems. To gain a quantitative and comprehensive understanding of oceanic MP contamination, detailed numerical Lagrangian particle tracking experiments were conducted to evaluate the regional oceanic transport and dispersal of MPs in the South China Sea (SCS) derived from three major rivers, Pearl (China), Mekong (Vietnam), and Pasig (the Philippines), which are known to discharge large amounts of plastic waste into the SCS. As previous field surveys have suggested, MP contamination spreads from the surface to the deeper ocean in the water column, we thus considered three types of MPs: (1) positively buoyant (light) MPs, (2) positively buoyant (light) MPs with random walk diffusion, and (3) full 3-D tracking of non-buoyant MPs that are passively transported by ambient currents. Transport patterns of these MPs from the three rivers clearly showed the intra-annual variability associated with seasonally varying circulations driven by the Asian monsoons in the SCS. Many MPs floating during the prevailing southwest monsoon are transported to the northwest Pacific Ocean and the East China Sea through the Luzon Strait and the Taiwan Strait to form MP hotspots. Non-buoyant MPs are broadly transported from the surface layer to depths of approximately 100 m or deeper, where in situ observations are rare. In addition, the buoyant MPs drifting on the continental shelf originating from southern China tend to be pushed toward the shore and beached by northward wind-induced currents more pronouncedly than the non-buoyant MPs. Therefore, the river-derived MPs to the SCS were found to serve as sources to adjacent basins and oceans, to be distributed not only in the upper layer but also in the abyssal ocean (non-buoyant MPs), and to be transported to the shores (buoyant MPs).

A modeling study on the oceanic dispersion and sedimentation of radionuclides off the coast of Fukushima

We developed a three-dimensional prognostic oceanic dispersion model that accounted for the phase transfer of radionuclides between seawater, suspended particles, and seabed sediments with multiscale grain sizes. A detailed hindcast of ¹³⁷Cs in the seabed sediment off the Fukushima coast was conducted to investigate the transfer mechanism of dissolved ¹³⁷Cs derived from the Fukushima Daiichi Nuclear Power Plant (FNPP1) accident toward the seabed sediment. Extensive model-data comparison demonstrated that the model could satisfactorily reproduce the oceanic structure and ¹³⁷Cs concentrations in the seawater and seabed sediment. The model successfully reproduced the major features of the observed spatial variation of the ¹³⁷Cs activities in the sediment, which represented more than 90% of the sedimentary radiocesium existing in the coastal area off Fukushima several months after the accident. Shear stress associated with the resuspension of the seabed sediment was induced by waves near the shore and by current velocity offshore of the study area. The adsorption of ¹³⁷Cs on the seabed sediment differed depending on the particle size, with adsorption on clay being the most substantial. The distribution of ¹³⁷Cs in the sediment off the Fukushima coast was formed mainly owing to adsorption from the dissolved phase by June 2011, when the impact of the direct oceanic ¹³⁷Cs release from FNPP1 was remarkable. After June 2011, seabed sediment became a source of ¹³⁷Cs released to the seawater owing to resuspension with and desorption from the sediment.

Investigating Pseudo-nitzschia australis introduction to the Gulf of Maine with observations and models

In 2016, an unprecedented Pseudo-nitzschia australis bloom in the Gulf of Maine led to the first shellfishery closures due to domoic acid in the region's history. In this paper, potential introduction routes of P. australis are explored through observations, a hydrodynamic model, and a Lagrangian particle tracking model. Based on particle tracking experiments, the most likely source of P. australis to the Gulf of Maine was the Scotian Shelf. However, in 2016, connectivity between the Scotian Shelf and the bloom region was not significantly different from the other years between 2012 and 2019, nor were temperature conditions more favorable for P. australis growth. Observations indicated changes on the Scotian Shelf in 2016 preceded the introduction of P. australis: increased bottom salinity and decreased surface salinity. The increased bottom salinity on the shelf may be linked to anomalously saline water observed near the coast of Maine in 2016 via transport through Northeast Channel. The changes in upstream water mass properties may be related to the introduction of P. australis, and could be the result of either increased influence of the Labrador Current or increased outflow from the Gulf of St. Lawrence. The ultimate source of P. australis remains unknown, although the species has previously been observed in the eastern North Atlantic, and connectivity across the ocean is possible via a subpolar route. Continued and increased monitoring is warranted to track interannual Pseudo-nitzschia persistence in the Gulf of Maine, and sampling on the Scotian Shelf should be conducted to map upstream P. australis populations.

Making sense of child and adolescent mental health services (CAMHS): An audit of the referral journey and the use of routine outcome measures (ROMS)

BACKGROUND

There is increased emphasis on the national reporting of Routine Outcome Measures (ROMS) as a way of improving Child and Adolescent Mental Health Services (CAMHS). This data needs to be viewed in context so that reasons for outcome completion rates are understood and monitored over time.

METHOD

We undertook an in-depth prospective audit of consecutive referrals accepted into the Bath and North East Somerset, Swindon and Wiltshire (BSW) CAMHS service from November 2017 to January 2018 (n = 1074) and April to September 2019 (n = 1172).

RESULTS

Across both audits 90% of those offered an appointment were seen with three quarters completing baseline ROMS. One in three were not seen again with around 30% still being open to the service at the end of each audit. Of those closed to the service, paired ROMS were obtained for 46% to 60% of cases. There were few changes in referral problems or complexity factors over time.

CONCLUSION

Understanding the referral journey and the reasons for attrition will help to put nationally collected data in context and can inform and monitor service transformation over time.

River Plume Liftoff Dynamics and Surface Expressions

The water surface expression of liftoff and its dependence on discharge are examined using numerical simulations with the Regional Ocean Modeling System (ROMS). Liftoff is the process by which buoyant river water separates from the bed and flows over denser saltwater. During low-discharge conditions liftoff occurs in the river and is accompanied by a change in the surface slope. During high-discharge conditions liftoff occurs outside the mouth and generates a ridge on the water surface. The location and height of the ridge can be described by analytical equations in terms of discharge, shelf slope, and river mouth aspect ratio. The offshore distance and height of the ridge are proportional to the river discharge and vary inversely with river mouth aspect ratio. For steep shelf slopes liftoff occurs close to the river mouth and generates a large ridge. The ridge is modified, but not eliminated, by the presence of tides. The water surface slope change at the ridge peak is large enough to be detected by the upcoming Surface Water and Ocean Topography (SWOT) altimeter and can be used to identify the liftoff location during high discharge. However, during low discharge the water surface slope change at the liftoff location is too small to be detected by SWOT. These results indicate that remote measurements of the presence or absence of the ridge may be useful to distinguish between low and high flows, and remote measurements of the ridge location or height could be used to estimate freshwater discharge.

On relaxation of the influences of treated sewage effluent on an adjacent seaweed farm in a tidal strait

An Eulerian passive tracer model coupled with a quadruple-nested 3D circulation model was used to assess the coastal dispersal of treated wastewater effluent from a sewage treatment plant and the associated impacts on an adjacent seaweed farm using three different operational scenarios. When the discharged volume and source effluent fluxes were decreased by ~16.7%, the accumulated effluent in the farm was reduced by ~25.4%. A tracer flux budget analysis revealed the apparent predominance of the transient component that accounts for the nonlinear interactions primarily from tidal currents and eddies. The transient flux promoted the effluent influx to impede effluent accumulation in the farm, whereas the mean flux contributed to the outgoing flux. A source flux reduction caused a remarkable decrease in the transient flux and thus an even greater effluent accumulation reduction. In turn, a modified source density scenario without total effluent volume change did not work as expected.

Coastal accumulation of microplastic particles emitted from the Po River, Northern Italy: Comparing remote sensing and hydrodynamic modelling with in situ sample collections

Microplastic research has mainly concentrated on open seas, while riverine plumes remain largely unexplored despite their hypothesized importance as a microplastic source to coastal waters. This work aimed to model coastal accumulation of microplastic particles (1-5 mm) emitted by the Po River over 1.5 years. We posit that river-induced microplastic accumulation on adjacent coasts can be predicted using (1) hydrodynamic-based and (2) remote sensing-based modelling. Model accumulation maps were validated against sampling at nine beaches, with sediment microplastic concentrations up to 78 particles/kg (dry weight). Hydrodynamic modelling revealed that discharged particle amount is only semi-coupled to beaching rates, which are strongly mouth dependent and occur within the first ten days. Remote sensing modelling was found to better capture river mouth relative strength, and accumulation patterns were found consistent with hydrodynamic modelling. This methodology lays groundwork for developing an operational monitoring system to assess microplastic pollution emitted by a major river.

Residual effects of treated effluent diversion on a seaweed farm in a tidal strait using a multi-nested high-resolution 3-D circulation-dispersal model

A high-resolution 3-D model was developed to assess the impact of a diversion outfall at the Tarumi Sewage Treatment Plant (TSTP) on an adjacent seaweed farm in Osaka Bay, Japan. The model was extensively validated to ensure a reasonable agreement with in situ observations. The western part of the farm is largely influenced by tidal currents, whereas the eastern area is mainly affected by subtidal residual currents that are primarily due to surface wind stress. The released effluent is transported by counterclockwise residual circulation formed off the TSTP. The model reveals that the diversion adequately suppresses the influence on the farm. While the instantaneous effluent concentration is diminished by about 50%, the effluent accumulated on the farm decreased from 2.83 × 10⁴ m³ to 2.01 × 10⁴ m³ due to the diversion, demonstrating an approximately 28% reduction of the effluent from the TSTP by the diversion outfall.

Occurrence and distribution of microplastics at selected coastal sites along the southeastern United States

To investigate the occurrence and distribution of microplastics in the southeastern coastal region of the United States, we quantified the amount of microplastics in sand samples from multiple coastal sites and developed a predictive model to understand the drift of plastics via ocean currents. Sand samples from eighteen National Park Service (NPS) beaches in the Southeastern Region were collected and microplastics were isolated from each sample. Microplastic counts were compared among sites and local geography was used to make inferences about sources and modes of distribution. Samples were analyzed to identify the composition of particles using Fourier transform infrared spectroscopy (FTIR). To predict the spatiotemporal distribution and movements of particles via coastal currents, a Regional Ocean Modeling System (ROMS) was applied. Microplastics were detected in each of the sampled sites although abundance among sites was highly variable. Approximately half of the samples were dominated by thread-like and fibrous materials as opposed to beads and particles. Results of FTIR suggested that 24% consisted of polyethylene terephthalate (PET), while about 68% of the fibers tested were composed of man-made cellulosic materials such as rayon. Based on published studies examining sources of microplastics, the shape of the particles found here (mostly fibers) and the presence of PET, we infer the source of microplastics in coastal areas is mainly from urban areas, such as wastewater discharge, rather than breakdown of larger marine debris drifting in the ocean. Local geographic features, e.g., the nearness of sites to large rivers and urbanized areas, explain variance in amount of microplastics among sites. Additionally, the distribution of simulated particles is explained by ocean current patterns; computer simulations were correlated with field observations, reinforcing the idea that ocean currents can be a good predictor of the fate and distribution of microplastics at the sites sampled here.

Analysis of bloom conditions in fall 2013 in the Strait of Hormuz using satellite observations and model simulations

In this study an algal bloom event in fall 2013 in the Strait of Hormuz was thoroughly investigated using satellite remote sensing and hydrodynamic modeling. The motivation of this study is to deduce ambient conditions prior to and during the bloom outbreak and understand its trigger. Bloom tracking was achieved by sequential MODIS imagery and numerical simulations. Satellite observations showed that the bloom was initiated in late October 2013 and dissipated in early June 2014. Trajectories of bloom patches were simulated using a Lagrangian transport model. Model-based predictions of bloom patches' trajectories were in good agreement with satellite observations with a probability of detection (POD) reaching 0.85. Analysis of ancillary data, including sea surface temperature, ocean circulation, and wind, indicated that the bloom was likely caused by upwelling conditions in the Strait of Hormuz. Combined with numerical models, satellite observations provide an essential tool for investigating bloom conditions.

Fundão Dam collapse: Oceanic dispersion of River Doce after the greatest Brazilian environmental accident

On 5 November 2015, the Fundão tailings dam collapsed and its content first reached River Doce and then the Atlantic Ocean by 22 November. This study focuses on the oceanic time and space patterns of river discharge dispersion. By using an ocean model together with nLw(555) and RGB images from MODIS sensors, the river plume was followed for 2months after the arrival of the tailings at the ocean. The results show the huge effect of this accident and reveal that riverine waters may have dispersed hundreds of kilometres, reaching regions as far as the shelf in front of the city of Rio de Janeiro. The movement of the freshwater was essentially to the south in accordance with the seasonal wind regime. Episodic frontal systems, leading to wind reversion, and oceanic mesoscale features contribute to the offshore dispersion of the plume. The region more often in contact with the riverine waters was located at the inner shelf between the river mouth and the city of Vitória, turning to the outer shelf and shelf break at lower latitudes.

Initial skill assessment of the California Harmful Algae Risk Mapping (C-HARM) system

Toxic algal events are an annual burden on aquaculture and coastal ecosystems of California. The threat of domoic acid (DA) toxicity to human and wildlife health is the dominant harmful algal bloom (HAB) concern for the region, leading to a strong focus on prediction and mitigation of these blooms and their toxic effects. This paper describes the initial development of the California Harmful Algae Risk Mapping (C-HARM) system that predicts the spatial likelihood of blooms and dangerous levels of DA using a unique blend of numerical models, ecological forecast models of the target group, Pseudo-nitzschia, and satellite ocean color imagery. Data interpolating empirical orthogonal functions (DINEOF) are applied to ocean color imagery to fill in missing data and then used in a multivariate mode with other modeled variables to forecast biogeochemical parameters. Daily predictions (nowcast and forecast maps) are run routinely at the Central and Northern California Ocean Observing System (CeNCOOS) and posted on its public website. Skill assessment of model output for the nowcast data is restricted to nearshore pixels that overlap with routine pier monitoring of HABs in California from 2014 to 2015. Model lead times are best correlated with DA measured with solid phase adsorption toxin tracking (SPATT) and marine mammal strandings from DA toxicosis, suggesting long-term benefits of the HAB predictions to decision-making. Over the next three years, the C-HARM application system will be incorporated into the NOAA operational HAB forecasting system and HAB Bulletin.

Coastal exposure to oil spill impacts from the Finisterre Traffic Separation Scheme

This study analyzes the coastal exposure to potential oil spills coming from the various corridors that constitute the Finisterre Traffic Separation Scheme (NW Iberia). A Lagrangian model was executed with results from a realistic configuration of an ocean model during 2012, validated here against High-Frequency (HF) radar-derived surface currents. Virtual particles were released each hour and followed during the next 4 days. A series of maps summarize which regions would be impacted and when. We have learnt, for example, that Cape Finisterre is the most affected area under a wide range of scenarios and that a sensitive area such as the National Park of the Atlantic Islands would require protective actions in less than 24 h if oil spills from the south eventually occurred. A complete analysis by corridor and during specific wind events is available through a web tool, which could be useful for decision makers in case of contingency.

A model-based insight into the coupling of nitrogen and sulfur cycles in a coastal upwelling system

The biogeochemical cycling in oxygen-minimum zones (OMZs) is dominated by the interactions of microbial nitrogen transformations and, as recently observed in the Chilean upwelling system, also through the energetically less favorable remineralization of sulfate reduction. The latter process is masked, however, by rapid sulfide oxidation, most likely through nitrate reduction. Thus, the cryptic sulfur cycle links with the nitrogen cycle in OMZ settings. Here, we model the physical-chemical water column structure and the observed process rates as driven by formation and sinking of organic detritus, to quantify the nitrogen and sulfur cycles in the Chilean OMZ. A new biogeochemical submodule was developed and coupled to the Regional Ocean Model System (ROMS). The model results generally agree with the observed distribution of reactive species and the measured process rates. Modeled heterotrophic nitrate reduction and sulfate reduction are responsible for 47% and 36%, respectively, of organic remineralization in a 150 m deep zone below mixed layer. Anammox contributes to 61% of the fixed nitrogen lost to N₂ gas, while the rest of the loss is through canonical denitrification as a combination of organic matter oxidation by nitrite reduction and sulfide-driven denitrification. Mineralization coupled to heterotrophic nitrate reduction supplies ∼48% of the ammonium required by anammox. Due to active sulfate reduction, model results suggest that sulfide-driven denitrification contributes to 36% of the nitrogen loss as N₂ gas. Our model results highlight the importance of considering the coupled nitrogen and sulfur cycle in examining open-ocean anoxic processes under present, past, and future conditions.