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Why does someone load a fish into a tube?
It's Whooshh. It is a high tech fish disposal system, much like a cross between a potato gun and a pneumatic tube on a bank.
And this fish is a common carp, one of the oldest and most invasive fish on the planet.
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Cyprinus carpio, the common carp, is a close relative of the goldfish, native to Eurasia. It is grown throughout Europe for about 2000 years. In the 1880s, at the request of new European settlers, the federal government imported from Germany more than 300 carp from Germany. They raised fish in ponds in Washington, loaded their offspring on railway cars, sent them across the country, sometimes spilling them directly into lakes and rivers.
By 1910, it was clear that it was a mistake. Common carps tolerate poor quality water. They travel miles to get to the spawning grounds. And they can live up to 50 years, especially without the pathogens, predators or weather conditions of their home regions.
Where they invaded, the lakes became brown and muddy. The plants and ducks are gone. They moved other fish and dominated.
They have thrived in the nutrient-rich waters of the Midwest, where they can reconfigure entire ecosystems. When they search for insects and seeds at the bottom of lakes, they attract sediment, uproot plants, alter the chemical composition of water, promote the proliferation of algae and leave only very little of food for waterfowl.
So, over the past decade, researchers from Minnesota Aquatic The Invasive Species Research Center has been researching the most effective ways to eliminate common carp from lakes, ponds and marshes where they cause the most damage. Last summer, the team implemented a comprehensive common carp campaign with year-round strategies that exploit the life cycle of fish. They have not found a single solution, and some approaches work better at times and places.
"In some cases it's very easy to control and in others it's very, very difficult," he said. Przemek Bajer, common carp researcher at the head of the Whooshh team. "Once you see the life cycle, it becomes much, much easier."
Building on the failures and successes, the team hopes that wildlife managers will be able to develop elimination strategies that are tailored to their own invasive species, ecosystems and geography. Here are some tactics they have tested.
During the spring spawning period, tens of thousands of adult carp migrate on lakes and streams to marshes where they were born. If conditions permit, a single carp can produce 2,000 babies per season. But sometimes natural predators swallow their eggs and larvae.
The team has conducted many experiments to better understand this method of natural elimination. In one of them, they hung carp eggs tied to green thread in different lakes. In the waters dominated by voracious bluegill, the eggs had disappeared the next day. But without bluegills, they survived.
It is not practical to lay blue geese in carp nesting areas. Researchers are therefore looking for ways to help more bluegills survive in winter conditions that deplete oxygen in their waters. In this way, they could be alive and ready to eat when the carp come to spawn during the spring thaw.
The team is also testing barriers that prevent juveniles from surviving from dispersing outside their nurseries, and first blocking adults from spawning sites. Electrical guidance systems are promising.
These deployable underwater fences produce small electric fields that guide fish to traps. During their tests last April, they helped eliminate more than a third of the 15,000 carp in a lake.
From the end of summer to the beginning of autumn, you can also actively feed common carp so that they fall under the spell of classic baits. Researchers train carp to swim around large nets baited with food at the bottom of lakes. As long as fish find it, the rest follows. All are then picked up.
In November and December, the shallow lakes begin to freeze. Carps congregate in large groups under thin ice. Then, they are at the mercy of what researchers call "the technique of Judas".
As the most common carps follow the leaders, researchers can catch and tag a few fish in the fall, then follow their signal to locate the rest in the winter. Scientists can pick up most fish at the same time with special nets. This requires a careful strategy, because after a few breakouts, fish learn to avoid the nets.
This summer, the team is testing a combination of bait and Judas switches, tagging and training many carp in search of food placed by sensors to collect behavioral information. This can help them target carp that lead others to subsequent experiments or retreats.
They also experiment with toxins and pathogens.
It worked in ponds and testing laboratories. But as long as fish congregate around food, a net is cheaper, nontoxic and just as effective.
Nicholas Phelps, a veterinary pathologist who studies KHV, studies how and when the virus spreads, and hopes to better understand if the disease could be used safely to control common carp.
"I understand that sounds like a scary idea, releasing viruses to kill fish," said Dr. Phelps. But with cautious and progressive tests, he thinks that "at some point, it may not be a scary idea anymore".
Meanwhile, there is Whooshh, the fish cannon. It was originally developed to help spawners cross crossing breaks in their migratory route, but these researchers hope that it will laboriously reduce the laborious formation of large groups of carp traps.
They tried to coax the fish for one by one in the Whooshh, but the common carp are smart, stubborn, cautious and sometimes shy. Unlike salmon, they "do not want to swim in the void of carp," said Dr. Bajer. For the moment, it's just a transport system.
After fishing the fish, they are loaded into the Whooshh, one by one, to be sank and thrown into a container. They are then euthanized and turned into compost or food for bears and wolves in the wildlife centers.
Mr. Bajer wonders if the fish will ever feel comfortable entering a fish vacuum voluntarily: "It could be possible, we have not cracked it yet."
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