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  • In a world that's as connected as ours,

  • it's no wonder that species sometimes end up in habitats that aren't their own.

  • But these invasive species can cause serious trouble.

  • They often compete with native species for food, steal their homes,

  • nom on them for lunch, or otherwise wreak havoc in their new habitats.

  • The survival of entire ecosystems can depend on getting rid of them.

  • But that's not so easy.

  • Without predators to keep them in check, invasive species tend to stick around and multiply,

  • despite our best efforts to fend them off.

  • That means that we have to get pretty creative to have any hope of eradicating them.

  • And in some cases, humans have risen to the challenge.

  • Here are five of the strangest ways that people have fought back against invasive species.

  • The brown tree snake invaded the tiny island of Guam in the 1940s,

  • after stowing away on a U.S. military plane coming from another Pacific island.

  • Since then, the snake population, which is now about two million strong,

  • has eaten its way through the island, devastating the local ecosystem.

  • The snakes have hunted ten of Guam's twelve native birds to extinction.

  • Without birds, the spider population has gone unchecked.

  • Forests have also thinned because there aren't enough birds to spread seeds.

  • To make matters worse, since these tree snakes live in trees,

  • it's tough to weed them out with traditional methods like traps or snake-sniffing dogs.

  • So to try to eradicate these predators,

  • the U.S. government has been experimenting with a more creative solution:

  • air-dropping dead mice filled with acetaminophen,

  • the active ingredient in Tylenol, over the jungles of Guam.

  • The mice come sailing down in little parachutes, which is kind of tragically adorable.

  • Then the parachutes get stuck in trees

  • and dangle the mice in places where snakes can find and eat them.

  • And the method is pretty deadly.

  • A year-2000 study by the National Wildlife Research Center found that

  • 100% of brown tree snakes die after ingesting acetaminophen.

  • Unlike in humans, this medicine prevents the snakes' blood cells from carrying oxygen.

  • Just 80 milligrams of the stuff, about a child's dose of Tylenol,

  • makes the snake go into a coma and die within 60 hours.

  • Dead mice seem to work really well as a vessel for the poison,

  • because they attract the brown tree snake but not Guam's native species,

  • according to a preliminary study.

  • And so far, research suggests that this approach is pretty effective.

  • One study looked at a site where two rounds of poison-mice

  • had been dropped at different times.

  • The researchers found a 40% decrease in the number of baits eaten after the first round,

  • suggesting that there were fewer snakes to eat them by round two.

  • So this method could go a long way in clearing these invasive predators out of the island.

  • While the brown tree snake snuck its way into its co-opted home,

  • many invasive species waltz into foreign environments as pets.

  • That's probably how the spiky, colorful lionfish

  • got from its native Indo-Pacific seas to the Atlantic Ocean.

  • Lionfish have been terrorizing the Atlantic since the late 1980s,

  • taking over reefs, shipwrecks, and other places.

  • It seems likely that these invaders started out as pets

  • whose owners dumped them in the ocean when they didn't want them anymore.

  • Which sounds nice and humane!

  • Except, these fun, zany-looking fish are actually fierce predators.

  • They eat mostly fish and are super-venomous,

  • so they don't really have predators in their foreign territory,

  • which makes them pretty much unstoppable.

  • Lionfish have drastically reduced the populations of fish where they live.

  • And it doesn't stop there.

  • Lionfish devour other fish that typically eat algae,

  • and unchecked algae growth crowds out coral reefs.

  • So lionfish are indirectly killing our reefs.

  • That's a pretty serious problem.

  • But it's not like we can just fish them out of the ocean.

  • Lionfish have been moving into deeper and deeper waters,

  • making them hard to catch with a hook and bait.

  • That depth poses another problem, too:

  • it gets too risky for divers to catch a fish with, say, nets

  • because the water pressure gets dangerously high.

  • So, to stave off the lionfish invasion, the the CEO of iRobot,

  • which made the Roomba, yeah, that little robot vacuum,

  • has developed human-controlled, pressure-resistant robots

  • that can go where humans can't.

  • Deep underwater, the goal is for these weird tube robots to track down lionfish,

  • give them a good zap to stun them, and then suck them up with a vacuum.

  • The good news is lionfish are a pretty easy catch.

  • Since they aren't used to having predators around,

  • they don't really run away from things that approach them,

  • even weird robots with little clappers attached.

  • Which is pretty convenient for the robot.

  • Along with clearing the water of invasive species,

  • this underwater robot collects lionfish that could ultimately be served at restaurants.

  • Lionfish actually makes a pretty tasty dish that some people compare to snapper.

  • As of 2019, the robot is still being refined, so it's not on the market yet.

  • But its makers are perfecting the design

  • and preparing the machine to suck the invasive lionfish out of the seas.

  • The lionfish isn't the only invasive fish that's been hard to root out.

  • In the Upper Missouri River Basin, brook trout from the Eastern U.S.

  • have been crowding out the area's native trout species since the 19th century,

  • when people introduced them as a way of replenishing fish populations around the country.

  • In the past, people have gotten rid of invasive fish

  • by dumping toxic chemicals in the river to poison them,

  • but it probably doesn't surprise you that that solution leaves something to be desired.

  • The toxins kill invasive fish and native fish alike, including ones we rely on for food.

  • So researchers in Montana have developed

  • a much safer way of removing the trout without killing everything else.

  • The technique is called backpack electrofishing, and it's pretty much what it sounds like.

  • Essentially, researchers wade into the water wearing backpacks with electric generators.

  • The generators are connected to wands with positive charge flowing through them,

  • and researchers stick them in the water.

  • Fish are naturally programmed to swim toward positive charge, so they approach.

  • That's when the scientists unleash an electric burst

  • that can temporarily stun hundreds of fish in one go.

  • The stunned fish float to the surface and get scooped up in nets.

  • From there, the researchers separate out the invasives, which can become meals,

  • and return the native fish to the water.

  • Researchers have taken out tens of thousands of trout from the basin with this method,

  • and the best part is, it doesn't hurt the environment they're trying to protect.

  • It's nice to be able to tackle invasive species in bulk,

  • but sometimes you just have to go one by one.

  • That's the case in Washington state,

  • where invasive mountain goats are wreaking havoc in Olympic National Park.

  • After hunters in Alaska introduced them in the 1920s,

  • these goats quickly spread into their new habitat.

  • As of 2018, around 700 goats were roaming the peninsula,

  • grazing on the rare plants and eroding the landscape as they trampled across it.

  • Oh, and there's another detail.

  • The Olympic goats are addicted to human pee.

  • Turns out pee, and human sweat,is a rare source of salt in the park;

  • and the goats just love it.

  • As the goats have gotten used to humans, they've also gotten aggressive.

  • Unfortunately, getting rid of the goats is not a walk in the park.

  • According to the National Park Service,

  • typical approaches to invasive species won't cut it for all sorts of reasons.

  • We can't just introduce goat predators, like wolves,

  • because they'd happily gobble up the park's native animals too, like elk and deer.

  • And we can't just give the goats salt so they lay off the pee,

  • since they'd keep eating up native plants and eroding the landscape.

  • So the U.S. government has come up with a solution:

  • airlift the goats to their natural habitat in the Cascade Mountains.

  • To do that, they first paralyze the goats with a dart,

  • then blindfold them to keep them from panicking.

  • After that, they hoist the goats up in a harness attached to a helicopter

  • and take them to a staging area, where a truck picks them up

  • and delivers them to the Cascades.

  • And that may sound like overkill, but there is some logic to the idea.

  • Because of overhunting, the number of mountain goats in the Cascades has been dwindling.

  • Some experts believe that bringing the goats back to their natural habitat

  • could help the population bounce back.

  • Not only would this forced migration add hundreds more goats to the ecosystem,

  • it would also increase the genetic diversity of the goats in the region,

  • which could ultimately help the population thrive.

  • When it comes to removing invasive species,

  • it's often the last few stragglers that are the hardest to weed out.

  • But if you don't get the stragglers, the population will likely bounce back.

  • That was the problem on Isabela Island in the Galapagos.

  • Across the archipelago, goats had reduced or completely wiped out

  • almost 80% of plant species, which seriously messed up the ecosystem.

  • In 2004, helicopter crews managed to wipe out

  • about 90% of the goats on Isabela Island by shooting them,

  • but then they had to deal with the last 10 percent.

  • Unfortunately, it can get pretty expensive looking around for goats in a helicopter.

  • So researchers turned to undercover goats.

  • They captured around 800 female goats, neutered them,

  • and laced them with hormones that make them seem like they're always in heat.

  • These chemically altered goats are called Judas goats.

  • Researchers then fit them with a collar so they could track them,

  • then released them into the wild.

  • Since they were chemically aroused all of the time, they sought out other goats,

  • especially males, and scientists were able to follow their trackers to the stragglers.

  • They did that every few weeks, and then shot all of the goats who weren't Judas goats.

  • After all the stragglers were gone, the Judas goats, which couldn't reproduce,

  • were left to carry out the rest of their lives alone.

  • Of course, it takes a lot of resources

  • to be able to pull off any of these creative ways of fighting off invasive species.

  • But even without a helicopter or an underwater fish vacuum,

  • you can still do things to help control invasive species where you live,

  • like cleaning off your shoes after hiking or planting native plants in your garden.

  • Even small steps like these can help keep our ecosystems in balance.

  • Thanks for watching this episode of SciShow!

  • And thank you to our patrons for your support and curiosity about the universe.

  • You're the reason we can keep making videos like this one.

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