Concerns about a number of dead fish observed at McLaren Dam could be alarming, but can often be expected in the summer, says a biologist from Alberta Fish and Wildlife.
A Drumheller Mail reader alerted the paper to occurrence of fish discovered dead on the McLaren Dam in Starland County. The dam is a popular destination for anglers and was stocked this year by Alberta Sustainable Resources Development with 12,000 rainbow trout.
Vance Buchwald senior fisheries biologist for Alberta Fish and Wildlife confirms they have also received calls about the fish.
“We have had reports from anglers there are dead fish there and a number of fish ponds,” said Buchwald. “It is associated with anytime we get an extended period of hot weather. The fish can die in the hot weather or as soon as we get a cold spell.”
He explains there are a couple reasons associated with warm weather that can cause fish to die. He says warmer temperature weakens the water’s ability to sustain dissolved oxygen. He says the warmer weather also encourages algae growth. As the algae grows, it can deplete the nutrients it needs, and die out. Similarly, when the hot snap ends, and the water cools, it can also kill off large amounts of algae.
“That is a stress on the fish,” he says. “When the algae dies it uses up oxygen as they decompose. The other thing that can happen is in the daytime plants produce oxygen, and in the nighttime, use up oxygen. The other thing that can happen is you can have high oxygen in the day time, but in the nighttime when there is a large plant biomass, it can use up the oxygen and can kill the fish.”
He says they have not taken any water samples to measure dissolved oxygen content as often by the time they take the sample the levels are back to normal, and the results are inconclusive. He does say this phenomenon is typical in ponds in Alberta.
“You have to remember, being a small pond out in the prairie, it is not the normal habitat for rainbow trout,” said Buchwald. “Some people tend to forget that. These fish dying out in ponds like that because normally they are found in pristine waters in the east slopes.”
Having said that, he explains rainbow trout are a good fish for stocking purposes because they are relatively easy to reproduce in large numbers, and when not faced with poor conditions, they are hardy and grow fast. They are also popular for fisherman.
He says now that the peak heat of the summer may have passed, summer kill conditions have likely passed as well.