Print PageShipping within the Great Lakes is considered an important vector for the spread of invasive species, though it has rarely been quantified. We have built three alternative spatial models in ArcGIS to identify the possible role shipping has played in spreading an invasive species, viral hemorrhagic septicemia virus (VHSv), within the Great Lakes. VHSv is a fish disease that has caused several outbreaks within the Great Lakes in the past couple of years. Each model consists of a long-distance spread component, via ships, and local spread from the point of infection. The random model randomly selects six points/yr within the Great Lakes as VHSv infection points. The random ballast water discharge model selects six ballast water discharge points/yr. The nonrandom ballast water discharge model selects discharge locations based on a binomial distribution with the probability of infection being the percent of discharge received and the number of trials being the number of boats discharging at the port. The local spread simulates the spread of the disease via water and infected fish. We used known locations of VHSv outbreaks to compare the results of our models.
Results/Conclusions
The random model with a local spread of 10-km was least effective at predicting past reported VHSv occurrences (15.6%), and the random discharge model with a 20-km local spread was most accurate (59.1%). Our results suggest that within lake shipping play an important role in spreading invasive species, including VHSv.
