Location: Kill started between Keosauqua and Bentonsport (distance of 8 miles). The exact location of the start of the kill was not observed. For purposes of this investigation the Highway J40 bridge at Bentonsport is assumed the starting location. The kill was tracked to Keokuk, Iowa. The kill zone ended at St Francisville, MO.
Cause of Kill: Attributed to high water temperatures associated with relatively low flows and high daily temperatures. Research conducted at the time by Ryan Hupfeld (presently of the Iowa DNR, Fisheries Bureau) after the similar kill that occurred in 2012 supports this determination.
Responsible Party: No immediate party is known to be directly responsible. Alterations to stream flow during high water temperatures may represent a stressor that is indirectly contributing to these mortality events.
Fish Killed:
Only Shovelnose Sturgeon were affected in this kill. A total of 4,099 Shovelnose Sturgeon were killed in the 28 mile zone from near Bentonsport, IA to St Francisville, MO. Replacement costs of these fish values are as listed in AFS Special Publication 35. Please note that AFS replacement cost guidelines For Shovelnose Sturgeon >13” are assessed on a bulk weight basis. These fish are valued at $154.20 / lbs. The mean length of fish involved in this kill was 23.3 inches and the mean weight was 1.94 lbs. / fish. Each fish is given a value of $299.15 for replacement. Total fish losses then are 4,099 Shovelnose Sturgeon with a replacement cost of $1,226,215.85.
Additional Comments:
The kill was reported by Richard Daugherty, Director of the Van Buren County Conservation Board at 1:00 PM on 8/28/24. Field Office 6 has been informed. Mark Flammang was on site in Ottumwa by 2:30 PM and worked his way down stream at each bridge crossing.
Methods: Specific procedures for enumeration of dead fish and the associated value of those fish can be referenced in “Investigation and Monetary Values of Fish and Freshwater Mussel Kills” (American Fisheries Society, Special Publication 35). A total of 14 Stratum I locations (50 yard segments above and below the influence of road bridges) were identified and 28 Stratum II sites (100 yard segments above and below the Stratum I sites) were identified in the kill zone. Subsamples were obtained from five Stratum 1 sites and five Stratum II sites. All estimates are based on expansion of these subsamples.
Water quality parameters were collected at six locations in the kill area. Data included water temperature and dissolved oxygen. Oxygen concentration routinely exceeded 20 ppm with high levels of saturation recorded at all sites. Water temperature ranged from a low of 85.4°F and a high of 90.1°F in the affected zone.
Freshly dead fish were rare. Most fish observed appeared to be dead for at least 24 hours. The kill may be ongoing and will be evaluated on a daily basis.
Flows in the lower Des Moines River basin have been high for several months and have only dropped below 10,000 cfs within the last few weeks. At that point, the hydropower project at Red Rock Lake resumed its hydropeaking operations. Figure 1 and 2 demonstrate the seven-day discharge pattern below the Red Rock facility and at Keosauqua, near the fish kill origination site. The effects of hydropeaking are seen downstream at Keosauqua, delayed by approximately 24 hours from Pella. While these changes in daily discharge cannot be directly tied to sturgeon mortality at this time, changes in daily water temperature accompanying these daily fluctuations in flow should be investigated.
