The phrase "occasional turtle" refers to a turtle that is seen or encountered only sometimes or rarely. It suggests that the turtle is not a common sight but appears infrequently. Full definition
Long Caye, Aquarium, and the Cathedral provide a stunning underwater landscape of coral formations amidst occasional turtle and eagle ray sightings. (liveaboard.com)
Scuba divers love the variety of marine life found amongst the cracks and crevices on this reef, including the occasional turtle. (baliocean.com)
You might also come across the occasional turtle. (gapyear.com)