Study on backscattering from fish school near pump intake

Abstract

In this master project, acoustic method was applied for estimating the gradually changed fish density during the crowding near the pump intake in salmon plant. The purpose was to detect if the sensitivity of the echo sounder is feasible for density estimation. The experiment was conducted at the Salmar Innovamar harvesting and processing plant with two 200 kHz single beam echo sounder ?Simrad EK15. Two transducers holding by plates were used to collect the acoustic data. The distance between the plates was set as 4, 3, 2.5 and 1.5m, respectively. The experiment consisted of two parts: the first one was a normal group including two tests conducted during two harvesting periods; the second one was a control test that was done after harvesting in a nearly empty cage. Raw data from the echo sounder were processed by Matlab to extract the power data without range compensation. There were some features of the acoustic results which can be explained with the harvesting operation log. However, the fish density was so great that the acoustic energy was decreased rapidly within a range of 2m, thus it is hard to connect the distribution of power with fish density within the sample volume. Additionally, the volume of the netting was always changed manually and it was impossible to quantify the real density.