Banda Sea Research Articles

The Effect of Season and The Implications For Sustainable Fisheries on The Catch Results of Yellowfin Tuna In Indonesia

This study assessed the purse seine, handline and pole and line catches at PPS (Samudera Fishing Port Kendari) specifically targeting skipjack and yellowfin tuna in the Banda Sea. Although there has been a rise in tuna output over the past two years, the examination of fish size in September until November revealed substantial fluctuation. Additionally, the implementation of the moratorium policy had a detrimental effect. Ensuring the sustainability of fisheries in the Banda Sea, particularly for large pelagic fish like skipjack and yellowfin tuna, necessitates the implementation of adaptive management and selective fishing practices, with a particular focus on enforcing mesh size regulations. The aims of this study were to examine the patterns of tuna fisheries landing at PPS, specifically focusing on the sorts of catches made using purse seine, handline, and pole and line fishing methods. Additionally, the study aimed to assess the length frequency distribution of Thunnus albacares caught using purse seine, handline, and pole and line fishing gear. The methodology offers a thorough framework for eval_uating the sustainability of Thunnus albacares fisheries in PPS Kendari. Policymakers can develop effective management plans for long-term resource sustainability by assessing catch composition, productivity, and size distribution across various fishing gears. The analysis of this study conducted in September - November 2023 revealed that the fish catches varied in size, ranging from 13 cmFL to 124 cmFL.

Internal tidal dynamics and associated processes at highly supercritical slopes in Banda Sea: Lessons from the oceanic island of Ambon, eastern Indonesia

Interactions between the deep sea and steep-sloping oceanic islands generate physical processes with potential impacts on sediment resuspension and ocean productivity. While studies have been conducted in the open oceans, those focusing on oceanic islands of the deep Banda Sea in eastern Indonesia are lacking. Here, we present the first observational evidence of vertical mechanisms (i.e. internal tidal reflection, internal hydraulic jumps) at the highly supercritical slope in outer Ambon Bay (OAB) in Ambon Island – an oceanic island in the Banda Sea. A 23-h CTD yoyo experiment combined with ADCP measurements conducted during spring flood and ebb tides demonstrated tidally-varying vertical temperature, salinity and density profiles. During spring flood tide, incoming internal tides were reflected by OAB's highly supercritical slope back to the deep sea with isopycnals and isotherms showing sharp downward plunges (downward vertical velocity = 6.5–8.3 × 10−3 m/s), and the internal tidal amplitude reaching 90–110 m. The reflection during flood tide caused seaward overturning flow at deeper depths despite the prevailing landward flow at the upper layers. During spring ebb tide, internal hydraulic jumps (upward vertical velocity = 6.1–6.48 × 10−3 m/s) occurred to rebound the downward plunges of isopycnals and isotherms as flood tide relaxed with the observed amplitude of internal tides of 90 m. We also observed weakened seaward ebb flow during the isothermal uplifting (when hydraulic jumps occurred), and subsequent intensified landward flow at the end of spring ebb tide indicating strong upslope flow when isotherms reached the maximum shoaling depths. Taken together, the observed vertical mechanisms indicate the conservation of energy at the highly supercritical slope of OAB evident by the comparable vertical velocities. An embedded turbidity-chlorophyll profiler in the CTD reveals that internal tidal activities at the highly supercritical slopes OAB may induce bottom nepheloid layers, and influence ocean productivity by regulating the vertical distribution of phytoplankton biomass.

ANALYSIS Catch Per Unit Effort (CPUE) AND Maimum Sustainable Yield (MSY) MALE MACKEREL (Rastrelliger kanagurta) FLYING IN THE SAMUDERA FISHING LAND (PPS) KENDARI

The Banda Sea is an Indonesian water body that holds potential for small pelagic fisheries resources. Situated between Sulawesi Island and Maluku, it is part of the Fisheries Management Area Of The Republic Of Indonesia (WPP-NRI 714), Male mackerel (Rastrelliger kanagurta) is one of the fish species with high economic value, greatly favored by the community for consumption. This has led to an increase in its capture rates. Therefore, the research aims to determine the CPUE and MSY of Indian mackerel in the Kendari Ocean Fisheries Port. Data collection was conducted at the Kendari Ocean Fisheries Port from logbooks, and the research lasted from November to December 2023. The results showed that the standard fishing gear used to catch these fish is purse seine. The status of the utilization of the fishery resources is said to be experiencing underfishing. Based on the research results, the maximum sustainable yield (MSY) is 96,386 kg/year, with an optimal fishing effort of 2,300 trips/year (Fox model).

An Integrated Study of Age and Formation of the Aru Trough, Eastern Banda Arc, Indonesia: Implications for Seismic Hazards

AbstractThe Banda Arc in eastern Indonesia has a complex tectonic history involving oceanic and continental subduction, arc‐continent collision and slab rollback. Among these the subduction rollback that began at 16 Ma shaped the regional tectonic configuration, causing notable upper plate extension evidenced by the Banda Sea and Weber Deep. However, the effects of subduction rollback on the lower plate remain less understood. The Aru Trough, part of subducting Australian continental margin, shows strong deformation and high seismicity, making it ideal for studying these effects. Utilizing multibeam bathymetry, seismic reflection profiles, GPS observations, seismicity and focal mechanisms, we investigate the crustal deformation, driving mechanisms and seismic risks in the Aru Trough under the background of Banda slab rollback. The Aru Trough shaped like an inverted triangle narrows from 160 to 40 km southward. It has a fast 53.8 mm/yr extensional rate at present, when combined with its maximum width suggesting a 3 Ma age. High‐angle faults (>60°) are present at its margins and interior. The trough has a high density of seismicity up to 5.9 events per 25 km2, with dominant normal and strike‐slip events, consistent with observed deformational patterns. The low seismic b‐value of 0.82 ± 0.01 suggests a high‐stress state with potential for strong earthquakes (Mw ≥ 6.5). Our findings indicate that lower plate deformation is profoundly influenced by subduction rollback, oblique arc‐continent collision and regional strike‐slip faulting. Understanding deformation in the Aru Trough is crucial for grasping the broader tectonic evolution of the Banda Arc and assessing seismic risks.

Biology reproduction and population dynamics of Caesio cuning (Family: Caesionidae) in Kendari Waters, Banda Sea, Indonesia

Abstract The Redbelly yellowtail fusilier with the local name Ekor Kuning (Caesio cuning) is a reef fish species found in the waters of the Indo-West Pacific. In Indonesia, it is an economically important fish and is dominantly caught by gill nets, traps and handlines. The intensity of fishing that is carried out continuously is feared to threaten the stock of the species in nature. In order to make its use sustainable, this study attempts to evaluate population dynamics and reproductive biology. The study was carried out in the Kendari waters of the Banda Sea, Indonesia, between April and December 2018. The findings indicated that this fish’s length distribution covered a range of 11,6-29,0 cm FL and the growth pattern was isometric with the length-weight relationship equation W=0,0206L3,0612. The spawning season peaked in November, and the sex ratio did not deviate considerably from 1:1. The length at first maturity (Lm = 21,73 cm FL) was longer than the length at first capture (Lc =15,5 cm FL) The VBGE for yellowtail was Lt = 30,45 [1 – e−0,89(t+0,171)]. The value of mortality due to capture (F = 2,19 per year) is greater than natural mortality (M = 0,44 per year). The exploitation rate (E) was recorded as 0,72 per year and the SPR value is 0,22 per year. Based on these parameters, it indicates that the level of exploitation of Caesio cuning in Kendari waters is in overfished so that management needs to be implemented by limiting the smallest fish size that can be caught and to reduce fishing operations during the spawning season.

The Seasonal Variations of the Thermocline in the Banda Sea and its Water Mass Characteristics

This research was conducted to examine the seasonal variations in the Banda Sea's thermocline layer and its water mass characteristics. The research was conducted by analyzing Argo Float data. The data consists of six observation stations in West Season and Transitional Season II, and four stations in Transition Season I and East Season The thermocline layer thickness was identified based on the depth where the temperature decreased ≥ 0.05oC/m. The thermocline layer's distribution of depth and thickness and the distribution of temperature and salinity seasonally in the thermocline layer were analyzed with Microsoft Excel 2010. The analysis results showed that East Season and Transition Season II have a shallower upper boundary depth of the thermocline layer, a deeper lower boundary of the thermocline layer, and the thermocline layer is thicker when compared to the West Season and Transition Season I. The average temperature distribution is higher and the average salinity is lower in the West Season and Transition Season I. The mean rate of change in salinity and temperature in the thermocline layer seasonally ranged from 0.002-0.004 PSU/m and 0.06-0.08oC/m. The thermocline layer's stratification is stronger in the West Season and Transition Season I.

Seasonal and Fortnight Variations in Internal Solitary Waves in the Indonesian Seas From the SWOT Measurements

AbstractUsing the wide‐swath sea surface height (SSH) data from the 1‐day repeat calibration/validation phase of the Surface Water and Ocean Topography (SWOT) mission, we explored fine‐scale evolution of nonlinear internal solitary waves (ISWs) in the Banda/Molucca Seas in the Indonesian Archipelagos. Generated in the Ombai Strait and Lifamatola Passage through semidiurnal tide‐topography interaction, respectively, ISWs in the Banda/Molucca Seas have a SSH amplitude of 10–20 cm and exhibit multiple wave packets with the leading wave crest followed by a series of rank‐ordered secondary wave crests. Due to nonlinearity, the ISWs are observed to propagate northward at a speed faster than the regional mode‐1 internal gravity waves and their amplitudes are modulated fortnightly following the regional spring‐neap tidal cycle. On longer timescale, the observed ISW amplitudes are controlled by seasonal upper ocean stratification changes with a weaker stratification favoring a larger amplitude. By converting the SWOT‐measured SSH data to the interior ocean pressure signals, we quantified the depth‐integrated energy flux associated with the northward‐propagating ISWs to be 5 and 2 kW m−1 in the central Banda and Molucca Seas, respectively. Comparisons with past studies indicate that the ISWs contribute to close to 100% and 40% of the tidally‐induced, northward energy fluxes, respectively, across the Banda and Molucca Seas.

Numerical Modelling of the Potential Hazard Due to Future Flores Back Arc Thrust Earthquake Generated Tsunami

Abstract Indonesia is situated at the conjunction of four major plates: Eurasia, India-Australia, the Pacific, and the Philippine Sea. Therefore, Indonesia is exposed to a considerable threat from natural hazards every day. Tectonic-related marine geohazards, particularly earthquakes-generated tsunamis periodically affect Indonesia, causing great loss of life and extensive damage to property and infrastructure in coastal areas. Many studies on tsunami modeling have been addressed in western Indonesia. In eastern Indonesia tsunamis, however, are even more frequent in occurrence and may be more hazardous, there is a lack of study and less attention. The Flores Back Arc Thrust (FBAT) is an active fault that lies on the sea floor of the Flores Sea in the north of Flores Island, extending from north of Bali to the east that may be connected to the Wetar thrust at the north of Wetar Island in the western Banda Sea. The FBAT is a source of seismicity in this area. From 1900 to 2022, there were 79 earthquakes with a magnitude of more than 6.0 Mw, and 11 of them generated tsunamis, and the most devastating one was the 1992 Flores earthquake tsunami. This study presents an estimated FBAT-induced future earthquake-generated tsunami runup based on numerical modeling.

New observations of fluorescent organisms in the Banda Sea and in the Red Sea.

Fluorescence is a widespread phenomenon found in animals, bacteria, fungi, and plants. In marine environments fluorescence has been proposed to play a role in physiological and behavioral responses. Many fluorescent proteins and other molecules have been described in jellyfish, corals, and fish. Here we describe fluorescence in marine species, which we observed and photographed during night dives in the Banda Sea, Indonesia, and in the Red Sea, Egypt. Among various phyla we found fluorescence in sponges, molluscs, tunicates, and fish. Our study extends the knowledge on how many different organisms fluoresce in marine environments. We describe the occurrence of fluorescence in 27 species, in which fluorescence has not been described yet in peer-reviewed literature. It especially extends the knowledge beyond Scleractinia, the so far best described taxon regarding diversity in fluorescent proteins.

Sea surface temperature budget in Indonesian seas: the role of vertical turbulent flux and its east–west variations

Abstract The vertical turbulent flux, which comprises heat flux and vertical mixing, is one of key processes governing seawater temperature changes in the vertical direction. In this study, the influence of vertical turbulent flux on sea surface temperature (represented by a layer between the free-surface and approximately 20 m depth) in Indonesian seas was diagnosed from an eddy-permitting ocean modeling experiment result. The heat flux, as the sum of the net heat flux at the surface and penetrative shortwave radiation at the base of the surface layer, induced a net cooling tendency in both eastern and western Indonesia (represented by the Java Sea and Banda Sea, respectively). The cooling tendency due to the heat flux was opposed by the warming tendency induced by vertical mixing at the base of the surface layer, preventing excessive heat loss in the surface layer. An exception occurred during the Boreal Autumn in the Banda Sea, when the heat flux and vertical mixing resulted in warming and cooling tendencies, respectively. It was further found that the effect of vertical mixing on the surface layer heat budget was sensitive to the selection of the base layer depth, highlighting the mixing-related dynamic variation within the water column. In summary, this study provides additional insights into the near-surface dynamics that govern sea surface temperature seasonality in Indonesian Seas.

Variability of Indonesian Throughflow Transport in the Indonesian Seas during Triple-Dip La Niña

Abstract The Indonesian seas serve as an important conduit for the Indonesian Throughflow (ITF), a critical system of warm water and freshwater transport connecting the Pacific and Indian Oceans. El Niño-Southern Oscillation (ENSO) significantly impacts the regional variability in the Pacific and exerts a profound influence on water mass transport from the Pacific to the Indian Oceans. This study focuses on the influence of triple-dip La Niña events during two distinct periods (1998 – 2001 and 2020 – 2023) on the variability of ITF transport in key areas of the Indonesian seas, including the Makassar, Lombok, and Ombai Straits, Flores and Banda Seas, and Timor Passage. Using forecast and reanalysis data from the Copernicus Marine Environment Monitoring Service (CMEMS), transport calculations are conducted across cross-sectional profiles representing the study areas. The results reveal that the volume transport is significantly higher at depths ranging from ∼50 – 300 m. It also shows seasonal fluctuations in volume transport across all regions, with lower transport during winter (DJF) and higher transport during summer (JJA) and transition period (SON) in the Makassar and Lombok Straits. In the Flores and Banda Seas, Ombai Strait, and Timor Passage, the surface volume transport follows seasonal patterns, while at deeper depths (∼50 – 300 m and 300 – 800 m) exhibits distinct fluctuations compared to the surface. Triple-dip La Niña events lead to an overall increase in volume transport during both periods, with the 2019 – 2023 period showing larger values (∼19 Sv) compared to the 1997 – 2001 period (∼14 Sv). The strengthened ocean current during triple-dip La Niña events results in more significant variations in total transport, leading to larger differences between minimum and maximum transport during these periods. The volume transport in Makassar Strait is further analyzed using the Empirical Orthogonal Function (EOF) that identifies three dominant modes (86.4%), revealing the influence of semi-annual, interannual, and decadal factors on the observed variability.

Vertical Characteristic of Water Mass in The Flores Sea: The Effect of The ITF on The Transitional Season

Abstract Indonesian Through Flow (ITF) forms unique water mass characteristics in Indonesian Marine Waters. This water mass enters through the Makassar Strait into the Banda Sea by crossing the Flores Sea. This study aims to analyse the characteristics of water masses in the Flores Sea during the transition season. In situ data was obtained using conductivity temperature depth (CTD) at four stations in the Flores Sea from April to May 2023. Next, the data was processed and analysed for layer thickness through vertical stratification and water mass characteristics using T-S diagrams. The analysis results show that the thickness of the homogeneous layer in the Flores Sea in the first transition season is between a depth of 0-40 m, the thermocline layer is at a depth of 40-300 m, and the depth layer is from a depth of 400-900 m. Apart from that, the characteristics of the water mass identified through the T-S diagram are: North Pacific Subtropical Water (NPSW) is found at a depth of 100-150 m with a temperature between 20-26° C and a salinity between 34.9-35.4 psu. Another water mass is South Pacific Intermediate Water (SPIW) at a depth of 500-800 m with a temperature of 6-8° C and a salinity of 34.55-34.65 psu. In contrast, the Antarctic Intermediate Water (AAIW) was found at a depth of >750 m with a temperature of 5-6° C and a salinity of 34.5-34.6 psu.

Ocean Circulation and Variability in the Seram and Northern Banda Seas

Abstract The Seram and Banda Seas (SBS) convey the eastern pathway of Indonesian Throughflow (ITF) from Maluku and Halmahera inflow portals. This study aims to investigate circulation and variability at near-surface and thermocline layers in the SBS region using validated INDESO model output datasets (2008-2015). It is shown that much warmer and saltier thermocline ITF water (24,36°C and 34,65 psu) from Halmahera is predominant, flowing southward and impinging on the northern coast of Seram near 128.5°E. The flows then bifurcate eastward into the Banda outer ring arc and westward into Banda via the Manipa Strait and western Seram Seas. In Banda, two clockwise eddies are found related to these inflows. Secondary southward inflow via Lifamatola is associated with cooler and less salty water (23,3°C and 34,45 psu), which merges with ITF Halmahera. The variability of oceanographic parameters is dominated by the annual period. However, on an interannual scale, the response of seawater temperature to ENSO is evident, and its amplitude, as shown by the principal component time series EOF, is much stronger in Banda than in Seram at -2.7. A decreasing trend of seawater temperature was also found in 2015.

Observations of Barrier Layer Seasonal Variation in the Banda Sea

AbstractThe Banda Sea is of crucial importance for the circulation of the world's oceans, as it is part of the connection between the Pacific to the Indian Ocean. One peculiarity of the upper ocean hydrography in the Banda Sea is the occurrence of barrier layers. The regionality and temporal variability of barrier layer thickness (BLT) in the Banda Sea are examined in this study utilizing in‐situ observations and ocean reanalysis output. It is found that a barrier layer occurs in over 90 % of the observational data profiles, and in over 72 % of those profiles, the BLT is shallower than 10 m. Furthermore, we find a seasonal cycle in BLT with a maximum thickness of about 60 m occurring during austral autumn and winter and coinciding with the presence of low saline waters fed by the regional river discharge and rainfall from the Java Sea and Makassar Strait. In addition, we identify the existence of a quasi‐permanent anticyclonic circulation cell in the Banda Sea that may support the trapping of surface freshwater by retention. The anticyclonic circulation is most likely wind‐driven because it coincides with the regional Ekman pumping pattern. Modulation of the anticyclone is via seasonal variability in the wind stress curl which in turn may explain the efficiency of freshwater retention and thus the BLT. The annual mean BLT distribution in the Banda Sea shows a preferential region of thickened barrier layers around 6o‐8oS and 124o‐126oE and resampling the pattern of the monthly mean climatology.

Analysis of internal wave in the Buru Island coastal waters, Banda Sea, Indonesia

The Indonesian throughflow (ITF) in the eastern part of Indonesia passes through the Maluku, Taliabu, Sula, and Buru Islands to the Banda Sea. The average depth of the Buru and Sula Islands is between 1000 m and 5000 m, with a narrow gap (sill) located to the north and south at a depth of 165 m on the sea map. This topography makes for interesting research on the western waters of Buru Island. Therefore, this study aimed to obtain salinity, temperature, and density values as water column stratification associated with the internal wave (IW), thermocline area, and current patterns at specific depths in the waters of Buru Island, Banda Sea. Data were collected from initial observations of Sentinel 1 satellite imagery of Buru Island to obtain an image of the waves in the water area. Furthermore, a single beam echosounder (SBES), conductivity temperature depth (CTD), and Copernicus Marine were analysed at the same position and time. The research found a non-linear IW Mode 2 at depths of 440–540 m with an estimated amplitude length is 40 km and an amplitude height of 100 m. Based on SBES echogram imaging, CTD data analysis, and modelling, there was an increase in IW density, a 35.25 PSU increase in salinity value at depths of 50∼200 m, a temperature decrease of 27.5 °C to 10 °C at depths of 50∼300 m, and a density stratification of 23.5 kg/m³ to 27 kg/m³ at depths of 50∼300 m.

Spatial Distribution of Nutrient in The Waters of Haruku Strait, Central Maluku Regency, Maluku Province

Strait waters are influenced by tides, water masses and surrounding land. This study aims to analyze the spatial distribution of nutrients in the waters of the Haruku Strait, Central Maluku Regency, Maluku Province. The research method used is the survey method by taking water samples. Water samples were taken from 17 observation stations spread across the Haruku Strait at depths of 1 meter, 25 meters and 50 meters using the Niskin Bottle Water Sampler. Nitrate concentration analysis using the OPTIZEN Alfa equipment (Spectrophotometer UV-Vis) and the Brucine Sulfate method (SNI: 06-2480-1991) and phosphate concentration analysis using the Ammonium Molybdate method (APHA 10th ed. 5400-PD, 1998). The time of observation took place on July 23, 2022. The results showed that the average concentration of nitrate at a depth of 1 m was 1.146 ± 0.647 mg/L, a depth of 25 m was 1.148 ± 0.709 mg/L and a depth of 50 m was 1.136 ± 0.701 mg/L while the average concentration of phosphate at a depth of 1m was 0.051 ± 0.028 mg/L, a depth of 25 m was 0.053 ± 0.029 mg/L and at a depth of 50 m was 0.049 ± 0.020 mg/L. The waters of the Banda Sea, the Seram Strait and contributions from the rivers on the coast of Ambon Island play a role in the distribution of nutrients in the waters of the Haruku Strait.

Genetic Diversity of Flying Fish (Exocoetidae) in Southeast Sulawesi, Indonesia

Flying fish (Exocoetidae) is a pelagic fishery commodity that holds economic value among the people of eastern Indonesia. Flying fish are advantageous as they are abundant in Indonesian sea waters, making them an affordable source of omega-3, which is beneficial for human health. However, the high demand for flying fish has resulted in overfishing, which poses a risk of reducing their natural population. Proper management of this commodity is necessary to minimize these risks. Effective management requires adequate information, including genetic diversity data. This study aims to determine the genetic diversity of flying fish in Southeast Sulawesi, specifically in the Banda Sea and Bone Bay populations. Tissue samples were collected from flying fish in the two populations during the study in March 2022. The results show that the genetic diversity values of flying fish in Bone Bay and the Banda Sea were 0.984 and 1.00, respectively, while the nucleotide diversity values were 0.021 and 0.018. High genetic diversity values and nucleotide diversity values were found between the two populations, with values of 0.990 and 0.020, respectively. Based on phylogenetic analysis, the two populations in Southeast Sulawesi are genetically similar.

Heterogeneous multi-stage accretionary orogenesis — Evidence from the Gunnison block in the Yavapai Province, southwest USA

Proterozoic rocks exposed in the southwestern U.S.A. represent one of the best examples of crustal growth by arc-related magmatism and accretionary orogenesis. Within the Southwest the 1.8–1.7 Ga Yavapai Province is widely regarded as a classic example of juvenile arc crust, however 1.8–2.5 Ga inherited zircon and Nd and Hf model ages have been recognized near Gunnison in central Colorado. These data have led to questions regarding the extent and nature of pre-1.8 Ga crustal material and the genesis of the Yavapai Province. We present evidence for a geochemically distinct, spatially restricted crustal block underlain by pre-1.8 Ga crust material (referred to here as the Gunnison block) in central to western Colorado within the Yavapai Province. The Gunnison block is characterized by 1.8–1.9 and 2.4–2.6 Ga inherited zircon, Pb isotopic systematics (μ = 9.8 ± 0.1, κ = 3.7 ± 0.1) elevated relative to 1.8 Ga depleted mantle values, 1.8–2.5 Ga Nd and Hf model ages, and a distinct pressure-temperature-time history. The geochemical data are consistent with mixing between juvenile 1.8 Ga and pre-1.8 Ga sources. The older crustal component is most similar to the isotopically enriched Mojave Province of eastern California and western Arizona, suggesting greater similarities between these provinces than previously recognized. Monazite and xenotime petrochronology indicate ca. 1.75–1.74, 1.72–1.69, 1.67, and 1.47–1.38 Ga tectono-metamorphic events. These data suggest that the Gunnison block accreted to other components of the Yavapai Province outboard of Laurentia at 1.75–1.74 Ga. The composite Yavapai Province was accreted to the margin of Laurentia during the 1.72–1.69 Ga Yavapai orogeny. Later overprinting is associated with the ∼1.68–1.60 Ga Mazatzal and ∼1.47–1.37 Ga Picuris orogenies. Identification of distinct crustal terranes within the Yavapai Province supports models involving multiple arcs and back-arcs that were progressively assembled prior to their accretion to Laurentia, perhaps akin to the present-day Banda Sea in Indonesia.

Optimizing chlo and sst for skipjack tuna fisheries in the banda sea and its surroundings using GAM and ECDF

This study aims to determine the optimal values of chlorophylla (Chlo) and Sea Surface Temperature (SST) for skipjack fishing (Katsuwonus pelamis) in the Banda Sea and its surroundings using the GAM model and ECDF function. The GAM model yields the formula CPUE = 33.07 + s(Chlo, edf = 7.14, Ref.df = 8.09) + s(SST, edf = 8.95, Ref.df = 8.99), with a significant value for Chlo of 0.58 mg/m3 and an SST of 28.26°C, as well as the highest CPUE value of 51.84. Due to the low performance of the GAM model, ECDF is used to determine the optimal values of Chlo and SST. The results of the Kolmogorov-Smirnov test on the ECDF value showed a p-value for Chlo of 0.0016 and SST of 4.45e-14 (p < 0.05). Thus, there was a significant difference between the f(t) and g(t) distributions at Chlo = 0.28 mg/m3 and SST = 30.57°C. K-Means analysis shows that the optimal value range for Chlo is 0.075 - 0.33 mg/m3 and for SST is 29.47 - 30.47°C. The optimal months are January to June as well as October, where the combination of SST and Chlo concentrations reaches levels that support the productivity of skipjack fishery. However, from July to September, lower SSTs begin to dominate, which can reduce fishery optimality, although some regions still have supportive Chlorophyll. In November and December, SSTs reach very high levels, potentially reducing productivity efficiency.

Simulated ocean circulation and its variability in the Northern Banda Sea from CROCO model

A simulation of 1/24º resolution 3-dimension regional ocean circulation of CROCO was successfully performed from 2015 to 2022 (8 years), covering the ENSO year in El Niño 2015 and La Niña 2022 in the northern Banda Sea (NBS). The model and data comparison of sea surface temperature/height reproduced the observed satellite datasets well, with correlation coefficients above 0.9. It is shown that the mean circulation in the NBS is fed by two inflows from western Buru and the Manipa Strait, resulting in a meandering eastward mean circulation with warmer water accumulated in the eastern NBS, associated with high current variance south of Buru and along the Manipa Strait. Seasonal variations in the oceanographic parameters were dominant in the study area. For example, during the southeast (northwest) monsoon period, the seawater temperature is minimum (maximum) and the salinity is maximum (minimum). Furthermore, the interannual timescale ENSO and IOD significantly modulated seawater temperature and salinity variation, particularly at the thermocline layer (110 m). Much cooler and saltier water is associated with El Niño 2015 and a positive IOD, in contrast to warmer and fresher water during La Niña 2022 and a negative IOD.