Probing Poop and the River for Asian Carp

By JoshMogerman in News on Nov 3, 2012 8:00PM

There hasn’t been any splashy Asian carp news since the invasive fish were served to brave Taste of Chicago goers this summer. But activity in the battle against aquatic public enemy #1 has seen a big uptick in recent weeks.

State and federal biologists have been busy trolling Chicago’s waterways with two different intensive fishing operations in recent weeks after repeated tests showed silver carp DNA. Tuesday and Wednesday, they fished and netted in the murky waters of Lake Calumet on the South Side (it was a return trip, as numerous water samples showing the invasive fishes’ potential presence initiated a similar expedition in July). A couple weeks earlier, boats were dispatched to find the carp in the North Shore Channel and more recognizable portions of the Chicago River like Wolf Point (where the main stem of the River splits into the North and South Channels, near the Chicago Sun-Times offices), Bubbly Creek (which passes through Bridgeport and China Town) and near the Chicago Lock (next to Navy Pier, one of the spots where the River and Lake Michigan connect) after positive tests in September.

No carp were caught in either fishing effort. That is good news, though reporting from the Milwaukee Journal-Sentinel implies we cannot take too much comfort:

Asian carp expert Duane Chapman said nobody should be surprised all the intense fishing expeditions in the past two years have proved fruitless, particularly if there are only a small number of Asian carp beyond the barrier system.

"These fish are extremely difficult to catch, compared to our native fish," said Chapman, a biologist for the U.S. Geological Survey.

Chapman once marshaled four boats and chased three radio-tagged Asian carp for two days on a Missouri River tributary using electroshocking gear and commercial fishing nets. The radio tags were emitting a signal that told the crew the precise location of the fish, which had been trapped between two sets of nets stretching the entire width and depth of the river. But the water evidently was too deep for the electroshockers to force the fish to surface, and the carp proved cagey enough to avoid getting snarled in the nets.

"They know what nets are," said Chapman, "and they avoid them."

The “Environmenal DNA” tests triggering these efforts are used as a monitoring tool in the battle to keep the carp out of the Great Lakes by identifying the presence of genetic material from silver or bighead carp in water samples routinely collected in Chicago’s waterways. They do not conclusively prove the presence of the fish and some alternative theories for the positive tests have been floated, including fish riding barges and traces of the fish in bird poop. Though barges are plentiful in Lake Calumet, they rarely ply the waters of the North Shore Channel. The Army Corps of Engineers are readying a report done in coordination with Brookfield Zoo that investigates the carp crap theory. The zoo is feeding the fish to pelicans to see if their DNA can survive the bird’s digestive tract---different intent, but similar in concept to the Taste!