Silent ships do not always encounter more fish (revisited): comparison of acoustic backscatter from walleye pollock recorded by a noise-reduced and a conventional research vessel in the eastern Bering Sea

• Published in: ICES Journal of Marine Science
• Main Authors: De Robertis, Alex, Wilson, Christopher D.
• Format: Text
• Language: English
• Published: Oxford University Press 2011
• Subjects: Article; Bering Sea; Theragra chalcogramma
• Online Access: http://icesjms.oxfordjournals.org/cgi/content/short/fsr146v1; https://doi.org/10.1093/icesjms/fsr146

<qd> De Robertis, A., and Wilson, C. D. Silent ships do not always encounter more fish (revisited): comparison of acoustic backscatter from walleye pollock recorded by a noise-reduced and a conventional research vessel in the eastern Bering Sea. – ICES Journal of Marine Science, doi:10.1093/icesjms/fsr146. </qd>Vessel-induced avoidance behaviour is potentially a major source of error in surveys of fish populations. Noise-reduced research vessels have been constructed in an effort to minimize fish reactions to auditory stimuli produced by survey vessels. Here, measurements of acoustic backscatter from walleye pollock ( Theragra chalcogramma ) made on the eastern Bering Sea Shelf from the conventional NOAA ship “Miller Freeman” (MF) are compared with similar measurements made on the noise-reduced NOAA ship “Oscar Dyson” (OD). As in a previous study, acoustic abundance measurements from these vessels were equivalent during daylight, when large-scale acoustic surveying is conducted. However, significant differences were observed at night: on average, 44% more pollock backscatter was observed from OD than MF. Observations with a free-drifting echosounder buoy suggest that the night-time discrepancy is attributable to a stronger behavioural response to the passage of the louder MF, and a resulting decrease in pollock target strength. Pollock did not exhibit a strong reaction to the passage of OD. These observations are consistent with previous comparisons of these vessels, which show that with vessel differences, the noise-reduced OD detects more pollock.