Waterfowl succumb to botulism outbreak in the Great Lakes
Monroe, Mich. — At least 1,000 loons fell to botulism (Clostridium botulinum) Type E this past fall again along Lake Michigan, along with thousands of other water birds. Great Lakes state, provincial, U.S. and Canadian federal biologists are saying recent outbreaks in all of the Great Lakes can be traced to ecosystem changes caused by invasive zebra and quagga mussels and delivered through consumption of gobies.
Two forms of botulism, Type C and E, has been reported from the Great Lakes since as early as 1941 in Lake Erie and 1963 in Lake Michigan respectively.
Botulism Type C was first seen in Monroe, Michigan in the Erie Marshes in 1941 and has occurred in other marshes ever since and lately in Put-in-Bay Harbor.
Puddle ducks are initially poisoned by feeding on aquatic vegetation and sediments that harbor the bacteria. Symptoms-including wing, leg, neck, eyelid, then lung paralysis develop and birds begin often die by drowning or exposure to the elements or predators.
Dead carcasses attract flies and as healthy ducks and also gulls consume maggots that emerge. As few as five maggots can kill another duck since they concentrate the toxin, while being unaffected themselves.
Only after temperatures decrease do bacteria colony counts decline for the year. Picking up all dead carcasses and disposing of them properly helps dramatically reduce the number of affected birds.
According to a presentation given in a 2008 botulism workshop by Michigan DNR, the first recorded cases of botulism Type E in the Great Lakes was in 1963 along the east shore of Lake Michigan, when approximately 3,300 loons were documented.
Botulism Type E involves a few more steps in the food chain, but ends with the deaths of diving ducks and other fish-eating birds such as loons, gulls, mergansers, grebes, and also fish, turtles, mudpuppies and in some documented cases, mammals.
Ever since zebra mussels, then quagga mussels invaded the Great Lakes in the late 1980s, the water clarity has become much clearer as a result of their filtering. Increased water clarity allows deeper sunlight penetration, resulting in higher populations of aquatic vegetation and warmer sediments.
Dying plants and algae falling onto the sediments allow these bacteria to multiply in anaerobic (oxygen-free) conditions. They are initially consumed by protozoa, then larger invertebrates (animals without backbones) such as aquatic worms and insect larvae and when sediments are ingested by zebra and quagga mussels.
When gobies and other bottom-feeding fish eat this small prey when the bacteria are present in high concentrations, they are sickened and become slow-moving targets for the fish-eating birds, which in turn become stricken. Symptoms of
Type E mimic those of Type C mentioned above.
The following year, another 3,570 fell ill on the northern shoreline. In 1965 and 1966 the same area, plus Saginaw Bay in Lake Huron, saw a small outbreak, resulting in less than 100 total loon deaths combined.
Things were quiet until 1976 when some 592 loons washed onto the east shoreline of Lake Michigan again. In 1981, 13 dead loons were counted near Whitefish Point on Lake Superior, then 592 again on the north shore of Lake Michigan in 1983.
In 1999, birds were infected again in Lake Huron and for the first time in Lake Erie. In 2000, 18 species of water birds, 20 species of fish, three species of turtles, mudpuppies, a raccoon and an opossum were documented.
In 2003, Lake Ontario was the last lake to join the club, and had another outbreak the following year.
In the years since, there have been almost annual outbreaks of various intensities somewhere in the Great Lakes, with especially high counts in Lake Michigan again in 2006 and in 2007 when all but Lake Superior had outbreaks.
It is likely that we will continue to see outbreaks of botulism for a long time to come, due to changes in the lakes that allow conditions favorable to the bacteria to persist.
Clearer and lower water will allow deeper plant production and warmer sediments. Warmer sediments support more bacteria colonies. Thicker piles of decaying submersed plants and algae will continue to allow dead zones in the sediments to persist and enlarge. Because of the expanding dead zone, fewer scuds and mayflies remain to stir the sediments.
Affected in 2012 were about 1,000 loons as they migrated around the Lake Superior and Lake Michigan shorelines. Hundreds were collected and counted at Sleeping Dunes National Seashore and near the towns of Charlevoix, Manistique, and Gulliver to name a few.
Determining the full effect of these outbreaks is difficult to assess, because many die offshore and may, depending upon prevailing wind direction, either be washed onto the shorelines or drift further away and never be counted.
Because the older loons are the first to migrate, they appear to have taken the highest losses. Juvenile loons migrate later, often after the outbreak subsides. The loss of breeding age loons is particularly harmful to their population because of the low number of offspring they produce each summer, usually only one or two chicks. This may allow the reversal of population rebounds enjoyed prior to the heavy tolls suffered beginning in the late 1990s.
Botulism Type A and Type B are the ones sometimes associated with improperly canned food and can often prove deadly. Type C does not usually cause symptoms in humans, according to Canadian Health Department bulletins. Some fatalities from Type E occurred in the 1960s from smoked fish, according to a New York Sea Grant Fact Sheet.
Anglers and hunters are urged to avoid eating any fish or waterfowl during botulism outbreaks that appear to be sick or reluctant to flee from danger. Thorough cooking helps, but does not assure their safety for human consumption.
In affected areas, even with healthy looking game, wear rubber gloves when handling or field dressing fish and waterfowl, being careful not to allow any meat to be contaminated by the entrails, which should be properly disposed with the carcass as described below. Disinfect knives and cutting boards after they are used.
Citizens who want to help stop the outbreak can do so by picking up dead animals off the beaches using rubber gloves and properly disposing of them.
Proper disposal includes double wrapping carcasses in plastic trash bags for placement at a secure landfill or incineration to keep them away from further consumption by scavengers. At the end of the job, dispose of the rubber gloves as well.