Heyvaert and his associates describe this as a process of cold condensation. Analyses of crayfish and Mackinaws in the lake show that they are accumulating mercury as they age, and much of that mercury is in the methyl form. Fortunately, concentrations in both fall below health standards. According to UC-Davis researcher, Sudeep Chandra, crayfish have higher concentrations of mercury compared to Mackinaw. Crayfish accumulate mercury by feeding in the sediments.
Mackinaw accumulate mercury by eating other critters, such as crayfish.
But Mackinaw now seem to prefer shrimp to crayfish. So they aren't accumulating as much mercury as they would by eating crayfish. On the other hand, Chandra notes that bass are now living in the Keys. Bass do eat crayfish, so there's a potential that they could accumulate mercury. And, it seems that bass could also find a home in Lake Tahoe and proliferate.