A beginner’s guide to photo ID

Photo identification, or photo ID, is a staple of marine mammal research. The natural patterns of pigmentation and scarring on specific parts of a cetacean’s body – most commonly, their tail, dorsal fin, or back – are unique, much like our own fingerprints! This means that we can identify individuals from something as simple as a good photograph.

Photo ID is used in the research of various marine mammal species and is undoubtedly the most efficient way of gathering information on population demographics and social structure. Many other research techniques also rely on photo ID; for example, when taking a biopsy of a whale or dolphin, or attaching a tag, it is important to know who you’re studying! This means that we can link information on genetics, diet, and short- or long-term movements to a particular individual.

You may be surprised to hear that one of the most widely used techniques in marine mammal science is, for the most part, very simple. Essentially, this is a game of ‘spot the difference’ – or maybe more like ‘spot the similarities’ – there’s not much more to it than comparing pictures until you find a match. Of course, researchers will have tens of thousands of photos of whales to sort through and a catalogue of thousands to match them to, so you can imagine that it’s a task requiring patience more than anything else.

For those of you still interested in taking the plunge – you have been warned...

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The photos

To start off with, you need a decent photo of a whale – so grab your camera and get shooting! To be usable, the photo needs to be in focus and the whale needs to be clearly visible (not just a speck in the distance). Rapid shutter speeds are best, typically 1/1000 or faster, and a fairly wide aperture; however, depending on the lighting and weather conditions on the day, you may want to adjust these a bit.

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The whales

Another important factor to consider is which part of the whale you’re photographing. The areas of the body used for photo ID vary between species, so it’s good to know what you’re looking for before you start shooting!

There are almost 90 cetacean species in the world, so I’m not going to list every single one of them here, but here is a brief overview of how we ID some of the most common and well-studied whales and dolphins.

Humpback whales and sperm whales are identified based on their tail flukes. Humpback whales make it especially nice for us as they have mottled black and white markings on the underside of their fluke – very useful for photo ID! As well as their pigmentation, we can also use the shape of the trailing edge of the fluke. Sperm whales have no pattern on their fluke, so only the 'trailing edge' can be used for photo ID.

Most dolphins are identified from their dorsal fins. Some rorqual whales, like fin whales and minke whales, are also primarily identified by the shape of the dorsal fin. In these cases, where there are very few other distinguishing features, the scars and nicks on the fin become especially important for identification.

Because of their natural markings, we can use the larger area encompassing the dorsal fin and upper back of species like killer whales, blue whales, and beaked whales. In the case of killer whales, it is the shape of the pale ‘saddle patch’ behind the dorsal fin, as well as rake marks and scars, which we use for identification; blue whales can be identified by the mottled blue-grey pattern on their back.

All three right whale species are identified by the pattern of callosities on their face – these are patches of very thick, tough skin, much like a callus, which become colonised by barnacles and other parasites. The number, size, and position of these bumpy white callosities is unique on each whale.

The ID

Once you have your photos, you need to find your local catalogue. These are available online for free more and more often these days – for example, in Iceland, we have an online catalogue for humpback whales, killer whales, and northern bottlenose whales.

Pick out the most distinctive features of your whale. This could be the shape of the dorsal fin, a particularly large nick in the trailing edge of the fluke, a prominent scar, or a pattern of pigmentation.  

Bear in mind that the photo you are using was taken after all the photos in the catalogue. Markings like scars and nicks could be very clear in the older photo but have faded away over time or, equally, could have been acquired more recently than the photo in the catalogue was taken. The natural shape of the fin and/or skin pigmentation typically doesn’t change once the whale reaches maturity, so, if possible, these are more reliable features to base your ID on.

Now you have all the tools at your disposal to go ahead and try and identify your whale!

The science

As I mentioned previously, photo ID is something which requires patience more than it does any inherent skill. Having said that, there is definitely some sort of knack to it – if I’ve been away from it for a while, it can take me a few days to get back into it – and it’s not for everyone! So if you have taken some photos of a whale or dolphin and you want to know who it is but you don’t want to spend your whole afternoon comparing them to thousands of other photos (which is entirely fair!) the good news is that somebody else might be willing to do it for you.

Most online photo ID catalogues have an option to submit photos. Any photos that you take of whales and dolphins are crucial data for the scientists who study them – even more so if they are of a high enough quality to allow photo ID. When sending in your photos, including the date and time they were taken and where they were taken, as exact as possible, means we can track the movements of these particular individuals on their travels across the ocean.

Photo ID has been used to map the migration routes of humpback whales, to identify the population structure of blue whales, and to understand how the seasonal movements of killer whales are related to their prey.

While dedicated whale research is the best way to gather high-quality data, the inclusion of photos from the members of the public means that photo ID catalogues cover a much greater geographic area than is possible for any research team. By opening up the catalogue to include so-called ‘citizen science’ data, we therefore get a more complete record of a population’s movements, social structure, and size.

Just recently, a huge collaboration in the North Pacific combined photo ID catalogues from 43 different research organisations and the citizen science-based platform Happywhale. The final data set included 30,100 individual humpback whales throughout the entire North Pacific, photographed between 1977 and 2022. A massive 34% of the catalogue – documenting 15,298 humpback whales – came from photos taken by citizen scientists and uploaded to Happywhale.

This proves beyond a doubt just how big a role citizen science can play in marine mammal research. Our datasets are larger now than ever before, thanks in part to the effort of citizen scientists; perhaps even more importantly, citizen science platforms like Zooniverse, iNaturalist, and Happywhale are encouraging more and more people to engage with the natural world. Even if you’re not a scientist yourself, you can still contribute to the understanding and conservation of our living planet. Every sighting you report and every photo you take counts!