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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 :
Initial study report
SuWa 207
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Draft initial study report
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Susitna-Watana Hydroelectric Project document number 207
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[Anchorage : Alaska Energy Authority, 2014]
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February 2014
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Alaska Energy Authority
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Study plan Section 10.11
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Draft
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iv, 15 p.
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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
Initial Study Report
Prepared for
Alaska Energy Authority
Prepared by
ABR, Inc.—Environmental Research & Services
Fairbanks, Alaska
February 2014 Draft
INITIAL STUDY REPORT AQUATIC FURBEARER ABUNDANCE AND HABITAT USE STUDY (10.11)
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TABLE OF CONTENTS
Executive Summary ..................................................................................................................... iii
1. Introduction............................................................................................................................ 1
2. Study Objectives .................................................................................................................... 1
3. Study Area .............................................................................................................................. 2
4. Methods and Variances in 2013 ............................................................................................ 2
4.1. Beaver and Muskrat Surveys ......................................................................................... 2
4.1.1. Variances................................................................................................................. 3
4.2. River Otter and Mink Surveys ....................................................................................... 3
4.2.1. Variances................................................................................................................. 4
4.3. Information for Mercury Assessment ............................................................................ 4
4.3.1. Variances................................................................................................................. 4
5. Results ..................................................................................................................................... 5
5.1. Beaver and Muskrat ....................................................................................................... 5
5.2. River Otter and Mink ..................................................................................................... 6
5.3. Information for Mercury Assessment ............................................................................ 6
6. Discussion ............................................................................................................................... 6
6.1. Beaver and Muskrat ....................................................................................................... 6
6.2. River Otter and Mink ..................................................................................................... 7
6.3. Information for Mercury Assessment ............................................................................ 8
7. Completing the Study ............................................................................................................ 9
8. Literature Cited ..................................................................................................................... 9
9. Tables .................................................................................................................................... 11
10. Figures .................................................................................................................................. 12
LIST OF TABLES
Table 5.1- 1. Number and Percentage of Beaver Colonies, by General Location and Activity
Level, October 2013...................................................................................................................... 11
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LIST OF FIGURES
Figure 3- 1. Aquatic Furbearer Study Area. ................................................................................. 13
Figure 5.1- 1. Beaver Colony Locations, October 2013. .............................................................. 14
Figure 5.1- 2. Locations of Muskrats, River Otters, and Mink Observed Incidentally during Other
Project Surveys in 2013. ............................................................................................................... 15
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
ILP Integrated Licensing Process
ISR Initial Study Report
Project Susitna-Watana Hydroelectric Project
RSP Revised Study Plan
USR Updated Study Report
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EXECUTIVE SUMMARY
Aquatic Furbearer Abundance and Habitat Use Study, Section 10.11
Purpose The goal of the Aquatic Furbearer Study is to collect baseline data on aquatic
furbearers in the study area to enable assessment of potential Project-related
impacts.
Five specific objectives are established in the Study Plan:
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 the Mercury
Assessment and Potential for Bioaccumulation Study (Study 5.7).
5) Collect hair samples from river otters and mink to characterize
baseline tissue levels of mercury for the Mercury Assessment and
Potential for Bioaccumulation study.
Status The study is in progress. An aerial survey of beaver lodges and caches in the
Project area and Middle Susitna River segment was conducted in October
2013. Other researchers conducting surveys for Waterbird Migration,
Breeding, and Habitat Use Study (Study 10.15), Landbird and Shorebird
Migration, Breeding, and Habitat Use Study (Study 10.16), and Surveys of
Eagles and Other Raptors (Study 10.14) in May 2013 recorded incidental
sightings of muskrats and muskrat pushups. The study team compiled
observations of river otters and river otter and mink tracks recorded
incidentally during surveys for other Project studies.
Study
Components
This study consists of the following components:
1) Aerial surveys of beaver and muskrat.
2) Aerial surveys of river otter and mink.
3) Collection of hair samples from river otters and mink for analysis of
mercury levels.
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2013 Variances Aerial surveys for beaver were broadened to include areas outside the study
area (see RSP Sections 10.11.3 and 10.11.4.1), to cover the entire riverine
physiography area delineated for Riparian Vegetation Study Downstream of
the Proposed Susitna-Watana Dam (Study 11.6), which provided more data
than would have been collected otherwise.
The planned survey of muskrat pushups (RSP Section 10.11.4.1) was not
conducted because of the unusually late spring and persistent snow and ice
cover in 2013; instead, researchers conducting surveys for the Waterbird
Migration, Breeding, and Habitat Use Study (Study 10.15) and Surveys of
Eagles and Other Raptors (Study 10.14) in May 2013 recorded the presence of
muskrat pushups.
Track surveys for river otters and mink were not conducted in February–early
April 2013 (RSP Section 10.11.4.1) due to unanticipated delays in contract
approval and study initiation, or in November/December 2013 due to the lack
of a suitable weather windows in relation to pilot and aircraft availability.
Incidental observations of river otters and river otter tracks were compiled
from surveys conducted for other Project studies, however, to help meet study
objectives.
Steps to
Complete the
Study
As explained in the cover letter to this draft ISR, AEA’s plan for completing
this study will be included in the final ISR filed with FERC on June 3, 2014.
Highlighted
Results and
Achievements
During the 2013 beaver survey, the study team observed 186 beaver lodges in
the survey area and 37.1% were determined to be active based on the presence
of a fresh food cache. The study team compiled 60 incidental observations of
river otters and river otter tracks and 14 incidental observations of muskrats
and muskrat pushups. A review of scientific literature on the food habits and
diets of river otters and mink was undertaken to provide data inputs to the
pathways analysis for the Mercury Assessment and Potential for
Bioaccumulation Study (Study 5.7).
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1. INTRODUCTION
On December 14, 2012, Alaska Energy Authority (AEA) filed with the Federal Energy
Regulatory Commission (FERC or Commission) its Revised Study Plan (RSP) for the Susitna-
Watana Hydroelectric Project No. 14241 (Project), which included 58 individual study plans
(AEA 2012). RSP Section 10.11 described the Aquatic Furbearer Abundance and Habitat Use
Study (Aquatic Furbearer Study). This study was designed to assess the distribution of aquatic
furbearers among habitats, to estimate population size for beavers (Castor canadensis), and to
assess the relative abundance of other aquatic furbearers (muskrat, Ondatra zibethicus; river
otter, Lontra canadensis; mink, Neovison vison). Additional work is being done to provide
information on the food habits and diets of piscivorous furbearers (river otter and mink) to
inform the Mercury Assessment and Potential for Bioaccumulation Study (Study 5.7). RSP
Section 10.11 described the goal, objectives, and proposed methods for data collection regarding
aquatic furbearers.
On February 1, 2013, FERC staff issued its study determination (February 1 SPD) for 44 of the
58 studies, approving 31 studies as filed and 13 with modifications. RSP Section 10.11 was one
of the 31 studies approved with no modifications.
Following the first study season, FERC’s regulations for the Integrated Licensing Process (ILP)
require AEA to “prepare and file with the Commission an initial study report describing its
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)). This Initial
Study Report (ISR) on the Aquatic Furbearer Study has been prepared in accordance with
FERC’s ILP regulations and describes AEA’s progress in implementing the study, as set forth in
the FERC-approved RSP (referred to herein as the “Study Plan”).
2. STUDY OBJECTIVES
The goal of 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.
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 the Mercury Assessment and Potential for
Bioaccumulation Study (Study 5.7).
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5) Collect hair samples from river otters and mink to characterize baseline tissue levels of
mercury for the Mercury Assessment and Potential for Bioaccumulation Study.
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) to provide comparative data on the extent of use of
those drainages in comparison with the Susitna mainstem.
4. METHODS AND VARIANCES IN 2013
The methods implemented for each of the Aquatic Furbearer Study components in 2013 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 an aerial survey 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). The survey of the beaver study area was conducted in a small piston-engine helicopter
(Robinson R-44) in October 2013, 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 survey was 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 corridor and part of the Chulitna corridor) were
surveyed on October 1–2 and the remainder of the study area was surveyed on October 9–10.
The locations of beaver lodges were recorded and mapped using a handheld Global Positioning
System (GPS) receiver.
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Although the planned aerial survey 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) was not conducted in spring 2013 (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 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 was somewhat wider in the lower 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 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 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 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. The incidental sightings in 2013 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 on subsequent surveys in the next year of study, are expected
to enable the study team to achieve the study objective for this species.
4.2. River Otter and Mink Surveys
AEA did not implement the survey methods proposed in the Study Plan for river otters and mink
in 2013 (RSP Section 10.11.4.2), as 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 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 (Study 9.5, Fish Distribution
and Abundance in the Upper Susitna River; Study 9.6, Fish Distribution and Abundance in the
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Middle and Lower Susitna River; Study 9.7, Salmon Escapement; Study 10.14, Surveys of
Eagles and Other Raptors; 10.15, Waterbird Migration, Breeding, and Habitat Use) also provided
data from incidental observations of river otters.
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)
because of an unanticipated delay in contract approval and study initiation. 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). The combination of these incidental data with the results of
aquatic furbearer surveys to be conducted in the next study season will enable the study team to
meet the study objectives.
4.3. Information for Mercury Assessment
AEA implemented the methods described in the Study Plan, with the exception of the variance
explained below (Section 4.3.1).
The intent of RSP Section 10.11.4.3 is to obtain hair samples from river otters and mink for
laboratory analysis to characterize preconstruction levels of mercury for the study of Mercury
Assessment and Potential for Bioaccumulation (Study 5.7). Because the Alaska Department of
Fish and Game (ADF&G) requires that the pelts of river otters be sealed by an authorized
ADF&G representative, the study team planned to collect hair samples from river otters that
were harvested in the study area and presented to ADF&G for sealing. No river otter carcasses
were presented for sealing from the study area in 2013, however, 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. Another potential
source of mink hair was incidental capture in hair-snag traps set for marten as part of Study
10.10, Terrestrial Furbearer Abundance and Habitat Use, but the marten trapping component of
that study had to be postponed in 2013 (see ISR Study 10.10).
The study team reviewed scientific literature in 2013 to locate and synthesize information on the
food habits and diets of river otters and mink in freshwater aquatic systems to support the
pathways analysis being conducted for Study 5.7, Mercury Assessment and Potential for
Bioaccumulation. The results of that review, which is still in progress, will be incorporated in the
USR after the next study season.
4.3.1. Variances
The Study Plan anticipated the possibility that hair samples from river otters and mink might not
be obtained from trapper-harvested animals. In that event, then the Study Plan proposed that
hair-snag traps (e.g., DePue and Ben-David 2007, Pauli et al. 2008) would be deployed in late
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winter during track surveys at locations in the stream survey area where river otter and mink sign
was recorded. Because the track surveys were not conducted in 2013 (see Section 4.2.1 above),
however, no hair-snag traps were deployed in 2013. The study team will meet Study Plan
objectives by deploying hair-snag traps during future track surveys in the next study season.
5. RESULTS
Data developed in support of the Aquatic Furbearer Study are available for download in the
following files at http://gis.suhydro.org/reports/isr:
• ISR_10_11_AFUR_Data_2013.accdb.
5.1. Beaver and Muskrat
The study team began the aerial survey of beaver colonies on October 1–2 and completed it on
October 9–10, 2013. The survey was conducted in two phases to sample areas at higher and
lower elevations under similar conditions (after leaf fall and before ice formation, which
occurred earlier at higher elevations). During the first part of the survey, the study team surveyed
the Denali 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.
A total of 186 beaver colonies were recorded and mapped in the study area (Table 5.1-1; Figure
5.1-1), 69 (37.1%) 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. 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); 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.
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 5.1-2). Muskrats or muskrat pushups were
recorded on four lakes during waterbird surveys in May, 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. All of the incidental sightings from waterbird and raptor surveys in May were
recorded during May 21–24. Two muskrats were observed during landbird/shorebird point-count
surveys in late May and early June and a muskrat was observed in a lake between Indian River
and Portage Creek during a waterbird brood survey in July 2013.
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5.2. River Otter and Mink
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 (Figure 5.2-1). Fourteen
sets of river otter tracks and one set of mink tracks were recorded on seven of the 14 transects
sampled during aerial surveys of winter tracks for Study 10.10, the Terrestrial Furbearer Study:
three sets of river otter tracks on February 26; seven sets of river otter tracks, a river otter, and
one set of mink tracks on March 27; and four sets of river otter tracks on April 19. A total of 17
river otters in 12 groups were observed during aerial surveys of waterbirds (Study 10.15,
Waterbird Migration, Breeding, and Habitat Use) between early June and mid-October 2013.
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 (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 one set of otter tracks between Jay Creek and
Kosina Creek in the Upper Susitna River Segment.
5.3. Information for Mercury Assessment
To date, the review of literature on the food habits, diets, and mercury exposure of river otters
and mink has encompassed 30 references from scientific journals, reports, and books. The
review, which is still continuing, focuses primarily on documenting the proportion of the diet
composed of fish, the types and size classes of fishes eaten, and the amounts consumed. This
review will provide important input data for the pathways analysis of Study 5.7, Mercury
Assessment and Potential for Bioaccumulation, to be completed in the next study season.
6. DISCUSSION
6.1. Beaver and Muskrat
The beaver survey completed in October 2013 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 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 (Gipson et al. 1982, 1984). In contrast, no signs of beaver
activity were found in the active floodplain of the Susitna River between the Tyone River (above
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the upstream end of the proposed Watana reservoir inundation zone) and Devils Canyon (Gipson
et al. 1982, 1984), similar to the 2013 survey results, which found very little beaver sign in the
reservoir inundation zone.
The fall survey planned for the next year of this study will provide more data to assess potential
differences in the distribution of active colonies. 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).
Another beaver survey is planned for spring in the next study season to assess overwinter
survival of the colonies that were active in fall 2013 and to quantify the presence and activity
status of beaver colonies on another fall survey in the next year of study. A similar 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).
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 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 Devil 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 14 incidental observations of muskrats and muskrat pushups in and
near the study area in 2013, with most pushups being observed in the Fog Lakes area and at
Watana and Clarence lakes. The late spring and delayed breakup in 2013 did not provide good
conditions for the muskrat survey, 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. The spring survey planned for the next year of
study, combined with additional incidental observations, will provide more data on the
distribution and relative abundance of muskrats in the study area.
6.2. River Otter and Mink
Incidental observations of river otters and river otter tracks in 2013 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
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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 in 2013 conducted for Terrestrial Furbearer Abundance and Habitat Use (Study 10.10)
found sign of river otters on a total of seven of the same 14 transects, suggesting that fewer river
otters may have been present in 2013 (although direct comparisons are difficult because of the
small number of surveys).
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 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
between their tracks and those of marten, which are more numerous in the study area than are
mink (Gipson et al. 1982). The results of additional track surveys are needed to better assess the
relative abundance of mink in the study area.
The researchers who conducted the track surveys 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 reported thus far in this study, although the planned survey in November/December 2013
could not be conducted. Nevertheless, the Bald Eagle roosting and foraging surveys (Study
10.14, Surveys of Eagles and Other Raptors) flown periodically during October–early December
2012 and 2013 did not produce any indications of unusual concentrations of river otter tracks.
6.3. Information for Mercury Assessment
River otters and mink are piscivorous carnivores that have been reported to be susceptible to the
accumulation of mercury in their body tissues (e.g., Wobeser and Swift 1976, Yates et al. 2005,
Sleeman et al. 2010). Hence, obtaining tissue samples from these species in the study area is an
important objective of the current study, which will be addressed in the next study season. That
information, combined with the results of the literature review, will provide crucial input data for
the pathways analysis to be conducted for Study 5.7, Mercury Assessment and Potential for
Bioaccumulation, in the next study season.
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7. COMPLETING THE STUDY
[As explained in the cover letter to this draft ISR, AEA’s plan for completing this study will be
included in the final ISR filed with FERC on June 3, 2014.]
8. LITERATURE CITED
AEA (Alaska Energy Authority). 2012. Revised Study Plan: Susitna-Watana Hydroelectric
Project FERC Project No. 14241. December 2012. Prepared for the Federal Energy
Regulatory Commission by the Alaska Energy Authority, Anchorage, Alaska. Available
online: http://www.susitna-watanahydro.org/study-plan.
DePue, J. E., and M. Ben-David. 2007. Hair-sampling techniques for river otters. Journal of
Wildlife Management 71: 671–674.
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.
Pauli, J. N., M. B. Hamilton, E. B. Crain, and S. W. Buskirk. 2008. A single-sampling hair trap
for mesocarnivores. Journal of Wildlife Management 72: 1650–1652.
Payne, N. F. 1981. Accuracy of aerial censusing for beaver colonies in Newfoundland. Journal
of Wildlife Management 45: 1014–1016.
Sleeman, J. M., D. A. Cristol, A. E. White, D. C. Evers, R. W. Gerhold, and M. K. Keel. 2010.
Mercury poisoning in a free-living northern river otter (Lontra canadensis). Journal of
Wildlife Diseases 46: 1035–1039.
Wobeser, G., and M. Swift. 1976. Mercury poisoning in a wild mink. Journal of Wildlife
Diseases 12: 335–340.
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Yates, D. E., D. T. Mayack, K. Munney, D. C. Evers, A. Major, T. Kaur, and R. J. Taylor. 2005.
Mercury levels in mink (Mustela vison) and river otter (Lontra canadensis) from
northeastern North America. Ecotoxicology 14: 263–274.
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9. TABLES
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 Corridor 10 (17.5%) 47 (82.5%) 57
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 (37.1%) 117 (62.9%) 186
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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. Locations of Muskrats, River Otters, and Mink Observed Incidentally during Other Project Surveys in 2013.