carptracker

Well, the DNA is loose in the water, from sluffed off cells of the fish, especially from within the digestive tract of the fish. River water is a soup of fish DNA, it seems, and all kinds of other DNA. But we can take a sample of only a few liters, filter it out, and test for genetic barcodes specific to an individual species, once you have generated and identified those barcodes. In theory, ballast water could be taken on downstream, transported upstream, and released, in effect transferring the DNA with it. But there is VERY LITTLE ballasting going on in the barges and tows, even before the new regs. There are some barges that leak pretty darn bad, and conceivably those could move some dna. But overall, the pattern of hits does not seem like they are likely to be the result of anything but actual fish. Any one particular sample could be an anomaly that results from something other than a fish, but multiple hits in the observed pattern - doubt it. But remember that any SINGLE hit, like the one in the Lake, is more suspect than the project as a whole. There are lunatics out there that might even be throwing dead fish or fish guts around. This would not probably provide the pattern we have observed, but any single hit could be an anomaly that is not a fish. And remember that we have NO idea how to interpret these data into numbers of fish.