Retired DNR research biologist Jim Johnson.

The Great Lakes and their fisheries are, today, relatively healthy. We tend to take that for granted. We shouldn’t. As recently as the 1960s, because of unchecked water pollution, invasive species, and collapse of their most important fisheries, the Great Lakes were deemed by some to be an “attractive nuisance” – they looked inviting from a distance, but could be unspeakably repulsive up close. Just one example: Sleeping Bear Dunes and other important public beaches were plagued by billions of dead alewives. The stench of dead fish, the flies, and the sanitation issues that ensued forced the closure of these beaches during the height of the tourist season in 1969. To understand the causes of this calamity, we need first to take a “look under the hood” to understand how Great Lakes fisheries are supposed to work and what went wrong.

Lake trout is the top native offshore predator of Lake Huron, and walleye the top nearshore predator and is especially important in the Saginaw Bay area. These two fish were the “wolves” of the Great Lakes, maintaining ecological balance by pruning numbers of smaller fish that otherwise would have become overabundant. Technically, this means lake trout and walleye are “keystone predators”. Just as wolves are keystone predators in Yellowstone, where they control deer and elk numbers, walleye and lake trout have for millennia shaped fish communities.

In addition to their critical ecological roles, both species supported valuable Great Lakes commercial fisheries – tens of millions of pounds were netted annually from the 1830s to the 1940s. But this harvest grew to become unsustainable.

By the late 1940s, lake trout and walleye had collapsed in all the lakes, succumbing to a combination of overfishing and depredation by the invasive sea lampreys, which had become Lake Huron’s largest aquatic vampire. And in the case of walleye, the pollution of the Saginaw River and Saginaw Bay was a major cause of their decline. Lake Erie, the world’s most important walleye fishery, was considered “dead” – like Saginaw Bay, it had succumbed to water pollution.

Lake trout and walleye had been dominant, top predators in lakes Huron and Michigan. As long as they reigned, the whole ecosystem was stable. In ecological terms, healthy lake trout and walleye meant Great Lakes fish communities were “balanced” with the predators (the hunters) balancing prey (the hunted). Lake trout and walleye were the keystone predators, that groomed the lakes’ prey populations and prevented them from becoming too abundant.

But sea lampreys were the final nail in this remarkable fishery’s coffin. The other two ‘nails’ were the incredible amount of commercial fishing going on at the time, and extreme pollution of Saginaw Bay and the Saginaw River system where walleye once thrived. Their combined effects decimated lake trout and walleye, leaving a void where predators used to be and an opportunity for invasive species like alewives.

Like lampreys, the alewife colonized Lake Huron by way of navigation canals that bypassed Niagara Falls. The alewife is a prey fish, never reaching more than about 8 inches and prolific enough to be a copious food supply for larger predators.

In other words, the absence of keystone predators caused an imbalance between predators and prey which enabled explosive growth of the invasive alewife and rainbow smelt (another invader) populations.

By the late 1960s, some scientists described lakes Michigan and Huron as “alewife soup”. During the 1960s and 1970s, in Lake Michigan alone, there were an estimated 175 billion alewives. But what caught everyone’s attention was the annual spring die-off of alewives.

In 1967, 20 billion dead alewives washed up on the Michigan shore of Lake Michigan. A pile of dead alewives, a foot high and 300 miles long, extended from Chicago to Mackinaw City. Important tourist-destination beaches were deemed unsanitary and had to be closed. Repercussions to the tourist-based economy of coastal communities were enormous.

And there were similar problems on Lake Huron, though not as noticeable to Michiganders because prevailing winds blew most of the dead alewives over to the Canadian side.

This is what happens when prey fish die of old age. Prey fish are meant to be eaten by bigger fish. They have the reproductive capacity to feed millions of pounds of predators in the Great Lakes. But in the late 1960s, without those predators, that fecundity was unleashed on Michigan’s beaches.

Recovery would require four fundamental ingredients:

Sea Lamprey control

The Great Lakes would be mired down with dead prey fish unless something could be done about the sea lamprey. Fortunately, scientists at the Hammond Bay Biological Station north of Rogers City, after screening over 6,000 compounds, discovered that the pesticide 3-trifluoromethyl-4′-nitrophenol – or “TFM” – would selectively kill sea lamprey larvae without significantly harming other plants or animals, or having any long-term impacts on the ecosystem. Sea lamprey, like salmon, migrate up tributary streams to spawn and the adults die after spawning. The juveniles spend several years in the tributaries before transforming into parasitic adults. This was their weak link: treat a few dozen spawning tributaries each year and you can suppress the sea lamprey population of Lake Huron. There was just one rub: one of those

tributaries is the enormous St. Marys River, the channel that drains Lake Superior into Lake Huron. Gaining control of the St. Marys River would take further research and investment.

Sea lamprey suppression was the first of four essential ingredients to restoring lake trout and walleye. And for the past 50 years, it’s been a key ingredient of fisheries management in the Great Lakes.

Improve regulation of commercial fishing

But sea lamprey control was only the first step: the resource agencies could not hope to restock the Great Lakes when they were saturated with gill nets. In 1966, 73,000 miles of gill nets were fished in Michigan waters of the Great Lakes, enough to go around the Earth 2.9 times! It would be pointless and a waste of tax dollars to stock fish that would only end their lives in gill nets, dead before they had the opportunity to mature and reproduce.

The gill net is a nonselective type of commercial fishing gear: the fish caught in them are likely to die because, as their name implies, the nets work by entangling the fish by the gills, which can damage the delicate gill filaments or cause suffocation. Thus, commercial fishers couldn’t release fish that they were not entitled to and expect them to live.

Thus, in 1973, the Michigan Department of Natural Resources (DNR) proposed banning gill nets in most of Michigan’s Great Lakes’ waters (other states, Ontario, and the tribes chose to take a different approach to gill nets). This did not mean an end to commercial fishing; the solution was to require the fishery to convert to trap nets. The trap net, like an underwater corral, holds fish alive in a confined area. The “pot” of the trap can be raised to the surface and the fish removed and sorted. The commercial fisher can release both undersized fish and species that they might not be entitled to, such as protected lake trout, walleye, various salmon, and lake sturgeon.

Now the resource agencies could begin restocking the Great Lakes with predators.

Massive restocking efforts

This would require hatcheries that in the 1960s were simply not up to the task. Lakes Michigan and Huron, combined, are huge – about 25,000,000 acres. To stock just one yearling lake trout per acre would cost about half the budgets of Great Lakes fisheries resource agencies on those lakes. Plus, there were not enough lake trout eggs available. Then the DNR’s Fisheries Chief, Dr. Howard Tanner, learned that there were surplus salmon eggs available from the states of Washington and Oregon. Thinking it might take an ocean fish to prey effectively on alewives, also an ocean fish, Dr. Tanner jumped at the opportunity. But would Chinook or Coho salmon from the Pacific Ocean survive in fresh water? And would they feed on alewives, or would they prey on other more valuable species? The Governor had just pleaded with the DNR, after the massive 1967 alewife die-off, to “do anything” that might bring the alewives under control and restore Michigan’s beach-based tourism, so Dr. Tanner went for it. This, at the time, was a huge gamble. On the plus side, Chinook salmon were inexpensive to raise; it cost about the same to

raise 6 fingerling Chinook salmon as one yearling lake trout. It took 20 years for a lake trout to eat enough alewives to reach 20 pounds. A 20-pound Chinook salmon was only 3 years old. This means the annual alewife-eating-capacity of salmon was many times that of the native lake trout. On the downside were the unknowns and potential unintended consequences of an introduced species from elsewhere. (This became the first research mission for the Research Vessel Chinook, which will be the subject of another future column.)

Here is how Dr. Tanner described the decision to stock Coho salmon in an interview in 2008*.

“A problem is really an opportunity to make something better. And so, the alewife problem wasn’t really a problem. It was a wonderful food supply.”

“I got a call from the West Coast, and for the life of me, I can’t remember who it was. He said, you know, there’s a surplus of Coho eggs. And it knocked me right off my chair. And I went home that night and couldn’t sleep.”

“And there it was. There was a fish that could utilize the alewife.”

Now the agencies could begin restocking the lakes. What ensued was one of North America’s largest-scaled, successful keystone predator recovery projects.

Control the excessive number of alewives

The fourth and final issue facing ecosystem restoration of the Great Lakes was to improve the quality of the prey supply in the lower lakes where pure-alewife diets were proving toxic (alewives are scarce in Lake Superior where the water is too cold for them to do well). Chinook and Coho salmon were stocked each year after 1966. And they did eat alewives. At first, they grew exceptionally fast on this cornucopia of prey. On the West Coast, their native range, mature Coho average 8 to 12 pounds. But Lake Michigan Coho were commonly reaching 16 to 20 pounds. Chinook salmon seemed to be perfectly designed to prey on alewives, reaching 20 to 35 pounds, with one recorded at over 40 pounds.

Alewives presented a two-edged sword; on the one hand they were the backbone of multibillion dollar salmon fisheries; on the other, alewives continued to hamper recovery of native lake trout and walleye and suppress reproduction of the introduced salmon. They did this by feeding on the young walleye and lake trout and also by causing serious vitamin deficiency in trout and salmon that fed heavily upon them. (You could call this the alewives’ revenge – more on this intriguing syndrome in future columns). The invasion of the Great Lakes by zebra and quagga mussels, combined with predation by the stocked fish, finally brought the alewives down, nearly eliminating them from Lake Huron and reducing their numbers in Lake Michigan. The mussels reduced alewife populations by efficiently filter feeding, which decreased the availability of plankton (tiny drifting animals) to alewives (and other species). For Lake Huron, there was to be no happy medium, which would have been a reduction in alewives but with enough of them remaining to support a salmon fishery. Instead, the alewife population almost disappeared, and Chinook salmon proved to be unable to switch to other prey species. With

alewives virtually gone, Chinook salmon also disappeared from all but the northern-most regions of Lake Huron. The suppression of invasive alewives indeed benefited the native walleye and lake trout, but the loss of plankton caused by invasive mussels proved to be devastating to other fish such as lake whitefish and Chinook salmon. Managers were forced to reassess predator stocking and formulate new plans to balance predator fish with a new prey base, now composed largely of a newer invasive, round gobies.

So where are we today? On the plus side, walleyes are self-sustaining and offering up one of the planet’s best walleye fisheries in Saginaw Bay – second only to the now recovered Lake Erie fishery. And Saginaw Bay walleyes are roaming all of Lake Huron, benefiting fisheries throughout the main basin of the lake. Lake trout are finally reproducing again and appear to be self-sustaining in northern Lake Huron, but reproduction is still flagging in central and southern Lake Huron where harvest, particularly from the Canadian commercial fishery, remains a serious impediment. Lake trout readily adapted to the collapse of alewives and are now enjoying a much healthier, thiamine-rich diet composed of gobies, smelt and other species. But Chinook salmon were unable to adapt to the new prey base. The decline in salmon caused a sharp decrease in angler use and harvest of Lake Huron’s main basin. Similarly, lake whitefish have been unable to reproduce in the presence of so many quagga mussels and, consequently, Lake Huron’s commercial fishery is in serious trouble. Today, we have two native keystone predators reproducing again and a balance has been established between predators and prey, but the declines in plankton caused by invasive mussels have undermined lake whitefish and Chinook salmon numbers. Consequently, our offshore commercial and recreational fisheries are just shadows of what they have been in the past, with serious economic consequences, particularly to Lake Huron’s coastal communities such as Alpena. Unlike sea lampreys, these new invaders, the quagga mussels in particular, seem to not be susceptible to control. Unless the mussel problem can be solved, our fisheries are not likely to recover to levels Lake Huron was capable of in the past.

Jim Johnson worked as a research biologist at the DNR’s Alpena Fishery Station. He and the DNR’s research vessel, the RV Chinook, as well as Boat Captain Clarence “Tuffy” Cross retired to the Besser Museum where they