Some say Guntersville isn't what it used to be: Why?
For years, Lake Guntersville in Alabama has been considered one of the top bass fishing lakes in North America. It has consistently held a Top 10 spot in the annual Bassmaster 100 Best Bass Lakes list. But recently, anglers and guides have expressed concern that fishing has declined. For the first time in years, Guntersville was not ranked in the 2016 Top 10, and was ranked fifth in the Southeast region
All Captions: Gene Gilliland
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The Alabama Division of Wildlife and Freshwater Fisheries (ADWFF) and Auburn University have teamed up to conduct a series of studies to address these angler concerns. Let’s take a look at the results of these studies to see what they tell us about the status of the Guntersville bass population and fishery.
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Declines in inland fish populations are usually related to a decrease in reproduction (commonly referred to as recruitment), an increase in mortality, or both. Mortality can be caused by natural occurrences such as disease, or fishing-related causes such as harvest or catch-and-release mortality. No recent disease outbreaks have been reported from Lake Guntersville, so if the bass population has declined, then it is probably due to either fishing-related mortality or a dropoff in reproduction.
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If anglers are harvesting a lot of bass to eat, then clearly that could create a problem with fishing mortality. The Alabama Wildlife and Freshwater Fisheries Division (AWFFD) conducted a creel survey in 2015 to see how many bass the anglers were catching and/or harvesting.
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The creel survey interviewed more than 800 anglers on randomly selected weekend days during the peak spring fishing season. Although the bulk of the fishing effort was directed toward bass (88%), only 5% of anglers harvested bass, and very few bass were being kept (average of only 0.07 bass per angler per day).
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The second phase was a tagging study conducted by Auburn University from 2014 to 2015 to determine what percentage of largemouth bass in the population were being caught, released or harvested and who was doing the catching. Rewards of $5 to $150 were offered for tag returns to ensure anglers reported the tags.
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The tagging study found that anglers harvested about 5% of the population each year, which is low, and is consistent with the strong catch-and-release ethic of bass anglers.
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Non-tournament catch-and-release anglers captured about 36% of the bass population annually. Based on previously published studies, we assumed that 5% of these fish died as a result of catch and release. These fish are represented by the black part of the bar; the yellow represents the likely survivors.
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Tournaments captured about 12% of the population. Previously published studies suggest that a higher percentage of these tournament release fish likely die when compared with non-tournament catch-and-release. And tournament post-release mortality rates were assumed to increase with increasing water temperature. After applying these post-release mortality rates, the mortality impact (the black part of the bar) was still relatively small.
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In total, about 50% of the population was caught by anglers each year and around 10% died due to harvest or catch-and-release mortality. A 10% mortality rate is pretty low and is similar to what we see in other catch-and-release fisheries.
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The bottom line in the catch-and-harvest surveys? A sizable percentage of the bass in Guntersville are caught each year but most are released. Overall fishing mortality is low enough that it is not a cause for concern over the quality of the fishing recently.
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The agency’s (ADWFF) tournament results reporting system (B.A.I.T. – Bass Anglers Information Team Report) shows some ups and downs in the average tournament weights at Guntersville over the last 30 years, but overall it shows an increasing trend.
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Likewise, the time it takes to catch a 5-pound or better bass has seen its ups and downs (it took a lot of hours to catch a quality bass after the largemouth bass virus breakout in the late ’90s) but overall the time is declining, meaning it’s easier to catch a quality bass now than in years past.
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Biologists use electrofishing surveys to determine the relative numbers of different sizes and ages of bass in the population. ADWFF has been conducting these surveys with consistent methods at Guntersville since the mid-1990s. We can use these data to look at trends in abundance and see which years had good reproduction and which years had poor reproduction.
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Often, strong reproduction is the key to a good fishery. Biologists call this recruitment — the number of young bass surviving to enter the population as age-1 fish. We can use the electrofishing data to look at the relative changes in recruitment from one year to the next. We call this year class strength. Let’s first take a look at how year class strength has varied over time at Guntersville.
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You can see from this graph that year class strength has had its ups and downs with the last couple of years being below average. But you also see that every so often, Guntersville cranks out a really big year class like the one in 2008, which was nearly twice the long-term average. We’ve also seen similar periods of relatively weak year classes in the past such as 2000 to 2007. Fish recruitment often varies naturally from year to year due to the many environmental factors that affect survival of the young during their first year in the lake, such as water levels, temperature and food availability.
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Environmental factors that affect recruitment often affect nearby populations in the same way, so looking at other lakes in the area can be useful. When we look at largemouth bass recruitment at Wheeler Reservoir, just downstream from Guntersville, we can see that, although year class strength does not match up perfectly with Guntersville, there is a similar pattern of average or below-average recruitment for the past few years.
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So what’s up with the recent lower recruitment at Guntersville? We know it’s not people taking home the adult spawners; fishing mortality is low and large adult bass are abundant. The most likely reason for lower recruitment is natural variation. Recruitment is usually highly variable from year to year for most fish populations, including largemouth bass, and this variability can be hard to predict.
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To illustrate just how much recruitment can vary from year to year for fish populations, let’s step away from Guntersville largemouth bass and take a look at another example of variable recruitment — walleye in Lake Erie, the walleye capital of the world.
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Here, we see a similar pattern for Lake Erie walleye — highly variable with most year classes being average or below average, and a really big recruitment event approximately once per decade. We see these patterns time and time again in many different fish populations from inland reservoirs to large lakes, and even in the marine environment.
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Now, back to Guntersville largemouth bass. As you might expect, variation in year class strength results in changes in the abundance of different sizes/ages of fish over time. From the electrofishing surveys, we estimated that in 2015, the number of bass from 15 to 18 inches was right at the historic average but had declined recently after a big peak in 2011 and 2012 that was the result of the huge 2008 year class of bass growing up to legal size.
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Follow that superabundant 2008 year class a few more years, and you see how they have grown into the big numbers of bass longer than 20 inches seen in the last three years. In fact, the relative abundance of these 20-inchers is currently the highest it has been in the last 21 years that data have been collected.
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We conclude that the huge 2008 year class is currently producing lots of large bass at Guntersville. However, the 15- to 18-inchers have declined back to the long-term average due to recruitment variation that is probably due to natural causes. This decline is consistent with angler reports of declining fishing quality because these medium-size bass are often more catchable than other size classes. We also don’t see evidence that fishing mortality is causing a decline in fishing quality.
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Thank you to all the people who made this study possible.