DNA collections from seawater

Whale sharks are the world's largest species and often very hard to locate since they live so far from shore. Recently, researches have been able to extract their DNA from environmental DNA-eDNA- in the ocean to understand more about this mysterious species. 

In 2007, there was a sighting of 100 whale sharks at a oil field, approximately 80 kilometers off the coast of Qatar; these became a very popular sight to study this endangered species. A group of researchers came from the Natural Museum of Denmark at the University of Copenhagan, and began to collect samples of the seawater from this sight. The water collected had many materials and cells from the whale sharks. They isolated the cells, extracted and sequenced the DNA, and assigned these DNA to whale sharks; they were good indicators that whale sharks had passed through those waters and interacted in that area. The DNA they sequenced, was then used to estimate the number of reproductive female whale sharks which was approximately 71,000. It is quite amazing that eDNA can be used to estimate such large numbers. This DNA can be used to learn so much about a species, we know so little about. 

http://www.worldwildlife.org/species/whale-shark