Reservoir crappie populations are notoriously cyclic. A strong year-class is produced once every few years and is usually followed by one or more weak year-classes. When the fish reach catchable size, the abundant cohort supports good to excellent fishing for a few years until members of the once abundant year-class are caught or die of old age.
For crappie populations with fast growth rates and low natural mortality, which is the case with crappie in Mississippi’s flood-control reservoirs — Arkabutla, Sardis, Enid and Grenada — high length limits can improve yield, measured as the pounds of fish in the cooler at the end of a trip. They may help stretch the good fishing for an extra year or two, hopefully long enough for another strong year-class to enter the fishery. But good reproduction is needed to produce strong year-classes.
Vegetation is key
Inundated vegetation is essential for successful crappie reproduction and survival of the fry. In the main bodies of Mississippi’s flood-control reservoirs (FCRs), the only remaining vegetation is terrestrial plants high on the bank. Fisheries researchers at Mississippi State have found the vegetated flood-plain in the upper ends of these reservoirs can be important crappie spawning and rearing habitat.
Whether upstream or down, high water is needed to flood the vegetation. Keith Meals, a fisheries biologist for the Mississippi Department of Wildlife, Fisheries and Parks responsible for fisheries management on these reservoirs, has learned that strong year-classes generally follow high-water springs.
It would seem crappie management in the FCRs is simple: raise the water before the spawn. Indeed, that would probably work, but recreational fishing is secondary to safeguarding people and their livelihoods.
The flat, fertile Yazoo River Basin contains some of the most-productive agricultural acreage in North America, but you can’t live on or farm flooded land. High, spring flood waters on the Mississippi River raise the water in the Yazoo Basin and reduce Yazoo River discharge. Heavy rains in the Yazoo Basin, coupled with high Mississippi River stages, result in extensive flooding in the lower Yazoo Basin.
In the decades after the epic 1927 flood, the U.S. Army Corps of Engineers was charged with minimizing flooding in the Mississippi River valley. Mississippi’s four FCRs are part of this effort. A complex series of water-control structures was installed in the lower Yazoo Basin, and the FCRs were built to hold water flowing down from the upper Yazoo Basin. Although the product of extensive surveying and engineering design, the reservoirs are essentially large, water-storage tanks with a valve at the lower end. The greatest flood-control benefits would be achieved if the tanks were empty before the late winter and spring rains.
Recreational purposes, including fishing, were added to the benefits of the FCRs as an afterthought, and “rule curves” were developed to provide guidance for seasonally adjusting water levels. The rule curves were designed to accomplish the primary purpose of flood control while trying to accommodate other interests.
To provide flood-storage capacity in Enid, Sardis and Granada lakes, the rule curves specify maintaining low water in December and January, allowing a slow rise in February and March, and then a rapid rise to full pool in April. In Arkabutla, the water level is supposed to remain low from December through April and then allow a rapid rise to full pool in May. With most of the crappie spawn occurring in March and April, the rule curves are imperfectly conducive to crappie spawning in these denuded-shoreline reservoirs. But these reservoirs were built for flood control in an area far larger than the area of the reservoirs.
Spring rain gains
Rule curves specify water-management targets, but rains upstream fill reservoirs, and downstream flooding determines whether water can be released. Thus, despite rule curves, high water occurs before and during the crappie spawn in some years, and they usually produce strong year-classes, according to Meals.
The fishery management challenge is how to sustain quality crappie fishing in a dynamic, unpredictable environment.