Lessons learned from field chemical immobilization of northern elephant seals over two decades
Data files
Feb 05, 2026 version files 1.48 MB
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AnimalMetadata_2025_10_17.csv
44.81 KB
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BloodTimes_2025_10_17.csv
56.78 KB
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DrugData_2025_10_17.csv
637.39 KB
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DrugDosages_2025_12_04_Dryad.R
102.39 KB
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DrugDosages.Rproj
218 B
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grateful-report_2025_10_20.html
634.88 KB
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README.md
3.95 KB
Abstract
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.
Dataset DOI: 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.