Environmental biology of fishes, tập 93, số 3, 2012

Environ Biol Fish (2012) 94:363–375
DOI 10.1007/s10641-011-9967-z

Migration characteristics of hatchery and natural-origin
Oncorhynchus mykiss from the lower Mokelumne
River, California
S. Casey Del Real & Michelle Workman &
Joseph Merz
Received: 28 January 2011 / Accepted: 12 October 2011 / Published online: 22 November 2011
# Springer Science+Business Media B.V. 2011

Abstract The lower Mokelumne River (LMR), located
in the California Central Valley, supports a
population of natural-origin Oncorhynchus mykiss.
In addition, the Mokelumne River Fish Hatchery
(Hatchery) contributes hatchery produced O. mykiss
to the system annually. We conducted a 3 year
acoustic tagging study to evaluate the migratory
characteristics of LMR hatchery and natural-origin
O. mykiss to the Pacific Ocean. Specifically, we
analyzed downstream movement and migration rates,
routes, and success of acoustically tagged O. mykiss
of hatchery and natural origin under variable release
locations in non-tidal and tidal habitats. Results from
our study suggest there are significant differences in
the proportion of hatchery and natural O. mykiss that
demonstrate downstream movement. Fish origin, size,
and release location all had a significant effect on
whether an individual demonstrated downstream
movement. Mokelumne origin O. mykiss that initiated

S. C. Del Real (*)
East Bay Municipal Utility District,
One Winemasters Way, STE K-2,
Lodi, CA 95240, USA
e-mail:

downstream movement utilized numerous migration
routes throughout the Delta during their migration
towards the Pacific Ocean. We identified four primary
migration pathways from the lower Mokelumne
River through the Sacramento-San Joaquin Delta
while the Delta Cross Channel was closed.
However, several other pathways were utilized.
Origin had a significant effect on O. mykiss success
in reaching key points in the Delta and through the
Estuary. Fish size had a significant effect on whether
an individual reached the marine environment. Of the
467 O. mykiss tagged, 34 successfully reached the
Pacific Ocean (Golden Gate Bridge), and of these, 33
were hatchery-origin and 1 was natural-origin. A
higher proportion of hatchery-origin fish (10% of
tagged) migrated to the ocean compared to naturalorigin fish (<1%). Our study provides valuable
information on the differences between hatchery and
natural-origin O. mykiss migration characteristics as
well as unique insight into the migratory behavior of
little studied non-Sacramento River origin salmonids.
Keywords Mokelumne River . Oncorhynchus
mykiss . Acoustic telemetry . Migratory behavior .
Hatchery release strategies

M. Workman
United States Fish and Wildlife Service,
4001 N. Wilson Way,
Stockton, CA 95205, USA

Introduction

J. Merz
Cramer Fish Sciences,
13300 New Airport Road, Suite 102,
Auburn, CA 95602, USA

Steelhead rainbow trout (Oncorhynchus mykiss) exhibit one of the most complex life histories of the
Pacific salmonids (Oncorhynchus spp.) including the
ability to utilize a variety of diverse habitats and


364

flexible life history traits ranging from resident (rainbow
trout) to anadromous (steelhead) forms (Behnke
2002; Good et al. 2005; Zimmerman et al. 2008).
Populations of O. mykiss once extended throughout
many of the tributaries and headwaters of California’s
Central Valley (CV) (Busby et al. 1996; McEwan
2001). Due to the popularity of O. mykiss propagation, they were widely stocked throughout the state
dating back to the 1870s (Behnke 1992; Moyle 2002).
Today, the majority of CV O. mykiss are restricted to
nonhistorical or remnant spawning and rearing habitat

below nonpassable dams and these populations are
heavily subsidized by hatchery production to
mitigate habitat loss and support a large sport
fishery (Yoshiyama et al. 1996; Lindley et al. 2006).
Even so, numerous stressors continue to impact CV O.
mykiss including water diversions and withdrawals,
dams and in-stream structures, conversion of riparian
areas, species introductions, water pollution, and
disruption of coarse sediment supplies (McEwan
2001).
The steelhead component of CV O. mykiss is
difficult to monitor because they often migrate and
spawn during periods of high, turbid waters and may
survive spawning or die away from spawning grounds
(McEwan 2001). Furthermore, O. mykiss juveniles
often emigrate at larger sizes than CV Chinook salmon
(O. tshawytscha) making them less susceptible to
the most common migrant monitoring techniques
used for CV salmonids (DuBois et al. 1991;
McEwan 2001). In addition, data on the relationship,
interaction, and contrasting dispersal patterns of
steelhead and resident rainbow trout are limited
(Busby et al. 1996; NMFS 2003). Recent advances
in acoustic telemetry technology have allowed for the
tracking of movement and migration of individual
fish providing essential information in developing
resource management objectives and recovery goals
for CV O. mykiss (Welch et al. 2004; Hall et al. 2009).
In this study we employed acoustic telemetry
technology to characterize migration patterns of

hatchery and natural-origin O. mykiss in the lower
Mokelumne River, California (LMR), a system with
both hatchery and natural production. Specifically, we
analyzed four parameters of migration: downstream
movement, migration rates, migration routes, and
migratory success to the Pacific Ocean (as defined
by reaching the Golden Gate Bridge) against three
variables: fish origin, size, and release location.

Environ Biol Fish (2012) 94:363–375

Our objectives were to assess the differences in
migration characteristics using the biological
parameters identified above.
Study site
The Mokelumne River is a snow-fed system that
drains approximately 1624 km2 of the central Sierra
Nevada. The river presently has 16 major water
impoundments, including Salt Springs (0.175 km3;
completed 1931), Pardee (0.244 km3; completed 1929)
and Camanche (0.515 km3; completed 1963) reservoirs. The LMR stretches 103 river kilometers (rkm)
from Camanche Dam, the lowest nonpassable dam,
to its confluence with the San Joaquin River within the
central Sacramento-San Joaquin Delta (Delta) (Fig. 1).
The river is considered part of the North Valley Floor
Critical Habitat for CV O. mykiss (NMFS 2005).
Between New Hope Landing and the San Joaquin
River confluence, the Mokelumne River is connected
to the Sacramento River via the Delta Cross Channel
and Georgiana Slough and to the Central Delta via

Little Potato and Little Connection sloughs (Fig. 2).
The LMR currently supports two anadromous salmonids which are supported by hatchery production, fallrun Chinook salmon and O. mykiss. The Mokelumne
River Fish Hatchery (Hatchery) produces O. mykiss to
compensate for the decrease in natural fish production
and habitat loss due to the construction of Camanche
Dam. During years when the projected O. mykiss egg
take did not meet the Hatchery’s production goals,
Mokelumne River stock was augmented with
imported eggs and/or fry from the Nimbus Hatchery
(American River), the Feather River Hatchery, and the
Coleman National Fish Hatchery (Sacramento River)
(Fig. 1). Anadromous, natural-origin O. mykiss in the
LMR are listed as threatened under the Endangered
Species Act (ESA) (NMFS 1998). However, the nonanadromous forms (rainbow trout) and hatcheryproduced O. mykiss are not ESA listed. Both resident
and anadromous forms of O. mykiss are present in the
LMR (Satterthwaite et al. 2009).
Salmon and steelhead that emigrate out of the
LMR must negotiate a maze of natural and man-made
tributaries, sloughs, and river channels as they migrate
through the interior Delta to reach the Pacific Ocean.
As salmonids navigate the complex network of
channels that have been significantly altered by water
resource project operations, they are influenced by


Environ Biol Fish (2012) 94:363–375

365

Fig. 1 Lower Mokelumne River in relationship to Sacramento, San Joaquin, Feather, and American rivers, Sacramento-San Joaquin

Delta, and San Francisco Estuary

both anthropogenic impacts and environmental processes that affect migration rates, straying, predation,
and survival (Perry et al. 2010). Migration through the
highly modified Delta system may be significantly
more risky than it historically was (Baker and
Morhardt 2001; Brandes and McLain 2001) and the
greatest management concern with respect to preserving
anadromy in CV O. mykiss may be reduced survival of
emigrating smolts (Satterthwaite et al. 2009).

Materials and methods
Fish collection
O. mykiss were collected from four sources within the
LMR: (1) Hatchery-origin O. mykiss directly from the
Hatchery, consisting of either Mokelumne River or

Feather River broodstock (1 and 2 year-old fish); (2)
Reconditioned kelts obtained from the Hatchery; (3)
Natural-origin O. mykiss of various life stages
collected using standard boat electrofishing techniques (Meador et al. 1993) at several locations
throughout the non-tidal river (within 20 km of
Camanche Dam); and (4) Actively outmigrating
natural-origin O. mykiss captured at two rotary screw
traps (RST) (downstream migrant traps used to
sample emigrating anadromous salmonids) (Volkhardt
et al. 2007) (Table 1). The downstream RST (Lower
RST) is located near the Mokelumne River tidewater
downstream of Woodbridge Irrigation District Dam
(WIDD) below the Lower Sacramento Road Bridge,

61.8 rkm upstream of the confluence with the San
Joaquin River. The upstream RST (Upper RST) is in
the non-tidal portion of the LMR above the Elliott
Road Bridge at rkm 87.4 (Fig. 1).


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Environ Biol Fish (2012) 94:363–375

Fig. 2 Mokelumne River O. mykiss migration pathways through the Sacramento-San Joaquin Delta, California

Surgical implantation of tags
We surgically implanted acoustic transmitters and
passive integrated transponder (PIT) tags in 467
hatchery and natural-origin O. mykiss between 2007
and 2009 (Table 1). The tag types included Vemco
V9-2L-69 kHz R64K coded transmitters (implanted in
442 hatchery and natural-origin O. mykiss of various
life stages) and Vemco V13-1L-69 kHz R64k coded
transmitters (implanted in 25 reconditioned hatchery
kelts). The V9-2L coded transmitters were 29 mm
long, weighed 4.7 g in air, and had an estimated
battery life of 292 days. The corresponding values for
V13-1L coded transmitters were 36 mm long,
weighted 11 g in air, and had an estimated battery
life of 616 days. The PIT tags (manufactured by
Destron Fearing) were 12.5 mm long and 2.0 mm
wide and weighed 0.11 g in air. The minimum fork

length (FL) of tagged fish was 180 mm to obtain an
optimal transmitter-to-body-weight ratio that did not
exceed 5% (Adams et al. 1998). Tag burden for all
weighed fish was (mean±SE) 2.8±1.4%.
Surgical tagging occurred in the field at various
locations along the LMR and in the Hatchery.
Standardized tagging procedures were used at each
location. O. mykiss were anesthetized with tricaine
methanesulfonate (natural-origin) or carbon dioxide
(hatchery-origin) in aerated water until reactivity and
responses to handling were minimal, but operculum
movement was still present. Fish fork length and weight
were measured and fish were placed ventral side up in a
V-shaped wooden platform with a foam rubber saddle
secured to a transportable open tank. Water within the
tank was maintained at a level sufficient to keep the gills
wetted and was changed every seven to ten surgeries.
An acoustic transmitter and a PIT tag were inserted


Environ Biol Fish (2012) 94:363–375

367

Table 1 Mokelumne River O. mykiss acoustic telemetry release groups between 2007 and 2009
Year

Release Period

Origin

Life History

Release Group

Number

Ave. FL mm (SD)

Tag (number)

2007

February

hatchery

Yearling smolt

New Hope

2007

February

hatchery

Kelts

On Site (Kelt)

2007

Feb–May

natural

>1-year-olda

2008

January

hatchery

Yearling smolt

2008

February

hatchery

Yearling smolt

San Pablo

2008

February

hatchery

Kelts

On Site (Kelt)

10

506 (46)

V13 (10)

2008

April

hatchery

Yearling smolt

On Site

30

252 (24)

V9 (30)

2008

Feb–April

natural

>1-year-olda

Upper RST

2

226 (33)

V9 (2)

2008

Feb–April

natural

>1-year-olda

Lower RST

9

238 (31)

V9 (9)

a

57

210 (14)

V9 (57)

6

525 (74)

V9 (2); V13 (4)

In River

60

309 (89)

V9(59); V13(1)

Antioch

35

221 (12)

V9 (35)

35

219 (17)

V9 (35)

2008

Feb–May

natural

>1-year-old

In River

54

266 (63)

V9 (54)

2008

September

hatchery

2-year-old

San Pablo (2-year-old)

30

394 (31)

V9 (30)

2009

January

hatchery

2-year-old

Moke River (2-year-old)

V9 (8)

2009

February

hatchery

Yearling smolt

New Hope

2009

February

hatchery

Kelt

New Hope (Kelt)

2009

Feb–May

natural

>1-year-olda

Lower RST

a

8

477 (54)

110

245 (22)

V9 (110)

9

497 (51)

V13 (9)

12

244 (62)

V9(11); V13(1)

Length frequency data suggest these fish are 1–3 years of age (EBMUD unpublished)

RST Rotary Screw Trap; Ave. FL Average Fork Length

through a 2.54 cm incision into the peritoneal cavity of
each fish just off the midline and anterior to the pelvic
fins. The incision was made using a number 12 surgical
scalpel blade and closed with 2–3 interrupted stitches.
Tagged hatchery fish were held in raceways for 24 h
following surgery to allow for recovery and assessed for
abnormal behavior, tag shedding, or mortality before
release. Fish tagged in the field were allowed to recover
in aerated holding tanks prior to release the same day.

Fish release

In winter 2007, we initiated the first phase of the
3 year study by tagging and tracking three release
groups consisting of hatchery yearling smolts,
reconditioned hatchery kelts, and natural-origin O.
mykiss. Between January and May of 2008, we
implemented the second year of this study. In year
two, we released eight tag groups, incorporated new
release locations, and included hatchery-reared 2year-old fish and actively-outmigrating natural-origin
O. mykiss by focusing on RST captures. In 2009, year
three of the study, hatchery, post-spawn kelts, and
natural-origin O. mykiss of various life stages were
tagged and released between January and May
(Table 1).

O. mykiss releases at Antioch, Selby, New Hope
Landing, and in the LMR at Elliott Road (Fig. 1) were
pumped into a Freightliner transport truck, driven to
their respective release location, and gravity fed into
the receiving waters. On Site hatchery yearling smolt
releases were pumped directly from the raceways via
15.24 cm diameter aluminum irrigation pipe into the
LMR adjacent to the Hatchery. Kelts were placed in
hauling tanks, transported to the river below the
Hatchery, and released by using handheld dip nets.
Tagged hatchery-origin fish were released either with
other hatchery fish or independently. O. mykiss tagged
during electrofishing surveys were released upstream
of their collection site while fish tagged during RST
operations were released downstream of the traps. All
releases occurred during daylight hours.

Data collection
We used stationary Vemco monitoring receivers to
detect our Vemco coded transmitters. We deployed 10
acoustic receivers (Vemco VR2W-69 kHz) in the
LMR from the base of Camanche Dam to the
confluence with the San Joaquin River. Each receiver
recorded the identification number and time stamp
from the coded acoustic transmitters as tagged fish


368

traveled within the detection range, conservatively
estimated to be 250 m (Espinoza et al. 2011). Data
were downloaded quarterly in the field using a
wireless personal computer interface. Members of
the California Fish Tracking Consortium downloaded
data from over 300 receivers deployed throughout the
Sacramento-San Joaquin River System, Delta, and
San Francisco Estuary. Data from downloaded
receivers were submitted to the California Fish
Tracking Consortium database which provided access
to data from the full array of receivers. Following
each release of tagged O. mykiss, the Consortium
database was monitored for a minimum of 1 year to
track fish movement.
Data analysis
Acoustic tag detection data were processed to
eliminate false-positive detections following methods

of Pincock (2008) and Skalski et al. (2002). Falsepositive detections typically occur when more than
one tag is simultaneously present within the range of
a given monitor, and simultaneous tag transmissions
“collide” to produce a valid tag code that is not
actually present at the monitor (Pincock 2008; Perry
et al. 2010). We considered detections valid if a
minimum of two consecutive detections occurred
within a 30-min period at a given telemetry station
and the detections were consistent with the spatiotemporal history of a tagged fish moving through the
system of telemetry stations (Skalski et al. 2002).
Statistical analysis of movement, migrations rates,
migration pathway selection, and migration success
was based on fish detected by the array of receivers.
Release groups that resulted in an expected frequency
of less than five fish in more than 20% of the
analyzed categories or an expected frequency of less
than one in any category being analyzed were not
included in statistical analyses (Zar 1984), but
qualitative assessments were reported. All statistical
tests were performed using JMP version 8.0.1.
Downstream movement
We compared movement by fish origin and release
location across years using contingency table analysis
(Chi square) (Table 1 for categories). We compared
movement by size using ANOVA. Fish were classified
into two main movement groups: downstream (towards

Environ Biol Fish (2012) 94:363–375

the Golden Gate Bridge) or no downstream movement.

The no downstream movement group is made up of
those fish detected by the array of receivers that
demonstrated no migration (no net directional
movement) or upstream movement (movement away
from the Golden Gate Bridge).
Migration rates
We estimated migration rates for fish that exhibited
downstream movement as passage times of individual
fish between receivers. The migration rate of a fish
through each reach was calculated as the distance
between receivers divided by the time. Time was
defined as time of last detection at the previous
receiver to time of first detection at next receiver. We
analyzed migration rates (mean km/h) for each release
group using ANOVA.
Migration routes
We compared migration pathways used by O. mykiss
released in the Mokelumne River at New Hope or
upstream that demonstrated downstream movement
through the interior Delta to Chipps Island (Fig. 2).
Four pathways were identified: 1) Pathway 1 down
the North Fork of the Mokelumne River to the San
Joaquin River; 2) Pathway 2 down the South Fork of
the Mokelumne River to the North Fork and San
Joaquin River; 3) Pathway 3 down the South Fork of
the Mokelumne River into Little Potato Slough and
through Potato Slough into the San Joaquin River;
and 4) Pathway 4 down the South Fork of the
Mokelumne River into Little Potato Slough, Little
Connection Slough, and into the San Joaquin River.

Other important pathways through the Delta included
Franks Tract, Three Mile Slough, and Georgiana
Slough. A fish was categorized as using a specific
pathway if it was detected moving downstream through
each primary section of a pathway (represented by
detection stations) that led towards Chipps Island. Fish
that used a combination of pathways or used sections of
the interior Delta outside of these four pathways were
described by the alternative migration corridor that was
utilized. Statistical tests using contingency table analysis
(Chi square) were performed on migration route
selection of designated pathways through the interior
Delta based on origin and release location. Route


Environ Biol Fish (2012) 94:363–375

selection analysis based on size was performed using
ANOVA.
Migration success
Key reference locations were established to assess
migration success of each release group. These
locations include WIDD, New Hope, Chipps Island,
Richmond Bridge, and the Golden Gate Bridge
(Fig. 1). The proportions of fish in each tagged
release group detected at each reference location were
based on release group totals. Each reference location
site immediately downstream of release locations
accounted for 100% of the upstream release group.
Release groups located immediately upstream of a

reference location were excluded from the analyses of
migration success to the first downstream site.
Migration success of all release groups were compared
by origin using contingency table analysis (Chi square)
and by size using ANOVA. Migration success of
hatchery-origin yearling release groups were compared
by release location using contingency table analysis
(Chi square).

Results
In this study we tagged 330 hatchery-origin and 137
natural-origin O. mykiss of various life stages. Ninetyone percent (n = 301) of all acoustically tagged
hatchery releases and 37% (n=51) of natural-origin
releases were detected by the array of receivers.
Downstream movement
Of the 404 acoustically tagged hatchery yearling smolts
and natural-origin O. mykiss released, 169 demonstrated downstream movement, 124 demonstrated no
downstream movement, and 111 were not detected
by the array of receivers. Fish origin, size, and release
location revealed differences between migration and
residualization (no movement).
Fish origin had a significant effect on downstream
movement of all O. mykiss release groups independent
of release location between 2007 and 2009 (Chi
square=25.26; P<0.001; Table 2). Comparing all
hatchery yearling smolt and natural-origin O. mykiss
release groups, a significantly higher proportion of
hatchery-origin fish moved downstream (65%), than

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natural-origin fish (22%), independent of release
location (Chi square=33.58; P<0.001). Of naturalorigin fish that moved downstream, 64% were
considered ‘active migrants’, based on the collection
at RSTs. Of the natural-origin O. mykiss releases that
showed no downstream movement, 95% (n=38)
exhibited resident characteristics via non-directional
movements detected by the receivers in the non-tidal
LMR. Of the hatchery yearling releases that had no
downstream movement, 95% (n = 80) strayed
upstream.
Fish size had a significant effect on downstream
movement (F=11.29; df=1; P=0.001) across all
release groups (Table 2). The average fork length of
O. mykiss that demonstrated downstream movement
was 262 mm with a standard deviation of 82 mm. The
average fork length of O. mykiss that demonstrated no
downstream movement was 295 mm with a standard
deviation of 100 mm.
Movement of hatchery-origin O. mykiss yearling
smolts differed significantly (Chi square=8.52; P=
0.036) based on release locations. Downstream
movement was observed from all release locations.
The Antioch release had the highest downstream
movement with 83% towards the Pacific Ocean
(Fig. 3). The On Site release in the non-tidal LMR
had the second highest downstream migration (81%).
The proportion of fish that exhibited no downstream
movement from Antioch, San Pablo, and New Hope
releases varied from 17% to 39%.

During the 2007 to 2009 study period, there was
also a significant difference between the movement of
natural-origin O. mykiss release groups (Chi square=
17.23; P <0.001). Of the fish that exhibited no
downstream movement, 95% were part of the In
River release groups collected during electrofishing
surveys. Of the In River release group, 90% exhibited
no downstream movement. In comparison, a higher
proportion of the natural-origin fish tagged at the RST
sites demonstrated downstream movement. Six out of
eight tagged and released at the Lower RST and one
of one at the Upper RST exhibited downstream
movement (Fig. 3).
Due to the small sample size for release groups of
kelts and 2-year-olds, they were not included in the
statistical analysis of downstream movement by
release location. However, detected movement of
these life stages is noteworthy. Of the reconditioned
kelt releases, 54% (n=13) demonstrated downstream


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Table 2 The effect of O. mykiss origin, size, and release
location on downstream movement, emigration pathway, and
success to key landmarks within the lower Mokelumne River,
Delta, and San Francisco Estuary. Values represent all release

groups, except analyses of movement and migration success by
release location which analyze hatchery yearling release
groups. A P-value≤0.05 is considered significant (Bold)

Migration Success by Location
Qualifier

Movement

Pathway

WIDD

New Hope

Chipps Island

Richmond Bridge

Golden Gate Bridge

Origin

<0.001

ISS

ISS

0.001

0.007

0.045

0.018

Size

0.001

0.420

0.027

0.709

0.222

0.005

0.001

Release Location

0.036

0.618

ISS

ISS

0.105

ISS

ISS

WIDD Woodbridge Irrigation District Dam; ISS Insufficient sample size

movement. New Hope (Kelt) releases and On Site
(Kelt) releases demonstrated 75% (n=6) and 44% (n=
7) downstream movement, respectively. Of the 2year-old releases, 17% (n=6) demonstrated downstream movement. Of the San Pablo (2-year-old) and
Moke River (2-year-old) release groups, 14% (n=4)
and 33% (n=2) demonstrated downstream movement,
respectively.

with an average of 1.86 km/h. Kelt migration rates
ranged from 1.58 km/h (On Site) to 1.64 km/h (New
Hope) while 2-year-old O. mykiss migration rates
ranged from 1.29 km/h (Moke River) to 1.61 km/
h (San Pablo). The natural-origin In River release
group had the lowest average migration rate of
0.72 km/h (Table 3).
We recovered ocean travel time data on five
hatchery O. mykiss (two yearlings released at New
Hope; one yearling released at San Pablo; one Moke
River 2-year-old released at Elliott Rd.; and one kelt
released at New Hope). Travel rates were calculated

over approximate straight-line distances between the
Golden Gate Bridge and the acoustic receiver array
located off of Point Reyes (~54 km north of the
Golden Gate). The New Hope kelt showed the greatest

Migration rates
Between 2007 and 2009, there was no significant
difference between the migration rates of O. mykiss
from different release groups (F=1.80; df=9; P=
0.072). The Antioch hatchery release of yearling
smolts showed the greatest sustained migration rates

Downstream

No Downstream

100
5

Detected Fish (%)

4
80

2
10

65

60

40

38
24

17
100

7
17

20
4

0
Release Group On Site
Origin

New Hope
Antioch
Hatchery

San Pablo

In River
RST
Natural

Fig. 3 The proportion of Mokelumne River O. mykiss demonstrating downstream movement by release location, 2007 through 2009.
Values within the figure represent number of fish

Environ Biol Fish (2012) 94:363–375

sustained migration rate of 1.33 km/h and reached Point
Reyes in 1.7 days. Hatchery yearling migration rates
ranged from 0.02 km/h (San Pablo) to 0.17 km/h (New
Hope) while the Moke River 2-year-old O. mykiss
migration rate was 0.20 km/h. A New Hope yearling
last detected at the Golden Gate Bridge 2 h before the
New Hope kelt took 16 days to reach Point Reyes. A
yearling released in San Pablo Bay spent just over
145 days traveling between the Golden Gate Bridge
and Point Reyes.
Migration routes
Between 2007 and 2009, 67 acoustically tagged
hatchery and natural-origin O. mykiss of various life
stages released at or above New Hope Landing
demonstrated downstream movement via the designated
migration pathways. Migration route selection, based on
all release groups, was not significantly related to fish
size (F=0.88; df=2; P=0.420) or release above or
within tidal influence (Chi square=0.96; P=0.618)
(Table 2). Of the hatchery yearling smolts, 43% used
Pathway 1, 23% used Pathway 2, 4% used Pathway 3,
and 2% used Pathway 4. In addition, 28% used other
pathways including Franks Tract (13%), Three Mile
Slough (11%), and Georgiana Slough (4%). Fiftyseven percent of the reconditioned kelts migrated
through Pathway 1 while 29% utilized Franks Tract
and 14% migrated through Pathway 4. All of the fish

from the Moke River (2-year-old) release group
migrated through Pathway 1. Of the natural-origin
O. mykiss, 60% used Pathway 1, 20% used Pathway
2, and 20% used Georgiana Slough.
Migration success
While migration proportions reflect low overall
downstream success based on release totals, fish that
reached the first reference location subsequently had
relatively high migration success. On Site releases of
hatchery yearling smolts had the highest overall
success to the first downstream reference point with
57% detected. This was followed by 44% of On Site
kelts reaching the first reference location downstream.
Twenty-five percent of the Moke River release group
successfully migrated to the first downstream reference
point. In River releases of natural-origin O. mykiss had
the lowest overall downstream detection at the first
reference point (New Hope) with only 0.8% detected.

371

There was a significant difference in the size of fish
that successfully migrated to WIDD (F=5.32; df=1;
P=0.027; Table 2). The average fork length of fish
that reached WIDD was 332 mm while the average
fork length of fish that did not was 433 mm. In
addition, fish origin had a significant effect on
migration success to New Hope (Chi square=11.39;
P=0.001; Table 2).
Migration success between New Hope and Chipps

Island ranged from 100% for Moke River 2-year-old
fish to 50% of the natural-origin fish. Of the New
Hope hatchery yearling and kelt releases, migration
success to Chipps Island, the first downstream
reference location, was 17% and 22%, respectively
(Fig. 4). Fish origin (Chi square=7.29; P=0.007) had
a significant effect on migration success to Chipps
Island while size and release location did not
significantly influence migration success through the
Delta (Table 2).
Between Chipps and Richmond Bridge, migration
success between reference locations ranged from
100% of On Site kelts, Moke River 2-year-old fish,
and New Hope kelts to 36% of New Hope yearlings.
Seventeen percent of the Antioch yearling release
were detected at the first downstream reference
location. Fish origin (Chi square=4.02; P=0.045)
and size (F= 8.09; df= 1; P=0.005) significantly
influenced success to Richmond Bridge (Table 2).
Migration success from Richmond Bridge to
Golden Gate Bridge was relatively high in comparison to total release group success. Larger fish
had a better chance of reaching both the Richmond
and Golden Gate bridges (locations with higher
salinity). Fish origin (Chi square=5.55; P=0.018)
and size (F=11.18; df=1; P=0.001) had a significant
effect on migration success to the Golden Gate Bridge
(Table 2). Of the hatchery yearling smolt releases,
20% of On Site, 14% of San Pablo, and 9% of
Antioch releases reached the Golden Gate Bridge.
The New Hope release group had the lowest

percentages of success to the Golden Gate Bridge
with 4% in 2007 and 5% in 2009. On Site releases of
reconditioned kelts had the highest proportion reach
the Golden Gate Bridge with 33% in 2007. However,
in 2008, only 10% of On Site kelts reached the
Golden Gate Bridge. Twenty-two percent of the New
Hope reconditioned kelts and 25% of the 2-year-old
hatchery Moke River release group reached the
Golden Gate Bridge. One natural-origin fish was


372

Environ Biol Fish (2012) 94:363–375

Table 3 Migration rates of acoustically tagged O. mykiss with downstream final detections
Release Group

Mean Rates (km/h)

Standard Error of the Mean

Minimum

Maximum

On Site

1.52

0.24

0.25

4.11

New Hope

1.06

0.10

0.01

4.06

Antioch

1.86

0.23

0.31

3.78

San Pablo

1.52

0.24

0.01

2.87

In River

0.72

0.49

0.40

1.57

RST

1.51

0.37

0.15

2.76

On Site (Kelt)

1.58

0.37

0.39

3.99

New Hope (Kelt)

1.64

2.44

0.14

2.58

Moke River (2-year-old)

1.29

0.70

1.22

1.35

San Pablo (2-year-old)

1.61

0.57

1.24

1.81

recorded successfully migrating to the Golden Gate
(Fig. 4).

Discussion
Acoustic technology has provided a method to better
compare hatchery-origin and natural-origin O. mykiss.
In a state-dependent life history model, Satterthwaite
et al. (2009) predicted a mixture of anadromous and
resident O. mykiss in the Mokelumne River, but with
anadromous fish dominating given baseline survival
assumptions. Our results demonstrate the Mokelumne
River O. mykiss population is a mixture of resident
and anadromous fish and that origin (hatchery vs.
natural) has a significant effect on whether an
individual fish demonstrates migration tendencies.
We showed that hatchery fish had a significantly
higher propensity to migrate, while the natural
population demonstrates very little anadromy.

Downstream movement
In an effort to increase survival and promote returns,
the Hatchery has utilized numerous release locations
for hatchery-reared O. mykiss. However, returns have
remained low. We found that release location can

significantly influence downstream migration trends
in hatchery yearling smolt O. mykiss even though all
hatchery release groups demonstrated relatively high
downstream movement (59%).

The natural-origin O. mykiss population in the LMR
exhibits both anadromous and non-anadromous life
histories. Of the acoustically tagged natural-origin
fish detected by the array of stationary receivers, 78%
demonstrated no downstream movement. Conversely,
once a natural-origin fish began downstream migration
(for instance O. mykiss captured at a RST) they
continued in a downstream direction at a relatively
high proportion.

Migration rates
While results did not show significant differences in
overall migration rates, they did provide information on
O. mykiss ocean travel rates when currently little such
data is available. Limited information on coded-wire
tag recoveries suggest that hatchery steelhead may
travel together in the ocean environment as tagged
juvenile fish released at similar locations and times
were recovered together at sea up to 3 years later
(McKinnell et al. 1997). Burgner et al. (1992)
reported ocean travel rates across approximate
straight-line distances for steelhead tagged offshore
and recovered within 50 days. The mean migration
rate from release to recovery locations was 50 km/day
while the fastest fish averaged 85 km/day for 17 days.

The average ocean travel rate for Mokelumne River
hatchery-origin O. mykiss was 9 km/day and the
fastest fish averaged 32 km/day (kelt released at New
Hope). These data demonstrate O. mykiss exhibit a
wide range of variability in ocean movement and
migration rates.


Environ Biol Fish (2012) 94:363–375

373

100
Hatchery yearlings (On Site release)
Kelts (On Site release)
(a)

80
60

30

16

40
17

20

7

10

6

7

4

4
30

6

6

3

0

100

Natural Origin (In River and RST releases)
Hatchery 2-year-olds (Moke River release)

Downstream Migrants (%)

80
60

137

(b)

8

40
20

6

0

2

3

2

2

2

2

1

100
Hatchery yearlings (New Hope release)
Kelts (New Hope release)

(c)

80
60

167

40

9

20

29

0

2

10

2

2

7

100
80
60

Hatchery yearlings (Antioch release)
Hatchery yearlings (San Pablo release)
Hatchery 2-year-olds (San Pablo release)

40

(d)

35

35

30

6

20

3

5

5

0
Hatchery
(Rkm 211)

WIDD

(Rkm 173)

New Hope
(Rkm 142)

Chipps Island
(Rkm 70)

Richmond
(Rkm 15)

Golden Gate
(0)

Fig. 4 Proportion of release groups observed at key reference points. Release groups are organized by release location (a–d). Values
within the figure represent release group totals followed by fish detection totals at each downstream reference location

Migration routes
Steelhead emigrating from the Mokelumne River have
numerous migration pathway options when traversing
the complex network of natural and man-made channels
of the interior Delta. Each migration route poses
different benefits and risks associated with migration
rates, energy costs, predation, and entrainment that
ultimately affect migration success. Due to the small
number of fish migrating through the Delta and the
utilization of diverse migration routes, current and

future management actions in the Delta may disproportionately affect Mokelumne River O. mykiss.
Migration success

In seawater challenges, Beakes et al. (2010) found
that CV O. mykiss survival off the California central
coast varied significantly with fish size (with larger
fish being more likely to survive than smaller fish).
Similarly, we observed that success to key reference
locations within the saline environment of the San


374

Francisco Estuary was significantly related to fish
size.
If we gauge ‘successful’ migration as migration to the
Golden Gate Bridge, a majority of our successes have
been of hatchery-origin. Reconditioned kelts released
On Site in 2007 had the highest proportion reach the
Golden Gate Bridge, thus active reconditioning of
hatchery spawned kelts may be a viable option for
increasing anadromy. On Site releases of both hatchery
yearling and reconditioned kelts performed well during
the study period, but continued releases adjacent to the
hatchery will need to be weighed against potential
negative impacts to natural-origin salmonids rearing in
the LMR.
Management implications
The diversity of O. mykiss life history forms demonstrates the relative phenotypic plasticity of the species
(McEwan 2001). The year round presence of Age 1+
O. mykiss of various life stage categories sampled
during fish community surveys on the LMR (Merz
2002) reflects the flexible life history patterns of O.

mykiss within the Mokelumne River. Zimmerman et al.
(2008) revealed that the Central Valley O. mykiss
population is skewed towards the non-anadromous
resident form as 77% of the analyzed O. mykiss in his
study were progeny of resident rainbow trout.
Similarly, results from our study suggest a large
proportion of natural-origin O. mykiss in LMR
demonstrates a resident life history.
Due to the precipitous declines of O. mykiss in the
Central Valley and an apparent shift towards the nonanadromous life history forms, the connection between
anadromous and non-anadromous O. mykiss and their
management as a single or separate population has
profound implications for conservation and recovery
(Busby et al. 1996; Zimmerman and Reeves 2000;
McEwan 2001). Since anadromous and nonanadromous trout may form an interbreeding population
(Seamons et al. 2004; Araki et al. 2007) with females
producing progeny with opposite life history traits
(Viola and Schuck 1995; Riva-Rossi et al. 2007;
Zimmerman et al. 2008), steelhead management may
need to include protection of non-anadromous forms
and the connectivity between the resident and
anadromous fish (McEwan 2001).
The largest population declines of natural-origin O.
mykiss in California were a consequence of the dam

Environ Biol Fish (2012) 94:363–375

building era prior to the 1960s as spawning and
rearing habitats became isolated (McEwan 2001).
However, continued declines of O. mykiss numbers

imply additional threats and stressors still need to be
addressed. For anadromous species migrating out of
the Mokelumne River, Delta management remains a
critical issue influencing migration success. While the
Delta Cross Channel remained closed throughout
the study period, its management is presumed to
substantially influence Mokelumne River salmonids.
Further investigation is needed to assess its effects
on salmonid migration, straying, and survival. In
addition to Delta management, suppression of
anadromous life history traits, loss of genetic
diversity, and introgression of hatchery rainbow
trout into natural-origin populations continue to be
serious concerns for steelhead conservation and
management.
Acknowledgments Financial support for this work was
provided by East Bay Municipal Utility District, the California
Urban Water Agencies, and the Mokelumne River Partnership.
We gratefully acknowledge J. Miyamoto, J. Smith, J. Setka, E.
Rible, C. Hunter, M. Saldate, J. Shillam, P. Sandstrom, E.
Chapman, W. Heady, all field staff who helped develop and
collect data for this study, and the collaborative support of the
Mokelumne River Fish Hatchery and the California Fish
Tracking Consortium.

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DOI 10.1007/s10641-011-9954-4

Migration patterns of juvenile Lutjanus argentimaculatus
in a mangrove estuary in Trang province, Thailand,
as revealed by ultrasonic telemetry
Matiss Zagars & Kou Ikejima & Nobuaki Arai &
Hiromichi Mitamura & Kotaro Ichikawa &
Takashi Yokota & Prasert Tongnunui

Received: 31 January 2011 / Accepted: 27 October 2011 / Published online: 12 November 2011
# Springer Science+Business Media B.V. 2011

Abstract Migrational patterns of mangrove jack
Lutjanus argentimaculatus were studied in a mangrove estuary in Trang province, Thailand, using
ultrasonic telemetry. Ultrasonic coded transmitters
were surgically implanted in 18 fish and 16 of them
M. Zagars
University of Southern Denmark,
Campusvej 55,
DK-5230 Odense M, Denmark
M. Zagars : N. Arai : H. Mitamura : K. Ichikawa :
T. Yokota
Graduate School of Informatics, Kyoto University,
606-8501 Kyoto, Japan
K. Ikejima (*)
School of Environment, Resources and Development,
Asian Institute of Technology,
P.O. Box4, Kulong Luang, Pathumthani 12120, Thailand
e-mail:
P. Tongnunui
Rajamangala University of Technology Srivijaya,
Amphur Sikao, Trang 92150, Thailand

T. Yokota
Seikai National
Fisheries Institute, Fisheries Research Agency,
Taira-machi 1551-8,
Nagasaki, Nagasaki 851-2213, Japan
Present Address:
K. Ikejima
Faculty of Agriculture, Kochi University,
200 Monobe-Otsu,
Nankoku, Kochi 783-8502, Japan

were subsequently monitored by nine fixed receivers
installed along Sikao Creek estuary in June and
November 2006. Due to technical limitations all of
the individuals were released in the middle of the
creek. Their movements were monitored for a period
of up to 1 month, the data being used to describe short
term migration of juvenile Lutjanus argentimaculatus
in the creek and to find possible environmental cues
for the observed movements. All of the individuals
showed a tide related movement pattern, suggesting
foraging in the small mangrove channels and/or
mangrove forest during high tides. 50% of the fish
left the study area for the open coast area within a
short time following release, indicating that a part of
juvenile L. argentimaculatus may move in between
estuarine habitats instead of being site attached. As
the fish were reared in fish cages for a certain period
of time before the study this behavior could partly be
explained by the time spent in captivity. It was found

that L. argentimaculatus showed higher movement
activity during night high tides possibly explained by
an increased availability of the sough after food items.
Keywords Mangrove estuary . Lutjanus
argentimaculatus . Migration . Ultrasonic telemetry

Introduction
Many studies over the last few decades have focused
on evaluating the importance of mangrove habitats for


378

different fish species (e.g. Robertson and Duke
1987; Laegdsgaard and Johnson 1995; reviewed in
Robertson and Blaber 1992; Blaber 2000). Robertson
and Duke (1987) followed by Thayer et al. (1987)
compared fish assemblages in mangroves and proximal habitats. Both studies showed that mangroves
contained a considerably greater abundance and
species’ richness of fish than adjacent, nonmangrove habitats, such as seagrass beds and mudflats. In the years following, many studies have
confirmed the above findings throughout the tropical
seas (Sheaves 1992; Kimani et al. 1996; Nagelkerken
et al. 2000; Ikejima et al. 2003).
Inter-annual, seasonal, lunar and diel changes have
been recorded for mangrove ichthyofauna (Robertson
and Duke 1990; Laegdsgaard and Johnson 1995;
Ikejima et al. 2003; Mumby et al. 2004), suggesting
that the majority of species migrate in and out, or
within the habitat. For example, Robertson and Duke
(1990) showed a clear difference in fish assemblages

between high and low tides, implying a regular
pattern of tide-related fish movements in mangroves.
Sheaves (2005) pointed out the importance of
migration as an essential part of the life cycle of
fishes in mangrove habitats, indicating that mangroves are a part of an “interconnected habitat
mosaic” and should be studied within the context of
connectivity with other habitats. In many mangrove
systems, migration to alternative habitats is unavoidable because the habitat is exposed during low tide.
Even in areas where mangroves remain inundated
throughout the year, fish may shift habitats for
feeding, reproduction and life stage-specific habitat
use (Nagelkerken et al. 2002; Sheaves 2005)
Tidal fish migration has been studied by Krumme
and Saint-Paul (2003) and Krumme (2004) using
hydroacoustic equipment. Hydroacoustic techniques
are effective for showing overall patterns of fish
migration in mangrove creeks, although, as was noted
by Krumme (2004), they do not show behavioral
variations between species and individuals.
Ontogenetic migration of several reef fish species
has been successfully investigated using visual censuses. E.g. Cocheret de la Morinière et al. (2002)
observed relative density distributions of different
size-classes of selected species and demonstrated three
modes of post-settlement migration among mangroves,
seagrass beds and coral reefs. Furthermore, Nakamura et
al. (2008) described the ontogenetic migration of coral

Environ Biol Fish (2012) 94:377–388

inhabiting black tail snapper from mangrove habitat

to coral reefs, using stable isotope approach.
However, these methods do not provide evidence of
short term movements, such as diel or tidal
movements and visual censuses are not applicable in
highly turbid environments, such as mangrove creeks
in Thailand.
Ultrasonic telemetry allows direct monitoring of
the movement patterns of individual fish, giving an
insight into their behavioral biology. The method has
been widely applied in a variety of habitats, giving
new insights into fish migratory behavior, e.g. homing
and site fidelity of greasy grouper in coral reefs
(Kaunda-Arara and Rose 2004), homing behavior of
black rockfish in coastal waters (Mitamura et al.
2005), and the diurnal and tidal movements of
snapper Pagrus auratus in a river estuary (Hartill et
al. 2003). Recent studies have shown that this method
can also be successfully applied to study movements
of groupers (serranidae) and snappers (lutjanidae) in
mangroves and associated habitats. Frias-Torres et al.
(2007) used ultrasonic telemetry in a mangrove
habitat for monitoring individual fish movements.
Despite the limited number of individuals monitored,
they showed that the fish movements were correlated
mainly with tidal cycle. Luo et al. (2009) used
ultrasonic telemetry combined with tagging and video
recording to observe daily as well as seasonal
movement patterns of grey snapper in Florida Keys
and showing that the fish moved between the inshore
habitats for taking shelter and foraging, and performed longer movements to offshore reefs during the

reproductive season. Ultrasonic telemetry was also
successfully used in a Bahamian tidal creek to show
that individuals of two lutjanid species show intrapopulation variation in movement patterns contradicting the existing assumption that individuals of a
given population possess the same behavioral characteristics (Hammerschlag-Peyer and Layman 2010).
Mangrove jack Lutjanus argentimaculatus is a
relatively large fish, reaching up to 120 cm fork
length and 8.5 kg in weight, inhabiting the Indo-west
Pacific Ocean (Russell et al. 2003). It is commercially
important for fishery and aquaculture industries in
South East Asia, and sports fishing in Australia (Doi
and Singhagraiwan 1994; Russell and McDougall
2005). Spawning occurs in offshore habitats, post
larvae and juveniles then moving to coastal nursery
habitats, such as river estuaries and mangroves


Environ Biol Fish (2012) 94:377–388

(Sheaves 1995; Russell and McDougall 2005). After
reaching reproductive maturity (at around 450, and
500 mm fork length for male and female, respectively; Russell et al. 2003) L. argentimaculatus returns to
offshore habitats. A study of movements of L.
argentimaculatus in Australia using conventional
tagging suggested that during their period of residence in inshore areas, the species underwent local
migration within the river systems (Russell et al.
2003). It has also been noted that during high tides L.
argentimaculatus enters mangrove forests in order to
feed, indicating that the local tidal cycle was an
environmental cue for short term migration (Russell et
al. 2003; Sheaves 2005). Nevertheless, since movements have not been followed directly, uncertainties

remain concerning the movement pattern of L.
argentimaculatus within estuarine habitats.
In the present study we described short term
migration of L. argentimaculatus in the Sikao
mangrove creek using ultrasonic telemetry. In contrast
to previous studies of snappers in mangrove systems
we examined short term movements of juvenile fish
within their nursery habitat. We specifically examined
to what extent cyclic changes in tidal height and time
of day are shaping the short term movement pattern of
L. argentimaculatus. The availability of food items
for predatory fish in mangrove habitats varies with the
tidal pattern due to the migration of smaller fish and
changing accessibility of the forest (Sheaves 2005).
The daily cycle is also known to influence migration
patterns in many lutjanids (e.g. Nagelkerken et al.
2000; Luo et al. 2009). Thus we hypothesized that the
frequency of movements of L. argentimaculatus in
Sikao creek change with tidal and diel cycles.

Materials and methods
Study area
The study was conducted in Sikao Creek, a mangrove
estuary located in Trang province, west coast of
Thailand (Fig. 1). The particular study site was
chosen due to its relatively small size, the presence
of undisturbed mangrove forest, and the availability
of periodically inundated side creeks making it
suitable for the examination of movement patterns
of L. argentimaculatus and its relation to tidal

changes. The forest, dominated by Rhizophora

379

apiculata, has been designated as a protected area.
A relatively short dry season (January to April) is
followed by a long wet season (May to December).
The estuary is subject to semi-diurnal tides with a
tidal range of 1.0 (neap tide)–2.5 (spring tide) m
(Ikejima et al. 2003). One kilometer from an open
bay, Sikao Creek splits into two main creeks (A and
B; Fig. 1), there being numerous side creeks branching from the main creeks. The main creek and the
first level side creeks remain inundated throughout the diel and lunar tidal cycles, the mangrove
forest and smaller side creeks are inundated only
during high tides. Sikao Creek is connected to a
shallow bay lined with large rocks. The closest
neighboring mangrove system is located ~4 km
away in the NW direction, the closest seagrass
bed ~5 km away in NW direction and the closest
coral reef ~18 km away in SW direction. There is
no major river input. L. argentimaculatus is
commonly found in the area and an active fishery
for the juveniles and subadults has been observed
within the creek, individuals often being caught using
cage traps for culture in fish cages.
The first study was conducted in the middle of
the rainy season from 6 June 2006 to 22 July 2006
during 39 semi-diurnal tides. The second was
conducted at the end of the wet season, from
1 November 2006 to 2 December 2006 during 55

semi-diurnal tides.
Fish tagging
In total 18 fish were used in the two study periods
(Table 1), selection for tagging being based on the
criteria of size suitable for tagging and good health
(indicated by active movement, and no external
symptoms of injuries or diseases). TL of fish ranged
from 199 to 303 mm, with the mean (± SD) of 242±
37 mm (excluding 2 individuals discarded from the
analysis). All the individuals were within the size
range of juveniles of mangrove jack reported from
Australia (75–541 mm TL, Sheaves 1995;
<450~500 mm FL, Russell et al. 2003). It has been
estimated that transmitter mass should not exceed 2%
of the fish’s mass (Jepsen et al. 2002). For all the fish
transmitter weight in water never exceeded 1.4% of
the body weight. Due to logistical reasons it was
impossible to attain wild individuals directly from the
study area. Thus seven of the individuals tracked in


380

Environ Biol Fish (2012) 94:377–388

Fig. 1 Map of Sikao Creek showing mangrove areas and the
positions of the receivers during both study periods as well as
the detection range of the receiver array. Numbers indicate
receiver positions. A and B indicate the main creeks, and C, D

and E some of the larger side creeks, FC indicates fish cages
were the fish were reared location. Tagged fish were released at
Receiver 7

the first study period were wild L. argentimaculatus,
caught by fishermen in creek A and reared in fish
cages for 3 months in a near vicinity to the study site
(Fig. 1). One fish was caught by a sports fisherman at
the river mouth of the Creek. All ten fish used in the
second study period were wild L. argentimaculatus,
caught by fishermen within creek A and reared in fish
cages for 1 week. In order to evaluate if different
rearing periods in the fish cages had influence on fish
health condition allometric condition factor (K = W
L−b) was calculated for experimental fish (Godinho
1997). The value of b was obtained from the weight–
length relationship using linear regression: Loge W ¼
Loge a þ bLoge L, where W = weight, and L = total
length. The parameters (a, b) were obtained from
pooled data of all experimental fish (n=18), then K
was calculated for fishes of each study period. There
was no significant difference in mean K values
between the two periods (t-test, t=−0.13, p=0.86,
df=16), suggesting that the rearing conditions were
close to natural and longer rearing period did not
influence fish health condition. As the fish were
taken, reared for a short time period and released in
the Sikao Creek (Fig. 1) we suggest that there was a

minimal effect of rearing on their natural behavior,

which is further supported by the observed movement
patterns which were similar to those of other lutjanids
in coastal habitats (see Discussion).
Ultrasonic coded transmitters (V9-1L-R256, Vemco
Ltd, Canada), 8.5 mm in diameter, 25 mm long and
weighing 2.2 g in water were used. The min/max period
of pulse transmissions was 10–30 s maximizing the
possibility of tag transmission when the fish were within
the detection range of the receiver array. The transmitters were surgically implanted into the abdominal
cavity of anesthetized fish (induced by 0.1% 2phenoxyethanol). During the operation, fish were fixed
between rubber sponges in a bath of aerated seawater.
An incision of about 10 mm length was made in the
inferior abdominal wall of the fish in order to insert the
transmitter. An operating needle and sutures were used
for closing the wound. The antibiotics oxytetracycline
hydrochloride and polymixin B sulfate were applied.
After the surgery, the fork length and weight of each
individual were measured. The fish were held in an
aerated plastic experimental tank (500 l in volume) for a
further 1 day, allowing recovery before release. All
individuals were released at receiver 7 (Fig. 1).


Environ Biol Fish (2012) 94:377–388
Table 1 Summary of the physical parameters, tracking data of
individual fish, and the number
of movements each of day/night
time, and the tidal stage

381

ID
code

TL(mm)
BW(g)

Days
trackeda

Total
moves

Moves during
Daytime

Night-time

High tide

Low tide

High tide

Low tide

Period I, released on 9~13 June 2006
261

295

450

4

6

1

0

4

1

264

300

435

7

18

9

3

6

0

265

260

348

10

7

3

0

3

1

266

303

512

1

4

1

0

2

1

267

230

180

13

14

7

1

6

0

268

252

270

13

28

13

2

12

1

270

230

230

5

14

5

2

5

2
1

Period II, released on 14 Nov 2006

a

Non consecutive days

b

Two individuals were excluded
from the analysis due to the very
high frequency and fixed location of detections, indicative of
dead fish or shed transmitter

108

198

155

10

18

4

4

9

109

251

230

22

28

12

0

14

2

110

276

405

28

16

3

6

5

2

111

226

210

4

13

4

4

5

0

112

205

215

28

34

9

2

20

3

114

205

165

6

15

3

3

6

3

115

241

235

5

11

3

2

4

4

262

192

185

6

16

6

3

7

0

269

211

175

7

8

2

1

4

1

b

113

206

105

–

–

–

–

–

–

263b

279

400

–

–

–

–

–

–

Total

–

–

159

250

85

33

112

20

Tracking and monitoring systems

Detection range experiment

Nine fixed hydrophone receivers (VR-2, Vemco Ltd.)
were used in the experiment. The receivers were
60 mm in diameter and 340 mm long and logged data

on the presence of tagged fish. Receivers were
powered by lithium dry cell that lasted for up to
180 days and had a flash memory for data recording.
ID number, date and time were recorded when a
tagged fish was within the detection range of the
receiver. Creek B (Fig. 1) was chosen for the
experiment due to its smaller size allowing more
efficient monitoring of the area with the available
equipment. Nine fixed monitoring receivers were
installed within 5 km of the creek’s lower reaches
(Fig. 1) in order to monitor the movements of tracked
fish in the creek and to detect possible exits to coastal
waters or creek A. Due to the regular boat traffic the
receivers were positioned at the sides of the creek.

A boat was used to tow an activated transmitter
through the study area in a direction from receiver 1
to receiver 9 (Fig. 1) during spring high ebbing tide.
This was assumed to be the period with the highest
background noise level thus the lowest detection
efficiency due to the very high current speed. The
transmitter was towed through the main channel along
the opposite coast of the one where receivers were
positioned and into all the side channels. In addition
the transmitter was fixed for 15 min in the mangrove
fringe of the main channel in distances of 50, 150 and
250 m from the receiver 7 in order to assess if a
possible entrance of fish to the mangrove forest would
block the acoustic signal. Weights were used in order
to keep the transmitter 30 cm above the bottom of the

creek. Location of the boat was recorded continuously
using eTrex Vista HcX global positioning device


382

(Garmin Ltd, USA). To match the time of each
detected signal with GPS locations of the transmitter
the receivers and GPS clock times were synchronized
prior to the experiment.
In addition a fixed transmitter hanging 30 cm from
the creek bottom was set 80 m from the receiver 1 for
24 h in order to assess the influence of changes in
tidal height on the detection of the signals in the
present acoustic environment. During the first hour of
this experiment all the events of passing boats were
recorded in order to assess the influence of boat
noises on detection of the signals.
Data analysis
In this study detected signal patterns were interpreted
as fish movements in two ways: 1) the shift of signal
reception from one receiver to another, which
reflected movement from the detection range of one
receiver to that of the other, 2) the gaps in signal
reception by one receiver during an otherwise
continuous detection period. All changes in signal
reception from one receiver to another were defined
as movements, regardless of the length of signal gap
between the two receivers. If the fish was detected in
succession by two receivers with overlapping detection ranges, it was not defined as a movement. To

quantify movement patterns of fish based on recorded
signals, three levels of gaps in signal detection from
the same individual by the same receiver were tested
for definition as movements at intervals of −>10, >20
and >30 min.
In order to estimate if the appearance of the gaps in
signal reception had periodical nature Fourier
Analysis using Igor-Pro software was performed on
pooled data from all fish and all receivers separately
for the two study periods.
The chi-square goodness of fit test (Zar 1999) was
used to determine if the observed movements from
one receiver to another and appearance of gaps during
high and low tide periods differed significantly from
the expected frequency if they occurred randomly,
following ratio of high: low tide period. High tide
period was defined as that during which the predicted
water height (Hydrographic Department, Royal Thai
Navy) was 2 m or more above the lowest low water.
The rest was defined as a low tide period. This
resulted in 14 and 10 h of high and low tide periods a
day (i.e. a ratio of 58:42). Thus the null hypothesis

Environ Biol Fish (2012) 94:377–388

was that the fish movement frequency had a 58:42
ratio during high and low tide periods respectively.
The chi-square goodness of fit test (Zar 1999) was
also applied to determine if the observed frequency of
movements from one receiver to another and appearance of gaps during daylight and night-time differed

significantly from the expected frequency, if they
occurred randomly. Daylight was defined as the
period from 6 am to 6 pm, the reminder being night
time. This resulted in 12 and 12 h of day and night
periods (i.e. a ratio of 50:50). Thus the null hypothesis
was that the fish movement frequency had a 50:50 ratio
during day and night periods respectively.
At first, heterogeneity chi-square analysis (Zar 1999)
was performed to test the “interaction” between the
above two factors. The null hypothesis was that both
day and night samples has a 58:42 ratio of high to low
tide movements. As it was rejected the chi-square
goodness of fit test (Zar 1999) was performed for the
day and night samples separately. The sequential
Bonferroni test (Rice 1989) was applied to adjust the
significance level of the multiple tests. The same
procedure was applied to test if the movement ratio of
low and high tide periods had a 50:50 ratio of night
and daytime period. These analyses were performed
only for data pooled in categories of total movements
from all individuals during high/low tide and day/
night periods because 1) the objective of the test was
to examine the movement patterns of a group of
L. argentimaculatus, 2) there was a limited number of
observations for each individual.
In order to examine the dependence of movement
pattern on fish size, the mean TL of the group of
individuals which left the creek during the first 7 days
of the study and did not return during the study period
and those which stayed in the study area was

compared using T test. In addition, a linear regression
analysis was applied to determine if within the former
group there was a significant correlation between fish
size and days spent in the study area.
Probability level at α=0.05 was considered significant in all tests. Analyses were performed using
SPSS 17.0 software.

Results
Individual data on fish sizes, number of days tracked
are shown in Table 1. Eighteen data sets were


Environ Biol Fish (2012) 94:377–388

obtained during the two study periods. However, two
individuals (ID 113 and 263) were discarded from
further analysis due to the very high frequency and
fixed location of detections, indicative of dead fish or
shed transmitter. The hydrophone receiver array
recorded 127 497 signal transmissions from the 16
analyzed individuals over 169 non-consecutive days,
the longest tracking period being 28 days and the
shortest 1 day (Table 1).
Detection range of the receiver array
As a result of towing the activated transmitter along
the main channel detection ranges of each individual
receiver were obtained, and the resulting detection
area is shown in Fig. 1. It was determined that the
signal was lost (no signal was detected) when entering
any of the side channels as well as mangrove fringe in

distances of 50, 150 and 250 m from a receiver. The
results from the experiment to determine the influence
of tidal height on signal detection showed that the
signals were received continuously throughout two
full tidal cycles. It was also shown that the noise from
passing boats (approx. 10–30 m from the transmitter)
did not interrupt with signal detection.
Definition of movements
The frequency of gaps in signal reception of
>10 min did not differ significantly from the
expected frequency of random appearance of gaps
(x2 =2.23, p>0.05, df=1) during high and low tide
periods. However, the frequency of gaps in signal
reception of >20 and >30 min differed significantly
from the expected frequency of random appearance of
gaps (20 min, x2 =11.8, p<0.01, df=1; 30 min, x2 =
40.4, p<0.001, df=1). Because it was believed that
the appearances of shorter gaps were partially
associated with, for example, local topography or
background noises blocking signal reception, they
were excluded from further quantitative analysis.
Accordingly, for the final quantitative analysis, a
movement was defined as a gap in signal reception
for more than 30 min or the changing of detection
from one receiver to the other. The gaps in signal
reception defined as movements were present in all
fish (from 80% to 95% of movements of individual
fish).

383

Fourier analysis revealed notable 12 h periodicity
in the appearance of movements from one receiver to
another and appearance of gaps in signal reception for
fish from both study periods which is consistent with
the points of maximum tidal heights during the
diurnal tidal cycle (Fig. 2).
Movement patterns of L. argentimaculatus
Most fish could be categorized according to the
observed movement pattern. For 8 of 16 tagged fish
(ID’s 261, 264, 266, 108, 110, 114, 115 and ID 269)
the migrational pattern was characterized by a short
time period spent in the study area (1–10 days, except
ID110) with a following exit towards the open coast
(e.g. ID 264, Fig. 3a). For the first 3 days of tracking
ID 261 and ID 264 were found in the area around
receivers’ No. 7 and 8 and 6, 7 and 8 respectively.
Two days after release, ID 261 left the creek towards
the open coast and did not return. On the contrary ID
264 left and re-entered the study area several times,
swimming as far upstream as station 7 and returning
after a short time period. Nevertheless after 7 days
spent in the Sikao creek, ID 264 left the creek towards
the open coast and did not return. ID 266 stayed in the
study area only for 1 day, using two following high
tides to swim downstream and exit the creek. All the
fish in this group from the second study period spent
first 3–8 days of tracking in the area between the
stations 7 and 9 followed by exit towards the open
coast. However during all the study period ID 110

was irregularly detected by the receiver 1 indicating
that it spent time in the deep trench which connects
the Sikao creek to the open coast or in the coastal area
close to the Sikao creek.
For 5 of 16 tagged fish (ID’s 267, 268, 109,
112 and ID 262) the movement pattern was
localized. The fish spent the whole period of
tracking in the same area and no exit towards the
open coast was detected (e.g. ID268, Fig. 3b). ID
267, ID 268, ID 109, and ID 262 were found in the
area between stations 6 and 9. On the contrary ID 112
swam downstream and spent the tracking period in
the creek mouth. All the individuals regularly left the
area of detection ranges of the respective receivers
during high tides.
Three fish could not be included in the above
groups (ID’s 265, 270, 111). ID 265 spent 3 days
around receivers 6, 7 and 8. Only four signals from


384

Environ Biol Fish (2012) 94:377–388

Fig. 2 Fourier analysis of
movement periodicity for:
a – pooled data from the
first study period, and
b – pooled data from the
second study period. A 12

h periodicity was evident
for both groups

the receivers’ 3 and 1 were detected during the rest of
the study period indicating that the fish moved to the
creek A. In the first 5 days of tracking ID 270 stayed
in the area of receiver 5. After moving to the area
around receiver 1 the fish was caught by a sports
fisherman. ID 111 spent 4 days around receiver 9 and
left the study area towards the open coast without
detection by the receivers 8 and 7 but with signals
detected by all other receivers. This is unlikely to
happen in natural conditions and it may imply that ID
111 was caught by a fisherman and transported
downstream.
Comparisons of movement patterns with biotic
parameters
The movements of individual fish and the fraction of
movements during high and low tides are summarized
in Table 1. Of the total movements, ten were
directional the rest were indicated by gaps in signal
reception. On average 72.0% and 84.8% of the
movements during both day and night periods were
detected during high tide. Heterogeneity chi-square
test showed that the frequency ratio of movements
during high and low tide was not homogeneous in
day and night periods (x2 =4.2, p<0.05, df=1),

having greater skew toward high tide at night. The
following goodness of fit test detected significant

difference from the frequency of random movements
during the high and low tide periods for both day and
night (day x2 =9.5, p<0.01, df=1; night x2 =39.1, p<
0.001, df=1)
43.1% and 62.3% of high and low tide, respectively,
were detected in daytime, having significant heterogeneity in frequency ratio of day and night movements
between tidal periods (x 2 = 6.1, p < 0.05, df = 1).
However, following goodness of fit test for each of
high and low tide period detected no significant
difference in the frequency of movements during
day and night from the expected frequency (i.e. 50 :
50; high x2 =3.18, p>0.05, df=1; low x2 =3.7, p>
0.05, df=1).
The mean TL of fish that left the creek for the
open coast area during the study period was
determined to be 251 mm (211–303 mm) compared with 223 mm (192–252 mm) TL for those
that did not leave the creek; the difference
between the mean values was not significantly
different (t=1.23, p=0.24, df=11). Within the group
of individuals which left the creek for the open coast,
there was no significant correlation between fish size
and days spent in the creek (t=−.007, p=0.95, df=7).


Environ Biol Fish (2012) 94:377–388

385

Fig. 3 Time series of signal transmissions from ID 264 (a) and
ID 268 (b) detected at individual receivers plotted against

corresponding variations in tidal height. 1, 3, 6, 7, 8 indicate

receiver numbers. Each black dot represents a separate signal
reception. Water depths are given as predicted water heights
above extreme low water

Discussion

mangrove forest in Australia to feed at high tide and
retreated to subtidal areas during low tide.
Furthermore, Sheaves and Molony (2000) showed
that crabs inhabiting mangrove forest floor (Family
Sesaermidae) are a major food item of L. argentimaculatus in Australia. Our own observations show that
sesarmid crabs are an abundant group of benthic
animals in Sikao creek’s mangrove forests leading to
a suggestion that they are a sought-after food item of
L. argentimaculatus in the side creeks and/or mangrove forest during high tide periods. High tides are
also characterized by higher densities of small and
juvenile fishes in mangrove creek and forest habitats
(Thayer et al. 1987; Ikejima et al. 2003). Piscine prey
has been repeatedly shown to be of importance for
several lutjanid species (e.g. Rooker 1995; Kulbicki et
al. 2005). Additionally it has been found that
juveniles of grey snapper were hunting for small
fishes in mangrove prop root habitat in South Florida
(Thayer et al. 1987).

Influence of tidal cycle on the observed movement
pattern of L. argentimaculatus
We found that majority of the fish movements were

associated with high tides and a signal from a
transmitter was shown to be lost when entering
mangrove fringe or side channels.
Our observations showed that L. argentimaculatus
used the mangrove side channels and/or forest for
feeding during high tides and returned to the main
channels during low tide periods. High tides provide
access to increased food availability for fish in
mangrove systems (e.g. Robertson and Duke 1987;
Salini et al. 1990), triggering immigration of fish into
the mangrove habitats (Krumme and Saint-Paul 2003;
Sheaves 2005; Meynecke et al. 2008). Based on
observed changes in consumed food items, Sheaves
(2005) noted that L. argentimaculatus entered a


386

Sheaves (2005) implied that predation is another
factor modifying the tide-related migrational patterns
of fish in mangrove habitats, suggesting that during
the periods when the forest is exposed, fish move to
alternative microhabitats, such as fallen trees, to avoid
predators. Considering the relatively large size of the
individual fish studied here and the declining number
of large carnivorous fish, such as barracuda
(Sphyraena spp.) and barramundi (Lates calcarifer),
in the catches of local fishermen during the last
10 years (Tongnunui, personal observation) a strong
predation pressure on the studied fish is unlikely

within the study area. This is further supported by
Meynecke et al. (2008) who showed that during the
period a mangrove creek in Australia was accessible
larger Lutjanus russellii entered later and exited
earlier than smaller individuals suggesting that they
use the creek mostly for foraging in contrast to
smaller fish which spend more time in the creeks
due to the shelter provided by mangrove roots. We
found no correlation between fish size and days spent
in the creek. Thus we propose that in the current study
all L. argentimaculatus used mangrove side channels
and/or forest mostly for feeding.
Site fidelity of L. argentimaculatus
Six fish spent up to 28 days in the study area within
creek B (2 km long) revealing a considerable degree
of site fidelity (Fig. 3b). Previous studies have shown
that other species of Lutjanidae stay site attached in
estuarine habitats for a long time before reaching
certain size ca. 400 mm in mangrove jack (Sheaves
1995) and moving to permanent adult habitats (e.g.
Russell et al. 2003; Nanami and Yamada 2008). It has
also been observed that L. argentimaculatus are
associated with structural habitat such as mangrove
prop roots (Russell et al. 2003). The observed site
fidelity may be due to that the study area provided
suitable permanent habitat for a part of juvenile
mangrove jack population.
However, most of the studied fish moved towards
the open coast. The range of TL (192–303 mm) of the
fish in the present study was within the size range

(71–541 mm TL) of juvenile L. argentimaculatus
found in the mangrove estuaries of northeast Australia
(Sheaves 1995), so we assume that this movement
was not explained by permanent migration to adult
habitats. Our view is supported by Russell and

Environ Biol Fish (2012) 94:377–388

McDougall (2005) findings that juvenile mangrove
jack travel up to 130 km within coastal habitats in
Australia without moving to permanent offshore
habitats. Further proof comes from HammerschlagPeyer and Layman (2010) who showed that two
species of lutjanids exhibited considerable intrapopulation variability in movement patterns instead of
showing a constant pattern across the respective
populations. Thereby our observations could be
explained by a part of mangrove jack migrating to
other coastal habitats (i.e. nearby mangrove systems,
rocky and seagrass habitats) possibly in order to
optimize foraging or reduce intraspecific competition
(e.g. Hammerschlag-Peyer and Layman 2010).
Influence of diurnal cycle on the movement patterns
of L. argentimaculatus
Previous studies have found contradicting results
concerning changing activity patterns of snappers in
relation to diurnal cycle. Starck (1971) and
Nagelkerken et al. (2000) found that lutjanids are
inactive during day time but shift to active feeding
behavior during night time. Duarte and Garcia (1999)
showed that mutton snapper (Lutjanus analis) is
actively feeding throughout the day. L. argentimaculatus in this study were moving more actively during

night high tides. Krumme and Saint-Paul (2003)
observed a significantly higher flux of migrating fish
in the Brazilian mangrove creeks during night time
and our unpublished data showed a higher abundance
of fish in night time samples (Ikejima et al. 2003). In
addition it is known that sesarmid crabs are more
active during night time (e.g. Seiple and Salmon
1982; Moser and Macintosh 2001). Thus the nocturnal activity peak could be explained by an increased
abundance of mangrove jack’s foods in the mangrove
forest and/or side channels during night time.
Limitations of the study
It has to be noted that due to methodological
limitations some interpretations of the observed
migrational patterns of L. argentimaculatus have to
be viewed with caution. Due to logistical limitations
the studied fish were taken from aquaculture cages
and all the individuals were released at the same
location in the middle of the study area which could
influence their behavior. The fact that several


Environ Biol Fish (2012) 94:377–388

individuals left the creek towards open coast after a
relatively short time period could partially be explained
by unnatural behavior caused by this limitation. Another
methodological shortcoming of the study was the
limited coverage of the receiver array which did not
extend to creek A and nearby coastal habitats.
Increasing the coverage of the receiver array and the

length of experiment may reveal variation of individual
migrational patterns, and possible movements between
coastal nursery habitats.

Conclusions
Ultrasonic telemetry successfully depicted the migrational pattern of L. argentimaculatus in the mangrove
creek. We concluded that the tidal cycle is an
important environmental cue, determining the short
term migrational pattern of juvenile mangrove jack in
Sikao Creek, and suggest that individual fish utilize
the side creeks and/or mangrove forests for foraging
during high tide periods, retreating to the main creek
during low tides. Evidence was also found for part of
the juvenile L. argentimaculatus population leaving
Sikao Creek for other coastal habitats instead of
staying site attached. This supports Sheaves (2005),
who indicated that mangroves are part of an
interconnected habitat mosaic and should be studied
in the context of connectivity with other habitats. The
present data, together with the observed fishing
pressure on mangrove jack, revealed a pressing need
to develop a scheme for sustainable management of
the mangrove habitat in Thailand, so as to provide
protection for the habitat and associated fish stocks
from growing human interference.
Acknowledgements We thank the staff of Rajamangala
University for their help during the fieldwork, and M. Holmer
for provided helpful discussion and advice. We are grateful to
the National Research Council of Thailand for the granting of
permits to conduct this research in Thailand. We also thank G.

Hardy for English correction, and anonymous reviews for
invaluable comments on previous drafts.

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