Bright side of a fish kill

Theory: State scientists investigating the death of a half-million menhaden have been relieved to find no evidence of Pfiesteria, the deadly microbe. Too little oxygen is considered the likely cause.

July 24, 1999|By Chris Guy | Chris Guy,SUN STAFF

SHELLTOWN -- The stench of thousands and thousands of decaying fish wasn't exactly sweet for Charles Poukish and other state scientists out patrolling a remote tributary of the Pocomoke River yesterday, but they were nonetheless relieved.

After discovering a half-million or more dead menhaden this week -- the largest fish kill in the bay in 10 years -- state officials say they're happy to have found no evidence of Pfiesteria piscicida, the deadly microbe that attacked fish and sickened watermen in 1997, forcing the closure of the Pocomoke and two other state waterways.

This time, scientists believe, the main culprit was too little oxygen in the waters of Bullbegger Creek, a tributary on the Virginia side of the river about a mile southeast of the tiny Somerset County hamlet of Shelltown.

State researchers theorize that the small, oily menhaden, a favorite food for a number of Chesapeake Bay species, were chased to their deaths by a school of hungry bluefish or other predators that "corralled" them in shallow, brackish water.

"We believe that a massive school [of menhaden] swam up the creek and hit critically reduced oxygen levels," said Poukish, who heads a fish kill response team for the Maryland Department of the Environment. "This type of thing I would classify largely as a natural occurrence. Capt. John Smith documented fish kills in the bay in the 1680s."

Runoff from poultry manure, widely used as fertilizer through the Lower Shore, probably helped increase algae in the water, which deplete oxygen. The drought also has given the oxygen-depleting organisms a boost by increasing the water's salinity.

Watermen have reported seeing a number of large algal blooms in recent weeks, officials said.

"You've got reduced oxygen, and then that many fish using up whatever is there," said John Surrick, a spokesman for the state Department of Natural Resources, one of several agencies monitoring the Pocomoke, Big Annemessex, Nanticoke, Wicomico and Chicamacomico rivers and Kings Creek for signs of another Pfiesteria outbreak. "Another factor is that algae produce oxygen during photosynthesis, [and so] oxygen levels drop after dark."

With mounds of 3-inch silver menhaden piling up amid the cord grass yesterday, a team of experts found oxygen at 4 parts per million at the mouth of Bullbegger Creek, but levels of 2.9 per million were found about a mile upstream -- adequate for some creatures such as minnows, but lethal for menhaden, Poukish said.

Tests showed plentiful oxygen, more than 5 parts per million, in the main Pocomoke channel, which has average depths of 10 to 25 feet and troughs as deep as 70 feet.

After estimating that a million menhaden had died Wednesday and floated to the surface in large numbers a day later, Poukish said yesterday he thought the number is closer to 500,000.

None has been found with the bloody lesions that were seen on fish killed in 1997, sores that indicate the presence of Pfiesteria in a form toxic for menhaden and other species.

"You try to use statistical inference as best you can," he said. "It's difficult to get a firm number. There are a certain percentage underwater, a percentage that scattered, a percentage that were eaten by birds. It's a whole lot of fish either way."

As the early morning sun burned away a murky fog shrouding the river yesterday, scientists took water samples.

Bullbegger Creek at its mouth is about 100 yards wide, and quickly narrows as it meanders through a vast stretch of marsh.

Large numbers of gulls took no notice of the smelly, decaying fish floating at the mouth of the creek and accumulating in the surrounding marsh.

"There were so many fish [Thursday] morning that by noon all the sea gulls had consumed so many there wasn't a bird left on the water," said Cpl. Scott Richardson, a natural resources police officer. "They must have just been full."

Hundreds of cork buoys used to mark the location of crab pots bobbed on the river's surface as watermen who normally would work in Tangier Sound sought the more abundant supply of crabs they've found in the Pocomoke this year.

Ward Walker of Crisfield said this week's fish kill looked similar to others he has seen that were caused by oxygen depletion.

"I've seen fish kills before; it was like that up here last year, and it gets that way for crabs, too," Walker said. "I had my hands in the water here two years ago, and I didn't have any trouble."

State fisheries scientists seem to agree.

They are awaiting laboratory tests results to confirm their suspicions.

"From everything we're reading, it's good news [about Pfiesteria]," Poukish said. "We have some circumstances that are similar to what we experienced in 1997 but every year is different. The real good news so far is that we're not seeing lesions on fish."

Pub Date: 7/24/99

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