METHODS
Upstream extent of Brook Trout, change in distribution from 2005 to
2007 and presence of potential physical barrier in each Hubbard Brook
tributary were measured during fish surveys in 2005, 2006 and 2007.
Methods below are from Warren et al. 2008.
Electrofishing surveys in 2005, 2006, and 2007 were conducted using a
modified version of methods in Latterell et al. (2003). Fish
presence/absence was recorded using a backpack electroshocker with a
field crew of two people. In 2005, each tributary was surveyed in an
upstream direction from its confluence with the mainstem until fish
were no longer observed. Surveys were conducted a minimum of 100 m
past the last fish observed to be sure that fish were not present
further upstream. The distance upstream from the mainstem was measured
with a field tape to the nearest of the 100-m markers that were
established during the 2001 valley-wide surveys (Likens and Buso
2006). The 2006 electrofishing surveys were initiated at least 150 m
downstream from the furthest extent of fish found in that tributary
during the previous year, then surveys were continued upstream using
the same methods as in 2005. In all cases, fish were encountered when
initiating surveys in 2006. The 2007 surveys were conducted beginning
at the confluence with the mainstem for each stream. All major
tributaries within the Hubbard Brook watershed were surveyed in 2007.
After we surveyed a minimum of 100 m past the last fish observed, we
returned to the point where the last fish was observed and
qualitatively evaluated stream characteristics at that point. We noted
if there were cascades, waterfalls, stream sections with very steep
gradients, a lack of water, or “unknown barriers.” We noted an
“unknown barrier” when fish were absent beyond a given point in the
stream with no obvious physical limits to upstream distributions. This
category included cases where the last fish was located below a
cascade of a size comparable to other cascades in that system, which
had clearly been passable for fish to reach that point. Potential
physical barriers to fish movement were documented and included
waterfalls or a series of two or three large cascades that reached
heights of 2 m or more over a short distance and with no pools below
from which fish could jump (e.g., Zig-Zag Brook). In some cases,
individual barriers were not large but cascades or granite
outcroppings were frequent, leading to a consistent high gradient
reach (e.g., Falls Brook). In other streams, a lack of water was
clearly limiting upstream distributions, and in these cases, we noted
that “streambeds were dry.”
Likens, Gene E, and D. C Buso. 2006. Variation In Streamwater
Chemistry Throughout The Hubbard Brook Valley. Biogeochemistry 78:1-30
Warren, D. R., G. E. Likens, D. C. Buso and C. E. Kraft. 2008. Status
and Distribution of Fish in an Acid-impacted Watershed of the
Northeastern United States (Hubbard Brook, NH) Northeastern Naturalist
15(3):375-390. https://doi.org/10.1656/1092-6194-15.3.375
