Pendugaan Distribusi Spasial Ikan secara Hidroakustik di danau Ranau, Sumatera

Abstract

Ranau Lake is classified as volcanic lake with maximum depth of 229 m. abiotic factors like temperature and oxygen hold the important role in organism distribution expecially in the deep lake. The aimed of this study was to obtain the distribution of fish schooling, as a part of fisheries management in Ranau Lake. Research was conducted in Ranau Lake that covered South of Ogan Komering Ulu (OKU) and West of Lampung, in November 2012 and February 2013. Acoustic survey covered all part of lake that lies in South of OKU and West of Lampung. Acoustic data acquisition has done continuously during cruise with motor vessel velocity range about 5-10 knot. Acquisition track covered the width of lake in order to be analyzed spatially from the start point in South of OKU. Acoustic data was analyzed by using Echoview 4.8. Data analyzed from 5-125 m depth that divided into 5 layers. Elementary Sampling Distance Unit (ESDU) used by 100 ping. Data was limited by minimum threshold -90 dB and maximum threshold -20 dB. Hydroacoustic instrument used in this study are the split beam echosounder Simrad EY60, length of fish was measured by equipment of fish length measurement, Dyssolved Oxygen (DO) was measured by DO meter, Nansen bottle was used to take sample water, temperature of water in specific depth was taken by CTD. Based on Sv value, it is known that fish doesn’t distributed evenly. Fish group distributed in littoral zone of lake spatially. Small group found in west part of lake, while the largest group concentrated in south east and east part of lake. Vertical distribution showed that all of size class (small to large) found in 5 to 75 m depth (-90 to -34 dB), while the largest size found in 101 to 125 m depth (-76 to -35 dB). Temperature and Dissolved Oxygen show the unstratified water layer. Both of Coefficient of correlation between Sv and DO (71%) also Sv and temperature (74%) show the strong relationship respectively. Target strength (TS) vertical distribution show that the larger fish (28-50 cm) found in 51-100 m depth and small fish found in 5-50 m and 101-125 m (0.9-11.3 cm). The present of target in water colomn are link to the food abundance (plankton), metalimnion layer from micro stratification as a boundary of nutrient movement from the layer above and below it, adaptation form of the lower temperature and oxygen also prey avoiding. Strong correlation showed between TS and temperature (63.4%) and TS with plankton abundance (55.2%).