In more than 30 years working on the Chesapeake Bay, Larry Simns has never seen anything like the crab run of 1986. Crabbing's so good it has him worried.

"Right now, if you drained the bay, I bet they'd be two feet thick on the bottom," said Simns, president of the Maryland Waterman's Association. "There's so many, if we weren't catching them, I believe they'd come right out of the water and eat your house.

"Everybody who goes out in a boat is catching crabs, wherever they go. The potters are taking 50 to 100 bushels a day, day after day. It's unbelievable how many crabs there are."

Russel Dize, 25 years a waterman, sees the same thing on Tilghman Island across the bay. "We've had the biggest run this year I can remember. It's been going on since the second week of June, although it's starting to fall off now. Beautiful crabs, a beautiful run. And there's more crabbers than ever."

Even scientists concur. "Crabs have been good, indeed," said Mike Osterling of the Virginia Institute of Marine Science. "With all the problems in the Chesapeake, our blue crab population is proving the most stable of all. This is a tough critter. From our data, it doesn't appear that water quality problems have adversely affected crabs at all."

So what, in the face of an abundance that has been building five years and shows no sign of abating, is Simns worried about?

He's afraid the same thing that happened to rockfish could happen to crabs.

Check the parallels: Fifteen years ago, rockfish were so abundant in the bay that any weekend duffer could catch a cooler full just about anywhere he went, just as a crabber can today. Commercial fishermen netted so many rockfish each fall in the early 1970s that the bottom fell out of the market, just as the crab market now collapses every autumn, when crabs sell for as little as $4 a bushel.

The outlook on rockfish changed quickly when their reproductive success fell off, apparently because of declining water quality up the rivers. Two years ago, rock were so scarce that Maryland shut its season down for four years and Virginia restricted its season sharply, in hopes of saving the species.

Said Simns, "What we need to do is take a lesson from the rockfish and start looking at the crab population now, while it's healthy."

Simns reckons that a crab decline is inevitable, whether because of a natural cycle or some degradation of environment. He figures when it comes, if scientists can't pinpoint a cause based on research done in better times, commercial crabbers will be accused of overharvesting and face strict, probably unnecessary restrictions.

"Virginia, Maryland and the Chesapeake Bay Commission should be approaching the federal government and the state legislatures now for money, to make sure crab reproduction is researched and understood while things are good," said Simns.

Lee Zeni, head of Maryland's Tidewater Division, said Simns "has a hell of a point. You won't get any argument from me." He said he was surprised to discover that crabs weren't on a list of 18 major species for which Maryland resource management plans are being developed, even though they are now the No. 1 commercial species in the bay, having eclipsed oysters.

The problem, of course, is that no one looks for problems. With the bay awash in crabs and so many other species in decline, it's hard to generate enthusiasm for crab research.

But as surely as water runs downhill, said Simns, the bay's troubles will get to its mouth, where crabs spawn.

Bureaucrats wait for disasters to happen before they act, said Simns, but watermen can't. They've already watched shad, rockfish, yellow perch, blowfish, croakers and spots disappear from commercial viability.

Said Simns: "The state of Maryland can't afford to take chances and hope the water in Virginia won't go bad. At the very first hint of trouble, we have to be able to go in there and say, 'Okay, here's the problem.' "

Osterling, the VIMS scientist, said the astounding reproductive capacity of crabs and their short, two-year life span make them almost impervious to overfishing.

"Most people in the scientific community don't think blue crab populations are affected by size of spawning population or by overharvesting," he said. "They're affected primarily by environment: rainfall, wind and currents."

The theory, he said, is that if summer winds and currents carry microscopic crab larvae up the bay where salinity is right (24-26 parts per million), they thrive. If larvae are washed out to sea, they perish. In either case, more eggs are hatched than ever would be needed to replenish the population. Osterling said only 1/10,000th of one percent of crab eggs hatched survive to adulthood.

That means when we catch a six-inch jimmy in the Severn or Patuxent or Potomac, we're catching a miracle.

Which is exactly how it tastes.