Notes for figure showing estimates of the hearing thresholds for some groups of marine mammals and typical ambient noise levels at different frequencies. Figure is adapted from Office of Naval Research (2001) Figure 3.2-2.

• Thresholds shown for Odontocetes and Pinnipeds are a composite of measured lowest thresholds for multiple species. (Richardson, et. al., 1995)
• Range for Mysticete thresholds is estimated from mathematical models based on ear anatomy or inferred from emitted sounds, with the dashed line suggesting the region of best sensitivity (Ketten, 1994, 1998; Frankel, et. al., 1995)
• Ambient noise and sea state noise curves from Urick (1983) are spectral levels in 1 Hertz wide frequency bands, with units of dB re 1 µPa²/Hz

Full References
• Frankel, A.S., Mobley, J.R., Jr., and Herman, L.M. 1995. Estimation of auditory response thresholds in humpback whales using biologically meaningful sounds. In: Kastelein, R.A., Thomas, J.A., and Nachtigall, P.E. (eds.). Sensory Systems of Aquatic Mammals. De Spil Publishers, Woerden, Netherlands.
• Ketten, D.R. 1994. Functional analyses of whale ears: Adaptations for underwater hearing. IEEE Proceedings of Underwater Acoustics 1: 264-270.
• Ketten, D.R. 1998. Marine mammal auditory systems: A summary of audiometric and anatomical data and its implications for underwater acoustic impacts. NOAA Technical Memorandum NOAA-TM-NMFS-SWFSC-256.
• Office of Naval Research. 2001. Final Environmental Impact Statement for the North Pacific Acoustic Laboratory, May 2001. Office of Naval Research, Arlington, VA.
• Richardson, W.J., Greene, C.R., Jr., Malme, C.I., and Thomson, D.H. 1995. Marine Mammals and Noise. Academic Press. San Diego, CA.
• Urick, R.J. 1983. Principles of Underwater Sound. New York: McGraw-Hill.