Northern elephant seals (Mirounga angustirostris) have been integral to the development and progress of biologging technology and movement data analysis, which in turn continue to improve our understanding of this and other species. Adult female elephant seals at Ao Nuevo Reserve and other colonies along the west coast of North America were tracked annually from 2004 to 2020 for a total of 653 instrument deployments and 561 recoveries. Here, we describe the compilation and curation of these high-resolution diving and location data which are now publicly available through two Dryad repositories. All the processing code and workflow are also publicly available through GitHub and Zenodo. This data set represents 3,942,130 dives and 610,372 locations collected from 475 individual seals with 178 repeat samplings over 17 years.

Description of the data and file structure

This repository consists of netCDF-4 files containing processed tracking and diving data. Each file represents a single instrument deployment. A detailed index of the data and metadata fields within each file can be found in NES_netCDF_README.pdf in the associated article. NetCDF files are self-descriptive, so all metadata are included within the file.

In addition, the repository includes a csv (NES_TrackingDiving_MetaData.csv) with all of the high-level metadata (animal, deployment, and tag information) from all of the netCDF files (for all deployments) to facilitate easier use of the dataset. This metadata is identical to the contents of the global attributes of the netCDF files.

The data processing and the structure of the netCDF files are described in detail in the associated data paper, Costa et al. 2023, and a full list of variable names and descriptions can be found in the paper's Supplemental Information.

Sampling Bias

Generally, we have been careful to select presumed healthy animals for sedation and instrumentation. For animals deployed at Ao Nuevo (most of the tracks), individuals with known site fidelity to the colony were typically selected and if age was known it was usually restricted to 4 to 12-year-olds. Furthermore, the data reported here span two decades of work. During this time, different studies prompted additional non-random population sampling. Examples include focusing on one cohort for a year, repeatedly tracking the same individuals (multiple trips in a row or across multiple years), and intentionally selecting previously tracked females who had used a coastal foraging strategy. Lastly, this data set is exclusively adult females. Data collected from other sex and age classes indicate some differences in habitat use and movement between these demographic groups, so species-wide inferences cannot necessarily be made from these data alone. We strongly encourage researchers to evaluate the metadata provided carefully and contact the data owner with inquiries.

Sharing/Access information

These files contain processed data only. The raw data, as well as intermediate processing steps, are also publicly available here.

Code/Software

All of the code used to process the data is available on GitHub and Zenodo. Diving data were processed using custom functions in Matlab and tracking data were processed in R using the {aniMoum} package. Software and package versions used to process the data are included in the global attributes of each file. A full description of data processing can be found in Costa et al., 2024.

Required Matlab toolboxes:

• {Statistics and Machine Learning}
• {Mapping}

Required R packages:

• {tidyverse}
• {aniMotum}
• {rgeos}
• {ggspatial}
• {naturalearth}
• {naturalearthdata}
• {ncdf4}

Change Log

27-Dec-2024

There were no changes to processing methods, we corrected the data and metadata contents of a few files:

• Around a dozen wildlife computer TDR records had been incorrectly cut off at the start or end of a trip during manufacturer decoding. These were re-decoded and re-processed.
• The assignment of records to TDR1 or TDR2 changed in one or two cases after this correction.
• Kami timestamp corrections were reassessed and changed as needed for all records where the primary TDR was fixed.
• Small changes to metadata (startstop and tagmetadata reference files) to correct how a few records were being identified, processed, and included in .nc files. (in particular, KamiLight instruments were not being identified correctly).

In addition to uploading corrected *.nc files, we included an updated NES_TrackingDiving_MetaData.csv to reflect those changes.