Seasonal and interannual dynamics of Weddell seal ecology in East Antarctica: influences of sea ice and bathymetry
Description
In this study, we tried to: i) provide a detailed description of the foraging ecology of the Dumont d'Urville Weddell seal population, describing their distribution throughout the year and the seasonal and circadian dive cycles in relation to key physical parameters of their habitat; ii) examine the potential interannual variability in their diving and foraging behaviour and its relationship with landfast ice dynamics; iii) investigate the link with fish distribution in the area, for known Weddell seals’ prey. Three types of data are available in this dataset: i) Conductivity Temperature Depth Satellite Relayed Data Loggers (CTD-SRDLs) were deployed on Weddell seals in Terre Adélie (East Antarctica) at Dumont d'Urville Station (−66.66◦, 140.00◦) between 2066 and 2024, to study animals’ movements and dives. The tags transmit information on their behaviour and location using the Argos satellite system. The data presented here includes the raw data transmitted by the tag, and the filtered data for analysis. ii) In February 2006 and 2007, 33 high-definition video surveys were performed at the Pierre Lejay Bay, around the Dumont d’Urville station using a remotely operated vehicle (ROV). The data presented here include all fish data observed on the ROV footage (number of individuals per hour per ROV station), and summarised data for Weddell seals prey species. iii) Antarctic landfast ice data were obtained from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) satellite visible and thermal infrared imagery with a spatial resolution of 1 km and a fifteen-day time stamp. Prior to March 2018, landfast ice data were taken from the dataset of Fraser et al. (2020, Earth Syst. Sci. Data, doi: 10.5194/essd-12-2987-2020). After March 2018, landfast ice maps were produced ad hoc for the Dumont d'Urville region using individual cloud-free MODIS visible and thermal infrared imagery. Dive behaviour varied among years with no consistent inter-annual trends and high degree of inter-individual variability. The foraging range this population is more restricted than that of other populations. They foraged within 50 km of Dumont d’Urville station (75% of locations). As landfast ice formed in April, dive locations were concentrated near Dumont d’Urville. Fish were more abundant near canyons, dominated by Nothotenioidei (99.9%), mainly Trematomus newnesi, with Pleuragramma antarcticum larvae along canyon edges. Seal dive patterns aligned with fish distributions, with spatial and vertical overlap. Further details on the data and codes are presented in the ReadMe file.
Files
Steps to reproduce
All data were analysed using R statistical software, version 4.5.1, within RStudio, except for the ROV data, which were analysed directly from the .xlsx file using Microsoft Excel. The codes are numbered in the order in which they should be run. The data are grouped into folders and numbered according to the analysis steps. The tags were glued onto the heads of adult Weddell seals. Deployments took place in February or November, over 13 years between 2006 and 2024, and the tags recorded data until they stopped working or fell off. Males were excluded from the filtered data, but are present in the raw data. Tag data is divided into two: dive data (folders 1 and 2) and location data (folders 4 and 5). Raw dive data includes a summary of the dives (4 points + 2 surface points), depth and time, and information that was not used in this analysis. Location data includes time, latitude and longitude (decimal), and additional information that was not used in this analysis. In both files, each line corresponds to a dive. Analyses start with the preprocessing of raw data to filter and prepare the datasets, and compute hunting and behavioural indices (codes 1 to 6), and extraction of environmental variables at the location of dives (codes 7 and 8), and ends with statistical analyses (codes 9 to 17). Antarctic landfast ice data were obtained from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) satellite visible and thermal infrared imagery, and are available as NetCDF files (folder 8). They contain information on the presence of landfast ice in pixels of 1 km for the first 15 days of each month, for years corresponding to the tag deployments. Codes in folder 14 describe the analysis steps. It includes extracting fast ice presence (codes 12a) and persistence at the dive location (codes 12b), and plotting (codes 12c). Fast ice data are included into the whole dataset in code 12d. The high-definition video surveys performed in Pierre Lejay Bay were collected in February 2006 and 2007, in an area of 18 x 25 km and over 33 stations. They were done using a high-resolution camera (Sony HVR-A1E) placed in a waterproof case attached to a remotely operated vehicle (ROV) (Comex, Achille M4). ROV data are presented in Excel files (folder 9). The raw data (file 1) includes the presence and abundance (mean number of individuals per hour per ROV station) of all fish species observed on the ROV footage. Files 2 to 6 include data for Weddell seal prey species only: a summary of the raw data, and the timestamp of the images used in Fig. 10 of the paper linked to this dataset. File 7 contains the year, latitude and longitude (decimal) of all 33 ROV stations for code 16. Bathymetry grids from GEBCO database (2023) and Beaman et al. (2011, Antarctic Science, doi: 10.1017/S095410201000074X) are also included to extract topographical parameters under the dives. Further details on the data and codes are presented in the ReadMe file.
Categories
Funders
- Centre National d'Études SpatialesFranceGrant ID: TOSCA program “Weddell seals bio-oceanographers of the Antarctic sea ice”