On Monday, the U.S. Coast Guard shut down 24 of its American Loran-C transmitters around the country and afar. For many older commercial fishermen it marked the end of an era.

Fishermen today use the Global Positioning System (GPS), the same satellite system now used in automobiles and hand-held computer devices.

Capt. Gregory Mayhew, 64, of Chilmark grew up with Loran, a radio positioning system that told him where he was when he was fishing far from land. His earliest memories of fishing include going out with his father, Benjamin C. Mayhew Jr., around 1952 and 1953. In those days, Loran wasn’t yet available for most Island fishermen. “We fished with a compass and a lead line,” Mr. Mayhew said.

In that era dead reckoning skills involved lining the boat up with trees, houses, lighthouses and buoys to find favorite fishing spots. But it only worked when the weather was clear and land was in sight.

Offshore navigation involved ingenuity. A lead line was made up of a piece of lead with a hollowed out bottom where grease or butter could be placed. A fisherman dropped the line over the side, read the depth and judging by the kind of sand or pebbles stuck on the bottom of the lead line, a fisherman had a sense of where he was.

Motoring and speed were also tools. The time it took to motor from one spot to another also helped to establish position. Mr. Mayhew said they often would set a temporary buoy and fish around the buoy to keep a sense of place. When a better fishing spot was found, they’d drop another buoy and fish around it. It was tricky, but a seasoned fisherman could get around and find his favorite spots.

Mr. Mayhew stopped using a sextant in the 1960s. Radar came along in the 1970s and helped in fog.

His earliest memory of Loran was going fishing with Capt. Jimmy Morgan of Chilmark in 1961. They fished in a 48-foot dragger called the Mary B. Mr. Mayhew recalled one time when they went out to Veatch Canyon, a fishing spot on the edge of the continental shelf about 100 miles south of the Vineyard. “Jimmy had a surplus World War II Loran. It was a big box in the pilot house,” he said, remembering that its effectiveness was questionable.

They went harpooning for swordfish and dragging for fish. Loran-A had an accuracy of about a half mile at best. Mr. Mayhew said Mr. Morgan was an expert in the buoy system of marking fishing spots. The Loran helped them find their way back to the buoy.

Loran had improved by the time Greg and his brother Jonathan acquired the fishing boat Quitsa Strider in 1976. The 55-foot fishing boat was brought up from Houston. The Loran was housed in a metal box about two feet by one foot by 18 inches, and weighed 30 pounds. It occupied an important place in the pilot house.

When Mr. Mayhew acquired his current vessel, Unicorn, in 1984, Loran-C was available. “It was a much smaller box,” he said. That, together with radar and a compass, made traveling the seas easier, safer and more precise. Mr. Mayhew said they hunted swordfish as far away as Yarmouth, Nova Scotia on trips that would last as long as two weeks. “You wouldn’t go fishing without Loran or radar,” he said.

GPS became available in the 1980s. The first satellite was launched in 1978, and the last of the 24 satellites was put in place in 1994. For navigation at sea it was a small miracle. Just as the driver in a car can pinpoint a location precisely, a fisherman in the pilothouse of his boat can put his net or his hook into a favorite fishing spot.

At its best, Loran-C had an accuracy of one quarter mile, according to the U.S. Coast Guard.

But the permanent retirement of the Loran system this week was little more than a moment for nostalgia; Mr. Mayhew has been using GPS in his pilot house for almost 20 years. “My feeling is that it is bad for fish stocks,” he said, noting that fish have no place to hide. “It also allows anyone with no skill at fishing to go out and catch fish,” Mr. Mayhew said.

He agreed GPS is now the essential tool. “Years ago when you came near a shipwreck you could hang your net on the wreck,” he said. GPS has changed all that. “Wrecks attract fish. Now you can fish right next to the wreck,” Mr. Mayhew said. He knows fishermen who like to fish close to the Andrea Doria, a ship that sank 80 miles south of Nantucket Island in 1956.

There were times when Loran-C didn’t work. Mr. Mayhew recalled a time in the summer of 1973 when he was fishing for swordfish far out at sea, 30 miles south of Nova Scotia, and there was a problem with the engine below deck.

“We drifted about 60 miles,” he said. On the sixth day without the engine, his brother Jonathan showed up, in a swordfish spotter airplane, looking for him.

Using Loran-C, Mr. Mayhew said: “He couldn’t find us.” He said it was nearly impossible to pinpoint the area, because it was a wide expanse of ocean. Fog was coming in. His brother’s plane was running low on fuel.

Luckily there was a long stretch of floating buoys marking offshore lobster pots that they both could see. Jonathan dropped the part his brother needed to fix the engine, attached to a float, within 50 feet of the fishing boat.

With the engine repaired, Mr. Mayhew said they went on to catch seven or eight more swordfish before heading home.

On another occasion, Loran failed to help the captain as he tried to avoid running aground while navigating the entrance to Great Round Shoal near the tip of Nantucket at night. “We saw the characteristics of a buoy, but it turned out to be Pollack Rip buoy. That was very nerve wracking,” the captain said.

There are aspects of the old system that Mr. Mayhew won’t forget. He has memorized a number of inshore and offshore Loran coordinates. Fortunately the GPS receiver in the pilot house can mimic the Loran numbers. On the waterfront, they call it phantom Loran.

There is a Loran line north of Menemsha that Mr. Mayhew fishes: 14215, 43900. It took years of fishing to learn the coordinates in his head, and he is not about to unlearn them. “I don’t want to go through all that. I am an old dog, I don’t need to learn that trick,” he said. Latitude and longitude are more suited for younger fishermen, he said.

The Nantucket Loran-C 400,000-watt transmitter was shut down at 3 p.m. on Monday. The antenna for the transmitter rises 625 feet above ground and is located just south of the Nantucket Golf Club in Siasconset. The antenna will continue to transmit signals useful to Canadaian and Russian mariners, through an international agreement. Nantucket is one of five stations in the country that will continue to operate until the middle of this year, according to Lisa Novac, a Washington, D.C. spokesman for the Coast Guard. Other stations that will continue to transmit are in Alaska, Washington and Maine.

Shutting down Loran-C transmitters is expected to save the government $190 million over the next five years. The decision to turn off the transmitters was made by the president early last year.

In the Mayhew family home in Chilmark, new technology is not always better. Mr. Mayhew said when analog television disappeared last June and was replaced with digital signaling, his television reception took a dip. “My reception is worse,” he said.

But he doesn’t feel that way about GPS. “You’d be at a distinct disadvantage to go fishing without GPS. I wouldn’t fish without it.”