Lake Pontchartrain 'snapshot': Saltwater fish dodged fresh water, but stuck around after spillway opened in January _lowres

Graphic presented by Ashley Ferguson -- Tracked speckled trout and redfish moved to the north shore of Lake Pontchartrain during the opening of the Bonnet Carre structure in January. They didn't leave the lake, but instead generally moved out of the plume of sediment-ladden, fresh and colder Mississippi River water.

NORCO — Like sidestepping an approaching glacier, redfish and speckled trout in Lake Pontchartrain just moved out of the way as colder, fresh water poured through the Bonnet Carre Spillway after it was opened in January to lower water levels in the Mississippi River.

Rather than leaving the lake, the fish just moved to the north shoreline, where the river water was more scarce. Once the spillway gates were closed, the fish returned to their normal routine.

“Overall, we found the fish didn’t leave,” Ashley Ferguson, a biologist with the state Department of Wildlife and Fisheries, told the Diversion Subcommittee of the Governor’s Advisory Commission on Coastal Protection, Restoration and Conservation on Tuesday.

Researchers were able to make the determination because of a fish tracking system, which has been used by the department in the lake since 2012, coupled with fish tagging work that was done in partnership with LSU from 2007 to 2009.

Since 2012, the tracking program has had 244 speckled trout and 64 redfish fitted with electronic transmitters, and their position is monitored by 90 receivers in and around Lake Pontchartrain. By the time the spillway was opened in January, there were 32 speckled trout and 40 redfish trackers still active.

“The point of the project is to see when the fish are coming in and out of the system,” Ferguson explained. Fortunately, she said, the program was able to record normal fish movements and to study changes in activity with the opening of the Bonnet Carre Spillway.

Whenever a tagged fish swims within a half-mile of one of the receivers, the date, time, the temperature of the water and depth of the fish are recorded. This information gets collected about every six weeks.

Given names like Spider, Rye, Jet or Hazel, the fish tracks can be watched over time on the fish tracker website at fishla.org/fish-tracker. The site also includes a number of shark species and tarpon, showing their time in Lake Pontchartrain.

Members of the subcommittee were intrigued by how this could be used to monitor fish species as the state builds and operates future river diversions to help answer concerns over fisheries impacts.

There had been plans to expand the monitoring program across the coast, but so far, Lake Pontchartrain is the only place the system is operating.

“These receivers give you a snapshot right there,” Ferguson said. “But you want that panoramic view.”

Follow Amy Wold on Twitter, @awold10.