Abstract

Marine mammals along the California coast (U.S.) are negatively impacted by anthropogenic activities both directly and indirectly. Despite California sea lions (Zalophus californianus) being protected under the U.S. Marine Mammal Protection Act, cases of human interaction are increasing in prevalence.^1-4 While some negative human interactions can be detected via visual examination, such as entanglements and external hooks, others can be missed without diagnostic imaging. Radiographs are an important diagnostic tool that can improve sensitivity of detecting human interactions, in particular metallic objects including bullets, pellets, and fishing hooks.

The goal of this study was to determine the frequency of human interactions in California sea lions stranded in Orange County, California and assess if radiographs significantly improve identification of human interactions. Radiographs of yearling, subadult, and adult California sea lions that presented to the Pacific Marine Mammal Center from January 1, 2021 through November 8, 2023 were evaluated for evidence of human interactions. There were 74 California sea lions that presented alive (n=46) or deceased (n=28) within the study period. Radiographs were performed on 57/74 (77%) of patients, with a higher percentage performed on patients who were alive on arrival (42/46 [91%]).

Performing radiographs significantly improved the ability to identify human interactions. Approximately one-third (24/74 [32%]) of patients had evidence of human interaction, the vast majority of which were gunshot wounds (airsoft pellets, shotgun pellets, and/or bullets). One patient with evidence of human interaction did not have radiographs performed; of the remaining 23 patients with human interaction, 21/23 (91%) were captured on radiographs. Of patients with human interaction identified on radiographs, 17/21 (81%) had evidence of metallic projectiles including bullets, shotgun pellets, and airsoft pellets, 5/21 (24%) had active entanglement wounds, and 4/21 (19%) had internal hooks present. Adult male patients were the most likely to have evidence of human interaction. Without radiographs, the prevalence of reported human interaction would have been 5/74 (7%), and human interaction would have been missed in 19/24 (79%) of patients with human interactions.

These findings suggest the number of human interactions in California sea lions are grossly underreported when radiographs are not performed. Radiographic evaluation can be limited in wildlife rehabilitation settings due to cost, availability, and patient and personnel safety. This study demonstrates that the majority of human interaction cases in our patients would have been missed had radiographs not been performed; consequently, reporting to governmental agencies (e.g., the National Oceanic and Atmospheric Administration) would undercount the occurrence of illegal human interaction. Therefore, we recommend radiographs as best practice for examining all stranded California sea lions prior to determining if an animal has evidence of human interaction.

Acknowledgments

The authors wish to thank the staff and volunteers at the Pacific Marine Mammal Center for their contributions to this study and efforts in marine mammal rescue, rehabilitation, and release. We would also like to thank the McBeth Foundation for their generous donations and support towards PMMC’s rescue, rehabilitation, and research efforts. Rescue and rehabilitation activities were conducted under a NOAA stranding agreement.

*Presenting author
+Student presenter

Literature Cited

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