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January 6, 2010

Improvement expected for Lake Murray striped bass fishery

The conventional wisdom among Lake Murray striped bass fishermen is that 2009 was a tough year to catch keeper sized fish on the lake. According to S.C. Department of Natural Resources (DNR) biologists Hal Beard and Ron Ahle that conventional wisdom is backed up by the data and sampling from the winter of 2008/2009 predicted that the "keeper ratio"(percentage of fish over 21 inches) would be poor on Lake Murray this year. There is good news for the upcoming year. At DNR's annual "State of the Lake" presentation at Midlands Striper Club's December meeting, Hal and Ron stated that preliminary results from this winter's sampling indicate that 2010 will be a better year for striped bass fishing on the lake.
           
Each winter DNR undertakes three major gill net samples to collect information about the striped bass population on Lake Murray. Fish collected in the winter of 2008/09 sample had the worst keeper ratio in at least a decade. The average length of fish collected was 17.1 inches, the shortest in many years, and the data showed that "there was an absence of larger fish." The one bright spot was that the total number of striped bass caught was higher than in the winter of 2007-08 sample.
           
The better news is that preliminary results from the winter of 2009-10 indicate that the keeper ratio is much improved a year later. An important caveat is that only one of three major samples has been taken, but there is also a chance that with a couple more months of growing time an even more optimistic picture will emerge after the second and third samples are taken. Preliminarily, though, the average length fish is up to 18.2 inches, and the keeper ratio is up several percentage points to 18%. By next summer the population should look even better.
           
Anglers will be pleased to hear that the chances of catching fish over 21 inches should be improved in 2010. But what accounts for the annual fluctuation, and why is the keeper ratio not steady from year to year? According to Hal Beard and Ron Ahle a number of factors impact the quality of the striped bass fishery. These include 1) summer water quality, 2) gill maggots, 3) problems with stocking and recruitment, 4) hooking mortality, 5) reductions in forage base, 6) prolonged drought, 7) competition with other species and 8) white perch.
           
Factor 1, summer water quality, is especially important to striped bass survival. Good evidence of low summer water quality is the prevalence of fish kills and evidence of these is dead striped bass floating on the surface (usually large fish which are more sensitive to temperature). Studies on the Lake Thurmond fish kill last summer, where more than 1000 striper were found dead on the surface, indicated that for each floating fish many more sink to the bottom. Fortunately Lake Murray had only minimal fish kills in the summer of 2009 and DNR counted only 98 dead fish with most of these coming in August. By way of comparison, 325 striped bass were counted floating dead in the summer of 2008 and that summer there were several weeks throughout the summer when fish kills occurred.
           
It is generally understood that striped bass kills are likely when water temperatures get very hot and the depth that fish seek for thermal refuge contains too little dissolved oxygen for them to survive.
           
Factor 3, problems with stocking and recruitment (which includes the survival rate of small fish), could involve a relatively simple problem that could have dramatic effects on the fishery. For example, Ron Ahle pointed out that a malfunctioning aerator on a stocking truck could seriously affect the survival rate of young striped bass.
           
To learn more about Factor 4, hooking and mortality, DNR is considering undertaking a tag and release study.
           
Factor 7, competition factors, includes competition from other fish, but could also include competition from other animals. Largemouth bass, catfish and other fish compete with striped bass. As littoral habitat is degraded largemouth bass are more likely to become pelagic species and roam open water like striper. Ron also mentioned the population of blue catfish and although the numbers of blue cats does not seem to be expanding rapidly bigger fish are being caught each year. As far as other animals competing with striped bass, DNR does not believe that cormorants are having a significant impact on Lake Murray, although they may be a factor on the Santee lakes. In fact, loons almost certainly eat more fish than cormorants on Murray.
           
Closely related is Factor 8, white perch predation, and DNR believes that white perch may be eating significant numbers of small stocked striped bass. This is one of the motivations behind delisting perch as a game fish and the biologists made a point of reminding the audience that there is no limit on perch. They encourage everyone to keep as many as they catch.
           
One last subject which the biologists touched on, in response to an audience question, was the eradication of aquatic vegetation in the lake. Sterile grass carp, which are almost certainly the biggest fish in the lake right now, actually become less efficient eaters as they grow older. The biggest fish do not eat as much as the smaller ones. As the population of grass carp ages that is good news for Lake Murray anglers hoping for a rebound of aquatic vegetation.
           
Overall, while results are still preliminary, and two more winter studies have yet to be completed, early signs point to a significantly better striped bass population next year than in 2009.
             
Anglers with more questions can reach Ron Ahle at ahler@dnr.sc.gov and Hal Beard at beardh@dnr.sc.gov.           

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