Guess who? – Identifying seals from pictures

Harbour seals’ coat is mottled and each seal has a unique pattern of spots in their pelage which can be used to identify them individually. This technique is known as photo-identification, and it is of great use to study wild populations of animals that are naturally marked (e.g. whales, seals, giraffes, tigers, salamanders, turtles, whale sharks and manta rays among many others). By photographing animals repeatedly over time and identifying them based on their unique natural marks we can start building up individual sighting histories. These can then be used to infer different individual and population parameters, such as the number of animals using an area, their survival and birth rates, or patterns of residency or movement between different haulouts.

When we visit a haulout, we take photographs of individual seals from a distance to avoid disturbing them, using a camera attached to a scope. At the end of the day, we download the photographs and we grade them according to their photographic quality. Then the “Guess who” game starts, to identify individual seals based on the spot pattern, mainly from the head and neck areas. This allows us to identify seals that have been previously photographed as well as adding newly seen individuals to the catalogue.

photoID match
Harbour seal identified in May and June 2015 from its pelage pattern of the head and neck area

In harbour seals, newborn pups are already born in their first adult coat. This is a much darker pelage compared to the adults, but their spot pattern can already be seen. The colour coat changes through the year, from a pale sandy-brown shortly before they moult to a fairly dark charcoal-grey just after moulting. Yearlings (one-year-old seals) begin to moult first, followed by adult females and finally adult males, although there is considerable overlap between all groups.

pup coat
Harbour seal pup
Yearling with its pre-moult coat
Yearling with its pre-moult coat
adult coat
Adult harbour seal

Summer 2015 recap

The summer of 2015 was our first fieldwork season for the Harbour Seal Decline Project. During June and July we had 4 teams of adventurous explorers walking different parts of the Scottish coast in search for harbour seals. The teams where searching for haulouts that could be accessed easily by foot (not always the case!) and where seals could be observed without disturbance. We were especially interested in identifying those haulouts used by female harbour seals to give birth to their pups, as the project will be collecting data on female survival and birth rates.

Crossing 60° N in search of harbour seals!
Crossing 60° N in search of harbour seals!

Overall we visited more than 100 different haulouts located all over Scotland: we visited sites in the East Coast, further north in the Highlands along the Pentland Firth and in the north-west corner of mainland around Lochinver and Kylestrome. We also took the ferry to Orkney and Shetland, exploring the islands’ mainland as well as some of the smaller islands. In the West coast we explored Isle of Skye, Applecross, and went to check haulouts in Mallaig and Arisaig. Further south we also visited sites in the Sound of Mull and along the coast of Kintyre.

Photo-ID shot showing unique pelage pattern
Photo-ID shot showing unique pelage pattern of a harbour seal

At each site visited we counted the number of grey and harbour seals on shore and in the water, looked for pregnant females and pups, and described how suitable each site was for collecting data. When possible we also collected photo-identification data, to start building a catalogue of individually identified seals based on their pelage pattern. The many hours spent observing harbour seals were rewarded with many entertaining sights and behaviours from adults and pups, as you can see in the video below.

The field season finished at the end of July, when harbour seals start their annual moult. After that there were many hours of data entry in the computer and looking through pictures of sites and seals. We all felt very lucky to have been able to explore the beautiful Scottish coasts, under all kinds of weather, finding some amazing spots and seeing plenty of wildlife. We are looking forward to the 2016 field season!

New project, new blog!

Welcome to the Harbour Seal Decline Project blog! In this blog you can find information about this project lead by the Sea Mammal Research Unit (SMRU) and meet the team that will be in the field collecting data and behind computers conducting the data analysis. You can also learn about the biology of harbour seals or know how to distinguish between grey and harbour seals.

We will post updates on the fieldwork that we will be collecting in different parts of Scotland. We hope you’ll enjoy following us!

Harbour seals hauled out in Orkney
Harbour seals hauled out in Orkney