What Are the Odds? Factors Influencing Potential Asian Carp Migration Past the CSSC Fish Barrier

摘要

An electrical barrier system within the Chicago Sanitary and Ship Canal (CSSC) is considered to be critical to restraining the migration of invasive Asian carp species from the Illinois River system to Lake Michigan. The system as constructed consists of three separate barriers capable of generating electric fields meant to either immobilize or dissuade individual fish from swimming upstream. To this point there is no evidence that Asian carp have been able to successfully traverse this barrier, but studies indicate that previous operational settings may have been ineffective to prevent the movement of some fishes. This paper uses risk assessment methodologies such as event trees and the development of subjective probabilities to investigate the potential means by which fish would be able to travel upstream through the barriers and thereby access Lake Michigan and the Great Lakes. This analysis indicates that some of the foreseeable failure mechanisms are much less likely than others to occur, allowing managers to focus on addressing the more likely mechanisms. Another significant factor is that although adult fish are likely to be at least occasionally present at the barrier, it is believed that juvenile fish are not yet able to reach that location. Even though juvenile fish passing through the barrier are far less likely to establish a reproducing population than would the same number of adult fish, consideration of differential barrier effectiveness on juvenile fish suggests that a shift in operating strategies may be warranted in the future should juvenile fish be detected further upstream.