Gizzard shad are a critical component of the Missouri River reservoirs, and are an important forage base in Lake Oahe, Lake Sharpe, Lake Francis Case, and Lewis and Clark Lake. Gizzard shad are incredibly productive, and grow walleyes quickly. It’s important to understand the importance of this forage base to these fisheries.
Gizzard shad are a warm water species, and South Dakota is at the northern edge of their range. This means that over winter mortality is a critical component of the gizzard shad life cycle. It had previously been believed that gizzard shad mortality occurred due to sustained cold temperatures, but recent information has indicated that rapid changes in temperature in both the fall and the spring is also a major driver of mortality.
Whether it’s sustained cold temperatures or rapid temperature fluctuations, it can be assumed that a significant portion of the gizzard shad population is going to die by the next open water season. However, this is what makes this species so special.
While many anglers think of gizzard shad as a very small prey species, only a couple inches long, adult gizzard shad can actually reach substantial sizes. These adult gizzard shad are incredibly productive, and will utilize warm water areas to survive the winter and produce the next crop of forage for the coming open water season.
While many fish species spawn once, generally in the spring or early summer, gizzard shad can spawn multiple times throughout the season. Once water temperatures hit 55 degrees, gizzard shad will begin spawning and can continue to do so until water temperatures dip below that 55-degree mark again in the fall. This means gizzard shad are producing more offspring every few weeks throughout the entire summer season.
This is important for anglers to consider, because this means that there will be shad of all sizes present in the system. By fall, there will be relatively large shad, that could be 3-5 inches long, and there could be smaller shad that are as small as 1-2 inches long. When it comes to selecting bait sizes, a #5, #7, or #9 sized crankbait could theoretically all “match the hatch.”
This also has a major impact on bite windows. In the springtime, there is very minimal forage in the system as this is when the bulk of the gizzard shad have died due to the winter months. This has much to do with the very strong spring fishing that can be had on Lake Francis Case and Lake Sharpe.
By summer, the balls of gizzard shad will begin to appear on electronics, and at this time is when the bite begins to slow down. By August, the “summer time blues” are in full force, and this is because of the abundance of forage in the system. Multiple spawns of gizzard shad, combined with mayflies and other juvenile fish species, keep walleyes fed and happy throughout the summer.
Fortunately, the bite will begin to pick up as fish begin to load up on calories in preparation for winter. At this time, gizzard shad are still present in the system and anglers continue to compete against these natural forage options. As fall gives way to winter, gizzard shad can really slow down an ice fishing bite.
Warmer than normal winters will also lead to increased shad survival, and this can lead to a slower bite for the upcoming open water season. When this happens, fish are much less active, needing to feed less, and overall are in much better condition. Anglers will often notice the plumpness of these fish, when they are fortunate to catch them!
In regard to the fishery itself, gizzard shad play a vital role. Shad are the main forage species in Lake Sharpe, Lake Francis Case, and Lewis and Clark Lake, and can grow fish very quickly. Gizzard shad help walleyes reach the 15 inch mark by age-3, a common benchmark in fisheries management, and walleyes in all three of these reservoirs are often at or exceeding these numbers in three or four years.
While gizzard shad offer an excellent food source for small to medium size walleyes, they are less effective at growing fish into the “over” category, or greater than 20 inches. While fish exceeding this size are present in these reservoirs, the bulk of the fish caught will be between 14-18 inches, which is because of how effective gizzard shad are at growing fish quickly to these sizes.
In waterbodies that have a larger body prey species, such as Lake Oahe, walleyes can then transition off of gizzard shad and onto this larger body species once they reach the 20-inch mark. This is what develops a true trophy walleye fishery.
Gizzard shad are a critical component of walleye fishing on the Missouri River. They are the predominant forage species, grow fish quickly, and play a major role in the seasonal bite windows that anglers experience on the fisheries. Understanding the dynamics of gizzard shad is critical for understanding how to pattern walleyes on these fisheries.
South Dakota Fisheries Focus
Learn more about the dynamics of the Missouri River reservoirs, as well as other fisheries across the state, on the South Dakota Fisheries Focus page!
