Science & Environment

Shark eDNA study could be conservation 'game-changer'

Judith Bakker swimming with hammerhead shark (Image: Nicolo Roccatagliata) Image copyright N.Roccatagliata
Image caption Analysing shark DNA in the water could allow scientists to gather data that has previously eluded them

Conservationists are eagerly awaiting the results of a UK study into whether it is possible to track endangered sharks via environmental DNA (eDNA).

If successful, it could result in scientists being able to create global maps of life beneath the waves.

Current methods are costly and labour intensive, requiring teams to spend long periods at sea with no guarantee of getting the required information.

Almost half of all known shark species are classified as data deficient.

"Basically, all living things are made of tissue and if you break them down into smaller and smaller units, you end up with cells," explained lead scientist Stefano Mariani from the University of Salford.

"Every cell of every organism contains DNA. Every time an organism loses bits - this could be the result of dying, producing eggs or losing some skin, spitting or pooing - there are cells containing DNA.

"Theoretically, it is possible to trawl water and retrieve some DNA coming from this environment," he told BBC News.

Prof Mariani and his colleague, PhD student Judith Bakker, hope their study will help shed light on the feasibility of a new method to gather data on shark populations around the globe and overcome obstacles that have hampered efforts to date.

"For example, if you go to a rainforest and you know there are a bunch of jaguars spread over hundreds of kilometres, you are not going to see them unless you spend many months in the wild or you install camera traps," Prof Mariani observed.

"The same is applied to large animals that are distributed in the ocean, such as whales or sharks. In order to see them and monitor them, the budget required is generally huge, meaning that very few people can do good studies on whales or sharks.

"We decided it was worthwhile having a go at this approach of finding out about the biodiversity in the DNA left in the environment.

"If this works to the extent we hope it is going to work then it is going to be a game-changer because all you will need to do is collect enough water."

Limited data

One of the study's funders is the US-based Pew Charitable Trusts, and Katie Matthews - manager of Pew's Environmental Science programme - agrees with Prof Mariani's assertion that eDNA monitoring could revolutionise this area of marine biology.

Image copyright J.Bakker
Image caption If it proves successful, eDNA could revolutionise the monitoring of marine species populations

"Current methods for identifying the various species of sharks in an area - for example, divers in the water visually identifying sharks or the use of baited underwater cameras - require a significant commitment of people, time and/or money," she told BBC News.

"For this reason, there are many places in the world where we have very limited or no data on which species of sharks are present and in what numbers, and this creates significant challenges when trying to assess the status of a population, or even its range."

And Dr Matthews added: "But with eDNA, it may be possible to send a single person out to collect water samples with standard one-litre bottles, which can then be quickly filtered and sent off to a laboratory to analyse the DNA and determine what species had been in the area.

"Given the rapidly decreasing cost of processing DNA samples, it seems likely that eDNA as a tool for marine conservation will become increasingly common in the coming years."

Having a better understanding of the state of shark populations will aid conservation groups, allowing them to highlight their concerns about the main threats facing these animals, such as overfishing.

'Extremely vulnerable'

"Shark mortality is at an unsustainable level," explained Imogen Zethoven, director of Pew's global shark conversation campaign.

"Scientists estimate that approximately 100 million sharks are killed each year by commercial fisheries."

She told BBC News: "Because sharks are slow-growing, late to mature and generally have few young, they are extremely vulnerable to overfishing.

"Nearly 30% of all known shark species fully assessed by scientists are threatened with extinction, and more than 25% are close to becoming threatened in the near future.

"A major driver of decline is the global shark fin trade. The demand for shark meat is also a growing threat in some parts of the world."

Before eDNA can be used as a reliable, effective and efficient tool by scientists, more work has to done to standardise and calibrate the gathered data to ensure it is a representative sample, Prof Mariani explained.

"This is still a pioneering approach to science so there is still a lot of ground-truthing to be done.

"However, we do know a number of basic things. For example, we know that environmental conditions and time affect the persistence of DNA in the water.

"Generally, the longer cells and strands of DNA from an animal are left drifting in the water, they will be degraded because it is normal for these micro-molecules to be broken down.

"It is a constant trade-off. The bigger the fragment, the least likely I am to get it out of the environment but the more confident I can be that it refers to that area and a recent time.

"If it's a smaller fragment, it could be because it has been in the environment for a few weeks and reached that area via a particular current."

Colleague Judith Bakker has recently returned from a field trip in the Caribbean where she had been collecting water samples as part of the team's work to assess the effectiveness of the eDNA technique.

Prof Mariani said: "We have been collecting samples from areas where we know what particular animals are being observed, etc.

"We will be able to see to what extent the DNA matches and fits what we expect it to show."

The team hope to have provisional results during the summer and final findings from their study by the end of the year.

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