Northern Maine has a problem.

Northern pike, a voracious invasive fish that kills native species, are moving down from Canada into the St. John River and nearby bodies of water.

Except the St. John River is already teeming with muskellunge, an invasive fish better known as muskie.

In a first for Maine, the northern part of the state suddenly finds itself home to two types of aggressive invasive fish. What this might mean for the waters supporting both types of pike is a complete unknown, but it isn’t good news for any native fish remaining there, according to a Maine regional biologist.

Frank Frost has a lot of experience with the fishery in the Crown of Maine. He grew up in Caribou and has been a biologist in northern Maine for about 30 years.

He’s seen a lot of changes in that time.

The St. John River and Glazier and Beau lakes have all but lost their brook trout and landlocked salmon fisheries. The mouths of tributaries into the river at one time teemed with trout, but now there are just scattered stand-alone populations of both trout and salmon.

The invasive fish are making it difficult for the native species to use the river in May, June and early July for their traditional feeding grounds, the biologist said.

Courtney holds a large northern pike from the Belgrade Lakes. Credit: Courtesy of Ryan Brod

A salmon caught in Beau Lake during the recent ice fishing season was scarred and had fresh wounds from muskie that have taken over there.

Any data he and fellow biologists obtain about how muskie and pike are coexisting are likely to come from fishermen because with a small staff, the largest territory in Maine and few resources, they are not well-equipped to carry out any formal studies in the near future, he said.

Frost didn’t know if the two aggressive killer species would co-habitate in the same watersheds, but with the pike and muskie so similar in how they live, he doesn’t see a lot of potential for the late-comer pike to thrive.

“They likely won’t expand much because of the muskie,” he said.

Glazier Lake, which is a 1,000-acre body of water with a maximum depth of 118 feet, had brook trout, lake trout and landlocked salmon until the late 1980s and early 1990s, according to logs kept by local anglers. Those fish are essentially gone now, Frost said.

Now Glazier is well-known for its muskie fishery and is one of the bodies of water included in the local fishing derbies that target the species, the most famous of which is the Fort Kent International Muskie Derby held in August.

Muskies are long established in northern Maine, having colonized the Upper St. John River in the early 1970s. The first one was found in May 1971, Frost said. The fish moved downriver in the 1980s and soon were found in the Mataquac fishway in New Brunswick.

They pushed into the St. Francis River that forms the boundary between Maine and New Brunswick and its watershed. Now Glazier and Beau lakes have muskie. The species also has colonized the Fish River and Allagash River up to the natural barriers of Allagash Falls, and up to Fish River Falls in Fort Kent.

A U.S. Army Corps of Engineers study from about 15 years ago suggested that it would be possible for muskie to get past Allagash Falls through a back channel of the river if some loose rocks in that area dislodge over time and give the fish access to more of the water system, including the Fish River chain of lakes.

Although the state received a couple of reports about a dozen years ago of muskie beyond the falls, they could not be substantiated and there have been no reports since, Frost said.

“The falls is the main factor holding the fish back,” he said.

This 36-inch muskellunge, or muskie, was caught by BDN Contributor Kevin McKay in the Fort Kent area. Credit: Courtesy of Kevin McKay

Northern pike entered the water system from Canada via Big Black River. Pike now have the same access to the St. John and St. Francis watersheds that muskies do. The pike have been seen in Big Black, plus in the upper St. John River and its watershed.

Many lakes and ponds in central and southern Maine are infested with pike, although they do not have muskie. Jason Seiders, regional biologist for the Belgrade Lakes area since 2012, describes his central Maine t erritory as the state’s pike epicenter. 

Pushaw Lake in Penobscot County on the outskirts of Bangor has been taken over by pike too. Scientists plan to tag about 500 of them this year to see how far they travel into other waters.

Muskie and pike have open access to and from the lakes connected to the St. Francis and St. John rivers. The sizes of tributaries and streams out of those lakes will limit how far the fish can travel, Frost said. For example, Yankeetuladi Brook is a tributary from Falls Brook Lake, which has a large waterfall that keeps muskie and pike out.

Muskies’ favorite food is rainbow trout smelt, but they also eat chubs, suckers, round or lake white fish, or small ducks and mammals in the water. Pike have a similar diet.

They both prefer cool water at 65-70 degrees Fahrenheit in the summer, but actively feed during the winter. They live in the same part of the water column where brook trout would live in the summer, supplanting the native species.

No pike have been caught beyond Big Black River, where there likely are a fair number of them, Frost said. One was caught there in September 2024.