The Iowa Department of Natural Resources (DNR) was notified on July 10 of a fish kill on the lower Des Moines River.
DNR staff from the Fisheries Bureau investigated and found an estimated 20,000 dead shovelnose sturgeon in a 60 mile river stretch from near Ottumwa to Farmington in southeast Iowa. Freshly dead fish collected on July 11 were submitted to Iowa State University for testing.
The investigation began with determining the start and end of the fish kill. DNR fisheries staff collected water temperatures and dissolved oxygen levels at nine locations along the fish kill path and sampled for ammonia. Using the American Fisheries Society (AFS) guidelines, staff started counting dead fish at bridge accesses and then expanded their count to free-flowing areas.
“We didn’t find low levels of dissolved oxygen or high levels of ammonia which is usually indicative of some sort of spill, so it comes down to high water temperatures coupled with the low flows that we are experiencing at present. Water temperatures are in the upper 80s and exceed levels known to cause shovelnose sturgeon mortality,” said Mark Flammang, Iowa DNR fisheries biologist. “It was also limited to shovelnose sturgeon; no other species were impacted.”
Shovelnose sturgeon are relatively abundant below Ottumwa, as many of these fish move from the Mississippi River into this section of the Des Moines River during the spring and summer. “Ottumwa has one of the largest populations of shovelnose sturgeon in the world,” explains Flammang.
The shovelnose sturgeon population is a unique resource in the Des Moines River. “Many of these fish are over 40 years old. It will take several years to repopulate this long-living fish,” Flammang said.
This section of the Des Moines River has had sizable fish kills over the years caused by low water levels and high water temperatures, with the most recent in 2012. DNR fisheries staff partnered with Missouri Conservation to research the cause of that kill and learn more about the effects to shovelnose sturgeon populations.
