by Ronald F. Dodson, Ph.D. The first report of a largemouth iridovirus (LMBV) was in 1995 in bass kills in four southeastern states
In Texas, Sam Rayburn bass succumbed first, then bass at Fork and now the bass in Lake Conroe have the virus.
The location of schools of bass can be most predictable during long periods of consistent weather patterns. I usually save up vacation time until the summer and average being on the water at least one day, if not more, during the week and on weekends. Over the last five years I have found Lake Fork (Texas) to be one of the best and consistent lakes for midday fishing I have been on since Palestine (Texas) was in its prime.
You could set your watch for various groups of fish and catch 20 to 30 in several upper-lake spots. From July through September, schools of large bass were all over the place in Birch Creek, at the dam, and under any of the major bridges. I therefore was primed for a great summer and worked my schedule accordingly.
I checked on several schools of fish in early May and, as expected, they were just getting into a couple of summer haunts. The next time I tried the spots was on May 16, 1999. I caught 25 or so fish out of secret hole number one. These were between four and six pounds. I found nothing at secret hole number two. My explanation was it hadn't gotten hot enough yet to concentrate them. Boy was I wrong!
I was involved with trying to piece together the puzzle of what happened at Sam Rayburn in the late summer and early fall of 1998, but never dreamed we would be looking at the second major bass die-off in one of our best bass fisheries within a year.
The Rayburn event resulted in a die-off selectively of largemouth bass and no other species. The episode occurred during a major heat wave, with low water conditions and with a noted loss of hydrilla. I did an article on this hydrilla issue and ended up getting all sorts of explanations as to the cause. My experience with Rayburn goes back to the time when there was still green timber and I would drive over from college and stick my 5-1/2 on the back of a rent boat. Then while in Houston I fished it extensively. In June of last year I found it to be the same old Rayburn. By October I never saw a school, or found any concentrations of bass.
The stories I uncovered about the cause of the die-off included wide spread spraying of the lake to eliminate hydrilla or in the surrounding forest. The hydrilla didn't cut much interest since the lake had been so low, most was on the bank anyway. Several folks finally got responses from the management agencies for the national forest, which indicated limited spraying a considerable distance from the lake.
Then we had the fisherman "catch-and-stress" concept. Really couldn't get anyone to identify what major tournaments occurred during this period, nor how the bass managed to swim 10 to 15 miles from the site of most major tournaments before they died in the mid-lake areas. The argument that stress was caused by low water and high temperatures didn't wash either. The lake has been extremely low several times and that wasn't the only hot Texas summer. Also, if hot water was a player, how do fish survive in power plant lakes where the temperature often greatly exceeds that of other lakes?
I concluded in the article (to the chagrin of everyone who had a pet theory) that the fish had to be dying from some sort of infection.
That brings me to Lake Fork in the summer of 1999. On the first weekend of June I began to notice some dying bass near the dam. It isn't uncommon to find some bass that die after the stress of the spawn, but these weren't acting right. Their bodies were torqued, so that the fish were in a bow shape, as though their muscles had been paralyzed on one side.
The events began to unravel over the next few weeks with more bass dying. Like Rayburn, it was species specific. Unlike Rayburn, Fork was slightly above full when it started and the water temperature was eight to 10 degrees below that of the same time the previous year. Some fish are going to die from various causes in a lake, but a major pollution or environmental cause kills various species, not just one.
The fishing got progressively worse during the summer, but I made a commitment to myself that my summer was going to be spent tracking the process on the lake. Certain things became immediately obvious. The fish kill affected only three-pound plus bass. It also occurred from one end of the lake to the other. Fish were coming up in the back ends of creeks, in shallow water, and deeper open-water areas as well. My weekly stints were from Highway 19 in the upper end to the back of Coffee Creek, Little Caney, Wolf, and all creeks on the Mustang side of the lake.
Fork has been an outstanding summer schooling fishery with many of the schools being comprised of appreciable numbers of fish, some even being five-pound plus bass. A very interesting spot for schools has been under the major bridges where one could, from June through September, see numbers of bass chasing shad during the afternoon.
I have not seen a school break under one of the bridges since the die-off began. In fact, with the exception of a small area in Birch Creek and an occasional small school in Dale, the lake has looked devoid of school bass.
Both the Sabine River Authority and Texas Parks and Wildlife began collection of bass, and releases in the media kept referring to the "limited number" of bass in the kill, stating the worst was over. Actually, I found a nine, three sixes, and one seven dead in Dale Creek as late as August 31.
In late August, after the first in-state tests of specimens were negative, a positive finding was observed from tests at Auburn University. The conclusion was that the bass had a viral infection. The first report of a largemouth iridovirus (LMBV) was in 1995 in bass kills in four southeastern states. We know about virus-induced diseases in man such as colds, chicken pox, measles, mumps, and rubella, but it might be helpful to briefly look at the culprit.
A virus is a very small organism, which can only grow and multiply inside of a cell. It essentially tries to take over some of the genetic mechanisms of the cell to manufacture more of the virus as opposed to the normal products that the cell genes make. A virus is simple, yet very tough. It is a survivor, and has sometimes been considered the ultimate predator in that it can sustain itself for long dormant periods and then activate when the right target is present thus controlling complex cells, which it infects.
So what do we know about this bass virus, and maybe more importantly, what do we not know?
I sought information from two Texas Parks and Wildlife officials. Dr. Larry McKinney, Senior Director for Aquatic Resources and Dan Jones, Resource Protection Biologist who is coordinating much of the study currently ongoing at Lake Fork.
The virus was first isolated from Santee-Cooper Reservoir in South Carolina and 12 reservoirs in Alabama, Georgia, South Carolina and Mississippi in 1995.
Fish collected from Fork in June and July were also found to be positive. Fish were also sampled from the hatchery in a quality control check to see if it could have been a source. This is a scary thought, but the contribution of hatchery-spread Whirling disease among trout fisheries in Colorado is well documented. I understood the hatchery fish are at present negative.
Tests are also being done on bass from several other lakes including Rayburn and Toledo Bend. Department officials advised me, as I was working on this article, that Conroe bass also have the virus.
There are some basic scientific questions that I posed to agency officials. Remember this is a new event so the fact that there weren't clear answers is not a condemnation, but simply a true status of the perplex confusion regarding the problem. Perhaps the best way to approach the problem is to list the questions and give the departmental thoughts and my own scientifically thought out proposals based on my observations and a little common sense.
