This rototag shows a unique identifying number on one side, and the contact information of the Southwest Fisheries Science Center on the other. The tag is attached to the dorsal fin of sharks that have been injected with oxytetracycline. If fishermen catch a rototagged shark, they can contact the laboratory for a reward for information and a vertebral sample. The oxytetracycline marked vertebrae assist scientists in determining the age of the shark, in a manner similar to counting the rings on tress.