Rockfish began their annual run down the Chesapeake Bay to deep water last week and anglers above and below the Bay Bridge were catching them in respectable numbers.

One fisherman from Kent Island put 25 in the boat one day, and another from Chesapeake each reportedly picked up 32. Ben Florence, who heads rockfish research for the Maryland Department of Natural Resources, said he had a productive day near Love Point on Wednesday, though he caught mostly small fish.

This is good news to Chesapeake Bay fishermen, who have watched rockfish (striped bass) stocks decline dramatically over the last eight years.

The run came late this year, held up by the mild fall. Many wondered if it was going to come at all, and now that it's here they are wondering if it will be the last rockfish run of all.

To that concern Florence brings some moderately comforting news. The state runs seine net surveys all summer long to check on the production of young rockfish. This year officials believe there was an average reproduction. That "average" is based on reproduction over the last several decades, and marks an increase over the last four years, Florence said.

Florence and his colleagues are being careful not to drive anglers' hopes up unjustifiably. He concedes that reproduction in most of the rivers of the lower Eastern Shore was not good. But the seine net surveys showed increases in rockfish fry in the rivers at the head of the bay, which are the major spawning areas for the fish, and in the Potomac, as well, but expressed concern because the fish in the Potomac were small and unhealthy. "We don't know if they will survive the winter," he said.

The last four years have been disastrous for striper reproduction. State officials have watched commercial catches of the prized table fish drop from 5 million pounds in 1973 to 3 1/2 million in 1974; 2 3/4 million in '75; 2 million in '76; less than 1 1/4 million in '77, and only 900,000 pounds this year.

What's needed to reverse the trend is a dominant year class. That means extraordinarily good reproduction, as there was in 1970, 1966, 1964, 1958 and 1956. The "average" spawn this year won't do it.

No one knows why reproduction has fallen off. There are theories about the effects of tropical storm Agnes, which stripped the upper bay of protective grasses in 1971; about increased use of pesticides and other chemicals along the eastern seaboard; about changes in water quality in the Chesapeake itself. The bay is spawning headquarters for the vast majority of East Coast rockfish, which travel here from hundreds of miles away to deposit their eggs in the spring.

If the modest upswing this year indeed marks the start of a trend, it would be years before its effects were felt among commercial and sport fishermen in the Chesapeake. Young rockfish use the waters of the bay as a nursery, but they don't grow to legal 12-inch size for two or three years.

Dick Houghland, a charter boat skipper and member of the Citizens Advisory Committee for the Use and Management of Striped Bass, says his talks with Florence and others on the panel have led him to the conclusion that this year's upswing is only a token victory.

"Average," he said, "can encompass anything from moderately poor to moderately good reproduction. The news from the upper Bay is good, but before it can have any real effect we need a systemwide improvement."

Natural Resources officials feel the spring ban on fishing in spawning areas imposed for the first time last year may have contributed to the spawning success.

No decision has been made yet on whether that ban will be enforced again next year, DNR officials said.

Meantime, the mature rockfish are on the move. Houghland, who is something of an expert on catching them, said the technique that has been working is deep-trolling bucktails tipped with pork rind over hard bottom. He goes to specific spots, usually 50 to 55 feet in depth, and fishes just off the bottom.

He said fish are being caught from Love Point above the Bay Bridge to Cove Point at the mouth of the Patuxent.

Not many people are chasing them, though. "We had a tremendous time lag this year between when the bluefish left and the rockfish started moving south," he said. "For all practical purposes, everyone's stopped fishing."