Fish reaction to tonal vessel noise – Comparison with ICES CRR 209 methodology

There is concern that research vessels used in fish stock appraisals may have biased data due to fish avoidance reaction. One possible mechanism inducing this avoidance reaction is tonal noise. This paper assesses fish reaction to vessel noise on the basis of a detailed paper on the tonal auditory characteristics of cod [8]. Specifically, narrow band underwater radiated noise from certain research vessels, but mainly “R.V. Scotia”, is used to establish a cod reaction range. This is then compared to the calculated reaction range using a 1/3rd octave band assessment as set forward in International Council for the Exploration of the Sea (ICES) Cooperative Research Report No. CRR 209. These comparisons were also carried out for another low-noise research vessel, namely “CEFAS Endeavour”.It is tentatively concluded from this paper that, based upon the “30 dB above hearing threshold” criterion, vessel tonality is not a strong mechanism for fish reaction to the low-noise ICES compliant vessels. However, it should be appreciated that this generalisation is based upon one (sensitive) specific species of fish and two specific research vessels. It is considered that further analysis should be carried out on other commercially important, but noise-sensitive fish, such as herring. Also, narrow band underwater noise should be investigated for other fisheries research vessels – ideally including those where strong fish reactions have been observed viz. G.O. Sars and Oscar Dyson. It should also be noted that, in this paper, each tone has been considered separately from all others; whereas, in reality, vessel noise is rich in tones and harmonics. This paper has attempted to separate out the tonal audibility aspect from the general issue of vessel broadband radiated noise by solely looking at the tonal level above the spectrum level to gain some insight into the importance of this issue.Comments are also made on various issues including masking noise, very low frequency tonal noise and the associated issue of particle acceleration sensitivity for cod.