ROBERT SIEGEL, HOST:

If you want to protect rare species, first, you have to find them. In the last few years, biologists have developed a powerful new tool to do that. They've discovered that they can find traces of animal DNA in streams, ponds, even in oceans.

NPR's Richard Harris tells us that was a hot topic this week, at a meeting of the Society for Conservation Biology in Baltimore.

RICHARD HARRIS, BYLINE: It was just five years ago that French biologists discovered they could detect invasive American Bullfrogs simply by sampling pond water and looking for an exact genetic match to the frog's DNA. Now, all sorts of biologists are eagerly putting this test to use. Stephen Spear, for example, has been sampling water to study one of the oddest creatures in American streams, the hellbender salamander.

DR. STEPHEN SPEAR: It's a really neat critter. It's actually the largest salamander in North America. But a lot of people even that live where it is - which is mostly in Appalachian region from New York down to Georgia - don't know about it because it's totally aquatic in river and streams. It spends time under large rocks.

HARRIS: Nicknamed snot otter, it can grow to two feet long and live for more than 30 years. Biologists usually look for it by prying up enormous stream boulders and snorkeling under them. Spear, who works for a nonprofit amphibian group called the Orianne Society, has found a gentler way. He's been taking water samples from the streams where he's looking for these salamanders.

SPEAR: And we can actually extract the DNA from this water sample and be able to tell that it's hellbender DNA. And we know that a hellbender is there without ever having to lift a rock or maybe even see one.

HARRIS: And it turns out that when hellbenders are breeding, they shed a lot more DNA into the water.

SPEAR: So we might be able to tell where they're successfully breeding, which would be huge for understanding where the healthy populations are, and also where we need to put our conservation efforts.

HARRIS: Hellbenders are apparently in decline and may end up protected by the Endangered Species Act at some point. So it's important for biologists to know where they are and where they're breeding.

Spear's report at the Society for Conservation Biology meeting was just one of more than a dozen looking at DNA in the environment. Philip Francis Thomsen, from the University of Copenhagen, says he's successfully used it to study fish in the ocean. He sampled water near Elsinore, "Hamlet's" setting. He found DNA from 15 fish species, including one big surprise, the sardine. It usually inhabits much warmer waters to the south.

PHILIP FRANCIS THOMSEN: This sardine has never been sighted in the area and it's a very rare species in Denmark.

HARRIS: Fisheries biologists think the sardine may be moving north as a consequence of climate change. So sampling DNA in the environment may help them track changes like this. In fact, Thompsen says, it should be possible to look for DNA from hundreds of species simultaneously. If he could do that, he could monitor the diversity of life in a place like a coral reef, simply by taking water samples.

Thomsen even had a bit of success tracking the endangered Harbor Porpoise by sampling ocean water off the coast of Denmark. And at one point, he detected DNA of a related species, the long-finned pilot whale.

THOMSEN: And that is a species that is very rarely sighted in Danish waters. And funnily enough, when I checked up on this afterwards, there have been two sightings in Denmark that same year.

HARRIS: In other settings, DNA sampling is being used to monitor the Great Lakes for signs of the dreaded Asian carp, which is threatening to invade. It's being explored as a way to look for signs of land-dwelling animals that visit watering holes. Yes, drool contains DNA.

Ultimately, biologists would like to be able to use these tests to determine the size of animal populations but, so far, that's just a dream. And Thomsen notes that finding animals though their DNA doesn't by itself help vulnerable species.

THOMSEN: We still need to convince managers and authorities and governments to do the proper actions.

HARRIS: But he says the emerging DNA technology can at least help guide those policies.

Richard Harris, NPR News.

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