Lessons learned from field chemical immobilization of northern elephant seals over two decades

Chemical immobilization is essential for ensuring the safety and welfare
of wildlife and researchers during animal handling. We analyzed 1,464
immobilization procedures on 625 northern elephant seals (Mirounga
angustirostris) conducted between 2004 and 2025 to describe our practices
and insights. Inductions used tiletamine-zolazepam (Telazol®), with
supplemental doses of ketamine, diazepam, and/or Telazol for augmentation
(required to achieve complete induction) and maintenance (required to
maintain chemical immobilization for the procedure duration). Procedures
spanned a wide range of body masses (57–668 kg) across the annual cycle
(i.e., seasons) and life stages, including juveniles of both sexes and
adult females up to 18 years old. For adult females, 68% received Telazol
induction doses within ± 0.1 mg/kg of the 1.0 mg/kg target, indicating
accurate mass estimation and a broad safety margin when paired with
vigilant monitoring and respiratory support as needed. Lower induction
doses increased the likelihood that augmentation drugs were required,
whereas higher doses were more often associated with faster-than-typical
inductions and the administration of respiratory stimulants. In procedures
with no augmentation or respiratory stimulant administration, smaller
juveniles required disproportionately higher doses than adults, regardless
of sex. These findings show that age- and season-based mass estimates can
refine dosing precision within a safe range. Our long-term dataset
provides empirically derived guidance to improve immobilization efficacy,
safety, and consistency for elephant seals and related species.