Photo-identification in grey seals: legibility and stability of natural markings

The stability of natural markings is critical to all photo-identification s tudies. In this study we assessed the stability of naturel pelage markings in grey seals, comparing visually a series of photos taken from a small pop ulation over several years. We observed that the pattern tends to darken wi th age, and that this process seems to occur more quickly in the first year s of life. Consequently the pattern legibility is reinforced in females, sh owing dark spots on a white background. In contrast, patterns in males (bei ng originally darker) tend to become completely black and difficult to dist inguish. The proportion of seals identifiable from their pelage markings, i nformation needed for estimating population size, was also assessed. Sixty- three percent of all the seals around the haulout sites could be photo-iden tified (100% of the females and 44% of the males).