|
||||
|
|
EXPERTS SHARE GOOD NEWS OKLAHOMA CITY , Okla. - The good news far outweighed the bad at this year's Largemouth Bass Virus (LMBV) Workshop, sponsored by BASS. "LMBV prevalence has declined and maybe LMBV is gone or going away," said Mike Maceina, a fisheries professor from Auburn University. In speaking at the fifth annual gathering, Maceina was referring specifically to findings from fieldwork conducted at Alabama reservoirs. But his words accurately reflected the generally optimistic tone of the Feb. 27 meeting, which was attended by resource managers and scientists from across the country. State biologists reported only two minor kills linked to LMBV during 2003, at Lake Wes Watkins in Oklahoma and Lake Paho in Missouri. Fieldwork, meanwhile, revealed that fisheries once damaged by kills continue to rebound, and research confirmed that warm water and crowding contribute to the prevalence and transmission of the virus. "Altogether, we've had five kills and 23 of 55 lakes tested positive," said Dave Terre, regional director for Texas Parks and Wildlife. "But we've had no kills recently, and Fork and Rayburn have rebounded tremendously." In Alabama, Maceina's team worked with tournaments to look at bass populations in Wheeler, Eufaula, and other fisheries. "At Wheeler, the virus was first detected in 1997," he said. "Then we lost the big fish in 1999 and 2000." While LMBV is noted to be a killer of large bass when it turns deadly, scientists found the highest prevalence of the virus in bass 12 to 15 inches long. "You just don't see it in bass over 20 inches," Maceina said. Those infected smaller fish experience slower growth rates and that, combined with a die-off of big bass, explains why anglers report more difficulty catching fish of 5 pounds or larger following an LMBV-related kill, the scientist explained. "A decline in big fish is due to slower growth and lower survival," he said. "The good news is that, by 2003, growth and survival rates had improved in most Alabama reservoirs." And by implication, that is good news for other fisheries damaged by LMBV, from Texas to Michigan. Maceina also confirmed what biologists have long believed regarding the role that stress and warm water play in LMBV outbreaks. "Holding fish for two to five days seems to increase the prevalence of the virus," he said. "And higher temperatures do, too." In the laboratory at the University of Illinois, professor Tony Goldberg discovered "a slight tendency for crowded fish to have higher viral loads. "The difference (between being crowded and not crowded) is small, but statistically significant," he said. During 2002, Goldberg and his associates found that LMBV-infected fish died more quickly at 30 degrees Centigrade (87 Fahrenheit) than at 25 degrees Centigrade (77 Fahrenheit). "The virus replicates more efficiently at that temperature," he said. "And it's important to remember that we're working with northern largemouth bass in Illinois. The thermal optima may be different in different places." Goldberg rated elevated water temperature as a high risk factor, with crowding, direct contact, and water-quality change as medium risks. "Expect kills when water quality changes rapidly or fish are crowded," he said. "Catch-and-release angling is okay (during hot weather), but do not subject fish to elevated temperatures and crowded conditions." To simulate stress from angling, Goldberg's team attached fishing line to small tank-held bass infected with LMBV and "played them." "The angling event made no difference in survival," he said. "Temperature, not angling, alters susceptibility." At least in the laboratory, he noted. "We need more field studies to help determine how these factors (angling, crowding, temperature) affect fish in complex ecosystems," added Goldberg. At the Warm Springs Fish Health Center, scientists were unable to isolate live virus from the feces of herons and cormorants. That suggests that fish-eating birds do not spread LMBV. They also found that LMBV is a tough and hardy virus, surviving both temperature changes and drying. Just allowing a livewell to dry for two or three days, in fact, likely is not enough to keep an angler from transporting the virus from one fishery to another. Researchers suggest thoroughly bleaching, then thoroughly rinsing, livewells between visits to different bodies of water. Throughout this past year's research, scientists continued to refine and improve their methods of checking bass for LMBV. Finding a quick and non-lethal way of testing, however, remains a research priority. Others include further examination of LMBV's long-term effects on fisheries populations and investigating a possible connection between the virus and bacterial infections. Scientists also want to trace the virus' movement through infected fish and try to determine why LMBV kills some fish and not others. And they want to find out how long antibodies remain in previously infected fish. Those attending this fifth annual meeting agreed that, overall, resources managers are in "monitoring mode" and that LMBV now seems to pose far less of a threat than it did in 1998 and 1999. Nevertheless, they will remain ever vigilant. "Sub-lethal effects are of concern to me," said Louisiana's Mike Wood, a state fisheries biologist. "Maybe we have problems that we haven't recognized yet." Oklahoma 's Gene Gilliland, a senior fisheries biologist for the Oklahoma Department of Wildlife Conservation added, "What's going to happen 10 or 15 years from now is of concern to all of us." ABOUT BASS BASS is the world's largest fishing organization, sanctioning conservation activities, youth initiatives and more than 20,000 tournaments worldwide through the BASS Federation. Since its inception in 1968, BASS has championed conservation and sportsmen's initiatives, including the modern catch-and-release movement born from the 1972 "Don't Kill Your Catch" campaign, free access to public waterways, and anti-pollution efforts. For more information, contact BASS Communications at (334) 551-2375 or visit www.bassmaster.com . Please, Also See LMBV Fact Sheet
|
|||
