In Central Florida’s
Lake Weir, what has come to be known as the Largemouth Bass Virus (LMBv) was
discovered in 1991. Four years later, in
Cooper Reservoir, South Carolina, the first related incident of fish mortality
was reported, and the virus proved itself to be one worthy of state department
attention.
In 2001, the Virginia
Department of Game and Inland Fisheries first tested impoundments for the
presence of LMBv, many showing no signs of infection or otherwise low exposure
rates; but the virus’s presence was nonetheless realized in Virginia.
Because LMBv is a
potential threat to America’s favorite game fish, panic and dismay surrounded
the initial discovery. However, the
course of the disease, as studied in southern waters, supports biologists’
assurances that LMBv poses a relatively insignificant effect on infected
fisheries.
Fishermen first noticed
only a decrease in the catch rate of quality fish—defined as being three pounds
and larger—as a result of a decrease in fry survival and growth rates. Now, 12 years since the initial discovery, it
seems the worst has passed, and some of the early detection sites are returning
to post-infection fishing conditions.
Testing resumed in
Virginia waters in the summer of 2010.
Of the three impoundments tested, all returned positive for the virus,
and two replied with notably significant exposure rates—Kerr Reservoir (Buggs
Island) showing 41% exposure, and Briery Creek Lake showing 30%--both of which
also tested positive in 2001. Both “big
fish” fisheries, Buggs and Briery became the martyrs for the cause.
A year later, 16 bodies
of water were tested across the state, ranging from small, department-owned
lakes to large impoundments and major rivers.
All locations showed signs of infection, save for the tidal James River. From this, VDGIF fisheries biologist Dan
Michaelson can infer that “LMBv will probably be found in most of the water
bodies in Virginia. Some will be
impacted by the disease and others may never show indications that the fish
have been exposed.”
There is a silver
lining, however. In the 2011 tests,
Briery Creek and Buggs Island showed exposure rates of 30% and 23%,
respectively, indicating that, as compared to results from 2010, the virus in
those fisheries has surpassed its peak of potency, and is now on the decline.
According to Dan
Michaelson, “the southern states that experienced this outbreak in the late
1990s showed about a 3-year recovery cycle after LMBv was detected. Considering Virginia’s cooler temperatures
and slower growth rate, he speculates that “the cycle will be about five years
in Virginia.”
For those fish that do
survive the initial exposure, immunity can be developed. “Unfortunately, they do not pass the
resistance on to their progeny,” says Michaelson. However, the good news is that states that
met the virus early on, like Texas, Mississippi, and Florida, no longer observe
noticeable impacts of the disease. Most
biologists predict that in Virginia, too, LMBv will become little more than a
means of population control, similar to old age.
As for what causes the
virus to emerge, biologists again claim little knowledge. Outbreaks and the few small mortality events
that have occurred are most frequent in the warmer months of the year due to
stress that may be linked to low oxygen levels, high water temperatures, and
increased tournament pressure.
Effected fish usually
show no signs of the virus, but may suffer from loss of equilibrium or the
inability to stay below the surface due to an over-inflation of the swim
bladder.
But despite the large
presence of LMBv in Virginia, most of the infected areas still maintain
exceptional angling opportunities for the angler, which will only increase in
status as the virus runs its course and shrinks into the background of
biological issues.
Still, it is important
to help stop the spread of the virus which, as it is not known exactly what
causes an outbreak, includes a wide range of responsible practices. Using common sense boat hygiene, like
cleaning trailers and not emptying water from a livewell into a foreign water
body, is an effective measure for stopping the spread of both LMBv and invasive
species. Also, it is encouraged to limit
the practice of bass tournaments in the hottest months of the year, and to
handle fish delicately and briefly. To
help prevent the spread of the disease and other biological issues, the
transplantation of fish into foreign impoundments is discouraged. More information concerning preventative
measures can be found on the Department’s website.
Considering the facts,
LMBv carries little long-term threat for Virginia’s bass anglers, and the end
of the tunnel is in sight. Biologists
continue to monitor bass fisheries and educate anglers to help stop the spread
of the disease. Michaelson assures
anglers, “we fully expect all of these fisheries to recover.” There is no cause for concern.
*Originally published in the Rural Virginian