Seahorse fingerprints: a new individual identification technique

Individual identification is particularly important for ethological studies and sampling design. Previous studies have developed various types of marking by tags and chemical marks, but these methods involve significant manipulation of the individuals. Other studies have reported natural marks as an efficient method for individual recognition. Our study aims to elucidate a new method for natural mark identification of seahorses, which we tested with the endangered Brazilian seahorse Hippocampus reidi. We avoid pseudoreplication by recognizing individuals. Seahorses have a hard bony structure on the top of their heads called the coronet, which has a different shape for each individual, corresponding to a fingerprint. We tagged seahorses in the field with collar tags and photographed their coronets. After two days, we identified seahorses by their photographs and verified their identification with the collar tags. We correctly identified all individuals by fingerprint identification. Although this method was only tested with adults, we suggest that it applies to seahorses in general, as all species possess the coronet structure.