SummarySnohomish Public Utility District #1 (SnoPUD) proposes to deploy two OpenHydro tidal turbines in Admiralty Inlet, Puget Sound. The fisheries service of the National Oceanic and Atmospheric Administration (NOAA Fisheries) has expressed concerns that the turbines may cause a risk for the highly endangered Southern Resident Killer Whale (SRKW) population if a whale is struck by an operating turbine. NOAA Fisheries is responsible for protecting the (fewer than 90) SRKWs under the Endangered Species Act and the Marine Mammal Protection Act. Because the SRKW numbers are so small, significant injury of a single animal could place the population in jeopardy.The potential risk to a SRKW can be parsed into the probability that a whale would encounter a turbine, the probability that the encounter would injure the whale, and the severity of any injury. During a meeting with representatives of SnoPUD, OpenHydro, the Department of Energy, and NOAA Fisheries, participants agreed that the probability of a SRKW encountering a turbine by chance is negligibly small as the whales spent greater than 97 percent of their time in Admiralty Inlet in the top 30 meters of water, while the turbines are located at 55 meters of depth, and the SRKW have highly evolved acoustic sensory capabilities that would help them detect the presence of a turbine. NOAA Fisheries expressed concerns over the potential severity of a strike on a SRKW should it occur. A proposed solution was to conduct an estimate of the level of injury that might occur from an encounter between a turbine blade and a SRKW, which would allow NOAA Fisheries to determine the permitting requirements for the tidal project.Pacific Northwest National Laboratory (PNNL) and Sandia National Laboratories (SNL) were tasked by the Department of Energy to carry out an analysis of the mechanics and biological consequences of strike of a SRKW by an OpenHydro turbine blade. The approach taken by the two laboratories was to: 1) develop a scenario for the most severe strike of a SRKW; 2) determine the morphological and biomechanical properties of SRKW tissues that might be affected by a strike; 3) model the forces of a strike; and 4) estimate the potential effects on SRKW tissue and bone of a strike.PNNL and SNL developed a worst case exposure scenario for strike of a SRKW. SNL modeled a turbine blade (based on proprietary design data obtained from OpenHydro), and calculated the force of blade impact on the head of an adult male SRKW, weighing approximately 4000 kilograms. The adult SRKW was selected for the model because an adult has a large body mass where more of the energy in a blade strike will be absorbed by the whale's tissue rather than going into momentum transfer that would push the whale out of the path of the turbine blade. This scenario would maximize the risk of injury to the SRKW. Although a juvenile SRKW might intuitively be considered to be at greater risk of injury, because of much smaller mass (~500 kg) more of the energy in the blade strike would go into momentum trans...

No abstract