DOI: 10.5061/dryad.c2fqz61kc
title: Spatial modelling of aerial survey data reveals an important European storm-petrel hotspot and its underlying drivers within the North-East Atlantic

description: Determining the distribution and population size of marine species is
 crucial for conservation and management. However, for many species, the
 abundance and at-sea distribution are poorly known because of their large
 geographic ranges, high mobility, and cryptic breeding habits. This is
 especially true for small pelagic seabirds such as the European
 storm-petrel. Large-scale observer-based aerial surveys were conducted
 over four summers in the North-East Atlantic extending 200 nautical miles
 from the coast of Ireland. Species distribution models were produced using
 generalised additive models with a combination of static and dynamic
 environmental variables to assess the impact of survey altitude on
 storm-petrel detectability, and to model their abundance and distribution.
 Reduced storm-petrel detectability was identified at higher survey
 altitudes and rougher seas, and an at-sea abundance of 154,044 (95% CI:
 94,347 – 452,299) individuals was estimated. Our results reveal fine scale
 variation in the spatial distribution of storm-petrels and highlight the
 unsuitability of foraging radius distribution models for such species.
 Storm-petrels were found to avoid coastal areas, which we speculate is
 linked to the avoidance of large coastal avian predators during the day.
 Although the continental shelf edge was highlighted as a significant
 feature in the distribution of this pelagic species, a more prominent
 hotspot was identified in neritic areas, 20-40km off the south and
 south-west coasts of Ireland in a region highly influenced by shelf
 fronts, coastal currents, upwellings, and eddies in the summer months. The
 identified hotspot has global significance since Ireland holds more than
 20% of the entire European storm-petrel breeding population.
description: # **Spatial modelling of aerial survey data reveals important European
 storm-petrel hotspots and their underlying drivers within the North-East
 Atlantic**
 [https://doi.org/10.5061/dryad.c2fqz61kc](https://doi.org/10.5061/dryad.c2fqz61kc) ## Description of the data and file structure Offshore broad-scale and coastal fine-scale aerial surveys were conducted in the Irish Exclusive Economic Zone (EEZ) by a team of trained observers between May and September in 2015, 2016, 2021, and 2022, following a standard strip-transect methodology. All sightings of storm-petrels within 200m of the transect line on each side of the aircraft, and the group size, were recorded. Generalised Additive Models (GAMs) were used to predict the distribution and abundance of storm-petrels in the study area using this extensive survey dataset and a combination of static and dynamic predictor variables.  ### Files and variables #### File: aerial\_survey\_data.zip **Description:** Folder containing aerial survey effort and storm-petrel sightings for each survey period. **Files:** * *aut_fs_16.csv:* Autumn, fine-scale, 2016 * *aut_fs*_*21.csv:* Autumn, fine-scale, 2021 * *aut_fs_22.csv:* Autumn, fine-scale, 2022 * *sum_bs_15.csv:* Summer, broad-scale, 2015 * *sum_bs_16.csv:* Summer, broad-scale, 2016 * *sum_fs_16.csv:* Summer, fine-scale, 2016 * *sum_bs_21.csv:* Summer, broad-scale, 2021 * *sum_fs_21.csv:* Summer, fine-scale, 2021 * *sum_bs_22.csv:* Summer, broad-scale, 2022 * *sum_fs_22.csv:* Summer, fine-scale, 2022 **Variables:** *timestampUTC* - date time *transect* and *transect_ID* - identification code for individual survey transects *latitude* and *longitude* *effort_num* - indicates whether both, one, or neither side of the aircraft were "on effort" and collecting data. * 1.0 = both sides of aircraft on effort * 0.5 = one side of aircraft on effort, one side of aircraft off effort * 0 = both sides of aircraft off effort *species* - indicates when storm-petrels were observed *number* - group size of storm-petrel sightings *sea_state* - Beaufort sea state recorded by observers *stratum* - indicates which stratum within the Irish EEZ the survey transects were conducted in (broad-scale surveys only) **Usage notes:**  R or Microsoft Excel can be used to view these csv files. #### File: storm\_petrel\_colonies.csv **Description:** Location of European storm-petrel colonies in Britain and Ireland sourced from Burnell et al. (2023). Burnell, D., Perkins, A.J., Newton, S.F., Bolton, M., Tierney, T.D., Dunn, T.E., 2023. *Seabirds Count: a census of breeding seabirds in Britain and Ireland (2015-2021).* Lynx Nature Books, Barcelona. **Variables:** *country, county -* general location of colony *site -* colony name *latitude -* latitude of colony *longitude -* longitude of colony *pairs -* number of breeding pairs at colony **Usage notes:** R or Microsoft Excel can be used to view this csv file. #### File: shapefiles.zip **Description:** Shapefiles of (1) Irish EEZ, and (2) Ireland and Britain **Usage notes:** These shapefiles can be opened and used in any GIS software and in R. A shapefile consists of multiple file types. The user only interacts directly with the .shp file but the other files need to be in the same directory. #### File: env\_data\_download.csv **Description:** Chlorophyll-a concentration (mg m^-3) and Sea Surface Temperature (degrees celsius) for the centre point of each 4x4km grid cell. Data is at 8 day temporal and 4km spatial resolution and was interpolated using inverse-distance-weighted interpolation. Sourced from Movebank's Env-DATA service ([https://www.movebank.org/](https://www.movebank.org/)) which uses NASA's MODIS satellite data. ##### **Variables:** *season:* survey period *id:* grid cell ID *timestamp:* date time *location-long:* longitude of grid cell centre point *location-lat:* latitude of grid cell centre point *MODIS Ocean Aqua OceanColor 4km 8d Chlorophyll A (OCI):* Chlorophyll-a concentration (mg m^-3) *MODIS Ocean Aqua OceanColor 4km 8d Daytime SST:* Sea Surface Temperature (degrees celsius)   **Usage notes:**  R or Microsoft Excel can be used to view these csv files. #### File: salinity.zip **Description:** Folder containing daily Sea Surface Salinity (SSS; so / 10^-3) data sourced from Copernicus Marine Service Ocean Products database ([https://marine.copernicus.eu/](https://marine.copernicus.eu/)). This folder contains separate .nc files for each day of the months aerial surveys were conducted and cover the area of the Irish EEZ. File format: NetCDF. Each filename in this folder is structured as SSS_date.nc (e.g. SSS_20150601.nc).  **Usage notes:** The data are provided in NetCDF-4 (.nc) format and can be opened in R, Panoply or HDFView. #### File: chl\_8d.zip **Description:** Folder containing 8-day 4km Chlorophyll-a concentration (CHL; mg m^-3) data for the median Julian day of survey transects for all years from 2015-2022 used for model predictions. Sourced from NASA's Ocean Biology Processing Group ([https://oceandata.sci.gsfc.nasa.gov/l3/](https://oceandata.sci.gsfc.nasa.gov/l3/)). File format: NetCDF. Each filename in this folder is structured as CHL_startdate_enddate.nc (e.g. CHL*_*20150712_20150719.nc).  **Usage notes:** The data are provided in NetCDF-4 (.nc) format and can be opened in R, Panoply or HDFView. #### File: sst\_8d.zip **Description:** Folder containing 8-day 4km Sea Surface Temperature (SST; degrees celsius) data for the median Julian day of survey transects for all years from 2015-2022 used for model predictions. Sourced from NASA's Ocean Biology Processing Group ([https://oceandata.sci.gsfc.nasa.gov/l3/](https://oceandata.sci.gsfc.nasa.gov/l3/)). File format: NetCDF. Each filename in this folder is structured as SST_startdate_enddate.nc (e.g. SST*_*20150712_20150719.nc).  **Usage notes:** The data are provided in NetCDF-4 (.nc) format and can be opened in R, Panoply or HDFView. #### File: sss\_8d.zip **Description:** Folder containing daily Sea Surface Salinity (SSS; so / 10^-3) data from which the 8-day mean for the median Julian day of survey transects for all years from 2015-2022 can be calculated for model predictions. Sourced from Copernicus Marine Service Ocean Products database ([https://marine.copernicus.eu/](https://marine.copernicus.eu/)). File format: NetCDF. Each filename in this folder is structured as SSS_date.nc (e.g. SSS_20150712.nc).  **Usage notes:** The data are provided in NetCDF-4 (.nc) format and can be opened in R, Panoply or HDFView. ## Code/software #### File: R\_code.zip All analysis was completed using R. R is required to run the code scripts in this folder. ## Access information Data was derived from the following sources: The environmental variables used in this analysis were sourced from: * Movebank's Env-DATA service ([https://www.movebank.org/](https://www.movebank.org/)) * NASA's Ocean Processing Group ([https://oceandata.sci.gsfc.nasa.gov/l3/](https://oceandata.sci.gsfc.nasa.gov/l3/))  * Copernicus Marine Service Ocean Products database ([https://marine.copernicus.eu/](https://marine.copernicus.eu/)) Location of European storm-petrel colonies was sourced from: * Burnell, D., Perkins, A.J., Newton, S.F., Bolton, M., Tierney, T.D., Dunn, T.E., 2023. *Seabirds Count: a census of breeding seabirds in Britain and Ireland (2015-2021).* Lynx Nature Books, Barcelona.