Abstract

The Vancouver Aquarium Marine Mammal Rescue Society (VAMMR) recently celebrated the tenth anniversary of its first successful sea lion disentanglement in October of 2013. Over the past decade, efforts in sea lion darting and disentanglement have evolved, presenting a unique opportunity to review and analyze the collected data and highlight key trends, successes, and challenges in the field.

Over the last 10 years, the VAMMR team conducted 37 sea lion disentanglement trips in British Columbia, Canada, resulting in the successful disentanglement of 27 animals. These included 8 adult females and 5 juvenile and subadult Steller’s sea lions (Eumetopias jubatus) and 14 adult male California sea lions (Zalophus californianus). Estimated weights ranged from 70 to 700 kg. Darts were shot from a boat in 21 animals, and 11 shots were taken from land. All animals were darted with a combination of medetomidine (0.03–0.04 mg/kg), midazolam (0.15 mg/kg), and butorphanol (0.15 mg/kg), which was partially reversed with atipamezole (0.15–0.2 mg/kg) and naltrexone (0.15 mg/kg) based on estimated weight. Two animals only had scars and did not have an active entanglement. An additional 9 animals were successfully darted but were not recovered due to an insufficient level of sedation produced. Most of these animals were observed quickly removing the dart after impact, and some drug spray was noted at impact. These animals were followed but could not be approached. Two mortalities were confirmed. Reasons for not attempting a disentanglement included poor weather (high wind or wave action), local geography posing a risk to a successful landing, lesions on an animal most consistent with scaring rather than active entanglement, and inability to locate the target animal.

The most common material removed was plastic packing bands (n=17). Braided nylon and monofilament fishing gear, along with a variety of plastic waste, were removed from most of the remaining cases. One mortality was likely due to strangulation by a thick rubber band after the animal was sedated and could no longer reposition its neck to maintain its airway. This was also the smallest animal darted (approximately 70 kg). The second animal’s body was recovered after it did not resurface after darting.

It is strongly recommended that at least two boats be used in field disentanglement efforts to maximize the location and recovery of animals in the water. A skilled crew experienced in working together is essential. The use of drones has enhanced animal monitoring after darting and during recovery. Marine radios with headsets distributed among all team members have increased communication efficacy.

Sea lion disentanglement programs are logistically challenging and resource-intensive. However, entanglement represents a significant human-caused animal welfare issue, causing suffering for long periods of time, with most neck entanglements resulting in mortality. Our findings offer valuable insights for future wildlife disentanglement strategies, demonstrating the critical role of continuous monitoring and adaptive management in marine mammal rescue and rehabilitation efforts.

Acknowledgements

The authors wish to thank the Vancouver Aquarium Marine Mammal Rescue Society volunteers and staff, including our veterinary fellows over the last 10 years, for their dedication to providing the best care possible for the animals at our facility and in the wild.

*Presenting author