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

approximately 14°C”. These temperatures, 9-14°C ar e ideal for migrating salmon
smolts, and raises increased concern for the predation of smolt during migration. If
an Atlantic salmon population exists all migrating smolts may pass through areas
where pike have congregated. As pike dispersal tends to occur in a downstream
manner (Casselman, conference call March 13, 2009), this perpetuates the risk of
pike predation on smolts as new pike populations become established throughout
the down stream salmon migration corridor. This could also be the case if pike
populations established themselves up a river system, which has been the case in
Alaskan rivers and streams (Dave Rutz, Alaska Department of Fish and Game
Division of Sport Fish, e-mail conversation with Tim Obrey, Regional Fisheries
Biologist Moosehead Lake Region Maine Inland Fisheries and Wildlife, March 20,
2009).
Returning adult salmon have presumably reached a size, which in general has
excluded them from being prey for juvenile and sub-adult pike. If a substantial pike
population persists, larger adult pike could pose a threat to one sea winter and some
two-sea winter adult salmon, in estuaries, head ponds and bogin areas leading to
summer thermal refugia or spawning shoals. This migration may pose a threat to
returning salmon when larger pike are seeking food sources.
Potential Habitat Model for Northern Pike
General
Northern pike are distributed throughout much of the northern hemisphere, including
North America and Eurasia (Brautigam 2001). They are not native in Maine or the
rest of New England except in Lake Champlain in western Vermont.
Northern pike can tolerate a wide range of environmental conditions but are primarily
a cool-water species best adapted to shallow (< 12 m), productive, mesotrophiceutrophic
environments (Brautigam 2001; Casselman and Lewis 1996). Pike
generally become well established in habitats that are relatively shallow and contain
abundant emergent wetland and submerged aquatic vegetation, which is needed for
spawning, nursery and for juvenile and adult foraging habitat. Pike can occur in
oligotrophic waters, but more commonly inhabit mesotrophic or borderline eutrophic
lakes and ponds (Inskip 1982). They are known to tolerate brackish water
conditions (salinities less than 7 ppt).
Northern pike show age-based and seasonal shifts in habitat. As northern pike
mature, their vegetation preference changes from emergent wetland for fry to
emergent wetland and aquatic macrophytes (submerged and floating) for juveniles
to submerged aquatic vegetation for adults (Casselman and Lewis 1996). They
typically occur in shallow water in the spring and fall, and seek relatively deeper
water during the height of the summer and in winter in response to environmental
conditions. During the summer, northern pike will seek cooler temperatures when
water temperature exceeds 20°C and are physiologica l impacted (lose of weight) at
surface temperature above 25°C (Casselman and Lewis 1996). In winter, northern
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