Acoustic Systems (Split Beam Echo Sounder ) to Determine Abundance of Fish in Marine Fisheries

Acoustic waves are transmitted into the subsurface ocean will experience scattering (scattering) caused by marine organisms, material distributed in the ocean, the structure is not homogeneous in seawater, as well as reflections from the surface and the seabed. Estimation of fish stocks in the waters wide as in Indonesia have a lot of them are using the acoustic method. The acoustic method has high speed in predicting the size of fish stocks so as to allow acquiring data in real time, accurate and high speed so as to contribute fairly high for the provision of data and information of fishery resources.  Split beam echo sounder comprises two aspects, and a transducer. The first aspect is the high-resolution color display for displaying echogram at some observations and also serves as a controller in the operation of the echo sounder. The second aspect is transceiver consisting of transmitter and receiver. The Echosounder divided beam first inserted into the ES 3800 by SIMRAD beginning of the 1980s and in 1985 was introduced to fishermen in Japan as a tool for catching up. Split beam transducer is divided into four quadrants.  Factors that contribute affect the value of Target Strength (TS) fish Strength target can generally be influenced by three factors: a target factor itself, environmental factors, and factors acoustic instrument. Factors include the size of the target, the anatomy of fish, swim bladder, the behavior of orientation.


Int r oduct i on
Acoustic w aves are transmitted into the subsurface ocean w ill experience scattering (scattering) caused by marine organisms, the material distributed in the ocean, the structure is not homogeneous in seaw ater, as w ell as reflections from the surface and the seabed. Part of the initial acoustic energy on an object and is reflected back to the source called backscattering (M aisonhaute et al., 2002). According to (Benoit -Bird and Whitlow , 2001), a good fisheries resource management must control the number of catches in conjunction w ith the number of stocks that can be exploited. It required an estimate of the number of fish stocks at the time and acoustic survey t echniques can be used to estimate the abundance of fish at a time and under certain conditions. The use of echo sounder and echo integrator for the purposes of exploration of fishery resources today are grow ing rapidly.
Hardw are echo integrator aims to get the echo signal integration. The accuracy of this method is very high so it can be applied to estimate the abundance of fish in t he w aters (Benoit-Bird and Whitlow , 2001),. According to , the hydroacoustic method w ith detection backscatter value of mangrove crab (scylla sp.) using cruzpro fishfinder pcff-80 hydroacoustic instrument. According to (Pujiyati, 2008) hydroacoustic method is an underw ater detection method that use acoustic devices, among others: echosounder, fish finder, sonar, and Acoustic Doppler Current Profiler (ADCP).  (M acLennan and Simmonds, 1992) a good fisheries resource management must control the number of catches in conjunction w ith the number of stocks that can be exploited. It required an estimate of the number of fish stocks at the time and acoustic survey techniques can be used to estimate the abundance of fish at a time and under certain conditions. The use of echo sounder and echo integrator for the purposes of exploration of fishery resources today are grow ing rapidly. Hardw are echo integrator aims to get the echo signal integration. The accuracy of this method is very high so it can be applied as an estimate abundance of fish in the w aters (Benoit-Bird and Whitlow , 2001).
Estimation of fish stocks in the w aters w ide as in Indonesia have a lot of them are using the acoustic method. The Acoustic method has high speed in predicting the size of fish stocks so as to allow acquiring data in real time, accurate and high speed so as to contribute fairly high for the provision of data and information of fishery resources (M acLennan and Simmonds, 1992) in Fig 3 and 4.
The second aspect is transceivers consisting of transmitter and receiver. The echosounder divided beam first inserted into the ES 3800 by SIM RAD beginning of the 1980s and in 1985 w as introduced to fishermen in Japan as a tool for catching up. Split beam transducer is divided into four quadrants (Foote, 1987) in w hich the transmitting w ave conducted by the merger of four full beam . The signal reflected by the target is received by each quadrant and reassembled to form a full beam . The direction on the ship split beam is divided into four (4) ie Fore, Aft, Port, and Starboard. While in principle Split Beam is divided into four quadrants that FP.FS.AP and AS in  In Fig 3, Split beam echo sounder has the function of Time Varied Gain (TVG) in acoustic data acquisition system serves as a reliever TVG attenuation (Amplifier) w het her caused by geometrical spreading and absorbs noise as it propagates into the w ater. There are t w o types of functions, nam ely TVG function that w orks to echo a single fish called TVG 40 log R and a function for a group of fish that TVG 20 log R.  (Arnaya,1991).
In ( Figure 6) by SIM RAD, fish axis A located right above the maximum transducer gain, w hile fish B is located at the end (edge) transducer beam w here the gain is low er. A fish echo thus more likely to result stronger than the backscattered echo in fish B. Although both of these fish are at the sam e depth and the sam e size. To determine the size of the fish from the echo strength alone is not enough, how ever, know ledge about the pattern beam transducer and the fish in the beam position is very important to correct transducer gain strength and determining the target value of real fish. An estimate obtained approximate angle of incidence and factors beam pattern in the acoustic signals can be obtained by using a processor of the split beam w hich has a signal source X leads to Phase detection and w ill produce energy or pow er by means of calculating the result s of input and w ill generate output w aveform display in Fig Then according in (Love, 1997) introduced the equation w hich connect s the backscattering cross section ( ), fish length (L) and w avelength (λ) by the follow ing equation: / λ 2 = a(L/ λ) (dB) w here a and b are constants that depend on the anatomy, fish size, and w avelength. Equation (4) can be converted into a logarithmic form becomes: Then obtained the possibilit y of the average best performing measurements on the measurement of the target strength of the dorsal aspect: = 19,1 log (L) 0,9 (f) 62 But according to (Natsir et al., 2005)  Fish length (L) associated w ith óbsis: óbs=a (10) Associated of target strength and L is: Where : A = the value of the target strength to 1 cm long fish (normalized target of strength) Conversions strength target value into a length (L) for pelagic fish used equation: TS = 20 log L-73.97 (Natsir et al., 2005) . According in (Effendie, 2001) the relationship length (L) and w eight (W) of a species of fish that is: W=aL (12) In addition ( Factors that contribute affect the value of target Strength (TS) fish Strength target can generally be influenced by three factors: a target factor itself, environmental factors, and factors acoustic instrument. Factors include the size of the target, the anatomy of fish, sw im bladder, the behavior of orientation (Priatna. A & Wijopriono, 2011). Factors such targets are: 1. Si ze of fi sh: There is a relationship bet w een the size of the fish w ith a value of TS, but the relationship varies greatly depending on the species. Generally, for fish species, the larger the fish the greater its value TS. This is especially true for the region of the graph geometrical relationship betw een the size of the target and TS, for the region, resonance, resonance region and the transition region, the tendency of the relationship is not valid (M aclennan et al., 2002). Anatomy such as the head, body, tail and fins have different sound reflections. Likew ise, stomach, intestine, liver, bones, flesh and gills have a specific gravity = (ρ) and the speed of sound = (c) different so acoustically w ill have the ability to reflect a different sound. 2. Sw i m bladder of fi sh: Acoustically fish and marine organisms are divided into tw o major groups, nam ely bladder fish (have a sw im bladder). Fish that have a sw im bladder generally do not have the right maximum TS on the dorsal aspect, w hile fish that do not have a sw im bladder w ith a maximum value of TS is generally right on the dorsal aspect. TS value of fish that have a sw im bladder (Furusaw a, 1998(Furusaw a, in M anik et al., 2006. With deformed-cylinder model (DCM) w ith Approximation of> 5 and the value of Tilt Angle w as not until (<40 °) according to (Yasuma et al., 2003). results from the resultant corner of a fish that has sw im bladder that is: Fig 9. Sw im bladder Geometry for Soft spheroid models, Source in to (Yasuma et al., 2003).
3. Behavi or / ori ent at i on fish: Results of a previous study conducted by (Henderson et al., 2008 andFässler et al., 2008) states t hat the value of Target Strength (TS) is determined by the orientation of the fish, especially the slope of the body to a line connecting betw een the head and tail. Fish orientation w ill include tilting, yaw ing and rolling along. Yaw ing no effect because generally spherical transducer position so that the fish does not cause changes in the angle w hen view ed from the transducer, for Rolling no real effect because the fish have a sw im bladder due partly reflected energy is derived from the sw im bladder did not come from the dorsal aspect. Tilting lead to a change in angle-position transducer is good for fish that have a sw im bladder or not (Arnaya, 1991). 4. Inst r um ent al fact or : The small big factor value Beam pattern depending on the extent of the transducer w ill be greater the beam angle of the transducer, and vice versa. Large beam angle changes cause TS great value, separately it is better to use a relatively narrow beam . Acoustic reflections of fish and plankton that are returned in the form of echo are detected by the receiver has an appeal. Estimation of biomass can be seen from how much force t he target and how to interpret it. TS plankton is numbers t hat indicate the size of the echo. The larger the value, the greater echo energy is returned to the receiver by the target. Unit of measure Standard International (SI) for the TS expressed in decibels (dB). A decibel is a logarithmic form of a comparison or ratio of the tw o intensities due to the values involved can be very large or very small. According to (Lurton, 2002) TS formulated as backscattering cross-section of the target w hich returns a signal and is expressed in the equation: Then the value of TS theoretical spherical object is: TS = 10 Log Volume Backscattering Strength (SV) is defined as the ratio betw een the intensity reflected by a group of single targets (target located at a w ater volume of certain invocation of instantaneously measured at a distance of 1 m from a target w ith the intensity of sound that hit the target. Definition Volume Backscattering Strength (SV) has the sam e meaning as the target strength for a single target, w hile Volume Backscattering strength (SV) for a group of fish.
Each individual targets is the source of the reflected sound w ave, so that the output of the integration w ill be proportional to the quantity of fish in the group. Echo integration methods used to measure Volume Backscattering Strength (SV) based on t he measurement of the total pow er backscattered on the transducer (Arnaya 1991).
Volume Backscattering Strength (SV) is the ratio betw een the intensity reflected by a single group target w here t he target is located at a w ater volume (Xie and Jones, 2009). This is similar to the definition of TS w here TS value is the result of the detection of a single organism, w hile SV is the value for detection organism groups in (Kaartvedt and Aksnes, 2012) states SV is defined as the equation: Information : I s : Intensity scattering volume measured 1 m from the cent er of the acoustic w aves. I i : Scattering intensity emitted 4. Fi sh densi t y (Abundance Fi sh) To date research on fish stock estimates done by cruise track using a SIM RAD EK 60 Scientific split beam echo sounder system w ith a frequency of 70 kHz and acoustic data acquisition is performed continuously during the day and night during the period boat cruise at speeds ranging betw een 7-8 knots. Trails include a data acquisition area of an area that allow s the analysis of spatially made w ith the zig-zag shape according to (M acLennan and Simmonds, 1992in (Diez et al., 2016, Jurvelius et al., 2016 w ith the lengt h of each transect approximately 12 nmi of bounds islands outw ards. Density values for fish processing performed on M s. Excel. The treatm ent may be carried out after the integration process SV and TS. Density is generated by using the formula (Lubis and Anurogo, 2016). SV (dB) = 10 log (N τbs) = 10 log N + TS (18) Assuming the numerical density is proportional to the density of individuals, then the equation (1)