Quantifying the Likelihood of Human-mediated Movements of Species and Pathogens: The Baitfish Pathway in Ontario as a Model System

Estimating the risk associated with species and pathogen movements involves considerable uncertainty. One key uncertainty concerns the extent and frequency of human-mediated species and pathogen movements relative to the distribution of recipient ecosystems. Baitfish use in Ontario, Canada is one of many pathways with the potential to introduce and spread biota to beyond their current geographic range. To determine the biological risk associated with baitfish use, models were used to estimate the probability of species occurrences throughout pathway levels, from the commercial harvest level, to retail tank and angler purchases, to movement and release by the end-user (i.e., the angler). Vector activity, as the primary contributor of species movements and introductions associated with this pathway, was modeled within a spatial interaction framework that incorporated landscape structure (e.g., the distribution of angling populations, lake size and sportfish richness, and their physical separation via least-cost routing of transportation networks) to predict the extent of movement. Agent-based models of vector activity were used to relate vector movements to region-specific probability thresholds of risk activity. Model outputs were used to estimate the movement and introduction of species and pathogens to lake ecosystems resulting from a variety of infection scenarios. Species results identified a pronounced reduction in the probability of non-target species occurrences throughout pathway levels. However, the occurrence of biological invaders and other non-target fishes at retail levels implied incidental bycatch throughout the pathway. Relatively short, frequent vector movements associated with incidentally purchased species were very likely, yet would not contribute to species range expansions due to the homogeneity of biological communities at those levels. However, rarer, yet considerably lengthier, vector movements associated with key species and pathogens implied the potential for low-probability, long-distance species and pathogen movements resulting from human activities.Ph