Virus That Was Feared In 1990s Still Around, But Not Impacting Lakes

Published on Saturday, 6 July 2013 23:52 - Written by By STEVE WRIGHT

Throughout July 1999 bass — big bass — were found dead on Lake Fork.

Texas Parks and Wildlife Department biologists found 5,000, but they didn’t count every cove every day. The count was sure to have been higher, but how much no one knows.

Biologists looked at the common culprits, low oxygen, water quality, etc., but nothing matched. The die-off was similar to one the year before at Sam Rayburn Reservoir though that one had yet to be explained either.

Texas biologists began to compare notes with biologists nationwide and came across

Largemouth Bass Virus, a disease first noted in Florida in the 1980s, but not associated with a fish kill until 1995 at Santee-Cooper Reservoir in South Carolina.

Lake Fork fishermen believed the virus had an impact on the fishery disproportionate to the number of dead fish discovered. The concern really hit in 2001 when the lake produced just one ShareLunker entry. That argument went away in subsequent years when the lake went back to producing six and seven fish for the program annually.

“It seemed, from my recollection, that we didn’t detect a difference (in surveys),” said TPWD fisheries Kevin Storey. “It wasn’t a prolonged effect, but there were some who were convinced it had a much more severe impact on the population than our surveys showed.”

The Fork die-off, and the one on Sam Rayburn Reservoir a year earlier, led to a statewide search for the disease as biologists hoped to at least anticipate where the next outbreak might come even if there was nothing that could done to prevent it. The virus was found on 26 lakes, but die-offs happened on only three other reservoirs and those were considered minor. It was also found in some of the state’s fish hatcheries, which resulted in a change of where fish were delivered. Hatcheries with the virus did not take bass to lakes where it had not been found.

Basically what biologists found was that there was no rhyme or reason about the disease. There was nothing to connect the dots between where it had been and where it was to be found, or why it suddenly appeared at all.

“We know bass virus can be transmitted from water to fish and from fish to fish. There are a number of ways it could be spread,” said Dave Terre, TPWD Inland Fisheries’ management and research chief.

The disease has been found primarily from Central Texas and Oklahoma to the East Coast, but also as far north as Michigan and Wisconsin. It was also detected in Vermont, but that is the only case in the Northeast. Terre said in recent years the disease has been detected on Texas’ Lake Amistad and it has been found on several lakes in Arizona, but no other western reservoirs yet.

Terre, who was regional director in Tyler when the outbreak on Fork occurred, said all of the states with the disease worked together during the late 1990s and early 2000 when the disease was most active.

“We had a series of seminars annually. It was a great collaborative process where we discussed how does it spread, how does it impact fish populations, how does it impact anglers and how to keep from there being an overreaction,” Terre said.

What the biologists determined is that it affects both native and Florida largemouth bass, it was seldom prolonged and once an episode is over the number of fish with the virus quickly declined.

Although the majority of the dead fish found after an outbreak were bigger bass, Terre said it is possible that smaller fish were also impacted, but may have been eaten by other fish as they floundered on the surface.

“One theory is that it has been here forever. Our theory is that when it hit a system not all the fish were hit. It is not a complete die-off. Some had immunity,” Terre said.

Biologists attempted to tie outbreaks to environmental factors, but there wasn’t anything among all the states. Terre said biologists in Texas suspect drought conditions at the time might have played some role here.

The disease can still be found in bass in Texas lakes, but there hasn’t been an outbreak in years.

“It changed the way we do business. Anytime we have bass die we run a sample,” Terre said.

