How the Hawaii Unchartered Cooperative Research (HURC) Team Identifies Unique Oceanic Whitetip Sharksarks
The dorsal fin markings of oceanic whitetips are thought to be unique identifying features for individual sharks. More specifically, the patterns of the white ‘cap’ on the dorsal fin are primarily used to identify individuals, but surprisingly, markings on each side are unique to that individual, i.e. each side of the dorsal fin is different. HURC uses photo-editing software to crop and enhance the pictures submitted to our database in order to get a clear image of each shark's dorsal fin. For the most accurate identification, it’s best to have images of both the right and left side of the dorsal fin so they can be viewed side-by-side.
Identification always starts with the left side of the animal and if there isn't a match in the database, the picture receives a new ID number. If there is a corresponding right side image, this is also checked with known and unknown right-side images already in the database to help form a match. This works as a second check for identification and also allows any unknowns to be identified. If there is only a right side, HURC will look through each ID and unknown right side pictures to find a match. If no match is found, the individual gets a unique unknown ID number.
Unique scarring and markings can sometimes be used in the photo-ID process but are mainly used as extra information to compliment the markings on the dorsal fin. This is because scarring and markings can sometimes be obscured by photo angles, lighting, etc.. Also given that most of the individuals are very likely exposed to similar environments, there is a lot of overlap in scarring and markings. Though scars and markings are not often used in photo-identification directly, they do hold important clues about the individuals, their lives and interactions.with their environment. This can provide invaluable information about their threats and habits that can be critical to consider for conservation efforts.
Some interesting things that are noted in the database if HURC notice them on individuals are:
Mating scars on females (indications that she may have mated relatively recently and may be pregnant)
Hooks and trailing fishing gear: This can also sometimes help to match left and right sides to the same individual when sightings include more than one individual. If there are multiple individuals seen that are same sex and approximate size, it can be difficult to verify which individuals are which when series of images have both sides. Hooks and trailing lines are often visible in photographs from both sides of the individual so they can help to confirm identification.
Scarring from other animals in the ocean. Deron Verbeck had a sighting of an Oceanic Whitetip that had markings from squid tentacles (click here for more information). HURC have also seen evidence of "rake" marks or parallel scratches along the side of the body that are likely from the teeth of large odontocetes like pilot whales or killer whales.
HURC are currently working on developing some software of their own that will be tailored to the specific needs of this project.