Target Strength Analysis of Fresh Water Giant Prawn (Macrobrachium rosenbergii De Man) Using Split Beam Acoustic in Mahakam River

Abstract

Fresh water giant prawn is one of the most abundant species of the high quality economic. Unfortunately water quality condition was changed and it’s feeding ground and nursery ground. This Population declined by indicated fishermen catches were tends to decrease, one of them is fresh water giant prawn. On the other hand, information of the spatial dispersal is limited and the identification of fresh water giant prawn still used by visual. This research tried to estimate target strength value of fresh water giant prawn influenced by biological factors associated with the ontogeny (total length, carapace length and weight) and physiology (gravid and non-gravid). The research was conducted by using stationary position and controlled the acoustic method in Mahakam River, East Kalimantan. The hydroacoustic instrument used was Simrad EY 60. Five samples of prawns were measured for memories 50 kB and 200 region on echogram each of. The variables of ontogeny were analyzed by simple regression model, principal component analysis and z test. The results showed that target strength of each samples were -64,45; -65,30; -65,15; -65,21; and -55,27 dB, respectively. The regression (r2) between target strength with carapace length were 0,9103; total length 0,4704 and weight 0,3633, respectively. Calculation of principal component analysis (PCA) is used the fourth variable (target strength, total length, carapace length and weight) reduced to 2 variables. Then two new variables can explain 99.8% of the total variability of the four variables. PCA biplot graph shows that have a carapace length greater closeness when compared with the other variables. Samples 2, 3, and 4 have similar characteristics, but samples 1 and 5 do not have similar characteristics with each other. Z test results are tcalculate> ttabel then H0 rejected. This result show the sample gravid and non-gravid are not the same, because the t value falls in the region of the right of criticism. The gravid conditions suspected exerts a greater influence on the value of the target strength than the conditions non-gravid. The conclusion are value of the target strength on fresh water giant prawn influenced by the length of the carapace (ontogeny) and gravid condition (physiology).