Longtime followers of this fishery will remember
that 20 years ago there were a number of
outfitters who booked clients for pack trips into
this area for the incredible early summer fishing.
Then, with the population crash, the trips stopped.
Walt and Dave took a chance and made the 30
mile trip and the results surprised both of them.
The fish were there, were large and the fishing
was spectacular. Below is a picture of Walt with
one of those tremendous fish, another sign of a
recovering population. The Spring 2017 issue of
"Trout" magazine will report on his trip.
Last June, one of our Trout Unlimited staff members, Walt Gasson of Cheyenne, had the opportunity to
pack into the Thoroughfare District of the Bridger Teton National Forest with Dave Hettinger Outfitting.
Dave was considering offering fishing/pack trips into this remote area that is the headwaters of the
upper Yellowstone River above the Lake. Reports had been circulating that the spring spawning runs
of cutthroats into that system were once again robust and the fishing was outstanding.
|Update on Yellowstone Cutthroat Trout Recovery
in Yellowstone Lake and the Upper Yellowstone River
January, 2017 View update as .pdf
|Save the Yellowstone Cutthroat
Wyoming Trout Unlimited (WY TU) and the East Yellowstone Chapter of TU (EYCTU) have
collectively been focused on recovering the Yellowstone Cutthroat Trout (YCT) population of the
upper Yellowstone River and Yellowstone Lake system (YL) since 2008. Our focus has been on
aiding and encouraging the National Park Service (NPS) in their efforts to suppress the invasive
and predacious lake trout (LT) that were introduced into that system around 30 years ago and in
aiding the US Geological Survey (USGS) in their multi-pronged efforts to locate the LT spawning
beds in that system, to learn about LT spawning behavior, and to develop alternative suppression
techniques focused on LT ova and fry.
The primary focus of the USGS/TU joint effort is a major telemetry study of LT movements through
fundraising source for the USGS efforts along with the Greater Yellowstone Coalition (GYC), the
National Parks Conservation Association (NPCA), the Federation of Fly Fishermen (FFF), and TU
chapters and councils in many states but especially Colorado, Montana and Idaho.
Yellowstone Lake Working Group:
The Yellowstone Lake Working Group consists of representatives from all of the above agencies and
non-governmental organizations (NGO's) along with representatives from Montana State University
Fisheries (MSU), and the Yellowstone Park Foundation which is now named Yellowstone Forever
(YF, the major funding source for the gill netting on the Lake).
Overall Summary of the Progress:
The efforts to remove LT from the YL system and recover the YCT population is a long term project
that has no simple and quick fix. The LT is a voracious predator with high reproductive potential in
the YL system. Its population numbers roughly 700,000 age two and older fish. YL itself is a huge
lake with great depths (up to 400 ft.) making suppression a difficult and lengthy process. The effort
has at its core a major netting campaign to remove both adult and juvenile LT. Longer term
suppression is focused on finding the LT spawning beds through telemetry, then developing specific
techniques aimed at cutting off LT recruitment by targeting the LT ova and fry. The netting campaign
is now over 20 years old, although only in the last 6 years has it reached the level that is
acknowledged to be sufficient to reverse the population expansion. The telemetry study is currently 6
years old. The population of LT in the system is in decline although only modestly so. A crash has
not yet occurred although it is anticipated. It is most heartening that the adult LT population is
definitely showing signs of decline.
This Working Group along with several contract researchers meet on a regular basis to review
progress and to set the agenda for future efforts. They most recently met on December 7th in
Bozeman, MT to review the current status and direction for 2017 of the program. This report is a
synopsis of that meeting.
The telemetry study has met its primary goal of identifying many (although certainly not all) of the
LT spawning areas. Due to funding limitations, this telemetry study is scheduled to be
discontinued for the 2017 season. Ova and fry suppression studies are progressing and results
are encouraging although the "silver bullet" for LT ova and fry suppression has not been found.
Meanwhile, the YCT population is showing signs of recovery. Every metric studied to monitor this
population is on a positive trend, including: angling catch rates, spawning stream monitoring,
distribution netting results, by-catch rates, and visual observations in critical YCT spawning areas.
The population of YCT in the system is not yet where it should be; progress is being made.
The ecosystem that depends upon the YCT population as a food source has been negatively and
in some cases, severely impacted. But, there are signs of recovery. In 2016 and for the first time in
many years, a grizzly was filmed while feeding on YCT during the spring spawning run.
Status of the Gill Netting:
Gill netting remains the primary defensive method of LT population control. During summer, 2016, a
total of 365,000 LT were removed from the system by netting. See Graph 1 below for the yearly
breakdown. That number pushes the total number of LT removed to date to approximately 2.3
million. Four gill netting boats are now operated by the contract crews from the Hickey Bros. and a
fifth boat has been added in 2016, operated by the NPS. This yearly removal of LT is higher than the
average removal of the last four years which was about 300,000 per year. The increase in LT removal
was predominantly in juvenile LT while the mature LT removal number stayed about the same. There
was an increase in total netting effort units (100 meters of net soaked for one night equals one unit)
from about 76,000 in 2014 and 2015 to 78,000 in 2016. The resultant catch per unit of effort (CPUE)
for all mesh sizes was up slightly in 2016 over the past three years but remains significantly lower
than the highs of 2010, 2011, and 2012. This decline in CPUE over these past four years is a very
strong indicator that the LT numbers have declined during this time.
This is especially true of the adult lake trout numbers. Netting crews continued to gain experience
every year in locating LT and were further guided by a mobile tracking study initiated by the NPS in
2016 that increased crew efficiency especially for adult LT. Graph 2 shows the division of netting
effort between small mesh nets, targeting juvenile LT and large mesh nets which target adult LT.
The proportion of net targeting adult LT has grown over the years, stabilizing for the past 3 years.
Graphs 3 and 4 show the catch numbers of LT in small mesh and large mesh nets respectively
over the past 15 years as well as the CPUE values for those net sizes. Of particular note is that the
CPUE (which is an indicator of relative LT abundance) in the large mesh netting has declined
significantly for the past several years. This is strong evidence of a declining adult LT population.
Indeed, when a population model is compiled for the LT, a clear decrease in adult LT is seen (see
Graph 5). The slight increase in juvenile LT numbers this year shown on Graph 5 is believed to be
a compensatory reaction to the adult LT decline.
Graph 1: Total LT removal
by gill netting by year
since 2001 and CPUE for
the same time period.
Total netting effort for 2001-2016 (1
unit = 100 meter of net for one night).
Graph 2: Division of the gill
netting effort into small mesh
(targeting juvenile LT) and large
mesh (targeting adult LT).
Graph 3: Lake trout catch
numbers and CPUE
values for 2000-2016 in
small mesh gill nets.
Graph 4: Lake trout catch
numbers and CPUE
values for 2000-2016 in
large mesh gill nets.
Graph 5: Estimated
LT abundance in YL
by age structure.
By-catch of cutthroats in the nets is always a concern (see Graph 8). During the early years of the
netting (late 1990's and early 2000's) by-catch as a percentage of LT harvest, was a significant issue
as the cutthroat population was still somewhat strong and the knowledge of how to avoid the
cutthroats was being developed by the netters. Since the total amount of netting was relatively low,
the total YCT by-catch was low even though it was high on a percentage basis. Then, during the early
to mid 2000's, by-catch declined as a percentage of LT harvest. This was due to cutthroat population
decline and cutthroat avoidance knowledge being gained. Now, for the past four years, by-catch as a
total number has increased even though the by-catch rate relative to LT catch is still low. This is most
likely due to a recovery of the cutthroat population. Although we would like to avoid all by-catch, the
increase certainly indicates a recovering population of cutthroats.
Graph 6: Gill netting actual
locations in Yellowstone Lake
for 2016 with CPUE ranges for
the nets indicated. The darker
the red, the higher the catch rate
in those nets.
Graph 7: Overall catch rates
(CPUE) in various segments
of the Lake over the past 4
Graph 8: By-catch of YCT
in gill netting over time.
Netting distribution across the area of Yellowstone Lake has continued in 2016 as shown in Graph 6.
This is due to the widespread and very mobile distribution of the LT across all areas of the Lake as
determined by the telemetry study. Another significant development in the netting effort since 2014 is
that crews have been allowed to net in the South, Southeast and Flat Mountain Arms for the past 4
years. This is a result of a relaxation of the boating restrictions in those areas which is especially
important as we try to keep pressure on the population throughout the system. Graph 7 shows the
CPUE over all areas of the lake over the past four years and also demonstrates the wide distribution of
|Details of the Status of the LT Suppression|
2016 was also a good year for the telemetry study. During this summer, a total of 97 hydro-acoustic
transmitters were surgically implanted into LT. This was accomplished by the biggest volunteer effort
on the Lake since TU's involvement. A total of 125 volunteers and 25 fishing boats spent 8 days on the
Lake catching LT for the study. The number of tags has to be constantly replenished as the tagged LT
are being caught in the gill nets and the tags harvested for re-implantation. The signals from tagged
fish are picked up anytime one of these fish swims within listening range (roughly 500 meters
depending on water conditions) of a semi-permanently positioned receiver. There are about 50
receivers in the system. This provides data on movement patterns, congregation areas, and travel
corridors of the LT. All of this information aids the netting crews. These data that indicate broad scale
movement patterns are analyzed by Dr. Lee Gutowsky of Carleton University under contract with TU.
Just one of many maps of the Lake showing movement patterns is shown in Graph 9. It is obvious that
the LT move dramatically throughout the system. However, by studying this information it is possible to
locate travel corridors and "hot-spots" of LT congregation by season. See Graph 10.
In the fall, the goal of the telemetry study changes, repositioning the receivers in close proximity
arrays to pinpoint suspected spawning areas. These VPS (Vemco Positioning System) arrays, with
the help of a reference signal and triangulation, determine the exact location of each fish within the
array. This helps identify specific sites for further study as potential spawning beds. These data are
analyzed by Dr. Jason Romine of the US Fish and Wildlife Service again under contract with TU.
During fall of 2016 the areas studied with these arrays were the SE Arm and Breeze Channel (see
Graph 11). Complete data analysis is not yet complete from these arrays but Graphs 12 and 13 show
the type of kernel density plots that lead to suspected spawning sites. Data from these arrays set in
2015 revealed spawning areas that are now confirmed in the Flat Mountain Arm, the South Arm, and
at Carrington Island. After suspected spawning areas are identified by the arrays, they are confirmed
or ruled out by underwater divers, egg collection baskets, fry traps, and/or the use of underwater
robotics and cameras. Much of this work is done either by NPS personnel or under contract with Dr.
Ellen Marsden, University of Vermont.
Graph 9: Typical
movement patterns of
LT in YL as developed
by telemetry study.
Graph 10: Broad
patterns of LT
showing areas of
Graph 11: VPS arrays deployed in
2016 (circled) with the previous
arrays indicated. Breeze Channel
and Southeast Arm.
Graph 12: Kernel density
plots which show areas of
high LT concentration and
potential spawning areas
(indicated by red areas).
Graph 13: Individual LT
movement patterns at
spawning bed showing
Graph 14: Potential and
sites on YL.
Alternative Suppression Techniques:
Trout Unlimited has had a long term goal of not only knowing where lake trout spawn, but also the
development of alternative suppression technology which will allow NPS crews to target the other life
stages (ova and fry) of lake trout. It is anticipated that once the time consuming and expensive netting
operation has reduced the lake trout population to the point that the cutthroats can rebound, a less
expensive and less time consuming method will be needed to keep the numbers of LT from
rebounding. Several potentially useful techniques are under study. Among them electro-shock
treatment, suction dredging, tarping with or without treatments such as rotenone under the tarp, and
the deployment of LT carcasses onto the spawning beds. Each has its advantages and
short-comings. Electro-shocking has been shown to be effective on both ova and fry but has some
limitations on penetration into the large cobble substrate and is difficult to deploy on deep water
spawning beds. Some have been found as deep as 65 feet.
It has been shown to be lethal to eggs at up to 20 cm into the substrate but eggs can penetrate
deeper than that. There are also limits due to the low conductivity of YL water. See graph 15 for a
picture of the electro-shocking gear. Suction is focused on LT eggs, but also difficult to deploy at
depth. See Graph 16. Rotenone is effective at killing both ova and fry but the exposure times are long
limiting its effectiveness. The use of LT carcasses is the most recent technique being evaluated. It
has shown potential to be effective as the decaying of the carcasses depletes the oxygen from the
water and also introduces fungus into the spawning beds which is believed to be lethal to the eggs.
During 2016, NPS crews evaluated the LT carcass technique at both Carrington Island and Flat
Mountain Arm spawning beds. The results are encouraging but the robustness of this technique still
needs to be determined. Development of the most effective technique(s) for killing LT ova and fry is an
ongoing project that will extend into 2017 and beyond. It will become an important part of the TU effort.
Graph 15: Getting ready to
gear at Carrington Island
at Carrington Island to
remove LT eggs.
Graph 17: LT carcass
treatment of spawning
|(Please click thumbnails to enlarge photos.)
The ultimate goal is not just removing lake trout. It's to recover the cutthroat population. Many direct
indicators show progress towards this goal. By-catch numbers discussed above is one of those
indicators. A better indicator is the YCT distribution netting. This scientific tool utilizes a specific set of
nets placed at exactly the same locations around the Lake at the same time of year (early August) and
soaked for the same length of time.
Although the results are not a true population estimate of the cutthroats in the system; they are very
important and meaningful if multi-year trends are compared. During the mid 2000's and into 2011, the
population distribution by size of the cutthroats was very skewed to the very large cutthroats. There
simply were very few young cutthroats left in the system. The most logical reason was that small
cutthroats were being eaten by the lake trout either as they emerged from the spawning tributaries or
shortly thereafter. This was particularly disturbing since there were also very few mid-sized (mid-aged)
cutthroats in this system that provide the bulk of the spawning age class. Starting in 2012 and
continuing through 2016, this trend is being broken. For five years, we have seen both a higher
number of cutthroats in the distribution netting and more significantly, a stronger survival of young and
mid-aged fish. The results are extremely encouraging. See Graph 18 for details.
An additional indicator of cutthroat population health is the number of cutthroats entering the tributaries
in the spring to spawn. The most famous of these streams is Clear Creek. Spawning runs up this
stream were epic, with tens of thousands counted every year. The numbers counted in 2006-2007
declined to less than 500 per year. After the weir blew out in 2008 from high water, this count was lost
and still hasn't been recovered in spite of efforts to install an automated system called a Didson.
The only other spawning stream monitoring that is still in place involves visual monitoring of about a
dozen smaller spawning streams along the road system around the Lake. This has been going on
for years by the grizzly monitoring crews. The observed cutthroats declined precipitously during the
early years of LT predation until essentially no cutthroats were observed.
In recent years, a small but significant rebound has been observed. See Graph 19. The presence of
these spawning cutthroats in tributaries to Yellowstone Lake is having another positive impact. The
ecosystem of the YL area was significantly impacted by the cutthroat decline; some 40 species
depend on these fish for at least a portion of their diet. With the decline, the species had to rely on
other food sources or suffer from population decreases. No species was impacted more than the
grizzly. They used to rely on cutthroats for a major portion of their diet in the spring as the cutthroats
ascended the tributaries to spawn and the grizzlies had a high protein feast. Over the past dozen or
so years, no grizzlies had been observed feeding in these tributaries; until last spring. One bear, in
particular, set up on Little Thumb Creek last June and spent many days there feeding on the
recovering cutthroat numbers found. To see a video of this bear go to
https://www.youtube.com/watch?v=jzxVkes0i_Q (Copy and Paste).
And finally, anglers are reporting more cutthroat in their catch. The best measure of this is the angler
survey results. During the "glory years" of cutthroat fishing, anglers reported catch rates of 1.5-2
cutthroats per hour of angling. That number declined to around 0.5 in the mid 2000's. It has now
rebounded somewhat and is approaching 1.0 again. See Graph 20.
Graph 18: YCT distribution
netting results (number of
fish versus size in mm) for
Graph 19: Visual survey
results of 12 small
streams for YCT spawning
Copy and paste YouTube
Graph 20: Angler survey results
for the past 30 years showing
YCT catch rates per hour.
Yellowstone Forever continues as the principle funding source for the gill netting outside of the NPS
fisheries budget. They have pledged $1 million per year.
Trout Unlimited, along with the other NGO's on the Working Group, are the principle funding sources
for the telemetry study, spawning bed identification, ova/fry life history studies, and other alternative
suppression studie. To date, these groups have raised almost $1.1 million. The biggest contributor
has been the Wyoming Wildlife and Natural Resources Trust with a 4 year grant of $771,000 secured
by Wyoming TU. This grant has to be matched by private funding so the NGO's are constantly looking
for assistance and donations. The year 2017 will be the last year of this significant grant. Other
funding sources are being explored. To help with these efforts, click on our tax deductable PayPal link:
The Yellowstone cutthroat trout population in the
Yellowstone Lake system is recovering. However, that
population is still a long way from its historical levels.
The lake trout problem is not over. It has been lowered,
but it will never be wiped out. We must continue to drive
down the adult and juvenile LT populations while
working on reducing recruitment of this voracious
predator by targeting the ova and fry. With everyone's
constant vigil, we will "Save the Yellowstone
Cutthroats" of this system.
|Yellowstone Cutthroat Trout Recovery|
For more information please call
Dave Sweet, campaign coordinator,
|Donate to Save the Yellowstone Cutthroats
June 2018 Fishing Trip