But earlier this decade, several factors squeezed the alewives out of Lake Huron's main basin. Their food supply dwindled when zebra and quagga mussels sucked the nutrients to the bottom and edges of the lake. Heavily stocked Chinook salmon began large-scale wild reproduction and required significantly more food. The alewives couldn't withstand the double whammy, and their population collapsed.

Their absence soon caused Chinook salmon to virtually disappear. Without its dominant predator and its dominant prey species, Lake Huron became home to a series of cause-and-effect relationships that are still playing out. Without alewives, native walleye and lake trout are thriving. Without alewives, native whitefish and yellow perch have become prey. Forage species that biologists expected to rebound, like rainbow smelt and bloater chubs, have not.

“This is a loss of the whole prey base,” said Johnson, a Michigan DNR biologist. “Nothing is replacing the alewives and that's what is puzzling everybody. Normally niches don't just go away. … It's not one species went down, it's the whole complex of species that went down.”

Lake Huron's charter fishing industry has contracted severely, and those who still fish for a living are targeting walleyes in Saginaw Bay. Meanwhile, fisheries managers are staring at a monumental task: finding a way to replace Chinooks with some other high-profile, open-water sportfish while favoring native species better adapted to Lake Huron's ecosystem and making sure everybody has something to eat -- with little or no money in the budget. New techniques will be adapted for stocking brown trout and steelhead within the next year. The state is also studying the restoration of lake herring, a native fish that originally occupied the same niche as the alewife but whose range has been greatly reduced.

“These are large-scale management experiments,” said Kurt Newman, the Lake Huron Basin Coordinator for the Michigan Department of Natural Resources. “We're kind of taking what we can do and trying something different. Lake Huron is wide open for us to be trying some things.”

Johnson, with input from other biologists and stakeholders such as charter boat captains and citizen groups, is in the process of developing a lakewide management plan. The two-year process is designed to lay out a blueprint for managing the lake that will encompass the entire food web, recommend stocking strategies and attempt to anticipate problems.

“My feeling has been that we need to do that so we can be better prepared,” Newman said.

What's there to eat?

Alewives fed many more species than Chinook salmon, serving as a buffer for smaller fish like yellow perch. Without alewives, the entire gallery of Lake Huron predators – from walleyes to cormorants, the fish-eating birds -- has turned its attention to what's left.

“Anything that's small gets eaten now, and it used to be they just ate alewives, and that kept the cormorants and the walleyes away from the more valued fish,” Johnson said. “Now, with both cormorants and walleyes you see a lot of game fish in their stomachs, and that's hurting the reproduction of the species.”

Another effect of the alewives' demise is the resurgence of lake trout and walleyes, both of which are native to Lake Huron. Alewives are rich in thiaminase, an enzyme that causes lake trout to have difficulty reproducing. And alewives appear to have fed heavily on walleye fry, preventing them from reaching adulthood.

Now both those species have recovered, but that has created another problem: Since they're more numerous, they require more food, and they're both fish eaters. Lake trout, which inhabit the cold, deep the bottom.

Shallow-water walleyes, meanwhile, have turned to yellow perch, especially in Saginaw Bay. “Because of the scarcity of alewives, now what predators there are, instead of eating alewives, now they're eating perch,” Johnson said. “The perch are still reproducing fine, but they've become bait and that's really too bad.” The walleyes also appear to be taking a toll on whitefish and lake trout, which spawn in shallow water. But Michigan has been aggressively controlling the cormorants on Lake Huron, which means there's less pressure on the young of those species, Johnson said. “We're hoping that there will be some surplus production of young perch and whitefish and lake trout to grow up as those three species become more self-sustaining.”

Walleye populations have exploded in Saginaw Bay since alewives collapsed, but their expansion has had a negative effort on yellow perch.

That effort could be helped along by a resurgence of gizzard shad, a small fish similar in its ecology to the alewife, according the DNR shallow-water specialist Dave Fielder. If gizzard shad numbers hold up, they could serve as a buffer between walleyes and other gamefish, especially yellow perch.

“Gizzard shad have come on strong,” he said. “That prey base is holding up and it seems to be striking a balance. We're hopeful that it will find an equilibrium because that's natural reproduction.”

The U.S. Geological Survey has started a diet study this summer designed to find out exactly what those predators are eating. They're signing up anglers and teaching them how to collect fish stomachs and freeze them for later study.

“So we're going to find out how predators are interacting with what we see as a very interesting forage base,” said Jeff Schaeffer, a USGS biologist. “It's really exciting. We initiated this study at the request of the anglers. I think there is unprecedented interest in the resource and we have some amazingly well-educated stakeholders. People are very interested in making a contribution for the resource.”

Stocking issues

Michigan once stocked 3 million Chinook salmon a year in Lake Huron . That was cut in half in 2006, but that still means 1.5 million Chinooks are going into the lake. They're planted in spring and most spend their first summer near shore getting eaten by walleye, cormorants and even lake trout if the water stays cold enough.

“We think most of the fish we stock are becoming prey to the things inshore that are looking for fish to eat,” Johnson said.

Chinook salmon were originally chosen for a couple reasons. They're unmatched as fighters; anglers compare lake trout to mules that stay deep and tug, Chinooks are more like thoroughbreds that run fast and jump high.

They're also very easy to raise in hatcheries and super cheap: It costs the state about 15 cents to raise a Chinook salmon to smolt size. That's a bargain compared to a steelhead, which costs about $1.05. And Atlantic salmon, which creel studies show are the most catchable salmonid in Lake Huron , cost twice that.

For now, Michigan's DNR will incorporate some new stocking techniques designed to put big fish in the lake that can feed around the edges where the food is, and that means brown trout and steelhead. It is also looking into rotating lake trout plants so stocked lake trout can mature without competition from new plants every year, a technique called “pulse stocking.”

The DNR's existing program puts roughly 280,000 fingerling brown trout into Lake Huron every spring, right when predators are looking for an easy meal near shore. This October, Michigan will stock 85,000 brown trout in the 10-inch range in five separate locations. It costs less money to raise fewer fish, and by waiting until fall fewer fish can be stocked with more survivors.

“That happens to be the time when the migration of the cormorants has gone and they're too big for walleye to eat,” Newman said. “We have good evidence that when a brown trout makes it through that first season they can do well in Lake Huron .” Newman said.

The state will also employ net pens formerly used to raise Chinooks next spring to raise steelhead to a similar size. The DNR will produce the normal 120,000 steelhead for Lake Huron next year, but only half will be released as usual. The other 60,000 will be held in net pens in Lake Huron and allowed to grow before they're released. Those programs will be reevaluated after three years.

Johnson said the Atlantic salmon stocked in the St. Mary's River seem to thrive once they reach Lake Huron, but expanding that program would be time consuming, expensive and no sure thing.

“I can see that it's going to be a long and arduous process, and full of uncertainty to bring Atlantics back,” he said. “We feel we have a much better chance of working with steelhead.”

The unassuming lake herring

Even if the DNR is successful with its plans for lake trout, brown trout, steelhead and possibly even Chinook salmon, the question remains: What will all those predators eat?

Biologists are hopeful that the answer lies in the lake herring. Lake herring are pelagic planktivores, open-water feeders like alewives, but they're much more adaptable. They can go deep for food or come in closer to shore. They eat plankton, but they'll also eat insects. Because they're a native species, they're less sensitive to climatic extremes than alewives, and they don't tend to die off in large numbers.

The lake herring has been tabbed by biologists as a species that could fill an important niche in Lake Huron, as well as provide a recreational fishery. (Michigan Sea Grant image)

And probably the biggest draw is that they can be easily caught on hook and line from shore, especially when mayflies hatch. “It would be awesome to have lake herring come back in lake huron to help provide for a lot of our predator needs and maybe create some fishing opportunities,” Fielder said. “It’s a win-win situation if we can make it happen.” Lake herring are still found in parts of Lake Huron, especially in the north. But they’re a homing fish, meaning they return to

their place of birth to spawn. And since they're no longer in some key spawning areas, like Saginaw Bay and Thunder Bay near Alpena, it’s not likely they’ll return to those areas naturally.

For the past three years, biologists and hatchery managers have been collecting eggs, rearing lake herring in hatcheries and working out the logistics of restoring populations to their historic spawning grounds.

It turns out that lake herring are pretty easily raised in the same way as Chinook salmon. They thrive in raceways and eat artificial food. The hard part is collecting eggs: lake herring spawn in the last half of November, when winter weather tends to make Lake Huron an unhospitable place.

Fielder said the goal would be to stock a half million lake herring in Saginaw Bay and a quarter million in Thunder Bay, then see what happens before expanding the program further. But so far the lake herring effort appears to fit the philosophy of working with what Lake Huron offers.

“Maybe we’ve just got to get some fish reproducing and utilizing what’s out there and if that’s the lake herring, then that’s a proactive thing we could to try to address and help shape and steer this change into something to work for us,” Fielder said. “We have to work with nature, because you can’t fight it.”

Later this summer Fielder will present a report on the lake herring effort and DNR officials will decide if it’s worth trying.

Newman said if lake herring restoration makes sense on an ecological level, the department will take a long, hard look at the costs of implementing it and decide whether to redirect money to the program.

“If we’re doing smart things and trying to return the lake to some native ecology, with species doing what they were meant to do, we may see some success,” he said.

Next week: What do the changes in Lake Michigan signal?

Part I : Lake Huron's new food web
Part III: Lake Michigan: Another shifting food web