Use of Acoustic Transmitter-Equipped Remote Sedation to Aid in Tracking and Capture of Entangled California Sea Lions (Zalophus californianus)

Free-ranging California sea lions (Zalophus californianus) with marine debris entanglements were darted with a combination of medetomidine, butorphanol, and midazolam by using acoustic transmitter-equipped darts. Of the 15 animals sedated, 13 (87%) reentered the water and were tracked by using a unidirectional hydrophone. Sea lions that entered the water continued to surface and breathe postsedation. There were three mortalities (20%) during the course of this study due to the following: suspected drowning caused by entrapment under a dock, overdose due to inaccurate weight estimation, and trauma caused by a dart puncturing the animal's abdomen. The drug combination, new dart design, and tracking techniques allowed for successful remote sedation and capture of California sea lions in high-risk situations and improved our ability to determine the final outcome for all cases. These methods allow targeting and capture of individual animals, while minimizing disturbance to other animals.