Online advertisements for crayfish decrease after a provincial ban

The parthenogenetic marbled crayfish, Procambarus virginalis, is an unwanted species introduced in many countries. There are no established populations in North America to date. Several jurisdictions in the United States and Canada have specifically banned ownership of marbled crayfish, but it is unclear if such bans effectively reduce ownership. The Canadian province of Saskatchewan prohibited marbled crayfish in 2020. We tested whether the introduction of this law affected behaviour by comparing online advertisements in Saskatchewan and other Canadian provinces over two years before and after the ban. The number of online advertisements and sellers in Saskatchewan for all crayfish – not just marbled crayfish – was significantly smaller after the ban. No other province showed this pattern. This suggests banning marbled crayfish reduced the online availability of crayfish and may be an example of a successful policy to reduce availability of aquarium pets.