While salmon fishing has declined sharply in the open basin of Lake Huron, anglers in Saginaw Bay have seen walleye numbers rise dramatically. So why would fishing go one way in the big bay off Lake Huron and the other way in the main basin?

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The answer to both questions seems to be the same -- the disappearance of alewives that once fed the salmon but preyed on baby walleyes.

"The alewives used to come into Saginaw Bay to spawn in huge numbers just when the perch and walleye fry were hatching," said Dave Fielder, a state Department of Natural Resources fisheries biologist who monitors Saginaw Bay. "The perch and walleye fry were just the right size prey for alewives."

Perch and walleye fry compete with zebra mussels and other organisms at the bottom of the food chain, but the competition doesn't seem responsible for the increase in walleyes. Zebra mussel numbers in the bay haven't changed recently.

"Alewives are the single thread that connects the main basin with what's happening in Saginaw Bay," Fielder said.

There is still debate about why alewife numbers have collapsed in Lake Huron, down 90-99% in most areas. Fisheries biologists originally thought that higher natural reproduction of salmon in Lake Huron had reached the point that salmon overwhelmed their food supply.

But new information from bottom trawls suggests that zebra and quagga mussels have filtered so much food from the bottom of the food chain in the main basin that there is little left for baby alewives or the tiny organisms that small alewives eat. The result is what biologists call a bottom-up collapse.

Biologists and anglers say they caught lake trout and brown trout in Saginaw Bay last year, fish normally found only in the open lake. The fish apparently were drawn into the bay in search of food.

Even though Saginaw Bay connects to Lake Huron, it's almost a separate entity. It resembles a smaller Lake Erie, with shallow waters that warm faster and rivers that bring in huge amounts of nutrients. The bay is about 50 miles long by 20 wide, and most of it is less than 30 feet deep. It has a maximum depth of 100 feet at its northeast opening, compared to 300-750 for most of Lake Huron.

The resurgence of natural walleye reproduction -- with excellent spring spawning success in 2003 followed by good years in 2004 and '05 -- has led the DNR to shift its stocking efforts from the bay. Those fish now are going into nearby inland lakes.

That decision has split the Saginaw Bay walleye angling fraternity. Some agree with the move, but others are demanding that the DNR continue stocking until the anglers have proof that natural reproduction will provide them with good fishing.

Dennis Delmage is president of the Saginaw Bay Walleye Club, which provides most of the money for rearing walleyes in the watershed. He likes the idea of giving natural reproduction a chance and stocking inland lakes, but with some reservations.

"It doesn't make much sense to put a bunch of (walleye) fry in there if they are just going to become bait," he said. "They are seeing cannibalism by walleyes in the bay for the first time, and we know that the fry are also eaten by pike and bass and other predators."

Mark Romanack, a professional angler from Tustin, near Cadillac, has written several books on walleye fishing. He thinks Saginaw Bay might be developing a self-sustaining walleye population, but "the conservative approach I like is, let's back off on the stocking, but let's not stop it entirely. The DNR is hurting for funds, and I think it sees this as a way to stock walleyes in inland lakes at no increase in cost.

"I'd like to see reduced stocking in Saginaw Bay until we have enough good year-classes to maintain fishing at a high level. I'm afraid that if we lose stocking, we'll never get it back, and we'll see natural reproduction providing a boom-and-bust cycle."

Fielder said the DNR would watch for further changes in the bay.

"The one we can't figure out is the perch fishery," he said. "It's getting better, but there's something strange happening with perch. We're getting tremendous reproduction, then we see an almost total loss of the fry over the winter. It's probably predation and competition for food. They just don't get enough to eat to survive the cold weather."

Despite progress that seems to be two steps forward and one back, Fielder is convinced Saginaw Bay is on the verge of a renaissance "that will bring us the best walleye fishing since the 1940s. It's hard to believe, but when I started working on Saginaw Bay problems in 1990, I never thought we'd see that happen in my lifetime. Now we're right on the doorstep."