in Pathfinder and Seminoe Reservoirs?
From Wyoming Game & Fish
The Wyoming Game and Fish Department collects adult gizzard shad in Nebraska in the spring and stocks them in several walleye reservoirs nearly every year. These adult gizzard shad typically reproduce 3 to 5 times over the summer with each female shad producing up to ½ million eggs at each spawning event. This results in an extraordinary number of 3 to 6 inch shad from mid summer through fall, which is ideal forage for predatory fish such as walleye.
Gizzard shad typically do not survive Wyoming winters due to prolonged periods when our waters are iced over so annual stocking is necessary to maintain gizzard shad in most cases. The Glendo Reservoir walleye population has benefited enormously from this practice. So, if it has worked this well for Glendo walleye, why are we not doing the same for Seminoe and Pathfinder walleye?
The potential benefits of gizzard shad introductions to walleye fisheries are substantial enough that gizzard shad are routinely stocked (Glendo, Keyhole, and Goldeneye reservoirs) or have self-sustaining populations (Grayrocks Reservoir) in waters where walleye are the primary sport fish.
However, when walleye are not the only sport fish present, the decision to stock gizzard shad becomes much more difficult. This is the case for Seminoe and Pathfinder, which also support regionally important rainbow trout fisheries. We must carefully consider all of the potential benefits and problems of gizzard shad stockings to ensure that we are doing the right thing for the fisheries resource.
The potential benefits include:
- 1) Increased food availability for walleye potentially leading to increased growth
and more, larger walleye for anglers to catch.
2) Walleye may prey on gizzard shad instead of rainbow trout thus benefiting the rainbow trout fishery. In the short term this idea “theoretically” makes sense, however, there is very little information supporting this notion.
These risks include:
-
1) Gizzard shad compete with rainbow trout and young walleye for zooplankton
and their populations may be impacted. Rainbow trout have grown skinnier in
recent years in Seminoe and Pathfinder due to the drought and low water
levels, which have impacted the zooplankton in these reservoirs. Further
competition with gizzard shad for the remaining zooplankton could prove
devastating for the rainbow trout population.
2) Gizzard shad may produce more, larger walleye, which are likely to consume more trout and thus impact the rainbow trout fishery.
3) Gizzard shad may effectively “wipe out” an entire year-class of walleye by readily consuming any larval fish that will fit in their mouths. If walleye reproduction was delayed through a cool spring, gizzard shad may reproduce first and reach sizes where they can consume larval or newly hatched walleye. Given the number of gizzard shad that may be produced, this may completely eliminate an entire year’s worth of walleye reproduction.
However, this certainly does not mean that we won’t consider stocking gizzard shad in Seminoe and Pathfinder in the future. When we exit the drought and these reservoirs gain water and maintain more substantial zooplankton populations, gizzard shad stocking will be considered.