Published: Feb 18, 2012 4:55 AM EST

SANIBEL, Fla. - Shells are free for the taking on Sanibel Island, but selling them under the wrong circumstances could land you in hot water.

The city has already caught wind of people peddling shells without the proper license, and with the first day of Shellabration wrapping up, it wants to remind people about a couple rules regarding one of its most precious resources.

Sanibel's Planning director James Jordan says while seashells are in abundance on the island, when they are sold, they become just like any other good or service.

"In the city of Sanibel, you have to have a business tax receipt in order to conduct business," Jordan says.

Selling shells illegally can carry a fine, and some, like shell salesman Bill Strange, say on top of that, it puts legitimate businesses at a disadvantage and cheats the city out of taxes.

"All the tax dollars everybody pays helps maintain the island and keep it the beautiful island that it is," says Strange, who has run Sanibel Seashell Industries for more than 20 years.

Another important rule to keep in mind while shelling, is to leave the live ones untouched, as failing to do so can land you a $500 fine and up to 60 days in jail.

Live shell means any shell with a creature still inside, including sand dollars, starfish, and sea urchins.

"The idea is to make sure there are shells around for future generations to enjoy as well, so we really restrict the taking of shells to any shell that washes up on the beach that isn't live," says Jordan.