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photo identification

Photo-identification of cetaceans

What is the purpose of photo-identification?

The study of cetaceans at sea is usually accompanied by photo-identification. This method of work consists of photographing specific areas of the animals observed at sea: caudal fin, dorsal fins, blanks ... and to list all the photographs in a catalog.

Each individual has its own characteristics, so we can know if the same individual has been observed in several different places, or if he is rather subservient to a very limited area. Photo-identification is for the cetologist the equivalent of banding or marking animals on land. It makes it possible to study them better and understand their behavior on an individual basis. Photo-identification catalogs are for the most part shared between different research programs.

When this work is continued for a long time, this opens up for scientists the possibility of advanced analyzes, mainly focused on population dynamics. Clearly, this can for example make it possible to estimate the abundance of a species, to show the fidelity of a group to a given zone, or to better know its social organization.
These analyzes are crucial because they can lead to more effective and relevant protection strategies. However, this requires a large amount of good quality data, and therefore many years of hard work, as well as a rigorously and consistently applied protocol.

Method

Photo-identification is based on the use of certain physical characteristics specific to each individual, as are fingerprints for humans. Some animals have particular traits that make them recognizable among other individuals of the same species.

The first step is to get pictures of the animals. Most of those used are taken from a boat. The characteristics used to identify individuals are therefore all observable on the animal when it is on the surface: notches in the fin, scars or pigmentation on the upper body ... In addition, some individuals may unfortunately have visible marks related to human activity, such as scars or injuries caused by a propeller or collision with a boat.

Once on the ground, the photos are retrieved and examined one by one to determine if they contain details that can be used to identify the individual. Photos of poor quality, or nothing useful, are left out.

After this phase of sorting, it is a question of precisely describing each individual photographed: number, size and position of the scars, form of the fin, notches, pigmentation, etc. This description step is repeated for each photo containing the individual. These carefully described photos will form a profile of the animal, and all profiles form a Photo-identification catalog.

Later, when new pictures of cetaceans are taken at sea, they can be compared to the photos in the catalog to try to recognize previously identified individuals.

Cybelle Planète has its own photo-identification catalog, created thanks to the photographs taken during expeditions in Pelagos, and by boaters contributing to our participatory science program, Cybelle Méditerranée.

Species studied

Our efforts are focused on the most commonly observed cetacean species, and those with the most frequently identifying details:

  • fin whale : its fin may have a particular shape or recognizable notches. The right side of his head also has white patterns specific to each animal.
  • Bottlenose dolphin : like fin whales, their fins may have characteristic details. It also often has visible scars on the skin.
  • Risso it is usually covered with scars forming a pattern of each individual, which makes them very recognizable between them. The oldest dolphins of Risso seem even completely white.
  • Sperm whale : having the peculiarity of widely out their tail when diving, it can be used to identify individuals. In fact, the sperm whale's tail often has characteristic details (notches, shape, pigmentation, etc.). The bumps on his back can also be a clue to recognizing an individual.
  • pilot whale it usually has few distinctive signs, which makes it difficult for individuals to recognize each other. He may still have scars or scratches on his body or notches on the flap.

Cuvier's beaked whales, minke whales and common dolphins are not observed often enough in our study area to be effectively photographed.

Blue and white dolphins, for their part, are observed in too many numbers and do not have enough distinctive features to be easily photo-identified.

Returns

As explained above, the photo-identification of cetaceans is a long-term endeavor, the results of which usually appear after several years of continuous monitoring. Patience is in order. The photographic information associated with the observations at sea carried out by the Cybelle Méditerranée program have already been contribute to studies combining databases from several different sources. In particular, the GIS3M estimated in 2016 the populations of sperm whales, pilot whales and fin whales in the north-west of the Mediterranean, using data provided by various scientific and associative structures in the Mediterranean, including Cybelle Planète.


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