Dataset: Habitat Use by Iberian Harbour Porpoises: Ecological and Human Factors
Description
Data collected from 195 daily boat surveys spanning eight years along the north-western coast of Spain, we observed 287 harbour porpoise groups comprising 1383 individuals.
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Data collected from 195 daily boat surveys spanning eight years along the north-western coast of Spain, we observed 287 harbour porpoise groups comprising 1383 individuals. A total of 8050 20-minute samples were collected during the study period. Initially, samples collected under optimal conditions for detecting harbour porpoises were selected, which included a smooth sea state (force 1 or lower on the Douglas sea scale), wind speed less than 7 km/h, wave height below 0.2 m, and no fog or rain. This selection reduced the number of samples to 6144, considering previous research that indicated that sea state conditions ≥ 2 on the Douglas scale might affect the ability to detect harbour porpoises from the boat (Díaz López and Methion, 2018). Before starting the spatial modelling process and to avoid serial dependence between successive observations, a dataset equivalent to one third of the total (n = 2048 samples) was randomly generated from the total number of 20-minute samples collected under optimal conditions for harbour porpoise detection (n = 6144 samples) (Díaz López and Methion, 2018). This selection of samples was used for successive spatial modelling analyses where the response variable was the presence/absence of harbour porpoises. For analyses where the response variable was harbour porpoise group size (relative abundance), data corresponding to the 287 harbour porpoise sightings made between 2014 and 2021 in the study area were used. To analyse the spatial distribution of observation effort, the study area was divided into 8.9 km² hexagonal cells using QGIS software. The cell size and shape were designed to align with both the research vessel's visual range and the distance travelled between each 20-minute sample (Giralt Paradell et al., 2019). The number of samples in each cell served as a proxy measure of observation effort.