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Behavioral Response of Harbor Porpoises to Vessel Noise in a Tidal Strait

Behavioral Response of Harbor Porpoises to Vessel Noise in a Tidal Strait. Brian Polagye 1 , Jason Wood 2 , Chris Bassett 1 , Dom Tollit 2 , and Jim Thomson 1 1 University of Washington Northwest National Marine Renewable Energy Center 2 Sea Mammal Research Unit (SMRU), Ltd.

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Behavioral Response of Harbor Porpoises to Vessel Noise in a Tidal Strait

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  1. Behavioral Response of Harbor Porpoises to Vessel Noise in a Tidal Strait • Brian Polagye1, Jason Wood2, Chris Bassett1, • Dom Tollit2, and Jim Thomson1 • 1University of Washington • Northwest National Marine Renewable Energy Center • 2Sea Mammal Research Unit (SMRU), Ltd. Ambient Noise and Marine Mammals May 23, 2011

  2. Tidal Energy Project Site Overview Admiralty Inlet, Puget Sound, WA Turbine Site Admiralty Head • 3.5 m/s (7 knot) maximum currents • 60 m depth • Outside of commercial shipping and ferry lanes Water Depth (m) Study Site Source: OpenHydro

  3. Study Motivation • Acoustic effects of tidal energy projects on marine mammal behavior are not well-understood • High relative abundance of harbor porpoise in project area • Post-installation, use as a marker species • Evaluate pre-installation species response to existing anthropogenic noise sources • Investigate habituation – received noise levels do not uniquely determine species response (e.g., Southall et al. 2007)

  4. Data Collection: AIS >150 AIS Receiver Turbine Site Vessel-Minutes Study Site

  5. Data Collection: Sea Spider Deployment Time: 93 days Hydrophone Loggerhead DSG Click Detector CheloniaCPod • Evaluate relative presence/absence of echolocating harbor porpoise • Continuous detection and logging of clicks trains to range of 200 m • Train classifier (KERNO) post-processing ADCP 600 kHz

  6. Hourly Trends

  7. Effect of Anthropogenic Stressors • Harbor porpoises expected to display avoidance to high received levels of noise • Exposures exceeding 140 dB re 1 µ Pa result in sustained avoidance (Southall et al. 2007) • Use passenger ferry as a pre-installation source of opportunity • Broadband source level: 170±2 dB re 1 µPa at 1 m • Source duration in CPod range ≈ 1 minute • Difficult to implement control site/study • Ferry operates 7 days/week on same schedule

  8. Click Train Analysis • Focus on temporal trends in activity and click train properties after closest point of approach by outbound ferry • 16 time series (60 minutes) duration satisfy inclusion criteria • Ferry closest point of approach must result in an average ensonification of CPod detection range to 140 dB re 1 µPa • No other vessel within 2.4 km of CPod • Estimate ferry ensonification using sonar equation: • Broadband SL = 170 dB re 1µPa @ 1m • Practical spreading – N = 15 • Neglect absorption – α≈ 0

  9. Ferry Acoustic Stressor Measured Ferry Positions Modeled Received Levels Received SPL (dB re 1µPa) Average ensonification by ferry at closet point of approach = 141 dB

  10. Strong Reaction – Activity Is there an extended period of inactivity after ferry passes? • N=16 • ≈20 DPM/hr (median, N=93): No Detections Positive detection latency (minutes)

  11. Moderate Reaction – Activity Does activity increase over time? N = 16 R2 = 0.1, F = 5.5, p = 0.02

  12. Moderate Reaction – Click Properties Do mean click train properties change over time? R2 < 0.01, F = 0.2, p = 0.7 R2 < 0.01, F = 0.2, p = 0.6 R2 = 0.1, F = 6.2, p = 0.02 R2 = 0.04, F = 2.7, p = 0.1

  13. Summary • Relatively high levels of porpoise activity in vicinity of proposed turbines – up to 60 detection positive minutes/hour • Relatively high ambient noise from existing vessel traffic – ambient noise levels can exceed 140 dB • Results suggest that local harbor porpoise population is habituated to periodic received levels ≥ 140 dB • No apparent cessation or modifications on time scales ≥ 1 minute • Less severe effects and non-vocal effects not studied • Extending results to the study of tidal turbine effects • Effects may be more subtle than expected due to habituation

  14. Questions? Acknowledgements Joe Talbert and Alex deKlerk for designing and maintaining the Sea Spider. Washington State Parks for hosting the AIS receiver and data logger. • This material is based upon work supported by the Department of Energy and Snohomish Public Utility District under Award Number DE-FG36-08GO18179.

  15. Relative Echolocation Activity

  16. Receptor Response Framework • Modified version of severity scale devised by Southall et al.

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