Sea Surface Temperature Research Articles

Estimation of sea surface temperature in the Arctic based on Fengyun-3D/MERSI II data

Sea surface temperature (SST) is a critical parameter in understanding Arctic amplification of climate change. In this study, SST in the Arctic was estimated based on data from the Medium Resolution Spectral Imager (MERSI) II on board the Fengyun-3D (FY-3D) satellite and in-situ measurements. To improve the quality of the MERSI thermal data, an optimization model for stripe noise removal based on the alternating direction multiplier method was employed. Clear-sky SST was estimated based on the nonlinear SST (NLSST) algorithm and tripe NLSST algorithm. When compared with the SST product retrieved from the Visible Infrared Imaging Radiometer Suite (VIIRS) in September 2019, the mean difference between VIIRS SST and MERSI II SST is −0.21℃ with a standard deviation of 0.29℃ in the daytime, while the mean difference is −0.15℃ with a standard deviation of 0.34℃ at nighttime. Results indicate that the accuracy of MERSI II SST meets the requirements for high-accuracy SST retrieval. Furthermore, these algorithms demonstrate the potential for long-term SST estimation in the Arctic using the FY-3D/MERSI II data.

Behavioral patterns of Chum salmon (Oncorhynchus keta) during spawning migration across the coastal water-river continuum in Northeastern Korea

Korea’s northeastern coastal waters (NECWs) represent the southwestern range of chum salmon (Oncorhynchus keta), spanning temperate and boreal zones. However, understanding their migration to the NECWs in association with environmental changes remains challenging. Using tagging and tracking techniques, we studied salmon migration behavior and timing during spawning in ascending rivers. When sea levels rose, resulting in a decrease in sea surface temperature, salmon exhibited active vertical movement through the water column and migrated to the surface layer. The number of salmon ascending rivers between early October and early December increased when the sea surface temperature decreased below 18 °C, peaking when the water column was mixed during spring tides, and decreased when sea surface temperature dropped below 14 °C. In rivers, salmon favored gravelly riverbeds over sand/silt substrates, stayed in deep and shaded areas during the day, and advanced upstream at night. Our findings emphasize that water temperature and tidal elevation are key factors affecting salmon distribution in coastal waters and the timing of river entry. Riverbed composition, water depth, and photoperiod also influenced migration speed and timing in rivers. This research enhances our understanding of salmon behavior during spawning in the NECWs and adjacent rivers at their southern limits.

Internal variability effect doped by climate change drove the 2023 marine heat extreme in the North Atlantic

The year 2023 shattered numerous heat records both globally and regionally. We here focus on the drivers of the unprecedented warm sea surface temperature (SST) anomalies which started in the North Atlantic Ocean in early summer and persisted later on. Evidence is provided that 2023 should be interpreted as an extreme event in a warmer world because of superimposed internal variability on top of human forcing, which altogether, made the 2023 event all-time high due to extreme air-sea surface fluxes in the subtropics and eastern basin. The effect of internal variability has been considerably boosted by the long-term ocean stratification increase due to combined anthropogenically-driven ocean warming and multidecadal variability. The 2023 event would have been impossible to occur without anthropogenically-driven climate change but at the current warmer background climate state, it is assessed as a decadal-type event when considering the full North Atlantic ocean and a centennial event in the subtropics and eastern basin. Considering the regional distribution of anomalies is crucial for risk assessment in a warming climate.

Understanding the driving mechanisms behind triple-dip La Niñas: insights from the prediction perspective

This study investigates the mechanisms and predictability of multi-year La Niña events, focusing on the 1998–2001 and 2020–2023 triple-dip events, using a physically based statistical ENSO prediction model (EPM). The results highlight distinct driving mechanisms behind these two events. The 1998–2001 event was primarily initiated by substantial negative heat content anomalies in the equatorial Pacific, which resulted from the preceding strong El Niño. These negative heat content anomalies played a crucial role in sustaining cold sea surface temperature anomalies (SSTA) into the third year. In contrast, the 2020–2023 event, which lacked significant negative heat content anomalies, was characterized by persistent equatorial easterly wind anomalies induced by extratropical forcing from the Southern Hemisphere. The EPM successfully captures these differences, with tropical ocean-atmosphere coupling being the dominant factor in predictability for 1998–2001, especially during the second year, whereas extratropical forcing played a key role in improving forecasts for 2020–2023. These findings highlight the importance of incorporating extratropical influences to enhance the prediction skill of multi-year La Niña events, especially those with atypical tropical precursors.

Pacific Meridional Mode Implicated as a Prime Driver of Decadal Summer Temperature Variation over Taiwan

Abstract The Pacific meridional mode (PMM) is a climate phenomenon in the eastern Pacific, characterized by strong wind–sea surface temperature (SST) interactions. During its positive phase, an atypical north–south SST gradient develops in the northeastern subtropical Pacific, leading to significant global teleconnections, which refer to the mutual influence or correlation between atmospheric or oceanic changes in two distant regions of Earth. This study examines the relationship between historical summer temperature data for Taiwan (June–August) and PMM indices over a 59-yr period (1960–2018), revealing a significant correlation between the two. Regressed large-scale circulations indicate the eastward propagation of a wave train across the northern Pacific into East Asia, inducing anticyclonic circulations near southeastern China and Taiwan, accompanied by subsidence, which refers to the vertical downward movement of air masses in the atmosphere, typically associated with high pressure systems and dry weather conditions, that stabilize the atmosphere. This stabilization reduces the influence of seasonal southwesterly winds while increasing shortwave radiation at the surface, thereby raising surface temperatures in Taiwan. Our findings are further supported by linear baroclinic model (LBM) experiments featuring PMM-like heating forcing and by large-scale responses to PMM-related SST patterns simulated in CMIP6 historical runs. While these results suggest that the PMM could be a valuable tool for predicting Taiwan’s summer climate on decadal time scales, we also observe model uncertainties in simulating the teleconnection patterns of PMM-related SSTs in East Asia, including Taiwan’s summer temperature response. These findings underscore the need for further investigation into the complex interplay between PMM circulation responses, seasonal monsoons, and other components of climate systems simulated in climate models.

Interdecadal Change of Relationship between North Atlantic Oscillation and Tropical Cyclone Genesis Frequency over the Western North Pacific

Abstract This article investigates the relationship between spring (March–May) North Atlantic Oscillation (NAO) and the tropical cyclone genesis frequency (TCGF) over the western North Pacific (WNP) from June to November. It is found that their relationship appears insignificant from 1950 to 1971, intensifies significantly from 1972 to 2010, and then weakens again since 2011. The interdecadal change of this relationship is strongly influenced by the meridional displacement of the North Atlantic jet stream (NAJS). During 1972–2010, the NAJS is located southward, facilitating the spread of Rossby wave energy to the equatorial region and enhancing the NAO impact on sea surface temperatures (SSTs) over the tropical North Atlantic (TNA). Generally, positive (negative) phases of the NAO relate to negative (positive) TNA SST anomalies in spring, subsequently triggering positive (negative) SST anomalies in the central Pacific through the wind–evaporation–SST feedback. The central Pacific SST anomalies, intensifying from summer to autumn, lead to a basin-uniform circulation anomaly over the WNP and ultimately control the WNP TCGF. Conversely, in the other two periods, owing to the northward shift of the NAJS, the influence of the NAO is constrained to the extratropics, thereby disrupting the linkage between the NAO and TNA SST anomalies. As a result, the interannual relationship of spring NAO with the WNP TCGF weakens. The decadal meridional shift of the NAJS is supposed to be associated with the phase transition of the Pacific decadal oscillation. Significance Statement To enhance the understanding of the relationship between tropical cyclones and mid- to high-latitude climate systems, we explore how the North Atlantic Oscillation affects the genesis frequency of tropical cyclones in the western North Pacific and why their relationship encounters interdecadal changes. We propose that the North Atlantic Oscillation can trigger sea surface temperature anomalies over the tropical North Atlantic during spring, which subsequently affect the tropical cyclone formation over the western North Pacific in summer and autumn. Importantly, this relationship experiences interdecadal changes, aligning with changes in the meridional shift of the North Atlantic jet stream which may be related to the phase change of the Pacific decadal oscillation. Understanding these dynamics is crucial for climate predictions and addressing the potential impacts of extratropical systems on tropical cyclones.

Establishment and Comparison of Two Types of Statistical Monthly Spatial Prediction Models for Weddell Sea Ice

Abstract In recent years, the Weddell Sea ice loss accounted for nearly half of the Antarctic sea ice loss, whose prediction has attracted much attention. In this study, we developed two types of monthly spatial statistical prediction models for sea ice concentration (SIC) in the Weddell Sea, specifically the multiple linear regression (MLR) and multivariate empirical orthogonal function (MEOF) prediction models. Both prediction models shared a common set of advanced oceanic and atmospheric variables, including the Pacific decadal oscillation, eastern tropical Pacific Ocean sea surface temperatures (SSTs), western tropical Indian Ocean SST, southern tropical Atlantic Ocean SST, Antarctica sea level pressure, and Amundsen–Weddell dipole of surface air temperatures with the leading times of 1–57 month(s). The first-month Weddell SIC ahead of the predicting time was also individually incorporated or together with the 12th month advanced one as the predicting factors. Although the MEOF method is excellent at extracting the spatial mode of meteorological variables, it is unexpected that the MLR prediction model demonstrated enhanced performances. The median of the average anomaly correlation coefficient (ACC) of the MLR prediction model was up to 0.45 and that of the average RMSE was as low as 0.8, which was significantly better than those of 0.34 and 1.12 of the MEOF prediction model. This study highlights the advantages of the MLR prediction model and the importance of employing advanced sea ice to improve the spatial predictive performance of statistical models.

Contrail Cirrus Climate Impact: From Radiative Forcing to Surface Temperature Change

Abstract Contrail cirrus has been regarded as the most important individual component of aviation-induced global climate impact, a conclusion prompted by radiative forcing estimates from a variety of models. However, there have been indications of a reduced effective radiative forcing of contrail cirrus with respect to its instantaneous radiative impact, as well as indications of a reduced contrail efficacy to force surface temperature changes. Here, we present a set of global climate model simulations driven by either upscaled contrail cirrus or a CO2 increase, first with prescribed and then with interactive sea surface temperature, yielding self-consistent results for forcings, feedbacks, and climate sensitivity. If contrail cirrus and CO2 induce the same classical (stratosphere adjusted) radiative forcing, we find the contrail cirrus effective radiative forcing reduced to about 55% compared to that from CO2, qualitatively confirming previous results. The surface temperature response per unit effective radiative forcing (the climate sensitivity parameter) is also smaller (reduced to about 40%) for contrail cirrus. In total, the simulations indicate an efficacy value as low as 0.21 for contrail cirrus, with an estimated statistical uncertainty between 0.10 and 0.32, while consolidated knowledge to quantify the respective systematic uncertainty is currently lacking. Our results indicate a much smaller relative contrail cirrus impact on global warming than classical or even effective radiative forcing estimates suggest. The analysis of radiative adjustments and feedbacks reveals a major role of natural clouds in driving the differences in the response behavior. We discuss consequences of the results for aviation climate impact assessments and promising further research directions. Significance Statement To date, the impact of contrail cirrus on global surface temperature change is largely unknown. Based on a set of climate model simulations, this study provides a first determination of respective key parameters explaining global surface warming (climate sensitivity and efficacy). The obtained climate sensitivity is lower for contrail cirrus than for CO2. The simulations were further examined by feedback analysis to identify the radiative processes which are most relevant for the exceptionally low efficacy of contrail cirrus radiative forcing to induce surface temperature changes.

Seesaw of Tropical Cyclone Frequency between Eastern and Western Regions of the Western North Pacific

Abstract Because of the limited length of observed tropical cyclone (TC) data and low confidence in modeling TC genesis frequency, it has been difficult to understand why the genesis frequency of global TCs has remained nearly invariant while regional variations are highly pronounced. Investigating the covariability of TC genesis frequency between different regions may shed light on this question. Here, we identify that TC genesis frequency varies out of phase between the eastern and western regions of the western North Pacific (WNP). Such a seesaw relationship could be explained by the east–west dipole patterns of low-level vorticity and midtropospheric relative humidity in the WNP, associated with variations in atmospheric conditions. Composite analyses and numerical experiments show that a combination of cooling in the WNP and warming in the north Indian Ocean (NIO) exerts a significant influence on the seesaw pattern. Our study adds more evidence to believe on number conservation of worldwide TC genesis. Significance Statement Little had been known about why the genesis frequency of global tropical cyclones has remained nearly invariant in a changing climate. To find out whether there is any covariability of tropical cyclone genesis frequency between different regions may provide a chance to understand such a steady trend. The western North Pacific is the ocean basin where tropical cyclones are the most active in the world. In this study, it is observed that tropical cyclone genesis frequency between the eastern and western regions of the western North Pacific has a negative correlation. It is demonstrated that the zonal contrast of sea surface temperature in the western North Pacific to the north Indian Ocean plays a significant role in driving the seesaw relationship of tropical cyclone genesis frequency by moderating the large-scale atmospheric circulation.

Regional Multiyear Predictability of Antarctic Sea Ice in CESM2 and Its Implications for Marine Ecosystems

Abstract Antarctic sea ice exhibits considerable regional variability that is influenced by ocean and atmospheric conditions. Previous studies have suggested that this variability may be predictable on seasonal-to-interannual time scales. Here, we use initial-value predictability experiments of the Community Earth System Model, version 2 (CESM2), paired with analysis of the CESM2 large ensemble, to further assess the inherent predictability in regional Antarctic sea ice conditions. As in previous studies, we find that Antarctic sea ice area predictability is high for several months after initialization. It is then lost when ice retreats, and predictability is regained in the following ice advance period. In our simulations, this process acts on multiyear time scales with little sensitivity to the seasonal initialization timing but has a strong regional dependence. Long-lived ocean temperature anomalies in the vicinity of the winter ice edge are the primary source of sea ice predictability. Different predictability characteristics occur across regions, depending on how these ocean temperature anomalies are advected relative to regional sea zones. Our results show that sea ice predictability can impart predictability to primary productivity in the Southern Ocean due to its impact on light availability. This has implications for the understanding and management of Southern Ocean marine ecosystems.

What Drives Interannual Rainfall Variability Over Northern Australia?

AbstractThe interannual variability of northern Australian (NA) rainfall is caused by local processes as well as remote teleconnections, many of them being interrelated. Their influence evolves throughout the wet season, from October through April. Using a stepwise linear regression and examining individual months, we identify the key drivers for rainfall variability over northwest and northeast Australia. Our research shows that the El Niño‐Southern Oscillation (ENSO), followed by local sea surface temperatures (SSTs), are the key sources of rainfall variability in October and November. More specifically, the Arafura and Coral Sea SSTs contribute to rainfall variability over northwest Australia, while the Coral Sea SSTs strongly impact on northeast Australian rainfall during these months. The combined ENSO and local SST indices explain up to 50% of variance in observed NA spring monthly mean rainfall. However, the SST influence from both seas breaks down with the onset of the Australian summer monsoon in late December, and by January, SST indices explain zero variance in rainfall. Instead, December to March rainfall variability is associated with a wind‐evaporation feedback, which is particularly strong over northwest Australia. The evaporation index is the only predictor that we investigated that can explain any variance in northwest Australian rainfall in January. While the more purely monsoonal northwest of Australia is dominated by variability internal to the monsoon system, rainfall variability in the northeast retains some influence from remote climate drivers throughout the monsoon season. Further research is needed to clarify the processes and timescale involved in the wind‐evaporation feedback.

Environmental Effects on the Ecological Carrying Capacity of Marine Ranching in the Northern South China Sea

The marine ecological carrying capacity (MECC) of marine ranching serves as a crucial indicator for assessing the conservation effect of fishery resources and forms a significant basis for scientific management of coastal fisheries. The environmental impacts on the MECC of marine ranching in the northern South China Sea were analyzed quantitatively by employing Generalized Additive Models (GAMs), which have been successfully applied to the study of the relationship between fishery resources and environmental factors, and factor analysis, using satellite and survey observations. Results showed that 95.40% of the total variation in MECC was explained by these factors. Based on the GAMs, the most important factor was Year (calendar years), with a contribution of 66.20%, followed by Chlorophyll a concentration (Chl-a), Sea Surface Temperature (SST), Dissolved Inorganic Nitrogen (DIN) and Water Current, with contributions of 20.60%, 4.40%, 3.60%, and 0.60%, respectively. The findings of this study inspire us to establish a long-term marine ranching resource and environment monitoring platform, and an early warning and forecasting expert decision-making system, providing scientific references for planning and management of coastal marine ranching.

Distinct Impacts of the Central and Eastern Atlantic Niño on West Antarctic Sea Ice

The sea ice variabilities in West Antarctica, crucial for both local and global climate systems, are profoundly affected by the sea surface temperature anomalies over the tropical Atlantic. Analyses based on observational data and numerical model experiments demonstrate that the two recently identified Atlantic Niño types, central and eastern Atlantic Niño (CAN and EAN), have distinct impacts on the sea ice concentration in West Antarctica. The CAN stimulates two atmospheric Rossby wave trains in the Southern Hemisphere through both direct and indirect pathways, collectively strengthening the Amundsen Sea Low. In contrast, the EAN only excites one atmospheric wave train over the South Pacific through an indirect pathway, due to its associated weaker local Hadley circulation, which fails to establish a significant Rossby wave source in the subtropical South Atlantic. Consequently, compared to the EAN, the atmospheric circulation and the associated sea ice concentration anomalies in West Antarctica during the CAN are stronger and more extensive. Therefore, distinguishing between the two Atlantic Niño types could potentially enhance the seasonal prediction capabilities for sea ice concentration in West Antarctica.

Global warming drives a threefold increase in persistence and 1 °C rise in intensity of marine heatwaves

Marine heatwaves are extreme climatic events consisting of persistent periods of warm ocean waters that have profound impacts on marine life. These episodes are becoming more intense, longer, and more frequent in response to anthropogenic global warming. Here, we provide a comprehensive and quantitative assessment on the role of global warming on marine heatwaves. To do so, we construct a counterfactual version of observed global sea surface temperatures since 1940, corresponding to a stationary climate without the effect of long-term increasing global temperatures, and use it to calculate the contribution of global air temperature rise on the intensity and persistence of marine heatwaves. We determine that global warming is responsible for nearly half of these extreme events and that, on a global average, it has led to a three-fold increase in the number of days per year that the oceans experience extreme surface heat conditions. We also show that global warming is responsible for an increase of 1 °C in the maximum intensity of the events. Our findings highlight the detrimental role that human-induced global warming plays on marine heatwaves. This study supports the need for mitigation and adaptation strategies to address these threats to marine ecosystems.

Intercomparison of bias of global sea surface temperature products associated with tropical cyclone passages in the western North Pacific

Intercomparison of bias of global sea surface temperature products associated with tropical cyclone passages in the western North Pacific

Acute heat stress and the extirpation of a threatened coral species from a remote, subtropical reef system

Abstract The ecological significance of the reef-building elkhorn coral, Acropora palmata, is threatened by heat-stress-induced mortality. The intensity and duration of the ocean heatwave affecting Dry Tortugas National Park in the summer of 2023 was historically unprecedented in its early timing and maximum temperatures reached and resulted in 100% A. palmata mortality. To understand the lethality of this event, we examined temperature data measured by in situ data loggers and estimated from satellites (National Oceanic and Atmospheric Administration’s Coral Reef Watch) to investigate the timing of peak ocean temperatures and coral mortality. The in situ dataset revealed warmer water temperatures during the heatwave than those reported from the satellites, and the difference between the datasets was significantly pronounced during the summer. Our results support that, at least for this subtropical population, A. palmata may have an upper-threshold temperature that caused lethality faster than expected from the gradual accumulation of heat stress.

Physiological acclimation of Porites panamensis (Scleractinia: Poritidae) under high-latitude marginal conditions

Hermatypic corals living at high latitudes face suboptimal environmental conditions associated with seasonal changes. In the central Gulf of California, the coral Porites panamensis is acclimated to eutrophication, low light availability, and a wide range of seasonal fluctuations in sea surface temperature (SST). The physiological adjustments of its resistance thresholds are associated with phenotypic plasticity. This study evaluated the interannual acclimation responses of P. panamensis to the warm and cold seasons of 2022 and 2023 using the physiological markers of endosymbiont density, chlorophyll a (Chl a) concentration, and the total lipid content in coral tissue. In addition, the abiotic variables of SST, Chl a, particulate organic carbon (POC), and the diffuse attenuation coefficient (Kd490) were compared between seasons. The results indicated a significant difference in endosymbiont density between seasons (cold season: ~4 × 106 cell·cm–2; warm season: ~2 × 106 cell·cm–2), and an increase in the Chl a concentration during the warm season of 2023. We also observed a significant increase in total lipid content in the warm season of 2023. However, seasonal changes did not negatively affect lipid content, likely due to the high concentrations of Chl a and POC throughout the year (2022: 4.47 ± 1.75 mg·m–3; 2023: 403.3 ± 132.2 mg·m–3), suggesting the existence of a potential year-round food source for P. panamensis. Our results indicate that P. panamensis acclimates to seasonal changes in temperature and turbidity. We suggest that regulating mixotrophy could be a key nutritional strategy for P. panamensis to withstand fluctuating environmental conditions. The ability to alternate between different nutritional pathways according to seasonal environmental conditions may allow P. panamensis to distribute throughout the Eastern Tropical Pacific, even inhabiting suboptimal regions for reef development.

Sea temperature and pollution are associated with infectious disease mortality in short-beaked common dolphins

The concurrent pressures of climate change and chemical pollution, often studied in isolation, have been linked to increases in infectious disease that threaten biodiversity. Understanding their interconnected nature is vital, as the impacts of climate-mediated environmental changes can be exacerbated by chemical pollution and vice versa. Using data from 836 UK-stranded short-beaked common dolphins (Delphinus delphis) (n = 153 (analysed for polychlorinated biphenyl (PCB) blubber concentrations)) necropsied between 1990 and 2020, we show that PCB concentrations and sea surface temperatures (SSTs) are associated with an increased risk of infectious disease mortality. Specifically, a 1 mg/kg lipid increase in PCB concentration correlates with a 1.6% increase in disease mortality risk, while a 1 °C rise in SST corresponds to a 14% increase. Additionally, we derived a novel PCB threshold concentration (22 mg/kg lipid), defined as the level where PCB blubber concentrations are significantly associated with infectious disease mortality risk. International efforts to reduce carbon emissions have mostly failed, and despite regulatory efforts, PCBs remain a significant threat. We demonstrate the urgent need for conservation strategies that address both risk factors simultaneously to protect marine biodiversity.

The Impact of Mesoscale Eddies on Surface and Subsurface Sound Channels in the Kuroshio Extension

Mesoscale eddies induce significant variations in the temperature and salinity of the upper ocean, thereby exerting a substantial impact on sound propagation. Specifically, they can form or dissipate surface sound channels (SCs) and subsurface sound channels (SSCs). However, the specific impact of mesoscale eddies remains unclear at present. In this paper, META2.0, Argo, and SODA are employed to analyze the sound propagation characteristics of mesoscale eddies in the Kuroshio Extension (KE) by using a composite analysis method and a ray-tracing model. Results demonstrate that cyclonic eddies (CEs) cause the disappearance of the original SCs in winter, while simultaneously generating SSCs. Conversely, anticyclonic eddies (AEs) induce SCs in spring and winter, while in summer they induce SSCs and in autumn create dual-duct sound channels (DCs). This study quantitatively reveals the influence of mesoscale eddies on the genesis and demise of SCs and SSCs, providing technical support for sonar equipment to utilize mesoscale eddies.

Reconsideration of Parapatric Distribution Between Pacific Saury (Cololabis saira) and Japanese Sardine (Sardinops melanostictus) in the Western North Pacific Ocean: Comparisons of Two Long‐Term Field Survey Results

ABSTRACTPacific saury (Cololabis saira) and the Pacific stock of Japanese sardine (Sardinops melanostictus) are dominant small pelagic fishes and are targeted by international fisheries in the western North Pacific (WNP). Using monitoring results of a pelagic trawl survey during 2003–2019 in WNP and central North Pacific, a previous study detected a shift in the center of distribution along sea surface temperature gradient (GT) of saury only in WNP, together with “parapatric” horizontal distribution between the two species during the 2010s, when saury biomass declined and sardine biomass increased. Thus, it suggested biological interactions between the two species. To corroborate this “parapatric” distribution, we applied basically the identical statistical analyses to driftnet survey results along longitudinal transects at 155°E, 170°E, and 175.5°E during 1979–1999, when saury stock was abundant and sardine stock declined since 1989. Our results indicated GT of saury slightly shifted after 1989 at 155°E, and spatial distribution of the two species largely overlapped before 1989, which do not support the previous study. While saury biomass drastically declined in the western areas of their overall distribution since 2003 and age‐0 sardine dominated in the pelagic trawl survey, age‐0 sardine occupied the southern area of overall distribution in the driftnet survey. These observations suggest that interspecies interactions between saury and sardine, if existed, are unlikely to take a form of parapatry. The apparent parapatric distribution can be explained by different age compositions of sardine between the two surveys and biomass‐derived eastward shrinkage of saury distribution since 2003.