Operational Plan for the Restoration of Diadromous Fishes to the ...

occurs at a lower mean rate (1.15 introductions per year) than humancaused
introduction (2.63 introductions per year).
b. There is a high probability that one or more annual introductions will occur
by either pathway. The annual probability of one or more human-caused
introductions is very high ( ρ =0.93). The annual probability for one or
more natural dispersals is also moderately high ( ρ =0.68). When
comparing the two probabilities, the probability of having one or more
introductions is 31% higher through human-caused introductions than
under natural dispersal.
c. Human-caused introductions are more likely to result in multiple
introductions in one year than introductions through natural dispersal. The
probability of three or more introductions in one year is 0.49 for humancaused
introductions in contrast to a probability of 0.11 for natural
dispersal. This higher probability may arise from the mechanism of
dispersal. Human-caused introductions can occur through a watershed in
watersheds that are disassociated from those that contain northern pike.
Introductions through natural dispersal occur in watersheds where pike
are found and more likely to occur in habitat adjacent to or downstream of
existing populations (J. Casselman, personal communication, March 13,
2009).
d. Both pathways pose a risk for introduction of northern pike, however
human-caused introductions pose a greater risk. They have a very low
probability of resulting in no introductions in any one year, they have a
much higher mean rate of introduction, they have a much higher
probability of multiple introductions in one year, and they can result in
introductions in watersheds removed from those watersheds with
populations of northern pike.
PRFP Page 250