It's muster-up time on the Chesapeake Bay. Large schools of bluefish, sea trout, croakers and summer flounder are gathering for the swim south.

In a month they'll be gone, following their food and their instincts to the deep waters off the Atlantic coast. The chilly bay will be left to it's year-round residents, oysters and clams, silver perch and the few remaining juvenile rockfish.

"Yep," said Charlie Nicholson, "this is the time to catch 'em. Come first frost and they'll be gone.

At Scheible's Fishing Center, Nicholson's home base, Bruce Scheible was moaning, "Why do people stop fishing on Labor Day? We've got so many fish we don't know what to do with them.

Fishing camp operators always look on the brightest side, but this time Scheible wasn't kidding. That day Nicholson had returned to the dock with a party of six and an unbelievable haul of 290 blues.

"I don't usually believe in taking that many," the captain said. "I think you ought to stop after you've had your share, and I usually tell my clients that. But today I said, "Why not?" I wanted to go after the record, if there is one. I don't guess there's many boats that have landed that many blues in a day."

All this boded well for our party of six. We were traveling with Nicholson the following day, and it didn't look as if anything would change, as long as the weather stayed with us.

A northeaster was due. Trouble? "Not really." said Nicholson as he hosed down his bay-built workboat, Antonia. "This time of year I only worry about northwesters. They can blow for days. A northeaster usually dies down and doesn't seem to bother the blues. They'll bite in anything."

Next morning we barreled into the teeth of 20-knot winds, heading east from Point Lookout to the middle grounds, 10 miles away. As we burbled along. Nicholson told tales of his days as a bus driver, and the terrible tension that would arrest his sleep after a victory Washington-New York run.

He was at ease at this helm, in a boat he knew and with people he enjoyed squiring.

The dept-finder registered 25 feet as we passed a ledge near the shipping lane. Nicholson backed off the throttle, dropped the hook and we baited up.

The captain manned the chum grinder, mashing whole alewives into gruel and dishing it over the side. An oil slick spread with the tide, and we cast into it.

In five minutes I had the first strike. The three-pound blue snatched a chunk of cut bait and skittered off. Line spun from my six-pound outfit, which I was using to fulfil requirements of a light-tackle bet shared with one of my colleagues. The fish was in the boat in three minutes.

From that point on the action seemed nonstop. Hardly a moment passed that someone wasn't hooking, fighting, losing or landing a fish.

The big success was coming from an unlikely source, Robann Spargo, a disminutive secretary who had insisted on the ride out that she knew next to nothing about fishing.

It wasn't showing, and we five men were getting a bit frustrated. Everytime we looked over, she was battling a fish.

Spargo stopped by my spot at one point and I expressed my admiration and asked her how? "I don't think you 're letting out enough line," she said.

Humbug, I thought, and watched her land a dozen more while I fumed.

So I let some more line out. Bang Fish.

I didn't have any trouble the rest of the day, and my six-pound outfit got easier to use after I switched to nine-foot surf rod, which provided the backbone to set the hook.

I asked Spargo on the way back how she'd worked out her technique.

"Well," she said, "usually I ask Capt. Nicholson what to do and then I do whatever he tells me."

"Today he didn't have time, so I just did what came to mind.

By 1 o'clock both the huge Igloo coolers were full (150 in full) and we were still hauling them in as fast as we could set the hooks. Nicholson called a powwow.

"We haven't got any more room," he said. "What do you want to do?"

Faced with the best fishing any of us had had all year, we elected to press on, we could return all undamaged fish after they'd been caught. At 3 the bait ran out.

I grabbed the last piece and plunked it on the hook. In 10 seconds I hooked the last blue of the day probably the year. Nicholson who was swabbing the decks, stopped for a second and watched.

He smiled. "It never stops feeling good, does it?" he asked.

It doesn't.