Responses of a polar predator to a glacier calving event
Description
In this study, we tried to document the behavioural response of a polar marine predator to a glacier calving event in Antarctica. We focused on Weddell seals’ (Leptonychotes weddellii) response to the calving of the Mertz Glacier Tongue in 2010, by: i) providing a detailed description of fine-scale changes in the sea-ice landscape following the calving event; ii) examining how these changes influenced the movement and diving behaviour of Weddell seals. Two types of data are available in this dataset: i) Conductivity Temperature Depth Satellite Relayed Data Loggers (CTD-SRDLs) were deployed on female Weddell seals in Terre Adélie (East Antarctica) at Dumont d'Urville Station (−66.66◦, 140.00◦) between 2006 and 2024, to study animals’ distribution 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) 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. Following the calving of the Mertz Glacier Tongue in February 2010, seals spent more time in Commonwealth Bay (from 0.9% to 13% of their post-calving dive locations), consistent with earlier formation of landfast ice and its persistence post-calving (February 2019–2024). Landfast ice persisted in Commonwealth Bay from May onwards, although it was absent before the calving event (2006-2009). In Commonwealth Bay and west of Pointe Géologie Archipelago, seals also dived deeper after calving than before, suggesting changes in foraging strategies. Further details on the data are presented in the Metadata file.
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Steps to reproduce
All data were analysed using R statistical software, version 4.5.1, within RStudio. 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 female Weddell seals. Deployments took place in February, over 8 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 (codes 1 to 6), the computation of hunting indices (code 7), and Utilisation Distribution areas (codes 8 and 9). Then landfast ice data are analysed before and after the calving (codes 10 and 11). The analysis ends with a comparison of the seals behaviour before and after the calving (code 12). 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. Landfast ice persistence cumulated over the months from February to August for each year is computed in codes 10. It is plotted to compared the landfast ice habitat of seals before and after the calving in code 11. Bathymetry grids from GEBCO database (2023) and Beaman et al. (2011, Antarctic Science, doi: 10.1017/S095410201000074X), and contours of the Mertz Glacier Tongue before and after the calving are also included to plot the data. Further details on the data and codes are presented in the Metadata file.