BITE INTO RESEARCH​: Environmental DNA illuminates the dark diversity of sharks

The Fins United Initiative is excited to showcase a BRAND NEW section to our program: the "Bite into Research" segment! TFUI officers will be reading articles that were published in regards to Chondrichthyans (those are the sharks, skates, rays, and chimaeras... and include any sector) and explain it in terms that everyone can understand. Today, we have TFUI Officer Chelsea Stein reviewing the following paper: Environmental DNA illuminates the dark diversity of sharks.

Access the paper: http://advances.sciencemag.org/content/advances/4/5/eaap9661.full.pdf

what did the researchers do?

​Let’s dive into this study! The researchers wanted to shed light on something called “dark diversity,” which is basically when a species that should naturally be found in a specific habitat is not being found there. They outlined two major reasons why this could be happening:

1. Localized extinctions, likely to be related to human activity
2. A failure of traditional research methods to accurately detect the species

​The focus of this study was on the accuracy of research methods, so they compared the following:

• Underwater Visual Census (UVC) - an observer is equipped with underwater gear (data sheets, pencil, etc) to observe the species in a given area
• Baited Remote Underwater Video Systems (BRUVS) - a submersible device which is controlled remotely, consists of a camera (to record activity in the area) and a canister filled with bait (to attract the specimens)
• Environmental DNA (eDNA) - gathering water samples and using various filtration and lab testing methods to analyze the genetic material naturally released by organisms

​UVC and BRUVS are considered traditional research methods today.
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how did they do it?

​The study was conducted in New Caledonia, located in the southwestern Pacific Ocean, an area historically known to be home to 26 species of shark. Here are the highlights: 

Both UVC and BRUVS detected fewer shark species over larger sample sizes and longer lengths of study, suggesting a higher dark diversity. On the flipside, eDNA detected more shark species over a smaller sample size and shorter length of study. In addition, the eDNA method produced the highest frequency of samples with sharks detected and the lowest dark diversity.

Ideally, what we are looking for is a higher number of species detected overall, a higher frequency of samples with sharks detected and a lower dark diversity. Based on the information collected for this study, UVC and BRUVS have not been accurately detecting the shark diversity in New Caledonia, compared to eDNA

​The bottom line: ​eDNA required less time to detect a higher number of shark species. 
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​Why does it matter to people?

This matters to people studying sharks and maintaining regional inventories and records. The eDNA method is noninvasive and less time-consuming than traditional methods - we can obtain better information in a shorter amount of time. There is potential for this to be used worldwide to uncover information about the more elusive and rare species that we know very little about.

​However, some additional work is needed to improve accuracy of this method further, as noted by the researchers. For instance, eDNA methods cannot determine “size, condition, developmental stage (eggs, larvae, juveniles, and adults), sex, behavior, and movement patterns of the target organism.” If eDNA can be improved further to reveal such information it could prove to be a more accurate and efficient way to study important and vulnerable shark species.
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​How does it help Chondrichthyans? 

​Accuracy of data will better inform conservation efforts. For instance, the International Union for Conservation of Nature (IUCN) uses various criteria, including physical numbers of species, to add a species to its Red List, which categorizes it for risk of extinction. Accurate data will inform such conservation lists and allow decision-makers to more precisely protect species.

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GUEST BLOGGER AND TFUI OFFICER chelsea stein

​Chelsea (aka "Chelsie") Stein loves the great white shark and epaulette sharks. She is currently located in Michigan, USA and is available for in-person and Skype classroom visits!