J Nedwell, A W H Turnpenny * J Lovell ** *Jacobs Babtie Aquatic ** Plymouth University

1. A validation of the dBht as a measure of the behavioural and auditory effects of underwater noiseProject: RDCZ/011/0004 J Nedwell, A W H Turnpenny* J Lovell** *Jacobs Babtie Aquatic ** Plymouth University Subacoustech Report No. 534 R 1305

2. Introduction • Effects of underwater noise include lethal and physical injury, auditory effects (avoidance and deafness) • Behavioural effects occur at relatively low level and hence can affect much larger areas than physical injury, can have secondary lethal effects e.g. stranding. • Behavioural effects related to perceived loudness.

3. The dBht (Species) • Frequency weighting technique for determining the level of sound relative to hearing threshold (ht), hence dBht. • Generalisation of dB(A) used for human behavioural effects and noise induced deafness; can be applied to any species where hearing sensitivity (audiogram) for species known. • Sound passed through filter that mimics the hearing ability of the species; level of sound is measured after the filter; dBht (Species) proposes effect of the sound for any species primarily related to this perceived level (“loudness”).

4. Some history…. • Concept of dBht grew out of work on hearing of divers • Led to concept of audiogram based metric (generalisation of dB(A) • Now in use for 10 years

5. Concept of dBht

6. Project aims and objectives Aim: To validate the dBht as an objective metric for measuring the behavioural and auditory effects of sound on marine animals and implement as “Species Sound Level Meter”. Programme: • Formation of an open standard for the dBht(Species). • Report on noise sources and classification into bands of noise pollution. • Nedwell J.R. and Edwards B. A review of measurements of underwater man-made noise carried out by Subacoustech Ltd, 1993 – 2003. Subacoustech Report ref: 534R010929 September 2004 • Controlled laboratory tests. • The provision of dBht(Species) sound level meters • Implementation within industry

7. Controlled tests Programme: • Re-interpretation of existing data. • Level vs. reaction – Calibrated measurements of noise and reaction to establish the dBht levels at which an avoidance response is evoked. • Audiograms – Pressure and particle velocity hearing thresholds required for experimental fish species; measured using the Auditory Brainstem Response (ABR) technique.

8. Re-interpretation of existing data: Doel

9. Measurements of efficiency The efficiency (percentage reduction in catch) in the cooling water of the Doel nuclear power plant; measurements on c. 350,000 fish by Leuven University. Signal swept sine from 20 Hz to 500 Hz.

10. Re-interpretation of existing data: INHS • Bighead Carp barrier experiments at Illinois Natural History Survey’s Wolff Hatchery in Illinois USA; same signal as Doel • Number of successful and unsuccessful attempts to pass recorded continually over 6 hour period. • Found to be 57% effective • Good quality audiograms available; sound had maximum level of 55.2 dBht (Hypophthalmichthys molitrix)

11. Re-interpretation of existing data: Marine mammals

12. Re-interpretation of data Reaction vs dBht level; free water

13. Open water results • PV results not available, dBht calculated on pressure alone • Significant size of Doel data set (350,000 fish) yields good reliability of data • Note difference in results from lab tests – “hide” reaction of flatfish will yield positive result • Indicates clear increase of reaction with increasing dBht level • Indicates 90 dBht as “strong reaction” level, confirmed by other experimental evidence • May be possible to measure audiograms and make use of more results from Doel (Sprat, prawns etc.)

14. Laboratory tests: Reaction trials Choice chamber and sound projector set-up Block diagram of experimental set-up

15. Laboratory tests: Reaction trials • ‘Choice-chamber’; 5 fish per species x 7 sounds; two transducers outside mesh cage drive fish alternately one side to another. • Avoidance response defined as move into opposite half of cage • dBht calculated for pressure and particle velocity, pressure dominated in calibrated results

16. Laboratory tests: Reaction trials • 100 % avoidance (movement away from transducer) • but only 60% effectiveness

17. Lab tests • Reaction tests have been performed on 7 species; goldfish, 5-bearded rockling, dab, flounder, sand-smelt, smelt and pout • Good-quality pressure and particle velocity audiograms only available for goldfish, dab and pout (hence only this calibrated data presented); • Other audiograms affected by artefacts due to experimental conditions, also due to sensitivity to handling (esp. sand smelt and smelt). We are in process of retesting with improved handling methods.

18. A typical reaction for Flounder • Flounder instinct is to hide - react to noise by staying motionless on the bottom, hence no avoidance reaction • The dBht offers a criteria for the likelihood of a behavioural reaction, but requires biological interpretation as to the nature and significance of the reaction

19. Reaction vs dBht level for swept sine

20. Difference of open water and lab results • Significant differences between lab tests and open water results • May in part result from different way in which reaction is measured in each. • However, may also indicate that fish reactions in caged tests are suppressed; open water tests or observation are therefore the preferred method. • Red Funnel piling project 2003 studied caged brown trout, some surprise that there was no apparent reaction even at 25 metres from piling, may be similar effect.

21. Factors affecting reactions • Physiological state of fish • Different reaction behaviours, e.g. move away, move close to bottom etc.) • ‘Follow-my-leader' effect, i.e. they all follow or stick by one sensitive or insensitive leader (found in other types of fish test,e.g. temperature: Clough & Turnpenny 2002) • Balance of pressure to move away from source with pressure to stay away from cage walls and other members of shoal

22. Typical reaction (for Sand Smelt) In this case, statistically significant reaction at 15 dBht.

23. All calibrated results

24. Regressions No significant differences between different sound types (damped 300 Hz and 50 Hz simusoid, swept sine, modulated and unmodulated noise and 100 Hz and 400 Hz “sonar pings”

25. Fit to reaction data

26. Results • Results generally indicate region of no reaction for < 40 dBht • > 40 dBht increased reaction with increasing level • Peak dBht level collapses the data better than 1 second average level (perhaps not surprisingly) • No significant difference in reaction to the different sounds • Difficult to assign a unique fit to data

27. Data averaged over all signals in 5 dB bins • Some indication that Goldfish and Pout are reacting differently in lab tests • May be specific to caged tests, no equivalent behaviour in open water results

28. Further deliverables Standard for dBht. Have standard approach to constructing dBht filters using FIR approach (details already published in I of A conference). • Implementation required by industry • Main issue is lack of suitable audiograms. In particular, they typically do not span a sufficient frequency range and dynamic range. Those chosen are suitable for a limited range of applications. Species Sound Level Meter. Have constructed a SSLM based on an FIR filter – can select species; can be made available as executable for implementation on modest laptop; user has to provide A/D card and hydrophone (c. £2500) Six sets available for partners. • Method of facilitating takeup by industry/regulators?

29. Summary (1) Experimental results indicate: • In all cases, increasing reaction with perceived dBht(Species) level. • Butsignificant difference between lab scale and open water tests. Free water reactions: • Good fit indicating response (avoidance) proportional to dBht(Species) level • Indicates 90 dBht as “strong avoidance” (~100%) limit Lab tests: • Peak dBht level best to collapse the data • No significant difference in reaction to the different sounds • No reaction for < 40 dBht • > 40 dBht increased reaction with increasing level

30. Summary (2) Results indicate: • Better audiograms required, including repeated audiogram tests under different conditions/labs/methods to provide confidence in result Benefits of metric: • A simple metric relating noise to its effect in an identical manner to airborne noise criteria. • Enables simple criteria (“the sound shall not exceed 90 dBht at the stated range for the specified species….”). • Allow non-expert personnel (e.g. MMOs) to measure and interpret noise (Species Sound Level Meter)

31. Current status Technical issues: • Dynamic range” - important or not? • No information on habituation - shortcoming of validation Political issues • Would like to see metric adopted as best practice, usually gives “right” results, easy to understand and use, only validated metric, 10 years of use, vast body of data • Has run into powerful political lobby - well heeled team in US, Subacoustech sidelined