DISTRIBUTION AND DENSITY OF DEMERSAL FISHES IN YOUTEFA BAY, PAPUA, INDONESIA: A STUDY USING HYDROACOUSTIC TECHNOLOGY

A study was conducted to estimate the distribution and density of demersal fish in Youtefa Bay, Papua, Indonesia, using hydroacoustic technology. The hydroacoustic survey was carried out using a single beam echosounder SIMRAD EK-15 which operates at a frequency of 200 kHz. The hydroacoustic data was processed using Echoview software with a threshold between -70.00 to -34.00 dB. Schooling fish were detected at a maximum distance of 3 m from the seabed, with average volume backscattering strength ranging between -60.13 and -42.01 dB. The demersal fish density in the Youtefa Bay ranged from 0.09 to 42.19 fish m-3 with an average density of 12.62 fish m-3. The schools of demersal fish were dominantly detected in the coastal waters of Enggros Village to Abe Pantai Village. The condition of substrate and water depth seems to influence the spatial and vertical distribution of demersal fish in the Youtefa Bay.

FISH POPULATION OF GORNOSLINKINSKAYA RIVERBED DEPRESSION OF THE LOWER IRTYSH IN WINTER PERIOD

Fish distribution was studied using sonar computerized complex in the deep part of the water column of Gornoslinkinskaya riverbed depression in winter. In the horizontal aspect there was estimated the number of fish registrations, in the vertical aspect the fish density was analyzed in three conditional horizons of the water column: surface, pelagic, bottom. Additionally, the bathymetric characteristics of the riverbed depression in the fish registration areas were evaluated. In the study period the depths were lower than 40 m. On the trajectory of the planned research route there were drilled holes in ice with a motor-drill (screw D=200 mm). Hydroacoustic survey was performed for each drilled hole. To control the species composition control fishing was carried out by gillnets. The hydroacoustic survey files were further processed in the laboratory using AsCor and Taxonomy applications for carrying out dimensional-taxonomic identification of fish. It has been established that fish inhabits the water area of the riverbed depression non-uniformly, both horizontally and vertically. The density of fish in the horizons of the investigated water area is distributed in descending order: pelagic - 105 sp./ha, bottom - 61 sp./ha, surface - 18 sp./ha. The features of the taxonomic distribution of fish are the following: in the surface horizon there are not found percid species and non-identified fish, their shares are decreasing from the bottom to pelagic horizons. The groups of cyprinids and whitefish-pike fish are registered throughout the water column of the riverbed depression: their shares increase from the bottom to the surface. The uneven distribution of different taxonomic fish groups in the investigated water area can be explained by the ecological features of different species in winter, as well as their trophic-defensive behavior.

DIMENSIONAL AND TAXONOMIC STRUCTURE OF FISH POPULATION OF THE KONDINSKAYA RIVERBED DEPRESSION

On the basis of modern hydroacoustic techniques the article presents features of the dimensional-taxonomic structure and vertical distribution of fish in the water area of one of the largest riverbed depressions in the lower reaches of the Irtysh river - Kondinskaya (Khanty-Mansiysky district, Tyumen region, Russia). There have been analyzed the conditioned water column horizons: from the surface to the bottom < 10 m, 10-20 m, 20-30 m, > 30 m. Maximum depth of the riverbed in the studied period exceeded 43 m. Research work was done by software-hardware sonar system AsCor. To perform hydroacoustic survey from the small boat in the investigated water area there were made displacements on a grid of transects (in zigzags). Recorded information of the hydroacoustic survey was processed in the laboratory using special software programs AsCor and Taxonomy which enable remote dimensional-taxonomic identification of fish with calculation of their density and number. It has been established that in each subsequent depth horizon the proportion of planktivorous fish (Cyprinidae) decreased in direction from the surface to the bottom; the proportion of predatory fishes (Percidae, Coregonidae, Esocidae), and a group of unidentified fishes (Acipenseridae, Lotidae), on the contrary, increased. The features of vertical distribution and taxonomic structure in the water column of the riverbed depression is an element of the survival strategy, primarily for juveniles of planktivorous species. More than 90% of fish from the total recorded population are concentrated at depths up to 20 m. In the research period among the fish population of the riverbed depression cyprinids dominated, in the size groups there prevailed individuals with body lengths up to 15 cm.

Research on Accuracy of a Boat Position Determination Using GNSS Techniques in Kinematic Mode

The main aim of this work is research on the use of satellite positioning GNSS – RTK / RTN techniques to estimate the trajectory of a hydrographic boat. Modern hydrographic boat is the carrier of advanced bathymetry system, integral with GNSS positioning techniques. The key elements of the correct execution of the hydroacoustic survey are two elements: the height of the water surface and precise determination of the position in the moment of performing depth measurement. Integrated Bathymetric System (ZSB) is installed on a floating platform which is in constant motion. To obtain correct results of the hydroacoustic survey, it is necessary to know the precise (3D) position of the platform. In this paper the author presented his own research on the precise determination of accurate and reliable trajectory of a boat. The proposed method uses Real Time Kinematic (RTK) techniques of satellite positioning GNSS (Global Navigation Satellite Systems). The article presents examples of the results obtained during the research work at the largest Polish river.

ESTIMASI HAMBUR BALIK DASAR PERAIRAN DAN SUMBER DAYA IKAN DEMERSAL MENGGUNAKAN METODE HIDROAKUSTIK

Survei hidroakustik dilakukan pada bulan Oktober 2002 dengan menggunakan kapal penelitian Mutiara IV (115,19 GT) milik Balai Riset Perikanan Laut, Muara Baru-Jakarta. Alat hidroakustik yang digunakan adalah echosounder EY-500 dengan program pengolahan data EP-500, menu analisis expanded bottom dan bottom layer. Data yang diperoleh adalah nilai back scattering volume dari dasar perairan yang selanjutnya disebut dengan hambur balik dasar perairan, target strength dan densitas ikan demersal dilengkapi dengan data trawl untuk verifikasi. Tujuan penelitian ini adalah untuk mengetahui nilai hambur balik dasar perairan, dan penyebaran ikan demersal secara hidroakustik. Penyebaran nilai hambur balik dasar perairan sepanjang lintasan penelitian yang diperoleh berkisar antara -38,29 sampai dengan -20,02 dB, dengan rata-rata -28,09 dB. Kisaran nilai target strength dari –51,00 sampai dengan –24,01 dB, dengan rata-rata -41,11 dB, adapun nilai densitas ikan berkisar 0,001 sampai dengan 1,640 g m-3 dengan rata-rata 0,342g m-3. Hydroacoustic survey was conducted in October 2002 by using research vessel Mutiara IV (115,19 GT) owned by Marine Fishery Research Institute, Ministry of Marine Affairs and Fisheries. The hydroacoustic apparatus used echousounder EY-500, used software EP-500 for data processing with menu for analyzing the expanded bottom and bottom layer. The obtained data were backscattering volume as sea bottom reflection, target strength and density of demersal fish. The research objectives are to analyze the sea bottom reflection and to explore demersal fish resources by hydroacoustic method. The distribution of sea bottom reflection along cruising area ranges between -38,29 to -20,02 dB, with average value of -28,09 dB. The range of target strength values is distributed between -51,00 and -24,01 dB, with and the average of target strength -41,11 dB. The density of fish ranges between 0,00 dB until 1,64 g m-3 with 0,33 g m 3 in average.