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Elasmobranch Egg Case Predation in the Dutch North Sea


Since 2014 elasmobranch egg cases that are washed up on the Dutch North Sea beaches can be registered by beachcombers using the Great Eggcase Hunt database. For this study, individuals often registering multiple egg cases were asked to send these to the authors for a predation study. After disposing of heavily damaged (over 50% gone) egg cases, a total of 736 egg cases of six different elasmobranch species (Raja microocellata, Raja brachyura, Raja montagui, Raja undulata, Raja clavata, Scyliorhinus canicula) were examined. All egg cases were scored for number of predation marks, the condition of the egg case and status of the hatching slit. The shape of the predation marks was classified into five types: parabolic, circular, elongated, scratched and irregular shaped and it was noted whether or not the boreholes were complete. Predation rate across species was 14.4%. Results show no discernible difference in proportion of egg cases with any kind of predation mark between species, which is beneficial for future analysis and conservation strategies, as the same approach can be used for all species. The presence of multiple incomplete predation marks on 38% of predated egg cases shows evidence of site selection by the predator. This site selection, as well as borehole shape and diameter found points to gastropods and octopus as potential predators.

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Data Availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Code Availability

The coding generated during and/or used during the current study are available from the corresponding author on reasonable request.


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The authors would like to thank WWF for funding the time and location at Blue Linked to carry out this research. We would also like to thank the Shark Trust for involving us in their project and creating the initial database. But most of all we would like to thank the many Dutch beachcombers that have sent us the egg cases they found while searching the beaches, making our data collection so much less time consuming.


This study was funded by the Dutch Shark Society and WWF Netherlands.

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Authors and Affiliations



D.S. has performed the literature study, data collection and has written most of the paper. G.S. has performed the statistical analysis. G.W. has provided feedback on text and enabled citizen science data collection. P.V. has provided the photographs. M.L. has provided space for data collection, as well as knowledge on egg case incubation. All authors read and approved the final manuscript.

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Correspondence to D. Schröder.

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To the best of your knowledge everybody who participated substantially in the study is not omitted from the article. To the best of your knowledge, all persons listed as authors qualify for authorship. All persons who have made substantial contributions to the work but do not meet the criteria for authorship are listed in Acknowledgments section. All persons named in the Acknowledgment section of the manuscript have given their permission to be named. Sampling and field studies: All necessary permits for sampling and observational field studies have been obtained by the authors from the competent authorities and are mentioned in the acknowledgements, if applicable. The study is compliant with CBD and Nagoya protocols.

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Schröder, D., Schröder, G., Wiersma, G. et al. Elasmobranch Egg Case Predation in the Dutch North Sea. Proc Zool Soc 74, 211–218 (2021).

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