The Chesapeake Bay looks much the same, day in and day out, but big things occur under the surface as the seasons change, things we can never fully understand. The mystery keeps us returning.

The bay stretched south to an indistinct horizon when we set out from Point Lookout at dawn last week in a slick calm. We were bound for Virginia waters to try to intercept the huge rockfish that swarm in from the sea each winter and linger in deep holes till spring, then head up the rivers to spawn.

Capt. Joe Scrivener on the Poor Boy, one of the top charter boats on the lower bay, had his doubts about our chances of intercepting them. "The last few days, they've been hard to find," he said. "Most of the bigger fish seem to still be up north in Maryland waters, but Maryland rockfish season is closed. We'll catch some keepers today across the [state] line, but I don't know how big they'll be."

He struck a course for Smith Point Lighthouse on the Virginia side of the Potomac's mouth and raised binoculars to scan for birds diving on bait. The bigger the birds, the bigger the fish, he said. The best sign would be gannets. They are huge white seabirds with droopy beaks and black wingtips that fly in from the ocean, following from above the same schools of fleeing bait on which big rock prey from beneath.

We saw a few gannets and a lot of gulls, but nothing wheeling and diving with the abandon that signifies a school of fish underneath in a feeding frenzy. The radio crackled with reports from fellow anglers in the vicinity. Nobody was doing a thing.

The bottom drops off sharply just outside Smith Point Light, and the deep hole there is a traditional gathering point for wintering rock. We were setting out 10 lines to troll when word came by radio of a bonanza to the south.

"We had five on the first pass," said an unidentified charter skipper, fishing off the mouth of the Rappahannock River at Windmill Point, 12 miles down the bay. You could almost see the gears spinning in Scrivener's head as he calculated time, distance, tide, the height of the sun and all the other variables that govern a bite. Could we get there in time?

"Take 'em up," he said decisively, and we rushed to reel in lines just set out. He jammed the throttle forward and we were off on another long run across shimmering, smooth water.

Two miles from the destination, Scrivener could make out on his radar screen clouds of birds diving over bait. The depth when we arrived was 50 feet, a fleet of boats was already circling and, as we neared, the skipper saw splotches on the depth-finder signifying rockfish suspended below. We could see rods on the other boats bent nearly double as anglers strained to fight fish.

We'd traveled four hours to reach this amazing place--two by car and two by boat--and it was worth every minute. We scrambled to get the lines overboard, each one trolling an umbrella rig with multiple wriggling soft plastic lures at depths from 20 to 40 feet. Rod bristled from every corner, and soon half the lines were tangled in a colossal mess--for all the right reasons.

Bang! Down went a rod on the starboard transom. Bang! Down went another. We looked at each other and lunged for the nearest one.

George Turner from Annapolis is an old hand at this sort of thing. He waited long enough to judge which rod looked to be loaded the heaviest and went for it. When I had fought my fish to the boat--a plump 34-incher that weighed close to 20 pounds and was covered with wiggling sea lice--Turner was still patiently pumping and reeling, a contented smile on his face.

We had the wreckage cleared by the time Turner's fish came to the net. It emerged from the depths like some primitive sea monster, silver-white, with a mouth the size of a three-pound coffee can and a massive striped body. Down went the net, up came the fish, two men straining to lever it aboard. It hit the cockpit sole with a shuddering thud.

The impulse is to whoop and holler and exchange high-fives when a 43-inch fish hits the deck that way--the biggest Turner has caught in a lifetime of rockfishing. It's better to take a moment to absorb the import of the occasion, and maybe there was a 30-second delay before the whoops began. I'd like to think so, but who can remember at a time like that?

The cameras came out and the back-thumping began. It wouldn't end soon. The last time Turner caught a really big rockfish, he kept it on ice in a cooler in the back of his car for three days, transporting it around to show it to anyone who'd look. He even took it to the Navy-Maryland lacrosse game, parked next to a spectator entrance and dragged fans out at halftime for a glimpse.

The good news is that creel limits kept us from making pigs of ourselves. Each of us took home two fish, our legal allowance. Several of those will grace the table at Christmas, a growing tradition in our house and others now that the big rock are back in the bay as a result of rigorous conservation efforts over the past decade.

By the end of the month, rockfish season will be over baywide. Big rock can enjoy the remainder of the bitter months undisturbed in their deep lairs, waiting for the days to lengthen and the water to warm. Those are their signals to begin the voyage upriver in the cycle that brought them here, and will bring their offspring and their offspring's offspring back a decade from now, a century from now, and, one hopes, a millennium from now.

To touch that process with your own two hands on a calm winter's day is a blessing and a joy not soon forgotten.

Rockfish season runs through the end of the month in Virginia. A number of Maryland charter skippers run trips across the state line to participate. Among them are Joe Scrivener, 301-994-0398; Eddie Davis, 301-872-5871; Jim Gray, 301-872-4022; Gregg and Steve Madjeski, 301-872-4215; Bruce Scheible, 301-872-5185; and Butch Cornelius, 301-993-0347. On the Virginia side: David Rowe, 804-529-6725.