In late July 1884, a bottlenose dolphin popped above the waves of the Potomac River near Washington. It was a bad move, on the dolphin's part.

For two days, according to reports at the time, boats pursued the creature, as men repeatedly tried to shoot it. For all their effort, they failed to capture the dolphin, and it appears to have escaped.

That historical record, though, is testimony to just how far dolphins will swim up the Bay and its tributaries. In fact, there are reports of dolphins as far up the Chesapeake as Havre de Grace, at the mouth of the Susquehanna River.

While dolphins are not often thought of as a Bay species, they are no strangers to the Chesapeake. They are routinely spotted near the mouth of the Bay and in portions of the tributaries.

"We know they're a major fish predator, and that's probably what brings them into the Bay and the rivers," said Susan Barco, a research associate with the Virginia Marine Science Museum, who has studied bottlenose dolphins for years.

But no one knows the number of dolphins that frequent the Bay or the extent of their range. That information is important because bottlenose dolphins have been considered a "depleted" species by the National Marine Fisheries Service since a mysterious disease wiped out half the Atlantic coastal stock in 1987-88 - a period during which hundreds of the marine mammals were found dead along the beaches.

Today, the number of bottlenose dolphins along the coast is thought to be less than 12,000, Barco said, and could be as low as 2,000. The number in the Bay is even more uncertain.

To help fill that information void, efforts to monitor bottlenose dolphins are under way in Virginia and Maryland, relying heavily on volunteers. Scientists would like to learn more about why some dolphins seem to prefer the Bay to the ocean, while managers would like to know if further actions are needed to protect the animal in the Chesapeake.

"Before we can manage a species, you've got to know where they are," Barco said. "You've got to know their activity and their high concentration areas. We know that for ducks, we know that for fish, we know that for a lot of other species. But we have no idea about the Atlantic bottlenose dolphin."

Using a grant from the National Oceanic and Atmospheric Administration's Coastal Zone Management Program, Barco is training volunteer water quality monitors from the Alliance for the Chesapeake Bay and others that are frequently on the water to identify and report bottlenose dolphins sightings.

This information will be recorded on maps and made available to interested organizations and agencies.

The National Aquarium at Baltimore is gathering information about the numbers and distribution of dolphins, said David Schofield, the aquarium's senior mammalogist. Every two weeks, volunteers accompany Natural Resources Police on patrol boats to look for dolphins, the U.S. Coast Guard conducts surveys with researchers on board and the Environmental Air Force - a volunteer group that donates the use of their airplanes for environmental purposes - conducts surveys from the air once a month.

"There's been a growing interest in assessing what's going on in the Bay," Schofield said.

Over time, this information could provide the basis for more research, and management, in the Bay. For example, if particular areas appear to be widely used by dolphins, actions may be taken to protect those sites. If certain fishing techniques or other human activities pose a threat, they could be modified.

Researchers say dolphins may serve as an indicator of environmental conditions in the Bay and along the coast. Being top predators, dolphins concentrate toxics from fish they eat in their own flesh "very much like an eagle or an osprey," Barco said. The highest PCB level reported in a dolphin occurred off Virginia Beach.

"So while we see dolphins out there, we really don't know how healthy they are," Barco said. Contaminants in the dolphins may have made them more susceptible to the disease that wiped out such a large part of the population in 1987-88, she said.

Besides disease, other threats facing the dolphins include pollution, being caught as the by-catch of fisheries targeting other species, and ship and boat traffic which can strike animals or disrupt courtship, nursing or calving activities. "Probably one of the most common calls that we get in the summer is people approaching dolphins too closely, or jet skiers corralling them up into areas," Schofield said.

Bottlenose dolphins - the dolphins most often seen in captivity - can live 25 to 35 years. Males reach maturity in 10 to 12 years, and females in 5 to 12. Adults can reach lengths of 12 feet. They typically swim in groups known as pods. In and near the Bay, pods usually have 10 or fewer individuals; farther offshore, pods can be much larger.

All dolphins found in the Bay would belong to a coastal stock that migrates north in the spring and south in the fall. All dolphins from Virginia north are migratory; though some dolphins found along southern states remain in those areas year-round.

Besides the surveys, the only major source of information about Bay dolphins in the Chesapeake comes from the handful of reports each year to the marine mammal stranding programs in Maryland and Virginia, which rescue beached animals and research those that are recovered dead. Though strandings provide only limited information about dolphin populations, they do give scientists a chance to learn about their health.

Dead animals are examined for clues as to the cause of death and, if it was related to fishing activity, what kind of fishing activity contributed to the death.

"When we look at the animals, through the line marks on the body and the flippers, we can estimate a mesh size, and all this information contributes to the understanding of how fisheries is playing into mortality," said Joyce Evans, a Maryland Department of Natural Resources' aquatic pathologist at the Oxford Cooperative Laboratory.

Dolphins have not been the target of a directed fishery since the early part of this century; from 1797 to 1929, a sporadic fishery off North Carolina targeted dolphins for hides and oil.