CSI Cheesman: The mystery of the missing shrimp

Introduced in 1971 to boost the fish population, the shrimp appear to have vanished. And that might be a good thing.

October 19, 2016 | By: Tyler St. John
Ben Galloway prepares test equipment to collect eDNA, genetic markers in the shrimp’s DNA, from sediment in Cheesman Reservoir.
Ben Galloway prepares test equipment to collect eDNA, genetic markers in the shrimp’s DNA, from sediment in Cheesman Reservoir.

What happened to the shrimp?

In August, four researchers played detective on the waters of Cheesman Reservoir, dunking tubes, nets and various sensors below the surface and pulling up mud and algae. The team, from the Fisheries Ecology Laboratory at Colorado State University, was investigating the mysterious disappearance of the Mysis shrimp.

The shrimp are considered an invasive species in Colorado. First introduced into Kootenay Lake in British Columbia in 1949, the little creatures actually boosted the native fish population. The experiment was so successful that the shrimp were introduced to upwards of 400 more lakes in the world, including Cheesman Reservoir in 1971.

Fast-forward to 2013, when someone finally asked, “How are the shrimp doing in all of these waters?” That’s where the CSU team came in. They set out to test all of the waters in Colorado known to have the shrimp, but once they reached Cheesman, they couldn’t find a single one.

So what happened?

One possible culprit has left behind a number of footprints. Scattered throughout the otherwise beautiful landscape surrounding Cheesman are giant swaths of burned trees, bleak reminders of the Hayman Fire of 2002, the most devastating wildfire in Colorado’s history.

“If the fire wiped out the shrimp, the question is how?” said Doug Silver, a research associate with the Fisheries Ecology Laboratory. To find out, the researchers took soil core samples from the bottom of the reservoir by dropping a heavy tube down and pulling up sediment. To test the fire hypothesis, they will look for charcoal in the different layers of mud to determine if it came from the fire.

The researchers performed a second test by identifying genetic markers in the shrimp’s DNA, called eDNA. “If you get out of the bathtub, you still leave your DNA in the water,” Silver explained.

By taking samples from different levels of sediment, the team will be able to tell when the shrimp went missing, and from there they may be able to conclude the most likely cause.

Disappearing Mysis shrimp will help trout.
The disappearance of Mysis shrimp may end up helping Colorado’s trout population. Photo credit: NTNU, Flickr Creative Commons

The results of their work won’t be available for another three months or so, but the disappearance of the shrimp may turn out to be a good thing. At Cheesman, the shrimp were actually competing with the trout for zooplankton: their primary source of food. Now that the shrimp are gone, the fish populations should thrive.

So why bother to solve the mystery?

“We want to know about anything that alters environmental conditions,” said Brandon Ransom, Denver Water’s manager of recreation. “We try to be really good stewards of resources. That includes plants and animals, as well as water.”

If something that had been flourishing for more than 30 years suddenly disappears, Denver Water wants to know why, he said.

“This is why we are involved with wildlife research. The more we know about forest health and the ramifications of wildfires, the more we can be preventative instead of reactive.”

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