A fish kill affecting adult rainbow smelt is ongoing in portions of the upper half of Lake Sakakawea, according to Dave Fryda, Missouri River System fisheries supervisor for the North Dakota Game and Fish Department. Fryda said the cause of the die-off has been documented numerous times in North Dakota in the past. “The vast majority of the dead and dying smelt have physical signs of Columnaris bacteria,” said Fryda. “We’ve recovered infected fish from White Earth Bay downstream to Deepwater Bay and Van Hook Arm.”
Columnaris bacteria are present in all water bodies and outbreaks typically occur when rapid water temperature changes occur at a time when the fish are stressed, such as after spawning. “The smelt recently spawned in Lake Sakakawea, and were recovering from that stress when we experienced near record-high temperatures last week which boosted the water temperature in the shallow bays where the smelt spawned,” Fryda added. Smelt affected by Columnaris often develop visible skin irritations that have the appearance of fuzz or mold. Although there is no known cause for concern when in physical contact with these fish, the department suggests to leave the fish alone.
Lake Sakakawea has not had a widespread smelt die-off since the mid- to late 1980s, a time when the overall smelt population was very high. Fryda said the current smelt population is the highest it’s been for decades, so that is likely part of the reason the bacteria has spread over such a wide area. The overall significance of this year’s die-off will likely be minimal, however, Fryda said the effects on the population won’t be known until later this summer when fisheries crews assess the adult smelt population.
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