Silver carp caught for first time from St. Croix River

By Javier Serna
Assistant Editor

Hastings, Minn. — A pair of invasive Asian carp were netted by commercial fishermen last week just above the confluence of the St. Croix River at Point Douglas Park.

It was the first time an invasive silver carp, known for its jumping ability, was found on the St. Croix (the larger bighead carp previously had been found on the river), though the location is just upstream from where silvers previously have been collected on the Mississippi River. The commercial crews also netted a bighead carp.

Nick Frohnauer, the Minnesota DNR’s invasive fish coordinator, said it was the 11th silver carp to be caught in Minnesota waters, the first being caught in 2008. There have now been 25 bighead carp caught in state waters since 1996.

“It’s not a joyous thing, it’s pretty somber,” said John Waters, the DNR’s invasive carp fisheries specialist, when asked what the mood was like when the crew of about five commercial anglers and five DNR personnel discovered the fish. “We don’t want to catch them, but if they are there, we want to remove them.”

The commercial fishing crews are required to notify the DNR whenever they plan to net rough fish for commercial harvest, to give the department a chance to be on hand in case there are any invasive fish caught. In this case, it was a large and long seine net worked over a large and deep “overwintering” hole just upstream of the confluence, which is known to hold a lot different species of fish this time of year, Waters said.

“At this time, it’s hard to predict if these individuals would have moved farther upstream on the St. Croix River or back into the Mississippi River when water temperatures warm up in the spring,” Frohnauer said.

The Taylors Falls dam is believed to be as far as either species can make it up the St. Croix River – even the silver carp, which can jump as high as 10 feet – since they wouldn’t be able to clear the dam. Silvers are known only to jump when they are in larger numbers, in which case they are considered a hazard to boaters, Frohnauer said.

The last time an invasive carp was caught in the spot was a bighead carp in 2014, and Waters was on hand that time. These fish also have been caught farther upstream on the St. Croix. Two silver carp, along with a bighead carp, were caught farther north in Pool No. 2 of the Mississippi River on two occasions in July and October of 2014.

The two recent catches were taken to a lab and examined per U.S. Geological Survey protocol, Waters said. The bighead carp was a female, he said, that was carrying underdeveloped eggs.

“It didn’t appear that she was going to be spawning anytime soon,” Waters said. “They weren’t very mature.”

Those fish are believed to spawn in the summer, which would explain why the eggs weren’t ready, he said. The closest-known spawning population of invasive carp is on Pool No. 14 of the Mississippi River in Iowa, he said.

There is a theory held by some invasive carp researchers that it takes a critical mass, or a larger population of invasive carp, in order for them to pull off a successful spawn.

“We really don’t know if that’s the case,” Waters said. “That is an area of research that we are looking into. It seems to be the case, but there really is no hard evidence of that. … We haven’t seen any young-of-the-year or year-old fish here in Minnesota.”

As for the silver carp, it was measured at 33 inches long and weighed 13 pounds.

“The silver was a surprise,” Waters said. “We’ve caught bigheads there in that area this time of year, which is why it’s of interest for us to be there.”

Waters said the DNR crew hoped to join commercial anglers again earlier this week, after receiving a call that they would be doing more fishing in that spot again. The DNR also contracts commercial fishermen to net for fish in search of the invasive, which also have turned up in the Minnesota River.

DNR crews monitor for the species at all life stages, including looking for larval and egg-stage fish during the spring by using specialized nets that filter the top of the water column.

The DNR also is planning to sample near the King Power Plant near Bayport, where it tried recently but couldn’t reach open water. That’s where a number of bighead carp were caught two springs ago by a couple of anglers.

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