More than 400 species of seashell can be found on Sanibel?s beaches. Why there? Sanibel?s boomerang shape sticks out in the Gulf of Mexico like a crooked finger. The island?s east-west direction makes it the perfect receptacle for catching millions of seashells. Did you know the best time of day for shelling is two hours before low tide? Watch for more answers on this relaxing way to collect ocean gems.