@Jason1528 That's standard procedure in Croatia and some other countries and it is not new. All tourists have to register at the police by themselves, or, if they stay in a hotel or in Airbnb then their host or a hotel has to register them. Personal info includes name, passport number, citizenship, city of residence, date of birth, and the dates of check-in and out. It has to be done for all members of the group, including children and babies.
Look at it from the bright side - both, you and the police will always know who is using your property and who is responsible. This is a great way to prevent trash-parties and similar illegal activities at your place.