Dutch version of the WUR page says basically the same thing: "Uit het onderzoeksrapport blijkt dat Nederland juridisch gezien een bijdrage aan de wolvenpopulatie moet leveren van 23 tot 56 roedels. " -> the study concludes that the Netherlands has to contribute to the wolf population from 23 to 56 wolf packs.

Reading further:

https://edepot.wur.nl/690748

It seems that this is part of a european "habitats directive" for managing biodiversity within Europe. This directive (according to the above paper) determined there need to be around 500 wolf packs across Europe to keep wolves at a stable level without too much inbreeding. The Netherlands was found to be able to "contribute" 23 to 56 wolf packs in this sense.