Attenuation of sound by schooling fish

Area of Science:

• Acoustic ecology
• Marine biology
• Fisheries science

Background:

• Understanding how marine life interacts with acoustic signals is crucial for fisheries management and ecological studies.
• Previous research on sound attenuation by fish has yielded varied results, necessitating a standardized approach.

Purpose of the Study:

• To quantify and compare sound attenuation by schooling fish across different species and conditions.
• To normalize acoustic attenuation data for inter-species and inter-method comparisons.
• To estimate the impact of fish schools on echo sounder observations in natural settings.

Main Methods:

• Measurements and estimations of sound attenuation were conducted on yellowtail (Seriola quinqueradiata), sea bream (Pagrus major), and spotted mackerel (Scomber australasicus).
• Data were collected in controlled environments, including culture nets and a net cage.
• Results were normalized to extinction cross sections per 2/3 power of body weight for comparative analysis.

Main Results:

• Normalized cross sections for sound attenuation showed minimal variation among different fish species, sizes, and measurement techniques.
• A slight increase in sound attenuation was observed with increasing frequency.
• Estimated attenuations for field observations using echo sounders suggest that ordinary fish schools do not significantly attenuate acoustic signals.

Conclusions:

• Fish schooling behavior exhibits a consistent and low level of sound attenuation across various species and sizes when normalized.
• The findings suggest that echo sounder surveys are unlikely to be significantly hindered by the acoustic properties of typical fish schools.
• This research provides a valuable baseline for interpreting acoustic data in marine environments and understanding fish-school acoustics.