U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the U.S. Fish and Wildlife Service

Fish Tag Recovery from Anaho Island Nesting Colony, 

Pyramid Lake, Nevada

Open-File Report 2015–1242
Cover: Photograph showing American White Pelican on the Anaho Island nesting colony, Pyramid Lake, Nevada. 

Photograph by Donna Withers, U.S. Fish and Wildlife Service, 2013.
Fish Tag Recovery from Anaho Island Nesting Colony, 

Pyramid Lake, Nevada

By G. Gary Scoppettone, Mark C. Fabes, Peter H. Rissler, and Donna Withers

Prepared in cooperation with the U.S. Fish and Wildlife Service

Open-File Report 2015-1242

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

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Suggested citation:

Scoppettone, G.G., Fabes, M.C., Rissler, P.H., and Withers, Donna, 2016, Fish tag recovery from Anaho Island 

nesting colony, Pyramid Lake, Nevada: U.S. Geological Survey Open-File Report 2015-1242, 28 p., 

http://dx.doi.org/10.3133/ofr20151242. 

ISSN 2331-1258 (online)
iii

Contents

Abstract ...................................................................................................................................................................... 1

Introduction................................................................................................................................................................. 2

Description of Area ..................................................................................................................................................... 3

Material and Methods ................................................................................................................................................. 6

Cui-ui Tag Deployment ........................................................................................................................................... 6

Fish Tag Recovery.................................................................................................................................................. 7

Probability Experiment of Tag Recovery ................................................................................................................. 8

Tag Dispersal and Recovery Experiment................................................................................................................ 8

Tagged Fish Fed to Pelican and Tags Dispersed ................................................................................................. 10

Results and Discussion ............................................................................................................................................ 11

Tagged Fish Fed to Pelicans ................................................................................................................................ 14

Tag Dispersal Study.............................................................................................................................................. 15

Tagged Fish Fed to Pelicans and Tag Dispersal................................................................................................... 18

Spiny Ray Fishes .............................................................................................................................................. 23

Conclusions .............................................................................................................................................................. 24

Acknowledgments..................................................................................................................................................... 24

References Cited...................................................................................................................................................... 25

Appendix A ............................................................................................................................................................... 27

Figures 

Figure 1. Location of Anaho Island at Pyramid Lake, Nevada, with connecting waters. .......................................... 4

Figure 2. Boundaries of Anaho Island nesting sub-colony areas, Pyramid Lake, Nevada, 2014. ............................ 5

Figure 3. Locations of dispersal tags and tag deployment areas on Anaho Island nesting colony, 

Pyramid Lake, Nevada. ............................................................................................................................................. 9

Figure 4. Density distribution of cui-ui (Chasmistes cujus) tags recovered from Anaho Island nesting 

sub-colonies, Pyramid Lake, Nevada, 2001–14....................................................................................................... 13

Figure 5. Areal distribution of recovered tags dispersed on the Anaho Island nesting colony, Pyramid Lake, 

Nevada. ................................................................................................................................................................... 16

Figure 6. Assortment of hooked lures and stringers gathered from the Anaho Island nesting colony, 

Pyramid Lake, Nevada, 2001–2014......................................................................................................................... 20

Figure 7. Locations of tagged fish deployment taken by American White Pelican (Pelecanus erythrorhynchos) 

back to Anaho Island nesting colony, Pyramid Lake, Nevada ................................................................................. 22
iv

Tables

Table 1. History of cui-ui tags recovered from Anaho Island nesting colony, Pyramid Lake, Nevada, 2001–14. ..... 6

Table 2. Total number of tags recovered from 1,179 common carp (Cyprinus carpio) and Lahontan

cutthroat trout (Oncorhynchus clarkii henshawi) fed to pelicans, Anaho Island nesting colony, Pyramid Lake, 

Nevada, springs of 2011 and 2012.......................................................................................................................... 14

Table 3. Total number of recovered tags dispersed throughout Anaho Island nesting colony, 

Pyramid Lake, Nevada. ........................................................................................................................................... 15

Table 4. Dispersal tags deployed by sub-colony, tags recovered, and frequency of tag recovery, 

Anaho Island nesting colony, Pyramid Lake, Nevada.............................................................................................. 17

Table 5. Two sample Z-test to compare sample proportion for significance between tag recovery passes,

Anaho Island nesting colony, Pyramid Lake, Nevada.............................................................................................. 17

Table 6. History of salmonid tags recovered from Anaho Island nesting colony, Pyramid Lake, Nevada............... 19

Table 7. History of spiny ray fish tags recovered from Anaho Island nesting colony, Pyramid Lake, Nevada ........ 23

Conversion Factors

International System of Units to Inch/Pound

Multiply By To obtain

Area

square kilometer (km2) 0.3861 square mile

Length

meter (m) 39.37 inch

millimeter (mm) 0.0393 inch

kilometer (km) 0.6213 mile

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: 

°F = (1.8 × °C) + 32.
1 

Fish Tag Recovery from Anaho Island Nesting Colony, 

Pyramid Lake, Nevada

By G. Gary Scoppettone1, Mark C. Fabes1, Peter H. Rissler1, and Donna Withers2

Abstract

In 2001, tags applied to the federally endangered species cui-ui (Chasmistes cujus) to study their 

population dynamics were discovered strewn throughout the American White Pelican (Pelecanus 

erythrorhynchos) nesting colony on Anaho Island, Pyramid Lake, Nevada. Cui-ui are endemic to 

Pyramid Lake, and Anaho Island harbors one of North America’s largest nesting colonies of American 

White Pelican. Cui-ui are consumed by pelicans during the fish’s spring migration into the Truckee 

River to reproduce. The predatory success of pelican has been validated by determining the odds of 

finding a tag from a predated cui-ui within the Anaho Island nesting colony. It is unknown how many 

cui-ui tags are eliminated by birds before arrival to the colony versus how many are brought to the 

colony but never recovered. The focus of this study was to improve the estimate of the chances of 

collecting a tag from a predated adult cui-ui in the pelican nesting colony by feeding dead tagged 

Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) and common carp (Cyprinus carpio) to 

pelican and subsequently searching for these tags within the colony. We also randomly deployed 1,000 

dispersal tags throughout the nesting colony, searching for these after one and two breeding seasons. 

After adding 1,027 fed fish to 547 previously fed fish, we estimated 5.3 percent of the tagged cui-ui 

taken by pelican were recovered during tag searches. A study of dispersal tags randomly deployed

within the pelican nesting colony showed that 51.5 percent would be expected to be recovered after at 

least one breeding season after being deployed. Results of our studies indicate that more than 90 percent 

of tags from adult cui-ui are eliminated by birds outside the pelican nesting colony. Tags recovered from 

other species and the site at which they were tagged are also reported. Most notable were recovered 

Lahontan cutthroat trout tags, which were the highest in number, but their proximity to double-crested 

cormorant (Phalacrocorax auritus) nests suggests this species to be the primary predator. Tags from 

other species of fish came from as far as the Columbia River, Washington (about 600 kilometers). This 

study provides an important baseline for future tag recovery from the pelican nesting colony on Anaho 

Island and opens new questions to American White Pelican movement patterns. 

 

1

U.S. Geological Survey.

2

U.S. Fish and Wildlife Service.
2 

Introduction

Colonial piscivorous birds have the capacity to consume substantial portions of 

anthropogenically valued fish populations (Collis and others, 2002; Dalton and others, 2009; 

Scoppettone and others, 2014). Bioenergetics models have frequently been used to quantify fish 

consumed by piscivorous birds (Madenjian and Gabrey, 1995; Derby and Lovvorn, 1997; Wiese and 

others, 2008; Dalton and others, 2009). Another means of assessing the effect of predatory birds on fish 

populations is the detection and enumeration of fish tags eliminated by birds within a nesting colony 

(Collis and others, 2001; Scoppettone and others, 2006). However, without the knowledge of the 

probability of detecting a bird-ingested tag from a given marked fish population, this method lacks 

accuracy (Collis and others, 2001). These ratios have been established for the predator/prey relationship 

between American White Pelican (Pelecanus erythrorhynchos) and cui-ui (Chasmistes cujus) at 

Pyramid Lake, Nevada (Scoppettone and others, 2014), providing a unique opportunity to use fish tags 

for gauging the influence of American White Pelican on the adult cui-ui population and for evaluating 

the importance of cui-ui to their diet.

American White Pelican nest on Pyramid Lake’s largest island (Anaho Island), a National 

Wildlife Refuge within the confines of the Pyramid Lake Paiute Indian Reservation (Anaho Island 

National Wildlife Refuge). Pelicans begin arriving at Pyramid Lake in late winter coming from southern 

California and Mexico (Seegar and Fuller, 1997). At about the same time, adult cui-ui, which are 

obligate lake dwellers but stream spawners, migrate to the mouth of Pyramid Lake’s only perennial 

tributary, the Truckee River (Scoppettone and others, 1986, 2006). The American White Pelican is not a 

diving bird, so cui-ui typically become vulnerable to pelican predation when they enter the river on their 

spawning migration. Cui-ui are not an annual reliable food source for pelicans because they frequently 

skip spawning due to insufficient streamflow (Scoppettone and others, 1986, 2000). However, cui-ui 

can incur high mortality attributable to pelican predation when a spawning migration is attempted 

(Scoppettone and others, 2014). 

Although the probability of detecting a tag within the nesting colony from a tagged cui-ui 

ingested by a pelican has been established, the fate of pelican-ingested tags not detected in the colony is 

unknown. In this paper, we research the question of how many tags deployed on adult cui-ui arrived to 

the pelican nesting colony but went undetected versus how many were eliminated by birds outside the 

colony. This information is important because these data will enable future assessments of tags collected 

within the nesting colony for future tagging of cui-ui or other fish species. In this paper, we also report 

on all tags from all fish species collected from Anaho Islands’ colonial bird populations including when 

and where they were tagged and released. Information from this study is intended to give managers 

some insight into the influence of predatory birds on their subject tagged fish and provide a baseline for 

further research.
3 

Description of Area

Pyramid Lake is approximately 467 km2 in total area and lies within the Pyramid Lake Indian 

Reservation in west-central Nevada. Anaho Island is approximately 720 m off the eastern shore of 

Pyramid Lake and about 12 km northeast of the mouth of the Truckee River (fig. 1). The American 

White Pelican nesting colony occupies approximately 11 ha of Anaho Island’s 300 ha area and is 

primarily on the eastern side of the island. The colony is comprised of seven sub-colonies separated by 

50 m or more of no apparent nesting activity (fig. 2). American White Pelican are ground nesters (Evans 

and Knopf, 1993), and their nesting areas were not only defined by their large round nest, but by 

trampling activity of adults and juveniles with typically no signs of perennial vegetation nearby. Within 

the colony, there are patches of greasewood (Sarcobatus vermiculatus) and localized areas of tufa rock. 

Ground substrate is comprised of loose gravel, sand, broken tufa rock, and gastropod shells. Several 

species of colonial nesting waterfowl nest on Anaho Island (Scoppettone and others, 2006), but pelican 

nests were most closely associated with nests of double-crested cormorant (Phalacrocorax auritus). 

Cormorant nests, which were largely constructed of greasewood, along with their respective ground 

activity, contributed to defining the colony’s boundaries. There was some movement in colony 

boundaries during the study leading to a slightly greater search area over time.

American White Pelican prey upon cui-ui along the lower 18 km of the Truckee River, but are 

most successful at anthropogenically caused impediments to cui-ui migration. Most outstanding was the 

formation of a shallow delta at the mouth of the Truckee River caused by water diversion from the 

system (La Rivers, 1962). The shallow delta restricts fish passage in many years and is an area of 

pelican congregation and fish predation. The Marble Bluff Complex was completed in 1975 to mitigate 

the negative impacts to the Pyramid Lake fishery caused by federally funded water diversion from the 

Truckee River. The complex consists of Marble Bluff Dam, constructed approximately 5 km upstream 

of the mouth of the Truckee River, and serves to divert water down a 5 km bypass channel (Marble 

Bluff Fishway) to the delta, and also stabilizes the river upstream, which became erosive following the 

water-level decline of Pyramid Lake (Glancy and others, 1972). The dam has a trap and elevator to pass 

fish upstream should they successfully negotiate the delta. Marble Bluff Fishway has ice harbor type 

fish ladders along its course. Although the Marble Bluff Complex has been successful in facilitating fish 

passage, migratory impediments caused by the dam and ladders are areas of heavy pelican predation 

during the cui-ui spawning migration. Another site of notable predation is Numana Dam approximately 

18 km upstream of the Truckee River mouth. Numana Dam is also fitted with a fish ladder, but it

impedes migration sufficiently to become an area of heavy pelican predation (Scoppettone and others, 

2014). 
4 

Figure 1. Location of Anaho Island at Pyramid Lake, Nevada, with connecting waters.
5 

Figure 2. Boundaries of Anaho Island nesting sub-colony areas, Pyramid Lake, Nevada, 2014. 
6 

Material and Methods

Cui-ui Tag Deployment 

There is a long history of fish tag deployment on cui-ui (Koch, 1972; Sonnevil, 1981; 

Scoppettone and others, 1986, 2014). Tags were of several types and deployed by several organizations. 

A list of tags deployed, deployment dates, and organizations deploying tags is shown in table 1. 

There was a substantial increase in cui-ui deployment from 1989 through 2006 associated with a 

multi-year cui-ui population dynamics study. Within this time period, 10-mm-long numbered T-bar 

anchor tags were deployed on cui-ui netted annually from their spring-time prespawning aggregation to 

determine adult survival rate (Scoppettone and others, 2015) and around the periphery of the lake to 

determine juvenile survival rates. Number and tag color along with demographic information of 

captured fish were entered into a database at the time of tag deployment.

Table 1. History of cui-ui tags recovered from Anaho Island nesting colony, Pyramid Lake, Nevada, 2001–14.

[MBD, Marble Bluff Dam; PLPT, Pyramid Lake Paiute Tribe; RFS, Reno Field Station (currently under the U.S. Geological 

Survey, formerly under the U.S. Fish and Wildlife Service Region 8, and the National Biological Survey); UNR, University 

of Nevada Reno; USFWS, U.S. Fish and Wildlife Service]

Release 

organization Tag type Deployment date

Release 

location Season Number deployed

Number 

recovered

UNR - Dave Koch Carlin 1970–1972 River mouth Spring 329 1

USFWS Carlin 1976–1985 River mouth Spring 2,704 24

PLPT Hatchery Carlin 1980 River mouth Spring NA 1

USFWS T-bar anchor 1982–1985 River mouth Spring 3,082 7

USFWS Sonic 1983 River mouth Spring 6 1

USFWS T-bar anchor 1984–1987 MBD Spring 515 1

RFS PIT 1988 Lake periphery Summer 278 0

RFS PIT 1989 River mouth Spring 743 0

RFS T-bar anchor 1989–2006 River mouth Spring 251,749 7,357

RFS T-bar anchor 1988–2006 Lake periphery Year round 84,022 1,776

RFS T-bar anchor 1997 MBD Spring 5,088 354

RFS T-bar anchor 1988–2006 (unreadable tags) 1,206
7 

Fish Tag Recovery

The discovery and recovery of fish tags began in autumn 2001 and extended to winter 2014; 

there were 1–3 annual visual searches totaling 24 search passes over a 14-year period. Searches took 

place when there were no pelicans on the island, which was from October through February, and 

consisted of teams of 3–14 people looking for fish tags for a 3–4 hour duration (typically between 1000 

and 1400 hours). Searches took 5–6 days and 114–188 hours. Searches were considered equal effort, 

and time expended for each search influenced the number of tags encountered. When a fish tag was 

sighted, the searcher logged GPS location, tag type, color, and pertinent information on the tag (agency 

and identification number). Tag recovery densities were calculated using ArcGIS software 

(Environmental Systems Research Institute, 2010) to plot a percentage point density using the subcolony areas as a base layer. A variety of fish tags have been recovered over the course of this study 

(fig. A1). T-bar anchor tags deployed on cui-ui in the prespawning aggregation from 1989 through 1996 

were of primary interest. This time period and location was particularly important because when tag 

collections from Anaho Island began in 2001, the tags deployed from this time period were virtually 

absent from adult fish in the prespawning aggregation, indicating few tags from this period were 

eliminated by birds in the colony after tag searches began (Scoppettone and others, 2014). This 

knowledge of presences at the time of our collection was critical in the estimation of the impact of 

pelicans on adult cui-ui survival. Tags deployed around the periphery of the lake in 1989–96 were not 

used because the large majority were juveniles (less than 300 mm fork length [FL]) and sufficiently 

small enough to have been consumed by double-crested cormorants, which have been observed foraging 

on fish up to about 295 mm FL (Hobson and others, 1989). 

On survey passes 5 and 6, which occurred between 2003 and 2004, we used a Biomark® Scanner 

to detect PIT tags that we experimentally injected into 200 cui-ui that were fed to pelicans (not reported 

in table 1). The scanner also was used in an attempt to detect PIT tags from the 1,021 injected into cui-ui 

in 1988 and 1989. 
8 

Probability Experiment of Tag Recovery

To estimate the number of cui-ui consumed by pelicans from tags recovered, tagged dead fish 

were fed to pelicans in the lower Truckee River to determine the chance of tag recovery in the pelican 

nesting colony. Feeding began in 2003 and extended to 2008 using only tagged dead cui-ui. There were 

544 tagged dead adult cui-ui successfully fed to pelicans during this 6 years of feeding. The feeding of 

dead tagged fish greatly increased in 2011 and 2012 when Lahontan cutthroat trout (Onchorynchus 

clarkii henshawi) and common carp (Cyprinus carpio) were used as cui-ui surrogates. Methods of 

feeding and sizes of fish fed used in the experiment, as well as methods used for estimating probability 

of collecting these experimental tags within the Anaho Island nesting colony is described by 

Scoppettone and others (2014). 

Tag Dispersal and Recovery Experiment

To determine the probability of detecting a cui-ui tag eliminated by a pelican on Anaho Island, 

1,000 T-bar anchor tags (dispersal tags) were placed within the colony from February 10–16, 2012, 

before 2012 nesting began. Dispersal tags were a light blue color and similar to T-bar anchor tags 

deployed on cui-ui in the past and were identifiable by their label (the letters ANWR and a four-digit 

number). Each of the 1,000 tags was given a predetermined, randomized coordinate location using 

ArcGIS software (Environmental Systems Research Institute, 2010). The boundaries of the random 

coordinates were used from locations of tags that had been recovered from previous surveys within the 

sub-colonies. The overall percentage of tags recovered from each sub-colony was used to determine the 

number of coordinates to assign to each sub-colony. These random waypoints were loaded into GPS 

units and used for tag deployment (fig. 3).

Searches for dispersed ANWR tags were integrated into passes 21–24. Dispersed tags had been 

within the colony following one breeding season in searches 21–23 from October 20, 2012, to February 

13, 2013. In search 24 from November 26, 2013, to February 21, 2014, dispersed tags had gone through 

two breeding seasons. 

When a dispersed tag was located, the same information was collected as for the other tags 

except dispersed tags were returned to the exact spot they were recovered once all pertinent information 

was documented. 
9 

Figure 3. Locations of dispersal tags and tag deployment areas on Anaho Island nesting colony, Pyramid Lake, 

Nevada. 
10 

We used a two sample Z-test to compare sample proportions (Stangroom, 2014) to determine if 

there was a significant difference in dispersal tag recoveries among passes of the same year (passes 21–

23) and over 2 years (passes 21–23 with 24): 

Z = (p̅

1−p2̅ )−0

�p̅(1−p̅)� 1

n1

+ 1

n2

�

(1)

where 

p is the proportion of dispersed tags recovered and n is the total dispersed tags per 

search.

To account for differences in survey hours per pass, we adjusted the dispersal recovery 

percentage using the following formula: 

D tags = [Tn - T hour*(Pn - P24)]/1,000 (2)

where 

 Tn is the number of tags recovered for each respective pass, 

 Thour is the number of tags recovered per hour for each pass, 

 Pn are the hours for each pass, and 

 P24 is the total hours for pass 24, which was used as the baseline. 

We used a depletion estimator to calculate the total number of dispersal tags we would expect to 

find of the 1,000 tags had searches continued until all tags could be recovered. We used the jackknife 

regression heterogeneity model Mh (Polluck, 1990), as proposed by Chao (1987), in Program 

CAPTURE (Rexstad and Burnham, 1991) to calculate the depletion estimates.

Tagged Fish Fed to Pelican and Tags Dispersed

We used fish fed to pelicans and the tag dispersal study to calculate the relative percentage of 

cui-ui tags from the prespawning aggregation consumed and eliminated by birds outside of the pelican 

nesting colony. The estimated proportion of tags eliminated by birds outside of the colony was 

calculated using the following formula:

E = 1.00 – F/D (3)

where

 E is the number of cui-ui tags eliminated by birds outside the pelican nesting colony; 

 F is the chance of finding a tag from a fed pelican in the nesting colony (for this study 

we used 5.3 percent the value generated by Scoppettone and others, 2014); and

 D is the estimated percentage of dispersal tags in the nesting colony generated by the 

depletion calculation. 
11 

Results and Discussion

Cui-ui Tag Recovery

 Tags were recovered from almost all 36 years (1970–2006) of cui-ui tag deployment; recovered 

tags represented several tag types and deploying organizations (table 1). The tag with the longest history 

was a Carlin tag deployed on a fish by Dave Koch in spring 1972 (Koch, 1972) near the mouth of the 

Truckee River and recovered from the colony in 2004, 32 years following deployment. This Carlin tag 

was deployed on one of several of his tagged fish with no recorded data. The earliest T-bar anchor tag 

deployment was in 1982 from a cui-ui netted from the prespawning aggregation and recovered in the 

colony in winter 2002, 30 years following deployment. The presences of the dated Carlin and anchor 

tags is remarkable and may be due to them remaining on a live fish for many years before the fish was 

ingested by a pelican.

Another potential cause is that tags are continually buried and unearthed, which allows for their 

preservation, especially for the plastic T-bar anchor tag, which is especially subject to sun degradation. 

Although we scanned the entire colony twice (passes 5 and 6), we did not detect any of the 1,021 PIT 

tags injected into cui-ui from the prespawning aggregation or around the lake periphery in 1988 and 

1989. This is understandable, because signals from these early developed PIT tags were relatively weak, 

and even slight burial within the colony rendered them undetectable. We did detect 6 of the 200 PIT 

tags injected into dead fed fish, probably because of their stronger signal. Fed fish injected with a PIT 

tag also harbored a T-bar anchor tag, which was used to determine probability of tag recovery; thus, the 

PIT tags are not reported in table 1. The only sound or radio wave transmitting cui-ui tag we recovered 

from the colony was a 64-mm-long, 16-mm-wide sonic tag implanted in April 1982. The tag was from 1 

of 11 sonic tags deployed in cui-ui captured and released in the prespawning aggregation and used to 

track lake movement (Scoppettone and others, 1986). 

The large majority of tags deployed on cui-ui were from 1989 through 2006, with more than

251,000 tagged in the pre-spawning aggregation and an additional 84,500 around Pyramid Lake. From 

the 1989 to 2006 tag deployment, more than 10,000 were recovered from Anaho Island (table 1). The 

greatest return for prespawning aggregation fish came from those fish tagged from 1989 through 2000, 

with more than a 5.8 percent recovery rate. Recoveries from tags deployed from 2001 to 2006 were only 

1.6 percent. We attribute these results partially to the use of almost 25,000 white-colored tags deployed 

from 2000 to 2003, which were extremely difficult to detect amongst white bones and shells resulting in 

only 0.003 percent recovery. Rate of recovery was higher for tags with dark colors (such as blue and 

green), probably due to the tags contrast with the light-colored substrate. Also, there is about a 4.0–5.0 

percent annual shed rate of tags (Scoppettone and others, 2014), equating to a high number of tags shed 

before pelican predation in 2001–14 due to frequent years of drought and no cui-ui spawning migration. 

However, even in the wet year of 2006, when cui-ui were observed packed downstream of Marble Bluff 

Dam, few pelican focused on cui-ui predation, and apparently concentrated on a more reliable and 

continuous food source from another region of the Great Basin. Thus, cui-ui were less of a food source 

during the 2000s compared to the 1990s when there was a greater frequency of high water years. 
12 

Cui-ui tags deployed from 1989 to 2006 were recovered throughout the Anaho Island nesting 

colony. However, there were areas with disproportionally high tag density such as seen in sub-colony A 

and in sub-colony D (fig. 4). With regard to sub-colony A, the first arrival of pelicans to the colony 

typically settles in sub-colony A, giving these birds a more protracted period to take cui-ui, contrasted to 

birds settled on sub-colonies Bluff, Saddle, and Ridge (fig. 4), which typically arrive later. Also, nesting 

occurred within sub-colony A on an annual basis, unlike sub-colony B and Bluff. High cui-ui tag 

density in sub-colony D also suggests heavy pelican use, but this sub-colony along with sub-colony C is 

localized and consequently receives inordinately high search attention and probably slightly skewed 

results. No nesting, or virtually no nesting, typically occurred in dry years when cui-ui where not readily 

available for predation, but even modest collections of tags over time contributes to sub-colony A’s 

areas of high density. The cui-ui tag recovery history, as well as other species from Anaho Island 

between 2001 and 2014 is shown in appendix (table A1). Adult cui-ui consumed by pelicans ranged 

from 375 to 640 mm FL. The largest fish probably weighed about 3.5 kg. 

Searches were primarily within the pelican nesting colony, but we also recovered some tags 

outside sub-colony boundaries. Larger pre-fledging chicks have been observed moving to the shoreline, 

so perhaps birds fed there. Our subjective observation was that tags move in runoff events and in subcolonies with areas consisting of substantial sloping (Bluff, Ridge, B and C). Even at that, most tags 

appeared to remain within the confines of its respective sub-colony. 
13 

Figure 4. Density distribution of cui-ui (Chasmistes cujus) tags recovered from Anaho Island nesting sub-colonies, 

Pyramid Lake, Nevada, 2001–14.
14 

Tagged Fish Fed to Pelicans 

In the springs of 2011 and 2012, we successfully fed 1,179 dead carp and trout as cui-ui 

surrogates to foraging pelican around the mouth of the Truckee River and at the mouth of the Marble 

Bluff Fishway. These fish ranged from 222 to 750 mm FL. Only 673 were adult cui-ui size (>375 mm 

FL) and used by Scoppettone and others (2014), because smaller fish had a significantly greater chance 

of being retrieved within the nesting colony (Scoppettone and others, 2014). We suspect the reason for 

this is that pelicans expel indigestible matter (bones, scales, tags) of larger fish before returning to the 

colony, improving flight take-off and energy efficiency. However, the addition of cui-ui-size carp and 

trout fed to pelicans brought the sample size of fish fed to pelicans to 1,219, more than double the 

previous sample size, where only adult cui-ui (n=546) had been used. Of the 673 (>375 mm FL) carp 

and trout fed to pelicans, only 36 were recovered within the colony in the last seven passes (table 2). We 

estimated recoverable tags from adult cui-ui to be only 5.3 percent (95 % CI, 4.4–6.7 %) within the 

nesting colony (Scoppettone and others, 2014). 

Table 2. Total number of tags recovered from 1,179 common carp (Cyprinus carpio) and Lahontan cutthroat trout 

(Oncorhynchus clarkii henshawi) fed to pelicans, Anaho Island nesting colony, Pyramid Lake, Nevada, springs of 

2011 and 2012.

[Fish were released to foraging pelicans at the mouth of the Truckee River and Marble Bluff Fishway, Pyramid Lake, 

Nevada. Only 673 fish were greater than (>) 375 mm fork length (FL); mm, millimeter] 

Pass

Recovery occurrence

Common 

carp

Lahontan 

cutthroat trout

Fish 

> 375 mm FL*

Pass 18 11 6 7 

Pass 19 12 5 5 

Pass 20 5 3 3 

Pass 21 3 1 3 

Pass 22 4 6 6 

Pass 23 5 6 9 

Pass 24 2 3 3 

Total 42 30 36
15 

Tag Dispersal Study 

Of the 1,000 tags dispersed throughout the nesting colony, 45 percent (n=446) were recovered in 

four passes (fig. 5). There were 123 different tags recovered in the first pass (pass 21 overall of the 

colony); 117 in the second pass (pass 22 overall); 119 in the third pass (pass 23 overall); and 87 in the 

fourth pass (pass 24 overall). Tags recovered in the first three passes occurred after one breeding season 

and in the fourth pass after two breeding seasons. Because the tags were returned to the exact location 

where they were recovered, some tags were encountered multiple times between passes; 339 tags were 

recovered once, 90 were recovered twice, 16 recovered three times, and only 1 was recovered in all 

four passes (table 3). Total number of individual tags recovered for each pass was used for the depletion 

estimator because tags were returned to their respective dispersal location. 

Table 3. Total number of recovered tags dispersed throughout Anaho Island nesting colony, Pyramid Lake, 

Nevada.

[Passes 21–23 occurred from 2012 to 2013 after one pelican breeding season; pass 24 occurred from 2013 to 2014, following 

two breeding seasons] 

Survey Recovery occurrence Total

1st 2nd 3rd 4th

Pass 21 123 123

Pass 22 85 32 117

Pass 23 72 39 8 119

Pass 24 59 19 8 1 87

Total 339 90 16 1 446
16 

Figure 5. Areal distribution of recovered tags dispersed on the Anaho Island nesting colony, Pyramid Lake, 

Nevada. Passes 21–23 occurred from 2012 to 2013, after one pelican breeding season; pass 24 occurred from 

2013 to 2014, following two breeding seasons. 
17 

The highest percentage of recovery was from sub-colony C (59.4 percent), and the lowest was 

from the Ridge (20.0 percent) (table 4). The Ridge had few experimental tags dispersed within its 

expansive area, so only one or two dispersed tag discoveries greatly influenced its results, while subcolony C is comparatively confined in area and has received little colony bird activity in the last several 

years prior to this study, enhancing the probability of tag recovery without bird disturbance (being 

buried by movement throughout the colony) before searches. 

Table 4. Dispersal tags deployed by sub-colony, tags recovered, and frequency of tag recovery, Anaho Island 

nesting colony, Pyramid Lake, Nevada. 

Sub-colony Dispersal tags 

deployed

Dispersal tags 

recovered

Frequency 

(percent)

A 621 277 44.6

B 63 16 25.4

C 101 60 59.4

D 88 45 51.1

Bluff 57 14 24.6

Saddle 65 33 50.8

Ridge 5 1 20.0

Total 1,000 446

Tags recovered from passes 21–23 had been on Anaho Island after one breeding season, and tags 

recovered in pass 24 had been on the island following two breeding seasons. These two breeding 

seasons were in dry years with far less nesting activity on the island, equating to a few adults and their 

fledglings walking on and inadvertently burying tags in loose substrate. 

The two sample Z tests suggest there is a significant reduction in the opportunity to recover 

dispersed tags after a breeding season, even following drought. There was no significant difference in 

recovery of dispersed tags between our first three passes in 2012–13 (table 5), but significantly less 

recovered in 2013–14. Future searches for these dispersed tags would slightly improve estimates of tags 

lost following a breeding season. If we had continued our passes to depletion, we calculated that there 

would be 515 (51.5 %, 95% CI 48.4–56.0 %) initial encounters of the dispersed tags. 

Table 5. Two sample Z-test to compare sample proportion for significance between tag recovery passes, Anaho 

Island nesting colony, Pyramid Lake, Nevada. 

[Proportion is percentage of tags recovered per pass of the 1,000 tags dispersed. Two paired test where p is the number of 

identifiable tags recovered with significance at p < 0.05]

Pass Proportion Pass Proportion Z p p < 0.05

21 0.123 22 0.117 0.4129 0.68180 no

21 0.123 23 0.119 0.2743 0.78716 no

21 0.119 24 0.087 2.6259 0.00854 yes

22 0.117 23 0.119 -0.1386 0.88866 no

22 0.117 24 0.087 2.2165 0.02642 yes

23 0.119 24 0.087 2.3541 0.01878 yes

Mean 21–23 0.120 24 0.087 2.4224 0.01552 yes
18 

Tagged Fish Fed to Pelicans and Tag Dispersal

Results of the tagged fish feeding and tag dispersal studies suggest most tags deployed on adult 

cui-ui in the prespawning aggregation are eliminated by birds outside of the nesting colony. From data 

generated from these studies and using the equation E = 1.00 – F/D, we estimated that about 90 percent

(95-% CI 88.0–91.0 %) adult cui-ui tags are eliminated by birds outside of the nesting colony. This low 

percentage of cui-ui tags recovered on Anaho Island maybe due to the large size of cui-ui. After a 

pelican secures an adult cui-ui, it swims downstream into the lake rather than flying directly back to 

Anaho Island. We suspect that pelicans remain in the safety of aquatic habitat to digest their large catch 

and regurgitate indigestible matter (bones, scales, and foreign objects) into the lake. We found no sign 

of regurgitation of bones and other hard materials in loafing areas, which would serve as an attraction to 

coyotes and other potential predators. 

Whole carcasses of adult cui-ui have been observed on Anaho Island, which may have been 

transported by the largest of birds. We also have witnessed pelicans swimming to Pyramid Lake from 

the Truckee River, presumably after ingesting a cui-ui, and then proceeding to swim toward Anaho 

Island until completely out of site. Thus, large carcasses may have been transported to Anaho Island by 

pelicans that swam the roughly 12 km reach. Although tags are probably regurgitated with hard matter 

off the island, Ferguson (2010) found that some fraction can remain in the bird’s proventriculus for 

several days and then be eliminated by the bird in the colony, which may help to explain the numerous 

tags recovered in the nesting colony. 

Other Species

Salmonids

There were more Lahontan cutthroat trout tags (14,617) than cui-ui tags (10,722) recovered from 

Anaho Island (table A1). The large majority of these were collected from 2006 to 2014 and associated 

with a juvenile Lahontan cutthroat trout tagging program initiated by the U.S. Fish and Wildlife Service 

(table 6). Most fish were stocked in spring-time in Pyramid Lake and the lower Truckee River (Nancy 

Vucinich, Pyramid Lake Fishery Biologist, oral commun., 2014), as well as in Walker Lake, by the 

Nevada Department of Wildlife and the U.S. Fish and Wildlife Service. Tags from juvenile Lahontan 

cutthroat trout stocked in the Truckee/Pyramid Lake system were in high density in and around 

cormorant nests indicating that these birds were their primary predator. There were relatively few tags 

from juvenile Lahontan cutthroat trout stocked in Walker Lake, and these generally were more closely 

associated with pelican nests. Approximately 160 km from Anaho Island, Walker Lake is well outside 

the 30 km foraging range of double-crested cormorant (Hatch and Weseloh, 1999), but within the 

foraging range of the more efficiently flying American White Pelican (Evans and Knopf, 1993). 
19 

Table 6. History of salmonid tags recovered from Anaho Island nesting colony, Pyramid Lake, Nevada. 

[CDFW, California Department of Wildlife; CDWR; California Department of Water Resources; NDOW, Nevada 

Department of Wildlife; PLPT, Pyramid Lake Paiute Tribe; Private, Private Fish Derby; Sigler, Sigler and Associates; USFS, 

U.S. Forest Service; USFWS, U.S. Fish and Wildlife Service. km, kilometer] 

Release 

organization Tag type Deployment date Location Number of tags recovered

Distance

(km)

Lahontan cutthroat trout

Sigler T-bar anchor 1975–1976 Pyramid Lake 4 0–5

PLPT T-bar anchor 1993, 2000–04, 

2011–13

Pyramid Lake 825 0–5

USFWS T-bar anchor 2000s Pyramid Lake 13,561 NA

USFWS T-bar anchor 2000s Walker Lake 194 155

NDOW T-bar anchor 2006 Walker Lake 31 155

NDOW T-bar anchor 2005 Truckee River 2 55

Rainbow trout

CDFW Carlin 1985 Lake Isabella 1 510

CDFW Carlin 1982–2000 Eagle Lake 49 130

CDFW Carlin 1995 Baum Lake 1 205

CDFW Carlin 1998 Lake Davis 1 90

Private T-bar anchor 2000 Weber Lake 8 110

CDFW T-bar anchor 2001–2003 Boca Reservoir 2 80

Private T-bar anchor 2005 Crowely Lake 1 270

CDFW T-bar anchor 2008 Lake Davis 10 90

Private T-bar anchor 2012 Lake Isabella 3 510

NDOW T-bar anchor 2010–11 Topaz Lake or 

Hinkson Slough

46 125–140

USFS Radio 2004 Eagle Lake 130

Chinook salmon

CDWR T-bar anchor 2006 Feather River 175
20 

Large Lahontan cutthroat trout (>400 mm total length - TL) are consumed exclusively by 

American White Pelican, the only bird within the nesting colony capable of consuming such large fish 

(Evans and Knopf, 1993). Pelicans secure large Lahontan cutthroat trout on their spawning migration up 

the Truckee River, Marble Bluff Fishway, and the spawner channel at Sutcliffe. However, tags deployed 

are on trout after they were spawned at the Sutcliffe channel, suggesting that some may be in a more 

weakened condition. Numerous hooked lures and stringer ropes recovered from the nesting colony (fig.

6) suggest that pelicans benefit from hooked fish escapes of fisherman that are taken dead or flailing at 

the surface.

Figure 6. Assortment of hooked lures and stringers gathered from the Anaho Island nesting colony, Pyramid Lake, 

Nevada, 2001–2014. 
21 

The oldest probable Lahontan cutthroat trout tags recovered from the Anaho Island nesting 

colony were deployed between 1975 and 1977 by W.F. Sigler and Associates, Inc., who conducted an 

ecological study of Pyramid Lake (Sigler and others, 1978). Their report indicated that they captured 

and tagged trout from around Pyramid Lake. These tags remained within the nesting colony for 

probably more than 20 years before their recovery. Finding these tags, as well as those deployed by 

Koch (1972) and the U.S. Fish and Wildlife Service (written commun., 2014), deposited within the 

existing nesting colony is remarkable, not only from the standpoint of duration; we observed from old 

abandoned nest sites that nesting area has shifted over time. Our tag recoveries suggest that some 

nesting areas of the colony have been used for decades.

Rainbow trout (Oncorhynchus mykiss) tags collected from the colony came from the greatest 

number of deployment areas. Judging from the distances that tagged fish were taken, most were 

probably taken by pelicans. The greatest distance was from Lake Isabella in southern California, 

approximately 510 km from Anaho Island (fig. 7). Fish captured there were from a fishing derby, and 

we suspect captured by pelicans on their late winter/early spring migration from southern California and 

Mexico to the nesting colony at Anaho Island. Rainbow trout from Lake Davis were probably the 

largest brought to the colony (>500 mm TL) and were stocked by California Department of Fish and 

Wildlife to provide an immediate fishery following a chemical treatment of the lake to extirpate 

northern pike (Esox Lucius) (California Department of Fish and Wildlife, written commun., 2009). 

Eagle Lake contributed the greatest number of tags from rainbow trout, 49 Carlin tags deployed by the 

California Department of Fish and Wildlife, and a single radio tag deployed by the U.S. Forest Service 

(table 5). The location contributing the second greatest number of rainbow trout tags to the nesting 

colony is unclear because rainbow trout tagged at Mason Fish Hatchery, Lyon County in 2010 and 2011 

by Nevada Department of Wildlife were split between Topaz Lake, Douglas County, Nevada, and 

Hinkson Slough, Lyon County, Nevada. 

The only other salmonid species represented by tag collections from the Anaho Island nesting 

colony was from a Chinook salmon (Oncorhynchus tshawytscha) tagged in 2006 and taken on the 

Feather River downstream of Lake Oroville, California. 
22 

Figure 7. Locations of tagged fish deployment taken by American White Pelican (Pelecanus erythrorhynchos) 

back to Anaho Island nesting colony, Pyramid Lake, Nevada. 
23 

Spiny Ray Fishes

Other fishes represented by recovery of tags from the Anaho Island occur in table 7. Among 

these were five striped bass (Morone saxatilis) from the San Francisco Bay Delta. Finding these tags fit 

with the movement behavior observed by Seegar and Fuller (1997), who satellite-tracked pelicans flying 

from Anaho Island over the Sierra Nevada mountain range to the San Francisco Bay Delta and returning 

to the island after 2–3 days. This pattern gave these birds sufficient time to secure prey and partially 

digest their take while purging indigestible components (scales, bones), facilitating flight back to Anaho 

Island. We suspect these forays over the Sierra Nevada to secure food occur primarily in dry years when 

there is reduced forage within 50 km of Anaho Island. Movement patterns of American White Pelican 

from their nesting site at Anaho Island in wet years compared to drought years certainly is an area where 

further research is needed. How and why tags from some other locations arrived on the Anaho Island 

colonial bird nesting colony are, at this point inexplicable. For example, the flight to the Columbia River 

was well over twice the distance of birds foraging and returning from the San Francisco Bay Delta (fig.

7). Trips to the Snake River were also substantially farther than to the San Francisco Bay Delta. Again, 

further study is needed to better interpret the significance of this substantial movement. For example, 

are birds moving these distances to secure forage to continue nesting when foraging opportunities are 

poor within the immediate nesting area, or are these birds abandoning nesting efforts and only 

inadvertently returning to the nesting colony, or are they young non-nesting birds that do not return to 

the nesting colony on a regular annual basis. This information can be obtained by tracking pelicans 

associated with demographic, behavior, and movement of Anaho Island colonial bird nesting habitat. 

Table 7. History of spiny ray fish tags recovered from Anaho Island nesting colony, Pyramid Lake, Nevada. 

[CDFW, California Department of Fish and Wildlife; IDFG, Idaho Department of Fish and Game; NDOW, Nevada 

Department of Wildlife; ODFW, Oregon Department of Fish and Wildlife. km, kilometer] 

Release 

organization Tag type Deployment date Location

Number of 

tags

recovered

Distance 

(km)

White crappie

IDFG T-bar anchor 2007 Snake River 1 440

Northern pikeminnow

ODFW T-bar anchor 1998 Columbia River 1 735

Striped bass

CDFW Disc 1993–2009 San Francisco Bay Delta 7 310

Smallmouth bass

IDFG Jaw 2009 Snake River 1 440

Wiper

NDOW T-bar anchor 2008 Wild Horse Reservoir 1 355
24 

Conclusions

1. The primary tag recovery focus was for the federally listed endangered cui-ui. 

2. Cui-ui tags were recovered that had been deployed more than 30 years before their recovery 

from the Anaho Island nesting colony. 

3. The chance of finding a tag from an adult cui-ui taken by a pelican is only 5.3 percent within the 

Anaho Island nesting colony. 

4. Once a tag arrives within the nesting colony, there is about a 51.5 percent chance of finding it 

when searching to depletion. 

5. More than 90 percent of tags from adult cui-ui are eliminated by birds outside of the nesting 

colony. 

6. Tags from adult cui-ui are suspected to be eliminated by birds in Pyramid Lake.

7. Most numerous tags were from Lahontan cutthroat trout, and tag distribution within the nesting 

colony suggested double-crested cormorants as the primary predator. 

8. The fish species brought in from the greatest number of waters (10) was the rainbow trout. 

9. Fish from Eagle Lake, California, was the greatest contributor of rainbow trout tags. 

10. Tag recoveries indicate that fish were brought to Anaho Island as far away as San Francisco 

Bay, California, Columbia River, Washington, and Snake River, Idaho, and other areas with 

distances more than 150 km.

11. Studies that focus on the Anaho Island population of American White Pelican movement 

patterns in relation to wet and dry years may be useful and informative. 

Acknowledgments

We would like to thank the U.S. Fish and Wildlife Service Stillwater National Wildlife Complex 

for allowing us access onto this unique refuge and for funding this project through Intra-Governmental 

Agreements 84320-9-H430 (06/16/2011) and 4500038818 (08/13/2012). We would also like to thank all 

those who assisted over the years in tag searches on Anaho Island, too numerous to list here. 
25 

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27 

Appendix A 

Figure A1. Types of fish tags recovered from the Anaho Island nesting colony, Pyramid Lake, Nevada, 2001–2014. 
28 

Table A1. Number of identifiable tags recovered from the Anaho Island nesting colony, Pyramid Lake, Nevada, 

2001–14. 

[Table A1 is a Microsoft© Excel file and can be downloaded at http://dx.doi.org/10.3133/ofr20151242] 
Publishing support provided by the U.S. Geological Survey

Science Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the

 Director, Western Fisheries Research Center

U.S. Geological Survey

6505 NE 65th Street

Seattle, Washington 98115 

http://wfrc.usgs.gov/
Scoppettone and others—Fish Tag Recovery from Anaho Island Nesting Colony, Pyramid Lake, Nevada—Open-File Report 2015–1242

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20151242