RIVERDALE - The Garrison Dam National Fish Hatchery, and the Valley City National Fish Hatchery, are well on their way to another record-setting year for walleye production.
The North Dakota Game and Fish Department hopes to supply the hatcheries with enough walleye eggs to produce more than 10 million fingerlings. If successful, the young walleyes will be stocked into state lakes later this summer. The goal is to produce 8.7 million fingerlings at the Garrison Hatchery and another 1.4 million at Valley City. It is an aggressive undertaking.
To meet the lofty challenge, it is estimated that more than 50 million eggs will need to be collected from walleyes and brought to the hatchery. Netting operations for the purpose of inducing spawning walleyes have been under way at Lake Sakakawea and Devils Lake for the past few weeks. How much longer fisheries crews will continue their work depends somewhat upon the quality and development of eggs currently in the hatchery.
Although artificial spawning produces more walleyes than what would normally occur in nature, there are always several variables that effect hatching success. Water temperature plays an important role in egg development. A few degrees can be the difference between an egg that will produce a walleye and one that will not. Even when the process is deemed successful, it takes a considerable number of eggs to meet a stocking goal.
On average, 40 percent of the walleye eggs brought to the hatchery produce walleyes. Sometimes the percentage is much less. Occasionally is it more, but that is only to produce fry in carefully regulated hatchery jars that circulate water at an ideal rate to promote egg development.
A few days after the fry are hatched, they are moved to outdoor ponds. They will remain there until reaching fingerling stage, considered a good size for release into the wild. The success rate for fry, even under hatchery conditions free of most natural predators, is about 50 percent.
If you apply the accepted hatchery formula to this year's goal of producing more than 10 million walleyes for stocking into state lakes it would look like this: 51 million walleye eggs multiplied by a 40 percent hatching success rate equals 2.04 million fry. A 50 percent survival rate for those 2.04 million fry yields 10.2 million fingerlings.
While the walleye eggs continue to circulate in the jars at the Garrison Hatchery, the work of filling 40 outdoor ponds with water is under way. Walleye fry will be moved to the ponds as soon as possible after hatching. There they will be closely monitored as they grow to fingerling size.
The state request for 2012 is that more than 4 million walleyes be stocked into Lake Sakakawea. Stocking walleyes in the big reservoir was suspended during the recent low water years when the forage base, primarily rainbow smelt, was considered much less than what was required by the lake's predators. Many walleyes netted by Game and Fish, or caught by fishermen during, that time were emaciated. Growth rates were minimal.
Now, with more water in the system, the forage base and the walleyes have responded. Stocking resumed and growth rates accelerated. Dave Fryda, NDG&F fish biologist in Riverdale, closely tracks the status of fish in Lake Sakakawea. A particularly interesting statistic is the noticeable change in the growth rate of Lake Sakakawea walleyes when comparing the low water years to the recent higher water years.
The average size of a 3-year-old walleye netted by Game and Fish in July of 2007 was 12.7 inches. In July of 2011 the average size of an age 3 walleye increased to 16.3 inches. A similar increase was noted in 4-year-old walleyes too. The average size of a 4-year-old walleye jumped from 14.6 inches in 2007 to 18.5 inches in 2011. The message is simple - the walleyes have more to eat now than they did a few years ago. Increased forage also opens the door to increased stocking.