Hey Jimmer,
I'm wondering if Botulism Type E may be a potential culprit. I'm hoping not though...
I found this on the net when I googled Goby die offs:
"Field investigations have suggested that the die-offs observed in Lake Huron may be the result of botulism type E poisoning. Toxins from the bacterium Clostridium botulinum and specifically Type E botulism, which is found in fish-eating birds in the Great Lakes, cause these die-offs. The botulism toxin is produced in the absence of oxygen and with suitable temperature and nutrient conditions. It remains unclear which factors trigger the bacterium to produce the neurotoxin and the ensuing fish and wildlife die-offs.
Species commonly found during die-off events include: Freshwater Drum (Sheepshead), Smallmouth Bass, Rock Bass, Round Gobies, and Channel Catfish. Bird species include Loons, Cormorants, Mergansers, Gulls and other waterbirds. It is suspected that zebra and quagga mussels are ingesting the botulinum bacteria (invertebrates are not affected by botulism).
Round gobies are known to heavily feed on mussels; therefore, they are thought to be ingesting the bacteria. Native fish species such as those commonly associated with the die-off are starting to feed primarily on the round goby; thus, they become affected by botulism. This movement of botulism is believed to be leading to the fish die-offs commonly observed along Lake Huron."