Target Strength of Southern Resident Killer Whales ... - BioSonics, Inc

Code:46.2008-final-Feb9
I. INTRODUCTION
Prototype marine hydrokinetic energy devices are in the process of being deployed in coastal waters to
evaluate their performance and any environmental consequences of operation. No tidal power generating
devices are currently deployed in the United States. A Federal Energy Regulatory Commission
preliminary permit has been granted to Snohomish County Public Utility District No. 1 to deploy two
tidal turbines built by OpenHydro (Dublin, Ireland) at a site in Admiralty Inlet in Washington’s Puget
Sound to study their operation over a 5-year period. A criterion for final approval for deployment of tidal
turbines by regulatory authorities is demonstration of capability to manage the risk of injury to killer
whales from strike by moving turbine blades. Pacific Northwest National Laboratory researchers are
designing and testing a prototype of a marine mammal alert system (MMAS) for detecting the presence
of killer whales in the immediate vicinity of tidal turbines. The system will inform tidal turbine operators
about the presence of the killer whales to facilitate shut down of the turbines when there is high risk of
collision of the whale with the operating turbine. Both passive and active monitoring systems are being
considered for the MMAS. The passive monitoring system is being developed by modifying an energybased
juvenile salmon acoustic telemetry system (McMichael et al., 2010; Deng et al. 2011; Weiland et
al., 2011). Several commercially available sonars are being evaluated for the active monitoring system.
An object in water with acoustic impedance different from water scatters a portion of acoustic energy
incident from an active acoustic source back toward the insonifying acoustic system or other receivers
within range. The ratio of energy incident on the object to that backscattered from the object is defined as
the target strength (TS) for the object. With the exception of a sphere of uniform composition, the target
strength of an object, such as a fish or whale, is a complex function of the shape of the object and its
orientation to the insonifying sonar system. Target strength is a parameter in the sonar equation and is
required for the design of a sonar system to optimize design for detection of the targets of interest. The
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