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

of coho, chinook and sockeye salmon, rainbow trout, and Arctic grayling now contain
only northern pike.
Studies in lake ecosystems have shown negative effects on the native top predators.
In Sweden, northern pike replaced artic char (Salvelinus alpinus) as top predator
after invasion by a combination of predation and competition (Bystrom et al. 2007).
The study also reported a possible extinction of char and increases in zooplankton
and benthos. He and Kitchell (1990) documented changes after an experimental
northern pike introduction into a lake that was previously piscivore free. Changes
occurring in the fish community after northern pike introduction ranged from
decreased prey fish biomass, decreased abundance of dominant species and
decreased mean size for species most vulnerable to predation (He and Kitchell
1990). In a similar experiment, Findlay et al. (2005) reported that a non-native
northern pike introduction into a small boreal lake resulted in one native species
(Semotilus magariscus) was extirpated and another native species (Perca
flavescens) declined in abundance.
Native Species Habitat and Diet Preferences
Brook Trout -Stream populations: It has been well documented that brook trout
prefer cool water. Baldwin (1956) reported that optimum growth rates occurred
around 16.5 o C. Bonney (2006) reports the upper lethal temperature limit for brook
trout at 25 o C. Resident stream populations of wild/native brook trout will spawn in
shallow gravel areas of headwater streams. The spawning material may vary from
fine sand to coarse, loose gravel and rubble (Everhart 1976). Brook trout prefer
substrates that also are influenced with spring upwellings. Young of the year brook
trout are typically located in shallow gravel riffle areas of these streams throughout
the summer months and in areas around springs. Griffith (1972) reports that streamdwelling
juvenile brook trout prefer low water velocities (0.03 to 0.08 feet/second).
As stream resident brook trout reach older ages, they tend to prefer deeper habitats.
Bonney (2006) notes that adult fish tend to migrate to pools in late summer and late
winter and that pool habitat is critical to brook trout survival in periods of low water
and high water temperature. MacMillian (1998) also reports that predator marks
increased in frequency on brook trout crowded into pools during periods of warm
temperatures.
Brook Trout - Lake populations: Brook trout inhabit ponds and lakes in Maine with a
wide range of physical and biological characteristics. The vast majority of remaining
wild and native populations are located in the northern and western regions of the
state. Brook trout were distributed over the entire state prior to European settlement.
Since this time, habitat degradation associated with development and the
introduction of exotic species has greatly diminished the range of wild/native brook
trout in southern and eastern Maine. Most of the brook trout fisheries in these
impacted areas are supported entirely by stocking programs.
Brook trout in lakes and ponds typically inhabit littoral habitat during most times of
the year. Brook trout abundance is often related to the amount of littoral habitat in
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