Judul: Pendekatan metode hidroakustik untuk analisis keterkaitan antara tipe substrat dasar perairan dengan komunitas ikan demersal, The hydroacoustic method approach for interrelatedness analysis of sea bottom substrate type with demersal fish community
Abstrak: The sea bottom substrate has an important role for biota life in sea bottom area. Sea bottom is habitat for benthic, demersal fishes and other marine biota. Therefore, the accuracy and precision to classify the sea bottom substrate become essential. However, data and information on sea bottom substrate type and its relation to biota, particularly demersal fishes, are scanty. This condition is caused by the used method, in general, is limited to grab method which is only covered and mapped a very limited area based on sea bottom sampling station. Nowadays, the new method to obtain sea bottom substrate information has been developed very well, that is hydroacoustic method. Sea bottom substrate, sediments, benthic and vegetations can be accessed by using echosounder and processed digitally. The difference of sea bottom substrate types can be distinguished through the coarseness of topography and hardness of sea bottom substrate which consisted of coral, stone, sand, mud, and clay. The research objective is to analyze the interrelatedness of sea bottom substrate type with demersal fish community by hydroacoustic method approach. Therefore, the obtained data consisted of sea bottom substrate, demersal fish, oceanographic data, and other related data. Those data were obtained from several locations, i.e. Belitung Island in the years of 2002 and 2005, Java Sea (2002 and 2005), East Borneo (2004), and around Pari Island of Seribu Islands (2007). Data processing was done by using several echo data post processing programs, namely Simrad EP-500, Echoview version 3.5 and Simrad BI-60. The hydroacoustic data of sea bottom substrates and grab sampling results were classified based on Principal Component Analysis (PCA) and Cluster Analysis. The relation between the abiotic factors and demersal fish community was overlaid descriptively over horizontal distribution map of sea bottom substrate and demersal fish species by using surfer program. The result of bottom sounding shows that the harder the sea bottom substrate, the stronger the backscattering value. On the opposite, the softer the sea bottom substrate, the weaker the backscattering value. Based on PCA and cluster analysis, it is known that strongest backscattering strength value of sea bottom substrate is from coral substrate, followed by backscattering values from sand, muddy sand, sandy mud, and mud, which is weaker respectively. The obtained sea bottom substrate backscattering values can be applied to assess and distinguish sea bottom substrate type in other sea bottom area. The hydroacoustic detection of demersal fishes and swept area by trawl give information of fish density higher at shallow water (<36,5 m) and have small value of fish target strength. These small fish was identified as Leiognathus splenden (“ikan pepetek”). The relation between abiotic factors and demersal fish community in Java Sea shows that: 1) Fish species of Leiognathus splenden does not live in all sea bottom with muddy substrate. This fish was found in the muddy area in a shallow water near coastal zone. 2) Fish species of Upeneus sulphureus has high appearance frequency at all trawl swept area stations. This fish was encountered in a muddy substrate and the total weight of fish (swept by trawl) is gradually higher
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