Pupping habitat of grey seals in the Dutch Wadden Sea Sophie Brasseur, Alma de Groot, Geert Aarts, Elze Dijkman & Roger Kirkwood IMARES rapport C009/15 Vincent van der Meij Min. Economic Affairs PO Box 20401 2500 EK Den Haag The Netherlands BO-11-011.04-015 Cover photograph by RK: A grey seal pup on Griend. © 2015 IMARES Wageningen UR IMARES, institute of Stichting DLO The Management of IMARES is not responsible for resulting is registered in the Dutch trade damage, as well as for damage resulting from the application of Record nr. 09098104, results or research obtained by IMARES, its clients or any claims BTW nr. NL 806511618 related to the application of information found within its research. This report has been made on the request of the client and is wholly the client's property. This report may not be reproduced and/or published partially or in its entirety without the express written consent of the client. A_4_3_2-V13.1 Report number C009/15 1 of 104 Contents Summary ..................................................................................................................5 List of figures ............................................................................................................8 1 Introduction & Methodology .............................................................................. 10 1.1 Conservation status of grey seals in the Wadden Sea .................................. 10 1.2 Project objectives .................................................................................. 11 1.3 Methodology ......................................................................................... 11 2 Grey seals in the Netherlands ........................................................................... 13 2.1 Breeding biology .................................................................................... 13 2.2 Population trends ................................................................................... 13 2.3 Breeding sites in the Netherlands ............................................................. 14 2.4 Background for this report ....................................................................... 18 3 Geomorphology and vegetation of important pupping sites .................................... 20 3.1 Study sites............................................................................................ 20 3.2.2 Island development ..................................................................... 23 3.3 Methods ............................................................................................... 26 3.3.1 Pupping locations ........................................................................ 26 3.3.2 Geomorphology .......................................................................... 26 3.3.2.1 Long-term development ........................................................ 26 3.3.2.2 Elevation and location .......................................................... 26 3.3.2.3 Groundwater ....................................................................... 27 3.3.3 Vegetation ................................................................................. 27 3.3.3.1 Vegetation maps Griend ....................................................... 27 3.3.3.2 Oblique aerial photos (Engelschhoek and Richel) ...................... 27 3.3.3.3 Aerial ortho-photos .............................................................. 27 3.3.3.4 Species list (Richel) .............................................................. 27 3.3.3.5 Outline of embryonic dune field (Richel) .................................. 28 3.3.3.6 Relevés (Richel and Griend) .................................................. 28 3.4 Large-scale dynamics in the Vlie tidal basin ............................................... 28 3.5 Engelschhoek ........................................................................................ 30 3.6 Richel 33 3.6.1 Geomorphology .......................................................................... 33 3.6.2 Development of the embryonic dune field ....................................... 33 3.6.3 Dune types and sediment composition ........................................... 37 3.6.4 Elevation and flooding frequency ................................................... 37 3.6.6 Animal presence ......................................................................... 41 3.6.7 Seal influence on vegetation ......................................................... 42 3.6.8 Future ....................................................................................... 44 3.7 Griend 45 3.7.1 Geomorphology .......................................................................... 45 3.7.2 Seal pupping habitat ................................................................... 47 3.7.3 Seal influence on vegetation ......................................................... 49 3.7.4 Future ....................................................................................... 50 3.8 Discussion - habitat characteristics ........................................................... 50 3.8.1 Suitability for seals ...................................................................... 50 2 of 104 Report number C009/15 3.8.2 Future developments on Richel and Griend ..................................... 51 3.8.3 Influence of seals on their pupping habitat ...................................... 52 3.8.4 Knowledge gaps .......................................................................... 52 4 Exchange of grey seals with other areas ............................................................. 53 4.1 Introduction .......................................................................................... 53 4.2 Methods ............................................................................................... 55 4.2.1 Movement data ........................................................................... 55 4.2.2 Photo-ID .................................................................................... 55 4.2.3 Genetics .................................................................................... 56 4.3 Results ................................................................................................. 57 4.3.1 Movement data ........................................................................... 57 4.3.2 Photo-ID .................................................................................... 59 4.3.3 Genetics .................................................................................... 61 4.4 Discussion ............................................................................................ 61 4.4.1 Movement data ........................................................................... 61 4.4.2 Photo-ID .................................................................................... 62 4.4.3 Genetics .................................................................................... 63 4.5 Conclusions ........................................................................................... 63 5 Ameliorating errors in monitoring of pup production ............................................. 66 5.1 Introduction .......................................................................................... 66 5.2 Materials and methods ............................................................................ 66 5.2.1 Comparison of aerial and ground counts of grey seal pups at Griend ... 66 5.2.2 Comparison of aerial and ground counts of grey seal pups at Richel. ... 67 5.2.3 Alternative survey techniques ....................................................... 68 5.3 Results ................................................................................................. 68 5.3.1 Comparison of aerial and ground counts of grey seal pups at Griend ... 68 5.3.2 Comparison of aerial and ground counts of grey seal pups at Richel .... 70 5.3.3 Alternative survey techniques ....................................................... 70 5.4 Discussion ............................................................................................ 71 6 Conclusions & recommendations ....................................................................... 72 6.1 Geomorphology of key pupping sites......................................................... 72 6.2 Exchange of grey seals between Dutch waters and other areas ..................... 72 6.3 Ameliorating errors in monitoring of pup production .................................... 73 6.4 Recommendations .................................................................................. 73 7 References ..................................................................................................... 75 8 Acknowledgements ......................................................................................... 78 9 Quality Assurance ........................................................................................... 78 10 Justification .................................................................................................... 79 11 Appendix A. Development embryonic dune field on Richel ..................................... 80 12 Appendix B. Vegetation species list for Richel – August 2014 ................................. 84 3 of 104 Report number C009/15 13 Appendix C. Vegetation scoring table ................................................................. 91 14 Appendix D. Vegetation relevés on Richel – August 2014 ...................................... 92 15 Appendix E. Vegetation