Type E Botulism and Birds

The Great Lakes Have Become a Toxic Place for Fish Eating Birds

Nov 2, 2006

Invasive species of mussel and fish in the Great Lakes are fostering an increase in Type E botulism with a devastating impact on fish eating birds.

At the bottom of Lake Ontario, and all of the other Great Lakes, deadly Type E botulinum toxin is brewing: mats of zebra mussels and quagga mussels filter the water and create ideal conditions for production of the poison. Both of these mussels are invasive species, brought in with the ballast water of ships and discharged into the water of the North American Great Lakes. Both are doing well in an environment lacking effective predators – they are changing the ecology surrounding them.

One of the effects of their filtering activity is that oxygen in the water and mud around them is depleted, creating an ideal environment for anaerobic bacteria, bacteria that thrive in the absence of oxygen. One of these bacteria is Clostridium botulinum, the organism that produces botulinum toxin.

A few birds eat quagga and zebra mussels, but the main predator of these rapidly spreading mussel species is a fish – the round goby, another introduced species. The round goby, native to Europe, was first noticed in the Great Lakes in the early 1990s, and has since spread to all of the Great Lakes and into connecting rivers and streams. The goby cannot keep up with the mussels, but it can overwhelm native fish species and it can pass the botulinum toxin on to fish eating birds.

And that’s exactly what it’s doing. Since 1999, large epidemics of Type E botulism have been increasing in fish eating birds of the Great Lakes. In 2002, 25,000 birds died on the waters and shores of Lake Erie alone. This year, 2006, birds have been dying since July and the death toll continues to rise. Loons are particularly hard hit, along with mergansers, grebes, gulls, and shore birds. Fish are dying too, though even apparently healthy fish can contain the toxin. Many avian outbreaks are associated with obvious fish kills.

A bird suffering from botulism intoxication cannot fly or walk and often cannot hold its head up. In severe cases, the bird becomes completely paralyzed though it remains conscious. Some come ashore to die, while others die on the water and wash ashore later. When a bird has ingested a lethal dose of botulinum toxin, little can be done.

Clostridium botulinum is a ubiquitous organism that is found in soil and water all over the world. It emerges as a cause of botulism from time to time when conditions are right – cases of human botulism are predominantly caused by Types A, B, and E, but seven types, A through G, are recognized. It seems that environmental changes in the Great Lakes region, brought about by introduced species, are making conditions right for Type E botulism more and more often. The future looks grim for fish eating wild birds that rely on this area for their food supply.