Walleye Tagging Study Delivers Answers

On a cold, windy April morning better suited for telling fishing stories indoors, North Dakota Game and Fish Department fisheries biologists tagged and released 21 walleye caught in trap nets anchored in Lake Oahe’s Cattail Bay.

The 21 fish, plus an additional 166 from Beaver Bay later that same day, were welcomed as biologists worked closer to meeting this spring’s goal of tagging 4,000 adult walleye from Cattail Bay to Garrison Dam, located 140-plus river miles upstream.

The fish were fitted with metal jaw tags as part of a multi-year tagging study on the Missouri River System from Garrison Dam to Oahe Dam in South Dakota.

The study is a shared effort between biologists and researchers from North Dakota Game and Fish, South Dakota Game, Fish and Parks, and South Dakota State University.

Initiated in 2013 and entering its last year, the tagging study is designed to assess fish movements, mortality and what proportion of the population is harvested annually by anglers.

In early April, with the tagging effort ongoing in both states, it was estimated there would be around 36,000 tagged fish between Garrison and Oahe dams.

"One of the main reasons we are doing the study is to gather more information on walleye mortality rates, which is really an important piece of information to have to properly manage this fishery," said Paul Bailey, Game and Fish Department fisheries supervisor.

Bailey said annual walleye mortality rates across North America are typically from 40-55 percent, and the percentage of fish dying in the Missouri River System study area are well within acceptable rates for the long-term good of the fishery.

With this study, biologists are able to differentiate natural mortality – old age, disease and so on – from angling mortality, which is the influence anglers have on the fishery.

"The angling mortality rate that we’ve seen in the first three years of the study has been about 17-27 percent, depending on the region of Lake Oahe and the Missouri River that we are in," Bailey said. "Those are all acceptably low rates of mortality that basically says that anglers are not having a negative impact on the fishery at the present time."

Three years into the study, biologists have also learned some interesting information about walleye movement patterns, or lack thereof, between the dams.

"I think a lot of anglers are under the impression that there is a walleye migration that occurs here every spring, sort of like a spawning run," Bailey said. "The information that we are getting suggests that this really isn’t the case. What anglers are seeing is really an illusion, based on water temperatures."

Because the cold water released from Garrison Dam continuously warms as it moves downstream past Washburn, Bismarck and farther south, the warmest temperatures of spring that fisheries biologists typically see are in the Hazelton/Fort Rice area.

"Then as you go from the Hazelton area downstream toward Oahe Dam, you encounter colder, deeper water that is slower to warm up," Bailey said. "Understanding this, it’s no coincidence that you see the fishing first pick up in spring between MacLean Bottoms and the Hazelton/Fort Rice area."

Then as spring creeps into summer, the colder, deeper water in Oahe warms, as does the river much farther upstream.

"That leads to good fishing in, say, mid-June at both Washburn and Langeliers Bay due to water temperatures being right for walleye to cooperate with anglers," Bailey said. "So what anglers are seeing is the result of the temperature influence on walleye and their willingness to bite what anglers offer."

For the most part, the study has shown that the walleye between Garrison and Oahe dams are homebodies.

"Of the fish that we have tagged thus far that anglers have reported back to us, about 55 percent have moved 10 miles or less from where they were tagged," Bailey said. "The rule is that these fish aren’t moving very far, but for every rule, there are some exceptions."

For instance, some walleye tagged in the Garrison Dam area have been caught by anglers near Oahe Dam.

"While some fish have undergone large movements, as a rule walleye are not highly mobile in the Missouri River and Lake Oahe," Bailey said.

Reporting Tags

The metal jaw tags used in the study are stamped with unique numbers to identify fish, and a South Dakota phone number to report the tags. Tag information can also be registered on the tag reporting page on the Game and Fish Department’s website, or by calling 701-328-6300.

"We have to give a thanks to all anglers who’ve reported tags," said Paul Bailey, North Dakota Game and Fish Department fisheries supervisor. "A crucial component of this study is getting feedback from anglers on the tagged fish they are catching so we can gain an understanding of angling mortality, and to make sure that we have the best regulations in place for the long-term good of the fishery."

Anglers should record the date and location for tagged fish they keep or release, tag number and weight and length if the fish was measured.

Anglers who report tagged fish can keep the tag, and will receive a letter providing some history on the fish.

A small portion of the tags offer a reward to anglers. These tags are clearly marked "Reward."

Reward tags must be physically turned in to Game and Fish offices in Riverdale or Bismarck, or a Game, Fish and Parks office in South Dakota.

"We will wrap up the tagging this year, but anglers can continue to report tagged fish for years to come," Bailey said.