Mapping chlorophyll-a of Southern Java Waters using Seawifs and MODIS Aqua Abdul Basith Hydro-Oceanography Laboratory, Department of Geodetic Engineering, Gadjah Mada University Jln Grafika no. 2 Yogyakarta, Ph. +62 274 520226, Email: abbasith@yahoo.com Nani Hendiarti The Agency for Assessment and Application of Technology Syohraeni Graduate student of Department of Geodetic Engineering, Gadjah Mada University Abstract Four years of Seawifs and Modis Aqua data, spanning from year 1998 to 2000 and year 2004, have been used to investigate the spatial and temporal evolution of chlorophyll-a concentration and its relation to big fish pelagic catch in southward waters of Java. The data were interpreted during southern east monsoon (June-August) and season of transition II ( September-November) and also with the data of big fish pelagic catch. The algorithm for estimate chlorophyll-a concentration is Ocean Color version 4 (OC 4) and atmospheric correction algorithm by the multi-scattering 670/865 nm with NIR iteration. The algorithm was validated so that its information is accurate. By Analyzing of relationship can be generated the relation of the total fish catch to chlorophyll-a concentration. The Chlorophyll-a concentration in southern monsoon (0, 380 mg/m3) is higher than transition II season (0, 345 mg/m3)). Generally, the Chlorophyll-a concentration is slightly higher because influenced physical process in waters during southern monsoon. Height concentration of derived Chlorophyll-a correspond to high big pelagic catches, specially cakalang fish. But differing from tuna, that Tuna fish catches is relatively constant in each season. It means not influenced by high abundance Chlorophyll-a concentration. INTRODUCTION Indonesia has marine fish resources about 6.6 million tons/year. The potential marine resources, however, have not been caught optimally because it is only about 21 % of them those having been exploited. The unproductive utilization of marine resources is caused not only by limited fishing catch instrument but also by poor fishing technology to find good fishing grounds (Ningsih, et.al., 2002) Based on along history of a fish stock abundance in tropical and in temperate marine waters, it has been recognized that there exists an important relationship between environmental factors, such as monsoon system that affect sea surface temperature and Chlorophyll variability, and a fish stock abundance (Sitepu and Dahuri, 1995). On the other hand, tuna is a major fishery in many parts of the world. It is a pelagic fish and a good swimmer. If the population of tuna is higher in their preferred environments, then we may correlate the tuna and other big pelagic fish, such as Cakalang fish, catch statistic against the sea surface temperature (SST), sub surface temperature, ocean color such as sea surface chlorophyll (SSC), ocean current, thermocline depth,etc. Of course, SST is an important factor in the fish catch. To provide usable information to fishermen about the fishing ground, it will be much more effective by using the satellite sensed SST imageries and satellite ocean color imageries (Cho, et.al., 2002). However, SSC from ocean color satellite such as Seawifs and MODIS Aqua, is also another important factor to investigate the fishing ground of big pelagic fishes such as Tuna and Cakalang Fish. In this paper, we start with SSC and fish catch. AREA INVESTIGATIONS, MATERIALS AND METHODS The area of investigation covers southern waters of Java Island which is part of Indian Ocean. Fig. 1 shows the area of investigations and locations of fish catch.  Figure 1. Map of the area of investigation including positions of fish catch The Sea Surface Chlorophyll-a (SSC) data that we use here are monthly mean SSC derived from Seawifs and MODIS Aqua imageries data spanning from 1998 to 2004. Seawifs data used here is a level-3 that has contained chlorophyll-a concentration information. But, MODIA aqua used here is a level-1a and 1b that have to be processed to next level, level 2, so that chlorophyll-a information can be extracted. SEADAS (SEAawifs Data Analysis System) was used to process low level MODIS Aqua data using multiscattering algorithm with NIR iteration of 670/865 channels. In situ big pelagic fish catch data from DKP (Ministry of Marine Affairs and Fisheries of Indonesia) from 1998 to 2004 was used to relate between the chlorophyll-a abundant and fish catch. The investigation based on the pattern of temporal chlorophyll-a variation and the corresponding big pelagic fish catch of the same spanning years. Intensive attention is focused during east monsoon (June and August) and transitional season (September-November). RESULT AND DISCUSSION Fig. 2 and 3 show respectively images of SSC during east monsoon and transitional season. Fig. 2 shows that the concentration of SSC during monsoon season in 1998 is relatively poor compared with SSC in 1999 and 2000. There is, of course, small abundant of SSC in southern coast Banyuwangi, East Java. From both years, the SSC concentration in July and August are higher than in June. The abundant of SSC still take place in southern coast Banyuwangi, East Java. The monthly averaged of SSC concentration in this season from all verification points is 0.380 mg/m3.  Figure 2. Sea Surface Chlorophyll-a from Seawifs imageries during east season from 1998 to 2000  Figure 3. Sea Surface Chlorophyll-a from Seawifs imageries during transitional season from 1998 to 2000 Meanwhile, from fig 3 we can see that the abundant of SSC during transitional season happened along coast of Java Island and spreading southward. It mainly happened in June and July. In August, the concentration of SSC is smaller than the previous months. The monthly averaged of SSC concentration in this season from all verification points is 0.345 mg/m3. The amount of SSC concentration from two seasons is relatively the same. It may be explained that the strong influence of east monsoon is still working during transitional season. The SSC concentration obtained from those two seasons are then compared to big fish pelagic catch especially Tuna Fish and Cakalang. There are strong relation between the high concentration of chlorophyll-a and Cakalang fish catch for all years of study. Meanwhile, it is difficult to find the relation between high concentration of chlorophyll-a and Tuna catch. It can be inferred that there is a little correlation between the two. Figure 4 shows the correlation between Cakalang fish catch and concentration of chlorophyll-a in 1998. It also shows low correlation between SSC and Tuna catch. The east monsoon gives high SSC concentration and Cakalang fish catch.  Figure 4. Big pelagic fish catch (Tuna and Cakalang) vs monthly Sea Surface Chlorophyll-a CONCLUSION Above analysis shows that there is a relatively the same abundant of Sea Surface chlorophyll-a during east monsoon and transitional season about 345-380 mg/m3. The higher SSC concentration happened during east monsoon season. Meanwhile, we can find a strong correlation between Cakalang fish catch and the abundant of SSC concentration. This is not the case for Tuna fish catch which has low correlation correspond to temporal SSC concentration. REFERENCES
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