For as many pluses as fishermen credit for their trips to Lake Pontchartrain in recent years, there are as many minuses.

Maybe that’s because only the most dedicated Pontchartrain fishermen know the vagaries of Louisiana’s largest lake.

Maybe that’s because the lake changes so often: Rainfall, runoff from a half-dozen rivers and bayous that drain all or parts of 13 parishes, and runoff from the Pearl River that captures rain throughout south-central Mississippi. And that doesn’t include tides, storms, and the occasional spring when the Mississippi River gets so high that it threatens protection levees and the lake is forced to handle the Mighty Mississippi’s floodwaters through the Bonnet Carre Spillway.

There’s more to it than that: Speckled trout and redfish, the staples of Pontchartrain’s fishing action, follow some ages-old annual migration patterns into and from the lake proper, adding even more angling frustration.

And it’s that pattern that has state marine biologists spending more time in Pontchartrain. The next phase began last week with the Department of Wildlife and Fisheries’ next fall acoustic telemetry tagging study to determine the movement of speckled trout, redfish and bull sharks in the lake.

Ashley Ferguson is the lead biologist these days. She said the program began in the fall of 2012 to collect data on individual trout, redfish and bull shark movements, even to chart the difference in movements between the sexes of these three species.

To do this, Ferguson takes on the role of fish surgeon. She said the LDWF team relies on volunteers to catch fish, then transport their catches to a LDWF boat stationed in the vicinity.

It’s there the fish is weighed and measured. Then, a blue external tag is placed along its back. That’s when Ferguson’s work begins. A drug is used to calm each fish, which is then placed in a tray equipped to keep the fish alive, then she surgically implants and an acoustic tag into the fish’s cavity. After the procedure, the fish is held in a recovery tank until the team determines the fish has survived the implant and is healthy enough to be released.

LDWF marine biologist Craig Gothreaux said Thursday’s trip was successful.

“We were able to tag 24 fish, 22 very large speckled trout and two redfish,” he said.

During the three previous years — the LDWF team does this twice a year, in the spring and again in the fall — 218 speckled trout, 56 redfish and 18 bull sharks have been fitted with the device. This is only the second year for studying redfish.

“We are able to remotely monitor these tagged fish every time they swim within 500-700 meters of the 90 acoustic receivers (yellow buoys) that cover a variety of habitats in the lake,” Gothreaux said. “The (implant’s) battery life is upward of two years for these bigger tags, some of which are also able to record and transmit the water temperature and (depth) pressure of each fish.”

Teams from LSU and UNO supplement the LDWF’s efforts when it comes to retrieving data from the buoys.

“To date, there have been over two million detections of these tagged fish, which has revealed some very interesting movement patterns and habitat usage tendencies,” Gothreaux said.

Those patterns and tendencies include:

Speckled trout movement is influenced by salinity. Spring’s low salinity triggers trout to leave the lake from March through May. As salinity increases, trout begin returning in late October and November. Ferguson said that’s why anglers refer to “World Series trout,” because it’s around the time of baseball’s championship series when trout show up in catches.

Said Ferguson about redfish: “They can be observed using all habitats in the lake, but spend a majority of their time along natural shorelines.”

And bull sharks like the lake when it’s warm and leave the lake in the winter months.

And, Gothreaux said, anglers play a part in the study.

“These specially tagged fish are also marked with a light blue dart tag, and we ask anglers to report recaptures, but please release these fish so that they can continue to collect data,” he said. “Fishermen should note the date, time, location of catch, and health of the fish when released, and can call the number provided on the blue tag.”

Anglers interested in volunteering for the fall tagging event can email aferguson@wlf.la.gov for additional information.

The bonus is that anglers can check out the movement and patterns of the tagged fish by logging on to the LDWF website: louisianafisheries.net/telemetry/. The website also has information on electronically tagged offshore species.