Lake Look: How Lake Trout Made Their Comeback in Lake Champlain

The story of lake trout in Lake Champlain is one of mystery and hope. In spring 2023, the Lake Champlain Fish and Wildlife Management Cooperative – a working group of fisheries professionals from the New York State Department of Environmental Conservation, the Vermont Fish and Wildlife Department, and U.S. Fish and Wildlife Service – announced plans to halve the annual stocking of lake trout in Lake Champlain this year. They cut back because of increases in lake trout wild recruitment, or survival past the first winter of life. This follows a trend of jumps in lake trout populations and subsequent reductions in stocking—there was a 30% reduction in trout stocking in 2022. While thousands of animal populations across taxa around the world plummet, the native lake trout of Lake Champlain are making a comeback. Why?

Lake trout (Salvelinus namaycush) are deep-water dwellers, found in depths as low as 200 feet. Despite what their name suggests, they are not a true trout and are actually a type of char in the Salmonidae family. They are a cold-water species who prefer water temperatures between 40^o and 50^o F. As top predators, younger fish feed on smaller invertebrates and plankton and adults feed on other fish. Native to Lake Champlain, they have supplemented human diets since people started living here roughly 13,000 years ago, and have played a key role in the aquatic food web for even longer. That all came to a halt by the year 1900, when lake trout were completely extirpated from Lake Champlain. Interestingly, the exact cause of this population crash remains a mystery. Dr. Ellen Marsden, fisheries biologist and professor in the University of Vermont (UVM) Rubenstein School of Environment and Natural Resources, says the disappearance of lake trout from the lake remains a puzzle. “It seems unlikely that a shoreline seine fishery for whitefish and lake trout, primarily in the north lake in fall, would wipe out lake trout, and sea lamprey were not seen in the lake back then,” she said. “[There are] no good theories so far.”

In the Great Lakes, lake trout populations crashed later, in the 1950s, which is what spurred restoration and stocking efforts. This crash, unlike the extirpation from Lake Champlain, was well documented: it was partially caused by the usual suspects of overfishing and degraded water quality, but was largely caused by sea lamprey (Petromyzon marinus). By most standards, sea lampreys are the stuff of nightmares: they are jawless parasitic fish that grow up to 24 inches long with smooth, scale-less skin. In its parasitic life stage, the juvenile sea lamprey will latch onto a host fish with its suction disk mouth filled with spiraling rows of small, razor sharp teeth. After puncturing the skin of their host, sea lamprey release an anticoagulant in their saliva that prevents blood from clotting while they feed. The host fish often dies from blood loss or infection—mortality rates are between 45% and 75%—and fish that survive sea lamprey attacks will have decreased success in survival and reproduction later on. Sea lamprey love lake trout because of their thin skin and small scales which makes for an easy meal. Long referenced as an invasive species because of a lack of historical record in Lake Champlain, more recent studies suggest that sea lamprey may be native to Lake Champlain as a leftover from the last ice age. Genetic studies also strongly suggest that sea lampreys are native to Lake Ontario and the Finger Lakes, so theories of spread to Lake Champlain through the inland canal system have also been proposed. While it is possible that sea lamprey were present in Lake Champlain well before lake trout extirpation, their populations still skyrocketed in the 20^th century to the detriment of sea lamprey hosts like lake trout.

The restoration of lake trout populations in Lake Champlain needed a hands-on approach. In 1972, basin-wide efforts to restock lake trout began: from then until 1990, New York and Vermont hatcheries raised and released between 39,000 and 325,500 lake trout yearlings on an annual basis. Sea lampreys posed a major challenge in recruitment of these stocked lake trout—at its worst, 99 of every 100 lake trout in Lake Champlain were wounded by sea lamprey according to US Fish & Wildlife. In 1990, New York and Vermont started an experimental sea lamprey control program, which used physical barriers to cut off access to breeding ground and lampricides to cull their numbers. To this day, lampricides are controversial for the same reason pesticides are: the application of harmful chemicals to the environment does not affect just the target species. In 2009, about 500 mudpuppies (a type of rare aquatic salamander) were found dead floating on the Lamoille River after lampricide application. Far fewer turned up dead in following years, but whether this was from the improved application methods or from a decimation of mud puppies is still unknown. Population studies of mud puppies in the Lake Champlain Basin must be done in order to know the true unintended impact of lampricides. But lake trout abundance has gradually increased and stocking has gradually decreased since sea lamprey controls have started, leading to the surge in lake trout numbers we see today.

While controlling sea lamprey in the lake played a major role in lake trout population increases, it may not tell the whole story. Alewife (Alosa pseudoharengus) have been harmful to several species in Lake Champlain. The invasive fish were first discovered in Lake Champlain in 2003 and became abundant by 2007. Their voracious feeding habits and speedy reproduction give them an edge to outcompete rainbow smelt, the primary native prey species. But for lake trout, alewife may have provided the tasty boost that their recovery needed: food web modelling by UVM post-doc Justin Lesser and others in Dr. Marsden’s lab suggest that the introduction of alewife to the lake may have been another factor that helped lake trout populations bounce back. They are a fatty addition to the lake trout’s limited native prey base of smelt and sculpins and may have increased the fecundity of females and the ability of fry to survive. It goes against all common logic surrounding invasive species, showing that ecological relationships are rarely black-and-white, and just how complex aquatic food webs can really be.

Lake trout are not the only stocked fish in Lake Champlain. Landlocked Atlantic salmon (Salmo salar) have also been stocked since the early 1970s, and natural reproduction is just beginning to occur. In 2019, federal biologists discovered salmon fry swimming the Boquet River in New York after 150 salmon-less years. It is a hopeful sign but still a long way from recruitment. Dams are a major and literal barrier to success for salmon, as they block the routes needed for salmon reproduction upstream. LCC and other environmental organizations and agencies are working collaboratively on New York and Vermont dam removal task forces to help restore aquatic organism passage through the modification or removal of dams and other barriers that no longer function as intended and/or impede natural stream function. However, it is possible that salmon will follow in the footsteps (or rather, fin-steps) of lake trout in the coming years if conservation efforts continue.

Fish stocking efforts vary by coast on Lake Champlain. According to Dr. Marsden, Vermont and New York stock lake trout at different seasons and ages (fall fingerlings or spring yearlings). Lake trout of the same species still have varied genetic “strains,” (like apple varieties). New York stocks Seneca Lake strain whereas Vermont stocks Lake Champlain Domestic strain. The relative survival and growth of these strains have never been compared. Ben Marcy-Quay, another UVM post-doc in Dr. Marsden’s lab, is using modern genetic methods to evaluate which strain is most successful, which will allow managers to strategically focus stocking methods. Part of the 2022 scale-backs in lake trout stocking included the elimination of New York stocking altogether, so if this research determines that the dominate strain in recruited lake trout is from Seneca Lake, the restoration strategy may have to shift.

Stocked lake trout have clipped fins to help distinguish them from wild counterparts. In 2015, Dr. Marsden and her lab found adult lake trout in Lake Champlain with unclipped fins. That means these lake trout were born and raised in the lake, and never saw a hatchery: the first of their kind documented since before their mysterious extirpation over 100 years ago. While natural reproduction occurred before this, these were the first ones caught that made it to adulthood. The continued efforts from fishery professionals over the 20^th and into the 21^st century has caused the resurgence that we see today. Make no mistake—the success of lake trout does not negate the fact that the Lake Champlain and life in it are still in peril from water quality degradation, climate change, and invasive species. It does show, however, that when we make strong, science-based efforts towards conservation, success is possible.