Capt. Floyd Gross and the Ruby Ann left the dock at sun-up with a two-man crew and 10 members of the Heatwole clan, four of whom are Mennonite ministers. The party was headed for the Chesapeake Bay in search of bluefish. From an unofficial logbook:

Seven a.m.: No bites or signs of bluefish.

Eight: situation unchanged.

Nine: "This is the fun part, riding around in circles all day," Roy Heatwole exclaims unpersuasively.

Ten: Heatwoles lie about listlessly nibbling pretzels.

Eleven: Gross squints out at the water with a pained look on his face.

11:20 a.m.: Deliverance. Hearing a steel line go zzzzzz from a reel, Kyle Heatwole, 7, cries, "Fish! Fish!" Heatwoles scramble aft. DeWitt, the oldest, hefts the rod, cranks and puffs and finally yanks a bluefish from the Chesapeake to a chorus of cheers. These days on the bay that seems something of a miracle.

Charter boat captains in Maryland and Virginia are experiencing their worst season since bluefish emerged more than a decade ago as the top sport fish on the Eastern Seaboard. Though the catches have picked up recently, the daily net in Maryland in July plunged from about 50 fish a trip last year to as low as zero, and the captains think they know who's to blame.

As Mike Sullivan, who moved his boat Miss Dolly from Chesapeake Beach to Solomon's Island to get closer to the bluefish, puts it: "For three weeks we had normal-to-good fishing. Then those gillnet boats moved in and it was Tubesville. Eighty to 90 percent of the Maryland charter industry has been shut down. It's an economic disaster."

The Chesapeake bluefish imbroglio began in mid-May when four ocean-going gillnet boats from Florida moved into the mouth of the bay and began raking up tons of bluefish. It was settled for the time being this week with the intervention of Virginia Gov. Charles S. Robb and the Virginia Marine Resources Commission, which banned the practice of encircling bluefish with long gillnets--wide-meshed nets that entangle the gills of the blues in the mesh by the hundreds.

That technique had enabled the boats War Eagle IV, Captain's Lady, Foxy Michele and Eddie Boy to net more than 760,000 pounds of bluefish (35 percent of the commercial catch in Virginia as of June), which was then shipped to Egypt, Nigeria and Venezula. The emergency order "puts them out of business," said VMRC biologist Paul Anninos.

But the dispute is far from over. Fish biologists generally believe the arrival of the Florida gillnetters and the crash in the charter boat catch is "a coincidence," said Anninos. As measured by Virginia's commerical harvest, the number of bluefish in Chesapeake Bay has been declining for the last six years.

In Virginia, sport and commerical fisherman roughly divide the bluefish harvest between them. But in Maryland the prized blues are sought mostly by sport fisherman, who in 1979 landed 90 percent of the state's bluefish catch. Charter boat captains and state officials from Gov. Harry Hughes on down are worried that new techniques and an upsurge in commerical effort will upset the traditional balance between the sport and commercial harvest and jeopardize the state's $132 million sport fishing industry.

For the past decade bluefish have been so plentiful in Chesapeake Bay that they became part of the vernacular of exasperation. "Are there bluefish in the bay?" was the local version of "isn't it obvious?" But the Chesapeake's claim to the voracious sharp-toothed blues, which will eat anything in their path, including each other, is tenuous.

Every year, miles-wide schools of bluefish migrate up the Eastern Seaboard from Florida to Nova Scotia. A fraction of them take a left turn at Cape Henry and follow schools of menhaden and other favored foods into the Chesapeake. There they feed but do not spawn, prefering the open ocean.

While scientists believe the number of Atlantic bluefish has never been higher, the records of Chesapeake commercial fishermen show that locally the number of blues has been dropping since 1976, when the commerical catch was 4.2 million pounds. Last year, 2.4 million pounds were landed.

"Things shift for any number of reasons, we don't know why," said Stuart Wilk, a bluefish expert with the National Marine Fisheries Service in Sandy Hook, N. J. "Right now from Cape May to Block Island, the bluefish fishing is the best it's ever been. I have a friend who got 15 this morning and he really didn't try."

There are a number of factors that could contribute to the scarcity of bluefish in the Chesapeake. Bluefish like salt and the rains of a wet spring alter the bay's salinity to their dislike. The fish also are especially sensitive to changes in water temperature and food supply.

"The bluefish population is declining in the bay, but I can't say why it's happening. I don't even have a guess," said Anninos. "Nothing we can do to manage these stocks compares with what God does every year."

That leaves Maryland's nearly 400 charter boat captains with a bad case of the no-blues blues. "I personally have turned down 20 parties in July," said Harry Tayloe, secretary and treasurer of the Maryland Charter Boat Association. "Multiply that by $200 and it gives you some idea of the loss."

Meanwhile, marine radio bands on the Chesapeake Bay have been crackling with angry words. One exchange came over the radio on channel 88A aboard the Ruby Ann, which returned last week with the Heatwoles and, after eight hours of fishing, five bluefish:

"Hell, we let those Florida guys come up and fish, we might as well pull the plug and drain the bay."

"Plant it in corn."

"That's right, plant it in corn."