19 INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, 2 7 SEPTEMBER 2007

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1 19 INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, 2 7 SEPTEMBER 2007 INVESTIGATIONS ON THE STRUCTURE OF FISH STOCKS IN ATATURK DAM LAKE BY USING CLASSICAL AND ACOUSTICAL APPROACHES AKOGLU, Ekin; GUCU, Ali Cemal Institute of Marine Sciences, Middle East Technical University, P.O. Box 28, 33731, Erdemli, Mersin, Turkey; ekin@ims.metu.edu.tr; gucu@ims.metu.edu.tr ABSTRACT Ataturk Dam, of which construction was completed in 1992, formed an artificial lake located on e Euphrates River, wiin e borders of two provinces Sanliurfa and Adiyaman, in e sou western part of Turkey. The fish fauna of e lake consists of 16 species. Some of ese species are natural inhabitants of e river Euphrates. Oer species found today in is reservoir are artificially introduced in e 1990s by Turkish General Directorate of State Hydraulic Works. In e scope of is study, e structure of fish stocks present in e Ataturk Dam Lake was investigated by using two fundamental meodologies. Investigations were based upon gill net sampling, for e determination of fish species composition, and to assist in e data analysis collected by echo sounder. For acoustical investigations a SIMRAD EY500 Single Beam 120 khz echo sounder was used. According to e results, it was found out at a small planktonivorous fish species, Acanobrama marmid (Heckel 1843) was dominant in abundance wi more an 50 % roughout e lake. In biomass, 3 fish species, Capoeta trutta (Heckel 1843), Carasobarbus luteus (Heckel 1843) and Acanobrama marmid (Heckel 1843), were dominant. INTRODUCTION Ataturk Dam is e centrepiece of e 21 dams of e Sou eastern Anatolia Project of Turkey and is built on e Euphrates River and completed in It is one of e world's largest ear and rock fill dams, wi e embankment 184 m high and 1820 m long. The Ataturk Dam Lake has a total area of 817 km². Reservoir capacity is 48.7 km3. Drainage area is about ha. Ataturk Dam Lake is a multi purpose reservoir for hydro power energy, irrigation and domestic and industrial water supply. Therefore fishing in e lake is forbidden ever since its establishment in However, over e years, against e fishing ban, illegal fishing by e local people has continued in e lake. Since Ataturk Dam Lake is an artificial reservoir and e topography of e area upon which e lake's basin is located is alternating significantly (Figure 1), only one type of fishing gear, namely gill netting, is applicable roughout e lake.

2 Figure 1. Landsat images of e Ataturk Dam reservoir In is study, e baymetrical structure of e lake was researched and wi parallel gill net samplings along wi e acoustical investigations, fish stocks' structures were investigated. MATERIALS AND METHODS The study was carried out by an echo sounder and gill net sampling across e lake. The acoustical data were collected in 2 discrete cruises carried out between April 21st April 27, 2005 and September 20 September 27, 2005, respectively (Figure 2). Gill net sampling was carried out simultaneously wi e acoustical sampling. Figure 2. Transects covered by e acoustical sampling 2

3 In total, data from 2 different surveys were collected. A SIMRAD EY500 single beam echo sounder wi 120 khz operating frequency was used. Before each survey, e echo sounder was calibrated wi a standard metal sphere. The data collected from e acoustical surveys were recorded into a computer hard disk. The data en converted from binary format to ASCII format in order to be processed. From e converted data, deps corresponding to every geographical coordinate point were extracted. Then e baymetry of e lake s bottom was mapped. The corrected echogram values corresponding to e pelagic and bottom areas by e echo sounder were collected via a script written in MATLAB and converted to Sa (area backscattering) values using Equation 1. Eq. 1 Then calculated Sa values plotted against dep. Since ere is no significant differentiation in e Sa distribution dep ranges were determined arbitrarily. For each range, e mean Sa value was calculated. The mean Sa values for every region across e lake was processed wi each regional specific TS distribution tables and fish abundances per hectare were calculated. Afterwards, e abundance values were converted e biomass values by using gill net data. Gill net sampling was carried out in predetermined stations Figure 3. Figure 3. Gill net sampling stations Two fleets of gill nets were set simultaneously wi e hydro acoustics sampling schedule across e lake overnight. The fleets contained nets wi 9, 11, 22, 30, 40, 50 and 60 mm knot to knot mesh sizes. The single nets were 1 meter in height and lengs were 10 meters for e ree smallest mesh sizes and 100 meters for e remaining 4 bigger mesh sizes. Bo of e two fleets were set in e pelagic area beginning from ground zero to approximately 20 meters 3

4 deep. Every next morning e catch was counted and e fish measured (Weight and total leng to e nearest mm). Since gill nets were size selective, corrections were made to leng frequency distributions of species and leng weight relationships for each species were calculated accordingly. RESULTS The baymetrical contour map of e Ataturk Dam Lake was constituted (Figure 4). According to e sounder detected deps e maximum dep of e lake was about 152 meters and average dep was about 50.5 meters. Figure 4. Baymetrical map of e Ataturk Dam Lake In calculation of biomass and abundance distribution, e lake is divided into subareas according to e fishing zones defined by e Turkish General Directorate of State Hydraulic Works. 4

5 Figure 5. Regions determined by e Turkish General Directorate of State Hydraulic Works in e lake area. In hauls Acanobrama marmid was e most abundant fish roughout e lake. This fish is a small, planktonivorous pelagic fish and has no significant economic value in e market. The calculated biomass distribution of e economically important fishes and some oer fishes roughout e lake is in Table 1. Table 1. Biomass distribution of some economically important fishes along wi e most abundant fish species in e lake. Values are in kilograms. Fishes Regions A. marmid C. mossulensis C. luteus C. macrostomus C. trutta M. abu Sum

6 CONCLUSIONS It has long been known at fish can be detected remotely rough e reflection of sound waves. Following e pioneering work of Sund (1935), acoustical technology has had a major impact on fishing. Since en, location of fish by underwater acoustics has become an increasingly important aspect of commercial fisheries (Misund, 1997). In fisheries research, acoustical techniques have become increasingly important over e years (MacLennan and Forbes, 1984). This study is subject to some constrains due to e application of single beam echo sounder in acoustical research. In single beam application, direct and precise estimation of TS distribution of e fish in e water column is not possible since one cannot know e exact position of e fish wiin e insonified water column. If fish is on e axis of e beam, obtained TS values would be correct, oerwise e TS values of single individuals would be underestimated. In order to obtain a more precise biomass distribution results, ese studies should be carried out by dual or multi beam echo sounders. Anoer problem encountered rough e process phase of e acoustical data was e bottom separation. Since ere were a lot of binary files (about 300) created by e sounder, it was very time consuming to redefine e bottom by using graphical post processing programs. Therefore, a mini computer program was written in MATLAB programming language to automate e redefining bottom process. The MATLAB script seems to work fine down to e dep of 80 meters. Below 80 meters dep, due to e increasing distance, e averaging of e Sv (volume backscattering) values outputs high variance. Therefore, in is study e echoes below e dep of 80 meters were not considered. Furer study and work should be placed upon e MATLAB script to increase e performance of e redefining bottom procedure. References: [1] Sund, O Echo sounding in fisheries research, Nature 135, [2]Misund, O. A., Underwater acoustics in marine fisheries and fisheries research. Rev. Fish Biol. Fish. 7, [3] MacLennan, D. N., and Forbes, S. T Fisheries acoustics: a review of general principles, Rapp. P. V. Reun. Cons. Int. Explor. Mer 184,