Underwater Noise Radiated by Fishing Vessels in Visakhapatnam Fishing Harbor

Abstract

The sound has always been a better measure to understand the oceans. Among the various sources of underwater noise, mainly physical, biological and anthropogenic, it is seen that through the increase in anthropogenic noise in the oceans, the ambient noise levels are rising. Fishing vessel radiated noise has been a major concern in the fisheries acoustic scientific community due to the possible effects on altering the natural activities of the target species. The fishing vessel noise signature shall be valuable in building a quiet vessel with effective combination of the machinery in opposing excessive noise levels. In the present paper, the measurements of the underwater noise levels within the Visakhapatnam fishing harbor (VFH) limits are detailed to understand the fishing vessel radiated noise levels. The VFH is a bay spreading over 22 ha next to the Visakhapatnam Port channel entrance. At VHF, there are around 700 fishing boats engaged in fishing activity within the coast of Andhra Pradesh. A vertical omni-directional hydrophone and TASCAM handheld linear PCM recorder was deployed at five different locations with deployment depth of 2 m within the VHF bay. Fast Fourier Transformation spectral analysis program is used to post-process the time domain signal to the frequency domain. The measured data helped to understand the ambient noise levels within the VFH limits being ~120 dB re 1 μPa and with a distant boat idling having peak amplitude 136.97 dB re 1 μPa at peak frequency of 425 Hz. The regular fishing vessel movement recorded peak amplitude 160.39 dB re 1 μPa at peak frequency of 425 Hz. The changes in the ambient noise levels due to the fishing vessel movement recorded a significant increase in sound pressure levels (SPL) by about 20 dB. The increase in SPL is mainly due to propeller and machinery radiated noise which is clearly identified in lower frequency range <500 Hz. The measurements also helped to understand the effect of each vessel type on the ambient levels due to vessel movements, mainly during entrance and exit within the VHF bay. However, the noise pollution due to vessel movement has similar effects on the local environment, i.e., the residential area close to VFH.