Indian J. Fish., 67(1): 30-35, 2020 30 DOI: 10.21077/ijf.2019.67.1.88578-05 Distribution and density of demersal fishes in Youtefa Bay, Papua, Indonesia: A study using hydroacoustic technology BAIGO HAMUNA1, SRI PUJIYATI2, LISIARD DIMARA1, NYOMAN METTA N. NATIH2 AND ALIANTO3 1Department of Marine Science and Fisheries, Cenderawasih University, Kamp Wolker Street Jayapura City - 99351, Papua, Indonesia 2Department of Marine Science and Technology, Bogor Agricultural University, Lingkar Kampus IPB Bogor - 16680, West Java, Indonesia 3Department of Fisheries, University of Papua, Gunung Salju Street, Manokwari 98314, West Papua, Indonesia e-mail: [email protected] ABSTRACT 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 -3m 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. Keywords: Demersal fish, Fish schooling, Hydroacoustic technology, Volume backscattering strength, Youtefa Bay Introduction The objective of the present study was to apply Youtefa Bay in Papua Province, Indonesia supports hydroacoustic technology to estimate the distribution and several fish species. But the local fishermen have not been density of demersal fish in Youtefa Bay, Indonesia as such able to utilise the potential of these resources optimally, information is very important for fisheries management. due to lack of accurate information on fish distribution in The results of this study can support formulating strategies the Bay. Hydroacoustic technology has been often utilised for the management of demersal fish resources in the for fish characterisation and classification and fisheries Youtefa Bay and is expected to help the local fishermen surveys (Davison et al., 2015; Thompson et al., 2015; in the Youtefa Bay to identify potential areas for demersal Melvin, 2016; Pujiyati et al., 2016; Wurtzell et al., 2016) fishing activities. and for analysis and mapping of the seabed (Pujiyati et al., 2007; Cutter and Demer, 2014; Calvert et al., 2015; Materials and methods Hamuna et al., 2018a, b). This study was conducted in April 2017 in Measurement of fish population density has important Youtefa Bay waters, in Jayapura, Papua, Indonesia. applications especially for studying and management of Hydroacoustic data recording was carried out in fisheries (Gunderson, 1993). Hydroacoustic technology Youtefa Bay along 12.51 km of the survey line (Fig. 1), is considered to be an efficient fishery survey method to using a single beam echosounder SIMRAD EK-15 overcome the limitations of traditional survey methods (200 kHz). Instrument specification and parameter (Hewitt et al., 2002) and has several advantages compared setting during hydroacoustic data recording are listed in to the swept area trawl method because it can detect Table 1. Hydroacoustic data acquisition was carried out wider water columns continuously and simultaneously continuously with a maximum ship speed of 4-5 knots. (McQuinn et al., 2005). The utilisation of hydroacoustic technology for fishing is one of the effective methods to The Echoview 4.8 software was used for processing detect the existence of fish directly, quickly and accurately data. The elementary sampling distance unit (ESDU) used (Simmonds and MacLennan, 2005) and to study the fish in data processing was 100 pings (Mello and Rose, 2009) and their habitat (Pujiyati, 2008). and the hydroacoustic data obtained was divided into 320 Baigo Hamuna et al. 31 140041'0"E 140042'0"E 140043'0"E 140042'0"E ........... Cruise Track 35'0"S 35'0"S 0 0 Fish density: Tobati < 10 fish.m-3 10-20 fish.m-3 20-30 fish.m-3 36'0" 2 0 -3 36'0" 2 Enggros > 30 fish.m 0 Yos Sudarso Bay 2 2 Youtefa Bay 37'0"S 0 37'0"S 2 0 Abe Pantai 38'0"S 0 Nafri 38'0" 2 0 2 2 140041'0"E 140042'0"E 140043'0"E 140042'0"E Fig. 1. Hydroacoustic cruise track and spatial distribution of demersal fish inYoutefa Bay, Indonesia Table 1. Parameters settings during the hydroacoustic survey TS determines the accuracy of estimates of fish density Parameter Value and abundance (Kim et al., 2018). Data on the length Frequency (kHz) 200 of demersal fish (L) obtained in this study was used Power transmit (watt) 50 to determine the TS value of demersal fish using the Beam width (deg) 26 following equation (Hjellvik et al., 2003): Transducer depth (m) 0.5 TS = 20 log L - 68 Ping rate (Hz) >40 Pulse length (ms) 0.160 The TS value thus obtained was converted into a Pulse duration (ms) 0.128 backscattering cross section (<σbs>) by linearising the Sound velocity (m s-1) 1545.87 TS value using the following equations (Simmonds and Absorption coefficient (dB -1m ) 0.01872 MacLennan, 2005): Transducer gain (dB) 14.20 TS = 10 log10 (σbs) (TS/10) ESDU. The processing data used a minimum threshold σbs = 10 of -70.00 dB and a maximum of -34.00 dB (Manik and The result of data processing was an acoustic data Nurkomala, 2016; Park et al., 2016). Considering that matrix of Sv from fish schooling. The logarithmic equation the habitat of demersal fish is at the seabed or near the for measuring Sv value and volume backscattering seabed, integration and analysis of hydroacoustic data was coefficient (s ) is as follows: focused at a distance of 3 m from the seabed. Distance v from the seabed was added to 0.12 m (cτ/2; c = sound Sv = 10 log10 (sv) velocity; τ = pulse length) above the seabed line detected (Sv/10) sv = 10 in order to avoid the entry of sea bed echo. The spatial and vertical distribution of demersal fish Target strength (TS) and volume backscattering in Youtefa Bay during hydroacoustic surveys has been strength (Sv) are important parameters for estimating fish presented. Grouping of demersal fish density in each range densities. TS is a logarithmic measure of the proportion of 5 m depth was done to find out the distribution in each of the incident energy which is backscattered by the of these depth ranges. The density of fish was calculated target (Simmonds and MacLennan, 2005). Sv is the key using Sv and σbs values. This method is sometimes referred measurement for estimation of acoustical fish density and to as Sv/TS scaling considering that this density estimate abundance (Parker-Stetter et al., 2009). The accuracy of depends on the value of the integration of echo (Sv) and Hydroacoustic technology to study distribution and density of demersal fish 32 σbs. The Sv is defined as fish density (ρ) multiplied with fish, Sv values​​ obtained ranged from -60.13 to -42.01 dB the average backscattering cross section (<σbs>) (Parker- with an average Sv value of -54.66 dB. Stetter et al., 2009): Demersal fish distribution in the Youtefa Bay s = ρv . <σ > v bs The vertical distribution of Sv value for demersal fish The density of demersal fish per unit volume (ρv) schools is presented in Table 3. The spatial distribution of was obtained using the following equation (Parker-Stetter demersal fish was recorded mainly in the coastal waters et al., 2009): from Enggros to Abe Pantai villages (Fig. 1). The Sv values of demersal fish were in the range of -59.00 to ρv = s / <σ > v bs -52.00 dB. High Sv value (>-43 dB) was only found at Results one school around the waters of Tobati Village. The high number of demersal fish detected in the coastal waters Detection of demersal fish schooling from Enggros to Abe Pantai villages could be due to the During the hydroacoustic survey, 27 schools of influence of the seabed substrate, which was dominated by demersal fish were recorded. The position of demersal seagrass and mud. fish schools based on water depth is presented in Table 2. Demersal fish density in the Youtefa Bay Based on the result of hydroacoustic detection, schooling of demersal fish was found in the shallow waters of Youtefa The demersal fish aggregations could be clearly Bay. The schools of demersal fish in the Youtefa Bay were seen on echograms, through hydroacoustic detection. The found at an average distance of 0.26-2.93 m above the sea vertical distribution of demersal fish density in Youtefa bed with the height of the schools ranging between 0.49 Bay is presented in Table 4. Based on 320 ESDU which and 1.70 m. Based on the integration results for demersal contained 27 fish schools, highest demersal fish density of 42.19 fish m-3 was recorded at a depth of 0-5 m. The Table 2. The demersal fish school depth of occurrence based on echo integration average density of demersal fish detected in Youtefa Bay -3 Demersal fish waters was 12.62 fish m . No ESDU Water depth (m) school depth (m) 1 31 34.53 33.44 Discussion 2 62 28.85 27.07 Results of the study indicate that in Youtefa Bay, 3 78 12.15 11.70 demersal fish abundance was comparatively more in 4 81 11.68 10.20 shallow waters and decreased with increase in water 5 90 7.93 6.66 depth.