By Nick Simonson
In the wake of zebra mussels being discovered in Lake Ashtabula earlier this summer, and presumably residing in the outflowing Sheyenne River beneath Baldhill Dam which forms the reservoir in southeastern North Dakota, serious efforts are being undertaken by the U.S. Fish and Wildlife Service (FWS) to preserve the viability of the Valley City National Fish Hatchery located along the river. As the source of the hatchery’s water is the Sheyenne, Valley City Fish Hatchery Manager Aaron Von Eschen details a number of efforts underway to prevent the tiny larvae of zebra mussels – known as veligers – from entering the facility’s rearing ponds and possibly being transported to another water via stocking efforts.
“Water will be filtrated down to a rate of 25 microns which will eliminate zebra mussel veligers and to the best of my knowledge the smallest zebra mussel veliger ever found was 39 microns, so we’re going to be well underneath that,” Von Eschen explained, adding, “and we have UV-sterilization, which does kill zebra mussel veligers.”
Zebra mussels are small mussels with distinctive stripes on their shells, native to freshwater lakes in southern Russia and Ukraine, which were introduced into the Great Lakes of North America likely through the ballast water of tankers and other ships. From there, the invasive species, with females capable of producing more than 1 million offspring each year and living for four or five years, spread to nearby waters and are now found in many lakes and rivers throughout the United States, moved around through residual water in the boats of recreational boaters and anglers. Attaching with strong filaments to nearly any substrate, zebra mussels cover and outcompete other clams and mussels to the point of extirpation of the native species in many waters. Zebra mussels have now been confirmed in lakes as far away as Texas and California. Their filtration of water removes vital micronutrients and small items from the food web for other, more desirable species, including game fish. Zebra mussels were confirmed by the North Dakota Game & Fish Department (G&F) to be in the Red River in 2010 and in Lake Ashtabula in June of this year.
The finer filtration system in place at the Valley City hatchery, which screens the water coming in from the Sheyenne River, is not cheap and reflects the real costs which the continued spread of ANS have for such facilities. The first filter set the hatchery back approximately $20,000 and it is likely to require four additional filters to ensure the water used for the hatching of fish eggs and rearing of fingerlings and fry in the ponds is a process free of zebra mussels. The $100,000 price tag does not reflect the labor and additional efforts which may be required to ensure clean water, but it is significantly less than what other hatcheries have had to pay when zebra mussels were found in their adjacent water sources. Von Eschen points to the Gavin’s Point national fish hatchery on the Missouri River near Yankton, SD as an example. The drum filter setup used by that hatchery and its related sterilization process is considerably more expensive, with installation and testing costing more than a million dollars.
“We have an idea of some of the costs we could face in the immediate future, I’m still trying to put some of the numbers together of exactly what’s going to work for us,” Von Eschen advised, adding that a better idea will be had once the G&F and FWS have completed their work and come to an understanding of how effective the filtering will be when trying to keep zebra mussels out of the hatchery.
So far it appears the remedial measures are working, as zero veligers have been found at the Valley City hatchery when the waters were sampled by the G&F. While Von Eschen is cautiously optimistic about the early results, he points to the fact that with the recent discovery, populations in the system could be very low and the lack of established zebra mussels may play a huge part in those early negative survey results. Regardless of the early success in keeping this headlining nuisance species out of the facility’s water systems, arrangements were made for all fish on hand to go to places where zebra mussels had already been detected. The stock included two million walleye fingerlings for area lakes and thousands of lake sturgeon fingerlings growing for autumn stockings in Minnesota tributaries to the Red River.
“We harvested just over two million walleyes this year out of Valley City and Baldhill, and all of them except 180,000 went back into the lake; the other 180,000 went to the Iowa DNR and they went to a zebra mussel-positive location,” Von Eschen detailed, adding that the walleyes going to Iowa were carried in water treated with a chemical which kills zebra mussel veligers, and the fish made it in good condition to their destination.
This year, the G&F stocked 1.2 million walleye fry in Lake Ashtabula, which along with the additional 1.8 million fingerlings placed back into the lake from the hatchery as a precaution, totals more than 3 million new walleyes entering the system. In comparison, 1.9 million fingerling walleyes in total were stocked in Lake Ashtabula from 2014 to 2018.
“We let [the walleyes] set for a day in a quarantine period while running that filtered, UV-sterilized water over them, potentially flushing anything out that could have come in with them as a precaution,” Von Eschen related, “we took water samples throughout our harvest process on the walleye, and after that quarantine process and from our backflush cycles on our filters, to try to determine what kind of level these things may be coming in at…we found zero zebra mussel veligers,” he concluded.
For the hatchery’s sturgeon program, the FWS has been in communication with the Minnesota DNR and is coordinating this fall’s stocking effort to target only those tributaries of the Red River which have tested positive for zebra mussels in the past. As some Minnesota tributaries of the border water have not tested positive for the invasive species, they will be excluded from this year’s stocking process and reviewed in coming seasons, as the lake sturgeon restoration program slated to end in 2022 enters its final years. The continued improvement of filtration and sterilization upgrades, the lack of any veligers or mussels in the facility’s waters currently and the testing conducted with the G&F and coordination with other agencies are helping the Valley City hatchery adapt to the new challenge zebra mussels are bringing.
“As of now, I think we’re going to wait to see what the tests tell us and what these water samples that we took will tell us,” Von Eschen stated, concluding that with the demand for stocking around the region and tighter screening processes in conjunction with the early favorable results, “I don’t think we’re going to be going out of business.”
Featured Photo: Valley City National Fish Hatchery Manager Aaron Von Eschen inspects a holding tank containing lake sturgeon fry at the Baldhill Dam facility. The hatchery has had to adjust its water filtration as a result of the NDG&F Dept. confirming the presence of zebra mussels in Lake Ashtabula upstream on the Sheyenne River. Simonson Photo.