The importance of lake trout management in Moosehead Lake has driven state biologists to find a better way to monitor the fish.
If the numbers of lake trout, also known as togue, are too high, the fish can compete with brook trout and salmon for food and habitat, according to Moosehead regional biologist Tim Obrey. High numbers can result in an unhealthy population of brookies and salmon and an overabundance of lake trout, he said.
In an effort to solve this problem, biologists with the Maine Department of Inland Fisheries and Wildlife designed a new trapnet that does not have to be tied to shore and can be used in deeper water where the big lake trout spawn. It was funded through the Natural Resource Education Center at Moosehead.
The new tool will help biologists have a better picture of the numbers, health and habits of lake trout in Moosehead Lake, Maine’s largest body of water and home to one of the state’s most popular salmon and brook trout fisheries.
“I’m excited about it. We will learn a lot. A key piece of the puzzle for Moosehead is knowing what’s going on with togue,” Obrey said Tuesday.
Biologists use two major measurements to determine fish population: catch rates and fish physical condition. The greater the number of fish caught of a certain species, the more likely it is that the population is high. Skinny adult fish of a species mean there are too many for the food source.
Biologists have traditionally used trapnets to temporarily confine fish to an area to count them, check their body health and microchip them with a Passive Integrated Transponder tag commonly called a PIT tag. The tag, which is a pill-shaped cylinder half the size of a Tylenol containing a radio transponder, is inserted into the fish’s cheek and carries a specific code used to identify the fish. The chip is read with a wand passed over the fish.
But the normal trapnet is only 4 feet tall and must be attached to the shoreline. Mature lake trout like to hang out on deeper cold-water shoals. The department’s new trap net is 6 feet tall and has a 10-inch opening to allow bigger fish into the net. It can go in the deeper water and temporarily detain the larger adult breeding fish.
Two nets are tied off on either end of an 8-foot-tall net that resembles a tennis net. All the biologist needs beyond that is a shoal and a flat spot in 6-8 feet of water.
The pilot study is funded at least in part by the Natural Resource Education Center at Moosehead and is the next step after a successful three-year effort to reduce the lake trout population through increased catch limits.
Moosehead is a good lake for using that net, Obrey said. Biologists tried to use it in Sebec but although they had some success, the lake bottom wasn’t flat enough and the fish could escape underneath the net.
They found a nice spot in Moosehead that had gravel and baseball-sized material to rest the net on, he said. They netted 201 mature lake trout in 16 days, measuring fish ranging from 21 to about 31 inches long. After spawning, the lake trout dispersed all over the lake, which was information gained from the PIT tags, he said.
In regular trap nets, biologists were capturing fish that were between 16 and 20 inches long.
Early success means the department will expand the program. The department has plans to buy four more nets and hire additional staff for the study with matching money provided by Moosehead Lake Fisheries Coalition and Natural Resource Education Center at Moosehead.
Having more nets will mean three different shoals will be surveyed and fish from them tagged during spawning season from mid-October to early November in 2025.
“We hope to see some of these fish on the ice this coming winter. More importantly, we see the possibility of expanding this work to multiple shoals next fall and vastly increasing our sample size,” Obrey said.
The landlocked salmon and brook trout are healthy in Moosehead right now, he said Tuesday, but fishermen need to keep legal-sized togue instead of putting them back in the lake to keep the balance.
“You’re helping the fishery that way,” he said.
