Individual identification is a very powerful but challenging approach in zoological research. Characteristics such as the noseprint in dogs, footprint of giant pandas, face of monkeys, markings on leopard cats etc., can all be used to identify an animal. Using this approach, researchers can learn about the population dynamics and ranging behaviours of these animals like never before.

For animals that show less physical distinctiveness like the otter, individual identification is not possible with the typical field methods – namely, camera traps and finding animal traces. But with the advances in genetic research, we can now identify individual otters with their faeces. This is because as food passes through an otter’s gut, some of the cells at the gut wall are shed and then mixed with the faeces. Recently, our otter survey in Inner Deep Bay has put such technique to use, and the result would not only tell us about the number of otters living in the study area, but also how far can an otter range.

We analysed seven microsatellite loci on pairs of alleles in the DNA samples. Microsatellites are repetitive DNA sequences, for example, ACCACCACCACC (4 repetitions). The number of repetitions is mainly hereditary, and could be different among individuals. Figure 6 shows pairs of data for 2 microsatellites of 6 genetic samples. Although samples 3 and 4 have similar microsatellite A, they are different in microsatellite B, indicating all six samples came from different individuals.

A similar study on otters in Kinmen of Taiwan showed that more than half of the newborn otters would “disappear” in about six months of age. It was speculated that since most of the freshwater habitats in Kinmen are fully occupied, young otters are forced to leave the island once they reach adulthood.

Otter faeces are being collected from the field.

Genetic materials are being extracted from the samples.

Conducting PRC with the extracted genetic materials.

Conducting gel electrophoresis to separate DNA fragments.

Examining DNA bands photo taken by a UV light box.

Paired data of two microsatellites of six genetic samples.

Mai Po is the last stronghold of the otters in Hong Kong.