ASSESSING THE EFFECTS OF CULVERTS ON STREAM AMPHIBIANS
Winsor H. Lowe
Division of Biological Sciences
The University of Montana
Missoula, MT 59802
winsor.lowe@umontana.edu
406-243-4375
Objectives
This project will compare multiple methods for assessing the effects of culverts on stream amphibians.
Specifically, I will use extensive occupancy surveys, intensive mark-recapture sampling, and genetic
parentage analyses to investigate the effects of three culvert types on the distribution and movement
patterns of stream salamanders in Montana and Idaho. This project will not only quantify the impact of
culverts on these species, but also compare the efficiency of the methods themselves to inform other
monitoring efforts.
Focal species
This study will assess the effects of culverts on stream salamanders in the Lolo and Clearwater National
Forests of western Montana and eastern Idaho. The focal species will be the Idaho giant salamander,
Dicamptodon aterrimus. D. aterrimus occurs in mesic forests of northern Idaho and western Montana.
Dicamptodon aterrimus is facultatively paedomorphic: larvae develop in streams and reach maturation
after several years as either terrestrial or aquatic forms. Our observations in the field suggest that D.
aterrimus are present in headwater and higher-order reaches.
Scope of work
PHASE 1
OCCUPANCY SURVEY: These surveys will be conducted in 25 first-order streams in each region.
These will be paired surveys in 100-m long reaches located above and below culverts. I will also sample
reaches in streams without culverts. Sampling methods will be standardized at all sites to allow across-site
comparisons and modeling, and streams will be visited in random order three times during each of the two
field seasons (June-August). Using the data from these surveys, I will test the hypothesis that occupancy
is lower at sites above culverts than at sites below culverts. I will also test for an effect of culvert type on
occupancy. I predict that occupancy at upstream sites will be highest in streams without culverts,
followed by streams with natual culverts, followed by unimproved culverts. These results would indicate
that culverts affect stream salamander distribution by reducing movement to upstream sites.
MARK-RECAPTURE SURVEYS: At a subset of 6 streams where occupancy is sampled (2 with natural
culverts, 2 with d culverts, 2 without culverts), I will conduct intensive mark-recapture surveys at
downstream and upstream reaches. Mark-recapture surveys will be conducted monthly during each of the
two field seasons. I will use a cover-controlled active search method in these surveys, and each
salamander encountered during surveys will be marked individually with fluorescent elastomer. These
marks are retained throughout the life of animals. With the mark-recapture data, I will be able to quantify
rates of movement between reaches (through culverts or natural reaches), as well as rates of survival and
recruitment within each reach. With these estimates, I will test the prediction that rates of between-reach
movement are highest in streams without culverts, followed by streams with natural culverts, followed by
unimproved culverts.
PARENTAGE ANALYSIS: At six sites in the study region, I will also conduct parentage analysis, a
genetic method for assessing road-stream crossings. I believe this project is an important opportunity to
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assess the viability of this method for stream amphibians, especially because the samples needed for this
analysis could easily be collected during the occupancy and mark-recapture surveys described above.
Parentage analysis is currently being used to assess road-stream crossings in eastern brook trout and
appears to be both viable and economical for that species. If a similar assessment can be conducted for
stream amphibians, it may be possible to develop standardized tissue sampling protocols that can be used
to monitor road-stream crossing in both amphibians and fish – the two major groups of stream vertebrates
throughout North America. This multi-taxon approach would be far more economical than the taxonspecific methods currently being developed.
I will assess gene flow between downstream and upstream sites by assigning year-1 larvae to marked
parents based on microsatellite genotypes. Microsatellite diversity is high in D. atterimus, and markrecapture data indicate that few adults reproduce in each year – both of which increase the feasibility of
these methods. These genetic analyses will be conducted in the same subset of 6 stream in each region
used for mark-recapture surveys. Data from these analyses will allow me to quantify movement of year-1
larvae through culverts and natural reaches using low-impact genetic sampling techniques. Again here, I
expect movement of year-1 larvae between reaches to be highest in streams without culverts, followed by
streams with natural culverts, then streams with unimproved culverts.
PHASE 2
If funds become available beyond the $81,994 committed to this project by the USDA Forest Service, I
will apply these same methods to streams in New Hampshire’s White Mountain National Forest, where
similar culvert-improvement projects are underway. In New Hampshire, the focal species will be the
spring salamander, Gyrinophilus porphyriticus. G. porphyriticus belongs to the family Plethodontidae, the
lungless salamanders. This species is found in small, cool, well-oxygenated streams along the
Appalachain uplift, from Alabama to southern Quebec. Larvae are strictly aquatic and the larval period is
3-5 years. Adults are highly aquatic and maximum age is estimated to be 14 years. In daytime surveys,
larvae and adults are found beneath rocks and wood in the stream and along the wetted edge.
All three methods – occupancy surveys, mark-recapture surveys, and parentage analysis – are feasible for
G. porphyriticus, and I have worked on that species in New Hampshire for the last 12 years. A regional
comparison such as this (i.e., D. aterrimus in Montana / Idaho vs. G. porphyriticus in New Hampshire)
would be very valuable for developing national passage-monitoring protocols for stream amphibians.
Furthermore, differences in stream fish communities in the two regions (multiple migratory and nonmigratory salmonids in the Montana / Idaho vs. brook trout [Salvelinus fontinalis] in the New Hampshire)
may affect how stream amphibians move through culverts. For example, predator refuges within culverts
may promote dispersal by G. porphyriticus, but prevent dispersal by D. aterrimus. These culvert ×
predator interactive effects can only be revealed in multi-region studies.
By coordinating with Keith Nislow, my collaborator at the USDA Forest Service Northeastern Research
Station, I could replicate this study in New Hampshire for the same cost as the Montana / Idaho phase
($81,994).
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