State fisheries biologists are trying to learn what killed hundreds of bass on the Potomac River, just days after two fishing tournaments.
The fish were discovered and reported Monday by a fishing guide, a longtime opponent of the large number of tournaments held each year on the river near Smallwood State Park in Charles County.
Don Cosden, chief of Inland Fisheries for the Department of Natural Resources, said biologists on the water Tuesday estimated there were 600 dead bass along with several hundred catfish and other species over a six-mile stretch of the river.
"It's not unusual to see a number of dead catfish and gizzard shad this time of year, and all of the bass were legal size, so we believe that this was related to tournament releases," Cosden said. "There were more than 3,200 fish weighed in over the three-day period, so this would be about an 18.5 percent total mortality, which is unacceptably high."
Cosden said his staff is in contact with officials of the tournaments to get details. State biologists were at the smaller of the two events Saturday - the one-day National Guard FLW College Fishing tournament, which involved 80 anglers - to measure and tag about 100 fish for a mortality study. All those fish appeared healthy as the scientists handled them.
The larger event, the three-day FLW Stren Series, attracted 158 anglers, but only the top 10 fished the final day.
Guide Ken Penrod, who reported the problem and wants a complete investigation, said he has no issue with well-run events but is angry that "most of these 100- to 200-boat events are from out of state and they abuse our fishery - and our rights."
Cosden said most of the data on fish kills involve immediate mortality, not deaths two to three days after being released.
Some studies have linked poor water quality to a high degree of delayed mortality after tournaments. But water samples taken continuously at the docks by the Tidewater Ecosystem Assessment group indicate temperature and dissolved oxygen levels to be within acceptable ranges.
The state has sent tissue samples to a laboratory to be tested for largemouth bass virus. A recent study suggested that bass heavily infected with this virus might suffer higher release mortalities after being confined in livewells, the aerated holding tanks on bass fishing boats.
"Right now," Cosden said, "we don't have an answer."