Water guns effective but not perfect at repelling Asian carp

By on June 2, 2015
A silver and bighead carp, two of the Asian carp species threatening to invade the Great Lakes, collected from the Illinois River (Credit: Jon Amberg/USGS)

A test of the effects of fish-repelling water guns on Asian carp shows that the technology may help in the fight to keep these invaders out of the Great Lakes. But they won’t fire a silver bullet.

Scientists from the U.S. Geological Survey studied the effects of water guns on bighead and silver carp, two of the invasive Asian carp species in the Mississippi River Basin that many fear could enter the Great Lakes Basin by swimming through channels that connect the two watersheds.

The U.S. Army Corps of Engineers already operates a series of electrified barriers on the Chicago Sanitary and Ship Canal near Lake Michigan, but managers are interested in how well other technologies can do the job.

That includes water guns, a tool that creates blasts of acoustic pressure. They were originally developed in the 1980s for offshore geological profiling for petroleum exploration. Ships would tow long strings of guns whose signals could be interpreted to profile the seabed and identify locations for drilling on the sea bed.

“A lot of the earlier study was: How are they negatively affecting fish?” said Jason Romine, a fish biologist with the USGS Western Fisheries Research Center in Washington. “And now we want to ensure that they’re negatively affecting fish.”

The guns shoot a pulse of water at high speed that creates an empty void, which collapses on itself in an implosion. The phenomenon is similar to cavitation bubbles that can pit boat props, but at a larger scale. The implosions create a pressure field of around 10 pounds per square inch in the immediate vicinity of the guns, said Romine, who led the study.

Crews tested how the carp responded to the guns in an artificial pond at a USGS facility in Wisconsin. Romine’s lab specializes in tracking fish, and he has worked on projects tracking sharks, sturgeon and salmon. He used that expertise to tag carp and analyze how they responded to the guns.

Water guns were mounted below pontoons in the artificial pond. (Credit: Nick Swyers/USGS)

Water guns were mounted below pontoons in the artificial pond. (Credit: Nick Swyers/USGS)

In separate trials, bighead and silver carp planted in the ponds tended to avoid the side of the pond where two guns were installed. They also used less of the pond and swam more erratically. That’s a good sign that the carp don’t like the pressure created by the guns, and even avoid them.

But at least in this experiment, the guns weren’t a perfect barrier. Bighead carp swam past the guns 78 times when the guns weren’t firing, and 15 times during when they were. Silver carp passed the guns 96 times before firing and 13 times during firing. For species as aggressively invasive as the Asian carps, even those suppressed numbers could be too high for managers looking to lock them out completely.

It’s possible that the guns could be used in conjunction with other fish-blocking technologies for a more complete barrier, Romine said. It’s also possible that the carp swam past the firing guns as often as they did because they didn’t have anywhere else to go. If the pond would have been larger or offered an outlet for escape, the carp may have gone that route instead of swimming right at and past the guns. The USGS is testing the guns in a larger impoundment in Illinois where there carp will have more escape options.

“It wasn’t 100 percent effective in the pond,” Romine said. “In a different environment maybe it is. We just haven’t been able to get there yet.”

The results of the study were published in the North American Journal of Fisheries Management.

Top image: A silver and bighead carp, two of the Asian carp species threatening to invade the Great Lakes, collected from the Illinois River (Credit: Jon Amberg/USGS)

About Jeff Gillies

Leave a Reply

Your email address will not be published. Required fields are marked *