DNA Traces Prove To Be Useful Tool in Understanding Fish Populations 


Cownose rays are been found far north of their normal territory using eDNA

Scientists have discovered a revolutionary new tool for monitoring fish populations and biodiversity. Using the DNA left behind from marine animals, researchers can follow the clues that link animals to their habitats.

Tracking and tracing moving animals is difficult at best. The capture, tagging and releasing of animals is time-consuming, expensive and invasive. Scientists at Rockefeller University believe to have found a solution to that problem. Spending the last two years sampling water from an area off the coast of New Jersey, researchers have discovered genetic traces of animals that are not native to the area. The discovery of the environmental DNA (eDNA) from species such as the Brazillian cownose ray and Gulf kingfishes, lead scientists to believe that climate change is impacting the long-range migration patterns of these species.


water bottle

Samples taken with smile cups and stored in plastic bottles are proving to be a better way of tracking fish populations

A key step in conservation biology is understanding where organisms are distributed. Because of changes to ocean temperatures, chemical pollution and human interference such as noise and night-time light pollution; the number of species in a particular area is predicted to change. Scientists across the discipline are looking at how DNA found in the water from sources such as living organisms’ excrement and loose cells, can serve as markers for the presence of marine species without the need for direct observation.

Tracing moving animals using their DNA is a new and innovative technique for studying how animals are reacting to climate change. Dr Stockle from the Rockefeller university said that the research ‘offers a potential leap forward for sustainable fisheries and ocean management’.

DNA degradation occurs at a slower rate in water, which is useful when detecting marine animals. Other scientists also believe this to be true for freshwater. In one experiment genetic traces of bullfrogs could be found, 20 days after they had been removed from a reservoir. Tony MacDonald, director of Monmouth University said that the use of eDNA as an identification tool is ‘an easy way to estimate the distribution and abundance of diverse fish species and other forms of aquatic life in the dark waters of rivers, lakes, and seas’.



Bullfrogs leave eDNA traces for at least 20 days

Dr Stoeckle said that there is ‘promising work underway to confirm a relationship between the concentration of a species’ DNA in seawater and the abundance of that species in the water’. He added that the discovery of eDNA will improve ‘the rationality with which fish quotas are set and the quality and reliability of their monitoring around the world’.

One study in New Caledonia discovered that using eDNA proved to be a far more accurate way of evaluating shark populations in the South Pacific archipelago than the tried-and-tested methodologies of scuba diving visual censuses or baited underwater camera recording.

Researchers from the Forest and Rangeland Ecosystem Science Center in the US believe that eDNA tracing can help to detect the emergence of invasive species in a habitat. David Pillod said: ‘Some intensive eradication programmes for invasive species fail when a few surviving individuals recolonize the ecosystem.’

This has been a big problem with the attempts to limit lionfish invasion of the Atlantic and the Caribbean.

By developing DNA barcodes to identify fish, scientists are hoping to gain standardised data on the variety of underwater species for easy detection. For more secretive and elusive species, eDNA provides an attractive and low-cost approach for aquatic inventory and monitoring programmes. DNA can also be traced at low population densities, suggesting that animals do not need to be present in large quantities to be detected.

However, like all new scientific methods discovered, each is not without questions and finding solutions to new problems. There are current discrepancies on how effective the harvesting of eDNA is in the wild. Teruhiko Takahara and a group of researchers from the Research Institute for Humanity and Nature, based in Japan, has discovered that the amount of eDNA is highest when there is an increased amount of fish activity.

This could include competition between species or mating. It was also concluded eDNA is more abundant in warmer climates. In warmer waters, the metabolic rate of fish is higher thus their level of activity increases however, microbial activity and the subsequent breakdown of eDNA also rises. There are currently concerns for how levels of UV radiation, water temperature, strength of currents and number of species present can affect the amount of eDNA collected.

Despite current concerns, scientists are hopeful for the future. The study and collection of eDNA and the impact it can have on the environment continue to be an avenue of interest for ecologists. Dr Stoeckle said: "eDNA has a Goldilocks quality just right for research. If it disappeared too quickly, sampling wouldn’t tell us much, if it lingered too long, too much DNA would be in the water undermining useful timely insights’.

Next steps include fine-tuning and creating standardised methods of harvesting and extracting eDNA that create consistent results. There is also a look to the future potentially involving students and citizen scientists. ‘The collection process is simple enough for supervised schoolchildren or citizen scientists to help monitor changing ranges of all marine life,’ Dr Stoeckle said.



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