Strategies for weighting exposure in the development of acoustic criteria for marine mammals

1. Strategies for weighting exposure in the development of acoustic criteria for marine mammals by the Noise Exposure Criteria Group Presented to the 150th Meeting of the Acoustical Society of America 17–21 October 2005, Minneapolis, MN

2. Ann Bowles Roger Gentry William Ellison James Finneran Charles Greene David Kastak Darlene Ketten Noise Exposure Criteria Group (Authors) James Miller Paul Nachtigall W. John Richardson Brandon Southall* Jeanette Thomas Peter Tyack Former Contributors Whitlow Au Sam Ridgway* (ret) Ron Schusterman (ret) *Note that Brandon Southall was left off the author list in the program. An erratum will be published in the Journal and author list will be corrected online.

3. NMFS Charge to the Noise Exposure Criteria Group Develop science-based criteria for the onset of auditory injury and behavioral disruption from noise exposure. • It became clear that we needed to emphasize some frequencies and deemphasize others • It would be best if each species had their own weighting functions for injury and behavior. • But we don’t have the data to support the specification of these weighting functions. • While these data are being collected, we need interim weighting functions.

5. Marine Mammal Groups: Taxa were categorized into groups by hearing function Composite data (see: Richardson et al., 1995; Kastelein et al., 2002)

6. Nominal Range of Human Hearing 20 Hz – 20 kHz Human Hearing: Weighting Functions • In humans, an idealized version of the 40-phon equal loudness function (A-weighting) and • 100-phon equal loudness function (C-weighting) are used to filter sound when calculating • estimates of exposure. (source: Harris 1998)

7. Frequency weighting improves correlation between noise exposure and human response Log measure of annoyance Leatherwood, J.D., B.M. Sullivan, K.P. Shepherd, D.A. McCurdy, and S.A. Brown. 2002. Summary of recent NASA studies of human response to sonic boom. Journal of the Acoustical Society of America 111(1, pt. 2): 566–598.

8. (arb. dB) A-weighting (inverted) Example of sound exposure relative to human hearing and frequency weighting • A- and C-weighting admit different portions of the sonic boom spectrum (in arb. dB). • These weighting functions admit more low frequency noise than the human auditory threshold • function.

9. Example of noise exposure* relative to marine mammal hearing California Sea Lion Harbor Seal Northern Elephant Seal Pinniped threshold data from: Kastak, D. and R.J. Schusterman. 1998. Low-frequency amphibious hearing in pinnipeds: methods, measurements, noise and ecology. Journal of the Acoustical Society of America 103(4): 2216 – 2228. *Sonic boom spectrum (arb. dB)

10. Human Frequency Weighting Networks H. Singleton, “Frequency Weighting Equations,” http://www.cross-spectrum.com/audio/weighting.html, (2004).

11. Weighting Functions for Animals • Weightings should improve exposure estimates • i.e., reduce the variability of correlations between dose and response • Ad hoc weightings have been used historically • Human A- and C-weightings (whether or not they match the animals’ hearing range) • Species-typical auditory threshold functions (“O-weighting” for owls [Delaney et al. 1999], “R-weighting” for laboratory rats [NIH]). • “Flat” weighting • Rectangular weighting constrained by the upper and lower boundaries of the measurement system. • Rectangular weighting constrained by the upper and low boundaries of the animal’s hearing range. • The 1/3-octave band with the greatest energy

12. Threshold Weighting • The absolute auditory threshold function (audiogram) has been suggested as a surrogate weighting function for marine species exposed to underwater sound (Malme 1990; Heathershaw et al. 2001; Nedwell and Edwards, 2002; Nedwell et al, 2005) as well as terrestrial animals (Delaney et al. 1999; Bjork et al. 2000) • The utility of this approach has not been tested empirically.

13. Weighting Functions for Marine Mammals • S3 WG90 is developing recommendations for marine mammal weighting functions, but adequate science is needed to produce standardized, taxon-specific weightings • In the interim, a simple, conservative weighting scheme was developed for marine mammals

14. M-Weighting The frequency cutoffs can be obtained from anatomical studies. The numbers here are conservative estimate of the upper and lower boundaries for the most sensitive members of each group.

15. These groups are relatively heterogeneous – it was the breakdown that is supported with available data.

16. “M-weighting” for cetacean hearing Low-frequency cetaceans - flow: 7 Hz, fhigh: 22 kHz Mid-frequency cetaceans - flow: 150 Hz, fhigh: 160 kHzHigh-frequency cetaceans - flow: 200 Hz, fhigh: 180 kHz The resulting family of weighting functions should yield metrics that are most relevant for high-amplitude noise exposures (where loudness functions are expected to flatten) and are likely conservative.  

17. “M-weighting” for pinniped hearing Note that we are not taking into account the differences in best sensitivity among species.

18. Conclusions • The Noise Exposure Criteria Group has developed weighting procedures for exposure metrics that will be used as criteria for • injury • behavioral disruption • Noise exposure metrics for humans have proven to be more effective when they account for psychophysical properties of the auditory system, particularly loudness perception. • The Group has proposed to weight noise data by functions that admit sound throughout the frequency range of hearing in five marine mammal groupings. • This procedure is considered conservative • The “precautionary principle” is always used in developing criteria for species at risk. • Empirical data are essential to finding better estimators of exposure including refining the cutoff frequencies for the weightings.

19. References • Bjork, E., T. Nevalainen, M. Hakumaki, and H.-M. Voipio. (2000). R-weighting provides better estimation for rat hearing sensitivity. Lab. Anim. 34,136–144. • C. M. Harris, Handbook of Acoustical Measurements and Noise Control, 3rd ed., Acoustical Society of America, 1999. • R. A. Kastelein, P. Bunskoek, M. Hagedoorn, W. W. L. Au, and D. de Haan, “Audiogram of a harbor porpoise (Phocoena phocoena) measured with narrow-band frequency-modulated signals,” J. Acoust. Soc. Am., 112(1), 334-344, 2002. • D. Kastak and R.J. Schusterman, Low-frequency amphibious hearing in pinnipeds: methods, measurements, noise and ecology, J. Acoust. Soc. Am., 103(4), 2216 – 2228, 1998. • Heathershaw, A.D., P.D. Ward and A.M. David. 2001. The environmental impact of underwater sound. p. 1-12 In: 2nd Symp. on underwater bio-sonar and bioacoustic systems, Loughborough Univ., July 2001. Proc. Inst. Acoustics 23(4). Inst. of Acoustics, St Albans, Herts, U.K. 202 p. • J. D. Leatherwood, B.M. Sullivan, K.P. Shepherd, D.A. McCurdy, and S.A. Brown, “Summary of recent NASA studies of human response to sonic boom,” J. Acoust. Soc. Am., 111(1, pt. 2), 566–598, 2002. • J. Nedwell, B. Edwards, 'Measurements of underwater noise in the Arun River during piling at County Wharf, Littlehampton', Subacoustech Report Reference: 513R0108, http://www.subacoustech.com/downloads/513R0108.pdf, August 2002. • J. Nedwell, J. Lovell, A. Turnpenny, “Experimental validation of a species-specific behavioral impact metric for underwater noise,” J. Acoust. Soc. Am., 118(3), 2005. • W. J. Richardson, Jr., C. R. Greene, C. I. Malme, D. H. Thomson, Marine Mammals and Noise, Academic Press, 1995. • H. Singleton, “Frequency Weighting Equations,” http://www.cross-spectrum.com/audio/weighting.html, (2004).

20. Discussions