Bivalve aquaculture, while crucial for global food security, presents a complex environmental profile, simultaneously acting as a carbon sink and a source of nutrient pollution. A comprehensive and quantitative assessment of its environmental performance is essential for sustainable development. This study defines Environmental Pressure Efficiency (EPE) as the social benefit generated per unit of environmental pressure during product production. Based on this definition, a CRITIC-TOPSIS model was employed to quantitatively assess the EPE of major bivalve aquaculture areas in China from 2008 to 2023. The social benefit indicators included bivalve production yield, economic value, and carbon sink capacity, while environmental pressure indicators comprised greenhouse gas, nitrogen, phosphorus, copper, zinc emissions, and chemical oxygen demand. Our analysis reveals significant spatio-temporal dynamics: nationally, EPE demonstrated a stepwise increase over the study period, with coastal provinces consistently exhibiting higher efficiency than inland regions. Furthermore, marine bivalve species generally achieved superior EPE compared to their freshwater counterparts, mainly attributable to the inherent buffering capacity of marine ecosystems. Species-specific carbon sink coefficients varied considerably, with Razor clam showing the highest and Ark clam the lowest. We advocate for region- and species-specific management strategies, including the selection of environmentally efficient species and location-appropriate farming practices, to enhance ecological sustainability. This research provides a robust scientific foundation for spatially differentiated aquaculture planning and offers valuable insights for global bivalve production.

In the Duncan-Phillips framework for breaking wave energy dissipation, the underlying scale at which dissipation occurs is commonly inferred from a measure of the breaking-wave phase speed, most often taken as the spectrally informed phase speed the local phase speed at incipient breaking and the whitecap advancing speed . However, energy loss occurs across a finite spectral band, and the link between these single-speed measures and the representative dissipation scale requires further investigation. Using unidirectional laboratory wave groups, we identify the spectral range over which energy dissipation occurs in breaking waves (, with the peak frequency). From this, we define an energy-dissipation-weighted-frequency and a corresponding phase speed (via the linear dispersion relation), which characterize the effective scale at which energy is lost from the wave group. We show that for the waves studied here this dissipative scale is systematically smaller than local and spectral speed measures, with When inferred from whitecap-based measures (most commonly implemented in the field from optical remote sensing), corresponds to approximately of the time-averaged whitecap advancing speed, depending on how the whitecap speed is defined. Taken together, these correlations indicate that the commonly used measures , , and whitecap-based speeds are broadly connected, with our quantitative analysis further demonstrating that their relationships are modulated by the strength of breaking. Overall, our study provides a clearer physical basis for identifying dissipation scales in broadband breaking waves and helps reconcile existing laboratory, numerical, and field-based approaches.

Mesoscale eddies are prevalent in the Philippine Sea and frequently impinge on the Kuroshio Current, affecting internal tides (ITs) originating from the Luzon Strait (LS). This process is investigated in this study using idealized experiments, which provide a controlled environment to quantify variations of the M2 ITs as a single cyclonic eddy (CE) or anticyclonic eddy (AE) approaches the LS from the east. Our results reveal an asymmetric influence: AEs induce more pronounced changes in the M2 tidal conversion than CEs. Variations in conversion rates are primarily controlled by changes in bottom pressure perturbations, which are linked to the product of subtidal buoyancy gradients and IT vertical velocity. Another noteworthy finding is that these mesoscale eddies influence the M2 ITs differently in two stages: during propagation across the Philippine Sea and upon impingement with the Kuroshio Current. In the first stage, mesoscale eddies modulate the propagation of the M2 ITs through direct interaction, inducing incoherent M2 ITs in the Philippine Sea. The percentage of incoherent ITs exceeds 50% along the eddy paths. Advection from eddy-induced currents contribute significantly more than background stratification and relative vorticity. During the second stage, as the eddies impinge on the Kuroshio Current and move northward, variations in the M2 IT energetics within the LS are evident. The IT incoherence increases not only in the Philippine Sea but also in the LS and South China Sea. These findings are important for understanding the IT variability and incoherence in the Philippine Sea and South China Sea.

Bivalve aquaculture, while crucial for global food security, presents a complex environmental profile, providing ecological benefits while also generating environmental pressures during production. A comprehensive and quantitative assessment of its environmental performance is essential for sustainable development. This study defines environmental pressure efficiency (EPE) as the combined benefit generated per unit of environmental pressure during production, where the benefit dimension includes economic, social, and ecological benefits. Based on this definition, a CRITIC-TOPSIS model was employed to quantitatively assess the EPE of major bivalve aquaculture areas in China from 2008 to 2023. In the case of bivalve aquaculture, the combined benefit indicators included bivalve production yield, economic value, and carbon sink capacity, while environmental pressure indicators comprised greenhouse gas (GHG) emissions, nitrogen (N), phosphorus (P), copper (Cu), and zinc (Zn) discharges, and chemical oxygen demand (COD) loads. Our analysis reveals significant spatio-temporal dynamics: nationally, EPE demonstrated a stepwise increase over the study period, with coastal provinces consistently exhibiting higher efficiency than inland regions. Furthermore, marine bivalve species generally achieved superior EPE compared to their freshwater counterparts, mainly attributable to the inherent buffering capacity of marine ecosystems. Marked interspecific differences in EPE were also observed, with the ark clam showing the highest EPE and the freshwater mussel the lowest. Region- and species-specific management strategies, including the selection of species with high EPE and location-appropriate farming practices, are recommended to enhance sustainability of aquaculture. This research provides a robust scientific foundation for spatially differentiated aquaculture planning and offers valuable insights for global bivalve production.

Wave steepness is a key geometric variable for describing breaking occurrence and its consequences, including energy dissipation and air entrainment. Using three laboratory campaigns under varying spectral conditions and co-flowing wind forcing, we contrast two types of steepness commonly used for unsteady breaking waves: spectrally-informed wave-group steepness (prognostic), obtained from fixed-point surface-elevation records, and locally-measured crest steepness (diagnostic), obtained from spatial surface profiles extracted using the SDBW-I image-processing method developed herein. For the former, the long-adopted 𝒮_n (linear sum of Fourier-component steepness) increases appreciably within about two dominant wavelengths upstream of breaking because of its sensitivity to evolving high-frequency content. When measured sufficiently far upstream, however, wave-group steepness remains approximately linearly related to the local zero-crossing steepness 𝒮_b across bulk unforced conditions. Notwithstanding this, we argue that the crest-front steepness, 𝒮_front(t_b), which delineates the front-face slope at incipient breaking, is the most physically meaningful metric examined here. It exhibits a consistent breaking-onset lower-bound threshold of 𝒮_front(t_b)≈0.2, while values above this threshold decrease with wind speed as crests become less forward leaning. This may be attributed to wind-modified dispersion, enhanced high-frequency spectral content and aerodynamic sheltering, suggesting that wind–wave and wave–wave interactions act as competing mechanisms in triggering breaking through kinematic and energetic processes beyond what geometry alone can explain. Even so, 𝒮_front(t_b) has strong potential as a controlling variable for future studies of breaking energetics and crest-scale dynamics.

Internal solitary waves (ISWs) are a typical form of nonlinear wave phenomena in the ocean, characterized by large amplitudes and high energy, and they play a critical role in both marine engineering safety and ecosystem stability. Accurately characterizing their propagation properties and evolutionary mechanisms is essential for understanding ocean dynamic processes. Although traditional theoretical models have yielded certain achievements, their applicability in complex marine environments is limited due to reliance on numerous idealized assumptions. At present, constrained by the scarcity of in-situ observational data, it remains challenging to directly identify and validate the governing equations under realistic oceanic conditions. In light of the above considerations, this preliminary study proposes a data-driven modeling approach that employs sparse regression techniques to automatically discover the structural form of the governing equations for ISWs. Additionally, the Levenberg-Marquardt (LM) algorithm is introduced to optimize model parameters, thereby enhancing prediction accuracy and stability. The governing equations derived through this method are further solved numerically to enable high-precision simulation of the propagation process of ISWs. This study synthesizes laboratory observations and numerical simulations spanning a wide range of ocean stratification regimes and ISW generation scenarios. By imposing multiple physical constraints, this paper establish a comprehensive ISW dynamics database that enables systematic investigation of wave evolution characteristics and the associated dynamical mechanisms under diverse environmental conditions. The results show that, when multi-source data and physical constraints are jointly incorporated, the proposed method significantly outperforms traditional models in both equation identification accuracy and propagation-process prediction. Compared with traditional KdV-type models, the proposed method achieves significantly higher accuracy in predicting overall amplitude, with an average improvement of approximately 0.326 m in numerical simulations. For physical experiments, when the prediction horizon exceeds 10 steps, it attains an average amplitude prediction error of about 0.13 m, indicating its effectiveness in both simulations and experiments. While conventional approaches require selecting an appropriate model based on the specific physical setting, the proposed method relies solely on data and thus enables dynamical-process prediction without presupposing physical conditions.

Previous studies have demonstrated that the internal tides (ITs) near the Luzon Strait (LS) are significantly modulated by the Kuroshio Current (KC). However, the modulation, particularly the contributions of the KC's velocity and stratification to the modulation, remains incompletely understood. Based on the interaction theory between subtidal motions and ITs, and 9-month numerical simulation results, this study investigates the KC's modulation on the M2 IT energetics at the LS, with a focus on quantifying the contributions of the KC's velocity and stratification to the modulation. The KC directly modulates the IT energy budget through buoyancy production, shear production, and advection. Among them, the buoyancy production, associated with the KC's stratification, dominates over the shear production and advection, which are related to the KC's velocity. Furthermore, the KC influences the tidal conversion and energy flux of ITs by changing the pressure perturbation as well as barotropic and baroclinic tidal currents through nonlinear interaction with ITs. Sensitivity analysis indicates that the bottom pressure perturbation plays a more important role in the tidal conversion, whereas the baroclinic tidal currents are more crucial in the energy flux. Further analysis shows that the contributions of KC's velocity and stratification to the buoyancy and pressure perturbation are generally comparable. Moreover, the KC's velocity plays a more important role than the stratification in determining the phase speed of ITs, which leads to different energy flux patterns under different KC paths.

Larimichthys polyactis, one of the most commercially important fish species in the Yellow Sea in China, requires scientific stock assessment to improve its management for population recovery. This study aimed to estimate the growth pattern and stock status by using length-frequency data. A Length-Based Spawning Potential Ratio (LBSPR) and a length-based integrated model (LIME) methods were used. Projections and sensitivity analysis were also conducted to evaluate catch strategies and model robustness. Results showed that the fitted growth equation was Lt = 23.24(1 - exp[ - 0.27(t - 0.59|August 3rd) - S(t) + S(0.59|August 3rd)]). The exploitation rate was 0.58. LBSPR tended to output higher SPR estimates than LIME, with both methods indicating low SPR levels (0.16-0.3). LIME showed a more depleted stock status, suggesting start length at selectivity (SL) of 10.6-13.52 cm, while LBSPR suggested SL of 8.79-10.23 cm. Projections indicate that catches should be reduced to approximately 60,000 tons in the Yellow Sea to facilitate stock recovery. Sensitivity analysis showed that Natural mortality (M) and growth coefficient (K) inputs significantly affect both models. SPR decreased with increasing K, while showing a unimodal response to M. The effects on SL estimation were totally determined by M and K for LIME but insignificant for LBSPR. This study enhances understanding of life history traits and population dynamics of Yellow Sea L. polyactis stock, highlights its overexploitation status, and demonstrates the application of length-based integrated assessment methods in fisheries.

Internal solitary waves (ISWs) in the ocean can induce pressure perturbations throughout the water column, influencing underwater structures and material transport near the seabed. These pressure anomalies appear as sea surface height anomalies (SSHA), which can be detected by satellite altimeters. The launch of the Surface Water Ocean Topography (SWOT) mission provides a novel two-dimensional, high-resolution perspective for observing ISW-induced SSHA. However, the quantitative relationship between SSHA and subsurface ISW characteristics remains insufficiently understood. Through laboratory experiments, we estimated ISW-induced pressure anomalies and corresponding surface height. Both nonlinearity and nonhydrostatic effects play essential roles in estimating pressure anomalies. Within the experimental nondimensional parameter range, neglecting these effects during the calculation of ISW-induced SSHA leads to an overestimation of SSHA by up to 83 %, which in turn implies an underestimation of ISW parameters retrieved from remote sensing signals. Using the horizontal momentum equation, SSHA can be calculated from surface velocities and agrees well with the experimental results. By combining the SSHA and backscatter intensity patterns observed by SWOT, we applied the fully nonlinear ISW theory to retrieve ISW properties. According to the sensitivity of surface signatures to background conditions such as stratification and background shear flow, we further explored the potential of inferring ocean background information from these surface observations, and analyzed the uncertainty introduced by remote sensing sampling. This study provides a framework for linking SWOT signatures to ISW and oceanic environments, facilitating improved assessments of ISW dynamics and their impacts on ocean processes.

The Indian mackerel (Rastrelliger kanagurta) is a commercially important fish species in Bangladesh. This study was conducted by using two catch-based methods, Depletion-Based Stock Reduction Analysis (DB-SRA) and Catch-Maximum Sustainable Yield (CMSY), to determine stock status with length-based approaches to update the life-history estimates of Indian mackerel stock. Sensitivity tests and projection were also performed to find out how well the models predicted the estimates at different input parameter's value and evaluate catch strategies. The life-history parameters were estimated as L∞=33.25 cm and k = 0.92 year- 1. The fishery experienced a sudden increase in its landings to the abnormally highest point in 2012, followed by a state of equilibrium. However, the current spawning potential ratio (SPR) of 17% indicated a concerning sign regarding stock spawning capacity, where over 50% of catches were observed to be below the maturity level. This study suggests an optimum length limit of 18-22 cm to adjust the growth and recruitment overfishing. Hence, an annual catch limit of 1500 mt is recommended for the next 15 years under the maximum sustainable yield (MSY) reference bar (1967 mt), in convergence with the annual fishing ban, to gradually maintain the current overfished biomass of Indian mackerel approaching the BMSY level. Besides, the dynamic, transboundary nature of the Indian mackerel demands both national action and international cooperation for better management.

ABSTRACT The classical surplus production model is less explanatory when biomass is low and the catch is high, and also does not explicitly include a stock recruitment process. Nevertheless, a classical Schaefer surplus production function (SF) has been predominantly used for current anchovy ( Engraulis japonicus ) stock assessments in the Bohai and Yellow Seas in China. The Beverton–Holt‐driven production function (BHDPF) model may mitigate drawbacks of the classical SF model. To assess status of the anchovy stock in the Bohai and Yellow Seas, the SF, BHDPF, and Stock Synthesis 3 (SS3) (an integrated analysis model) were used. The SF suggested a recovered stock, with stable catch, whereas the BHDPF and SS3 models suggested that the stock biomass was the lowest during the study period, thereby necessitating a reduction in catch. BHDPF and SS3 were consistent with one another the SF. Under the BHDPF assumption, increasing and decreasing biomass trends may result in countertrend catches, and high catches at low biomass. The BHDPF may serve as an assessment alternative for fisheries lacking age‐structure data. Abundance index data plays a significant role in the current assessment of the Bohai and Yellow Seas anchovy stock, and more research is needed to improve its accuracy.

AbstractThe modulation of anticyclonic subsurface‐intensified mode‐water eddies (MWEs) on the oceanic physical and biological responses to tropical cyclones (TCs) is investigated using satellite measurements, in situ observations and numerical model outputs. Extreme cooling of the surface (4.2°C) and mixed‐layer (2.3°C) is observed in a MWE, which can be remarkably stronger than those in adjacent cyclonic eddy and non‐eddy environments. The special thermodynamic structure above the lens of MWEs, which would favor the TC‐induced entrainment more efficiently, facilitates the elevation of substantial subsurface cold water. It also leads to increased mixed‐layer salinity and deepening of the mixed‐layer. Additionally, variations in nitrate and chlorophyll‐a concentrations appear to be depressed and exhibit intricate multi‐layer patterns due to TC‐induced and MWE‐influenced vertical processes. This study provides novel insights into the interactions between TCs and subsurface‐intensified eddies.

Ocean mixing is a consequence of essential dynamic processes such as internal tides and lee waves that occur near the seafloor topography.Internal tides and lee waves are generated by barotropic tidal currents and geostrophic flows,respectively.Ocean current is composed of multiple flows;thus,internal tides and lee waves occur concurrently in the real ocean.In this paper,the Massachusetts Institute of Technology general circulation model(MITgcm)is used to conduct 2D numerical experiments.By varying background flow intensities,the energy and dissipation relationship between internal tides and lee waves are investigated.The results reveal that the internal tide beams become asymmetric due to the influence of Doppler shift.The lee wave structure gradually leads the wave field when the background flow velocity rises constantly.The presence of a background flow increases the energy portion of the high-mode wave by up to 15%-20%.Moreover,strong shear,owing to the background flow,considerably increases dissipa-tion.When the background flow velocity is higher than the barotropic tidal current velocity,the isopycnal overturn triggered by the lee wave generates a dissipation of the same order of magnitude as the shear.

ABSTRACTThe blackspotted croaker (Protonibea diacanthus) is among the highest‐valued commercial marine fish species in Bangladesh. Therefore, we assessed the stock status, economic significance, and market status of blackspotted croaker in the Bay of Bengal, Bangladesh. We estimated life history parameters and sustainability indicators to determine if the stock was being sustainably managed. Size of blackspotted croaker was significantly differ temporally. Blackspotted croaker increased in weight allometrically in relation to length. Length‐age life history parameters were L∞ = 161.16 cm, k = 0.39 year−1. Natural mortality M was 0.39 year−1 and fishing mortality F was 0.35 year−1. Catch composition and sustainably indicators revealed that the stock was prone to recruitment and growth overfishing. Medium to large sized blackspotted croaker (> 85 cm) fetched the highest price in commercial markets for the swim bladders that was worth many times more than the value of fillets. The highest demand of swim bladders in export commerce termed this species as marine gold to the fishers. Therefore, fishers were increasingly motivated to target the species. Ununiformed landing of blackspotted croaker, for domestic and international trade of swim bladder of blackspotted croaker, and poorly documented trading supply chains make this fishing industry luck‐driven. Management interventions are needed to sustain the fishery and economic value.

Tidal mixing in the Kara Gates Strait (KGS) modulates transport of warm water from the Barents Sea to the Kara Sea, playing a pivotal role in the transformation of Atlantic Water and the heat budget of the Arctic. Although previous studies have identified the presence of large-amplitude internal waves by the interaction of M 2 tidal currents with rough topography, understanding of the energetics and dynamics of M 2 internal tides (ITs) in the KGS remains limited. Using a high-resolution model, this study investigates the generation, propagation, and dissipation of M 2 ITs. The results reveal that, in addition to the previously identified source in the central KGS, the slope of Vaygach Island serves as another major source of ITs with energy intensity exceeding that of the central strait. Background circulation confines the ITs within similar to 10 km off the slope forming atypical coastal trapped waves (CTWs). Theoretical solutions for these CTWs reveal a dominance of high vertical modes with energy dissipation exhibiting a "sandwich-like" structure. Applying the Lagrangian filtering, internal tides and lee waves along the KGS are separated. Dissipation associated with lee waves ranges from 10-7 to 10-6 W/kg comparable to those induced by ITs, yet their role in driving local mixing has been largely underestimated in previous studies. These results provide new insights into the dynamics around the KGS and their implications for Arctic tidal mixing processes.

The South China Sea is abundant with intense internal tides (ITs) and typhoon-induced near-inertial waves (NIWs), which inevitably interact with each other. Based on the numerical simulation results, the interaction between the M2 ITs and typhoon Megi-induced NIWs in the deep ocean near the Luzon Strait is studied. The interaction gives rise to sum- and difference-frequency waves, denoted as the fM2 and M2-f waves. Results of this study highlight the contribution of the M2-f waves to shear enhancement: The kinetic energy of the M2-f waves is one order of magnitude smaller than that of the M2 ITs, but the domain-averaged vertical shear squared caused by the M2-f waves is comparable to that of the M2 ITs. The IT-NIW interaction is dominated by the product of vertical internal tidal velocity and vertical shear of horizontal near-inertial velocity, which is followed by the product of horizontal near-inertial velocity and horizontal shear of horizontal internal tidal velocity. The IT-NIW interaction influences the evolution of near-inertial kinetic energy through modulating the energy exchange and near-inertial energy flux, which are site-dependent. In the modulation of energy exchange, the terms associated with horizontal shear of horizontal internal tidal velocity play crucial roles. Whereas in the modulation of near-inertial energy flux, the terms associated with vertical shear of horizontal near-inertial velocity are dominant.

Fish stock assessment is essential for ensuring the sustainable utilization of marine resources. We evaluated the stock status of the Pomadasys olivaceus along both the Balochistan and Sindh coasts of Pakistan using Catch-based Monte Carlo Maximum sustainable yield (CMSY), Bayesian Schaefer model (BSM), and a stock production model incorporating covariates (ASPIC) models based on catch and effort data from 2000 to 2022. Results from all models indicate the B/B-MSY (relative biomass) values were below 1.0 and F/F-MSY (fishery exploitation) values>1, indicating that the stock is severely overfished in both regions. The estimated maximum sustainable yield (MSY) from the CMSY and BSM methods ranged between 2 440-2 670 metric tons (mt) for Balochistan and 2 430-2 650 mt for Sindh. The ASPIC model (Fox and Logistic) also indicated overexploitation, with MSY estimates of 1 585 mt (Fox) and 1 379 mt (Logistic) for Balochistan, showing critical stock depletion. In contrast, MSY estimates from Sindh were 3 260 mt and 3 024 mt, suggesting stock condition was not over fished. These findings offer a scientific basis for the formulation of targeted management and conservation strategies by the government, particularly emphasizing urgent intervention for the Balochistan coast to ensure the long-term sustainability of the P. olivaceus fishery.

The sustainable exploitation of fishery resources in Pakistan was assessed using the catch-based Monte Carlo method (CMSY) and the length-based Bayesian biomass (LBB) method to evaluate the data-limited fishery of the Spangled Emperor, Lethrinus nebulosus. CMSY relies on catch data, resilience parameters, and quantitative stock status metrics, while LBB exclusively uses length–frequency (LF) data for stock assessments. This study utilized twenty-two years of catch–effort and LF data from 7230 fish along the Balochistan coastline in Pakistan. The study revealed that the relative biomass of the exploited stock, with a B/BMSY ratio of 0.557, indicates significant depletion. The relative exploitation rate (F/FMSY = 2.47) confirms that the stock is being severely overfished. The discrepancy between the optimal length at first capture (Lc_opt = 43.1 cm) and the length at first capture (Lc = 38.8 cm) further proves the overexploitation of L. nebulosus. The convergence of findings from both methodologies strengthens the reliability of stock status estimates. By integrating diverse data types and analytical frameworks, this study provides valuable insights into the sustainability of L. nebulosus populations. This dual approach not only underscores the importance of varied data sources but also informs management strategies for effective fisheries conservation, contributing to a deeper understanding of resource dynamics along the Balochistan coast of Pakistan.