Six to eight million years ago, a snake related to swamp snakes or tiger snakes slithered into the sea. Over evolutionary time, descendants of that snake developed flattened paddle tails, an ability to breathe through the skin and a valve to stop water from entering the lungs. Today these creatures live their entire lives in the water. Clad in spots, triangles and stripes, they undulate across coral reefs or meadows of sea grass.

There are some 70 species of sea snakes in the world; they live in the Indian and Pacific oceans, in water less than 600 feet deep. Half of all species can be found in Australia, and they are particularly visible during their mating period, in July and August.

But sea snake populations have been declining rapidly for the last 20 years worldwide, as a result of climate change, pollution, fishing, habitat loss, mining exploration and disease. Although sea snakes are the most diverse group of marine reptiles — they outnumber sea turtle species by 10 to one — less is known about their ecology than that of any other group of reptiles.

This is because the research is difficult. If you want to find a sea snake, you have to go out searching for one.