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

Human-Caused Introductions
Background
There are three primary pathways for northern pike: human-caused introduction; natural
dispersal through volitional movement; and natural dispersal through non-volitional
movement. Human-caused introductions are intentional or non-intentional introductions
of northern pike by people. Natural dispersal through volition movement are
introductions that occur when northern pike disperse to other locations through
connected waterways. Natural dispersal through non-volitional movement are
introductions by other natural means, such as the transport of fish by raptors to water
bodies that may not have been connected to the waterbody of origin. The record of
northern pike discovery was analyzed to determine: 1) the pattern of introduction and
dispersal; 2) the rate for introductions and dispersal through these introductions; and 3)
the annual probability of an introduction through either pathway.
The discovery record is a historic account of the year that northern pike were
discovered in a lake or river. The introduction pathway is most often unobservable so it
is difficult to be entirely certain of the pathway or the period it took to discovery the
population (Costello and Solow 2003; Solow and Costello 2004). Nevertheless,
methods have been developed to model the discovery record to provide insight on the
process of introduction. This analysis is limited to human-caused and natural dispersal
through volitional movement and assumes that natural dispersal through non-volitional
movement (transport by birds) is a minor contribution to northern pike dispersal.
Method
The discovery record was developed from the MDIFW database used to track northern
pike introductions (M. Gallagher, January 2008). The database includes the lake (and
coordinate location); year of discovery; whether the introduction was confirmed by a
reliable source; and a MDIFW judgment on whether pike are present in the lake. The
discovery records were categorized based on the reliability (high, medium and low).
High reliability means that MDIFW determined that pike presence was likely and
confirmed; medium reliability was that presence was likely but pike were not confirmed;
and low reliability was unknown presence and confirmation. Only the records with high
and medium reliability were used in the analysis (Table 7).
The pathway for each discovery record was classified as either introduced or dispersal
by examining the hydrological characteristics of the lake and determining whether it was
isolated (first recorded occurrence in a watershed, geologically isolated through
glaciation, or located at a watershed terminus); whether a downstream barrier existed
that may prevent pike from migrating upstream; and what sources of pike were either
upstream or downstream of the lake. An assumption was made that the year of
discovery reflected the actual order of introduction or dispersal so that the discovery
past discoveries only influence the dispersal pattern.
All records were classified even if the pathway was unclear. In the Cobbosseecontee
and Messalonskee Stream watersheds pike were discovered and confirmed in many of
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