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

Summary of Ecological Risk
Introductions of large, top-predators such as northern pike (Esox lucius) negatively
affect resident fish communities by disrupting normal feeding behavior (Bystrom et
al. 2007), decreasing prey biomass and abundance (He and Kitchell 1990; Findlay et
al. 2005) and through extirpation of native species (Findlay et al. 2005; Bystrom et
al. 2007). Since 1985, the number of northern pike waters has increased from six to
49 (with 17 expected and one extirpated) statewide (Lucas 2008), representing
72,789 acres in lake surface area. Invasions or introductions of top predators into
new ecosystems have been shown to have negative effects on native top predators
and dramatic cascading effects on lower trophic levels (Vander Zanden et al. 2004).
Several studies have attributed large losses of stocked and migrating salmonids to
pike predation in riverine ecosystems.
A barrier to pike in the existing fishway at the Browns Mill Project in South Dover
would protect approximately 80% of the stocked salmonid area from the
establishment of pike through natural dispersal.
Pike are known to prefer soft-rayed fish as forage (Petrvozvanskiy 1988; Hakanson
2002), including stocked salmonids, and therefore, it is likely that there will be
impacts on the stocked brook trout fisheries in these river systems. Since young
pike do occasionally occur in small streams that have a source of coldwater and they
prefer soft-rayed fish there could be impacts at the local level for wild trout
populations, through direct predation or competition for thermal refuge.
There is considerable niche overlap between northern pike and brook trout in
lacustrine habitat. Both prefer the littoral zone and both may seek cool water during
the warmest periods of the summer. Direct predation is possible in situations where
pike and brook trout occupy the same areas, as well as competition for forage, such
as minnow species and rainbow smelts.
The potential for northern pike to adversely impact landlocked salmon populations is
higher in lakes than in rivers and streams primarily because of the differing habitat
requirements between the two species. Predation of salmon by pike could be a
factor at habitat edges. In addition, juvenile salmon may be vulnerable to predation
by adult pike if the migration route involves long stretches of dead water suitable for
adult pike or in the lake until they reach an adequate size to escape being eaten.
Competition for forage may exist between salmon and pike in lakes, particularly if
forage is limited resulting in a situation where both species are relying heavily upon
rainbow smelt.
The impact of Northern pike on populations of lake trout (togue) will likely be low, as
togue thrive in oligotrophic lakes and Northern pike tend to do better in mesotrophic
lakes.
At the youngest juvenile life stages of Atlantic salmon and northern pike, there is no
evidence for potential habitat overlap. With the onset of spring, longer days and
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