Really important methods for marine mammal researchers interested in ecology and conservation is defined as “mark-recapture”. These methods were developed for studies in which individual animals are physically captured and marked by the application of a tag, released, and then recaptured or resighted without capture.
The capture, marking, release, and recapture of individual animals can be used to study movement patterns, size, and structure of populations, and survival and recruitment rates.
In order to give you a concrete example of what I’m talking about you may think about the practice of “bird-ringing”, the most spread out (and maybe the oldest) and used technique of mark-recapture. Researchers capture birds (without harming the individuals) and ring their legs. Each ring has a code and then they release the animals. After that, it’s possible to sight or capture these animals and understand where they come from and collect data about the abundance of their populations.
Good photographs are essential for photo-identification; good enough that animals that are considered marked will be recognized with certainty if seen again later. Several studies properly describe the specific criteria to define “a good quality” photo for the research.
The list of cetacean species that have been studied using photo-identification includes most baleen whales, several large odontocetes, and many species of dolphins.
A large and increasing amount of what we know about the biology of these species has come through mark-recapture analyses of data collected through these studies. The number of marine mammal datasets that are sufficiently long and rich for robust analysis continues to grow, making mark-recapture through photo-identification an increasingly valuable technique.
Regarding dolphin species (such as bottlenose or Risso’s dolphins) the main target of the photographs is their dorsal fin. For whales, the target is mainly their large tale that flukes out of the water. I said “mainly” because good photos of other part of the body of the animals (for example the flanks of sperm whales) can support your Photo-ID research.
In my experience on board of the Jonian Dolphin Conservation research vessels, I could apply this research method with several species: Risso’s, bottlenose and short-beaked common dolphins and sperm whales.
Risso's, bottlenose, short-beaked common dolphins & sperm whales - the target species of my photoID experience on board of JDC research vessels - Photo by Stefano Bellomo
I really love to do Photo-ID. Hard to explain why. I love to observe nature. I love to observe animals and their behaviour and thanks to photograph, I can shoot the most important instant that I observe. I love this technique also because is a lot more than just “taking photos”. That’s the easiest part of the job (even if it’s not so easy).
The hard part is that you have to be able to predict the movement of the animals.
You have to be in exact position, in the exact moment while the dolphin is surfacing, or a whale is fluking and that is the moment where you are able to take your great shot.
What do I mean with “being in the exact position”?
Wild animals tend to escape from us if we don’t properly approach them. The same for dolphins. To collect good photographs for photo-ID, usually, you have to get closer than how close you are while you observe them as a tourist or in other studies, such us the one related to ethology.
Observe their behaviour, try to estimate how many individuals are around you (this may be useful because your goal is to take photos of all the animals sighted) and when you realize that your presence in not creating a disturb to them, in collaboration with your great skipper, start to navigate properly, in order to be on the left or right side of the animals (if you want to take photos of dorsal fins) or at the back of a whale (if you want to take photos of the fluke).
You have to take in consideration that these animals are always moving and you have to be able to follow those movements with your vessel in order to be in the correct position to shoot them and take the right photos.
After the emotions of the sighting and after collecting many photos, you need to archive them, and this is a really important part of a good (and smart) photoID research study.
It may sound easy, but my suggestion is to archive the photos day by day and go through your photos and delete the bad one (not focused, dark images and so on). You will save a lot of Gb at the end of the work. If you do it day by day, it won’t be a boring job.
I save each folder is this way: PhotoID Archive --> Name of the Species --> Data (year-month-day) (for example if I was going to archive photos today the name of the folder was going to be 20210130).
In this way, you archive will be automatically organized with all the data divided for species and dates of sighting ready to be analysed.
And here it is the other great part of the work, when you have to check which animals you sighted! In most part of the time, over all related to Risso’s dolphins and sperm whales I recognize the animals when I am already on board and I get so excited when I see calves growing up or mothers with new calves or when I see an animal that I didn’t see since a long time!
A juvenile Risso's dolphin named in this way because of the "m-shape" mark on its right side
Photo by Stefano Bellomo
Every researcher has its own method of analyses and many studies now use automatized methods thanks to artificial intelligence.
The most important thing to keep in mind, whatever method you choose, is that a good result depends on the catalogue you create. If the catalogue is not good, your result won’t be good.
A catalogue is the collection of photos of each animal you sighted.
About dolphins, you have the right and left side of the dorsal fin. About whales you have the photo of the fluke (plus of course all the other photos of the animal that may support your study) and here we are back to the main point: taking good photos!
Practice, practice, practice… and never forget, ENJOY WHAT YOU DO! ;)
One last thing! Which lens it the best in order to correctly implement this method?
It depends if you do it from land or on boat. On a boat, I use a lens 70-300 mm that, in my opinion, is the best compromise between good result of photos obtained even if the animals are a bit more far away and suitability of use, over all considering also life on a boat. Moreover, it’s not too heavy as larger lenses can be.
If you do photoID on land you are much more far away from the animals so you may need larger ones.
Let me share with you the scientific papers in which I am co-author (just click and you will go to the Google Scholar page).
Here you may find more information related to the methods we use for our photoID studies.
Write me to share opinions, ideas, results
or if you have further questions related to photoID! ;)