A noise assessment was performed to evaluate the effects of increasing Southern Resident killer whale (SRKW) minimum vessel approach distances from the historic 200 m to the present 400 m and to longer potential distances. The acoustic model estimated the following average broadband reductions across all the scenarios investigated:
- 3.5 dB when increasing the approach distance from 200 to 400 m,
- 6.1 dB when increasing the approach distance from 200 to 600 m,
- 7.5 dB when increasing the approach distance from 200 to 800 m, and
- 9.7 dB when increasing the approach distance from 200 to 1000 m.
The model also predicted the listening distance could increase between approximately 55 and 140% in the SRKW communication frequency band and between 40 and 80% in the SRKW echolocation band by increasing the vessel approach distance from 200 to 400 m.