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Susitna‐Watana Hydroelectric Project Document
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Title:
Aquatic furbearer abundance and habitat use, Study plan Section 10.11,
2014-2015 Study Implementation Report SuWa 289
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ABR, Inc. - Environmental Research & Services
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November 2015; Study Completion and 2014/2015 Implementation Reports
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Series (ARLIS‐assigned report number):
Susitna-Watana Hydroelectric Project document number 289
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[Anchorage : Alaska Energy Authority, 2015]
Date published:
October 2015
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Alaska Energy Authority
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Study plan Section 10.11
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iii, 22 pages
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Notes:
All reports in the Susitna‐Watana Hydroelectric Project Document series include an ARLIS‐
produced cover page and an ARLIS‐assigned number for uniformity and citability. All reports
are posted online at http://www.arlis.org/resources/susitna‐watana/
Susitna–Watana Hydroelectric Project
(FERC No. 14241)
Aquatic Furbearer Abundance and Habitat Use
Study Plan Section 10.11
2014–2015 Study Implementation Report
Prepared for
Alaska Energy Authority
Prepared by
ABR, Inc.—Environmental Research & Services
Fairbanks, Alaska
October 2015
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TABLE OF CONTENTS
1. Introduction ............................................................................................................................ 1
2. Study Objectives .................................................................................................................... 1
3. Study Area .............................................................................................................................. 2
4. Methods and Variances ......................................................................................................... 3
4.1. Beaver and Muskrat Surveys ......................................................................................... 3
4.1.1. Variances ................................................................................................................. 4
4.2. River Otter and Mink Surveys ....................................................................................... 4
4.2.1. Variances ................................................................................................................. 5
4.3. Information for Mercury Assessment ............................................................................ 6
4.3.1. Variances ................................................................................................................. 6
5. Results ..................................................................................................................................... 6
5.1. Beaver and Muskrat ....................................................................................................... 6
5.2. River Otter and Mink ..................................................................................................... 8
5.2.1. Incidental Observations .......................................................................................... 8
5.2.2. Aerial Surveys ......................................................................................................... 8
5.3. Information for Mercury Assessment ............................................................................ 9
6. Discussion ............................................................................................................................... 9
6.1. Beaver and Muskrat ....................................................................................................... 9
6.2. River Otter and Mink ................................................................................................... 10
6.3. Information for Mercury Assessment .......................................................................... 11
7. Conclusions ........................................................................................................................... 11
7.1. Modifications to Study Plan ......................................................................................... 11
8. Literature Cited ................................................................................................................... 12
9. Tables .................................................................................................................................... 13
10. Figures .................................................................................................................................. 17
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LIST OF TABLES
Table 5-1. Server Location and File Names for the Field Data for Aquatic Furbearers Collected
in 2013–2015. ............................................................................................................................... 13
Table 5.1-1. Number and Percentage of Beaver Colonies, by General Location and Activity
Level, October 2013. ..................................................................................................................... 13
Table 5.1-2. Number and Density of Active Beaver Colonies (Colonies/km²), by General
Location, October 2013 and 2014. ................................................................................................ 14
Table 5.1-3. Number and Minimum Overwinter Survival of Active Beaver Colonies, by General
Location, 2013. ............................................................................................................................. 15
Table 5.1-4. Number and Percentage of Beaver Colonies, by General Location and Activity
Level, October 2014. ..................................................................................................................... 15
Table 5.2-1. Location and number of river otter tracks observed during three aerial surveys
conducted March–December 2014. .............................................................................................. 16
LIST OF FIGURES
Figure 3-1. Aquatic Furbearer Study Area. .................................................................................. 18
Figure 5.1-1. Beaver Colony Locations, October 2013. ............................................................... 19
Figure 5.1-2. Beaver Colony Locations, October 2014. ............................................................... 20
Figure 5.1-3. Locations of Muskrats, River Otters, and Mink Observed Incidentally during Other
Project Surveys in 2012–2014. ..................................................................................................... 21
Figure 5.2-1. Results of Three River Otter and Mink Track Surveys Conducted March, April, and
December 2014. ............................................................................................................................ 22
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LIST OF ACRONYMS, ABBREVIATIONS, AND DEFINITIONS
Abbreviation Definition
ADF&G Alaska Department of Fish and Game
AEA Alaska Energy Authority
APA Alaska Power Authority
FERC Federal Energy Regulatory Commission
GIS Geographic Information System
GPS Geographic Positioning System
ILP Integrated Licensing Process
ISR Initial Study Report
Project Susitna-Watana Hydroelectric Project
RSP Revised Study Plan
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1. INTRODUCTION
This Aquatic Furbearer Abundance and Habitat Use Study, Section 10.11 of the Revised Study
Plan (RSP) approved by the Federal Energy Regulatory Commission (FERC) for the Susitna-
Watana Hydroelectric Project, FERC Project No. 14241, focuses on: estimating the number and
distribution of active and inactive beaver lodges in the area and assessing their overwinter
survival; locating winter tracks of river otter and mink to assess their relative numbers,
distribution, and habitat associations during winter; and identifying muskrat pushups to assess
muskrat distribution.
A summary of the development of this study, together with the Alaska Energy Authority’s
(AEA) implementation of it through the 2013 study season, appears in Part A, Section 1 of the
Initial Study Report (ISR) filed with FERC in June 2014 (ABR 2014a). As required under
FERC’s regulations for the Integrated Licensing Process (ILP), the ISR describes AEA’s
“overall progress in implementing the study plan and schedule and the data collected, including
an explanation of any variance from the study plan and schedule” (18 CFR 5.15(c)(1)).
Since filing the ISR in June 2014, AEA has continued to implement the FERC-approved plan for
the Aquatic Furbearer Abundance and Habitat Use Study. For example, researchers:
On October 21, 2014, AEA held an ISR meeting for the Aquatic Furbearer Abundance and
Habitat Use Study, along with meetings for each of the other wildlife studies.
Conducted a second aerial survey for beaver lodges in fall 2014;
Assessed overwinter survival of beaver lodges with aerial surveys conducted in spring
2014 and 2015;
Conducted two aerial surveys for river otter and mink tracks in late winter 2014;
Conducted one aerial survey for river otter and mink tracks in December 2014; and
Deployed modified snares in late winter 2014 to snag hair samples from river otters for
analysis of mercury content.
In furtherance of the next round of ISR meetings and FERC’s SPD expected in 2016, this report
describes AEA’s overall progress in implementing the Aquatic Furbearer Abundance and Habitat
Use Study prior to October 2015. Rather than a comprehensive reporting of all field work, data
collection, and data analysis since the beginning of AEA’s study program, this report is intended
to supplement and update the information presented in Part A of ISR 10.11 through September
2015. It describes the methods and results of the study efforts in 2014–2015, and includes a
discussion of the results obtained to date.
2. STUDY OBJECTIVES
The goal of the Aquatic Furbearer Abundance and Habitat Use Study (hereafter, the Aquatic
Furbearer Study) is to collect baseline data on aquatic furbearers in the study area to enable
assessment of potential Project-related impacts. This information will be used to develop
appropriate mitigation measures.
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Five specific objectives were established in RSP Section 10.11.1:
1) Delineate the distribution and estimate the current population size of beavers.
2) Describe the distribution and relative abundance of river otters, mink, and muskrats.
3) Describe habitat associations of aquatic furbearers.
4) Review available information on food habits and diets of piscivorous furbearers (river otter
and mink) as background for Study 5.7, Mercury Assessment and Potential for
Bioaccumulation.
5) Collect hair samples from river otters and mink to characterize baseline tissue levels of
mercury for Study 5.7, Mercury Assessment and Potential for Bioaccumulation.
As described in ISR 10.11, Part C, Section 7.1.2 (ABR 2014b), AEA has removed objectives and
methods related to mercury analysis of piscivorous furbearers (river otter and mink; RSP
Sections 10.11.1 and 10.11.4.3) and consolidated this work under Study 5.7, Mercury
Assessment and Potential for Bioaccumulation, including the literature review of food habits and
diets of river otters and mink (Objective 4) and the collection of hair samples for laboratory
analysis of mercury levels (Objective 5).
3. STUDY AREA
As established by RSP Section 10.11.3, the study area for aquatic furbearers varies according to
the species being surveyed. Beavers were surveyed in the riparian study area from the reservoir
inundation zone downstream to the confluence of the Susitna and Chulitna rivers, as well as in
other portions of the Project area. Muskrat surveys are restricted to water bodies and wetland areas
in the Project area, including the reservoir inundation zone. In addition to covering all portions of
the Project area, winter track and transect surveys for river otters and mink focus on the stream
survey area, consisting of the mainstem Susitna River above the dam site and on tributary streams
draining into the reservoir inundation zone, as well as on similar river and tributary stretches
immediately downstream from the dam site. Stream surveys extend upstream along tributaries at
least 3 miles (Figure 3-1) and north-south transects cover non-riparian areas in this zone to provide
comparative data on the extent of use of those drainages and upland areas in comparison with the
Susitna mainstem.
As described in the ISR Overview (Section 1.4) filed in June 2014 and subsequently the
Proposal to Eliminate the Chulitna Corridor from Further Study filed with FERC on September
17, 2014, AEA explained that it had decided to pursue the study of an additional alternative
north-south corridor alignment for transmission and access from the dam site to the Denali
Highway, referred to as the “Denali East Corridor Option,” and to eliminate the Chulitna
Corridor from further study. This change to the study area affected the Aquatic Furbearer Study
area as follows: beaver surveys were dropped in the Chulitna Corridor and added in the Denali
East Corridor after the first year of study, and river otter and mink surveys were similarly
changed in December 2014 (affecting a single survey).
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4. METHODS AND VARIANCES
The methods implemented for each of the Aquatic Furbearer Study components are described in
this section, along with explanations of variances from the Study Plan, where necessary.
4.1. Beaver and Muskrat Surveys
AEA implemented the methods described in the Study Plan (RSP Section 10.11.4.1), with the
exception of the variances explained below (Section 4.1.1).
The study team flew aerial surveys to assess the distribution and abundance of beaver colonies in
the Middle Susitna River Segment below the proposed dam site and in the Project area (reservoir
inundation zone, dam and camp facilities area, and access road and transmission line corridors)
and to assess overwinter colony survival. The fall surveys of the beaver study area were conducted
in a small piston-engine helicopter (Robinson R-44) in October 2013 and September–October
2014. Surveys were scheduled after deciduous trees had shed leaves but before most water bodies
froze. Active beaver colonies were indicated by lodges with fresh food caches nearby, consisting
of small-diameter trees and saplings, typically with leaves still attached, that had been cut and
stored underwater (Hay 1958, Payne 1981). Inactive colonies were noted as well, as indicated by
the lack of fresh caches near lodges or by the proximity of old caches lacking fresh cuttings from
the current season. The surveys were conducted in two phases to account for elevational and
latitudinal differences in the timing of leaf fall and ice formation. The portions of the study area at
higher elevations (Denali West corridor and part of the Chulitna Corridor in 2013; and the Denali
East and West corridors, dam/camp facility area, and inundation zone in 2014) were surveyed on
October 1–2, 2013 and September 26–27, 2014 and the remainder of the study area was surveyed
on October 9–10, 2013 and October 8–9, 2014. The locations of beaver lodges were recorded and
mapped using a handheld Global Positioning System (GPS) receiver.
Beaver lodges that were determined to be active during fall surveys were resurveyed during early
spring to estimate rates of overwinter survival of beaver colonies. The surveys were conducted in
a small piston-engine helicopter (Robinson R-44). Spring beaver surveys were conducted on May
2, 2014 and April 29 and May 17, 2015. We attempted to time the surveys for periods when there
was open water around the lodges, but still snow on the ground. The 2015 surveys were conducted
on two different days to adjust for widely varying dates of snowmelt between low elevations areas
along the Susitna River and Gold Creek Corridor and higher elevation areas along the Denali East
and West corridors, dam and camp facility area, and in the reservoir zone. The observer looked for
signs of recent beaver activity such as tracks, recently chewed sticks, or recent cuttings on nearby
trees and shrubs. Because signs of recent activity are not always apparent, the calculated
overwinter survival rates were considered to be minimum rates and the actual rate was expected
to be higher.
Although the planned aerial surveys of muskrat “pushups” (feeding structures consisting of small,
seasonally temporary domes of vegetation debris and mud pushed up through holes or cracks in
the ice cover of water bodies; Erb and Perry 2003) were not conducted in 2013–2015 (see Section
4.1.1 below), the presence of muskrats and muskrat pushups was recorded and mapped by
researchers conducting aerial surveys for other Project studies (Study 10.14, Surveys of Eagles
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and Other Raptors; Study 10.15, Waterbird Migration, Breeding, and Habitat Use; Study 10.16,
Landbird and Shorebird Migration, Breeding, and Habitat Use).
4.1.1. Variances
The downstream beaver survey area in the Middle Susitna River Segment that was sampled in
October 2013 and 2014 was somewhat wider in the southern end than was proposed in RSP Section
10.11.3 (as depicted in RSP Figure 10.11-1). The reason for this expansion was that the survey
area was aligned with the riverine physiography area, which was delineated for the Riparian
Vegetation Study Downstream of the Proposed Susitna-Watana Dam (Study 11.6), after
preparation of the Study Plan. As a result of using this refined survey area, more potential beaver
habitat was covered than was originally included in the Study Plan, providing a greater volume of
data to use in addressing the study objectives. The study area also changed after the first year of
beaver studies when the Chulitna Corridor was dropped from the Project and the Denali East
Corridor was added.
The unusually late spring, persistent deep snow cover, and delayed melt of snow and ice in 2013
led the study team to postpone and then cancel the aerial survey of muskrat pushups, which had
been planned for April (RSP Sections 10.11.4.1 and 10.11.6) for consistency with similar surveys
conducted in late winter 1980 for the Alaska Power Authority’s Susitna Hydroelectric Project
(APA Project) (Gipson et al. 1982). The intent of RSP Section 10.11.4.1 was to conduct the
muskrat survey before aerial surveys began for other wildlife studies. The same water bodies that
would have been surveyed for this study were covered by researchers conducting aerial surveys
for other Project studies (primarily spring migration surveys of waterbirds, but also nest occupancy
surveys of raptor nests). Hence, the presence of muskrat pushups in 2013, and again in 2014, was
instead recorded during spring surveys of waterbirds and raptors, which were conducted in the
appropriate time frame (spring melt) for identifying muskrat pushups. Several incidental sightings
of muskrats also were provided by researchers conducting point-count surveys of landbirds and
shorebirds. Aerial surveys specifically targeting muskrats were not conducted in spring 2014 or
2015. The incidental sightings in 2013 and 2014 provided useful information on the distribution
and relative abundance of muskrats in and near the study area, which, when combined with data
to be collected during the next survey, are expected to enable the study team to achieve the study
objective for this species.
4.2. River Otter and Mink Surveys
AEA implemented the survey methods proposed in the Study Plan for river otters and mink (RSP
Section 10.11.4.2), with the exception of the variances explained below in Section 4.2.1.
Although the planned aerial surveys of river otters and mink were not conducted in 2013, sightings
of river otters and the locations of river otter and mink tracks were recorded and mapped during
three aerial transect surveys conducted in February, March, and April 2013 and two aerial surveys
conducted in February and March 2014 for the study of Terrestrial Furbearer Abundance and
Habitat Use (see ISR Study 10.10). In addition, researchers conducting surveys for other Project
studies in 2013–2014 (Study 9.5, Fish Distribution and Abundance in the Upper Susitna River;
Study 9.6, Fish Distribution and Abundance in the Middle and Lower Susitna River; Study 9.7,
Salmon Escapement; Study 10.14, Surveys of Eagles and Other Raptors; 10.15, Waterbird
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Migration, Breeding, and Habitat Use; 10.16 Landbird and Shorebird Migration, Breeding, and
Habitat Use) also provided data from incidental observations of river otters.
Aerial surveys for river otter and mink tracks were conducted as described in the study plan on
March 7–8, April 10–11, and December 6–8, 2014 in a small piston-engine helicopter (Robinson
R-44) with a pilot and one observer. The survey crew followed the borders of the Chulitna, Denali
East and West, and Gold Creek corridors (the Denali East corridor was added and the Chulitna
corridor was dropped for the December 2014 survey), followed the courses of the Susitna River
and its tributary streams extending upstream 3 miles (5 kilometers) from the Susitna River, and
surveyed straight-line north–south transects spaced 3 miles apart across the survey area within 3
miles of the inundation zone. The surveys were conducted within 3 days of a snowstorm and
observed tracks were recorded as new (after the recent snowfall) or old (prior to the recent
snowfall). Locations where tracks crossed the survey transects were recorded with a handheld
GPS, and in most cases, the helicopter followed the tracks until they could no longer be followed
(e.g., entered thick vegetative cover or went under river ice) or they left the survey area. These
track segments were recorded with a handheld GPS and brought into a GIS for map production.
Some otter groups may have made more than one of these tracks segments, nonetheless, individual
track segments were considered to be from individual river otter groups for the purpose of data
summaries. The frequency of observing tracks (tracks segments/km) along transects was
calculated in different survey areas to determine where river otter tracks were most commonly
observed.
4.2.1. Variances
Aerial surveys of river otter and mink tracks were not conducted as planned in late winter 2013
(two or three surveys following fresh snowfall in February–early April; RSP Section 10.11.4.2).
The survey planned for early winter (November/December) 2013 was not conducted due to
logistical difficulties encountered in trying to match a suitable weather window (within three days
of fresh snowfall) with pilot and aircraft availability. Despite the lack of dedicated surveys in 2013,
the study team was able to compile incidental observations of river otters, river otter tracks, and
mink tracks in and near the study area recorded by researchers conducting surveys for the other
Project studies described above (Section 4.2).
Two late winter surveys were conducted in spring 2014 as outlined in the study plan (two or three
surveys following fresh snowfall in February–early April; RSP Section 10.11.4.2) and one early
winter was conducted in 2014 as outlined in the study plan (at least one per year in
November/December; RSP Section 10.11.4.2). The study area also changed after the first two
aerial surveys when the Chulitna Corridor was dropped from the project and the Denali East
Corridor was added, therefore only one aerial survey of the Denali East Corridor has been
completed at this time. However, by using a combination of the December 2014 survey, incidental
observations, and additional future surveys, the objectives of this study component will be met.
The combination of incidental data collected in 2013 and the results of surveys conducted in 2014
and the next winter survey will enable the study team to meet the study objectives.
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4.3. Information for Mercury Assessment
AEA implemented the study plan modifications proposed in ISR Part C Section 7.1.2 (ABR
2014b). The objectives and methods in this study related to mercury analysis, including the
literature review of food habits and diets of river otters and mink and the collection of hair samples,
have been consolidated in the Mercury Assessment and Potential for Bioaccumulation Study
(Study 5.7) as described in the ISR Part C Section 7.1.2 (ABR 2014b).
As was previously described in the ISR Part A (ABR 2014a), the study team was not successful in
obtaining river otter or mink hair samples in 2013. No river otter carcasses were presented to
ADF&G for sealing from the study area in 2013, so no hair samples could be collected for that
species. Similarly, no trappers were known to have harvested mink in the study area in 2013, so
no hair samples could be obtained for that species, either.
Hair-snag snares were deployed during late winter 2014 at sites where river otter tracks were
present in an attempt to collect river otter hair samples. Eight nonlethal, breakaway snares
modified to snag hairs were set at two main locations on March 8, 2014. Four snares were set at
three sites along Kosina Creek and four snares were set at three sites near Deadman Mountain.
Snares were checked on March 25 and April 11, 2014. In addition, a new sampling location was
established along Kosina Creek on April 11, 2014. All snares were removed on April 23, 2014.
4.3.1. Variances
As described in the ISR Part A (ABR 2014a), there were no variances from the study plan methods
for mercury assessment in 2014.
5. RESULTS
Data developed in support of the Aquatic Furbearer Study are available for download in the
following files at: http://gis.suhydro.org/SIR/10-Wildlife/10.11-Aquatic_Furbearer/
See Table 5-1 for details.
5.1. Beaver and Muskrat
The results of the fall 2013 beaver lodge survey were also previously described in the ISR Part A,
Section 5.1 (ABR 2014a). The study team began the fall 2013 aerial survey of beaver colonies on
October 1–2 and completed it on October 9–10, 2013. During the first part of the survey, the study
team surveyed the Denali West Corridor between the Denali Highway and the dam and camp
facility area, along with the Chulitna Corridor between Portage Creek and the dam and camp
facility area. Some shallow water bodies had begun to freeze by the time the survey was conducted.
The remainder of the study area at lower elevations was surveyed on the second part of the survey.
Colonies that were judged to be active in fall 2013 were resurveyed on May 2, 2014 to look for
evidence of activity to assess overwinter survival.
The study team began the fall 2014 aerial survey of beaver colonies on September 26–27 and
completed it on October 8–9, 2014. During the first part of the survey, the study team surveyed
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the Denali East and West corridors, the dam and camp facility area, and the proposed inundation
zone. The remainder of the study area at lower elevations was surveyed on the second part of the
survey. Colonies that were judged to be active in fall 2014 were resurveyed on April 29, 2015 or
May 17, 2015 to look for evidence of activity to assess overwinter survival.
A total of 184 beaver colonies were recorded and mapped in the 2013 study area during fall 2013
(Table 5.1-1; Figure 5.1-1), 69 (37.5%) of which were judged to be active, based on the proximity
of a fresh food cache consisting of fresh-cut stems of forage plants (typically with leaves still
attached) stored in water bodies as an overwinter food supply. This resulted in an estimate of 0.14
active colonies/km² although there was large variability in density of active colonies by survey
area (Table 5.1-2). A minimum of 33.3% of the colonies that were active in fall 2013 were judged
to be active in spring 2014 although poor snow and ice conditions made it difficult to accurately
assess overwinter survival (Table 5.1-3).
A total of 250 beaver colonies were recorded and mapped in the 2014 study area during fall 2014
(Table 5.1-4; Figure 5.1-2), of which 82 (32.8%) were judged to be active based on the proximity
of a fresh food cache consisting of fresh-cut stems of forage plants (typically with leaves still
attached) stored in water bodies as an overwinter food supply. This resulted in an estimate of 0.17
active colonies/km² although there was large variability in density of active colonies by survey
area (Table 5.1-2). A minimum of 69.5% of the colonies that were active in fall 2014 were judged
to be active in spring 2015 (Table 5.1-3).
Lodges built into banks were common in riverine areas with seasonal or permanently flowing
streams, whereas more typical mound-shaped lodges were generally found in “beaver ponds” away
from flowing streams. A greater proportion of the lodges located in the downstream survey area
(Middle Susitna River Segment) were active than in other parts of the study area (Table 5.1-1;
Table 5.1-4); it is possible, however, that the difference is related to lower detectability of inactive
bank lodges without caches nearby. Fresh food caches tended to be more visible than were beaver
lodges built in river banks, which are more likely to occur in riverine areas.
Beaver lodges were distributed widely throughout the study area during both years and were
located on a variety of aquatic habitat types including lakes, small ponds, creeks, sloughs, and as
bank lodges along main channels of the Susitna River. Lodges were also found at a wide variety
of elevations from the Susitna River to high-elevation areas of the Denali East and West corridors
where only shrubs were available for food and lodge construction.
A total of 19 observations of muskrats or muskrat pushups were recorded incidentally during 2013
and 2014. Twelve observations of muskrats or muskrat pushups were recorded incidentally during
aerial surveys of water bodies in the study area for waterbirds and raptors in 2013. Six of those
water bodies were located in the Fog Lakes area (Figure 5.1-3). Muskrats or muskrat pushups were
recorded on four lakes during waterbird surveys in May 2013, with the number of pushups ranging
from 3 to 50 per lake, and muskrat pushups were recorded on six water bodies during Bald Eagle
surveys in May 2013. All of the incidental sightings from waterbird and raptor surveys in May
2013 were recorded during May 21–24. Two muskrats were observed during landbird/shorebird
point-count surveys in late May and early June 2013 and a muskrat was observed in a lake between
Indian River and Portage Creek during a waterbird brood survey in July 2013. Observations of
muskrats and muskrat pushups also were recorded incidentally during waterbird surveys conducted
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in 2014; five observations were recorded in the Fog Lakes area during May and one was recorded
near the Denali East Corridor in September.
5.2. River Otter and Mink
5.2.1. Incidental Observations
Incidental observations of river otters or mink prior to 2014 were described previously in ISR
10.11, Part A, Section 5.2 (ABR 2014a). The study team compiled a list of 60 incidental
observations of river otters and river otter tracks that were recorded incidentally during surveys
for other Project studies in 2012 and 2013, but only one observation of mink tracks was recorded
during those surveys. An additional 21 incidental observations of river otters or mink were
compiled from 2014 field work (Figure 5.1-3). Twenty sets of river otter tracks and one set of mink
tracks were recorded during aerial surveys of winter tracks for Study 10.10, the Terrestrial
Furbearer Study (including observations that were not on survey transects): three sets of river otter
tracks on February 26, 2013; seven sets of river otter tracks, a river otter, and one set of mink
tracks on March 27, 2013; four sets of river otter tracks on April 19, 2013; two sets of river otter
tracks on February 17, 2014; and three sets of river otter tracks on March 25, 2014. A total of 45
river otters in 26 groups (presumably including an unknown number of repeated observations of
some of the same individuals) were observed during aerial surveys of waterbirds (Study 10.15,
Waterbird Migration, Breeding, and Habitat Use) between early June 2013 and mid-October 2014.
Two river otters and 23 sets of tracks were recorded in 25 sightings during raptor surveys (Study
10.14, Surveys of Eagles and Other Raptors) in May and October–December 2013. One river otter
and four sets of tracks were recorded in five sightings during raptor surveys in July and October–
December 2012. One of the river otters seen during a Bald Eagle survey on May 24, 2013, was
eating a muskrat at the time of the sighting. Incidental sightings from aerial surveys of radio-tagged
fish in December 2013 and January 2014 (S. Crawford, LGL Alaska, pers. comm.) included two
groups of four river otters each in the Middle Susitna River Segment, one at the mouth of Portage
Creek and the other near Slough 21, plus two sets of otter tracks between Jay Creek and Kosina
Creek in the Upper Susitna River Segment and along Portage Creek.
5.2.2. Aerial Surveys
Aerial surveys for river otter and mink tracks were conducted in 2014 on March 7–8, April 10–11,
and December 6–8. No mink tracks were identified on any of these surveys. During the March
survey, a total of 12 different fresh (since the last snowfall) river otter trails were observed,
although some of those may have been made by the same otter groups. During the April survey, a
total of 13 different river otter trails were observed (including observations of two animals),
although some of the trails may have been made by the same otter groups. During the December
survey, a total of 22 different otter trails were observed, although some may have been made by
the same otter groups (Figure 5.2-1).
As expected, river otters were detected most commonly in or near riverine habitats in the study
area. River otter tracks were most frequently observed along the Susitna River and along tributaries
of the Susitna River within the reservoir zone. Tracks were uncommon in the transmission
corridors, with the exception of five sets of tracks found in the Denali West Corridor during the
March 7–8 survey (Table 5.2-1).
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5.3. Information for Mercury Assessment
This task has been consolidated under Study 5.7, Mercury Assessment and Potential for
Bioaccumulation , as described in ISR 10.11, Part C, Section 7.1.2. Although no hair samples were
snagged by the modified snares deployed in 2014, one sample was collected from the snow
adjacent to one of the snares. That sample was sent for laboratory analysis and the results were
reported to the study team for Study 5.7.
6. DISCUSSION
6.1. Beaver and Muskrat
The beaver surveys provided current information on the number, distribution, and activity status
of beaver lodges in the study area (Project area and downstream survey area). Beavers were
distributed throughout most of the Project area and the downstream survey area, but the proportion
of active colonies was lower in the access/transmission corridors and dam and camp facility area
than in the riverine survey area downstream. Beaver lodges built in riverbanks were more
challenging to detect than were lodges in ponds and lakes, and fresh caches had higher
detectability; hence, the study team may have located a higher proportion of active colonies in the
downstream survey area. APA Project researchers in the 1980s (Gipson et al. 1982, 1984) noted
that beavers became more numerous with increasing distance downstream from Devils Canyon in
the Middle and Lower Segments of the Susitna River, and that beavers were more abundant on
side channels and sloughs with silty banks. In contrast, no signs of beaver activity were found in
the active floodplain of the Susitna River between the Tyone River (above the upstream end of the
proposed Watana reservoir inundation zone) and Devils Canyon (Gipson et al. 1982, 1984), similar
to the 2013–2014 survey results from this study, which found very little beaver sign in the reservoir
inundation zone.
Surveys for the APA Project revealed substantial differences in the number of active colonies
among years (e.g., twice as many in 1983 as in 1982), possibly related to the detectability of
colonies among years but also to differences in survival as a result of high-water events and
damage during breakup (Gipson et al. 1984). Many of the inactive lodges in the 2013–2014 surveys
were old lodges that were overgrown with vegetation or were collapsing. The proportion of active
lodges will be influenced by the number of old lodges that are detected and counted. The total
number of active colonies increased between 2013 and 2014, but that was partly a result of an
additional year of search effort as well as a change in the survey area.
A survey in late April 1984 found that 23 colonies (85 percent) had survived the winter, out of 27
colonies that had been classified as active in October 1983 (Gipson et al. 1984). The recent surveys
for this study found a minimum overwinter survival rate of 33.3% during the winter of 2013–2014
and 69.5% during the winter of 2014–2015. The estimate of overwinter survival rate likely was
influenced by survey conditions. The low estimate for 2013–2014 may reflect poor snow and ice
conditions for identifying activity in that spring rather than low colony survival.
Furbearer surveys for the APA Project were primarily restricted to areas within 3 mi of the Susitna
River, so information on beavers or muskrats in the potential access corridors for that project are
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scant. An aerial survey of muskrats and beavers in the upper Susitna basin also was flown in July
1981, but specific results were not reported (Gipson et al. 1982), other than a general statement
that most sign of these species was found in water bodies on plateaus above the river at elevations
of 2,000–2,400 ft. Sixteen beaver dams were found along the potential road access corridor for the
APA Project between Gold Creek and Devils Canyon, and 12 dams and 8 lodges were found along
Deadman Creek (Gipson et al. 1984), but it is not possible to compare numbers directly between
the APA Project surveys and those for the current study.
The study team compiled 19 incidental observations of muskrats and muskrat pushups in and near
the study area in 2013 and 2014, with most pushups being observed in the Fog Lakes area and at
Watana and Clarence lakes, at higher elevations south of the proposed reservoir inundation zone.
The late spring and delayed breakup in 2013 did not provide good conditions for muskrat surveys,
but the incidental observations from surveys conducted for other Project studies generally
corroborate the findings of the APA Project studies. Muskrat surveys were flown for the APA
Project studies in 1980 on March 10, April 24, and May 9, but the snow cover was too deep to
distinguish most pushups until the May survey, when 97 water bodies were surveyed within 3 mi
of the Susitna River from the Oshetna River at the upper end of the Watana reservoir zone
downstream to Gold Creek (Gipson et al. 1982). Pushups were found on 27 (26 percent) of the 103
lakes surveyed in 1980 (including several lakes from the earlier surveys), ranging from one to 32
pushups per water body. The range observed in this study was three to 50 pushups on individual
lakes.
6.2. River Otter and Mink
Incidental observations of river otters and river otter tracks indicated that the species is distributed
in low numbers along the Susitna River mainstem, tributary streams, and adjacent lakes and ponds
in the study area, as was indicated by the only survey of this species that was conducted for the
APA Project in the 1980s (Gipson et al. 1982). Surveys of river otter and mink tracks and sign
were conducted once for the APA Project during November 10–12, 1980, using both aerial and
ground observations. Fourteen aerial survey transects were flown, extending 3 mi perpendicularly
from each side of the Susitna River mainstem from just below Portage Creek upstream to just
below the Tyone River mouth. Tracks of each species were recorded on 11 (79 percent) of the 14
transects sampled on that survey (Gipson et al. 1982). Similar aerial surveys of tracks conducted
in 2013–2014 for Terrestrial Furbearer Abundance and Habitat Use (Study 10.10) recorded 17
river otter tracks during 5 surveys suggesting that fewer river otters may have been present in
2013–2014 (although direct comparisons are difficult because of the small number of surveys and
variations in snow conditions).
During the same survey period in November 1980, ground checks at 37 sampling points (spaced
approximately 1–2 mi apart) along the Susitna River from below Portage Creek to Vee Canyon
recorded river otter tracks at 17 (46 percent) and mink tracks at 22 (59 percent) of the points
sampled (Gipson et al. 1982). River otters were dispersed in low numbers along the length of the
river sampled, whereas mink were more numerous in the upper portion of the study area (Gipson
et al. 1982). The incidental sightings compiled for the current study in 2013–2014 included only
one occurrence of mink tracks, on lower Watana Creek, on an aerial survey of tracks in late March
2013. It is possible that the presence of more mink may have been masked by the similarity
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between their tracks and those of marten, which are more numerous than mink in the study area
(Gipson et al. 1982).
The researchers who conducted the track surveys for the APA Project in November 1980
considered the number of river otter tracks they encountered on Susitna River shelf ice in the two
impoundment zones proposed for that project to be unusually high (43 tracks at 17 locations), and
speculated that the high incidence of tracks may have resulted either from otters moving upstream
or downstream before freeze-up or from otters feeding on grayling that were moving out of
tributaries to overwinter in the river mainstem (Gipson et al. 1982). No such concentrations of
tracks have been observed or reported thus far in this study.
6.3. Information for Mercury Assessment
This task has been consolidated under Study 5.7, Mercury Assessment and Potential for
Bioaccumulation, as described in ISR 10.11, Part C (ABR 2014b).
7. CONCLUSIONS
The surveys of beaver lodges have been completed (RSP Section 10.11.4.1) and three additional
aerial surveys for river otter and mink tracks were completed in 2014. To complete this study,
AEA will implement the methods in the Study Plan, except as described in Section 7.1 below.
The study team expects that the combination of study results from 2013 –2015 (including the
variances described in Section 4), additional planned field work, and integration with other studies
will achieve the approved Study Plan objectives. This study is interrelated with Study 5.7, Mercury
Assessment and Potential for Bioaccumulation; Study 8.6, Riparian Instream Flow; and Study
10.19, Evaluation of Wildlife Habitat Use. AEA expects that the approved Study Plan objectives
for both this study and Studies 5.7, 8.6, and 10.19 will be achieved with the modifications to this
study, as these modifications will ensure consistency in methods and are expected to result in
improved data collection.
7.1. Modifications to Study Plan
As described in Section 7.1.2 of the ISR Part C (ABR 2014b), AEA has added the Denali East
Option road and transmission corridor to the study area. With regard to this study, the modified
study area showing the Denali East Option is depicted in Figure 3-1.
Aerial surveys of muskrat pushups (as described in RSP Section 10.11.4.1) are planned for the
Project area in spring 2016. Instead of conducting a second year of muskrat surveys in the future,
however, AEA proposes to substitute the two seasons of incidental observations of muskrats
obtained in 2013 and 2014 for one year of surveys, thereby making more data available to meet
this study objective.
As described in Section 7.1.2 of ISR 10.11, Part C (ABR 2014b), RSP Sections 10.11.1 and
10.11.4.3 provide objectives and methods for the study team to review available informa tion on
food habits and diets of piscivorous furbearers (river otter and mink) as background for Study 5.7,
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Mercury Assessment and Potential for Bioaccumulation, and to obtain hair samples from river
otter and mink for laboratory analysis of mercury levels, including possible collection of hairs
from trapper-harvested animals. After further consideration of all mercury studies for the proposed
Project, AEA has removed these objectives and methods related to mercury analysis of river otter
and mink (RSP Sections 10.11.1 and 10.11.4.3) and consolidated this work under Study 5.7.
8. LITERATURE CITED
ABR. 2014a. Aquatic Furbearer Abundance and Habitat Use Study Plan Section 10.11; Initial
Study Report, Part A: Sections 1–6, 8–10; Susitna-Watana Hydroelectric Project (FERC
No. 14241). Report for Alaska Energy Authority, Anchorage, by ABR, Inc.—
Environmental Research & Services, Fairbanks, AK. 14 pp.
ABR. 2014b. Aquatic Furbearer Abundance and Habitat Use Study Plan Section 10.11; Initial
Study Report, Part C: Executive Summary and Section 7; Susitna-Watana Hydroelectric
Project (FERC No. 14241). Report for Alaska Energy Authority, Anchorage, by ABR,
Inc.—Environmental Research & Services, Fairbanks, AK. 3 pp.
Erb, J., and H. R. Perry. 2003. Muskrats. Pages 311–348 in G. A. Feldhamer, B. C. Thompson,
and J. A. Chapman, editors. Wild Mammals of North America. 2nd edition. Johns Hopkins
University Press, Baltimore, MD.
Gipson, P. S., S. W. Buskirk, and T. W. Hobgood. 1982. Susitna Hydroelectric Project
environmental studies, Subtask 7.11: Furbearers—Phase I report. Report by Alaska
Cooperative Wildlife Research Unit, University of Alaska, Fairbanks, for Terrestrial
Environmental Specialists, Inc. 81 pp.
Gipson, P. S., S. W. Buskirk, T. W. Hobgood, and J. D. Woolington. 1984. Susitna Hydroelectric
Project furbearer studies: Phase I report update. Final report by Alaska Cooperative
Wildlife Research Unit, University of Alaska, Fairbanks, for the Alaska Power Authority,
Anchorage. 100 pp.
Hay, K. G. 1958. Beaver census methods in the Rocky Mountain region. Journal of Wildlife
Management 22: 395–402.
Payne, N. F. 1981. Accuracy of aerial censusing for beaver colonies in Newfoundland. Journal
of Wildlife Management 45: 1014–1016.
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9. TABLES
Table 5-1. Server Location and File Names for the Field Data for Aquatic Furbearers Collected in 2013–2015.
Server Pathway or File/Folder Name Description
/http://gis.suhydro.org/SIR/10-Wildlife/10.11-
Aquatic_Furbearer/
Pathway to data files
AFUR_10_11_Data_2013_2015_ABR.gdb
Geodatabase file containing spatial layers of the aquatic furbearer
survey areas, beaver lodge locations, miscellaneous aquatic
furbearer locations, hair-snag snare locations and river otter track
locations and segments.
Table 5.1-1. Number and Percentage of Beaver Colonies, by General Location and Activity Level, October 2013.
General Location Active Colonies Inactive Colonies Total
Chulitna Corridor 16 (41.0%) 23 (59.0%) 39
Dam and Camp Facility Area 2 (18.2%) 9 (81.8%) 11
Denali West Corridor 10 (18.2%) 45 (81.8%) 55
Gold Creek Corridor 6 (35.3%) 11 (64.7%) 17
Middle River 35 (57.4%) 26 (42.6%) 61
Watana Reservoir 0 (0%) 1 (100%) 1
Total 69 (37.5%) 115 (62.5%) 184
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Table 5.1-2. Number and Density of Active Beaver Colonies (Colonies/km²), by General Location, October 2013 and 2014.
General Location Active Colonies
2013 Density 2013 Active Colonies
2014 Density 2014
Chulitna Corridor (79.7 km²) 16 0.20 – –
Dam and Camp Facility Area (38.8 km²) 2 0.05 2 0.05
Denali East Corridor (118.4 km²) – – 12 0.10
Denali West Corridor (105.6 km²) 10 0.09 7 0.07
Gold Creek Corridor (74.9 km²) 6 0.08 2 0.03
Middle River (87.7 km²) 35 0.40 58 0.66
Watana Reservoir (95.3 km²) 0 0 2 0.02
Total (481.9 and 477.5 km²)l 69 0.14 82 0.17
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Table 5.1-3. Number and Minimum Overwinter Survival of Active Beaver Colonies, by General Location, 2013.
General Location
Active Colonies
Fall 2013 Checked
Spring 2014
Minimum Number
Active Spring 2014
Active Colonies
Fall 2014
Minimum Number
Active Spring 2015
Chulitna Corridor 0 – – –
Dam and Camp Facility Area 2 2 (100%) 2 1 (50%)
Denali Corridor(s) 10 1 (10%) 18 9 (50%)
Gold Creek Corridor 6 3 (50%) 2 2 (100%)
Middle River 30a 10 (33.3) 58 43 (74.1)
Watana Reservoir 0 – 2 2 (100)
Total 48a 16 (33.3%) 82 57 (69.5)
a. Five colonies were not relocated.
Table 5.1-4. Number and Percentage of Beaver Colonies, by General Location and Activity Level, October 2014.
General Location Active Colonies Inactive Colonies Activity Status
Unknown Total
Dam and Camp Facility Area 2 (13.3%) 13 (86.7%) 0 15
Denali East Corridor 12 (18.8%)a 52 (81.3%)b 0 64
Denali West Corridor 7 (12.5%)a 49 (87.5%)b 0 54
Gold Creek Corridor 2 (10.5%) 17 (89.5%) 0 19
Middle River 58 (51.8%) 51 (45.5%) 3 (2.7%) 112
Watana Reservoir 2 (50%) 2 (50%) 0 4
Total 82 (32.8%) 165 (66.0%) 3 (1.2%) 250
a. 1 colony in both east and west corridors.
b. 19 colonies in both east and west corridors.
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Table 5.2-2. Location and number of river otter tracks observed during three aerial surveys conducted March–December
2014.
Survey Dates
Reservoir Zone
Chulitna
Corridor
Denali
Corridorsa
Gold
Creek
Corridor Susitna
River
Susitna River
Tributaries Transects
Tracksb March 7–8 2 3 0 1 5 1
April 10–11 7 2 1 0 2 1
December 6–8 12c 8c 3 – 0 2
Tracks/km March 7–8 0.02 0.02 0 0.01 0.05 0.01
April 10–11 0.08 0.02 0.01 0 0.02 0.01
December 6–8 0.13 0.06 0.02 – 0 0.03
a. The Denali corridors included the Denali East Corridor during the December survey.
b. Some tracks may have been made by the same river otter groups.
c. Three tracks were located along both the Susitna River and tributaries.
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10. FIGURES
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Figure 3-1. Aquatic Furbearer Study Area.
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Figure 5.1-1. Beaver Colony Locations, October 2013.
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Figure 5.1-2. Beaver Colony Locations, October 2014.
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Figure 5.1-3. Locations of Muskrats, River Otters, and Mink Observed Incidentally during Other Project Surveys in 2012–2014.
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Figure 5.2-1. Results of Three River Otter and Mink Track Surveys Conducted March, April, and December 2014.