NOAA Protocols for Fisheries Acoustics Surveys and Related ...

The areas surveyed by the NWFSC range from shallow water through the shelf break to
deeper water, covering depths from 1,000 m;
see Protocol 1, Calibration and System Performance). Unusual noise levels can also indicate
problems external to the system, such as noise from damaged propeller or an object entangled in
the propeller (e.g., rope, kelp) or noise from other shipboard equipment (e.g., generators,
compressors, other acoustic gear).
Multiple scattering and shadowing
The NWFSC has not observed the conditions that would indicate the need to correct for
attenuation at high fish densities.
Considerations
Remediation – Under ideal circumstances, a volume backscattering threshold would not need
to be used, as a threshold is a purposeful bias of the backscatter. This bias usually
implemented to provide an improved signal to noise ratio, but can also have unintended
consequences. Consideration should be given to the possibility that using a consistent
threshold may not always yield consistent survey results.
See also Protocol 4, Sampling.
Improvements – Four new fisheries research vessels are currently being built for NOAA, one
for each fisheries science center. The first will begin work for the AFSC in 2005. Each will
meet ICES recommended noise standards (Mitson, 1995), reducing the potential for vessel noise
to affect fish behavior and bias survey results.
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