Smelt die-off no cause for alarm

Something has been smelling fishy lately in the North Arm of Rainy Lake and it’s not going to go away just yet.
Over the past week, reports have been coming in about the absence of seagulls around Mine Centre while, at the same time, there has been a huge influx in the North Arm.
Meanwhile, other reports indicated a disturbing number of dead and dying smelt washing ashore in the same location.
Is something wrong with our beautiful lake? Apparently not, says the Ministry of Natural Resources.
“This is an annual event,” MNR area biologist Darryl McLeod said yesterday. “It’s just later than usual.”
McLeod noted everything is late this year, including the peak of the summer thermocline, which triggers this event.
He said smelt are a cold-water fish that are more commonly found in lakes deeper and colder than Rainy. In fact, they are not even indigenous to this area.
“They are classified as an exotic species,” McLeod remarked. “That’s why this is not exactly a bad thing.
“We don’t have any data to suggest it’s any worse this year than in past years,” he added.
McLeod said the presence of smelt was first confirmed in Rainy Lake in 1990 and since then, they have established themselves well. However, the lake is not ideally suited to their needs.
The problem for the smelt is what McLeod refers to as “thermal stratification.”
During the summer months, the upper layer of the lake is warmed by the sun to a temperature that is dangerous to smelt. Therefore, they are forced to seek refuge in the cooler depths.
Trouble occurs at the area called the thermocline—a barrier that effectively separates the two layers.
As the summer progresses, the thermocline gradually is pushed deeper and the shrinking lower level gradually becomes depleted of oxygen. The upper level, on the other hand, is continuously oxygenated by surface winds.
This leaves the smelt with a Hobson’s Choice—either remain in the cool depths and suffocate or migrate to the warmer water and risk death by heat stress.
The fish that are native to Rainy Lake do not face this dilemma because they are tolerant of a wider range of temperatures.
McLeod said the situation should resolve itself in the next week or so when the “turnover” occurs.
This event happens twice a year (once in the spring and again in the fall) when the temperature spread between the upper and lower levels begins to narrow to the point where the lake literally turns over—bringing nutrient-rich water from the depths to the surface and sending oxygen-rich surface water down.
When that occurs, the smelt once again will be fine until late next summer. And since they are so prolific, McLeod thinks there is no danger they will disappear.

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