AGFC biologists strive to increase forage population in Greers Ferry Lake
GREERS FERRY — What is going on with the fish in Greers Ferry Lake? That’s a question the Arkansas Game and Fish Commission has been getting from concerned anglers over the past year. We know that historically low-water years result in a reduction in productivity in lakes such as Greers Ferry Lake. High-water years increase the nutrients in the lake through increased runoff and inundation of terrestrial vegetation.
As the flooded vegetation decomposes, nutrients are released into the water column. The nutrients made available are akin to putting fertilizer on your yard or garden. As the lake temperatures warm above 60 degrees, phytoplankton and zooplankton begin to bloom prolifically. These blooms are what cause the water to have a stained or dingy look. These microscopic plants and animals are the base of the aquatic food chain.
The AGFC can artificially induce these productive blooms on our smaller, commission-owned lakes through fertilization. Fertilizing a lake the size of Greers Ferry Lake is cost prohibitive, and there are limitations as a result of its use as a municipal water supply. This puts the AGFC and the U.S. Army Corps of Engineers at the mercy of the weather in trying to maintain adequate lake levels for good fish production.
In reviewing the hydrograph for the past 16 years, there have been high-water events on Greers Ferry Lake in 1999, 2002, 2004, 2008 and 2011, when the lake stayed up in the flood pool until at least July 1. In fact, 2008 (plus 23 feet) and 2011 (plus 18 feet) were the highest water levels on record with water levels in the flood pool well beyond July 1.
This means there’s only been one high-water year in the past seven years. For a
high-water year to be truly effective, the water level needs to stay up at least 60 days post-spawn, or until about July 1. The longer the water stays in the flood pool, the more it benefits the lake.
Gizzard and threadfin shad are the dominate forage species in the lake. Threadfin shad seem to be preferred because their maximum size is about 6 inches. Much research has been conducted concerning fish diets, and most predators (black bass, walleye, crappie and hybrids) prefer 2- to 4-inch shad because of the size of their mouths. Since both shad species feed entirely on plankton, they are especially sensitive to plankton densities.
The more nutrients available result in better plankton blooms, which result in better growth and production of shad. The stronger shad population results in better growth, reproduction and condition for predators such as largemouth bass, crappie, hybrid striped bass and walleye.
If high water levels occur every three years in the spring and early summer, sportfish populations remain plentiful. Unfortunately, that is impossible to control.
The management tools that the AGFC uses on Greers Ferry Lake are stocking, creel and length limits, and manipulation of habitat. The Corps of Engineers reservoir operating guide does not allow lake elevations to stay in the flood pool very long, unless the Corps is forced by downstream flooding as a result of congressional mandate for flood control and the negative effects it has on Corps facilities around the lake.
AGFC fisheries biologists have spent considerable time on the lake this winter and spring conducting gillnet sampling and electrofishing. They have taken all three black bass species (largemouth, spotted and smallmouth) to the AGFC fish pathologist for a complete health analysis, including viral swabs for the presence of largemouth bass virus. Data for age and growth were collected over the past year for walleye, hybrid striped bass, largemouth bass, spotted bass and smallmouth bass. This data is being processed and analyzed.
Biologists will compare the growth data to records to determine if low-water years are significantly affecting growth. They are also in the process of developing models that predict shad densities based on the hydrograph of Greers Ferry Lake. Preliminary results indicate that there is a relationship between lake elevation and shad production.
Once all of the data is analyzed, a report will be written documenting the impact of the low-water years on the game species. In addition to documenting game-species abundance, biologists have anecdotally noticed that threadfin shad are virtually nonexistent. This is likely a result of the cold winters the state has experienced the past couple of years.
Threadfin shad are a subtropical and Southern temperate fish preferring warm waters. Water temperatures in the low 40s can cause significant mortalities in threadfin-shad populations. In smaller lakes, the entire threadfin population can die. Threadfin shad may still exist in Greers Ferry Lake, but their abundance appears to be very low.
AGFC biologists are making changes to the management strategy to reflect the current forage limitation. They are going to start culturing forage (minnows, bluegill and threadfin shad) through the Greers Ferry Lake nursery pond. This year, they will raise bluegill and fathead minnows through the summer and release them in the fall. This will give the bluegill several opportunities to spawn prior to release.
Next year, biologists anticipate stocking threadfin shad in the pond and letting them spawn. In addition, they will not stock any predators until the forage population recovers. This includes black bass species (largemouth, spotted and smallmouth), walleye and hybrid striped bass. Once the forage base recovers, biologists will stock these species in a manner that lends itself to a more sustainable fishery that can withstand a series of low-water years.
To discuss this issue with a fisheries biologist, contact Matt Schroeder, District 10 management biologist, at (877) 470-3309, ext. 1204, or by emailing Matthew.Schroeder@agfc.ar.gov.