Informatiehuis Marien

Update of distribution maps of harbour porpoises in the North Sea (ITAW)

  • University of Veterinary Medicine Hannover, Foundation
  • Institute for Terrestrial and Aquatic Wildlife Research (ITAW)

This project aimed to update density surface layers for harbour porpoises in the North Sea by enlarging an existing database from the period 2005-2013 (Gilles et al. 2016) with dedicated aerial survey data from 2014-2019. The results of a model study are presented in this map: Predicted density surface for harbour porpoises in summer (i.e., June-Aug), based on aerial survey data collected between 2014-2019.

Methods

The model approach as detailed in Gilles et al. 2016 was closely followed, including the same candidate set of habitat variables or predictors, which are bathymetry and topography related predictors, closest distance to coast, distance to sandeel (Ammodytes spp.) fishing grounds and, as dynamic predictors, sea surface temperature (SST) and spatial and temporal standard deviation (SD) of SST (as proxies for fronts).

Results

Predicted density surface for harbour porpoises in summer (i.e., June-Aug), based on aerial survey data collected between 2014-2019:

  • AvgSu=average density in summer (Ind. km-2)
  • SDSu=(jackknife) standard deviations in summer
  • L90SdSu=Lower lognormal 90% confidence intervals summer;
  • U90SdSu=Upper lognormal 90% confidence intervals summer.

Predictions were made on a spatial grid holding static and dynamic covariates at a resolution of 5 × 5 km.

The map in our viewer shows the predicted average density of harbour purpoises in summer (AvgSU) (ind. km-2). Other parameters can be retreived from the attribute table.

Screenshot of the presented map in our viewer
Predicted average density of harbour purpoises in summer (AvgSU - ind. km-2).

For the presentation of the map in our viewer we had to convert the coordinate reference system from PROJCS["Lambert_Azimuthal_Equal_Area"] to EPSG:25381

Reference

Gilles, A., Viquerat, S., Becker, E. A., Forney, K. A., Geelhoed, S. C. V., Haelters, J., Nabe-Nielsen, J., Scheidat, M., Siebert, U., Sveegaard, S., Van Beest, F. M., Van Bemmelen, R., Aarts, G. (2016). Seasonal habitat-based density models for a marine top predator, the harbor porpoise, in a dynamic environment. Ecosphere 7. https://doi.org/10.1002/ecs2.1367

Other information

Report of the project (pdf, 2.3 MB):

Anita Gilles, A., Ramirez-Martinez, N., Nachtsheim, D., Siebert, U., (2020).  Update of distribution maps of harbour porpoises in the North Sea-final report. University of Veterinary Medicine Hannover, Foundation, Institute for Terrestrial and Aquatic Wildlife Research (ITAW), 16 pp.

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