Scaup and coot die-off at Lake Winnibigoshish
Scaup and Coot Die-off at Lake Winnibigoshish - 2008 Update 
Update: November 5, 2008
- DNR Wildlife staff has monitored the west shore of Lake Winnibigoshish and nearby areas since late September. Eagles and other scavengers may have consumed some of the few sick or dead birds that were present earlier.
- October 21, 2008: The first reports of sick and dead scaup were received this week.
- October 26, 2008: Approximately 50 sick and a few dead scaup observed by the mouth of the Mississippi on Lake Winnibigoshish.
- October 28, 2008: Examined most of the shore of west Winnie including the mouth of Sugar Lake and Raven Flowage. Estimate about 300-400 dead scaup from mouth of Mississippi to just N. of Raven Point. Many dead and sick birds in the bulrushes. Cleaned 77 dead scaup from a stretch of the west shore S. of Raven Point. No dead coot observed in this area. Raft of 250 and a few smaller rafts of 25-50 sick scaup observed in this area.
- October 29, 2008: Few dead and sick scaup (<30) reported on Bowstring Lake. We have not observed the snails that carry the trematodes on Bowstring. Four birds were submitted to the National Wildlife Health Center in Madison, Wisconsin. A few dead or sick coots (<25) and scaup (<50) were documented on Third River flowage of Lake Winnibigoshish. The coots were submitted to Madison. Aerial surveys of Lake Winnibigoshish did not reveal large numbers of scaup, but visibility of ducks on the lake was poor.
- November 3, 2008: Check of Bowstring indicates only one potentially sick scaup, but high winds and waves make searching difficult.
- November 4, 2008: We cleaned 2 stretches of the western shore of Lake Winnibigoshish of 532 dead scaup (85% male), 2 redheads, and 1 white-winged scoter. A field necropsy of the scoter indicated no signs of being shot, snails in the gizzard, and intestinal characteristics consistent with death due to trematodes. The stretch of shoreline that was cleaned last week (Oct. 28) had 121 dead scaup compared to 77 the previous week. There were 411 dead scaup on the 0.7 mile stretch of shoreline we cleaned last year. Total losses were estimated at 1200 scaup from the mouth of the Mississippi to just N. of Raven Point. Low-level aerial checks of the Lake Winnibigoshish shoreline indicated some other areas had a few dead birds, but there were no areas where the losses were as large as the west side. We have collected and had reports of dead scaup and coots in Third River flowage, too. The relatively few sick birds that were seen in the major die-off area may indicate that losses are slowing down, although >5,000 scaup remain on potions of the lake.
The 2007 Lake Winnibigoshish Die Off
- Trematodes, a small parasitic intestinal worm, killed about 6,000-7,000 scaup and 200 coots on Lake Winnibigoshish in north central Minnesota from late October through mid-November, 2007. The vast majority of the dead scaup were lesser scaup, Aythya affinis, with a few greater scaup, Aythya marila.
- Most of the dead scaup were concentrated on the west side of the lake from the SW corner to Raven’s Point (See map at right). Coots died in Rabbit/Raven flowage, which also is on the west side of the lake.
- This was the first known occurrence of these parasites causing a scaup die-off in north central Minnesota.
The Cause
- The scaup deaths were caused by Sphaeridiotrema globulus, a small trematode less than 1 mm in length. Coots had lesions in the intestine and cecae that were consistent with intestinal trematodes. One Coot had 30 Cyathocotyle bushiensis in the ceca that was most likely the cause of death. Two other coot had Leyogonimus polyoon and S. globulus in small numbers. During snail collections this summer, we found larval stages of all 3 trematodes in the faucet snail Bithynia tentaculata. Cyathocotyle bushiensis and Sphaeridiotrema globulus can infect both scaup and coots, but L. polyoon is specific to coots and similar birds. All 3 trematodes use snails as one or both or their intermediate hosts.
- Trematodes have a complex life history and require two intermediate hosts, such as snails or aquatic insects, for the parasites to develop. When waterfowl consume the infected snails, the adult trematodes develop and then attach to the intestinal wall, causing hemorrhages and feeding on blood of the birds. Heavily infected birds appear lethargic and have difficulty diving and flying before eventually dying due to blood loss or shock.
Monitoring Activities since Last Fall
- This spring, DNR Wildlife staff from Grand Rapids monitored Winnibigoshish and other nearby lakes weekly, and noted no loss of coots or scaup during the spring migration.
- In August, parasitologists with the National Wildlife Health Center (NWHC), in cooperation from DNR staff, collected snails from several sites on Lake Winnibigoshish. We located the invasive faucet snail (Bithynia tentaculata, see picture) at several sites in Winnie. This is the same snail that is a host of the trematodes that are causing the die offs at the Upper Mississippi Fish and Wildlife Refuge. Preliminary results indicate that approximately 1/3 of the faucet snails were infected with trematode parasites. DNR Fisheries biologists helped collect snails during their trawling activities on Winnie. Staff with the Leech Lake Reservation Natural Resources Department also helped collect snails.
What is the risk to humans?
- Avian trematodes are not known to be a health risk to humans but the DNR continues to recommend that hunters not consume sick waterfowl and use standard precautions, such as wearing rubber gloves and thoroughly washing hands when cleaning waterfowl. Waterfowl should be thoroughly cooked prior to consumption.
Other Information
- Last fall, DNR staff suspected the banded mystery snail, Viviparus georgianus, might be serving as the second intermediate host. The species is native to eastern North America (not Minnesota). It is very abundant on Lake Winnibigoshish and has also been documented in many other lakes in Minnesota. The scaup examined had been eating this snail; however, NWHC staff did not find the parasite in the sample of these snails examined to date.
- We checked some sites on Bowsting Lake this fall and found many banded mystery snails, however, we did not detect any faucet snails. They could be present, but undetected.
Why does the DNR not clean up all the birds or take other actions to stop the die-off?
- Based upon information from the U.S. Geological Survey National Wildlife Health Center, cleaning up the birds will not stop the spread of this disease or reduce the magnitude of the die-off.
- Hazing, or chasing the scaup elsewhere, would not be effective at reducing the losses and may move the sick birds to other lakes.
- These are wild animals, and the parasites are not a concern for other species such as bald eagles and raccoons that are scavenging the carcasses.
What does the DNR plan to do next?
- DNR and partners developed a monitoring plan for this summer and fall.
- DNR and partners will continue to monitor Winnibigoshish and nearby lakes this fall. We will monitor the magnitude of any die off and determine if we need to take further actions.
What can you do?
- Please let us know if you find 5 or more dead or sick waterfowl or other birds. Contact your local DNR Wildlife Office. Contact information can be obtained at www.mndnr.gov/contact/locator.html or by calling 1-888-MinnDNR (1-888-646-6367).
For more information
DNR Contacts
Faucet snails found on Lake Winnibigoshish in August, 2008.
Dead scaup on Lake Winnibigoshish, November 4, 2008.
DNR Enforcement Aircraft on low-level search for scaup.
