- DISCOVERY Yacht Valkyrie
Testing Tags for Sea Lion Tracking in the Channel Islands
- September 5 – 12, 2025
- Channel Islands, California
Project Overview
The Channel Islands are home to one of the largest breeding populations of California sea lions in the United States. Since the 1970s, conservation efforts have helped their numbers steadily increase. Just off the coast of Oxnard, California, near Channel Islands Harbor, lies a U.S. Navy base that conducts frequent testing of military equipment. While studies have shown that human-produced sonar can negatively affect cetacean populations, little is known about its impact on sea lion behavior. This project, funded by the U.S. Navy, is designed to determine how sonar may influence foraging, mating, and vocalization behaviors, ensuring continued protection of these beloved pinnipeds.
Application
Naval sonar has been proven to effect behaviors of other marine mammals (Bhagarathi et al. 2024), such as common dolphins (Southall et al. 2024), orcas (Samarra et al. 2025), and sperm whales (Curé et al. 2025). A literature review from the University of St. Andrews notes that there have been no free-ranging sonar exposure studies to date on pinnipeds (Harris et al. 2025). This research, led by UCSC and funded by the US Navy, aims to develop the first behavioral impact assessment on sea lions and determine how anthropogenic sonar may impact their behaviors at sea.
- Bhagarathi, L. K., DaSilva, P. N., Maharaj, G., Balkarran, R., & Baksh, A. (2024). The impact of anthropogenic sound on marine mammals: A review. International Journal of Life Science Research Archive, 7(2).
- Curé, C., Isojunno, S., Wensveen, P. J., Siemensma, M. L., von Benda-Beckmann, A. M., Kvadsheim, P. H., Burslem, A., Benti, B., Roland, R., Lam, F.P.A., & Miller, P. J. (2025). Severity Scoring of Sperm Whale Behavioral Responses to an Operational Sonar Source Reveals Importance of Received Level and Source-Receiver Distance. Aquatic Mammals, 51(5), 8-27.
- Harris, C. M., Isojunno, S., & Thomas, L. (2025). Behavioral Response Research Review.
- Samarra, F. I., Wensveen, P. J., Selbmann, A., Kvadsheim, P. H., Lam, F. P. A., Tyack, P. L., von Benda-Beckmann, A.M., & Miller, P. J. (2025). Killer Whale (Orcinus orca) Acoustic Responses to Naval Sonar. Aquatic Mammals, 51(5), 38-55.
- Southall, B. L., Durban, J. W., Calambokidis, J., Casey, C., Fahlbusch, J. A., Fearnbach, H., Flynn, K.R., Fregosi, S., Friedlaender, A.S., Leander, S.G.M., & Visser, F. (2024). Behavioural responses of common dolphins to naval sonar. Royal Society Open Science, 11(10), 240650.
Expedition Summary
From September 5-12, 2025, the International SeaKeepers Society and DISCOVERY Yacht Valkyrie assisted a collaborative team of researchers from UCSC, Southall Environmental Associates, and the University of St. Andrews in their mission to understand the effects of naval sonar on sea lion behavior. The week prior to the expedition, the team tagged five female sea lions as they rested on the shore. Two individuals were equipped with both a satellite tag and a VHF tag, while the other 3 received satellite tags only. The tags include technology to capture movement patterns and acoustic recordings of the sea lions and their surroundings, including naval sonar. These tracking systems have been used to monitor cetacean behavior, but have never been used on sea lions. On this leg of the expedition, the research team tested the viability of these systems on the sea lions, aiming to successfully track the females, whether at land or sea. They determined that these methods are effective in relocating tagged individuals and will return in the coming weeks to retrieve the tags, and the abundance of data stored on them, from the five sea lion females.
Location
Channel Islands (Anacapa and Santa Barbara), California
Duration of Project
2025-2026
Research Team
- Dr. Dan Costa, University of California Santa Cruz
- Dr. Caroline Casey, University of California Santa Cruz
- Dr. Ryan Jones, University of California Santa Cruz
- Dr. Brandon Southall, Southall Environmental Associates, Inc.
- Ellen Hayward, University of St. Andrews
- Katie Sheahan, MA, SeaKeepers- Videography and Photography
Photo Gallery
