Saw this on the AFC website. It pertains to Greers Ferry, but you can see the similarities to any Corps lake.
GREERS FERRY – What is going on with the fish in Greers Ferry Lake? That’s a question Arkansas Game and Fish Commission is 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 due to its use as a municipal water supply. This puts the AGFC and 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 had high water events on Greers Ferry Lake in 1999, 2002, 2004, 2008 and 2011 where the lake stayed up in the flood pool until at least July 1. In fact, 2008 (+23 ft.) and 2011 (+18 ft.) were the highest water levels on record with water levels in the flood pool well beyond July 1. This means there’s only had been one high water year in the past seven years. For a high water year to be truly effective it needs to stay up at least 60 days post spawn, or 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 since their maximum size is about 6-inches. Much research has been conducted concerning fish diets and most predators (black bass, walleye, crappie, hybrids) prefer 2 to 4-inch shad, due to the size of their mouth. 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 results 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, sport fish populations remain plentiful. Unfortunately that is impossible to control.
The management tools 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 they are forced by downstream flooding due to their Congressional mandate for flood control and the negative effects if has on their 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 currently being processed and analyzed. Biologists will be able to 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 due to the cold winters the state has experienced the last 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.