About the only suitable walleye spawning habitat was the small rock used to armor the base of the dam. Walleye will usually spawn around the end of March or the first of April, depending on water temperatures. Spring filling of the lake usually begins in mid-April. Unfortunately, there are years that the low-water levels leave the rock high and dry during the walleye-spawning period and natural reproduction is severely limited."
Because spawning success varies from year to year, fisheries biologists supplement the walleye's natural reproduction at Minatare by stocking fingerlings every other year - part of a long-term, statewide study of walleye. Annually biologists sample the walleye population, using nets and electrofishing equipment to gather fish, and track walleye year-classes.
The sampling information improves fish management in the lake. For example, sampling revealed that gizzard shad, a forage fish, plays a critical role in Lake Minatare's productivity. In 1992, gizzard shad failed to spawn in the lake, and sampling in subsequent years showed nearly complete losses of year-classes of walleye, yellow perch, crappie, and even sucker and carp. To ensure an ample forage base in the lake, gizzard shad are now stocked annually, and biologists conduct special shad-sampling projects to track their production and survival.
"We don't see carryover or large gizzard shad during our samples," Peterson said. "Minatare is on the northern edge of the gizzard shad's range, and our concern is high winter mortality. The supplemental stocking of adult gizzard shad in the reservoir is kind of an insurance policy. We seine shad from ten different locations in the lake each summer and check the size of young-of-the-year fish as part of the on-going walleye study. Our fall sampling finds very few shad survive to age one or two. We also use graph-recording sonar to provide additional information on schooling shad, not only the numbers of schools but the size of the schools help to identify the lake's shad base going into the fall, winter and spring.
"We also find an emerald shiner presence in Minatare, probably from upstream stockings in Wyoming reservoirs on the North Platte River. The emerald shiners don't appear to have a detrimental effect at this time, but they are predators for the smaller aquatic organisms that young-of-the-year game fish require."
Lake Minatare's forage base creates a fast-growing walleye population; they reach 7.4 inches at the end of their first year, 13.2 inches by the next year and 16.5 inches by the end of the third growing season. The average four-year- old walleye is 18.6 inches. Minatare samples show very few walleyes exceeding 20 inches - probably because of fishing pressure. What is certain is that walleyes exceeding the 15-inch keeper minimum are extremely popular with anglers.
The forage base also supports limited stocking of wiper, a tackle-busting hybrid of the striped bass and white bass. Minatare receives a small number of stocked wipers - 5 per acre, or about 10,000 wipers - every other year.
Peterson believes the wipers offer a bonus trophy fish to Minatare anglers. Recent sampling indicates Minatare has a larger than normal year-class of wipers exceeding five pounds - a fact that should mean good or excellent wiper fishing for the next several years. Anglers are also taking increasing numbers of smallmouth bass and the lake has an underutilized channel catfish fishery.
In 1998, Lake Minatare received the first major aquatic-habitat construction project in Nebraska's Panhandle. Contractors laid down nearly 8,600 tons of crushed concrete and cobble rock, creating aquatic reefs along the lake's Lighthouse Point and dam.
Funded by the Aquatic Habitat Stamp program and Nebraska Environmental Trust grants, the project provided additional structure and habitat for spawning walleyes and other fish species, and for organisms in the aquatic food chain.
Two reefs, separated by a 100-foot buffer, were built below the lighthouse, each 176 feet long and 213 feet wide, or about 37,500 square feet. Broken concrete was used to form the north reef; the south reef was constructed of cobble rock - gravel two to six inches in diameter - excavated nearby.
The location, dimensions and elevation of the aquatic reefs were designed with Lake Minatare's changing water levels in mind.
"The lake's water elevation usually varies almost 20 vertical feet during the irrigation season," Peterson said. "The sites and elevations selected ensures that rock will be available as the
In addition to the reefs, contractors created triangle-shaped windrows of cobble rock, 11/2 foot high on a 41/2- to five-foot base, around the tip of Lighthouse Point. Totaling 7,230 feet in length, the 48 windrows are separated by five-foot gaps. They provide aquatic habitat for fish, invertebrates and other organisms.
Cobble rock was also placed along the dam during the fall when the lake was down. The windrows and aquatic reefs are marked with buoys to alert boaters to the presence of underwater structures.
Peterson and Al Hanson, also a Commission biologist, sampled walleye during the 2000 spawning period to determine their use of the new reefs and windrows. They used electrofishing equipment mounted on a boat to temporarily stun fish in an area so they could be collected. The sampling was done during three nights in April, approximately a week apart.
Each night the researchers began sampling at sundown, spending equal time on each reef and nearby control areas. Several electrofishing passes were made over each area. All the captured walleye were transported away from the study area and marked to identify those recaptured later. The researchers also determined and recorded the sex of each fish.
During the three nights of sampling, the number of walleyes collected on the aquatic reefs totaled 868, of which 73 were recaptures. They collected 524 walleyes, or 60 percent of the total, over the cobble reef, and 344 fish, or 40 percent, from the crushed concrete reef.
"We also made one electrofishing pass over cobble rock on the face of the dam to count walleye," Peterson said. "A total of 375 walleyes were observed along this 800-foot section. We also made several survey passes over the windrowed area, but high winds that night made it difficult to accurately sample. But, it was apparent that walleye numbers on the windrowed sites were lower than on the aquatic reefs."
The recent aquatic reef projects at Lake Minatare have provided important submerged structure and habitat for game fish and other aquatic organisms. For the future, these projects and on-going efforts to assure an ample forage base should provide Nebraska Panhandle anglers excellent fishing opportunities and enhance Lake Minatare's reputation as a surprising fishery.