Sperm whales’ photo-ID

When there is a need to understand a little more about the behavior and ecology of a species, it’s extremely important to be able to identify the different individuals of a certain group. Photo identification (or photo-ID) emerges to solve this problem. This method can be used in cetaceans, both in whales and in dolphins, using their dorsal fins and flukes since the outline of these external organs varies from individual to individual. The use of photos began around the 1970s with bottlenose dolphinsTursiops truncatus), killer whales (Orcinus orca), Indo-Pacific humpback dolphin (Sousa chinensis chinensis) and the spinner dolphin (Stenella longirostis).

Throughout their lives, cetaceans have intra and inter-specific interactions that can be with objects of anthropogenic activities, such as fishing nets and boat propellers, and even interactions with the habitat where they live. These interactions can cause damage to the fins of these animals, making them irregular and easily recognizable through patterns of both cuts and scars that end up not changing over time. These marks then serve to establish the identity of a particular individual.

In addition to the fins, also variations in the pigmentation on the skin of individuals can contribute to their identification. Using the example of humpback and right whales, the scattering of callosities on the head and the pattern of spots on the caudal fins respectively are used to identify individuals. The use of cameras to photograph these animals turns out to be a non-evasive method and therefore does not disturb the animals.

By joining the information obtained from photo-ID data with other data, we can construct the life history of an individual and the size of the population, associations between different individuals, and the habitat itself. Also, the migratory patterns of these large animals can be obtained by using this method of identification whenever photos of the same individual are obtained in places quite distant from each other.

By associating photo identification data with data from ecology and behavior studies, we can learn important information about the life history of these animals, such as at what age they reach sexual maturity and even at what interval the offspring are born.

The sperm whale is a resident species in the Azores and individuals can be recognized over time through folds and scars on their dorsal fins, but mainly on their caudal fins. A survey carried out between 1988 and 1995 on the islands of the central group estimated that the number of sperm whales would not exceed 2500 using photo identification.

Throughout our trips, our guides will whenever possible, take pictures of the tails of the sperm whales that are found. As soon as these animals dive in search of their food, they end up placing their enormous caudal fins vertically in the air, at which point it becomes possible to obtain the material necessary for photo identification.

These photos are gathered and organized at the end of the year and only then is it possible to begin the long process of comparing the different tails with each other. The photos retain information about the date and time they were taken, which together with the geographic coordinates taken when they were taken, make it possible to create a time scale on the movements of individuals.

By looking to figure 2, we can see that it is the same individual but on different days in the same year (2022). This sperm whale was seen and photographed south of São Miguel Island, in the Azores, on the 30th of September and on the 4th of November. By analyzing the fluke, we can say that it is the same individual. Both photos show a circular cut in the trailing edge of the left fluke and a round cut in the trailing edge of the right fluke very close to the central notch. We can also notice lighter spots on both lobes that clearly correspond to both photos. Through the analysis of photos like these, we can build a time scale of their stay in each geographical area.

When we talk about animals that are only visible for brief periods on the surface, all the material that can be obtained from different individuals is extremely important. For this reason, it is important to continue this type of work to better understand the life of cetaceans, which in many cases remains a great mystery.

Article written by the biologist Alexandre Branco from Picos de Aventura team.

Find out more about our Whale Watching activities here and book your experience with us here.