Lake Pleasant striped bass

              Technical Guidance Bulletin No. 11 – February 2008
Lake Pleasant Striped Bass
State: Arizona
State Trust Grant: F14R
Study Duration: January 2004 – June 2007
Prepared By:
Bill Stewart, Marianne Meding, Diana Rogers
Research Branch
Arizona Game and Fish Department
Phoenix, Arizona
AZFGD—Research Branch Technical Guidance Bulletin No. 11
Arizona Game and Fish Department Mission
To conserve, enhance, and restore Arizona’s diverse wildlife resources and habitats through aggressive
protection and management programs, and to provide wildlife resources and safe watercraft and off-highway
vehicle recreation for the enjoyment, appreciation, and use by present and future generations.
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individual may file a complaint alleging discrimination directly with AGFD Deputy Director, 5000 W.
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Dr., Ste. 130, Arlington, VA 22203.
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this document in an alternative format, by contacting the AGFD Deputy Director, 5000 W. Carefree Hwy.,
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Suggested Citation:
Stewart B.S., M.M. Meding, and D.R. Rogers. 2007. Lake Pleasant striped bass. Arizona Game and
Fish Department, Research Branch, Technical Guidance Bulletin No. 11. Phoenix. 40 pp.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
1
Introduction
Lake Pleasant has historically been regarded as
one of the premier largemouth bass (Micropteus
salmoides) fisheries in Arizona. However,
the quality of the largemouth bass fishery has
decreased, resulting in low angler satisfaction
and a general concern for the health of the
fishery (Bryan and Kohagen 2003). The leading
hypothesis for the cause of this decline is the
recent invasion of striped bass (Morone saxatilis),
which may be responsible, in part, for the shift in
largemouth bass size structure through competition
for resources and predation.
Striped bass initially entered the Central Arizona
Project (CAP) canal system as eggs or larvae,
entrained in Colorado River water pumped from
Lake Havasu. Results from a four-year canal study
in the late 1980’s indicated a growing population
of adult striped bass and the potential for their
reproduction in the canal would increase as
favorable hydraulic operations evolved (Mueller
1989). Striped bass reproduction was expected
to be limited due to heat induced stress and
subsequent mortality. Nevertheless, striped bass
quickly found their way into Lake Pleasant soon
after it was connected to the canal system in
1992. Striped bass presumably entered Lake
Pleasant as eggs or larvae through the Waddell
Dam forebay. Preliminary results of an evaluation
of the Lake Pleasant fishery indicated striped
bass abundance was increasing; however, it was
unknown if the canal continued to act as the sole
source of recruitment or whether striped bass
were successfully reproducing within the reservoir
(Bryan and Kohagen 2003).
Lake Pleasant anglers and fishery managers are
concerned the striped bass population has become
established, and will eventually out compete the
favored largemouth bass and white bass (Morone
chrysops) fisheries by effectively eliminating the
primary prey source, threadfin shad (Dorosoma
petenense). Although studies in some reservoirs
have confirmed these fears (Hart 1978; Allen
and Roden 1978; Baker and Paulson 1983),
others have shown these predators can co-exist if
properly managed (Combs 1982). If reproduction
is occurring within the lake, extirpation of
striped bass from the system is unlikely, and lake
managers will need to develop a plan that allows
for the continued prosperity of the largemouth
and white bass fisheries, while developing and
promoting a valuable striped bass fishery.
To make the proper decisions for management
of the reservoir, the current status of the striped
bass population must be properly researched. We
addressed the following objectives with a 3-year
evaluation of the striped bass fishery in Lake
Pleasant:
i) Determine energetic requirements of striped
bass and other pelagic predators in Lake
Pleasant to predict the impact on prey resources
and to predict the potential for striped bass
population growth in the future.
ii) Determine seasonal spawning movements,
habitat preferences and reproductive success
and recruitment of striped bass in Lake Pleasant.
Study Area
Lake Pleasant is a water storage reservoir located
approximately 50 km northwest of Phoenix
(Figure 1). The original dam was built in 1927
for the purpose of irrigation and water storage
for Maricopa Water District. Increasing demands
prompted the United States Congress to authorize
the Bureau of Reclamation (USBR) to construct
the Central Arizona Project (CAP) in 1968 for the
purpose of transporting water from the Colorado
River to Central Arizona to meet these increasing
water demands. Lake Pleasant was the logical
location for water storage due to its proximity
to the Phoenix metropolitan area, the greatest
concentration for water demand in the state. Since
the storage capacity of Lake Pleasant was not
enough to meet CAP needs, USBR proposed the
construction of the New Waddell Dam, which
commenced in 1985 and was completed in 1992.
After the old dam was breached, surface area of
Lake Pleasant nearly tripled from 3,760 acres to
9,970 acres, and storage capacity increased from
157, 000 to more than 1.1 million acre-feet.
Water is pumped into and out of the reservoir
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through the same intake structure located at the
dam. Water is typically pumped from the canal
into the reservoir from November to April. The
water elevation is maintained (at least 90% of
full pool) until water consumption exceeds what
is available through the canal system alone, and
then water is pumped out of the reservoir to
meet downstream needs (D. Crosby, Personal
communication).
High water demand results in a substantial change
(up to 40 m.) in reservoir water elevation between
summer and fall/spring months. The Agua Fria
River and several small tributaries supply seasonal
inputs to the upper portion of the reservoir.
Because the upper basin is influenced by the Agua
Fria River and its various tributaries, it tends to
be more productive than the lower basin (Walker
Figure 1. Lake Pleasant is located approximately
50 km northwest of Phoenix, Arizona. The CAP
canal connects to Lake Pleasant at the south end
of the reservoir, and the Agua Fria and several
tributaries flow in from the north. Pipeline Canyon
is considered to be the dividing line between the
upper and lower basin.
1998). The lower basin is deep and makes up the
majority of the reservoir. Various fish surveys
since the construction of the new Waddell Dam
have identified 21 species (Table 1). A little
less than half of the species are sport fish with
largemouth and white bass identified as the most
sought after species by anglers (Bryan 2005).
Methods
Telemetry
Transplant Methods
Fifteen CTT 83-3-I (62 mm x 16mm, 22g)
(Sonotronics, Inc. Tucson, AZ) temperature
sensitive sonic transmitters with a 36-month life,
were implanted into 15 striped bass between
January 2005 and January 2006. Initial attempts to
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implant transmitters took place during early spring
2005. Striped bass were collected by angling
and gill netting in January, February and April
of 2005, and a total of 8 fish were tagged. Due
to Food and Drug Administration requirements
regarding the use of certain types of anesthesia on
edible fish, an alternative anesthesia was used and
consisted of a water bath of sodium bicarbonate
at a concentration of 442 - 642 mg/l as described
by Brooke et al. (1978). If needed, small amounts
of hydrochloric acid were added to the bath to
maintain a pH between 6.5 and 7.0.
Tags were surgically implanted in the body cavity
of striped bass greater than 770 g to keep tag
weights less than 5 percent of the fishes weight
using methods described by Hart and Summerfelt
(1975). Initial attempts in 2005 resulted in high
fish mortality (7 of 8 fish died) post-release due
to capture and handling stress. Methods were
revised and a second attempt was conducted in
Species Scientific Name
Yellow Bullhead Ameiurus natalis
Goldfish Carassius auratus
Sonora Sucker Catostomus insignis
Common Carp Cyprinus carpio
Red Shiner Cyprinus lutrensis
Threadfin Shad Dorosoma petenense
Mosquitofish Gambusia affinis
Channel Catfish Ictalurus punctatus
Green Sunfish Lepomis cyanellus
Bluegill Lepomis macrochirus
Redear Sunfish Lepomis microlophus
Sunfish Hybrid Lepomis sp.
Inland Silverside Menidia beryllina
Largemouth Bass Micropterus salmoides
White Bass Morone chrysops
Striped Bass Morone saxatilis
Golden Shiner Notemigonus crysoleucas
White Crappie Pomoxis annularis
Black Crappie Pomoxis nigromaculatus
Flathead Catfish Pylodictis olivaris
Tilapia Tilapia sp.
Table 1. List of species that have been identified at Lake
Pleasant from 1987-2006. In 2006, a new species to Arizona,
inland silverside, was discovered.
January of 2006, whereby all fish were collected
via angling. The use of the sodium bicarbonate
as an anesthetic was discontinued and fish were
released immediately following surgery. A portable
surgical station was set up on a pontoon boat
and Arizona Game and Fish enlisted the help of
public anglers to catch striped bass and quickly
transport each fish to the surgical station. The fish
were measured (TL mm) and weighed (g) prior to
tag implantation and release. In total, 10 striped
bass were successfully tagged (one from the first
attempt and nine from the second attempt).
Fish Tracking
Surveys were conducted bi-weekly from January-
May (spring) and September-December (fall) and
monthly from June-August (summer) using an
ultrasonic receiver (Sonotronics model USR-96).
When a fish location was identified, the date,
time, tag number, tag temperature, and global
positioning system (GPS) location of each fish
was recorded. The varying pulse intervals emitted
by the transmitter identified tag temperature; as
tag temperature increased, pulse intervals also
increased (Sonotronics, Inc. 2006). Mean monthly
temperature was calculated for all fish during each
survey for use in bioenergetics modeling.
Larval Fish Surveys
Larval surveys were conducted from May 19, 2004
to June 2, 2004 and March 16, 2005 to May 25,
2005 to determine presence/absence of striped bass
eggs and larvae. The presence of striped bass eggs
and larvae would indicate that striped bass are
naturally reproducing within the reservoir.
Larval Light Traps
Larval light traps, similar to the Quatrefoil trap
designed by Floyd et al. (1984), were deployed
bi-weekly in 2004 (May through June) and 2005
(March through April). The north end of the
reservoir including the Agua Fria River was
deemed the most suitable habitat for striped bass
reproduction. As such, most of the light traps were
set in that area. Traps were constructed with 4
clear PVC pipes with a slit cut longitudinally that
are glued to a Styrofoam frame (top) and Plexiglas
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to allow a 4 mm space between the pipes to permit
larval fish to swim into the inner chamber. A
string of three LED battery powered lights was
lowered into the center of the pipes. The light
trap was lowered into the water in littoral areas
typically less than 2 meters in depth, and anchored
to the lake bottom with a weight to prevent it from
being washed away. The Styrofoam enabled the
traps to float flush with the surface of the water
while the PVC tubing was submerged below the
water surface. The traps were deployed prior to
dusk in clusters of 2-3 and allowed to fish 4 to
7 hours until traps were pulled from the water
trapping any fish and zooplankton in a mesh
container attached to the bottom of the frame.
Samples were preserved in 5% formalin, and, upon
return to the laboratory, larval fish were counted,
identified to species (if possible), and measured
(mm).
Larval Tow Surveys
Bi-weekly larval tows began in mid-March
2005, when surface temperatures reached 16°C,
and continued until late May when surface
temperatures reached 27°C. Two 1-m diameter
conical (3:1 length to diameter ratio) 500μm nets
were supported via a modified side-mounted
portable push-net apparatus (Tarplee et al. 1979)
on a 5.85 m aluminum boat. A General Oceanics
Inc. (Model 2030R, Miami, FL) digital-mechanical
flow meter installed at the center of the mouth
of each net recorded the volume (m3) of water
sampled. Volume was determined using the
following calculations:
(1)
Volume (m3) = [3.14 * (diameter of net)2 *
Distance]/4
(2)
Distance = [(stop odometer - start odometer) *
26873]/999999
Six random transects were sampled each night
parallel to the shoreline. Tows lasted between 2
and 6 minutes based on the amount of plankton
in the water. Nets were set at a depth of ≈ 0.3 m
below water surface. At each run, surface water
temperature, start and end GPS coordinates, and
sample time were recorded. At the end of each
run, samples were preserved in 5% formalin.
All 3 basins were sampled over the course of 3
months with each effort occurring between the
hours of 15:00 and 20:00 mountain standard time.
All samples were sorted in the lab, were counted
and identified to family or species if possible. The
remaining sample was subsampled in order to
estimate zooplankton per cubic meter. Zooplankton
density was calculated as follows:
(3)
Density (#/m3) = Total Zooplankton/Tow
volume (m3)
Larval fish collected in larval traps and tows were
identified according to Preliminary Guide to the
Identification of Larval Fishes in the Tennessee
River, 1976, and Identification of Larval Fishes of
the Great Lakes Basin with Emphasis on the Lake
Michigan Drainage, 1982. Once identified, counted
to species (if possible), and measured (TL, mm),
fish were preserved in 10% ethanol. Moronidae
larval fish could not be identified to species, so
samples were sent to Colorado State University’s
Larval Fish Laboratory for taxonomic identification.
Fish Surveys
Gill Netting
Pelagic gill netting surveys were conducted in
August (summer), November (fall), and February
(spring) beginning August 2004 and ending
November 2006. Sites were selected using a
stratified random design whereby a 50 x 50 m grid
was superimposed on Lake Pleasant (Figure 2)
and quadrants were randomly chosen as long as
they were determined to be pelagic (greater than 6
meters deep and at least 10 meters from shore). If
a quadrant was located in unsuitable waters (i.e.,
not pelagic), the next randomly chosen site was
selected, until a suitable site was found. Nets were
55.38 x 3.08 m experimental monofilament gill
nets with 6 panels of varying bar mesh size (12.7,
25.4, 38.1, 50.8, 63.5, and 76.2 mm). Sixteen sites
were randomly sampled during the first 3 surveys.
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The number of random sites was increased to
24 to increase catch for diet analysis. An equal
number of surface and bottom nets were set during
each survey with the exception of the first survey
where nets were also set at the thermocline since
literature suggests striped bass school immediately
above the thermocline during summer (Matthews
et al. 1985). Thermocline nets were eliminated
from subsequent summers due to net entanglement
upon itself. For each trip, a target sample size of
10 striped bass and white bass per each 50-mm
length group was set to obtain an adequate number
of diet and aging samples. If this target was not
met, additional gill nets were set at locations where
the target species were known to be present (i.e.,
selected sites). Data from the selected net sets
were not included in relative abundance estimates.
All nets were set in the early evening prior to
sunset and retrieved the following morning unless
extreme weather conditions or other unforeseen
situations arose causing a delay in gill net retrieval.
Due to the littoral nature of largemouth bass,
very few were captured in the pelagic gill nets.
Hence, largemouth bass diet and age samples were
collected during electrofishing surveys conducted
the week following each gill netting survey with
a target of 10 largemouth bass per each 50-mm
length group.
All captured fish were identified to species,
measured (TL mm), weighed (g.), and, if needed,
scales, sagittal otoliths, and stomach samples
were removed. Fish not needed for age and diet
samples were measured, weighed, and released.
Several randomly selected nets that were run
over by boaters or badly tangled in debris during
spring flooding were not used for fish abundance
and population estimates. Extreme flooding in
spring 2005 resulted in extreme amounts of debris
becoming entangled in the nets. Consequently
data from only 11-gill net sets was suitable for
abundance estimates. Data from thermocline sets
during the first survey were also not included in
abundance estimates.
Fish Community Composition and Size Structure
Mean length and weight were calculated for each
species for each survey. Species composition and
catch-per-unit-effort (CPUE) were calculated for
each survey.
CPUE and percent composition are calculated for
each fish species as:
(4)
where Ci = catch in the ith net, Hi = length the ith
net was fished (hours), and n = number of nets.
(5)
where CPUEsi = CPUE of species in ith net,
CPUEti = total CPUE in ith net, and n = number
of nets.
Figure 2. Sample sites (n) were randomly selected within
pelagic waters (≥ 6 m deep and ≥ 10 m from shore). Sites
were 50 m x 50 m. This illustration is not drawn to scale, and
does not accurately represent Lake Pleasant pelagic water or
sample quadrant sizes.
!
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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In addition, size structures of individual species
were evaluated using Proportional Stock Densities
(PSD; Anderson 1978) and Relative Stock Density
(RSD; Gablehouse 1984).
PSD and RSD are calculated as follows:
(6)
and,
(7)
Relative weight (Wr, Wege and Anderson 1978)
was calculated for all species during each survey
to evaluate fish condition.
(8)
Where Ws is the length-specific standard weight
for individual species (Anderson and Neuman
1996, and Bister et al. 2000). ANOVA and Tukey’s
multiple comparison tests were used to compare
Wr in striped, white, and largemouth bass among
surveys, seasons, and years.
Growth
Length-frequency histograms for white and striped
bass were created for each of the 8 gill netting
surveys and used to estimate growth by following
changes in modal length for an age group through
time. Mean lengths for age-0, age-1, and age-
2+ were calculated based on modal distribution;
however, all age-2+ fish were grouped together
because of the difficulty of separating older age
groups. A weight-length power regression was
used to calculate weight from length frequencies
for each age group.
(9)
W = aLb
W = weight (g), L = length (mm), a = 1.42 x 10-5
and b = 2.97 for white bass, and a = 1.23 x 10-5
and b = 2.99 for striped bass. Growth was then
measured in weight difference of each age group
from one survey to the next.
Due to small sample size of many of the cohorts,
growth for bioenergetic modeling was used from
November 2004 to November 2005 and from
November 2005 to November 2006. These 2 time
spans were significant in that 2004 to 2005 found
very high production in the reservoir whereas 2005
to 2006 had very low production.
Aging
Sagittal otoliths and scales (just below the
anterior portion of the dorsal fin) were removed
from striped, white, and largemouth bass in the
field and placed in scale envelopes. Scales were
rinsed and mounted between 2 75mm x 25mm
slides. Otoliths were placed in glycerol for up to
10 days, washed with water, dried and placed in
vials. Small otoliths (usually YOY) were read in
whole view, but most otoliths were sectioned on
a transverse plane, mounted in Thermoplastic
Quartz Cement (Hugh Courtright & Co. Ltd.
Monee, IL) on a microscope slide, and read with
an Olympus Bx40 microscope (Center Valley,
PA) at magnification 4x/0.10. Two independent
readers viewed the otoliths and estimated fish
age; age discrepancies were re-examined and a
consensus was reached. A third reader was used if
consensus was not attained. Otoliths were digitized
using a Leica S8APO microscope (Bannockburn,
IL) mounted with an Olympus Q-Color-3 digital
camera (Phoenix, AZ) with QcapturePro software
(QImaging, Inc. Surry, BC Canada). Sectioned
otoliths were viewed at a 1.6 magnification and
whole otoliths were viewed at 1.0 magnification.
Measurements for back calculations were made in
pixels (converted to millimeters) from the nucleus
of the otolith to each annulus and to the edge
(Figure 3). Fish length-at-age was back calculated
and ages were assigned according to DeVries and
Frie (1996).
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Diet
Striped, white, and largemouth bass stomachs were
collected during gill netting and electrofishing
surveys to determine predator diet and
consumption. Upon removal from the fish, each
stomach was punctured to evacuate digestive
enzymes, placed in a labeled Whirl-Pak, stored in
an ice-filled cooler, and frozen upon return to the
lab until subsequent analysis.
In the laboratory, several guides were used to
identify stomach contents to species if possible
(Auer 1982, Hogue et al. 1976, Sublette et al.
1990). Prey items were counted, weighed (g) by
species, and volumetric displacement (ml) was
determined for each prey species. Vertebrae count,
otoliths, or other distinguishing features were used
for positive identification of partially digested fish
species. Spine length (atlas to last vertebrae before
caudal fin) of all prey fish was measured (mm). If
spines were not whole and no other distinguishing
features could be identified, fish were deemed
as unknown. All contents were stored in 70%
isopropyl alcohol following analysis.
Frequency of occurrence by species was used
to quantitatively measure prey presence and is
calculated as follows:
(10)
Percent composition by number is a measure of the
number prey items in the stomach of each predator
at time of collection. Percent composition by
number and percent composition by weight were
calculated for each prey species:
(11)
where C is the percent composition by number for
each prey species, n is the number of fish stomachs
with at least one prey item, pi is the count of an
individual species of prey in the ith stomach and ti
is the total number of prey in the ith stomach
and
(12)
where W is percent composition by weight, wi
is the total weight of a particular prey species in
the ith stomach and twi is the total weight of all
species in the ith stomach.
Prey items were grouped into 4 categories;
threadfin shad, invertebrates, crayfish, and other
fish. Threadfin shad, crayfish, and dipterans
were the only individual prey items that made up
more than 5% frequency of occurrence. As such,
threadfin shad and crayfish were each grouped
into their own category for bioenergetics analysis.
Dipterans, however, were put into the invertebrate
category because all other invertebrates were
very infrequent. All fish species in the “other
Figure 3. Cross sections of sagittal otoliths from white bass (age 6), largemouth bass (age 4), and striped bass (age 6).
White Bass Largemouth Bass Striped Bass
W 􀀝􁴱100* wi
i􀀝􁴱1 twi
􀀀􀁮 n
􀀀 􀀀 􀀀
􀀀
􀀀 􀀀 􀀀
n
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8
fish” category had less than 5% frequency of
occurrence. Percent composition by weight was
then calculated for each of the 4 categories.
Unidentifiable fish species were partitioned into
either the categories of threadfin shad or other fish
based on the proportion of known threadfin shad
to other fish for each trip.
Diet overlap was calculated between striped and
white bass (SB/WB), striped and largemouth bass
(SB/LB), and white and largemouth bass (WB/LB)
according to Schoener (1970) where:
(13)
n = number of food categories;
Pxi = proportion of food i in diet of species x;
Pyi = proportion of food i in diet of species y;
Diet overlap indices are on a scale from 0 (no
overlap) to 1 (complete overlap).
Prey Energy Densities
A literature search was conducted to find
energy densities of species in each of the 4 prey
categories. Mean energy densities were calculated
if multiple values were reported or if prey
categories were composed of more than 1 species
(invertebrates and other fish).
Water Quality
Water Quality Profiles
Monthly water quality parameters were collected
at 4 sites in Lake Pleasant: Waddell Dam (WD),
Max’s Point (MP), Aqua Fria Mouth (AF), and
Aqua Fria River (RV) (Figure 4). These sites were
in the inundated Agua Fria river channel and were
chosen because striped bass are often associated
with areas of inflow (Lewis 1985). A YSI 6920
Sonde and YSI 610 Display/Logger (YSI Yellow
Springs, OH) was used to measure and record
depth, temperature (ºC), specific conductance
(µS·cm-1), dissolved oxygen (mg·l-1), and pH at
1-meter intervals at each site. Thermocline depth
was plotted monthly from April to October for
both 2005 and 2006.
Additional water quality measurements were
taken following fish gill netting and electrofishing
surveys. These measurements included light
penetration via secchi depth (m), turbidity
(NTU), and chlorophyll–a (µg·l-1). Turbidity was
measured using a HACH 2100P Turbidimeter
(HACH Loveland, CO) and chlorophyll-a samples
were collected within 1 m of the surface and
filtered in the field through a Whatman GF/F
glass fiber filter (0.7 µm Whatman Florham Park,
NJ). Filters were wrapped in foil, placed on ice,
and transported to the lab where chlorophyll-a
concentrations were measured with a Perkin Elmer
UV/VIS spectrometer Lambda 2 (PerkenElmer
Waltham, MA) following extraction into acetone
(detection level of 0.005 mg/l) and corrected for
phaeo-pigments.
ANOVA was used to compare mean differences
among years, seasons, and surveys for both
turbidity and chlorophyll-a samples. Lake elevation
and daily precipitation data were gathered from
monthly CAP reports. Agua Fria River discharge
Figure 4. Four water quality sites: Waddell Dam (WD), Max’s
Point (MP), Agua Fria mouth (AF), and Agua Fria River (RV).
AZFGD—Research Branch Technical Guidance Bulletin No. 11
9
data was gathered from the USGS gauging station
(station number 09512800) near Rock Springs,
Arizona.
Temperature
Temperature sensitive transmitters were implanted
in to striped bass to accurately determine preferred
striped bass water temperature (see telemetry
methods). Tracking began in February 2005 and
continued through January 2007. Fish were located
bi-weekly from January-May and September-
December and monthly from June-August. Mean
monthly water temperature where tagged fish
were found was calculated. Due to the lack of
tagging success during the first year of this study,
temperatures from 2006 were also used for 2005
for the bioenergetics modeling.
Additional water temperature data were collected
using temperature loggers deployed at 7 sites
throughout the reservoir from March 29, 2005
to September 1, 2006 (Figure 5). One site had a
bottom temperature logger, 2 sites had a surface
temperature logger, and 4 sites had both a bottom
and surface temperature logger. Surface loggers
were suspended 2 meters from the surface of
the water and bottom loggers were suspended 3
meters from the lake bottom. Two types of loggers
were used: Optic StowAway Temperature loggers
and Hobo Temperature loggers, both produced
by Onset Computer Corporation (Bourne, MA).
StowAway loggers recorded temperatures every
hour and Hobo loggers recorded temperatures
every 2.5 hours due to limited battery life. Initially,
8 StowAway and 4 Hobo loggers were deployed.
Several of the loggers died or were damaged by
wave action and were refurbished and redeployed
and one of the Hobo loggers flooded before the
initial download and was not refurbished resulting
in no surface data for that site.
Hydroacoustics
Field Surveys
Hydroacoustic surveys were conducted during
February 2005 and February 2006 using a
200kHz split beam DTX echosounding system
from BioSonics Inc. (Seattle, WA). Transects
were run in a zigzag design from a randomly
selected start point for time efficiency and ease
of running the surveys. Transects were identified
with the intent of getting the highest coverage
possible. A total of 15 transects in February
2005 and 33 transects in February 2006 were
surveyed (Figures 6 and 7). Transects were run
at a boat speed of approximately 4 to 6 mph and
a ping rate of 5 pings per second. The face of the
vertical transducer was submerged approximately
15 centimeters below the surface of the water.
The horizontal transducer was mounted above
the vertical transducer and tilted such that the
top edge of the sound wave was parallel to the
surface of the water. Day and night time surveys
were conducted to capture diurnal changes in fish
behavior. The same transects were run during day
and night. Night surveys began after full dark.
Hydroacoustics data were analyzed in Echoview
3.0 (Echoview Hobart TAS, Australia). Lake
bottom was identified manually and fish target
(filtered at threshold of –55dB) densities (#/m3)
were calculated at 100 ping intervals, surface to
Figure 5. From March 2005 to September 2005, 11 temperature
loggers were set at 7 locations throughout the reservoir.
Aqua Fria
River Logger
Aqua Fria
Mouth
Logger
Honeymoon
Cove Logger
Coles Bay
Loggers
Sheriff
Station
Loggers
Balance
Rock
Island
Loggers
Castle
Creek
Loggers
!
AZFGD—Research Branch Technical Guidance Bulletin No. 11
10
bottom. Individual fish tracks were identified and
mean target strength (dB) was calculated.
Data Analysis
Analysis regions were defined by the morphometry
and productivity of the reservoir. The South Basin
is deep and oligotrophic. The North Basin is
shallow, but has higher nutrient concentrations.
The Agua Fria is riverine habitat, and has higher
productivity and a different temperature regime.
Transects collected in each region were imported
in to Echoview, cleaned, and analyzed by region.
The August 2006 survey was cancelled following
completion of the 2005 August survey because
stratification of the reservoir causing fish to
be compressed into the transition zone at the
thermocline. This resulted in a high density of
fish such that individual fish targets could not be
identified, and therefore fish tracks could not be
detected.
The following equation was used to estimate fish
number throughout the entire reservoir for both
February 2005 and February 2006 surveys:
(14)
Lake volume data was acquired from
monthly CAP reports (B. Henning, Personal
communication) at the time of each survey.
Love’s equation (Love 1977) was used calculate
the relationship between target strength and fish
length:
(15)
Figure 6. Hydroacoustic transects from February 2005.
Conducted at night using a 200Hz split beam DTX echosounder.
Figure 7. Hydroacoustic transects from February 2006.
Conducted at night using a 200Hz split beam DTX echosounder.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
11
where TS (-dB) is target strength, Lm is fish
length in meters, and λ (m) is acoustic wavelength.
Fish less than 125 mm TL and 150 mm TL were
determined not to be pelagic predators based
on the maximum sized threadfin shad collected
during gill netting surveys February 2005 and
February 2006 respectively. Percent composition
of white and striped bass from gill netting surveys
were used to estimate the total number of those
species in February 2005 and February 2006.
Bioenergetics
To determine the energetic demands of pelagic
predatory fish at Lake Pleasant, the Wisconsin
bioenergetics model (Hanson et al. 1997) was
used to estimate striped and white bass daily
consumption from November 2004 to November
2006. The Bioenergetics model is a mass balance
equation that assumes:
(16)
Energy consumed = Respiration + Waste + Growth
where energy consumed is the maximum daily
consumption rate (g of prey per g body mass per
day), respiration is the amount of energy used by
the fish for metabolism, which is dependent on
fish size, water temperature and activity, waste
is computed as a function of consumption, and
growth is in grams per unit time.
The Wisconsin bioenergetics model estimates
the energy consumption of an average fish using
4 basic input parameters: water temperature
(°C), diet proportion, prey energy densities (J/g),
and fish growth (g). Laboratory data (thermal
preference, size dependence, assimilation
efficiency, etc) from age-1, age-2, and adult striped
bass (Hartman and Brandt 1995) were used for
physiological parameters required by the model.
Since these physiological parameters are not
available for white bass, striped bass parameters
were used for white bass because the 2 species are
closely related.
Daily growth, total daily energy consumed, and
average daily diet consumption for each of the 4
prey categories was modeled for white and striped
bass. Simulations were run for YOY fish from
November 2004 to November 2005 and YOY fish
from November 2005 to November 2006.
Results
Telemetry
Tracking
A total of 10 striped bass were implanted with
transmitters (Table 2). Tagged fish were originally
captured in the Agua Fria River approximately
5 miles upstream from the mouth. One month
after tags were implanted, 2 fish moved out of the
Agua Fria River into the main reservoir and, by
July, all tagged fish moved out of the Agua Fria
River. While in the Agua Fria River, striped bass
were observed moving throughout the entire river,
however the area across from Tule Cove (~7.25
km upstream from mouth) is likely a preferable
Fish Number Date Tagged Length (mm) Weight (g) Months Tracked
69 1/25/06 406 780 10
71 1/12/06 565 1800 13
72 1/25/06 445 1000 13
74 1/12/06 460 970 13
76 1/24/06 453 1040 5
77 1/25/06 680 3080 6
78 1/25/06 615 2100 13
79 2/26/05 477 1140 25
81 1/25/06 491 1280 1
83 1/25/06 580 1680 7
Table 2. Fish ID, date tagged, fish length, fish weight, and months tracked for 10 striped bass tracking with sonic telemetry.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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spawning habitat of striped bass as indicated by
their frequency of occurrence.
Six months following tagging, 3 fish were lost:
1 to mortality, 1 to angling, and 1 for unknown
reasons. By January 2007, an additional 2 striped
bass were lost for unknown reasons.
Figures 8 and 9 are maps of locations for all 10
tagged striped bass. Figure 8 shows the various
locations of the striped bass during fall and spring
months (October through May) when most tagged
fish were observed in the Agua Fria River. Figure
9 shows locations of the tagged striped bass during
summer months (June through August) when
tagged fish moved out of the Agua Fria River.
Temperature Transmitters
Despite overall temperatures rising throughout
the reservoir during summer months, there was
a leveling off of water temperature occupied by
striped bass in June when striped bass moved from
the Agua Fria River to the main reservoir where
temperatures were cooler and dissolved oxygen
levels were higher. As surface lake temperatures
began to drop in August, mean temperatures
occupied by striped bass increased slightly in
September as the bass began moving back into the
Agua Fria River where water temperatures were
warmer (Figure 10).
Larval Fish Surveys
A total of 36 sites were sampled from March
16, 2005 to May 25, 2005: 11 sites sampled in
basin 1 (upper reservoir), 5 sites in basin 2 (lower
Figure 8. Locations of tagged striped bass during spring
(January-May) and fall (October-December) 2006. The high
frequency of striped bass at the upper end of the Agua Fria
River suggests a spawning location.
Figure 9. Locations of tagged striped bass during summer
(June-September 2006). Only 4 times was a fish found in the
Agua Fria River during this period. Fish were “squeezed” out
of the Agua Fria River during the summer months due to high
water temperatures and low dissolved oxygen levels.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
13
reservoir), and 20 sites in basin 3 (Agua Fria
River). The total volume of water sampled was
5,551 m3. Six different larval fish were identified:
common carp (Cyprinus carpio), threadfin shad,
largemouth bass, Morone spp. (white bass or
striped bass), Lepomis spp.(bluegill, green sunfish,
or redear sunfish) , and Pomoxis spp. (black
crappie or white crappie) Threadfin shad were
most abundant (0.62 fish/m3) followed by Lepomis
spp. (0.28 fish/m3) and Morone spp. (0.06 fish/m3).
Differentiating between larval Morone species
is extremely difficult and as such 13 Morone
larval samples from varying sizes and locations
within the reservoir were sent to Coloarado State
University Larval Fish Laboratory for analysis.
Two were positively identified as Morone
chropysis and the other 11 were indistinguishable.
Zooplankton densities peaked at just under 15,000/
m3 in March when surveys first began. During
the last survey in May 2005 zooplankton numbers
dropped considerably to about 1,000/m3 (Figure 11).
Fish Population Dynamics
Species Composition
Nine fish species were caught in pelagic nets
during the course of the study. Striped bass (n
= 230) and white bass (n = 250) numbers were
substantially greater in the November 2005 survey
than any other survey (Table 3). Threadfin shad
generally comprised the greatest composition
of the catch. Threadfin shad composition was
lowest in the summer (24%) and highest in fall
(65%). White bass composition was highest in the
summer (43%) and relatively low the rest of the
year, in most cases less than 15%. Striped bass
composition remained consistent at approximately
15% of the catch and did not vary seasonally
(Figure 12).
CPUE
Total CPUE of species collected in gill nets was
greatest during November 2006 survey. CPUE
for white and striped bass was greatest during
fall surveys, and in fall 2005 was nearly double
that of any other survey with 0.641 fish/hour (SE
= 0.473) and 0.562 fish per hour (SE = 0.169),
respectively (Figure 13). White bass CPUE was
greater than striped bass in all surveys with the
exception of February 2005 and November 2006.
The November 2006 survey was the only survey
where striped bass CPUE (0.321 fish/hour) was
significantly higher (t-test; p < 0.05) than white
bass (0.043 fish/hour). Appendix 1a shows CPUE
of the most caught species for each trip.
Figure 10. Mean surface temperature of 4 water quality sites
versus mean temperature of tagged fish by month. Striped
bass movement out of the Agua Fria River occurred in June
(first vertical line) and back into the River occurred in mid-
September (second vertical line).
Figure 11. Zooplankton densities from March 16, 2005 to May
25, 2005.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
14
Aug 2004 Nov 2004 Feb 2005 Aug 2005
N Mean (SE) N Mean (SE) N Mean (SE) N Mean (SE)
Common Carp Length 7 608 (24) 33 539 (17) 69 540 (6) 3 604 (10)
Weight 7 3064 (373) 33 2245 (203) 69 2071 (67) 3 3070 (257)
Threadfin Shad Length 12 102 (2) 94 104 (1) 57 103 (1) 65 106 (1)
Weight 12 10 (0) 94 14 (1) 57 10 (0) 65 10 (0)
Channel Catfish Length 5 371 (83) 29 388 (18) 8 356 (40) 18 322 (23)
Weight 5 738 (313) 29 652 (97) 8 523 (191) 18 387 (122)
Bluegill Length - ---- 1 152 - ---- - ----
Weight - ---- 1 60 - ---- - ----
Largemouth Bass Length 1 366 49 333 (10) 41 314 (10) 43 295 (13)
Weight 1 720 49 556 (44) 41 426 (44) 43 454 (53)
White Bass Length 41 384 (6) 179 315 (5) 18 356 (15) 174 217 (5)
Weight 41 726 (37) 179 434 (17) 18 550 (52) 174 186 (16)
Striped Bass Length 13 476 (49) 53 492 (20) 41 470 (18) 11 292 (30)
Weight 13 1345 (328) 53 1334 (126) 41 1169 (100) 11 333(68)
Black Crappie Length - ---- - ---- 4 171 (45) 38 205 (9)
Weight - ---- - ---- 4 115 (61) 38 162 (18)
Flathead Catfish Length - ---- 6 599 (36) - ---- - ----
Weight - ---- 6 2812 (550) - ---- - ----
Nov 2005 Feb 2006 Aug 2006 Nov 2006
N Mean (SE) N Mean (SE) N Mean (SE) N Mean (SE)
Common Carp Length 27 460 (25) 11 463 (47) 22 560 (14) 19 527 (19)
Weight 27 1549 (235) 11 1941 (468) 22 2382 (202) 19 2130 (205)
Threadfin Shad Length 70 101 (1) 98 102 (1) 76 99 (1) 53 109 (3)
Weight 70 10 (0) 98 10 (0) 76 10 (0) 53 70 (6)
Channel Catfish Length 20 484 (27) 2 441 (104) 33 445 (19) 14 446 (24)
Weight 20 1420 (256) 2 1000 (700) 33 976 (161) 14 881 (182)
Bluegill Length - ---- - ---- - ---- - ----
Weight - ---- - ---- - ---- - ----
Largemouth Bass Length 83 284 (10) 56 360 (15) 60 269 (12) 104 279 (7)
Weight 83 401 (41) 56 861 (114) 60 352 (54) 104 330 (39)
White Bass Length 250 285 (5) 77 324 (8) 101 334 (5) 37 332 (7)
Weight 250 370 (20) 77 515 (39) 101 442 (18) 37 423 (30)
Striped Bass Length 230 323 (7) 69 354 (15) 63 352 (14) 192 366 (3)
Weight 230 470 (34) 69 607 (72) 63 511 (83) 192 454 (15)
Black Crappie Length 14 266 (14) 2 267 (39) - ---- 2 226 (59)
Weight 14 320 (47) 2 315 (145) - ---- 2 220 (170)
Flathead Catfish Length 3 632 (77) - ---- - ---- 2 562 (29)
Weight 3 3233 (1230) - ---- - ---- 2 1860 (230)
Table 3. Mean total length (mm), mean weight (g) and number of each species caught for each of the 8 gill netting and 7 electrofishing
surveys from 2004 to 2006.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
15
Date
Figure 12. Percent composition of fish caught during gill
netting surveys from August 2004 to November 2006. Other fish
include crappie, sunfish, largemouth bass, and flathead catfish.
Figure 13. CPUE comparison between white and striped bass
with error bars from August 2004 to November 2006.
Species Aug-04 Nov-04 Feb-05 Aug-05
Mean (SE) N Mean (SE) N Mean (SE) N Mean (SE) N
Common Carp 96(2) 7 93(2) 33 92(1) 69 100(4) 3
Channel Catfish 93(3) 4 97(3) 28 93(6) 8 88(3) 18
White Bass 91(2) 39 87(1) 176 84(3) 18 102(1) 172
Striped Bass 76(4) 13 79(2) 52 80(1) 41 95(9) 11
Black Crappie 99(8) 4 103(2) 38
Flathead Catfish 100(5) 6
Largemouth Bass 88(2) 39 81(2) 38 93(1) 37
Species Nov-05 Feb-06 Aug-06 Nov-06
Mean (SE) N Mean (SE) N Mean (SE) N Mean (SE) N
Common Carp 90(1) 27 103(5) 11 93(2) 22 97(2) 19
Channel Catfish 96(4) 20 97(8) 2 89(3) 33 87(4) 14
White Bass 93(1) 249 92(1) 77 82(1) 101 80(2) 37
Striped Bass 78(1) 229 78(1) 69 73(1) 63 72 192
Black Crappie 92(3) 14 92(1) 2 88(12) 2
Flathead Catfish 93(2) 3 85(3) 2
Largemouth Bass 88(1) 71 89(1) 55 87(2) 57 83(2) 102
Table 4. Relative weight with standard error and number of fish (n) for all species.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Relative Weight
With the exception of channel catfish (Ictalurus
punctatus) and common carp, Wr was greatest
for all species in the August 2005 survey (Table
4). White, striped, and largemouth bass showed
similar trends throughout the study (Figure 14). In
2006, striped bass Wr was significantly lower than
2004 and 2005. White bass Wr was significantly
higher in 2005 than any other year during the
study (ANOVA; P<0.05). Largemouth bass Wr
did not differ significantly from year to year.
Largemouth and white bass had the greatest Wr
in the summer, while striped bass did not show a
statistical significant difference between seasons.
Striped bass and white bass Wr was significantly
higher (ANOVA; P<0.05) in August 2005 than any
other survey. Largemouth bass Wr was also highest
during this survey, but not statistically significant.
Proportional and Relative Stock Densities
PSD varied among species (Table 5). PSD for
white and striped bass were lowest in August 2005.
White bass had a higher PSD than striped bass for
each survey. Striped bass PSD was less than 50
for all surveys except August 2004. Memorable to
trophy relative stock density values were greatest
in most survey for white bass and common carp.
Appendix 1b shows RSD for the most caught
species for each trip.
Age and Growth
A total of 118 striped bass, 61 white bass and 100
largemouth bass were aged. The maximum age
of striped bass was 8 years, white bass 7 years
and largemouth 8 years (Table 6). Backcalculated
growth for white and largemouth bass was similar.
Striped bass growth, however, was greater,
especially during the first year (Figure 15). Mean
backcalculated growth to year 1 for striped bass
was 328 mm compared to 198 mm and 215 mm
for largemouth and white bass, respectively. Year 2
striped bass continue to have greater growth than
white bass and largemouth bass and, by year 3,
annual growth rates start to look similar (Table 7).
Species Aug 2004 Nov 2004 Feb 2005 Aug 2005
Common Carp 100 + I 94 + I 99 + I 100 + I
Channel
Catfish 75 + I 52 + 16 50 + I 40 + I
Largemouth
Bass 86 + 10 53 + 12 61 + 13
White Bass 100 + I 80 + I 89 + I 19 + I
Striped Bass 55 + I 40 + 11 29 + 12 0 + I
Black Crappie 100 + I 76 + 12
Flathead
Catfish 100 + I
Species Nov 2005 Feb 2006 Aug 2006 Nov 2006
Common Carp 56 + 16 78 + I 100 + I 89 + I
Channel
Catfish 68 + 17 50 + I 73 + 13 50 + 22
Largemouth
Bass 61 + 10 84 + 8 42 + 11 23 + 6
White Bass 69 + I 91 + 5 100 + I 100 + I
Striped Bass 17 + 6 26 + 13 19 + 10 3 + I
Black Crappie 93 + I 100 + I 50 + I
Flathead
Catfish 100 + I 100 + I
Table 5. Proportional stock density (PSD) of fish collected
using electrofishing and gill netting in Lake Pleasant,
2004-2006. Confidence intervals (80%) are also presented
(Gustafson 1988); an “I” indicates that sample size was too
small to determine the 80% confidence interval.
Figure 14. Relative weight of white bass, striped bass, and
largemouth bass from August 2004 to November 2006.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Striped Bass Age
Length (mm) n Number (age) in sample 0 1 2 3 4 5 6 7 8 Totals
0-100 0
101-150 1 1(0) 1 1
151-200 2 2(0) 2 2
201-250 9 6(0), 3(1) 6 3 9
251-300 11 5(0), 6(1) 5 6 11
301-350 13 12(1), 1(2) 12 1 13
351-400 10 10(1) 10 10
401-450 13 10(1), 3(2) 10 3 13
451-500 10 8(1), 2(2) 8 2 10
501-550 10 1(1), 9(2) 1 9 10
551-600 12 7(2), 4(3), 1(5) 7 4 1 12
601-650 11 1(2), 2(3), 7(4), 1(7) 1 2 7 1 11
651-700 11 1(2), 4(3), 3(4), 1(5), 1(7), 1(8) 1 4 3 1 1 1 11
701-750 3 2(5), 1(6) 2 1 3
751-800 2 1(4), 1(5) 1 1 2
All 118 14 50 24 10 11 5 1 2 1 118
White Bass Age
Length (mm) n Number (age) in sample 0 1 2 3 4 5 6 7 8 Totals
0-100 0 0
101-150 0 0
151-200 7 7(0) 7 7
201-250 7 6(0), 1(1) 6 1 7
251-300 10 7(0), 3(1) 7 3 10
301-350 10 4(1), 6(2) 4 6 10
351-400 13 1(1), 9(2), 1(4), 1(6), 1(7) 1 9 1 1 1 13
401-450 13 1(3), 5(4), 4(5), 3(6), 1 5 4 3 13
451-500 1 1(5) 1 1
501-550 0
All 61 20 9 15 1 6 5 4 1 0 61
Largemouth Bass Age
Length (mm) n Number (age) in sample 0 1 2 3 4 5 6 7 8 Totals
0-100 5 5(0) 5 5
101-150 9 9(0) 9 9
151-200 13 7(0), 6(1) 7 6 13
201-250 10 3(0), 6(1), 1(2) 3 6 1 10
251-300 10 3(1), 7(2) 3 7 10
301-350 10 3(1), 6(2), 1(3) 3 6 1 10
351-400 14 6(2), 4(3), 2(4), 2(6) 6 4 2 2 14
401-450 11 3(2), 4(3), 4(4) 3 4 4 11
451-500 10 2(3), 2(4), 4(5), 1(6), 1(7) 2 2 4 1 1 10
501-550 4 1(4), 1(6), 1(7), 1(8) 1 1 1 1 4
551-600 4 3(7), 1(8) 3 1 4
601-650 0 0
0
All 100 24 18 23 11 9 4 4 5 2 100
Table 6. Age/length frequencies for striped, white, and largemouth bass for each 50mm length category. n is the number of otoliths read.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Annual growth of both striped and white bass
varied from 2004 to 2006 (Table 8). The mean
weight of young-of-year striped bass in November
2004 was 149 g. This year class grew to a mean
weight of 1059 g one year later. During the same
time span, young-of-year white bass grew from
111 g to 541 g. The 2005 young-of-year class did
not see such growth. The mean weight of young-of-
year striped bass in November 2005 was 171 g
and grew to 503 g by November 2006, half the size
of the young-of-year class of 2004. White bass had
similar growth. In November 2005, the average
young-of-year white bass weighed 168 g and was
300 g by November 2006 (Figure 16).
Diet
Frequency of Occurrence
Stomach contents were examined from 329
largemouth bass (mean TL = 305 ± 5), 326 white
bass (mean TL = 327 ± 4), and 292 striped bass
(mean TL = 410 ± 8). A total of 30 prey items were
identified in 942 stomachs from the 3 predatory
species (Appendix 2a). Empty stomachs were
found in 23% of largemouth bass, 40% of white
bass and 36% of striped bass (Appendix 2b).
Percent Composition by Weight/Number
Diets were divided into 4 categories: threadfin
shad, crayfish, other fish, and invertebrates.
Threadfin shad consumption was greatest
in striped bass (74.40%) followed by white
bass (43.77%), and largemouth bass (9.69%).
Invertebrates consumption were the next highest
consumed item by striped bass (19.81%).
Invertebrates made up the greatest proportion in
largemouth bass (48.07%) and the second greatest
in white bass (33.55%). Crayfish consumption
was substantial for largemouth (27.64%) and
white bass (19.95%), but was low for striped bass
(1.28%). Largemouth bass also had a considerable
proportion of other fish in their diet (14.79%),
while striped (4.52%) and white bass (2.73%) had
relatively low proportions (Figures 17 and 18).
There appeared to be a seasonal difference in
largemouth bass diets. Proportions of invertebrates
in their diet were only 7.04% in summer compared
to 54.02% in fall and 80.21% in spring.
Diet Overlap
Diet overlap index ranges from 0 (no overlap) to 1
(complete overlap). Diet overlap between striped
bass (SB), white bass (WB), and largemouth bass
(LB) varied throughout the study. SB/WB had the
greatest overall diet overlap (0.68) while SB/LB
had the lowest overall diet overlap (0.35). In 2004
and 2005 SB/WB overlap was 0.60 and 0.85,
respectively. In 2006, SB/WB overlap reduced
to slightly more than half that of 2005 (0.38).
SB/LB overlap remained consistently less than
0.40 each year (Figure 19). While SB/WB overlap
decrease in 2006 compared to prior years, WB/LB
increased. The overlap index was 0.22 in 2004,
0.50 in 2005, and 0.71 in 2006 (Table 9).
Figure 15. Largemouth, white, and striped bass
backcalculated growth.
Largemouth Bass White Bass Striped Bass
Age Growth (mm) N Growth (mm) N Growth (mm) N
1 198(7) 72 215(7) 41 328(6) 92
2 96(4) 44 86(4) 27 136(5) 44
3 69(3) 28 56(3) 17 84(5) 25
4 54(2) 22 46(1) 16 62(3) 18
5 45(2) 14 40(2) 10 46(5) 5
6 40(2) 8 34(2) 5 43(2) 4
7 44(1) 2 32 1 48 1
Table 7. Mean backcalculated growth (mm) and number of
largemouth, white, and striped bass. Standard error in parentheses.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Figure 16. Growth of young-of-year white and striped bass across years. Growth of young-of-year white bass indicated by A for
November 2004 to November 2005 and B for November 2005 to November 2006. Growth of young-of-year striped bass indicated by
C for November 2004 to November 2005 and D for November 2005 to November 2006.
Energy Densities
Mean energy densities taken from literature were
calculated for each of the 4 prey categories (Table
10). Threadfin shad had the highest energy density
(5,450 J/g) and the invertebrates category had the
lowest (2,944 J/g).
Water Quality
Lake levels are generally highest from January
to March and lowest from August to October
(Figure 20). Lake Pleasant did not reach full
pool in 2004 or 2006. Due to heavy rains in
early 2005, however, Lake Pleasant remained at
or near full pool until May (Figure 21). In early
2005, substantial rainfall saw flow in the Agua
Fria River reach levels of over 481 m3/sec where
historical levels normally remain at 0 m3/sec and
rarely get above 14 m3/sec (Figure 22).
Temperature
Surface temperatures varied dramatically from
fall/spring to summer months. Mean surface
temperatures from the 4 water quality sites
ranged from 12.04°C in January 2006 to 29.85°C
in July 2005 (Table 11). Thermocline in Lake
Pleasant would typically develop in April and
remain stratified until October. Thermocline
depths ranged from 6 m in April 2005 to 16 m in
September 2006 (Figure 23).
Conductivity
Surface conductivity ranged from a low of
0.561 µS·cm-1 in March 2005 to a high of 1.018
µS·cm-1 in August 2004 (Table 11). In spring
2005, conductivity was lower than all other
months during this survey, likely due to heavy
precipitation during that time period.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Figure 17. Percent diet composition by number for largemouth,
white, and striped bass.
Dissolved Oxygen
Dissolved oxygen levels at the surface were highest
during March in both 2005 and 2006, 11.04 mg·l-1
and 12.30 mg·l-1 respectively (Table 11). Dissolved
oxygen levels were lowest during summer with
July 2005 being the lowest at 6.56 mg·l-1. Summer
mean surface dissolve oxygen levels were
significantly lower than fall and spring dissolved
oxygen levels (ANOVA; P < 0.05). Appendix 3
shows seasonal difference of temperature and
dissolved oxygen.
pH
Mean surface pH levels ranged from a minimum
of 7.63 in May 2005 to a maximum of 8.80 in
March of 2006 (Table 11).
Secchi Depth
Secchi depth ranged from 0.88 m in spring 2005
(Agua Fria River) to 10.50 m (Max’s Point) in
spring 2004 (Figure 24a). In 2005, secchi depth
was lower than that of 2004 and 2006. Mean
secchi depth in 2005 was 2.32 m (SE = 0.29) with
March 2005 having the lowest secchi depth of 1.38
m (SE = 0.29).
Chlorophyll
Chlorophyll level ranged from 0.70 mg/l (fall 2006,
Max’s Point) to 13.04 mg/l (spring 2005, Agua Fria
River mouth) (Figure 24b). Between years, 2005
mean chlorophyll levels (5.07 mg/l, SE = 0.84)
were higher than 2004 (2.12 mg/l, SE = 0.42) and
2006 (1.98 mg/l, SE = 0.41).
Figure 18. Percent diet composition by weight for largemouth,
white, and striped bass.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Striped Bass White Bass
Cohort Day Length Weight N SE Cohort Day Length Weight N SE
2002 1 652 3092 6 26 2002 1 398 775 34 4
2002 105 659 3192 19 10
2002 198 725 4245 1
2002 468 678 3475 1
2003 1 324 383 7 10 2003 1 311 372 7 5
2003 105 440 956 27 5 2003 105 331 446 88 1
2003 198 501 1408 34 11 2003 198 345 506 10 4
2003 468 574 2114 10 8
2004 105 236 149 7 9 2004 105 208 111 44 3
2004 198 249 175 6 7 2004 198 218 129 2 1
2004 378 344 460 8 17 2004 378 328 436 23 4
2004 468 455 1059 66 4 2004 468 353 541 39 2
2004 554 466 1135 29 8
2004 742 531 1671 11 17
2004 833 493 1340 13 8
2005 378 154 41 3 27 2005 378 188 83 142 1
2005 468 247 171 153 1 2005 468 238 168 170 2
2005 554 252 180 38 3 2005 554 259 215 38 4
2005 742 305 320 51 5 2005 742 283 279 44 2
2005 833 355 503 176 1 2005 833 290 300 18 2
2006 833 236 149 1
Table 8. Annual growth of striped and white bass. Cohort represents the year class for both striped bass (left) and white bass (right).
Day corresponds to the day of the study (day 1 = August 2004). Total length (mm), weight (g), number and standard error (SE) are
given for each cohort during corresponding survey.
Turbidity
Turbidity levels ranged from 0.45 NTU in spring
2004 (Waddell Dam) to 7.71 NTU in spring 2005
(Agua Fria River mouth). Turbidity levels in fall
2004 (4.63 NTU, SE = 0.96) and spring 2005
surveys (6.24 NTU, SE = 0.79) were higher than
any other survey from August 2004 to November
2006 (Figure 24c).
Striped bass prefer water temperatures less than
25°C and dissolved oxygen levels greater than
2.5 mg/l. At site 4 (Agua Fria River), the number
of meters within the water column that met the
striped bass preferred water quality dropped
considerably in summer with only 7 m of preferred
water quality in June, 3 m in July, and 0 m in
August. In addition, site 3 (Agua Fria River mouth)
had 0 m of preferred water quality in August
(Figure 25).
Hydroacoutsics
Hydroacoustic surveys were run in February 2005
and February 2006. Mean target strength in 2005
was -48.63 dB (TL = 64.04 mm), SE = 0.04. Mean
target strength in 2006 was –46.04 dB (TL = 87.41
mm) SE = 0.04. Total lake fish density was 4 times
greater in 2005 (0.0068 fish/m3) than in 2006
(0.0017 fish/ m3; Table 12). In 2005, the greatest
AZFGD—Research Branch Technical Guidance Bulletin No. 11
22
Figure 19. Diet overlap index for each survey for
striped bass and white bass (SB/WB), striped bass
and largemouth bass (SB/LB), and white bass and
largemouth bass (WB/LB).
Figure 20. Lake elevation from January 2004 to December
2006. Dashed line across the top indicates full pool.
Figure 21. Comparison of spring precipitation from 2005 and 2006.
Figure 22. Mean daily Agua Fria River flow from January 2004
to January 2007 at USGS gauging station 09512800.
Figure 23. Thermocline depths from April to October in 2005
and 2006.
Trip SB/WB SB/LB WB/LB
Aug-04 0.43
Nov-04 0.78 0.08 0.22
Feb-05 0.75 0.45 0.69
Aug-05 0.88 0.49 0.53
Nov-05 0.92 0.19 0.27
Feb-06 0.55 0.39 0.84
Aug-06 0.27 0.45 0.73
Nov-06 0.32 0.26 0.56
Year
2004 0.60 0.08 0.22
2005 0.85 0.38 0.50
2006 0.38 0.37 0.71
Total 0.68 0.35 0.66
Table 9. Diet overlap index by survey, year, and total for striped
bass and white bass (SB/WB), striped bass and largemouth bass
(SB/LB) and white bass and largemouth bass (WB/LB).
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Prey Mean Energy Density (J/g) Source
Threadfin shad 5450 Eggleton and Schramm 2002 (Threadfin shad)
Crayfish 3529 Roell and Orth 1993, Kelso 1973, Eggleton and Schramm 2002
Invertebrates 2944 Cummins and Wuychuck 1971
Other Fish 4766 Miranda & Muncy 1991 and Bryan et al 1996
Table 10. Mean energy densities for threadfin shad, crayfish, invertebrates and other fish from literature.
Figure 24. Secchi depth, (a) chlorophyll (b), and turbidity (c) at each water quality site taken
following each gill netting survey.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Month Parameter 2004 2005 2006
January
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
12.04 (0.02)
0.927 (0.01)
10.79 (0.13)
8.35 (0.03)
4
February
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
March
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
15.08 (0.26)
0.561 (0.05)
11.04 (0.36)
8.27 (0.12)
4
12.65 (0.26)
0.923 (0.00)
12.30 (0.19)
8.80 (0.24)
4
April
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
17.23 (0.12)
0.968 (0.00)
10.38 (0.20)
8.67 (0.01)
3
18.58 0.48)
0.714 (0.00)
9.18 (0.14)
8.54 (0.23)
4
15.73 (0.43)
0.939 (0.01)
9.66 (0.94)
8.49 (0.02)
4
May
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
22.38 (0.05)
0.771 (0.00)
9.26 (0.24)
7.63 (0.31)
4
24.84 (0.23)
0.951 (0.00)
7.73 (0.05)
8.40 (0.00)
4
June
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
27.29 (0.05)
0.811 (0.00)
9.23 (0.17)
8.42 (0.07)
4
27.47 (0.15)
0.970 (0.00)
7.16 (0.05)
8.45 (0.00)
4
July
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
29.85 (0.20)
0.838 (0.00)
6.56 (0.21)
8.54 (0.06)
4
28.05 (0.04)
0.907 (0.00)
7.62 (0.12)
8.46 (0.01)
4
August
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
29.19 (0.18)
1.018 (0.00)
8.28 (0.40)
8.41 (0.03)
4
29.02 (0.07)
0.836 (0.00)
8.47 (0.52)
8.71 (0.12)
4
28.19 (0.15)
0.992 (0.00)
7.86 (0.31)
8.55 (0.03)
4
September
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
28.46 (0.12)
0.845 (0.01)
10.87 (0.92)
8.44 (0.03)
4
24.83 (0.10)
0.957 (0.01)
7.11 (0.47)
8.27 (0.07)
4
October
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
25.20 (0.19)
0.859 (0.00)
11.02 (0.19)
8.36 (0.05)
4
20.17 (0.04)
0.984 (0.00)
7.90 (0.26)
8.23 (0.06)
4
November
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
17.08 (0.04)
0.898 (0.00)
7.74 (0.23)
8.48 (0.08)
4
16.47 (0.01)
1.000 (0.00)
9.82 (0.20)
8.19 (0.03)
4
December
Temperature (°C)
Specific Cond (mS/cm)
Dissolved Oxygen (mg/L)
PH
n
15.14 (0.17)
1.014 (0.00)
9.17 (0.20)
8.00 (0.05)
4
13.30 (0.05)
0.920 (0.00)
9.82 (0.45)
8.44 (0.01)
4
12.50 (0.05)
0.995 (0.00)
10.21 (0.28)
8.17 (0.04)
4
Table 11. Mean monthly surface temperature, specific conductivity, dissolved oxygen, and
pH of all 4 water quality sites from April 2004 to December 2006.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
25
Mean Density N
Season Lake Zone (#/m3) SE SD (100 ping cells)
Feb-05 Lake 0.0068 0.0005 0.0122 505
Agua Fria 0.0058 0.0007 0.0077 117
North Basin 0.0080 0.0011 0.0147 186
South Basin 0.0063 0.0008 0.0118 202
Feb-06 Lake 0.0017 0.0001 0.0046 1199
Agua Fria 0.0040 0.0004 0.0046 112
North Basin 0.0018 0.0001 0.0028 388
South Basin 0.0013 0.0002 0.0052 699
Table 12. Fish density #/m3 by basin (lake zone)
fish density (0.0080 fish/m3) was in the North
Basin and the lowest was in the Agua Fria River.
Fish density in 2006 was highest in the Agua Fria
River (0.0040 fish/m3) and lowest in the South
Basin (0.0013fish/m3; Figures 26 and 27). Lake
volume during the 2005 survey was 1,004 x 106
m3. Fish abundance was estimated at 6,822,368
± 501,856 fish. Based on the maximum-sized
threadfin shad caught during the February 2005
survey, fish greater than 125 mm were considered
potential predators and anything less than 125
mm were considered prey. Only 2.34% (159,734 ±
11,745) of identified fish were estimated as being
greater than 125 mm. Percent composition of white
bass during the February 2005 gill netting survey
was 11.9% for a total of 19,018 ± 1398 fish. Striped
bass composition was 25.38% for a total of 40,535
± 2,980. Lake volume during the February 2006
survey was 9,108 x 105 m3. Fish abundance was
lower in 2006 (1,547,782 ± 120,067) than in 2005.
The cut-off for what could be considered a predator
was estimated at 150 mm TL based on maximum-sized
threadfin shad during the February 2006 gill
netting survey. Estimates for white bass based on
gill net percent composition (white bass = 50.0%,
striped bass = 38.2%) was 35,672 ± 2,767. Striped
bass abundance was estimated at 27,229 ± 2,112.
Bioenergetics
Growth
Striped and white bass growth was modeled
for young-of-year fish from November 2004 to
November 2005 and November 2005 to November
2006 (Figures 28 and 29). Both species of fish had
a steady decline in daily growth starting in July.
Daily growth began to increase in September.
During 2004/2005 striped bass growth was lowest
in January (min = 1.09 g/day) and greatest in
October (max = 5.39 g/day). The following year,
striped bass growth was lowest in September (min
= -0.2 g/day) and greatest in October (max = 2.11g/
day). White bass growth during 2004/2005 was
lowest in January (min = 0.52 g/day) and highest
in October (max = 2.76 g/day). The following year,
white bass growth was lowest in September (min =
-0.82 g/day) and highest in November
(max = 1.25 g/day).
Figure 25. The number of meters within the water column that
fit the preferred conditions (water temperature < 25°C. and DO
> 2.5 mg/l) for striped bass at each water quality site. Site 1 =
Waddell Dam, Site 2 = Max’s Point, Site 3 = Agua Fria Mouth,
Site 4 = Agua Fria River. No water quality data were taken
during the month of February.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
26
Figure 26. Fish densities map from 2005 hydroacoustic survey. Figure 27. Fish densities map from 2006 hydroacoustic survey.
Figure 28. Striped bass daily growth from November 2004
to November 2005 (solid line) and from November 2005 to
November 2006 (dashed line) for age 0 fish.
Figure 29. White bass daily growth from November 2004
to November 2005 (solid line) and from November 2005 to
November 2006 (dashed line) for age 0 fish.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
27
Figure 30. a) Striped bass year 1 daily prey consumption from November 2004 to November 2005. b) Striped bass year 1 daily prey
consumption from November 2005 to November 2006.
Figure 31. a) White bass year 1 daily prey consumption from November 2004 to November 2005. b) White bass year 1 daily prey
consumption from November 2005 to November 2006.
Figure 32. Year 1 white bass daily energy consumption for
2004/2005 and 2005/2006.
Figure 33. Year 1 striped bass daily energy consumption for
2004/2005 and 2005/2006.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Consumption
Consumption of threadfin shad, invertebrates,
crayfish, and other fish was modeled for both
years for striped bass (Figures 30a and 30b)
and white bass (Figures 31a and 31b). Mean
consumption of threadfin shad dropped in half
from 2004/2005 (8.06 g shad/day) to 2005/2006
(3.79 g shad/day). White bass shad consumption
also dropped from the first year (mean = 4.15
g shad/day) to the second year (mean = 0.76 g
shad/day). However, white bass consumption of
invertebrates and crayfish increased from year 1
(1.67 g invertebrates/day and 0.01 g crayfish/day)
to year 2 (mean = 2.89 g invertebrates/day and
2.33 g crayfish/day). For both white and striped
bass total daily energy consumed was lower
during 2005/2006 than 2004/2005 (Figures 32
and 33). Mean white bass daily energy consumed
decreased by 25.62% from year 1 to year 2. In
year 1, white bass daily energy consumption was
28,753 ± 1,398 j/day and decreased to 21,385 ± 416
j/day by year 2. Striped bass energy consumption
had an even greater decrease from year 1 to
year 2 (40.91%). Year 1 striped bass mean daily
energy consumption was 49,091 ± 2,587 j/day and
decreased to 29,009 ± 989 j/day by year 2.
Discussion
Telemetry
Adult striped bass do not handle stress well.
It was determined that to successfully implant
transmitters, the striped bass needed cool water
temperatures, minimal handling, and an immediate
release back into the water upon completion of
the surgery. Other studies used electrofishing as
a means to catch striped bass (Hightower et al.
2001). However, Lake Pleasant is a deep reservoir
and attempts to electrofish for striped bass were
unsuccessful. Although time consuming, angling
proved to be the least stressful method of catch.
Striped bass were observed using the entire
reservoir throughout the course of the year. The
majority of the tagged striped bass remained in
the Agua Fria River from September to May
likely because this area has highest productivity
according to the hydroacoustic surveys. The
preferred temperature range for striped bass is
18-25 °C (Coutant and Carroll 1980; Crance
1984; Coutant 1985) and according to Crance
(1984) striped bass typically select habitats with
dissolve oxygen concentrations greater than 2.5
mg/l. During the summer months, the Agua Fria
River does not meet the preferred condition for
striped bass, which explains why movement out of
the river was observed from June to September.
Striped bass are able to find refuge outside of
the Agua Fria River either near the mouth of the
river or at the south end of the reservoir near the
Waddell Dam. Despite surface water temperatures
in the main reservoir peaking near 30 °C and
dissolved oxygen levels dropping to 2.30 mg/l,
a thin layer of suitable conditions exists near the
thermocline typically 9 to 15 meters deep. As
surface water temperatures began to drop (mean
20.14 degrees °C) in September, 5 of the remaining
6 striped bass returned to the Agua Fria River.
During this time, dissolved oxygen levels ranged
from 2.27 mg/L. to 7.13 mg/L and there were 14
meters of preferred water quality in the Agua Fria
River.
Although striped bass were observed moving
throughout the entire stretch of the Agua Fria
River, the area across from Tule Cove (about 7.25
km upstream from the mouth of the Agua Fria
River) is likely preferable spawning habitat for
striped bass as indicated by their frequency of
occurrence at that location. This area is restricted
to many anglers due to an eagle closure that blocks
the entrance to this area from mid-December to
mid-June. During these months, the only access
to this area is along Table Mesa Road, a dirt road
not suitable for pulling a trailer. In July 2007,
the Maricopa Parks and Recreation Department
and the Bureau of Reclamation closed this road
indefinitely to motorized vehicles to ensure
public safety and protect the natural and cultural
resources within the Agua Fria Conservation Area.
This leaves no boat access to the Agua Fria River
from mid-December to mid-June.
Spawning
Larval tow and light traps surveys were conducted
to determine if striped bass were spawning within
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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the reservoir or being fed in through the intake
pump at the Waddell Dam. Due to the difficulty
of distinguishing between striped bass and white
bass at the larval stage, alternative evidence was
needed to make a conclusion. In fall 2005, gill
nets set in the Agua Fria River, 9 miles from the
Waddell Dam, contained over nearly 100 young-of-
year striped bass. This was enough evidence to
suggest that striped bass were spawning within
the reservoir at the upper end of the Agua Fria
River. Striped bass broadcast spawn their eggs in
waters with considerable current where they will
remain suspended such that they do not sink to the
bottom and become smothered (Goodson 1966;
Barkuloo 1970). The upper reaches of the Agua
Fria River run dry most of the year and the lower
reach of the river, which is inundated due to the
dam, has little to no flow. The exception is during
heavy rains such as the case in spring 2005. As a
result of the heavy flow in 2005, striped bass had
very successful spawn. In contrast, the following
spring saw virtually no rain thus no flow and very
poor striped bass spawn. Although studies have
shown that striped bass are capable of spawning
in-reservoir with no flow (Gustaveson et al. 1984),
success is still low. The dependence on flow into
the Agua Fria River will be a limiting factor for
the success of striped bass in this reservoir.
Fish Surveys
Population Dynamics
In 2005, there was a boom in the numbers of white
and striped bass at Lake Pleasant. A wet spring
provided heavy flows in the Agua Fria River
creating suitable conditions for both white and
striped bass reproduction. As a result, catch for
white bass dramatically increased in August when
they were large enough to be captured in gill nets.
Then, in November, striped bass catch dramatically
increased as they became large enough to be
captured in gill nets. The majority of white and
striped bass during 2005 were young-of-year fish.
As a result, proportional stock densities in the
summer and fall surveys were low, indicating a
very successful spawn during the spring of 2005.
In 2006, striped bass catch was still high, but most
of the catch consisted of year 1 fish. No young-of-year
white bass and only one young-of year striped
bass was captured during the fall 2006 survey
suggesting poor reproduction in spring 2006.
White and striped bass share similar life histories.
Both are pelagic and rely on threadfin shad as
a primary source of food in Lake Pleasant. The
strong 2005 striped bass year class appears to
have caused a shift between white and striped
bass relative abundance. Fall surveys from 2000
to 2004 showed that white bass abundance
dominated striped bass abundance (Bryan 2005).
The successful spawn of both white and striped
bass in 2005 may be a turning point as relative
abundance estimates were similar. During the last
survey of this study in 2006, white bass abundance
was the lowest it had been since 2000 while striped
bass abundance was still high. The shift from
more white bass to more striped bass suggests that
striped bass may be out-competing white bass.
This is also suggested by the diet shift of white
bass during August and November 2006 following
the dry spring. Leading up to those 2 surveys,
white and striped bass consumed primarily
threadfin shad. While striped bass continued
to consume threadfin shad, white bass shad
consumption dropped to nearly zero in August and
November 2006.
Relative weight for white, striped, and largemouth
bass was greatest during the summer following
the wet spring in 2005 as lake productivity was
high. The following year, when shad forage was
low, both white and striped bass relative weights
dropped considerably while largemouth bass had
a slight drop in relative weight. This suggests that
largemouth bass are not as dependent on threadfin
shad and remain relatively healthy when shad
populations are low.
Age and Growth
White bass and largemouth bass otoliths were
much easier to read than striped bass otoliths.
Studies suggest the use of scales for aging striped
bass (Welch et al. 1993), but readers were more
consistent when using otoliths. Backcalculated
growth shows that striped bass grow at a much
greater rate during their first 2 years compared to
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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white and largemouth bass. White and largemouth
bass growth is similar for younger fish, but after
about age 3, white bass growth seems to slow
compared to largemouth bass. Growth comparisons
from 2005 and 2006 are good indicators of growth
extremes for young-of-year striped and white
bass. Due to the high productivity in spring 2005,
growth of young-of-year white and striped bass
nearly doubled that of young-of-year growth in
2006. Average growth for young-of-year striped
bass falls near the middle of the extreme ranges
from 2005 and 2006 as estimated by the mean
backcalculated growth for young-of-year striped
bass.
Diet
The primary concern for anglers at Lake Pleasant
is that striped bass will out-compete other sport
fish, specifically largemouth and white bass, for
the primary prey source, threadfin shad. Our
results show that largemouth bass exhibited an
opportunistic feeding behavior, as expected. The
majority of their diet was invertebrates, crayfish
and other fish (mostly sunfish). Threadfin shad
made up very little of their diet. The only survey
where largemouth bass diet contained a substantial
amount of threadfin shad was following the
productive spring of 2005. That summer, all 3
predator species had the highest proportion of
shad in their diet than any other time during the
course of this study. This suggests that largemouth
bass do not depend on threadfin shad, but will
take advantage when they are available. Striped
bass exhibited a specialist feeding behavior. Their
diet consisted mostly of threadfin shad with some
minimal seasonal change to invertebrates in the
spring. Wilde and Paulson (1989) noted that striped
bass in Lake Mead fed primarily on threadfin
shad except in spring when seasonal differences
in depth and horizontal distribution of striped bass
and prey cause spatial separation, causing striped
bass to rely on invertebrates. In January 2006,
the inland silverside (Menidia beryllina), a new
species to Arizona, was discovered. The following
summer, inland silversides began showing up
in the stomachs of white and largemouth bass,
and made up nearly a fifth of the striped bass
diet during the August 2006 survey. Striped
bass adults generally prefer soft-rayed, schooling
species (Setzler et al. 1980), which is likely why
inland silversides were so abundant in striped bass
stomachs during the summer of 2006 when shad
numbers were low. Because of angler concerns
that striped bass would eat largemouth bass, it
is important to note that not a single largemouth
bass was found in the diet of striped bass. There
is strong evidence that striped bass are out
competing white bass for threadfin shad. At the
beginning of this study, white bass diet consisted
mostly of threadfin shad with seasonal changes to
invertebrates in the spring. In 2006, when striped
bass abundance was still high and threadfin shad
numbers dropped, there appeared to be a shift in
the white bass diet but not in striped bass diet.
White bass diet shifted from primarily threadfin
shad to primarily crayfish. Competition between
striped and white bass is likely the cause for
this shift. Schoener’s (1970) diet overlap index
provides further evidence of a shift in white bass
diet. Prior to 2006, the striped bass/white bass
index was high indicating similarities in diet.
In 2006, however, the striped bass/white bass
index dropped and the white bass/largemouth
bass index grew. The striped bass/largemouth
bass index remained consistently low during
the course of this study indicating minimal diet
overlap. This suggests that during years of high
threadfin shad productivity, competition between
striped and white bass are minimal. However,
during years of low shad productivity interspecific
competition between striped and white bass cause
white bass to exhibit feeding behaviors similar to
largemouth bass. While striped bass do not directly
affect largemouth bass, a year of high striped
bass reproduction followed by multiple years of
low productivity has potential for interspecific
competition between largemouth and white bass
for feeding resources.
Water Quality
Precipitation and Flow
Spring of 2005 was one of the wettest on record.
The month of February provided nearly half of
the mean annual rainfall for Maricopa County.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
31
As a result Lake Pleasant was at full pool for
most of spring 2005. In contrast, spring 2006 saw
very little precipitation. The months of January,
February, and April had no measurable rain.
Striped bass require water with a considerable
amount of current in order for their eggs to remain
suspended during spawning. Such conditions
appeared to exist as flows in the Agua Fria
River in spring 2005 were the highest they have
been since the construction of the New Waddell
Dam in the mid 1990s. High flows flushed large
amounts of debris into the Agua Fria River
and subsequently the rest of the reservoir. This
increased chlorophyll levels in the Agua Fria
River in summer of 2005, indicating a substantial
amount of productivity within this portion of the
reservoir. In contrast, the following spring saw
very little flow in the Agua Fria due to minimal
amounts of rain.
Hydroacoustics
Hydroacoustic surveys run in 2005 showed much
more productivity compared to 2006. Estimates in
2005 were more than 4 times that of 2006. There
are a couple reasons that could explain such a
huge difference in productivity. After the 2005
survey, it was determined that more transects were
needed and the number was more than doubled to
increase accuracy. Also, extreme rainfall in 2005
flushed large amounts of debris into the reservoir.
The combination of fewer transects and extreme
amounts of debris may have prevented accurate
density estimates in 2005. In addition, many of the
gill nets set during February 2005 were damaged
due to debris and may have affected the percent
composition of white and striped bass captured,
which were used to estimate lake-wide fish
numbers. In both 2005 and 2006, biomass densities
were greatest in the Agua Fria River and North
Basin.
Bioenergetics
Bioenergetics provides great insight on growth,
consumption, and energy demands of predatory
species (Hanson et al. 1997). During the course
of this study it was likely that 2 growth and
consumption extremes were observed. Because
young-of-year striped bass were not detected in our
gill nets until November, measurements were made
in the fall. From fall 2004 to fall 2005, striped and
white bass growth was greatest it has been since
2000 (Bryan 2005). The following year from fall
2005 to fall 2006, growth was lower than it has
been since 2000. These 2 extremes provide an
upper and lower range of energy demands at Lake
Pleasant.
In 2005, striped bass growth rates steadily
increased leading into the summer months,
while rates remained relatively steady in 2006.
During both years in mid-summer, striped bass
growth slowed substantially and bottomed out
in September. Once water temperatures cooled,
however, rates increased dramatically. White bass
growth had similar patterns to striped bass growth.
The only difference is that in 2006, white bass
growth rates decreased slightly leading into the
summer months. Daily threadfin shad consumption
for striped bass was greatest in the early fall
during both years. The maximum daily threadfin
shad consumption in 2005 was nearly 3 times that
of 2006 for year 1 striped bass while consumption
of other prey species remained relatively similar.
White bass daily consumption of threadfin shad
in 2005 was also greatest in early fall. In early
fall 2006, white bass theardfin shad consumption
was nearly 0. To supplement for the lack of
threadfin shad, white bass increased consumption
of crayfish. Both striped and white bass total
energy consumption decreased from 2005 to
2006. However, the percentage decrease of energy
consumed by white bass was less than that of
striped bass. Because striped bass are specialists,
the dependence on threadfin shad combined with
the temperature extremes found at Lake Pleasant
will have a much greater effect on striped bass
survival. Even though white bass cannot compete
with striped bass for threadfin shad, the more
generalist white bass feeding strategies will
improve their survival.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
32
Management
Recommendations
Promote Striped Bass Fishing
2005 produced the greatest class of striped bass
since their introduction into Lake Pleasant. Now
is an opportunity to take advantage and promote
this fishery. According to Bryan (2005), less
than 1% of all anglers target striped bass at Lake
Pleasant. This same study determined that over a
third of anglers are generalists that do not target
a specific species of fish. In addition, there are
an estimated 150 largemouth bass tournaments
per year and not a single striped bass tournament.
Lake Pleasant is the only inland lake that provides
a white bass fishing opportunity. Also according
to Bryan (2005), 10% of anglers target white bass.
By increasing fishing pressure on striped bass,
this would reduce competition between striped and
white bass, allowing for a Lake Pleasant white bass
fishery to remain.
Increase Access to Upper
Agua Fria River
From December 15th to June 15th, an eagle closure
prohibits anglers from reaching the upper end of
the Agua Fria River. The area above the closure
provides prime spawning grounds for striped bass.
As such, striped bass tend to congregate in that
area during the time of the closure. In order to help
control striped bass populations, maintaining and
possibly increasing access (i.e. boat launch) along
Table Mesa Road would allow more anglers to fish
in these prime striped bass areas.
Continue Monitoring Populations
Data collected towards the end of the study
indicated for the first time that striped bass
abundance was significantly greater than white
bass abundance. Conducting fall surveys with
fixed sites in the Agua Fria River as a means to
monitor this trend will also provide information
about spawning success as young-of-year striped
bass typically are too small to be caught in gill
nets until the fall.
Acknowledgements
I would like to acknowledge all of those within the
Arizona Game and Fish Department who helped
with this project. Thanks to Bill Persons, Scott
Bryan, Jimmy Fulmer, Anne Kretchmann, David
Ward, Scott Rogers, Chris Cantrell, Kari Ogren,
Mike Childs, Chasa O’brien, Todd Pringle, Kevin
Bright, Nicole Brown, Mike Disney, Alicia Jontz,
Kyle Cooper, Gentry Burton, Richard Wiggins,
Jim Warnecke, Curtis Gill, Cori Carveth, Dave
Weedman, Ken Branson, and Jack Beyer. Without
the help of these individuals much of the field work
could not have been accomplished. Also thanks to
Sue Boe for her GIS expertise.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
33
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Aug. 2004 Nov. 2004 Feb. 2005 Aug. 2005
Effort 14.663 (0.259) 18.218 (0.477) 15.924 (0.573) 14.220 (0.192)
Common Carp 0.034 (0.014) 0.063 (0.025) 0.239 (0.073) 0.009 (0.007)
Threadfin Shad 0.056 (0.029) 2.024 (0.957) 0.357 (0.160) 0.105 (0.064)
Channel Catfish 0.025 (0.012) 0.055 (0.024) 0.037 (0.014) 0.043 (0.015)
Largemouth Bass 0.005 (0.005) 0.000 (0.000) 0.000 (0.000) 0.006 (0.004)
White Bass 0.191 (0.122) 0.215 (0.118) 0.054 (0.033) 0.357 (0.098)
Striped Bass 0.061 (0.040) 0.095 (0.031) 0.114 (0.055) 0.035 (0.013)
Crappie 0.000 (0.000) 0.000 (0.000) 0.006 (0.006) 0.096 (0.073)
Flathead Catfish 0.000 (0.000) 0.008 (0.005) 0.000 (0.000) 0.000 (0.000)
Total 0.371 (0.176) 2.460 (1.087) 0.807 (0.230) 0.6521 (0.208)
Nov. 2005 Feb. 2006 Aug. 2006 Nov. 2006
Effort 18.591 (0.792) 17.820 (0.429) 15.242 (0.135) 16.611 (0.163)
Common Carp 0.083 (0.043) 0.030 (0.013) 0.038 (0.015) 0.034 (0.013)
Threadfin Shad 0.594 (0.339) 0.475 (0.319) 0.312 (0.187) 2.258 (0.652)
Channel Catfish 0.059 (0.025) 0.006 (0.004) 0.069 (0.020) 0.030 (0.010)
Largemouth Bass 0.034 (0.018) 0.003 (0.003) 0.008 (0.004) 0.005 (0.003)
White Bass 0.641 (0.473) 0.183 (0.086) 0.173 (0.081) 0.043 (0.018)
Striped Bass 0.562 (0.169) 0.139 (0.053) 0.140 (0.044) 0.321 (0.084)
Crappie 0.042 (0.025) 0.005 (0.003) 0.000 (0.000) 0.002 (0.002)
Flathead Catfish 0.007 (0.007) 0.000 (0.000) 0.000 (0.000) 0.005 (0.003)
Total 2.021 (0.945) 0.841 (0.404) 0.740 (0.237) 2.698 (0.720)
1a. CPUE by trip of 8 species of fish caught during gill netting surveys from August 2004 to November 2006.
APPENDICES
Wege, G.J., and R.O. Anderson. 1978. Relative
Weight (Wr): a new index of condition for
largemouth bass. Pages 79-91 in G.D. Novinger
and J.G. Dillard, editors. New approaches to the
management of small impoundments. American
Fisheries Society, North Central Division,
Special Publication 5, Bethesda, Maryland.
Welch, T.J., M.J. Van Den Avyle, R.K. Betsill,
and E.M. Driebe. 1993. Precision and relative
accuracy of striped bass age estimates from oto-liths,
scales, and anal fan rays and spines. North
American Journal of Fisheries Management
13:616-620.
Wilde, G.R., and L.J. Paulson. 1989. Temporal
and spatial variation in pelagic fish abundance
in Lake Mead determined from echograms.
California Fish and Game 75:218-223.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
36
Aug-04 Nov-04 Feb-05 Aug-05
S-Q Q-P P-M M-T S-Q Q-P P-M M-T S-Q Q-P P-M M-T S-Q Q-P P-M M-T
Common Carp 0 14 71 14 6 19 72 3 1 35 62 1 0 0 100 0
Channel Catfish 25 75 0 0 48 52 0 0 50 50 0 0 60 40 0 0
Largemouth Bass 0 0 0 0 14 59 27 0 47 34 18 0 39 36 24 0
White Bass 0 3 38 59 20 4 61 15 11 0 56 33 81 1 16 2
Striped Bass 45 55 0 0 60 38 2 0 71 29 0 0 100 0 0 0
Black Crappie 0 0 0 0 0 0 0 0 0 50 50 0 24 58 18 0
Flathead Catfish 0 0 0 0 0 83 17 0 0 0 0 0 0 0 0 0
Nov-05 Feb-06 Aug-06 Nov-06
S-Q Q-P P-M M-T S-Q Q-P P-M M-T S-Q Q-P P-M M-T S-Q Q-P P-M M-T
Common Carp 44 22 30 4 22 33 44 0 0 32 59 9 11 21 68 0
Channel Catfish 32 53 16 0 50 50 0 0 27 70 3 0 50 43 7 0
Largemouth Bass 39 40 21 0 16 43 27 14 58 31 9 2 77 14 7 2
White Bass 31 37 14 17 9 40 23 27 0 41 38 22 0 46 32 22
Striped Bass 83 17 0 0 74 26 0 0 81 17 2 0 97 3 0 0
Black Crappie 7 36 57 0 0 50 50 0 0 0 0 0 50 0 50 0
Flathead Catfish 0 67 33 0 0 0 0 0 0 0 0 0 0 100 0 0
1b. Relative stock densities for common fish found in Lake Pleasant.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
37
Largemouth Bass White Bass Striped Bass
Fish n n N
Unidentified Fish 24 27 27
Threadfin Shad 25 70 123
Largemouth Bass 3 2 0
Centrarchidae 1 1 0
Common Carp 2 0 0
Green Sunfish 1 1 0
Bluegill 2 0 1
Lepomis 22 1 0
Moronidae 2 0 2
Golden Shiner 2 0 0
Black Crappie 1 0 0
Flathead Catfish 1 0 0
Inland Silverside 2 1 6
Channel Catfish 1 0 0
Invertebrates/Other n n n
Crayfish 80 40 3
Gammarus 8 14 9
Diptera 128 57 32
Coleoptera 1 1 0
Corixidae 3 0 1
Daphnia 21 4 0
Ditritus 4 1 0
Eggs 1 0 0
Ephemeroptera 26 12 5
Hemiptera 1 1 1
Nematode 2 0 1
Odonota 5 0 0
Orthoptera 0 1 0
Ostracod 1 0 0
Zooplankton 8 20 20
Hymenoptera 0 0 1
Arachnid spp. 4 0 0
Empty 75 131 106
Total Stomachs 329 326 292
2a. Prey items found in diet samples for largemouth bass, white bass, and striped bass.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
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Aug-04 Nov-04
Largemouth White Bass Striped Bass Largemouth White Bass Striped Bass
Freq N Freq N Freq N Freq N Freq N Freq N
Shad 0% 1 9% 32 46% 13 4% 27 37% 57 62% 45
Crayfish 0% 1 31% 32 0% 13 52% 27 2% 57 2% 45
Otherfish 0% 1 0% 32 0% 13 7% 27 4% 57 0% 45
Invertebrates 0% 1 13% 32 0% 13 15% 27 12% 57 2% 45
No ID fish 0% 1 22% 32 0% 13 4% 27 9% 57 9% 45
Empty 100% 1 34% 32 54% 13 41% 27 46% 57 31% 45
Feb-05 Aug-05
Largemouth White Bass Striped Bass Largemouth White Bass Striped Bass
Freq N Freq N Freq N Freq N Freq N Freq N
Shad 3% 39 18% 22 21% 39 45% 44 52% 44 64% 11
Crayfish 15% 39 0% 22 0% 39 27% 44 0% 44 0% 11
Otherfish 8% 39 9% 22 5% 39 16% 44 0% 44 0% 11
Invertebrates 64% 39 36% 22 18% 39 5% 44 11% 44 0% 11
No ID fish 8% 39 0% 22 8% 39 20% 44 16% 44 9% 11
Empty 21% 39 36% 22 54% 39 23% 44 32% 44 36% 11
Nov-05 Feb-06
Largemouth White Bass Striped Bass Largemouth White Bass Striped Bass
Freq N Freq N Freq N Freq N Freq N Freq N
Shad 0% 61 23% 53 38% 55 0% 55 12% 42 48% 44
Crayfish 25% 61 0% 53 0% 55 4% 55 0% 42 0% 44
Otherfish 2% 61 0% 53 0% 55 4% 55 0% 42 0% 44
Invertebrates 56% 61 11% 53 16% 55 71% 55 64% 42 39% 44
No ID fish 0% 61 9% 53 13% 55 4% 55 2% 42 7% 44
Empty 30% 61 58% 53 42% 55 20% 55 26% 42 16% 44
Aug-06 Nov-06
Largemouth White Bass Striped Bass Largemouth White Bass Striped Bass
Freq N Freq N Freq N Freq N Freq N Freq N
Shad 2% 53 0% 44 27% 45 4% 49 6% 32 50% 40
Crayfish 47% 53 43% 44 4% 45 12% 49 31% 32 0% 40
Otherfish 17% 53 2% 44 16% 45 27% 49 3% 32 0% 40
Invertebrates 19% 53 16% 44 13% 45 73% 49 28% 32 18% 40
No ID fish 9% 53 0% 44 11% 45 8% 49 6% 32 10% 40
Empty 25% 53 41% 44 40% 45 6% 49 38% 32 30% 40
2b. Frequency of occurrence of prey categories for largemouth bass, white bass, and striped bass.
AZFGD—Research Branch Technical Guidance Bulletin No. 11
39
White Bass Aug-04 Nov-04 Feb-05 Aug-05 Nov-05 Feb-06 Aug-06 Nov-06
Shad 42.86% 76.32% 28.57% 88.40% 72.73% 16.28% 0.00% 10.03%
Crayfish 46.55% 3.23% 0.00% 0.00% 0.00% 0.00% 70.18% 49.38%
Invertebrates 10.59% 16.21% 57.14% 11.60% 27.27% 83.72% 25.97% 39.97%
Other Fish 0.00% 4.23% 14.29% 0.00% 0.00% 0.00% 3.85% 0.61%
Striped Bass Aug-04 Nov-04 Feb-05 Aug-05 Nov-05 Feb-06 Aug-06 Nov-06
Shad 100.00% 98.54% 53.18% 100.00% 80.67% 61.40% 52.69% 78.47%
Crayfish 0.00% 1.26% 0.00% 0.00% 0.00% 0.00% 7.41% 0.00%
Invertebrates 0.00% 0.20% 33.47% 0.00% 19.33% 38.60% 15.76% 21.53%
Other Fish 0.00% 0.00% 13.35% 0.00% 0.00% 0.00% 24.15% 0.00%
Largemouth Bass Aug-04 Nov-04 Feb-05 Aug-05 Nov-05 Feb-06 Aug-06 Nov-06
Shad 6.47% 3.54% 49.47% 0.00% 0.00% 3.40% 4.78%
Crayfish 74.27% 17.23% 28.16% 29.26% 4.55% 59.70% 10.76%
Invertebrates 7.64% 71.38% 3.24% 69.19% 86.44% 8.99% 55.97%
Other Fish 11.50% 7.86% 19.13% 1.55% 9.02% 26.62% 28.49%
2c. Percent composition by weight for striped, white, and largemouth bass for all surveys.
Basin 1 Basin 2 Basin 3
Common Carp 8 2 6
Threadfin Shad 138 0 3289
Lepomis 64 1395 114
Largemouth Bass 2 0 2
Moronidae 19 0 335
Pomoxis 108 0 59
4. Number of larval fish collected by basin (basin 1 = upper reservoir,
basin 2 = lower reservoir, basin 3 = Agua Fria River).
40
3. Temperature and dissolved oxygen depth profiles during each season from 2004 to 2006.