Effects of mid-frequency active sonar on hearing in fish

Area of Science:

• Marine Biology
• Acoustic Ecology
• Environmental Science

Background:

• Mid-frequency active (MFA) sonar is used by the navy.
• Understanding the impact of anthropogenic noise on marine life is crucial.
• Fish hearing sensitivity can be affected by sound exposure.

Purpose of the Study:

• To investigate the effects of MFA sound exposure on the hearing sensitivity of rainbow trout and channel catfish.
• To determine if MFA sound causes temporary threshold shifts (TTS) or mortality in these fish species.

Main Methods:

• Caged rainbow trout and channel catfish were exposed to simulated MFA sounds (2.8-3.8 kHz sweep, 3.3 kHz tone) at 210 dB SPL.
• Sound exposure was repeated five times, resulting in a cumulative sound exposure level (SELcum) of 220 dB re 1 μPa(2) s.
• Hearing sensitivity was tested before and after exposure, with a focus on frequencies relevant to each species.

Main Results:

• Rainbow trout showed no changes in hearing sensitivity, as their hearing range is below the tested MFA frequencies.
• One cohort of channel catfish exhibited a statistically significant temporary threshold shift of 4-6 dB at 2300 Hz.
• The observed threshold shifts in channel catfish recovered within 24 hours, and no mortality occurred.

Conclusions:

• MFA sound exposure at the tested levels did not affect rainbow trout hearing.
• Channel catfish hearing sensitivity may be impacted by MFA sounds that overlap with their hearing range.
• The temporary threshold shifts observed in channel catfish were temporary and reversible, with no lasting harm.