**Data for Loch Ness from**:
Mackal RP (1976). The Monsters of Loch Ness. Swallow Press. Appendix G. https://archive.org/details/monstersoflochne00royp/page/214/mode/2up
**Data for Zeeschelde from**:
Verhelst P, J De Meyer, J Reubens, J Coeck, P Goethals, T Moens, and A Mouton (2018). Unimodal head-width distribution of the European eel (Anguilla anguilla L.) from the Zeeschelde does not support disruptive selection. PeerJ 6, e5773. https://doi.org/10.7717/peerj.5773. Supplemental Information: https://doi.org/10.7717/peerj.5773/supp-4.
Rights for these data belong to the authors of the original publications above. These data are reused under Fair Use.