DOI: 10.5061/dryad.44j0zpcv1
title: Lessons learned from field chemical immobilization of northern elephant seals over two decades

description: 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.
description: # Lessons learned from field chemical immobilization of northern elephant
 seals over two decades Dataset DOI:
 [10.5061/dryad.44j0zpcv1](https://doi.org/10.5061/dryad.44j0zpcv1) The
 Dryad authors represent the primary contributors to program leadership and
 code curation, while full authorship for data collection and
 interpretation is provided in the accompanying manuscript. ## Description
 of the data and file structure Immobilization procedures were part of a
 long-term monitoring program of northern elephant seals at Año Nuevo
 Reserve, California. Below, we describe the data files necessary to
 conduct all analyses and create all figures in the associated manuscript.
 ### Files and variables #### File: AnimalMetadata_2025_10_17.csv
 **Description:** .csv file with information on all animals immobilized
 between 2004 and 2025 ##### Variables * Year: year handled * Season:
 season handled; PB (post-breeding), PM (post-molt) * AnimalID: uniquely
 identifying alpha-numeric code * TOPPID: a seven-digit number (e.g,
 2004001) where the first two digits correspond to the species (20 is
 northern elephant seal), digits 3-4 indicate the year (04 is 2004), and
 digits 5–7 are the deployment serial number (001 is the first deployment
 for a given year and species)  * DeployDate: date of deployment handling
 (MM/DD/YYYY) * DeployMass: mass at deployment handling (measured in
 kilograms) * RecoverDate: date of recovery handling (MM/DD/YYYY); NA for
 animals that were not recovered * RecoverMass: mass at recovery handling
 (measured in kilograms); NA for animals that were not recovered *
 DeployAge: integer age (measured in years) at deployment; NA for animals
 in which age was not known * Sex: male (M) or female (F) #### File:
 BloodTimes_2025_10_17.csv **Description:** .csv file with information
 about when blood samples were taken for each animal during their
 deployment and recovery procedures. Blood sampling time was used as an
 estimated time of complete induction. ##### Variables * sighting_id:
 animal TOPPID (e.g., 2004001) and handling timepoint (deployment,
 recovery); there are more deployments than recoveries because not all
 animals returned from their foraging trips * BloodSamplingTime: used to
 filter the data; only non-"NA" values were included in analyses
 * Disposition: used to filter the data; only "Included" values
 were included in analyses #### File: DrugDosages_2025_12_04_Dryad.R
 **Description:** code to run all analysis and create all figures included
 in the manuscript #### File: DrugDosages.Rproj **Description:** R project
 for code and data #### File: DrugData_2025_10_17.csv **Description:** .csv
 file with information about each instance in which drugs were given to an
 animal ##### Variables * animal_field_id: uniquely identifying
 alpha-numeric code; same as AnimalID * topp_id: a seven-digit number (e.g,
 2004001) where the first two digits correspond to the species (20 is
 northern elephant seal), digits 3-4 indicate the year (04 is 2004), and
 digits 5–7 are the deployment serial number (001 is the first deployment
 for a given year and species)  * timepoint: period when the animal was
 handled; deployment or recovery * drugging_time: time (HH:MM) in which
 drugs were given; recorded in PST * drug_code: code for type of drug given
 * tel = telazol (Tiletamine/Zolazepam) * ket = Ketamine * val = valium
 (Diazepam) * ket/val = ketamine and valium * epi = epinephrine * dop =
 dopram (Doxapram) * atr = atropine * drugging_vol: volume of drugs given;
 measured in CCs * drugging_tech_uppercase: technique used to deliver drugs
 * IS = initial stick (target intramuscular) * IV = intravenous * NearIV =
 near intravenous * other = other (e.g., given in the tongue) *
 drugging_comment: comments about drugging ## Code/software All analyses
 were conducted using RStudio. #### File: grateful-report_2025_10_20.html
 All necessary packages and versions are listed.