Mega L. Syamsuddin

Effects of El Niño–Southern Oscillation events on catches of Bigeye Tuna (Thunnus obesus) in the eastern Indian Ocean off Java

The effects of El Nino–Southern Oscillation events on catches of Bigeye Tuna (Thunnus obesus) in the eastern Indian Ocean (EIO) off Java were evaluated through the use of remotely sensed environmental data (sea-surface-height anomaly [SSHA], sea-surface temperature [SST], and chlorophyll a concentration), and Bigeye Tuna catch data. Analyses were conducted for the period of 1997–2000, which included the 1997–98 El Nino and 1999–2000 La Nina events. The empirical orthogonal function (EOF) was applied to examine oceanographic parameters quantitatively. The relationship of those parameters to variations in catch distribution of Bigeye Tuna was explored with a generalized additive model (GAM). The mean hook rate was 0.67 during El Nino and 0.44 during La Nina, and catches were high where SSHA ranged from –21 to 5 cm, SST ranged from 24°C to 27.5°C, and chlorophyll-a concentrations ranged from 0.04 to 0.16 mg m–3. The EOF analysis confirmed that the 1997–98 El Nino affected oceanographic conditions in the EIO off Java. The GAM results indicated that SST was better than the other environmental factors (SSHA and chlorophyll-a concentration) as an oceanographic predictor of Bigeye Tuna catches in the region. According to the GAM predictions, the highest probabilities (70–80%) for Bigeye Tuna catch in 1997–2000 occurred during oceanographic conditions during the 1997–98 El Nino event.

Interannual variation of bigeye tuna Thunnus obesus hotspots in the eastern Indian Ocean off Java

Remotely derived environmental variables, including sea surface height anomaly (SSHA), sea surface temperature (SST), chlorophyll-a (chl-a), eddy kinetic energy (EKE), mixed layer data set of argo float (MLD), Niño 3.4 index, and bigeye tuna catch data for the period 1997–2008, were used to analyse ocean climate variability and how they relate to the hotspots of bigeye tuna catch in the eastern Indian Ocean off Java. The empirical orthogonal function (EOF) was performed to obtain a more detailed structure of the spatio-temporal ocean variability in the region. The results showed that the first EOF modes of chl-a, SSHA, and SST accounted for 42.8%, 36.5%, and 27.4% of total variance, respectively, and these corresponded to the interannual signal. The maps of spatial patterns of the first EOF modes of SSHA, SST, and chl-a gave very typical values for cold-water SSHA, low SST, and high chl-a concentration along the southern coast of the Indonesian archipelago; and warm-water SSHA, high SST, and low chl-a concentration in the offshore region to make frontal areas along the latitudinal line around 10–12º S. The EOF analysis further revealed a strong relationship between the El Niño event and favourable oceanographic conditions, resulting in a significant increase in bigeye tuna catch. The average hook rate of 0.71 (0.43) was recorded during El Niño (La Niña). Major hotspots were located away from the confluence region and frontal areas around 11–16° S and 110–118° E and were thus demonstrated as the most favourable oceanographic conditions for bigeye tuna fishing in the eastern Indian Ocean off Java.

Seasonal Variations of Oceanographic Variables and Eastern Little Tuna (Euthynnus affinis) Catches in the North Indramayu Waters Java Sea

The remotely derived oceanographic variables included sea surface temperature (SST), chlorophyll-a (Chl-a) and Eastern Little Tuna (Euthynnus affinis) catches are used as a combined dataset to understand the seasonal variation of oceanographic variables and Eastern Little Tuna catches in the north Indramayu waters, Java Sea. The fish catches and remotely sensed data were analysed for the 5 years datasets from 2010-2014. This study has shown the effect of monsoon inducing oceanographic condition in the study area. Seasonal change features were dominant for all the selected oceanographic parameters of SST and Chl-a, and also Eastern Little Tuna catches, respectively. The Eastern Little Tuna catch rates have the peak season from September to December (700 to 1000) ton that corresponded with the value of SST ranging from 29 °C to 30 °C following the decreasing of Chl-a concentrations in September to November (0.4 to 0.5) mg m-3. The monsoonal system plays a great role in determining the variability of oceanographic conditions and catch in the north Indramayu waters, Java Sea. The catches seemed higher during the northwest monsoon than in the southeast monsoon for all year observations except in 2010. The wavelet spectrum analysis results confirmed that Eastern Little Tuna catches had seasonal and inter-annual variations during 2012-2014. The SST had seasonal variations during 2010-2014. The Chl-a also showed seasonal variations during 2010-2011 and interannual variations during 2011-2014. Our results would benefit the fishermen and policy makers to have better management for sustainable catch in the study area.

Building up the database of the Level-2 Java Sea Ecoregion based on physical oceanographic parameters

The Java Sea (JS) is one of the sea with unique characteristic with especially in biodiversity and oceanographic condition. The purpose of this research is to identify the EL into level 2 in Java Sea based on oceanographic condition. The Java Sea, which covers an area of 467,000 Km2 with an average depth of 50m, is located on the Southeastern part of the Sunda Shelf. This research uses the temperature and salinity data provided by the INDESO, the sea surface height (SSH) data downloaded from the HYCOM website, and the level 2 Java Sea ecoregion shape file data from the Indonesian seas delineation team. The physical oceanographic conditions of the level 2 Java Sea ecoregions are influenced by the moonsun and their respective geographical positions. The results showed that the distribution of temperature, sea current, salinity, and Sea Surface Height differed in each Java Sea Ecoregion level 2 because it is influenced by the geographical and astronomical location of each Java Sea Ecoregion level and influenced by the monsoon that exists over Indonesia. In the east of Java Sea influence from Makassar Strait and in the west affected by Karimata Strait. Within the region, EL 6.1. (Sunda Strait), the physical oceanography condition is slightly different from other Java EL because it is strongly influenced by the Indian Ocean.

Variabilitas temperature laut pada fase IOD (Indian Ocean Dipole) di Perairan Barat Sumatera menggunakan data Argo Float

The objective of the research was to analyze the vertical variability of the water column in the West Sumatra waters. The data used to analyze the vertical variability was the temperature data sets from Argo float instruments which were operated from 2009 to 2011 in the West Sumatran sea region. The secondary data that used was the geostrophic current data sets which obtained from the Jason image satellite also sea temperature anomaly data. The method used in this research is by analyzing temporally and spatially and then describing while comparing the data. The result of the research showed that IOD formed from June to July with the peak of IOD was from September to November and the disintegration starts in December. The SST average on 2009 (Neutral IOD) during peak phase of IOD was 29.060C, in 2010 (Negative IOD) the SST mean is 28.690C, in 2011 (Positive IOD) the SST mean was 28.790C. The result from spatial analyzes showed that the strong IOD was the main reason for the movement of the mixed layer in West Sumatra waters, so the warm water cannot be found around the West Sumatra waters. The upper boundary depth of thermocline during peak phase of 2009’s neutral IOD starts from September was on 82.59 m, in October was 86.12 m and in November was 89.5 m. In Septemeber 2010 the upper thermocline boundary was found on 89.06 m deep, in October was 104.05 m, and in November was 107.36 m, the thermocline got deeper because the input of water masses from West Indian Ocean intensifies because of negative IOD event. In September 2011 the upper thermocline boundary was found on 64.16 m, in October was 75.35 m and in November was 79.88 m. The thermocline found more shallow because the mixed layer on East Indian Ocean moved westward so the thermocline lifted up to fill the water column emptiness. Penelitian ini bertujuan mengkaji variabilitas kolom air secara vertikal di perairan Barat Sumatera. Data yang digunakan yaitu data suhu dari instrumen Argo float yang beroperasi di perairan Barat Sumatera tahun 2009 – 2011. Data pendukung yaitu data arus geostropik yang diperoleh yang diperoleh dari citra Jason selain itu digunakan data suhu anomali laut. Metode yang digunakan adalah analisis temporal dan spasial serta deskriptif komparatif. Hasil penelitian menunjukkan proses pembentukan IOD terjadi pada Juni – Agustus kemudian mencapai puncak pada September – November dan proses peluruhannya pada Desember. Rata – rata SPL pada fase puncak tahun 2009 (IOD netral) yaitu 29.06 0 C; pada 2010 (IOD negatif) yaitu 28.69 0 C; dan pada 2011 (IOD positif) yaitu 28.79 0 C. Berdasarkan analisis spasial IOD dengan intensitas kuat mengakibatkan pergerakan massa air hangat melewati perairan Barat Sumatera sehingga tidak terdeteksi lagi di lokasi ini. Batas atas termoklin pada fase puncak IOD 2009 (September) yaitu 82.59 m; Oktober sekitar 86.12 m dan November mencapai 89.5 m. Selanjutnya pada 2010 yaitu pada September sekitar 89.06 m; Oktober sekitar 104.05 m dan November mencapai 107.36 m. Terlihat, termoklin semakin dalam karena massa air hangat dari Hindia Barat yang mengisi perairan Barat Sumatera menjadi semakin kuat pada fase IOD negatif. Sebaliknya, pada September 2011 termoklin berada pada kedalaman 64.16 m; Oktober pada kedalaman 75.35 m dan November sekitar 79.88 m. Pada periode ini termoklin terdeteksi lebih dangkal karena lapisan mixed layer bergerak ke Hindia Barat dan kekosongannya diisi lapisan termoklin.

Detection of pelagic habitat hotspots for skipjack tuna in the Gulf of Bone-Flores Sea, southwestern Coral Triangle tuna, Indonesia

Using remote sensing of sea surface temperature (SST), sea surface height anomaly (SSHA) and chlorophyll-a (Chl-a) together with catch data, we investigated the detection and persistence of important pelagic habitat hotspots for skipjack tuna in the Gulf of Bone-Flores Sea, Indonesia. We analyzed the data for the period between the northwest and southeast monsoon 2007–2011. A pelagic hotspot index was constructed from a model of multi-spectrum satellite-based oceanographic data in relation to skipjack fishing performance. Results showed that skipjack catch per unit efforts (CPUEs) increased significantly in areas of highest pelagic hotspot indices. The distribution and dynamics of habitat hotspots were detected by the synoptic measurements of SST, SSHA and Chl-a ranging from 29.5° to 31.5°C, from 2.5 to 12.5 cm and from 0.15 to 0.35 mg m-3, respectively. Total area of hotspots consistently peaked in May. Validation of skipjack CPUE predicted by our model against observed data from 2012 was highly significant. The key pelagic habitat corresponded with the Chl-a front, which could be related to the areas of relatively high prey abundance (enhanced feeding opportunity) for skipjack. We found that the area and persistence of the potential skipjack habitat hotspots for the 5 years were clearly identified by the 0.2 mg m-3 Chl-a isopleth, suggesting that the Chl-a front provides a key oceanographic indicator for global understanding on skipjack tuna habitat hotspots in the western tropical Pacific Ocean, especially within Coral Triangle tuna.