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What
has happened to Hiwassee Reservoir's walleye population? (Editor's Note: This column was posted online on January, 7 2004)
Hiwassee's walleye fishery has a long history. When Hiwassee Dam was finished in 1940, it created the third largest reservoir in southwestern North Carolina (behind Fontana and Chatuge reservoirs). Walleye were established by the mid-1960s, and since their establishment, they have been sustained entirely through natural reproduction and have not required additional stockings. Self-sustaining walleye populations are rare in the southeast and are one of the hallmarks of North Carolina's mountain reservoirs.
Walleye are predators and depend largely on forage species to survive. Historically, gizzard shad and threadfin shad were the only forage fish species in Hiwassee Reservoir. There is no such thing as a perfect forage species, and these species are no exceptions. Gizzard shad get very large (up to 18 inches) and often grow too big for walleye to eat. On the other hand, threadfin shad seldom grow too large, but they often die off in cold winters and must be restocked. Also, because threadfin shad and gizzard shad prefer warmer water, they stay near the water's surface, making them good forage for some species, such as largemouth bass. However, living near the water's surface keeps them out of reach of walleye, which live deeper most of the year. A big change in Hiwassee's forage fish community occurred in 1997 when blueback herring first appeared in the reservoir. Blueback herring are members of the Clupeidae family and are very similar to alewife. They grow to a smaller maximum length (10 inches) than gizzard shad and small (5-to-6 inch) individuals are common. They are more tolerant of cold winters than threadfin shad and don't die off as frequently or as completely. Also, they prefer cooler water and generally live deeper in the reservoir than threadfin shad or gizzard shad. Blueback herring were first discovered in the Hiwassee drainage in Chatuge Reservoir and Nottley Reservoir in 1996. Often used as bait for striped bass and hybrid-striped bass, they likely were introduced into these reservoirs by anglers and easily moved downstream through hydropower turbines into Hiwassee Reservoir. Since their arrival, blueback herring quickly have become the most abundant forage fish in the reservoir. How has the walleye population changed since the arrival of blueback herring? We started closely monitoring the Hiwassee Reservoir walleye population and discovered, as anglers pointed out, the number of walleye was declining. Our research has shown that this decline is due to poor walleye reproduction beginning in the late 1990s, coinciding with the blueback herring arrival. A similar species, the alewife, has been blamed for causing walleye reproduction to fail on many Tennessee reservoirs. Although some university research has been devoted to the subject, exactly how blueback herring and alewife can hurt gamefish populations remains a mystery. Researchers have suggested that one way blueback herring may reduce gamefish reproduction is by preying on larval gamefishes and gamefish eggs. We examined diet contents from over 1,500 blueback herring collected from Hiwassee Reservoir tributaries during the white bass and walleye spawn. Although we found very little evidence of larval fish predation, we found substantial numbers of fish eggs in blueback herring diets. Almost all the fish eggs were identified as white bass. Where does the Commission plan to go from here? For better or for worse, blueback herring are here to stay. There is simply no way to exterminate them from an entire reservoir and river system. Although we would mourn the loss of any self-sustaining fishery, we are considering stocking fingerling walleye. Stocking is rarely a solution to reservoir fishery problems, but in the case where a species simply cannot reproduce, it can be helpful. For this reason we will begin an experimental release of fingerling walleye in 2004. All fingerlings will be marked so we can determine if they contribute to the population and make a difference in the fishery. We will continue to monitor walleye reproduction closely. Also, to understand better the fishery and the fish, we are planning an angler creel survey and a walleye genetic study, both beginning in 2005. Understanding the effectiveness of the experimental release, along with collecting more information about angler catches and the walleye population, will help the Commission manage the fishery effectively and, ultimately, improve walleye angling in the reservoir. Powell Wheeler
is a fishery biologist I with the N.C. Wildlife Resources Commission’s
Division of Inland Fisheries. |
