CONOWINGO -- Hidden inside the massive Conowingo Dam, in a location as secret as any good fishing hole, officers from the Maryland Natural Resources Police scan a catwalk decorated with weekend fishermen.
Using binoculars and high-powered scopes, the search is on for poachers who aspire to hook a striped bass -- rockfish -- in the gushing, nutrient-rich waters of the Susquehanna River below.
Earlier this month, "Operation Fish Hook" started at the dam -- a police effort to halt rockfish poachers who catch the fish with illegal bait and often sell them for up to $6 a pound. The operation will soon expand to other problem areas in the state.
So far, 102 citations have been given out by the officers, 20 of them for illegal possession of the striped bass. Those caught face a hearing in Harford County District Court that could result in a fine of up to $1,000 per fish.
The officers, who gave out 40 citations over the weekend, operated undercover. Wearing jeans, T-shirts and baseball caps, they could hardly be distinguished from the anglers.
Some combed the catwalk with a rod and reel, hoping to meld with the crowd and snoop on the day's catch. A look inside their knapsacks revealed not a sandwich and tackle but walkie-talkies, a citation book and police badge.
"It physically requires several people to watch," said Cpl. George Ball. "They will hide them [illegally caught rockfish] in coolers, trash bags, take them to their cars in their jackets and put them in the trunk under a spare tire."
The population of striped bass -- once known as the "King of the Chesapeake Bay" -- is increasing as a result of a 1985 moratorium on striped bass fishing, which was partially lifted in 1991 to allow a monthlong, restricted fishing season.
But natural resources police Col. Franklin I. Wood ordered the covert protection of the fish. It includes the seizure of the poacher's personal property and even his or her car if the violation is extreme.
"We will use every means at our disposal to apprehend violators who ignore these regulations," Colonel Wood said.
Mostly, however, the operation has turned up 21 people fishing without a license and caught 47 using restricted bait such as shrimp, spinners and bloodworms.
The restrictions are posted on a huge orange sign at the entrance to the catwalk.
On Saturday night, a routine fishing license check resulted in the arrests of two men wanted in Maine for burglary, perhaps the most famous arrest in "Operation Fish Hook."
The men -- each of whom identified himself as Steven Mitchell -- were being held in the Harford County Detention Center yesterday awaiting extradition.
Their car, a Chevrolet Suburban, was seized pending further investigation, said Sgt. Charlie Rhodes, who heads "Operation Fish Hook."
Officers patrolling the catwalk wanted the anglers to be aware of the anti-poaching effort, which in some cases has discouraged people from fishing at the dam at all.
Only about 50 anglers were on the catwalk yesterday morning and early afternoon, times when there usually are about 500, said David Snider, a private security officer who patrols the Conowingo Park.
Rob Yurth, 18, who runs the snack bar at the park, complained that business has been slow recently.
"More people are coming up here, looking around and going home," Mr. Snider said. "Most of them are here to catch the rockfish. But some like to still try. They like to see if they don't get caught."
Most fishermen deny they have violated the law if confronted by the officers, even though some were caught red-handed.
"When you tell them what time they got there, what time they left, what time they went to the bathroom, they think you know more about them than they know about themselves," Corporal Ball said.
Police said that sources tell them that some poachers take up to 40 rockfish each, but Sergeant Rhodes said the most he has found in a crackdown is five bootlegged fish in a fisherman's possession.
When the undercover officers spot a fisherman catching a striped bass -- and not throwing it back into the river, as required by law -- they move in immediately, Sergeant Rhodes said.
"We are cutting very few breaks here," Sergeant Rhodes said. "We want people to know that the person fishing next to you could be the man. You could violate the law if you want to, but . . . "
No one was more aware of that yesterday than Craig Young, a 28-year-old carpenter from Elkridge in Howard County.
Mr. Young was heading toward the snack bar for a hot dog when he was stopped by the undercover officers and given a $35 citation for using illegal bait. In five hours of fishing from the catwalk, he had caught only one catfish, but his illegal bait of clams, peeler crabs and crawfish had attracted 18 rockfish to his line, which he caught and threw back into the river.
"I didn't know I was doing anything wrong," Mr. Young said. "The bait house at the end of the road sold me the bait; they didn't say anything about it being illegal. It was misrepresentation."