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Pink dolphins are also found in the Amazon river in South America. They are known as boto dolphins, and are so coloured for the same reason. However, boto adults become more pink over time as their skin is rubbed away. For this reason males are pinker than females because they are more frequently aggressive with one another, basically exposing the blood vessels as time goes on.

The Indo-Pacific humpback dolphin is listed in the Convention on the Conservation of Migratory Species as having an unfavourable conservation status. Research in the late 1990s found only a small population of around 200 remaining in the waters around Hong Kong and conservationists say there are now even fewer. They tend to stay in the inshore waters and are not migratory, limiting themselves to an area of around 100 km2.

This means they are vulnerable to the full range of human activities that take place around Hong Kong, which is one of the busiest ports in the world. As well as being caught in fishing nets and struck by ships, they are also disturbed by the noise from shipping and marine construction, which interferes with their communication, hunting and causes hearing damage. Recently, the Hong Kong Dolphin Conservation Society warned that plans to expand the city’s island airport and build a bridge to nearby Macau could drive the population away completely.

They are also vulnerable to pollutants from sewage and industry that are discharged into the area’s rivers and coastal waters. We judge the health of UK seaside bathing waters by the concentration of faecal coliform bacteria. We consider taking in just 200 coliforms on a single occasion unacceptable, yet the Hong Kong dolphins are ingesting over 100 times that amount daily.