Could an Asian carp population establish in the Great Lakes from a small introduction?

Abstract

Bighead (Hypothalmichthys nobilis) and Silver carp (Hypothalmichthys molitrix) have established populations in the Mississippi, Illinois, Missouri and Maumee rivers, and because of the hydrological connections, there is now a risk that these species may establish in the Great Lake basins. It has been suggested this risk is minimal because of the small number of fish that breach containment measures, and possible mating-finding difficulties as a consequence. Using literature data, we parameterize a stage- and river-structured population model and examine the probability of a small number of fish establishing a population in one of the Great Lakes. We find that for sexual maturity earlier than age 5, there can be a significant risk of establishment with a very small number of fish (<20) in a lake basin with 10 or fewer spawning rivers. If all fish locate spawning rivers, mating is quite probable for very few spawning rivers. The subdivision of a few spawning adults across a large number rivers does reduce the probability of successful mating, but once a threshold number of fish is reached (dependent on the number of spawning rivers and the probability of fish locating a river), then mating success is very likely. Environmental stochasticity that reduces spawning success and juvenile survival predictably reduces establishment probability, but if spawning rivers have environmental conditions that fluctuate out of phase, this impact is much reduced. As expected, the most hazardous containment breach scenario is if barriers are continually leaky, and a small number of fish are introduced into the lake basin each year. In contrast, a single introduction represents a lower risk of establishment. Overall, the model suggests that establishment is quite likely (>75 % probability) for a large number of scenarios involving a small number of founding individuals (<20 fish). We conclude that while propagule pressure does increase risk in this system, it is not the most important consideration. Instead, probable age at first maturity in a given Great Lake basin may be critical to determining risk. © 2013 Springer Science+Business Media Dordrecht.