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

equirements between the two species. Predation of salmon by pike could be a
factor at habitat edges, for example at points where riffle tail waters into a pool or
dead water section of stream. Foraging competition would likely be insignificant
where juvenile pike and salmon populations to exist in close proximity to one
another.
Juvenile salmon migrate from streams to lakes at age 1 to 3 years old
(smoltification) and may be vulnerable to predation by adult pike if the migration
route involves long stretches of dead water suitable for adult pike. Likewise, juvenile
salmon will be vulnerable to predation by pike in the lake until they reach an
adequate size to escape being eaten. However, even adult salmon in Long Pond,
Maine have been observed to have scars presumed to be from Northern pike.
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. Adverse interactions between juvenile life stages of the two species, either
through competition for resources or through predation is low, as lake trout utilize
deeper areas of lakes beginning at a very young age, while young pike prefer
shallow vegetated waters. Likewise, adult lake trout prefer much deeper water
depth’s than pike during the summer, so little interaction would be expected during
that time of year. Pike may compete with lake trout for forage. As with salmon, lake
trout prefer smelt when available, and may grow poorly if smelt are limited supply.
Lake trout are a slow growing; therefore they may be vulnerable to predation for a
longer time period than other salmonids.
At the youngest juvenile life stages of Atlantic salmon and northern pike, there is no
evidence for potential habitat overlap. Both species require very specialized habitats
for growth and survival. Juvenile pike generally require “increase of water depth by
approximately 10cm deep for every week after peak spawning, until fish reach
150mm in length” (Casselman, 1995), which tends to be the opposite of salmon and
will further distinguish habitat preferences.
During the smolt stage, pike may pose the greatest threat. At this time, all young of
year (YOY) pike (>150mm) as well as sub-adults have reached a size where the
average smolt size is within the prey size range for pike (Hart and Hamrin 1988,
Nilsson and Brönmark 1999, Vehanen 2004). With the onset of spring, longer days
and warmer waters stimulate mature pike to congregate near river and stream inlets
in preparation for spawning. At this time, salmon smolts may be at the greatest risk,
since they are going through physiological changes preparing them for a down river
migration through many varying habitats. In these river corridors, waters have
typically reached temperatures above 9°C (Casselman , 1978) where increases in
juvenile NP swimming activity occur; temperatures less than this and below 6°C
show less sign of swimming activity. Adult NP show “rapid somatic growth at
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