The sun was just beginning to rise above Lake Superior as I drove north on Highway 61 toward Grand Marais in mid-May some 25 years ago. As the Lake Superior fisheries manager for the Department of Natural Resources, I was going to stop along the way and meet individually with our assessment netters to gather information they had collected on Lake Superior lake trout (Salvelinus namaycush). Their job was to net lake trout and record biological information from each fish. They noted fish length and weight, sea lamprey wounds, and fin-clips of stocked fish. From a portion of their catch they took scale samples, stomachs, and otoliths (ear bones) for a more detailed examination of diet and fish age. The netters also recorded the number of lake trout caught and the length of gill net fished. Their compensation came not in dollars, but from the sale of lake trout they captured. This routine had taken place each spring since the lake trout population had collapsed and the commercial fishery had formally closed in 1962.
Click to see Lake Superior's lake-trout fishing zones and see a graph depicting the rise of naturally reproduced lakers.
As I approached a somewhat dilapidated fish house, I noticed smoke coming from a woodstove and knew I was on my way to school. This particular well-weathered assessment netter, a friend and mentor, normally began our conversations with a critique of the DNR's management of the fishery. After some venting, he would then more calmly describe his daily observations on the lake, discuss current fish behavior, and compare the present fishery with the past when he and his family fished near Isle Royale. Despite his predictable grumbling, I always appreciated his insights and history lessons. One statement will always stay with me: "We'll never see commercial fishing for lake trout again in Minnesota," he lamented.
I hoped he would be proven wrong. Cautiously, I told him that lake trout, including wild fish, were becoming more abundant, especially in the area where he fished.
Fast forward to today: The Lake Superior lake trout fishery has bounced back in a big way. "Lake trout rehabilitation in Lake Superior is a major success story for the Great Lakes," says Don Pereira, chief of DNR Fisheries and U.S. commissioner to the international Great Lakes Fishery Commission. "It provides a positive example of what can be accomplished when fish management agencies, user groups, and citizens work together toward a common goal."
This story tells how the collapse and the recovery played out.
Top Predators. Lake trout are native to the Great Lakes and were historically the top predator in the Lake Superior fish community. They are well adapted to these cold, clear, infertile waters. Once represented by many strains, lake trout have been reduced to two major strains in Minnesota waters. Lean lake trout, or leans, occupy the near-shore zone, usually at depths of less than 300 feet. Leans are the most popular and recognized form, pursued by anglers and sold in fish markets. They grow slowly and do not reach maturity until ages 8 to 9 for males and ages 9 to 10 for females.
The other strain, the siscowet or fat lake trout, typically lives in water deeper than 300 feet. Unfortunately, their high fat content carries high contaminant levels, so siscowet are not recommended for consumption. While lean lake trout occupy only about 20 percent of Superior, siscowet inhabit about 80 percent and outnumber leans by roughly 10 to 1 in many areas of the lake. Due to their slow growth rates and advanced age of maturity, both lake trout forms are vulnerable to overfishing. This story focuses on the recovery of lean lake trout, so the term lake trout will refer to leans only.
The well-documented decline of lake trout in the 1950s was initially caused by overfishing and accelerated with the invasion of the nonnative sea lamprey (Petromyzon marinus). A sea lamprey feeds by attaching itself to the fish's body and extracting blood and fluids, which can kill the fish. Sea lamprey invaded Lake Erie through the Welland Canal in 1921, migrated west to Lake Superior by 1938, and were found throughout the lake by the early 1950s. Following this invasion, commercial lake trout harvest declined sharply.
Minnesota tributaries to Lake Superior contain little reproductive habitat for sea lamprey since natural upstream barriers are close to the lake. However, migration of sea lamprey from other parts of Lake Superior to Minnesota waters resulted in some of the highest wounding rates in the lake.
Rehabilitation. To address the collapse of fisheries in the Great Lakes, the governments of Canada and the United States established the Great Lakes Fishery Commission in 1956. The commission aims to control sea lamprey, coordinate fisheries management, and foster communication and research on fishery problems. Early research by the U.S. Fish and Wildlife Service to control sea lamprey focused on testing chemicals that might kill ammocoetes, the stream-dwelling larval stage. After many trials, TFM (3-trifluoromethyl-4-nitrophenol) was found in 1958 to selectively kill ammocoetes.
The ability to control sea lamprey gave fisheries managers hope that lake trout populations could be rehabilitated. Managers realized that lamprey control had to be accompanied by strict harvest regulations. The DNR closed the commercial lake trout fishery and substantially restricted the sport fish harvest in 1962. In addition, they initiated massive lake trout stocking programs using remnant strains from Lake Superior as an egg source. All stocked fish were fin-clipped to distinguish wild from hatchery fish.
Progress toward lake trout rehabilitation in Minnesota was first measured in 1962 using large mesh gill nets set in the spring. A summer creel survey was added in 1972. Both surveys continue to this day. The spring gill net assessment tracks lake trout abundance, monitors sea lamprey control, and evaluates stocking efforts. Several commercial netters, such as my colorful friend, have assisted with the annual assessment.
Abundance indices are reported as catch per unit effort in either numbers or weight of lake trout captured per length of gill net. Trends indicate that stocked lake trout peaked in the mid-1980s. The high catch per unit effort in the early 1980s was likely driven by extremely high lake trout stocking levels, limited competition from wild lake trout, and abundant rainbow smelt, then the preferred prey. Beginning in the mid-1990s, abundance of wild lake trout surpassed that of stocked fish. By 2008 wild trout composed more than 80 percent of the total catch per unit effort. As the number of wild lake trout increased, the survival of stocked fish declined significantly. This relationship was observed in all areas of Lake Superior as rehabilitation advanced.
Sea lamprey wounding rates have decreased dramatically from 25 to 30 wounds per 100 trout in the 1960s and early 1970s to five to 10 wounds per 100 trout in the 2000s, to fewer than five wounds during the past five years. The reduced wounding rate increases fish survival, which leads to increased natural reproduction and sustainability of lake trout.
Creel survey information is critical for monitoring lake trout rehabilitation in Minnesota because sport harvest has exceeded the combined assessment, commercial, and tribal harvests over most of the last 40 years. An annual summer survey runs from Memorial Day weekend through early October. Lake trout harvest by sport anglers increased from less than 5,000 fish annually in the early 1970s to about 23,000 annually from 2000 to 2015. The total catch per unit effort of lake trout also increased dramatically (see chart). Wild lake trout in the Minnesota sport fishery now make up more than 95 percent of the harvest.
New Plans. Minnesota waters represent about 7 percent of the total surface area of Lake Superior. The Minnesota DNR manages lake trout within three zones, which differ greatly in size and physical characteristics. In the two northern zones, wild lake trout rebounded so well over the last 10 years that the DNR discontinued stocking and expanded the assessment fishery to allow limited commercial harvest during the entire summer season.
The 2016 Lake Superior Fisheries Management Plan calls for all stocking of lake trout to be discontinued. "We anticipate wild lake trout will replace stocked fish with no real loss to the angler since that is what occurred in the other management zones when stocking was discontinued," says DNR Lake Superior supervisor Cory Goldsworthy. "The key to complete restoration will be maintaining conservative harvest rules, especially in the heaviest fished zone around Duluth."
Pereira cautions that while "the recovery of wild lake trout populations in Lake Superior is considered a major success among North American fisheries, we must not forget that sea lamprey control is the basis of this success, and conservative regulations must be maintained for the wild fishery to sustain present harvest levels."
Anglers agree that the fishery has rebounded to levels that rival the good old days. Longtime angler and charter captain Charlie Haslerud says, "The lake trout sport fishery in Minnesota is as good now as it has ever been. And unlike the 1980s, the majority of fish we harvest are wild."
Local economies, including restaurants and fish markets, benefit from the rehabilitated lake trout population and the expanded summer assessment fishery. The assessment fishery allows commercial netters to harvest a limited number of lake trout from June through September under a special permit. Harley Toftey, owner of the Dockside Fish Market in Grand Marais, says, "It's great that the lake trout fishery has rebounded and the DNR has expanded the opportunity to net more fish. This allows tourists that do not fish to experience a locally caught lake trout meal during their vacation."
It took over 50 years for wild lake trout to recover from overfishing and sea lamprey predation in Minnesota. I wish my commercial fishing friend had lived to participate in the current netting opportunities. The hard work of many individuals and the sacrifices of the early commercial fishing families have allowed the fishery to rebound. I hope that we always maintain the efforts required to sustain the lake trout fishery. All Minnesotans should be proud that abundant wild lake trout are again roaming the cold waters of Lake Superior, providing both recreation and food for those who participate in this unique fishery.