Discover Mediterranean white sharks with environmental DNA

One of the best ways to tell if an animal is in an area is to see it with your own eyes. The next best thing? Environmental DNA.

DNA (short for Deoxyribonucleic Acid) is released by all living creatures on this planet through skin cells, hair, scales, and other bodily secretions as they move about. This leaves a “fingerprint” in whatever environment they were in, becoming environmental DNA (eDNA). Researchers can now scan a water, air or soil sample for tiny remnants of DNA to identify organisms using eDNA analysis, an emerging molecular technique that is taking the world by storm. wildlife science industry. The world of shark science has been using eDNA studies for years, testing waters around the world to explore where sharks are – even if they haven’t been physically seen! One of the areas of interest is the Mediterranean Sea. Despite being rarely seen, there are sharks here – which makes sense, since the United Nations has named the Mediterranean one of the world’s 25 biodiversity hotspots, home to up to 18% global marine biodiversity. Considered the largest semi-enclosed sea, it is home to around 47 species of sharks… including the famous great white shark (Carcharodon carcharias).

Research conducted in 2020 and coordinated by Professor Francesco Ferretti of Virginia Tech found that despite living in the area for centuries, the number of great white sharks has rapidly declined in the Mediterranean Sea. These sharks are now at high risk of being completely eradicated from the region, with unintended consequences for the entire ecosystem. It is partly because of this looming threat that Ferretti launched the White Shark Chase, an unprecedented multi-agency initiative to find, film and tag the last remaining white sharks in the Mediterranean Sea. The WSC team, including scientist Jeremy F. Jenrette of Virginia Tech’s Department of Fish and Wildlife Conservation, headed out to the Mediterranean Sea: “Our team has developed a particular interest in white sharks from the Mediterranean because of their unique history in the region. The Mediterranean white shark is one of the least known and most endangered populations in the world. We know that they have experienced a substantial population decline in recent decades due to the effect of intensive fishing, [so] we need to know how many individuals are left if we want to save this population from extinction.

To do this, researchers need to gain a better understanding of the shark’s biology and ecology (and even tag some of the remaining animals). “Searching for white sharks in the Mediterranean Sea is like finding a needle in a haystack. It’s a difficult task and so we used eDNA – a burgeoning approach in the marine world and extremely effective in detect cryptic animals – to sniff out the tracks of those elusive sharks,” says Ferretti. “In our research, we identified geographic areas where the likelihood of finding this animal was higher than in other areas, but even in these ‘hot spots’, we needed a ‘metal detector’ to find traces of the animal. […] But our team followed the breadcrumb trail to the last remaining strongholds by listening to local intelligence and predicting patterns of historical sightings in [previous research]adds Jenrette, who led eDNA operations.

The most common method of collecting eDNA is to use a special kit that filters water and traps biological materials. After capturing the material on the filter, the DNA can be extracted in the laboratory. But previous research guides the selection of water harvesting sites. In this case, the team used historical sightings of white sharks to develop relative abundance distributions for May and June to determine where they would collect water. In June 2021, the team obtained environmental water samples from 16 sites in the Sicilian Channel and then amplified a unique cytochrome B (CYTB) gene fragment found in white shark cell mitochondria. From there, they found that four samples (out of 69) had this unique gene fragment, which means great white sharks had recently passed through! It was a relief for Jenrette to have the results confirming that white sharks are present in the season and area where they predicted they would occur. “We were close to free-swimming individuals that our models could have been within an area of ​​about 12 nautical miles from where we detected them in two days. It was a very important result that motivated us to identify our research in the region,” he says.

Jenrette and his team believe that to learn more about the Mediterranean Sea, citizen scientists should be integrated into eDNA surveys to maximize sampling effort and reduce ship time costs. “The opportunity lies in the ease of collecting eDNA samples. This approach lends itself very well to a citizen science project. Any boat owner and sea enthusiast can help us collect eDNA samples around the Mediterranean Sea – and there are a lot of people in this area. It is one of the busiest and most visited areas on the planet, with a high density of boat owners and sea lovers, so that locals can potentially collect a lot of useful data for our research. Detection of white sharks with eDNA is enhanced by large-scale sampling, where each sample acts as a snapshot of the local ecosystem. is already partnered with the International Seakeeper’s Society to launch the Sailing Partners Initiative in the Mediterranean Sea, and they have also developed cost-effective, easy-to-use kits to sample and filter surface water and store eDNA to be returned to their lab for processing. “We plan to ship more kits to Seakeeper’s Society sailing partners and expand our sampling range. This year, with the support of the Augmentum Foundation and Yachts for Science, our team will investigate several recent sightings of white sharks in Tunisia. Specifically, we aim to extend our range of sampling from Malta to the Tunisian coasts.

This research was supported by the Discovery Channel, The Explorers Club, the Center for Coastal Studies, the Fish and Wildlife Conservation Department at Virginia Tech, and the Acorn Alcinda Foundation. The eDNA publication can be read here.

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