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

5.0 DISCUSSION
5.1
Under the existing conditions, it appears that it is theoretically possible for
northern pike to access the West Branch Penobscot drainage by way of East Branch
Lake. Pike established in the Piscataquis/Seboeis drainage would be able to ascend East
Branch Seboeis Stream to the outlet of the lake where the crib work of an abandoned dam
forms a partial barrier under low flow conditions. Under flow conditions found in this
survey, a pike would need to swim upstream against the riffle flow, then leap a 0.4 ft
hydraulic jump at the crib work. Bell (1990) gives the maximum darting speed of a 14inch
pike as 4 ft/sec., which is less than the observed velocity of the riffle immediately
below the lake outlet. This suggests that most pike would have a difficult time ascending
the riffle to the cribbing. At lower outflows, the velocity may be reduced, but channel
depth would also be reduced, which may also inhibit the ability of a pike to ascend the
riffle and complete a leap over the cribbing. However under spring run-off conditions
this barrier may be sufficiently submerged to briefly enable free swim passage upstream
to the lake.
East Branch Lake
Northern pike from East Branch Lake would next need to traverse downstream
via the unnamed stream to the north to enter the West Branch drainage via Nollesemic
Lake. This outlet stream appears to be impassible for adult-sized pike due to the
preponderance of wetland, blow down thickets and shallow braids, which limits
downstream passage to only shallow and interstitial channel routes. However it is
possible that young of year or juveniles produced by a breeding population of East
Branch Lake pike could be sufficiently small to potentially pass downstream through
these obstacles and thus colonize Nollesemic Lake.
We conclude that if pike were to become established in East Branch Lake, there is
potential for the species to eventually colonize their way downstream toward the West
Branch if juvenile fish traverse the un-named brook. Although the probability of this
occurring appears relatively low, it cannot be ruled out. Therefore, if a future fish barrier
solution is deemed justified, strategic options include construction of a barrier at a
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