Biologists fish for answers

Harvest: In a five-year project, the Maryland Department of Natural Resources is studying the decline of perch in state rivers and working to replenish the species.

March 20, 2003|By Laura Loh | Laura Loh,SUN STAFF

Leaning over the edge of a motorboat on the Severn River yesterday, the four fisheries biologists grappled with the weight of their catch -- hundreds of shining perch squirming in a large, black net.

Then, instead of rejoicing in the harvest, the men knelt silently by the flopping fish and began releasing them, dropping some over the boat's edge and throwing others over their shoulders into the water.

The final count for the harvest: 64 yellow perch, 360 white perch and a smattering of catfish and pumpkinseed sunfish.

The large proportion of "spent" female yellow perch -- those that have recently laid their eggs -- indicated that spawning season is well under way for the depleted species, which migrates upstream every spring to lay eggs in warmer, fresher waters.

The group of biologists working on this chilly, windblown day are part of a five-year project by the Maryland Department of Natural Resources. Its purpose is twofold: to look for reasons for the yellow perch's decline in the Severn and South rivers, which flow into the Chesapeake Bay, and to try to replenish them with millions of eggs and baby fish.

The project also is surveying development in the 40,000-acre Severn River watershed to assess its impact on water quality.

Yesterday's mission -- postponed for weeks because the rivers have been iced over -- was to gather data on adult perch during the weeks-long window of opportunity created by the concentrations of fish during spawning season.

"The long-term goal is to identify ... why we don't have a lot of perch here or a lot of reproduction," said DNR spokesman John Surrick, who accompanied the team of biologists.

Through mid-April, three times a week, the researchers will check the contents of fishing nets set up in the river. Armed with data on the length, sex and age of these adult fish, they will try to paint a picture of the health and size of the yellow perch population.

The state banned yellow perch fishing in the Severn and South rivers in 1989, but the numbers of fish did not rebound as expected. Biologists believe depleted oxygen levels in the perch's spawning waters, possibly caused by runoff, may be contributing to the low numbers. In the spring and summer, Surrick said, "it gets down to levels where it kills fish."

Researchers also are looking at a variety of other possible factors, including how scientific tagging and the commercial catch-and-release practice -- for fish that must be released because of size -- affect the mortality of the fish.

At a dock off the Severn River in central Anne Arundel County, biologist Rudy Lukacovic monitors the survival rate of fish held in two large tanks. One contains fish captured in large tube-shaped fyke nets, like those used in commercial fishing. The other holds perch that have been punctured near the dorsal fin with numbered plastic tags.

Recreational fishermen, who are allowed to catch yellow perch in some areas, return the tags for a reward -- a cap emblazoned with the words "yellow perch" -- and provide researchers valuable information about where the perch are feeding.

"You hope that what you're doing doesn't hurt the fish," Lukacovic said of the scientific and commercial handling. He peered into the tanks and liked what he saw. "I have not seen a dead fish yet," he said.

Lukacovic emptied one of the tanks, measuring the length of each fish and noting the sex. Nearby, biologist Bob Sadzinski jotted down the data in a notebook for his survey of adult perch.

"Two-hundred-eighty-nine [millimeters], spent female ... 248, male ... 311, female ... 296, female, spent," Lukacovic called out, as he examined and chucked each fish back into the river.

Leaving his colleagues to continue their painstaking data collection, Steve Minkkinen, director of the hatcheries where millions of baby perch are being raised to restock the rivers, slipped away from the group after getting what he came for -- several fertile female fish and a few males.

Last spring, Minkkinen and his staff released 1.2 million hatchery-reared larval and fingerling yellow perch into the rivers. They plan to release at least a million more in the next couple of months.

Besides increasing the rivers' stock, the young fish -- bearing distinctive chemical markings on their eardrums -- will help researchers estimate the total number of yellow perch when recaptured in random samplings.

"That will tell you how effective your restocking effort is, and when you can stop," said Steve Early, a biologist overseeing the hatchery effort.

Baltimore Sun Articles
|
|
|
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.