Sea Surface Chlorophyll-a Concentration Research Articles

Distribution pattern of potential fishing zones in the Bangka Strait waters: An application of the remote sensing technique

Information regarding fishing grounds was needed to assist fishermen in their fishing activities. Information about the sea surface chlorophyll-a concentration (SSCC) and sea surface temperature (SST) could be used as a reference to identify potential fishing zones (PFZ). The purpose of this study was to identify SST and SSCC data using MODIS (Moderate Resolution Imaging Spectroradiometer) satellite imagery for determining the PFZ and analyzing their distribution pattern seasonally. The determination of the PFZ point was carried out by overlaying the SSCC and SST data based on the results of image data processing. The results showed that the distribution pattern of PFZ points in the Bangka Strait waters was predominantly found in the Banyuasin waters. The distribution pattern of PFZ points in the dry season (June-August) and transition season II (September-November) had the same pattern and tended to dominate the coastal areas of the waters. The distribution patterns in the wet season (December-February) and transition season I (March-May) spread throughout the Bangka Strait waters. The most PFZ points were found in transition season I (636 PFZ points), while the minor PFZ points were found in transition season II (219 PFZ points). Integrating the remote sensing and GIS technique with statistical validation tests were useful and became a simple method for identifying the PFZ distribution. However, validating the PFZ distributions using the catch data was required.

Relationships between environmental variables and spatial and temporal distribution of jack mackerel (Trachurus japonicus) in the Beibu Gulf, South China Sea.

The jack mackerel (Trachurus japonicus) is both a dominant pelagic fish species and an important fishing target in the Beibu Gulf, South China Sea. However, the resource status of this species fluctuates dramatically, and it has recently been added to a “red list” of threatened species of the International Union for Conservation of Nature (IUCN). Despite its economic importance and decreasing population status, limited research on its spatiotemporal distribution has been undertaken over the last decades. In order to evaluate the most crucial factors that influence the spatiotemporal variability of T. japonicus and to determine GAM performance and predictability, we analyze catch per unit effort (CPUE) of T. japonicus from Beibu Gulf over four seasons (months) from 2013 to 2014. A generalized additive model (GAMs) is populated with water depth and remotely sensed sea surface temperature (SST), sea surface salinity (SSS), sea surface chlorophyll-a concentration (Chl-a) and sea level anomaly (SLA). The CPUE of T. japonicus varies seasonally, with higher CPUE in summer and autumn than in spring and winter, and the highest CPUE in summer. GAM results explain 57% of the deviation explained in CPUE, with the most important variables being SLA, Month, Depth, SSS, and SST , each explaining 21.2%, 18.7%, 10.7%, 5.1%, and 1.3% of the variation in CPUE, respectively. This species occurs mainly between 50 and 75 m depth, SSS values 32.3–33.5 PSU and SST 25–30.5 °C. High CPUE sites occur near SLA ≤ 0 m, on the edge of cold eddies, and there is a certain catch near the sea surface with SLA ≥ 0 m. The spatial and temporal distribution of T. japonicus is affected by the season and the marine hydrological environment. This study might contribute to a better understanding of the distributional patterns of T. japonicus as well as provide a basis for sustainable management in the Beibu Gulf.

Monthly anomalies of sea surface chlorophyll-a concentration in the Khanh Hoa waters of Vietnam related to ENSO phenomenon

Based on the monthly averaged sea surface chlorophyll-a concentration data continuously for more than 17 years (Jul. 2002–Dec. 2019), the analyzed results show that the averaged chlorophyll-a concentration in Khanh Hoa waters was 0.58 mg/m3, and the monthly average variation was ± 0.14 mg/m3 (that is equivalent to about ± 24%). Under the impact of ENSO phenomena, in the years when the double La Niña events occurred (two consecutive years in the La Nina event occurs), the chlorophyll-a anomaly index fluctuated from -0.99 mg/m3 to 1.62 mg/m3. These are very strong fluctuation levels, corresponding to the decrease or increase in chlorophyll-a concentration from 86% to 279%. In the El Niño years, the fluctuations of chlorophyll-a concentration were little affected unless the two previous years in which the double La Niña event occurred. These fluctuations have significantly impact nutritional resources and water quality because chlorophyll-a concentration is one of the key indices in studying the health status of any natural marine ecosystem. In addition, chlorophyll-a concentration in Khanh Hoa waters often varies between seasons. The averaged chlorophyll-a concentration reaches its maximum value in the winter, then decreases gradually in the spring and usually reaches the minimum value in the summer, then rises gradually again in the autumn.

Impact of tropical cyclone Amang on variability of wind speed, salinity, sea surface temperature, and their relationship to chlorophyll-a in sea waters of Sangihe Island

High concentrations of chlorophyll-a can be used to predict where fish gather. On the other hand, tropical cyclones are one of the triggering factors for vertical stirring and upwelling that cause fertility of waters. The Sangihe Island area is not an effective area for the formation of tropical cyclones. However, due to its geographical location with a tropical cyclone area and trajectory, the potential for disturbances caused by cyclones is impactful on Sangihe Island. The distribution of wind speed, salinity, sea surface temperature and chlorophyll-a concentration can be detected by satellite remote sensing imagery. This study aims to analyze the impact of Tropical Cyclone Amang on the variability of wind speed, salinity, sea surface temperature and on the concentration of chlorophyll-a in Sangihe Island. This study useswind speed, salinity, sea surface temperature and chlorophyll-a data during the Amang Tropical Cyclone (January 6-27, 2019) from the AQUA-MODIS satellite imagery. The results show that the relationship between wind speed and chlorophyll-a concentration has impact on other parameters where both parameters showed a strong correlation value. It was also showed on the relationship between sea surface temperature and chlorophyll-a.However, the relationship between salinity and chlorophyll-a concentration showed lowest effect among those parameters.Indonesian title: Dampak siklon tropis Amang terhadap variabilitas kecepatan angin, salinitas, suhu permukaan laut, dan hubungannya dengan klorofil-a di perairan laut Pulau Sangihe

Satellite-Observed Multi-Scale Variability of Sea Surface Chlorophyll-a Concentration along the South Coast of the Sumatra-Java Islands

The southern coast of Java is known as one of the most productive fishing grounds for tuna, feeding by nutrient-rich water along the coast caused by the subsurface water upwelling. This primary productivity can be evidenced by the high sea surface chlorophyll-a concentration (SSC). Based on satellite remote sensing products, we investigate the multi-scale variability in SSC along the Sumatra-Java coast. The results show that seasonal variability of SSCs is primarily due to monsoon-driven upwelling and rainfall in the Indian Ocean and Indonesian seas sides of the Sumatra and Java Islands, respectively. Local Ekman pumping plays a secondary role, while rainfall input to the ocean has little effect. Coastally trapped Kelvin waves and mesoscale eddies are responsible for the intraseasonal SSC anomalies in regions along the south coast of Java and off the Sunda and Lombok Straits, respectively. The interannual variability in SSC is caused by the anomalous upwelling related to the Indian Ocean Dipole. There was a weak increasing trend of ~0.1–0.2 mg/m3 per decade, above the global averaged trend, which may be related to enhanced local Ekman pumping. These analyses provide an overall description of SSC variations based on satellite observations; however, further investigations based on in situ observations are needed to achieve better quantification.

Model of Habitat Characteristics of Sardinella lemuru in the Bali Strait, Indonesia

This article describes a new approach to the study of the environmental conditions that relate to the Sardinella lemuru habitat in the Bali Strait, through remote sensing data and fish catch data using the generalized additive model. Data that are acquired daily and then compiled into monthly data for sea surface temperature, sea surface chlorophyll-a concentration, photosynthetically available radiation, and sea surface depth (SSD) were used for the years 2008–2010. The objectives of the study are to describe the variability of the environmental conditions in the Bali Strait, to analyze a combination model of environmental factors in estimating the Sardinella lemuru habitat, and to map potential Sardinella lemuru fishing areas. We illustrate the proposed method by constructing seven generalized additive models with catches of Sardinella lemuru as a variable response and use sea surface temperature, sea surface chlorophyll-a concentration, photosynthetically available radiation, and SSD as covariant models for assessing the environmental characteristics of the abundance of Sardinella lemuru. Predicted values were validated using a linear model. Based on the three model parameters, habitat selection for Sardinella lemuru was significantly (P < 0.0001) influenced by photosynthetically available radiation (50–55 Einstein m-2 d-1), sea surface chlorophyll-a concentration (0.2–2.0 mgm-3), sea surface temperature (28.95–29.64 °C), and SSD (60–150 m). Catch predictions show a consistent trend toward environmental conditions and water depth. Our method allows for improvement with the validation of catch predictions that were observed and collected monthly, and the result was significant (P < 0.001, r2 = 0.816). Photosynthetically available radiation explains the highest deviation in continued generalized additive models; therefore, it was considered to be the best predictor of habitat, followed by sea surface chlorophyll-a concentration, sea surface temperature, and then SSD. New research results supplement several previous studies that relate to the analysis of environmental parameters in estimating the fish habitat and can be used in mapping the distribution of potential Sardinella lemuru fishing areas in spatial and temporal scales.

Evolution of satellite derived chlorophyll-a trends in the Bohai and Yellow Seas during 2002–2018: Comparison between linear and nonlinear trends

The trends of sea surface chlorophyll-a (Chl-a) concentrations in the Bohai and Yellow Seas of China (BYS) were analysed based on the satellite-derived Chl-a dataset from August 2002 to December 2018. The result of linear trend analysis based on the seasonal Mann-Kendall test indicates a significant positive Chl-a trend during this period, with an average trend of ~1.15% year−1 (Slope: ~0.011 mg year −1). However, the linear trends of Chl-a varied seasonally, with strong and significant increases in spring and summer (about 2% year−1), and weak and non-significant increases in winter (lower than 1% year−1). The results of the ensemble empirical mode decomposition (EEMD) analysis revealed highly nonlinear and time-varying trends of Chl-a in the BYS, with gradually increased Chl-a during 2002–2011 and decreased Chl-a from 2012 to 2018. The instantaneous rate of Chl-a change was continuously reduced from 2002 to 2018, from a positive value of ~2.0% year−1 around the beginning year (2002) to a negative value of approximately −2.0% year−1 around the recent year (2018). The temporal evolution of the Chl-a trend was well in accordance with the changes in nutrient enrichment, suggesting that the status of eutrophication might be the primary driver of the long-term trends in Chl-a. The increase (decrease) in nutrient levels could alleviate (aggravate) the nutrient limitation for phytoplankton growth in spring and summer, thus regulating the changes in Chl-a. In contrast, the Chl-a trend seems to be unrelated to the trend of light intensity in this area. This is the first study aimed to discern and compare the linear and evolutionary nonlinear Chl-a trends in the BYS and provides a baseline against which future changes can be monitored.

On the robustness of an eastern boundary upwelling ecosystem exposed to multiple stressors

The resistance of an east border upwelling system was investigated using relative index of marine pelagic biomass estimates under a changing environment spanning 20-years in the strongly exploited southern Canary Current Large marine Ecosystem (sCCLME). We divided the sCCLME in two parts (north and south of Cap Blanc), based on oceanographic regimes. We delineated two size-based groups (“plankton” and “pelagic fish”) corresponding to lower and higher trophic levels, respectively. Over the 20-year period, all spatial remote sensing environmental variables increased significantly, except in the area south of Cap Blanc where sea surface Chlorophyll-a concentrations declined and the upwelling favorable wind was stable. Relative index of marine pelagic abundance was higher in the south area compared to the north area of Cap Blanc. No significant latitudinal shift to the mass center was detected, regardless of trophic level. Relative pelagic abundance did not change, suggesting sCCLME pelagic organisms were able to adapt to changing environmental conditions. Despite strong annual variability and the presence of major stressors (overfishing, climate change), the marine pelagic ressources, mainly fish and plankton remained relatively stable over the two decades, advancing our understanding on the resistance of this east border upwelling system.

Seasonal variability of gelatinous zooplankton during an anomalously warm year at Cabo Pulmo National Park, Mexico

The seasonal variability of gelatinous zooplankton (siphonophores, medusae, and thaliaceans) abundance was investigated at Cabo Pulmo National Park (CPNP) from weekly zooplankton samples collected throughout 2014. The Gulf of California had prolonged warming during 2009-2019, with 2014 as the anomalously warm year preceding El Niño 2015-2016 compared to the 2003-2020 SST time series. Gelatinous zooplankton accounted <1% of the entire zooplankton community abundance at CPNP during 2014, suggesting a low influence of predation pressure upon their zooplanktonic and micronekton preys. Siphonophores (57%), thaliaceans (42%), and medusae (1%) were present throughout the year. The abundance of gelatinous zooplankton had a significant negative association with sea surface temperature and a positive association with sea surface chlorophyll-a concentration and velocity and direction of the wind, increasing their abundance during October after the hurricane season. The gelatinous zooplankton species assemblage at the coastal CPNP was similar but less abundant than the gelatinous zooplankton species assemblage observed in the oceanic region of the southern Gulf of California during summer 2014. Tropical species Diphyes dispar, Abylopsis tetragona, Chelophyes contorta, and Thalia spp. numerically dominated the gelatinous zooplankton community associated with a regional heatwave period recorded during 2014. A high proportion of tropical zooplankton indicates that mesotrophic conditions sustain the current high biomass and diversity of nektonic and benthonic planktophagous fauna inhabiting CPNP. However, prolonged warming events might decrease zooplankton biomass in the southern region of the Gulf of California in the future.

Climate change drivers influencing Indian mackerel fishery in south-eastern Arabian Sea off Kerala, India

The Indian mackerel Rastrelligerkanagurta(Cuvier, 1816) is one of the most important marine fishery resources along the south-eastern Arabian Sea along the coast of Kerala, south India. The effect of selected environmental variables on the Relative effort (Effort) and weighted catch per unit effort (cpue)of the fish were investigated using simple correlation and Path analysis. Six major oceanographic variables, namely sea surface temperature (SST), sea surface chlorophyll-a concentration (SSC), sea surface salinity (SSS), Precipitation (Pr) Indian Ocean Dipole (IOD) and Southern Oscillation Index (SOI) (ENSO index) were selected for the present study. Among these SST had the highest direct negative effect (-0.282, p<0.01), followed by SSS (-0.152, p<0.1) and IOD (-0.006, p<0.01). The highest positive direct effect on the cpue was exhibited by Pr (0.514, p<0.001) followed by SSC and SOI (0.178, p<0.01). The environmental variables also exerted indirect effects on cpue through Effort. The residual variance indicated that there are spurious effects exerted by environmental variables not included in the study. According to the coefficient of determination (R2), the relative importance of the influence of causally dependent environmental variables on the cpue of Indian mackerel is Pr> SSC >SSS.

Copepod species assemblage and carbon biomass during two anomalous warm periods of distinct origin during 2014–2015 in the southern Gulf of California

Copepod species assemblage and biomass were studied during a weekly time series done during an anomalously warm and low sea surface Chlorophyll-a concentration period 2014–2015, compared with 2002–2018, at Cabo Pulmo National Park, Gulf of California, Mexico. Forty-nine copepod species accounted for 64% of the total zooplankton abundance. Three small copepods (Oncaea venusta 12.6%, Paracalanus parvus 11.5%, Clausocalanus jobei 8.6%) out of 45 species numerically dominated during 2014. The large copepods Subeucalanus subtenuis and Subeucalanus subcrassus out of 38 species recorded during 2015 increased in abundance accounting for 69% of copepod Carbon biomass. A Canonical Correspondence Analysis demonstrated SST drove copepod species assemblages. Copepod abundance was significantly higher during the cold (Nov–May) that during the warm (Jun–Oct) season and lower during Jan–Aug 2014 regional heatwave than during the Equatorial El Niño (Nov 2014–Dec 2015). Acartia tonsa was the only significant species indicator during the 2014 regional heatwave and Clausocalanus furcatus, Copilia mirabilis, and Cosmocalanus darwinii were significant species indicators of El Niño 2015. Copepod species assemblage had 87% tropical species during the Jan–Aug 2014 due to the regional heatwave that started the tropicalization of copepod community increasing to 95% of tropical species during El Niño 2015.

Multisatellite-Based Feeding Habitat Suitability Modeling of Albacore Tuna in the Southern Atlantic Ocean

Decision strategies in fisheries management are often directed by the geographic distribution and habitat preferences of target species. This study used remote sensing data to identify the optimal feeding habitat of albacore tuna in the Southern Atlantic Ocean (SAO) using an empirical habitat suitability model applying longline fisheries data during 2009–2015. An arithmetic mean model with sea surface temperature (SST) and sea surface chlorophyll-a concentration (SSC) was determined to be suitable for defining the albacore habitat in the SAO. The optimal ranges of SST and SSC for the habitat were approximately 16.5 °C–19.5 °C and 0.11–0.33 mg/m3, respectively. The study revealed a considerable positive trend between the suitable habitat area and standardized catch per unit effort (r = 0.97; p < 0.05); due to the west-to-east and northward development of the suitable habitat, albacore schools moved to the northeast of the SAO, thus increasing catch probability in April to August in that region. Overall, the frontal structure of SST and SSC plays an essential role in the formation of potential albacore habitats in the SAO. Our findings could contribute to the establishment of regional ecosystem-based fisheries management in the SAO.

Contrasting chlorophyll-a seasonal patterns between nearshore and offshore waters in the Bohai and Yellow Seas, China: A new analysis using improved satellite data

The seasonal cycles of sea surface Chlorophyll-a (Chl-a) concentration in the Bohai and Yellow Seas (BYS) were examined using new remotely sensed Chl-a products derived using a regional algorithm. Based on objective clustering analysis, two contrasting Chl-a seasonal patterns were delineated: 1) A nearshore pattern with a long-lasting Chl-a peak from spring to autumn, coinciding with sufficient nutrient supply and high light availability, and lower Chl-a values in winter due to the light-limitation as a consequence of low solar irradiance and high diffuse attenuation coefficient of light for the water column; 2) An offshore pattern with a strong spring bloom triggered by alleviated light limitation and abundant nutrients coinciding with high water column stability. A weak autumn peak induced by new nutrient replenishment from bottom re-suspension and horizontal transportation, a low Chl-a trough in winter mainly attributed to light-limitation, and a Chl-a trough in summer due to nutrient scarcity were observed. The linkages between the province-specific Chl-a seasonal patterns and the seasonal cycles of the corresponding environmental variables as well as other potential influencing factors are comprehensively delineated and discussed.

Foraging ecology of a marine top predator in the Eastern Tropical Pacific over 3\xa0years with different ENSO phases

The El Niño Southern Oscillation (ENSO) is a recurrent climatic pattern with important ecological consequences for seabirds due to its impacts on the abundance and distribution of food resources. We investigated the effects of ENSO phases on the foraging ecology of a marine top predator at Clarion Island in the Eastern Tropical Pacific using GPS and time-depth recorder data and regurgitates from incubating masked boobies (Sula dactylatra) during 3 consecutive years. Foraging locations were recorded in 2016 (El Niño, one female, three males), 2017 (neutral; six females, nine males), and 2018 (La Niña; eight females, ten males). Local sea surface temperature (SST) and chlorophyll-a concentration (CHL) within the birds’ foraging range were compared among the 3 years. Regurgitates were collected opportunistically from 25 and 31 incubating adults in 2017 and 2018, respectively. Average local CHL and SST were similar among years (mean SST 25 °C; mean CHL 0.10 and of 0.09 mg m−3 in January and March, respectively). Masked boobies travelled a maximum of 66 ± 34 km from the colony. The maximum trip duration was 7.7 ± 3.4 h and total distance travelled during a foraging trip was 164 ± 73 km, with no sex- or year-related differences. Masked boobies mainly caught flying fish, but their diet also included one squid and six other fish families. In contrast to previously reported changes in foraging ecology of seabirds, masked boobies at Clarion Island seemed to be unaffected during El Niño, because the local oceanography was relatively unperturbed by ENSO oscillations.

Morphological Variation of the Sea Silverside Odontesthes regia in Regions with Dissimilar Upwelling Intensity along the Humboldt Current System

We evaluated the influence of areas with dissimilar upwelling intensity along the Humboldt Current System on the morphological variation of the economically important sea silverside Odontesthes regia by using geometric morphometric (GM) and meristic data of populations sampled off Northern Peru, Central Peru, Southern Peru-Northern Chile, and Central-Southern Chile (CSCH). Multivariate analyses of variance, a UPGMA tree, and discriminant analyses of meristic counts separated CSCH individuals, which had slightly higher numbers of gill rakers and radius of the anal fin. Permutation tests and canonical variate analyses of GM data distinguished all populations and highlighted deformations in the head and fins. Variations in GM and meristic analyses were significantly correlated with values of the sea surface temperature and surface chlorophyll-a concentrations. Morphological differences among populations might be associated with the spatial coastal upwelling dynamic of the Humboldt Current System, which highlights the role that this system plays in relation to the phenotypic variation of fish.

Ecological Vulnerability of Coral Reef Ecosystem in Wakatobi National Park During Indian Ocean Dipole Event

This research examines coral reefs vulnerability which threatening its existences and functions by climate change. The ecological vulnerability in Wakatobi (Wangi-wangi, Kaledupa, Tomia, and Binongko) was assessed during Indian Ocean Dipole (IOD) event in 2016. Climate exposure was determined using sea surface temperature, chlorophyll-a concentration, and wind speed magnitude; sensitivity was determined using coral susceptibility, fish susceptibility, and macroalgae primary productivity rate; then adaptive capacity was developed by hard coral cover, coral size distribution, coral richness, fish biomass, herbivore diversity, and herbivore grazing relative to algal production. The values of Exposure, Sensitivity, and Adaptive capacity in Wakatobi were 0.93±0.02, 0.42±0.18, and 0.44±0.10, respectively. Site specific vulnerability scores ranged from 0.52 to 1.60 (mean 0.92±0.26). Binongko was the least vulnerable than other islands. Tomia was observed as the least adaptive capacity and Wangi-wangi was the most bleaching incidents. These results could help coral reefs monitoring priority during the event and then when the event is gone by focusing on the marked islands and sites. Sites that were observed as more vulnerable is urgently need a management strategy to overcome the vulnerability status in the future, such as increasing site adaptability.

Variabilidade Temporal das Concentrações de Clorofila -A e da Temperatura Superficial do Mar na Costa Central de Santa Catarina

O fenômeno das florações de algas é conhecido mundialmente devido aos impactos diretos na saúde dos ecossistemas aquáticos, nos recursos pesqueiros e aquícolas, nas atividades recreacionais e na saúde humana. O presente estudo avaliou o uso de sensores satelitais na quantificação dos parâmetros de temperatura superficial do mar (TSM) e concentração de clorofila-a na superfície do mar (Chl-a) na costa de Santa Catarina, durante o período entre 2002 e 2019, objetivando identificar a variabilidade temporal da TSM e da Chl-a a partir da decomposição das séries temporais em tendência, sazonalidade e resíduos. Para atingir este objetivo foram adquiridas estimativas de TSM e Chl-a oriundas dos sensores orbitais Moderate-Resolution Imaging Spectroradiometer (MODIS) a bordo dos satélites (Aqua e Terra) e Visible Infrared Imaging Radiometer Suite (VIIRS) a bordo dos satélites (SNPP e NOAA-20). Através da extração dos valores de TSM e Chl-a para um ponto ao largo da costa central de Santa Catarina foram geradas séries temporais para o período especificado e aplicada a metodologia de decomposição de séries temporais para identificar oscilações de baixa frequência. Foi possível identificar que os eventos com maior Chl-a estão relacionados com eventos com menores valores de TSM. As componentes encontradas poderão ser utilizadas para modelos preditivos auxiliando assim a minimizar os impactos associados às florações de algas.

The Fishing Ground of Large Pelagic Fish during the Southeast Monsoon in Indonesian Fisheries Management Area-713

Large pelagic fish (LPF hereafter) is an important group of fishes targeted by local fishermen in the Indonesian Fisheries Management Area-713 (IFMA-713). This IFMA includes the Makassar Strait, Flores Sea, Bali Sea, and Gulf of Bone. The objective of this study was to identify the preferred oceanographic conditions based on LPF fishing grounds in the study area. The experimental fishing was conducted from April to September 2018 by using local commercial fisheries (pole and line and purse seine). The fishing base of pole and line vessels operating in the Gulf of Bone was at Murante fish landing site, Luwu Regency, South Sulawesi. On the other hand, the fishing base of purse seine vessels operating in the Makassar Strait was at Siddo fish landing site, Barru Regency, also in South Sulawesi. Oceanographic factors such as sea surface temperature (SST), sea surface chlorophyll-a (SSC) concentration, and depth were derived from satellite data. The LPF fishing grounds were analysed and visualize using Geographic Information System (GIS) techniques. Based on the results, LPF distributions tended to be the highest in specific oceanographic conditions, including SST of 30.0 - 31.0 °C and SSC of 0.20 - 0.30 mg.m−3. They were mostly found in nearshore and offshore areas (maximum depth of about 2,000 m). The selected oceanographic factors played an important role in explaining the LPF fishing grounds. This information could be used for spatial prediction of potential LPF fishing zones in relation to the fish distribution and abundance during the Southeast monsoon in the IFMA-713.

Empirical habitat suitability model for immature albacore tuna in the North Pacific Ocean obtained using multisatellite remote sensing data

ABSTRACT This study developed an empirical habitat suitability model for identifying the optimal habitat of immature albacore tuna in the North Pacific Ocean (NPO) by using multisatellite remote sensing data and Taiwanese longline fisheries data between 2009 and 2016. An arithmetic mean model with five environmental variables is suggested to be appropriate for explaining the habitat variance of albacore in the NPO. A monthly albacore mean catch per unit effort (CPUE) of larger than 29.5 individuals/1,000 hooks occurred from November to March and was distributed over 25–40° N. The optimal range of environmental variables in the sea surface temperature, sea surface height, mixed layer depth, sea surface chlorophyll-a concentration of the previous month, and eddy kinetic energy for the habitat of albacore are suggested to be approximately 17–21°C, 0.24–0.84 m, 15–100 m, 0.07–0.29 mg m−3, and 0.0001–0.0031 m2 s−2, respectively. We discovered a significant positive relationship between the suitable habitat area and nominal CPUE of immature albacore in the NPO (Pearson’s correlation coefficient, r = 0.982). The mean position of the optimum habitat shifted southwardly from near 38° N in November to near 28–31° N during February to March. Overall, frontal structures play a major role in the stimulation of potential albacore habitats.

Chlorophyll variability induced by mesoscale eddies in the southeastern tropical Indian Ocean

Abstract High sea surface chlorophyll-a concentrations (CHL) and intensive mesoscale eddy activity coexist near the coast of Java in the southeastern tropical Indian Ocean (SETIO) in upwelling season (July–November). In this study, the modulation effects of mesoscale eddies on the local CHL variability are investigated by analyzing remote sensed as well as in situ observations together with ocean and atmospheric reanalysis data from 1997 to 2010. Within 400 km off the coast, the mean CHL inside cyclonic eddies (CEs) is 2–3-fold higher than background, and is obviously suppressed inside anticyclonic eddies (AEs). During upwelling season, more and stronger CEs are generated, which significantly contributes to the high mean CHL levels. A composite analysis revealed that CEs induce CHL anomalies through both vertical upwelling that elevates nutrient-rich water from the subsurface to the surface and horizontal advection that carries high-CHL water from the coast to the offshore area. These effects are particularly visible during the upwelling season, when advection of the background high CHL favors large eddy modulation on the CHL. The eddy-induced CHL anomalies also exhibit prominent interannual variability, which has a close relationship with the El Nino-Southern Oscillation and the Indian Ocean Dipole (IOD). The wind forcing of El Nino and positive IOD events can enhance the vertical shear of the background currents and favor energetic CEs off Java coast, which contributes to the interannual variability of the local CHL. These results underscore the fundamental role played by mesoscale eddies in the ocean dynamics, environment, and bio-system of this region.