The short answer is that it depends on the type of shell, its size, where you collect it, and whether there is a living creature still calling that shell home.
The issue of shell collecting has become contentious in the past thirty years since the first laws arrived. It may seem like an unenforceable law for a seemingly innocent act – beach combing for washed up shells seems rather innocent compared to smuggling animal body parts across borders.
Some governmental environmental agencies allow collectors with a permit, or will state which shells are not to be collected, such as the Philippines with this handy visual guide. However, if you are caught removing any live shellfish/molluscs, or endangered/rare species, you could be in hot water and face prosecution.
In fact, beach combing has caused some international tensions in the past. Russian diplomats complained that Chinese tourists were ‘stealing’ the colourful glass pebbles of Ussuri Bay. There was a sign claiming that removing them was ‘strictly forbidden,’ but it was only written in Russian.
Nature parks, such as Batemans Marine Park in Australia, limits the amount of shells that can be collected and stipulates that it must be for non-commercial use. It is worth noting that taking anything is prohibited in marine conservation zones. These areas protect the vulnerable species living there from human interference.
Some environmental agencies have taken this precaution a step further, and have legally banned tourists from taking any shells with them, regardless of size, quantity or species.
Anything that is recovered in customs when you return to the airport (at either end) could be confiscated if not declared, and you may face a fine for seized goods and breaking potential biosecurity restrictions.
While it is unlikely that the police will conduct bag searches on the edges of the shore, or empty out buckets in the search for contraband sea goodies, be warned that one woman in Florida was caught. She was discovered to have bags of conches, many of which were still alive, along with forty rare Queen conches in her possession. She was jailed for 15 days and fined $500.
Next time you see an enticing shell on the beach, it may be better to admire it then leave it where it is for others to do the same.
Read CITES checklist (Convention on International Trade in Endangered Species of Wild Fauna and Flora) to see whether the international trading standards allow you to take anything home.
If in doubt, it is best to leave it.