How to Identify an Individual Great White Shark. Part 2
There are two different approaches to identifying an individual Great White shark.
The first technique discussed in part 1 was by using a Dorsal Fin ID photo, we use this method at the Farallon Islands. Now in part 2 we will be discussing using the pigmentation patterns in 3 different regions of a white shark.
Since 2002 I have been recommending that Guadalupe Island Cage divers and guests share their photos to a larger data base of images for an ongoing Photo ID program curated by researcher Nicole Nasby-Lucas.
The images are collected with the photographer’s name, date and location each image was taken. Using these images and the pigment patterns from three regions of the shark, the gill flap, pelvic fin region, and caudal fin region the photos are used to identify each individual shark. Along with two non-pigment areas that are also recorded to aid identification the sex of the shark and any mutilations (i.e. major scars, damage and notches on the trailing edge of the dorsal fin).
By photographing the sharks on both sides and documenting each of these regions, we can identify the shark from a single photograph of any one region of the shark in the future. We then can document the shark being present at Guadalupe island.
Below is a photo of Cal Ripfin (aka Shredder) who is easily Identified by the unique mutilations on his dorsal fin.
It was determined that there are 3 different gill flap types.
They are defined by the presence of white pigmentation on individual flaps.
A type 1 Gill flap has white pigment only on the first gill flap, type 2 has white on the first and second gill flap and type 3 has white on the first, second and third gill flaps
It was determined that there are 3 different pelvic fin types.
Again, they are defined by the presence of pigmentation but of the gray color or the lack of.
Type 1 has gray pigment that is continuous from the pelvic fin up to the body,
Type 2 has gray pigment that continues above the pelvic fin upward onto the body but not continuous.
Type 3 has gray on the pelvic fin but does extend above onto the body.
It was determined that there are 4 different caudal fin types.
Type 1 caudal fins are completely gray
Type 2 Caudal fins have small island of white but otherwise are completely gray
Type 3 caudal fins have white on the bottom leading edge of the lower part of the fin
Type 4 has a leading edge of white with either an island of white or white extending towards the center of the lower fin.
A male shark is identified by the external reproductive organ called “claspers” (yes, there are two of them), and females have a “cloaca”
Sighting data is analyzed to determine the number of sharks per week, month and year as well as to calculate the ratio of males vs females. Year over year, the data can be used to see if the shark returns each year or every other year and if the population increases or decreases.
At this time, MarineCSI.org have 312 White sharks at Guadalupe Identified.
This is a great project to participate in for all of us Citizen Scientists
To read the peer reviewed paper
Annual re-sightings of photographically identified white sharks (Carcharodon carcharias) at an eastern Pacific aggregation site (Guadalupe Island, Mexico)
Michael L. Domeier · Nicole Nasby-Lucas