That's based on reports from the general scientific community. There actually have been two plant species reported in the last year; we're not sure if they're established or not. But that number for 2006 is for ballast-mediated species. The last species that was thought to have been brought in by ballast water was reported in 2006.
There is not a comprehensive monitoring program to sample all ports in the Great Lakes. This is based on what all the people who are out there doing the work are finding.
It's also based on our four lines of evidence, where we've sampled ballast water coming in from ships, identified what's in there, and looked at the effectiveness of the ballast water programs. With those four lines of evidence, we're able to comfortably say that the risk from ballast water has been reduced.