Casey Carp May Be Caput

Casey Lake Update - Winter 2013

Partners: Local citizens, City of North St. Paul, U of MN, DNR, and the RWMWD

By: Bill Bartodziej

U of MN researchers measuring a
carp caught via electrofishing.

The Watershed has been fortunate to be able to partner with the Sorensen Lab, U of MN, to study common carp in the Phalen Chain of Lakes. The ultimate goal of this work is to reduce levels of carp to a point where this invasive species is no longer causing water quality problems. So how does this fish affect water quality? Well, carp forage on the lake bottom for food, mainly targeting aquatic insects and plant parts. This feeding action stirs up the lake sediments which releases phosphorus into the water. Carp also excrete phosphorus as they digest their lake bottom morsels. Phosphorus is a food source for all plants, and too much phosphorus in lakes causes algal blooms. Large algal blooms will turn lake water green.

 

Over the last five years, the common carp population in Casey Lake has been studied in great detail. We learned that Casey supported an extremely high biomass (weight) of carp, estimated at over 500 pounds per acre. Carp biomass above 100 pounds per acre is considered detrimental to lakes. Last year, a lot of effort was invested into reducing the carp population in Casey. In terms of management, this is important for two reasons. First off, Casey can be thought of as a carp nursery area for the entire Phalen Chain of Lakes. We have learned that fish in Casey can move down the watershed during high water conditions and populate other lakes. Secondly, it is very plausible that the high numbers of carp in Casey is linked to poor water quality. Without carp, there is a good chance that Casey will experience better water quality and a more balanced ecological system.       

Activity	Number harvested	Total weight estimate (lbs)
February - netting (10’x50’ open water area)	1,617	1,446
March - Dead fish collection from shore (ice out)	900	2,250
April - Commercial netting (entire lake)	189	50
Summer electro-fishing and other	327	435
July - Box netting (baited trap)	142	189
TOTALS=	3,175	4,370

  

In November 2012, Casey’s water level was lowered by opening a valve in the lake’s outlet pipe. This water level draw down was done in order to make repairs to the outlet pipe. As a result of previous maintenance work, the pipe settled at an angle and needed to be modified slightly. The outlet pipe valve will be closed in late February of this year. Casey’s water level will remain at or near its current elevation until the spring of 2013, where snowmelt and spring rains will naturally refill the lake.

A side benefit of lowering the lake’s water level is that it allows the lake water to freeze almost entirely, and thereby greatly reducing the amount of water that carp typically use to survive through the winter. Lake level drawdowns are sometimes used as a fish management tool. Last month, watershed staff drilled over 100 holes in the ice to monitor water depth on Casey (see map below). Drilling was concentrated in deeper areas of the lake where water pockets may exist.

The map indicates points on Casey Lake where holes were drilled in the ice to look for
open pockets of water where carp may be surviving the winter.

This year’s drawdown resulted in a very effective reduction of water in this system. We detected small (< 25 sq. ft.) pockets of water in several locations, but water depth was less than a few inches. We did not see any evidence of fish, of any species, taking refuge in these pockets of water. Additionally, the U of MN research team located four radio-tagged carp in four separate areas of the lake (skull and crossbones on map above). These fish were frozen in the ice sheet.



RWMWD intern Tracy augering a hole on Casey. She found
 seven inches of ice and saturated, muddy lake bottom
substrate underneath.

These findings suggest that this year’s water level drawdown, coupled with normal winter temperatures, resulted in very minimal open water refuge areas for carp. Watershed staff and the U of MN research team are optimistic that a majority of carp in this system will not survive through the winter. If a lot of carp wash up on shore after ice-out, the Watershed will assemble a cleanup team. An electro-fishing survey in spring will determine if any carp did somehow make it through these extremely tough conditions.

In December 2012, the City of North St. Paul passed a resolution supporting the management of Casey Lake. The council voted unanimously to move forward with the management approach that was outlined in the council workshop by the U of MN carp research team and Watershed staff (December 4th, 2012). The following is a summary of the plan which was covered in the resolution:

Casey Management Plan Outline – 2013

• Water level drawdown to adjust outlet pipe – in progress, RWMWD
• Carp treatment – January or February – (Note: not necessary due to the lack of an open water refuge)
• Spring carp survey to determine treatment effectiveness – U of MN
• If deemed effective, DNR will stock bluegill this spring.
• Aeration system installation – late summer/fall – DNR, City, RWMWD
• If carp numbers are found to be high in spring, then a piscicide (a substance used to kill fish) will be considered for a fall, 2013 treatment. Bluegill stocking would then be postponed until spring 2014. 
• All parties will continue communication at each step of the management process.

Overall, our working goals for Casey Lake are focused on improving water quality through reducing carp densities. Without carp, it is likely that aquatic plant populations will increase. This will add to ecosystem stability and improve fish and wildlife habitat. Quality sport fishing (bluegill and bass) opportunities will be provided through DNR stocking and aeration. Also, bluegill eat carp eggs, and this will work to keep this invasive species at low levels.   

Soon after ice-out, the U of MN research team and Watershed staff will be electro-fishing Casey in search of the common carp. Please stay tuned this spring for a full report of our results and other findings!

U of MN researchers electrofish on the Phalen Chain of Lakes