White shark strike on a long-range AUV in Monterey Bay

Thirteen minutes after sunrise on September 30, 2013,16.5 m deep in northern Monterey Bay, a white shark (Car-charodon carcharias) struck the MBARI long-range autonomous underwater vehicle (LRAUV) Tethys and left bite grooves in the pressure vessel and tooth fragments embedded in the aft fairing. Tethys survived the attack and continued her mission measuring ocean properties in that area for another week. The operators did not know about the strike until recovering the vehicle normally at the end of the deployment, when the tooth fragments and apparent bite diameter provided sufficient information to identify the shark species. We discuss the motion of the vehicle during the strike, its control response after being released by the shark, and the environmental properties it measured near the time of the strike. We also provide a damage report — although Tethys was able to complete her mission after the strike, she did not get away without a scratch. This event is a good example for recent work aimed at detecting faults and performance anomalies onboard in realtime so that operators can be notified. We show that a statistical anomaly detector correctly identifies the strike and effectively highlights it as unexpected behavior for the operator to review.