Environmental biology of fishes, tập 90, số 4, 2011

Environ Biol Fish (2011) 90:329–342
DOI 10.1007/s10641-010-9744-4

Spatial and vertical patterns in the tidepool fish assemblage
on the island of O`ahu
Traci Erin Cox & Erin Baumgartner &
Joanna Philippoff & Kelly S. Boyle

Received: 26 February 2010 / Accepted: 9 November 2010 / Published online: 20 November 2010
# Springer Science+Business Media B.V. 2010

Abstract The microtides, wave regimes, and relative
isolation of the Hawaiian archipelago may provide
unique environmental and biogeographic effects that
shape the structure of tidepool fishes. We sampled
fishes across a narrow gradient at low tide from 6
sites on the island of O`ahu. We tested predictions of
the hypotheses that environmental conditions (pool
depth, volume, macroalgal cover, temperature, and
salinity) would result in a vertically structured tidepool fish assemblage unique to basalt or limestone
rocky shores. 343 fish were recorded from 40
pools, and 19 species from 10 families were
identified. Tidepool fish diversity (H’: O`ahu=2.4;
Sites Average=0.0–0.9) was typical for tropical
islands, with members from Gobiidae (5 species),
Blenniidae (4 species), Pomacentridae (3 species),
Acanthuridae (2 species) and Kuhliidae (2 species)

T. E. Cox (*)
Department of Botany, University of Hawai`i at Mānoa,

3190 Maile Way, Room 101,
Honolulu, HI 96822, USA
e-mail:
E. Baumgartner
Department of Biology, Western Oregon University,
345 N. Monmouth Ave,
Monmouth, OR 97361, USA
J. Philippoff : K. S. Boyle
Department of Zoology, University of Hawai`i at Mānoa,
2538 McCarthy Mall, Edmondson 152,
Honolulu, HI 96822, USA

among the most common. Endemism (32%) was
higher than other well studied assemblages yet
similar to Hawaiian reef fishes (25%). Assemblage
abundance varied among shores with basalt or
limestone substrate, among sites, and vertically
among high, mid, and low pools. In general, blenniids
occurred at higher proportions on limestone shores and
gobiids were more common on basalt shores. High pools
were characterized by an abundance of a small sized
(29.0 mm median standard length) blenniid Istiblennius
zebra, while the blenniid Entomacrodus marmoratus and
wrasses Thalassoma spp. were more common in low
pools. Temperature was the best environmental predictor
of assemblages and this relationship warrants further
investigation. Our findings indicate that assemblages can
vary across a narrow geographical range and intertidal
shore.
Keywords Intertidal . Assemblages .

Species richness . Tropics . Substrate . Island

Introduction
Intertidal fish assemblages are known to vary in
composition across latitudes and continents, between
regions, and within individual localities (Gibson and
Yoshiyama 1999). Geographic patchiness, dispersal
abilities, and evolutionary history explain the distribution of species across latitudes and continents,
while abiotic factors often contribute to patterns at


330

regional and local scales (Gibson and Yoshiyama
1999). Vertical gradients in temperature, air exposure,
wave action, and salinity can occur across the shore.
As water recedes during low tide, fishes that reside in
pools (residents) are more tolerant to these variable
conditions and the most physiologically tolerant
species occur higher on-shore (Yoshiyama et al.
1986; Zander et al. 1999). Substrate type also can
contribute to patterns in tidepool fish assemblages.
Examples can be found in central California, U.S.A.,
where stichaeids and pholids are found in tidal
boulder fields while heavy vegetated pools are often
dominated by cottids and clinids (Yoshiyama et al.
1986) and in the Mediterranean where rock structures
affect the species composition (Macpherson 1994).
Pool rugosity, volume, and depth can further contribute
to tidepool fish community patterns (Griffiths 2003).

Isolated oceanic island chains, like the Hawaiian
Islands, provide an opportunity to explore the importance of abiotic factors and biogeography in shaping
fish assemblage structure in these islands, as has been
done for numerous continental shores.
Tidepool fish assemblages are known to exhibit
distinct biogeographic affinities resulting from the
dispersal abilities of larvae and the degree of
geographic connectedness between populations
(Prochazka et al. 1999). For example, central
California and southern Chile have similar environmental regimes but distinct intertidal fish fauna
(Boyle and Horn 2006). Similarly, islands often have
different flora and fauna in contrast to nearby
mainland populations. The marine waters surrounding
the Hawaiian archipelago contain many tropical fish
species that co-occur throughout the Indo-West Pacific
and presumably these islands serve as a stepping stone
for dispersal across a vast oceanic barrier (Randall
2007). However, the isolation allows for a high
number of endemic fish species; 25% of the Hawaiian
island marine fish fauna are endemic (Randall 2007).
Therefore, the isolated nature of Hawaiian intertidal
zones in combination with the typically harsh environmental conditions may facilitate speciation and result
in a unique assemblage of intertidal fishes.
The tropical location and tidal conditions in the
state of Hawaii may influence the vertical and spatial
patterns of fishes in the intertidal zone. Tides in
Hawaii are considered microtidal with an amplitude
of less than 1 m (Gosline 1965; Abbott 1999). The
islands of Hawaii are located in the trade wind belt

Environ Biol Fish (2011) 90:329–342

and seasonally directed winds drive wave height and
determine which shores (north, south, east, or west)
experience wave swell at different times of the year
(Gosline 1965; Abbott 1999; Bird 2006). The
combination of microtides and surge limit air exposure
for intertidal organisms and the vertical span of the
intertidal zone is much reduced in comparison to the
extensive vertical span of other well studied intertidal
shores (Gosline 1965; Abbott 1999). Nonetheless,
pools are abundant along Hawaiian shores (Gosline
1965) and are apparent on spring low tides that occur
in summer daylight hours when temperatures are at
their peak. Additionally, O`ahu has both basalt and
carbonate based shores (Gosline 1965; Abbott 1999).
Basalt shores are often barren of lush macroalgae
unlike rough and porous limestone shores (Abbott
1999), thus these types of shores may provide different
habitats best suited for the survival of different species
of fishes.
During the approximately 35 years since the first
observational description of Hawaiian intertidal fishes
(Gosline 1965), much has changed in the near shore
environment. Changes include the invasion of
palatable and unpalatable alien algae (Stimson et
al. 2001; Smith et al. 2002), increased fishing
pressure (Friedlander and DeMartini 2002), and
altered temperatures and sea level from global
warming (Jokiel and Brown 2004). However, it is

not known if these changes have impacted the fish
assemblages in the intertidal habitat. Additionally,
comparable descriptive studies on tropical and
temperate intertidal zones focus on quantification
of resident fishes found in pools during the low tide
(Horn et al. 1999). Gosline (1965) detailed observations of fishes on high and low tides in these
coastal zones but robust quantification was not
provided.
The aims of this study were to describe the
tidepool fish assemblage for the island of O`ahu and
examine fish assemblage structure across and among
shores. We tested the hypothesis that tidepool fishes
would be vertically distributed. Further, we tested the
hypothesis that intertidal fish communities would
vary among shores with different substrate type
(basalt or limestone). Lastly, the isolation of the
Hawaiian archipelago is hypothesized to result in a
tidepool fish community for the island of O`ahu with
high species abundance but low richness and high
endemism.


Environ Biol Fish (2011) 90:329–342

Materials and methods
To describe assemblage patterns and abundances of
tidepool fishes on O`ahu, six rocky intertidal sites
were chosen for sampling: `Ewa Beach, Turtle Bay,
Nānākuli, Sandy Beach, Makapu`u and Diamond
Head (Fig. 1). These sites were selected to ensure a

representative sample of fishes and to test the
hypothesis that substrate type correlates with structure.
Sites are located on the south, east, west, and north
shores and included tidal benches composed of basalt or
limestone (Table 1).
To examine the vertical structure of tidepool fishes
across the shore, six to eight pools distributed in an
on-offshore direction within the intertidal habitat at
each site were chosen haphazardly for collection of
fishes. Because the Hawaiian Islands have microtides
and a limited range of vertical intertidal zonation,
tidal height was not obvious, hence pools were
sampled as high, mid, or low depending on their
location to the water at time of peak low tide. Pools
located near the water’s edge or subtidal zone and
usually covered in fleshy macroalgae were referred to
as low, whereas barren pools near terrestrial vegetation and above the gastropod Nerita spp. and within
the gastropod Littoraria spp. zone were referred to as
high. Any pools found between the high and low
Fig. 1 Map of the island of
O`ahu with the location of
six intertidal sites

331

pools were referred to as mid. Pools in the high zone
were within the intertidal and not supratidal as these
pools are submersed on the incoming high tide
(personal observations TEC). Fishes were collected
from at least two pools in each position (high, mid,

low) at each site for a total of 6–8 pools.
Each site was visited once and sampled for fishes
in high, mid, and low pools (Table 1). All sampling
occurred during the summer months May–August
2008, on a spring low tide. Multiple sites could not be
sampled in 1 day as microtidal conditions quickly
limits access to pools. Summer months were chosen
for the sampling period because this is when spring
low tides co-occur in daylight hours. These spring
low tides ranged from -0.12- to -0.06 m. The peak
low tides during the sampling period occurred in the
morning hours 06:00–10:11. Sampling began at least
1 h prior to peak low tide and continued until high
tide prevented accessibility of pools. High, mid and
low pools were haphazardly sampled during each site
visit.
Non-destructive sampling was preferred as it
lessens the impact on the tidepool community and
studies on methodology in other intertidal habitats
have found similar results regardless of techniques
(Gibson 1999; Griffiths 2000). A battery operated
submersible bilge pump and various sized buckets


332

Environ Biol Fish (2011) 90:329–342

Table 1 Site name, substrate type, location and date, tidal height sampled
Sites

Abbreviation

Substrate Type

O`ahu Shore Location

Date Sampled in 2008

Diamond Head

D

Basalt

Southeast

August 1

−0.06

Makapu`u

M

Basalt

East

June 30

−0.12

Sandy Beach

S

Basalt

East

May 30

−0.09

`Ewa Beach

E

Limestone

Southwest

June 3

−0.15

Nānākuli

N

Limestone

West

July 2

−0.12

Turtle Bay

T

Limestone

North

June 5

−0.12

were used to drain and bail each pool of seawater.
Any fishes present were scooped up by hand or with
hand-net. A chopstick or finger was used to probe
gently into holes and crevices to ensure the capture of
small cryptic fishes. Captured fishes were kept alive
and placed in aerated buckets of seawater for
identification and measurements.
To determine the abundance and diversity of fishes
each individual collected was counted, identified, and

measured prior to release. In the field, fishes were
anesthetized in buckets of seawater with MS-222 and
then identified to the lowest possible taxon using
dichotomous keys of Hawaiian Shore Fishes (Randall
2007). A hand lens was used to view any diagnostic
features difficult to observe with an unaided eye.
Once the species was identified and recorded, the
standard length of fishes greater than 15 mm SL was
measured. Each individual was assigned an id
number, and its size and locality (both site and pool
position) recorded. To minimize impact to the tidepool community, fishes were revived in aerated
seawater and released to the tidepool from which
they were collected after pools were inundated from
rising tides or to a nearby location. Fishes were kept
in buckets until all sampling had concluded to avoid
re-sampling. On rare occasions, fishes were returned
while sampling was ongoing but any sampled pools
were >20 meters from release site.
The statistical software package Primer-E (Clarke
and Warwick 2001) was used to analyze the spatial
distribution and abundance of fishes among and
across shores. Because of the difficulty in identifying
small Bathygobius spp. a conservative approach was
taken and in this analysis all Bathygobius spp. were
grouped into one taxonomic category. However,
results did not differ when all Bathygobius were
grouped by genus or when those identified to species
level were considered separately. These counts of

Low Tide Height (m)

fishes were expressed as a proportion of total number
of individuals found per pool and each pool was
considered a replicate of position (high, mid, or low)
nested within a site. Abundances were square-root
transformed to down-weight common species and
account for the patchy nature of tidepool species
(Gibson and Yoshiyama 1999). These data were then
used to construct Bray-Curtis similarity matrix
between sites and pool position. Dendrograms were
used to visualize the similarity of fishes by site,
shore substrate type, and pool position. Further,
PERMANOVA with pool position nested within
sites and sites nested within substrate was used to
statistically test the hypothesis that fishes were
vertically and spatially distributed. A series of
one-way SIMPERs were used to analyze which
species contributed to the observed similarity
patterns.
To examine if sizes of fishes varied across the shore we
compared the standard length (mm) of the most abundant
species that occurred on O`ahu: Abudefduf sordidus,
Bathygobius cocosensis, Entomacrodus maramoratus,
and Istiblennius zebra. Sizes of fishes across sites were
pooled for each tide pool position and differences
between length medians were tested with KruskalWallis or Mann–Whitney tests.
To describe the assemblage and test diversity
hypotheses, species richness (S) and Shannon (H’)
indices were computed for each pool position at each
shore and for the island of O`ahu. For site and

position comparisons, each pool was considered a
replicate sample and computed values were compared
statistically with a two-way ANOVA (sites and
position). Prior to testing data were log transformed
to meet parametric requirements and alpha values
were adjusted to account for multiple comparisons. To
determine S and H’ for the island of O`ahu all species
were pooled from every site and values reported.


Environ Biol Fish (2011) 90:329–342

333

To test if any of these physical features were
related to observed fish assemblage patterns a
distance based redundancy ordination analysis
(dbRDA) was used in combination with a distance
based linear model. The distance based linear
model (DISTLM function in PRIMER-E) models
the relationship between predictor variables and the
multivariate data cloud based on a multiple regression. This routine finds the linear combination of
variables that best explains the greatest variation in
the data cloud and the amount of variance each
covariate explains separately providing a pseudo-F
stastical value. dbRDA is an ordination analyses
that visualizes these results. Predictors that best
explain the data cloud are viewed as vectors in a
biplot. The longer the vector the larger the effect of
the predictor (Anderson et al. 2008).

To characterize conditions experienced by tidepool
fishes in O`ahu, a snapshot sample of physical
conditions and surroundings were collected from
tidepools during the sampling period. Prior to fish
collection, the maximum pool depth, length, and
width was measured with a transect tape and were
used to calculate a rough estimate of pool volume.
Salinity measurements (0/00) were collected with a
handheld refractrometer, and a visual estimate was
made of algal percent cover within and along the
edges of pools. The surface water temperature was
recorded with 2–3 Hobo temperature loggers placed
in sampled and unsampled pools during the low tide
window. At some sites measurements were not
collected because of instrument failure or observer
oversight, thus only sites with all measurements were
included in analyses.

Table 2 Proportion and total # of fish species by family (F) that were collected and identified in the high, mid, and low pools at the 6
sites. B. spp = Bathygobius, E. spp = Entomarcodus, T. spp = Thalassoma; see Table 3 for other taxonomic abbreviations
Taxa

F

Diamond Head

Makapu`u

H

M

H

M

0.6 0.0 –

L

L

Sandy Beach

`Ewa Beach

Nānākuli

H

H

M

–

M

L

H

M

L

–

–

B. cocosensis

G

–

0.6

0.6

–

0.8

0.3

–

I. zebra

B

0.3

–

–

0.7 0.1 0.0 0.1

0.2

0.2

0.2 0.4 –

A. sordidus

P

0.8

0.3

0.2

–

–

–

–

B. spp.

G

–

–

0.2

0.3 –

0.1 0.7

–

0.2

0.5 –

–

0.1 0.2 –

H

–

–

0.3 0.1 0.3 64

1.0 –

–

0.2 0.2 0.4 63

1.0 1.0 –

–

–

–

M

Total #

L

0.1 0.1 –
–

Turtle Bay
L

0.0 –

51

0.3 0.2 0.3 46

E. marmoratus

B

–

0.1

0.0

–

–

–

–

–

0.1 0.4 0.7 –

–

–

–

A. triostegus

A

–

–

–

–

0.1 0.2 –

–

0.3

–

–

–

–

–

–

0.1 0.1 –

K. sandvicensis

K

–

–

–

–

–

0.1 –

–

–

–

–

–

–

–

–

–

0.0 –

7

B. coalitus

G

–

–

–

–

–

–

–

–

–

0.2 0.1 0.0 –

–

–

–

0.0 –

6

E. spp.

B

–

–

–

–

–

–

–

–

–

–

–

–

–

0.1 0.1 –

6

–

–

0.1 0.1 36

20

K. xenura

K

–

–

–

–

–

0.1 –

–

–

–

–

–

–

–

–

–

–

–

5

T. purpureum

L

–

–

–

–

–

–

–

–

–

–

0.1 –

–

–

–

0.0 –

5

Creediidae

C

–

–

–

–

–

0.1 –

–

–

–

–

–

–

–

–

–

–

–

3

M. cephalus

M

–

–

–

–

–

0.1 –

–

–

–

–

–

–

–

–

–

–

–

3

B. cotticeps

G

–

–

–

–

–

0.0 –

–

–

–

–

–

–

–

–

–

–

–

2

–

T. spp.

L

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

0.0 –

2

A. abdominalis

P

–

–

–

–

–

0.0 –

–

–

–

–

–

–

–

–

–

–

–

1

B. gibbifrons

B

–

–

–

–

–

–

–

–

0.1

–

–

–

–

–

–

–

–

–

1

C. lunula

Ch –

–

–

–

–

0.0 –

–

–

–

–

–

–

–

–

–

–

–

1

C. obscurus

B

–

–

–

–

–

–

–

–

–

–

0.0 –

–

–

–

–

–

1

–

D. griessingeri

G

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

0.0 –

1

G. anjerensis

G

–

–

–

–

–

–

0.1

–

–

–

–

–

–

–

–

–

–

–

1

P. imparipennis P

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

0.1 –

–

1

S. balteata

–

–

–

–

0.1 –

–

–

–

–

–

–

–

–

–

–

–

–

1

12

15

25

6

14

7

12

19

11

17

23

18

3

18

16

50

16

327

Total #

L

45

334

Environ Biol Fish (2011) 90:329–342

A total of 343 fishes were recorded and 327 individuals
actually captured from six sites (40 sampled tidepools) on
the island of O`ahu. Fishes that were observed but not
captured were often young-of- the-year gobies or
blennies. Of the 327 captured, 25 taxa were recorded
and 19 species (H’=2.5) identified from 10 families
(Tables 2 and 3). Those taxa identified to only the

family or genus level were of small size and belonged to
the genera Bathygobius, Entomacrodus, Thalassoma, or
Family Creediidae.
The most abundant fishes were from 4 families and
include (in order of abundance) Bathygobius cocosensis
(Gobiidae), Istiblennius zebra (Blenniidae), Abudefduf
sordidus (Pomacentridae), Entomacrodus marmoratus
(Blenniidae), and Acanthurus triostegus (Acanthuridae)
(Tables 2 and 3).

Table 3 Distribution, habitat, and resident status of tidepool
species and their families (family abbreviation follows) with a
comparison to assemblage determined by Gosline (1965). R =
resident species (permanent inhabitants), PR = partial residents

(spend part of life in intertidal), T = transients (visitors); + =
present - = absent in Gosline (1965) splash zone assemblage.

Distribution and habitat according to Randall (2007), definitions follow Gibson (1982)

Results

Family
Genus species

Biogeographic
Distribution

Habitat

Resident
Status

Presence/Absence in
Gosline (1965)

Indo-Pacific,
Tropical E. Pacific

Juveniles in tidepools,
adults shallow water

PR

+

Indo-Pacific

1–3 m

R

–
–

Acanthuridae (A)
Acanthurus triostegus
Blenniidae (B)
Blenniella gibbifrons
Cirripectes obscurus

Hawaiian Islands

1–6 m

R

Entomacrodus marmoratus

Hawaiian Islands

Tidepools

R

+

Istiblennius zebra

Hawaiian Islands

High tidepools

R

+

Indo-Pacific

1–158 m on coral reefs

T

–

N/A

15–20 m

?

–

Bathygobius coalitus

Indo-Pacific, W. Pacific

Intertidal zone

R

–

Bathygobius cocosensis

Indo-Pacific

Tidepools

R

+

Bathygobius cotticeps

Indo-Pacific, W. Pacific

Rocky tidepools, lower intertidal

R

–

Chaetodontidae (Ch)
Chaetodon lunula
Creediidae (C)
Gobiidae (G)

Discordipinna griessingeris

Indo-Pacific

1–37 m

?

–

Gnatholepis anjerensis

Indo-Pacific

Usually occurs in >2 m, tidepools

R

–

Kuhlia sandvicensis

Indo-Pacific

Shallow-water

PR

+

Kulia xenura

Hawaiian Islands

Juveniles occur in tidepools,
adults offshore

PR

–

Hawaiian Islands &
Johnston Atoll
Indo-Pacific

Shallow-water to 22 m

T

–

Rocky shores shallow-water

T

+

Circumglobal warm-waters

Inshore protected waters

T

–

Hawaiian Islands &
Johnston Atoll
Indo-Pacific

Young often in tidepools,
adults inshore
Young often in tidepools,
adults inshore
Reefs usually >4 m

PR

–

PR

+

R

–

Kuhliidae (K)

Labridae (L)

Stethojulis balteata
Thalassoma purpureum
Mugilidae (M)
Mugil cephalus
Pomacentridae (P)
Abudefduf abdominalis
Abudefduf sordidus
Plectroglyphidodon
imparipennis

Indo-Pacific


Environ Biol Fish (2011) 90:329–342

335

The nMDS and dendrograms (Fig. 2) reveal a large
amount of overlap in assemblage similarity among sites
and pool position, although the centroid based nMDS
plot (Fig. 2, top) shows clusters of sites based on
substrate type (basalt or limestone). The limestone sites
are less clustered than basalt sites as the pool samples
from Nānākuli are more distinct. Furthermore, site
assemblages differed among high, mid, and low pools
(Fig. 2, bottom). Results from the PERMANOVA
support significant differences among pool positions,
sites, and sites with different substrate types (Table 4).
Different abundances of the common fishes
contribute to the dissimilarity among tested groups

(Tables 2 and 5). Although the presence of species
was similar among basalt and limestone based
shores, there were significant differences in the
proportion of blennies and gobies. Bathygobius spp.
occurred at higher proportions on basalt shores while
the blennies I. zebra and E. marmoratus occurred at
higher proportions at limestone shores (Table 5).
Within the basalt shores (Diamond Head, Makapu`u,
Sandy Beach) roughly 20% of community dissimilarity
was accounted for by the differing proportions of I.
zebra and Bathygobius spp. (Table 2). Abudefduf
sordidus was absent from Sandy Beach but abundant
at both Diamond Head and Makapu`u. This species

Distance

60
40

Stress: 0.15

20

B

Basalt = B
Limestone = L

Stress: 0

S

M

T

D

E

N

0

B
L

B

L

L

50
40
30
20
10
0

L

Stress: 0.15

Stress: 0.14
H

L

M

H
H

Distance

Fig. 2 Non-metric multidimensional scaling ordinations (nMDS plots)
on the basis of Bray-curtis
dissimilarity measure
of each pool (top left
symbols = sites, see
Table 1 for abbreviation of
site names; bottom left
symbols = position) and of
centroids (right) of sites (top
right) and pool position
nested within sites (bottom
right symbols = sites).
Dendrograms in upper left
corners are the similarity

distance between the
centroids of sites (top left)
and pool position (bottom
left) and serve as a legend
for symbols in nMDS
plots. Note the differences
shown as distance between
basalt and limestone
based shores, sites,
and pool position

accounts for 30% difference between Sandy Beach and
Diamond Head and 12% of the differences between
Sandy Beach and Makapu`u. Assemblages also varied
among limestone sites. Nānākuli assemblage was most
dissimilar from other limestone sites (84% dissimilar
from Turtle Bay, 88% dissimilar from `Ewa Beach) as
it has a higher proportion (0.7) of I. zebra (which
accounted for ~20% of said dissimilarities). The
composition at `Ewa Beach and Turtle Bay were only
65% dissimilar and the abundance of E. marmoratus
accounted for 20% of this dissimilarity.
The composition of fishes varied vertically across
the shore (Fig. 2). Assemblages differences were
greatest between high and low pools (Fig. 2; Table 5).
Istiblennius zebra was more common in high pools
and E. marmoratus, A. triostegus, and Thalassoma
spp. were more common in low pools (Table 5). Also,
out of four common species examined (A. sordidus,
Bathygobius spp., E. marmoratus, and I. zebra) the

median SL (mm) of I. zebra was smaller in high
pools (Kruskal-Wallis, p-value < 0.001, Dunn’s
Method, p-value<0.05) (Fig. 3). High pools can
therefore be characterized by a high number of small
sized individuals of I. zebra.
Diversity of fishes measured as species richness
and H’ did not statistically (at adjusted α=0.025)

M

M
L

H
L M
M
L

L

L M
M

H
H

H


336

Table 4 Results of PERMANOVA showing
the significant assemblages
of fishes. Results are out
of 1,000 permutations

Environ Biol Fish (2011) 90:329–342
Source of variation

df

SS

MS

Pseudo-F

P (perm)

Unique Perms

Substrate = Su

1

5742.7

5742.7

3.9

0.01

999

Sites (Su)

4

20119.0

5029.8

3.4

0.001

998

Position (Sites (Su))

12

41222.0

3435.2

2.4

0.001

997

Residual

22

32114.0

1459.7

vary across shores but did vary among sites (S: Twoway ANOVA, p-value<0.01; H’: two-way ANOVA,
p-value<0.001) (Fig. 4). Nānākuli (S=1.0±0.2 SE,
H’=0.0±0.0 SE) had low species richness and H’
index but was within range of values determined for
Diamond Head (S=2.0±0.3 SE, H’=0.5±0.2) and
Sandy Beach (S= 2.3 ± 0.2 SE, H’= 0.7 ± 0.1 SE).

Diversity was higher for Makupu`u (S=3.5±0.6 SE,
H’=0.9±0.3 SE), Ewa Beach (S=3.2±1.3 SE, H’=
0.9±0.2 SE) and Turtle Bay (S=3.7±0.7 SE, H’=0.9±
0.2 SE).
Measured conditions experienced by fishes during
sampling period varied between high, mid, and low
pools (Table 6). Temperature varied notably as pool

Table 5 Results from SIMPER analyses showing the species and their proportions that contribute to ~80.0% of the dissimilarity
among basalt and limestone shores and across high, mid, and low pools
Dissimilarity=71.3%

Basalt

Species

Av. Abund

Av. Abund

Av. Dissimilarity (Stdev)

% Contribution

Cumulative%

Bathygobius spp.

0.6

0.3

16.3 (1.2)

22.9

22.9

Istiblennius zebra

0.3

0.4

14.3 (1.1)

20.1

43.0

Abudefduf sordidus

0.3

0.2

11.8 (0.8)

16.5

59.5

Entomacrodus marmoratus

0.1

0.3

10.3 (0.8)

14.5

74.0

Acanthurus triostegus

0.1

0.1

3.5 (0.5)

4.9

78.9

High

Mid

Dissimilarity=67.3%
Species
Istiblennius zebra

Limestone

Av. Abund

Av. Abund

Av. Dissimilarity (Stdev)

% Contribution

Cumulative%

0.6

0.3

17.6 (1.2)

26.2

26.2

Bathygobius spp.

0.3

0.6

16.6 (1.2)

24.7

50.9

Abudefduf sordidus

0.2

0.3

12.6 (0.8)

18.6

69.5

Entomacrodus marmoratus

0.0

0.2

6.4 (0.7)

9.5

79.0

Acanthurus triostegus

0.0

0.1

1.0 (0.5)

2.8

81.8

Mid

Low

Dissimilarity=67.1%
Species

Av. Abund

Av. Abund

Av. Dissimilarity (Stdev)

% Contribution

Cumulative%

Bathygobius spp.

0.6

0.5

14.4 (1.1)

21.4

21.4

Entomacrodus marmoratus

0.2

0.3

12.5 (0.9)

18.7

40.1

Abudefduf sordidus

0.3

0.2

11.8 (0.9)

17.6

57.7

Istiblennius zebra

0.3

0.1

9.7 (1.0)

14.4

72.1

Acanthurus triostegus

0.1

0.1

4.6 (0.6)

6.8

78.9

Thalassoma purpureum

0.0

0.1

2.2 (0.5)

3.3

82.1

Low

High

Dissimilarity=79.5%
Species
Istiblennius zebra

Av. Abund

Av. Abund

Av. Dissimilarity (Stdev)

% Contribution

Cumulative%

0.1

0.6

20.9 (1.4)

26.4

26.4

Bathygobius spp.

0.5

0.3

14.6 (1.2)

18.4

44.7

Entomacrodus marmoratus

0.3

0.0

11.5 (0.7)

14.4

59.2

Abudefduf sordidus

0.2

0.2

10.2 (0.8)

12.9

72.0

Acanthurus triostegus

0.1

0.0

4.3 (0.5)

5.4

77.4

Thalassoma purpureum

0.1

0.0

1.7 (0.4)

2.2

79.6


Environ Biol Fish (2011) 90:329–342

80

337

A. sordidus

0.001) of assemblages but, the overall best model
included all variables (pool volume, depth, salinity,
macroalgal cover, and temperature). This can be seen
in the dbRDA biplots (Fig. 5). The first three axes of
the dbRDA explain 94% of the variation of the fitted
model but only 25% of the total variation in the data
pool. Tidepools at basalt and limestone shores fall
along these axes varying with temperature and
macroalgae; basalt shores tended to have a positive
correlation with dbRDA axes 1 while limestone
shores had a negative correlation with dbRDA axes
1. Sixty-eight percent of sampled tidepools had a full
set of environmental measurements and were included
in these multivariate analyses.

60
40
20
0

B. cocosensis

80
60

Standard Length (mm)

40
20
0

Discussion
E. marmoratus
100
80
60
40
20

I. zebra
120
100
80
60
40
20
0
High

Mid

Low

Pool Position

Fig. 3 Boxplots showing the distribution (median, quartiles, and
outliers) of standard length (mm) for four common taxa A. sordidus
(n=51), B. cocosensis (n=63), E. marmoratus (n=34), and I.
zebra (n=51) collected from high, mid, and low pools. Bars above
boxplots represent similar statistical groupings from Dunn’s
multiple comparisons test when Kruskal-Wallis or Mann–Whitney
test indicated significant differences among pool position

temperatures co-varied with substrate type. Basalt
shores were warmer than limestone shores. The
distance based linear model found temperature to be
a significant predictor (Pseudo-F = 2.9, p-value <

Our study revealed a tidepool fish assemblage for
O`ahu island composed of 19 species from 10
families. Results of this study support the hypothesis
that basalt and limestone shores have distinct intertidal fish assemblages and that these assemblages are
possibly related to temperature. Results also support
the hypothesis that the tidepool fishes are vertically
distributed. This vertical distribution coupled with the
variation of assemblages among sites and substrate
types, reveals a surprising amount of structure within
a limited geographical area and across a narrow shore.
The tidepool fish assemblage in O`ahu is similar to
other isolated tropical islands which have low species
richness and a high number of endemic species, yet
assemblage members are from taxonomic families
that occur throughout the tropics. The tidepool species
on O`ahu were largely distributed across the IndoWest Pacific (68%) and 32% were endemic to Hawaii
and Johnston Atoll. This level of endemism is within

range of the 25% determined by Randall (2007) for
all marine fishes in Hawaii and it is higher than
percentages recorded for most regions (Prochazka et
al. 1999) yet it is lower than 61.7% of endemic
rockpool fishes (mostly tripterygiids) that occur in cool
temperate New Zealand waters (Paulin and Roberts
1993). The most abundant fish families were Gobiidae
(5 species) >Blenniidae (4 species) >Acanthuridae (2
species) >Pomacentridae (3 species), and Kuhliidae (2
species). Most of these families are common in studied
tropical intertidal habitats throughout the world except
kuhliids which are absent in the west Atlantic (Hiatt and


338
12.0

6.0

10.0

5.0

a

a
a

8.0

4.0

6.0

3.0

4.0

2.0

2.0

1.0

0.0

0.0

2.5

1.2

ab

S

Fig. 4 Comparison of species richness (S, top) and
diversity (H’ bottom) for
tidepool fishes among six
shores (right: black = basalt,

white = limestone shores)
and among high (white),
mid (gray), low (black)
pools nested within site
(left) on the island of O`ahu.
Letter groups above bars
represent similar statistical
groups (Two-way ANOVA
with an adjusted α<0.025)

Environ Biol Fish (2011) 90:329–342

ab
b

a

a

a

1.0

2.0

ab

0.8

H'

1.5

ab

0.6
1.0
0.4
0.5
0.0

0.2
D

M

S

Sites

Strasburg 1960; Gosline 1965; Lee 1980; Greenfield
and Johnson 1990; Duhart and Ojeda 1994; Mahon
and Mahon 1994; Prochazka et al. 1999; Greenfield
2003). Notable differences include the absence of
serranids, muraenids, and gobiesocids. Gobiesocids
are common in many temperate intertidal regions and
are found in a few tropical localities but are absent in
Hawaii (Prochazka et al. 1999). Serranids are mostly
absent in shallow-water collections in Hawaii except
for a non-indigenous grouper that is common on coral

reefs (Randall 2007). In the Indo-West Central Pacific
province (where Hawaii is located) (Duhart and Ojeda
1994) muraenids are commonly found in tidepool
communities. Also muraenids are prominent in tidepool collections from Barbados (Mahon and Mahon
1994) and the Marshall Islands (Hiatt and Strasburg
1960) and have been observed in Hawaiian tidepools.
The absence of eels in this study could be because of
their high mobility and that they are likely to occur in
relatively low densities or are likely to be in larger
pools that are only isolated from the ocean on the
lowest of low tides. It is also possible that more
tidepool species on O`ahu would be found if sampling
occurred across the year, however, the tropics lack
strong seasonality and tropical fish assemblages can
be stable over short temporal scales (Chang et al.
1973; Castellanos-Gallindo et al. 2005). Similar

E

N

T

0.0

b

D

M

S

E

N

T

Sites

species richness is observed in tidepools at other
isolated island chains. For instance, five species were
recorded from a study on Easter Island (Duhart and
Ojeda 1994), and 23 species were reported in the
Seychelles (Prochazka et al. 1999), where as Taiwan,
also located in the Indo-West Pacific, has 122
species (Prochazka et al. 1999). Thus it is more
likely that low species richness is due to the isolated
nature of the island chain and the dispersal ability of
fishes.
We found many of the same species in O`ahu’s
tidepools that Gosline (1965) observed in the intertidal
zone for the main islands of Hawaii yet, this study
quantifies nearly double the number of species in the
intertidal zone. Species richness in exposed rockpools
on O`ahu is likely still higher than we determined as a
few species, such as holocentrids, were observed but
not sampled. Most of the fishes recorded during this
study but not included by Gosline (1965) were

transient or cryptic. Differences in methodology and
definition of habitat possibly account for the
discrepancy in species composition between studies.
Gosline (1965) made observations of near-shore
fishes for the Hawaiian Islands and refers to a spray,
splash, and a surge zone. The splash zone is strictly
intertidal and the surge zone he describes can be
above or below the mean tidal level. This study


Environ Biol Fish (2011) 90:329–342

339

Table 6 Average (SE) of environmental variables collected across the shore at 6 sites
Approximate Volume (m3)

Depth (cm)

Temperature (°C)

Salinity (0/00)

Algal Cover (%)

High

0.5 (±0.1)

33.8 (± 2.0)

28.1 (±0.7)

33.2 (±0.7)

22.2 (±14.5)

Mid

0.2 (±0.1)

42.3 (± 5.0)

27.4 (±0.5)

33.5 (±0.3)

60.7 (±16.0)

Low

1.0

40.0

28.1

33.0

100.0

High

0.0 (±0.0)

20.0 (± 0.0)

27.3 (±2.8)

33.2 (±0.7)

–

Mid

0.3 (±0.3)

27.1 (±21.2)

25.0 (±1.0)

32.9 (±1.4)

16.4 (±10.6)

Low

1.9 (±1.3)

37.3 (± 7.1)

25.0 (±0.8)

38.5 (±1.4)

5.3 (±14.1)

High

0.3

30.0

24.2

47.0

–

Mid

1.0 (±0.3)

40.0 (±14.1)

24.2 (±0.3)

40.3 (±6.4)

35.0 (±42.4)

Low

1.1 (±0.7)

29.7 (± 7.4)

24.4 (±0.4)

40.8 (±3.2)

77.2 (± 3.5)

High

0.5 (±0.2)

27.3 (± 2.0)

22.7 (±0.0)

36.7

–

Mid

1.0

45.0

23.8

35.0 (±0.4)

20.0

Low

0.1 (±0.1)

20.3 (± 8.9)

24.1 (±0.3)

41.0 (±3.6)

90.0

High

0.5 (±0.3)

43.3 (± 2.9)

–

34.7 (±0.3)

0.0 (± 0.0)

Mid

0.4

35.0

–

35.0

0.0 (± 0.0)

Low

0.6

35.0

–

35.0

0.0 (± 0.0)

High

0.2

15.0

25.0

35.0

25.0

Mid

0.5 (±0.2)

18.1 (±12.7)

25.3 (±1.3)

33.1 (±0.7)

59.5 (± 30.1)

Low

0.2 (±0.2)

12.9 (± 2.9)

25.3 (±0.7)

33.6 (±0.4)

74.1 (± 18.7)

Diamond Head

Makapu`u

Sandy Beach

`Ewa Beach

Nānākuli

Turtle Bay

quantitatively samples fishes in pools at mean low
low water for O`ahu and thus distinguishes the
boundary between intertidal and subtidal zones.
Although the density of fishes varied among
limestone and basalt based shores, it is unclear what
causes the differing assemblages. In this study basalt
shores tended towards higher temperatures and
temperature was a predictor of assemblage variation.
Bathygobius spp., more common on basalt shores, is
known to have a high temperature tolerance (thermal
maxima ~40°C) (Mora and Ospina 2001). However, a
limited set of predictor variables were collected and
used in the linear model and temperature alone did
not explain a high amount of variation observed in the
data pool. Further, I. zebra can tolerate conditions on
basalt shores as it was present at all shores. Intertidal
fishes commonly use holes and crevices for shelter

and nesting (Duci et al. 2009). Limestone shores
which maybe more easily eroded could provide

crevices that suit the recruitment or survival of
blenniid species, like I. zebra and E. marmoratus. A
similar conclusion was reached by Macpherson
(1994) in the Mediterranean as a blenny species was
absent in a habitat that lacked crevices in three
separate sites. Alternatively, this assemblage difference
between basalt and limestone shores could be the result
of small number of sites sampled in this study. The
addition of assemblages from more basalt and limestone
shores could clarify the relationship between substrate
and abundance patterns.
The among-site differences observed in this study
are surprising given the small geographic distance
between sites, the similarity in habitat within substrate
groups, and the similar small number of species that
occur in pools. These differences may be due to
temporal recruitment of juveniles or the variation in
the nearby subtidal habitat since the assemblages
differed in number of partial resident and transient


dbRDA2 (19.1% of fitted, 47% of total variation)

340

Environ Biol Fish (2011) 90:329–342

40

Site

Volume

D
M
S
E
T

20
Salinity
Temperature
0

Depth
Macroalgae

-20
-40

-20

0

20

40

dbRDA1 (56.9% of fitted, 14% of total variation)

Fig. 5 dbRDA ordination plot displays the relationship
between environmental predictors that best explain the variation
among pools at different sites. The vectors within the circle
show the “effect” of the predictor variables included in the
model, the longer the vector from the center the larger the
“effect”. Basalt pools are represented by solid symbols while
limestone shores are represented by open symbols. Assemblages sampled from basalt pools tend to positively correlate
with temperature while assemblages from limestone shores
negatively correlated with temperature and fell along the
macroalgae cover vector

species. Acanthurus triostegus, A. sordidus, and A.
abdominalis are known to recruit to tidepools in
summer months. These species grow quickly and
move to lower pools and onto reefs as they mature
(Randall 2007). Godinho and Lotufo (2010), in Brazil
found sites to differ in intertidal fish assemblages and
similarly suggested this relationship was due to
recruitment differences over a small geographical
scale. Seasonality and recruitment at the assemblage
level has not been studied for intertidal fishes in
Hawaii and no conclusive statements can be made.
Similar to several temperate intertidal environments (Zander et al. 1999; Griffiths et al. 2003), the
tidepool fish assemblages in O`ahu were found to be
vertically structured and these patterns in abundance
are hypothesized to be related to tolerances to harsh
conditions that vary across the shore. Diversity as H’

and species richness did not vary statistically across
the shore but, relatively small within-site sample sizes
likely hindered the ability to detect such differences.
For the island of O`ahu small sized I. zebra were
abundant in high pools while most other species and
larger sized I. zebra occurred in mid and low pools.
This pattern suggests that harsh conditions are found
near shore and that this “high” pool species may have

adaptations or morphological features which allow it
to survive (Nakamura 1976; Horn and Riegle 1981;
Martin 1995; Zander et al. 1999). Indeed another
species of Istiblennius, I. edentulus which emerges
into air in the wild have sense organs suited for
intertidal life and behavioral characteristics that
prevent rapid desiccation (Zander et al. 1999). In
temperate latitudes, temperature, salinity, aerial exposure,
ultraviolet radiation, and wave action are abiotic factors
that often vary with shore height or pool depth (Metaxas
and Scheibling 1992; Denny and Paine 1998; Zander
et al. 1999). Hawaii’s microtidal regime combined
with varying wave heights may alleviate or alter the
type of harsh conditions experienced by tidepool
fishes, especially in the mid to low pools. However,
regardless of microtidal conditions temperature is
likely to be a driving environmental factor in tropical
localities as organisms experience some of the
highest temperatures worldwide.
Biotic conditions, such as predation and competition, can also vary across the shore (Connell 1961)
and can contribute to tidepool assemblages (Zander

et al. 1999). For example, macroalgae that provides
food and shelter for fishes varied in abundance across
the sampled shores. Although herbivory tends to be
more prominent in the tropics (Horn 1989; Floeter
et al. 2005), the diets of many of these tidepool fishes
are not known. In addition, macroalgal cover could be
structured by similar physical factors and be unrelated
to fish distributions. Another biotic condition that can
structure communities is predation. Many have
suggested that tidepools serve as a nursery for
juvenile reef fishes providing a refuge from fish
predators (Gibson and Yoshiyama 1999). Indeed,
juveniles of the coral reef fishes Abudefduf sordidus
and Acanthurus triostegus were common in mid and
low pools. Partitioning through inter-specific competition or by different evolutionary histories could also
result in co-occurring species living in different
habitats (Zander et al. 1999; Davis 2000). On
O`ahu, species within the genus Bathygobius seem
to be partitioned into different zones or shores and
two blennies Istiblennius zebra and Entomacrodus
marmoratus are also distributed in different areas of
the shore (high-mid and mid-low respectively).
Additionally intra-specific competition could account
for the skewed smaller median size of I. zebra in high
pools as intra-competition outcomes usually depend
on body size (Mayr and Berger 1992). It is also likely


Environ Biol Fish (2011) 90:329–342

that other fishes in this study had skewed body sizes
with shore position but this could not be tested with
our current sample sizes.
In conclusion, O`ahu’s tidepool fish assemblage is
represented by high endemism and low species
richness similar in percentage and number to the
general shallow reef fish assemblage in Hawaii.
Additionally, O`ahu’s tidepools are dominated by
taxonomic families found in other tropical localities
(gobiids, blenniids, pomacentrids, and acanthurids).
Assemblages varied spatially among sites, among
shores, and vertically across shores with pool position.
High pool assemblages were the most distinct from low
pools and were dominated by small sized I. zebra. Future
experiments could expand on this study by investigating
1) temporal variation 2) the diets of common species 3)
perform more quantitative measurements of physical
conditions in pools 4) identify species tolerances to
physical conditions and 5) investigate inter-specific and
intra-specific competition.
Acknowledgements We would like to acknowledge Patrick
Aldrich, Ross Langston, and Louise Giuseffi for their assistance
in collection of fishes. In addition we thank Celia Smith for her
guidance and are grateful for the comments from anonymous
reviewers which helped to greatly improve this manuscript.

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Environ Biol Fish (2011) 90:343–360
DOI 10.1007/s10641-010-9745-3

Movement patterns of adult red drum, Sciaenops ocellatus,
in shallow Florida lagoons as inferred through autonomous
acoustic telemetry
Eric A. Reyier & Russell H. Lowers &
Douglas M. Scheidt & Douglas H. Adams

Received: 11 November 2009 / Accepted: 11 November 2010 / Published online: 27 November 2010
# Springer Science+Business Media B.V. 2010

Abstract Acoustic telemetry was employed to resolve

seasonal and daily movement patterns of adult red drum
(Sciaenops ocellatus) in the northern Indian River
Lagoon system, Florida. From May 2006 to September
2008, 44 tagged fish were tracked within an array of 34
autonomous receivers with individuals detected for up
to 654 days. Most red drum exhibited strong site
fidelity from winter through early summer with
movement rates increasing significantly during fall
spawning months. While some fish migrated to the
nearest ocean inlet at this time, the majority remained
within the lagoon year-round suggesting that true
estuarine reproduction, a behavior uncommon or
poorly documented elsewhere is the dominant life
history strategy locally. Diel movement patterns were
also pronounced and indicated changing depth preferences over a 24 h period. Despite a harvest prohibition
on large red drum, long-term estuarine residency
coupled with high angling pressure (41% recapture
E. A. Reyier (*) : R. H. Lowers : D. M. Scheidt
Kennedy Space Center Ecological Program/Innovative
Health Applications,
Mail Code: IHA-300,
Kennedy Space Center, FL 32899, USA
e-mail:
D. H. Adams
Florida Fish & Wildlife Conservation Commission,
Fish & Wildlife Research Institute,
1220 Prospect Avenue #285,
Melbourne, FL 32901, USA

rate in 50 months) suggest that post-release angling

mortality and sub-lethal effects to growth and reproduction may strongly influence the strength of adult
size classes.
Keywords Sciaenidae . Red drum . Estuarine
reproduction . Site fidelity . Diel movement . Acoustic
telemetry

Introduction
The red drum (Sciaenops ocellatus) is a large, long-lived
sciaenid (Pisces: Sciaenidae) which inhabits estuarine
and nearshore coastal waters from Massachusetts to
northern Mexico (Mercer 1984). While juvenile red
drum are largely confined to estuaries, studies in many
areas have concluded that as fish approach maturity at
2–5 years of age, most emigrate to the continental shelf
where they often form neritic migratory schools
(Overstreet 1983; Beckman et al. 1988; Pafford et al.
1990; Ross and Stevens 1992; Murphy and Crabtree
2001). Spawning occurs annually each fall along the
inner shelf, often near tidal passes (Overstreet 1983;
Comyns et al. 1991; Wilson and Nieland 1994; Holt
2008; Lowerre-Barbieri et al. 2008) with larvae recruiting back to estuarine seagrass, tidal creek, and marsh
nurseries (Peters and McMichael 1987; Rooker et al.
1998; Stunz et al. 2002).
In the U.S. South Atlantic and Gulf of Mexico, the
red drum has long been of considerable economic


344

value as the subject of both commercial and

recreational fisheries. By the early 1980s, growing
concern that red drum stocks were being overfished
resulted in the implementation of a suite of
increasingly stringent management actions (ASMFC
2002). These efforts began in state waters with
reductions in recreational landings through the use
of temporary closures and stricter daily bag and size
limits, as well as the eventual elimination of directed
commercial fisheries for the species in most areas.
This was followed by a federal moratorium of all red
drum harvest in the U.S. Exclusive Economic Zone
by 1990. A central assumption underlying both state
and federal management regulations was that a
harvest prohibition of adult red drum would safeguard the spawning stock biomass and help ensure
stable annual recruitment. These and subsequent
efforts have, in fact, allowed for some stock
rebuilding despite a continued expansion in the size
of the recreational fishery (Murphy and Crabtree
2001; Takade and Paramore 2007; Murphy and
Munyandorero 2009). Unfortunately, because red
drum occupying nearshore waters are difficult to
sample, little data are currently available regarding
adult biomass, distribution, or behavior, particularly
in the U.S. South Atlantic. Managers must therefore
rely primarily on indirect estimates of stock health
derived from indices of juvenile abundance within
the estuary (ASMFC 2002), an approach that may
introduce uncertainties which complicate long-term
management of the species.
In recent years, evidence has been gradually

accumulating that some adult red drum also reside
and spawn within the confines of certain estuaries
including Pamlico Sound, North Carolina (Ross
and Stevens 1992; Ross et al. 1995; Marks and
DiDomenico 1996; Luczkovich et al. 1999; Barrios
2004), Savannah River and Altamaha River Estuaries,
Georgia (Nicholson and Jordan 1994; Woodward
1994; Collins et al. 2001), Tampa Bay, Florida
(Murphy and Taylor 1990), and Chandeleur Sound,
Louisiana (Comyns et al. 1991). In the Indian River
Lagoon (IRL) and adjacent Mosquito Lagoon (ML),
Florida, this behavior has been particularly well
documented with conclusive evidence of estuarine
spawning first provided in the late 1980s via the
collection of both ripe individuals and red drum eggs
up to 45 km inside ocean inlets (Murphy and Taylor
1990; Johnson and Funicelli 1991). More recently, an

Environ Biol Fish (2011) 90:343–360

intensive 2 year ichthyoplankton survey consistently
collected preflexion (2–3 mm) red drum larvae up to
90 km away from the nearest ocean inlet from June to
October with average nightly larval densities as high
as 15 per 100 m3 of water (Reyier and Shenker 2007).
Conventional mark-recapture efforts also suggest that
some mature fish are year-round estuarine residents
(Stevens and Sulak 2001; Tremain et al. 2004) as
opposed to transient seasonal migrants from offshore
waters. Nonetheless, these studies have been unable

to resolve whether this estuarine spawning is a
prevailing local strategy or one adopted by a
relatively small fraction of mature fish.
The distinction as to where red drum reside and
spawn is not academic. In estuaries where individuals forego ontogenetically-cued migrations to the
continental shelf, adult fish face challenges to
survival and growth which may not be accurately
accounted for in stock assessments which typically
assume low adult mortality (e.g., Vaughan and
Carmichael 2000). Most critically, given their accessibility to anglers, adult estuarine red drum likely
experience elevated mortality rates relative to their
offshore counterparts due both to post-release
handling stress in the recreational fishery and illegal
harvest. In the ML and northern IRL specifically,
where the species is actively sought after by 75% of
anglers (Holloway-Adkins et al. 2005), adult red
drum schools support an intense year-round trophy
fishery in which they are targeted by anglers on a
daily basis. Estuarine red drum may also suffer sublethal effects on growth and survival in areas
of anthropogenically-degraded habitat and water
quality. Conversely, estuarine sub-populations
should conceivably respond positively to smaller
scale conservation actions which reduce fishing
mortality as well targeted habitat restoration efforts.
As with all estuarine sportfish, a prerequisite to
sound long-term management of red drum at any
spatial scale is to delineate seasonal movement
patterns, degree of fidelity to specific areas, and
locations of any high value spawning sites, the
details of which are difficult to discern from

traditional fisheries-dependant mark-recapture data.
Acoustic telemetry has become an essential tool for
assessing the behavior of coastal fishes although in
the case of adult red drum this technology has been
primarily applied for continuous short-duration
manual tracking studies (Carr and Smith 1977;


Environ Biol Fish (2011) 90:343–360

Aguilar 2003) or intermittent manual relocations over
longer periods (Nicholson and Jordan 1994). Recent
advances in autonomous acoustic systems now
provide the means to track movements of individual
fish over much larger geographic areas and extended
time intervals than has previously been feasible. This
technology is particularly well-suited for coastal
lagoons (like the IRL system) that contain narrow
ocean inlets, internal migratory constrictions, and
other obligate chokepoints where passing fish are
readily detected. In this study, we employ autonomous acoustic telemetry to resolve the seasonal and
daily movement patterns of adult red drum in
estuarine waters of east-central Florida.

Materials and methods
Study region
Red drum movements were studied within Mosquito Lagoon (ML) and the northern terminus of the
Indian River Lagoon (IRL) proper, two of the three
basins (along with the Banana River Lagoon)
comprising the IRL system (Fig. 1). This estuary

is isolated from the Atlantic Ocean by barrier islands
which are breached by only five widely spaced ocean
inlets, the nearest being Ponce Inlet, a natural inlet at
the extreme northern ML and Sebastian Inlet, a
manmade IRL inlet 95 km south of the study area.
ML and the IRL proper are themselves connected
only via Haulover Canal, a 2 km long manmade
canal completed in 1854. The study area lies largely
within the boundaries of Merritt Island National
Wildlife Refuge and Canaveral National Seashore,
both of which manage undeveloped areas of NASA’s
Kennedy Space Center.
The northern IRL system has a mean depth of only
1.5 m with prominent beds of shoal grass (Halodule
wrightii) and manatee grass (Syringodium filiforme)
fringing the lagoon’s shallow margins (Snelson 1983).
The deepest water (>2 m) occurs in the center of
lagoon basins as well as the dredged Intracoastal
Waterway (ICW) navigational channel which runs the
length of the IRL, Haulover Canal, and northern ML.
Due to the narrow width of ocean inlets, lunar tides
are weak, circulation is predominantly wind-driven,
and the water column is vertically mixed (Smith
1987). Waters are typically polyhaline although ML is

345

generally more saline than the IRL proper and can
become hypersaline in some years due to limited
freshwater inflow (Snelson 1983). The regional

climate is subtropical with a warm humid rainy
season from May to October and a cooler dry season
from November to April (Woodward-Clyde 1994).
Acoustic array
The acoustic array established to track red drum
movements consisted of up to 34 submerged Vemco
VR2 receivers, each of which houses an integrated
omni-directional hydrophone and data logger to
autonomously record date/time stamps of nearby
acoustic tags. All receivers were suspended vertically ~1 m off the bottom using screw anchors and
small floats following the protocol adopted from
Heupel and Hueter (2001). Range testing early in
the study suggested a tag detection radius of 800–
1,000 m under ideal conditions although performance is known to vary depending on tag power,
water depth, bottom substrates, sea state, and
receiver biofouling (Heupel et al. 2008). Tag detection data stored by each receiver was downloaded to
a field laptop computer at 1–2 month intervals.
At the inception of the study in May 2006, the
acoustic array consisted of 27 receiver stations, 23 of
which were dispersed in an irregular grid throughout
southern Mosquito Lagoon (Stations M1-M23; Fig. 1).
These stations were spaced 1–2 km apart in relatively
deep water and near the dredged ICW to maximize tag
detection distances. Two stations were also placed in
the IRL proper at the western terminus of Haulover
Canal (Stations I1, I2) to record any fish movements
between these lagoon basins. Northern ML is extremely shallow with over 200 closely spaced marsh islands
(conditions which impedes acoustic tracking) so
receivers were not deployed here except for two
moored within Ponce Inlet (Stations P1, P2) at the

extreme northern ML to detect any red drum emigration into the open Atlantic Ocean. The narrow widths
of Haulover Canal (60 m) and Ponce Inlet (470 m)
appeared to result in near-complete detection of any
red drum exiting ML. In August 2007, we were
informed by local fishing guides that large adult red
drum schools were often observed each fall in the IRL
proper to the northwest of Haulover Canal. In
response, six additional stations (Stations I3–I8) were
deployed here in the event that any tagged fish


346

Environ Biol Fish (2011) 90:343–360

Fig. 1 Map of the Mosquito Lagoon (ML) and Northern Indian River Lagoon (IRL) study area, east-central Florida. ML receiver
stations are numbered M1-23, IRL stations I1-8, and Ponce Inlet stations P1-3. Stars indicate red drum collection/release locations

eventually utilized this area. An additional station was
also placed in the ICW 16 km south Ponce Inlet (P3) to
document any estuarine-ocean migrations with better
resolution. Once installed, all receivers remained in
place until the termination of the study in September
2008.

Red drum collection and tagging
A total of 44 large red drum [749–1,125 mm fork
length (FL)] were collected within the southern half
of ML from May 2006 to June 2007 with most taken
at three schooling locations known to many local

Environ Biol Fish (2011) 90:343–360

fishermen (Fig. 1). Twenty-one fish were taken using
a 549 m trammel net after visually locating schools so
as to simultaneously capture and tag schoolmates.
Due to difficulty finding schools on certain dates,
especially in 2007, fish were also obtained with a
914 m longline (n=16), hook-line donations from
anglers (n=6), and a 183 m gill net (n=1). No
collections were attempted from August through late
October to avoid any tagging-induced changes in
spawning behavior. Red drum are not sexually
dimorphic so sex was not determined and maturity
state was not conclusively assigned. Murphy and
Taylor (1990), however, estimated through histological techniques that 50% maturity for IRL red drum
occurs at 511 and 900 mm fork length (FL) for males
and females, respectively. Fish tagged for this study
averaged 953 mm FL suggesting that most animals
were mature at the time of capture or would become
so by the onset of the next fall spawning season. All
fish exceeded the 457–685 mm (18–27″) total length
slot size in Florida and were not legally harvestable.
After collection, fish were transferred to a 125-L
onboard aerated tagging cooler where they were
anesthetized in a 75 mg L−1 tricaine methanosulfonate
water bath (MS-222, Western Chemical Inc.). Once
sedated, each fish was placed ventral side up in a
padded mesh cradle, 5–7 scales were removed, and a

25 mm incision was made parallel to the ventral
midline, 2–3 cm anterior to the anus. A coded
acoustic transmitter (Vemco V16-5 H, 40–114 s. ping
interval, 36 g in air) with an estimated battery life of
474 days was inserted into the peritoneal cavity and
the incision was then closed with 2–3 absorbable
sutures and cyanoacrylate tissue adhesive (Vetbond™,
3 M Corporation). Transmitter weight averaged 0.3%
of fish weight and never exceeded 0.8% of fish
weight. Each fish was then measured (FL), weighed
(kg), and fitted with an external dart tag (Hallprint Pty
Ltd) which offered a small reward ($10 equivalent) in
case of later angler recapture. Fish were allowed to
recover in a circular 600-L onboard flow-through
livewell until equilibrium and normal swimming was
regained (typically 30–60 min) and then released at
the capture site.
Movement analyses
The presence/absence of each tagged fish was
recorded daily with data used to determine its overall

347

time at liberty within the acoustic array (i.e., days
between date of release and date of last detection).
Scatterplots of this detection data were constructed to
visually interpret: (1) temporal residence patterns
within, and timing of any movements out of ML for
all tagged fish, and (2) detailed spatio-temporal
movement patterns for several representative individuals. Receiver stations were widely spaced so fish

were rarely within range of more than one station at
any time and considerable gaps (hours to days)
commonly occurred between sequential detections.
Consequently, exact fish position was often unknown
and accurate home range sizes could not be estimated.
As an alternative metric of assessing seasonal changes
in red drum movement, the number of unique stations
each fish visited was tallied for each month it was at
liberty within the array. To then formally test whether
this “activity space” varied throughout the year,
monthly values were averaged for all fish and
grouped into: (1) a March-June pre-spawning season,
(2) a July–October spawning season, or (3) a Nov-Feb
post-spawning season, and compared using a one-way
ANOVA (α=0.05) followed by a Tukey HSD posthoc test. The July–October spawning season was
defined using previous reports from the IRL of either
gravid adults (e.g., Murphy and Taylor 1990) or eggs
and preflexion larvae (Johnson and Funicelli 1991;
Reyier and Shenker 2007) collected during these
months. Mean values were first log transformed to
meet assumptions of normality and homogeneity of
variances (Sokal and Rohlf 1995). Year itself was not
considered a factor because the study spanned only
one complete (plus two partial) years.
The relationship between activity space (i.e., mean
stations visited per month) and seasonal fluctuations
in water temperature or salinity was determined using
a Pearson’s Product Moment Correlation. Water
temperature data was averaged from a USGS gage
inside Haulover Canal (Station No. 02248380)

and submersible temperature loggers (Onset Hobo
Stowaways) secured to three widely spaced ML
receivers. Salinity data was provided by the St. John’s
River Water Management District from readings taken
twice monthly at two fixed sites in ML and one in the
northern IRL proper. For all seasonal analyses, only
data recorded from the original 27 receivers (P1-2,
M1-23, I1-2) was used in order to ensure data
interpretability throughout the study. Fish tracked less
than 1 month were also excluded from consideration


348

as were any detects past a tags guaranteed 474 day
life span, after which tag power and detection range
gradually declined.
Several fish made excursions from ML to the IRL
proper via Haulover Canal or to Ponce Inlet during
fall. This timing may indicate directed movements to
preferred spawning locations. Since red drum reproduction is thought to peak during new and full moons
both locally (Johnson and Funicelli 1991) and in other
regions (Peters and McMichael 1987; Comyns et al.
1991), a G-Test was employed to assess whether
movements out of ML occurred disproportionately
during a specific lunar phase (new, first quarter, full,
last quarter). Further, a one-way ANOVA was used to
compare the sizes of fish (at time of capture) that
moved to Ponce Inlet to those which moved into the
IRL or remained in ML.

Daily variation in detection rates were displayed
graphically by summing total detections of all fish
into 24 1-hr bins (e.g., 12:00–12:59, 13:00–13:59),
irrespective of season. Periods of the day with high
detection rates were assumed to signify times when
red drum were utilizing deeper water where most
receiver stations were established. Day length
varies seasonally so detections were further classified as morning crepuscular (sunrise +/−1 h), day,
evening crepuscular (sunset +/−I hr), or night with a
G-Test used to determine whether fish were detected
more or less than expected during these periods. Finally,
to assess periodicity in diel movement (i.e., whether red
drum visited locations randomly or at recurring time
intervals), a Fourier analysis was performed using MS
Excel. Fourier analysis is a type of harmonic analysis
which decomposes time series data into the sum of its
sinusoidal components and can allow cycles in movements (if any) to be identified. Data were drawn from
nine fish (nos. 33–41) tagged from a single school in
April 2007 and repeatedly detected for several weeks
duration at Station M10. Total position detects for these
fish were summed hourly for 4,096 continuous
h (171 days), the maximum allowed by the software.

Results
Duration of estuarine residence
Forty-four red drum were tagged with releases
divided fairly evenly between 2006 (n=20) and

Environ Biol Fish (2011) 90:343–360

2007 (n=24). A total of 432,356 valid position detects
were recorded from May 2006 until September 2008
with a mean time at liberty within the acoustic array
(± 1 S.D.) of 271 (± 193) days (Table 1). The greatest
time at liberty (fish no. 17) was 654 days and a total of
12 red drum were regularly detected for a year or more.
A further ten individuals were tracked for several
months before disappearing from within the array
(Fig. 2), suggesting either natural or fishing-related
mortality inside the estuary (although tag expulsion or
failure cannot be entirely discounted). Only 11 red
drum were observed leaving ML without returning;
four fish were last detected within the IRL proper after
passing through Haulover Canal and seven individuals
apparently emigrated to the open Atlantic Ocean via
Ponce Inlet.
Seasonal movement patterns
During both pre-spawning (March–June) and postspawning (November–February) periods, most
tagged red drum demonstrated strong site fidelity,
visiting on average only 2.1 and 2.9 stations per
month, respectively, usually those nearest their
release location (Fig. 3a; Table 2). Several fish,
most notably those tagged in extreme southern ML
early in the study, often went undetected for
intervals of several weeks. However, intermittent
detections of these individuals also occurred at a
small number of stations near release points,
suggesting they too maintained site fidelity during
this time, albeit to locations outside the range of any
receiver. School fidelity during these periods was

also strong. In general, fish tagged together from a
single school were repeatedly detected together for
several weeks or months. Thirty-four red drum were
tracked through at least a portion of one spawning
season (July–October). Activity space increased
markedly during these months with fish visiting a
mean of 5.8 stations per month, significantly more
than either pre- or post-spawning periods (one-way
ANOVA, F= 11.9, 25 df, p <0.001). The largest
activity space was observed in September 2006
(mean of 11.1 stations visited) and again in
September 2007 (7.1 stations visited). This increase
in movement was not significantly correlated with
either regional water temperature (Pearson’s Correlation, r =0.288, p= 0.153) or salinity (r= −0.205,
p= 0.315).


Environ Biol Fish (2011) 90:343–360

349

Table 1 Summary information for all 44 red drum tracked
within Mosquito Lagoon and the northern Indian River Lagoon
from May 2006 to September 2008. Days at Liberty equals the
number of days between date of release and date of last
Fish
No.

Release
Date

Tag
Code

Fork Length
(mm)

Weight
(kg)

1

5/24/06

2720

995

2

5/24/06

2721

1,125

3

5/24/06

2722

1,040

10.6

4

5/24/06

2723

940

9.1

5

5/24/06

2724

965

10.1

6

5/24/06

2725

971

7

5/24/06

2726

958

8

5/24/06

2727

1,050

9

5/24/06

2728

950

10

5/24/06

2729

1,070

11

5/24/06

2730

12

6/22/06

13

6/22/06

14
15

detection. Percentage of days detected includes only those days
under the 474 day guarantee to battery life. Last Known
Location categories include Mosquito Lagoon (ML), the Indian
River Lagoon proper (IR), and Ponce Inlet (PI)
Days at
Liberty

% Days
Detected

Total
Detects

Stations
Visited

Last Known
Location

11.0

415

23

5,851

13

ML

13.0

517

20

8,275

15

ML

162

30

821

13

ML

0

0

0

0

ML

505

37

12,304

14

ML

11.8

25

28

135

1

ML

9.9

5

20

4

1

ML

12.1

28

36

153

2

ML
ML

8.9

517

18

2,198

13

13.7

316

11

5,106

10

ML

941

9.2

124

30

2,624

18

PI

2731

995

12.8

0

0

0

0

ML

2732

987

11.0

569

50

8,315

13

ML

6/22/06

2733

1,010

13.1

2

100

886

3

ML

6/22/06

2734

990

12.1

2

100

55

1

ML

16

6/22/06

2735

1,048

12.4

100

86

5,225

11

IR

17

6/22/06

2736

1,035

13.8

654

68

19,287

14

ML

18

6/22/06

2738

986

11.8

521

54

10,008

10

ML

19

10/30/06

2737

750

4.4

241

33

2,173

4

ML

20

10/30/06

2739

760

4.8

335

83

15,386

8

PI

21

1/4/07

0121

1,105

15.7

295

5

182

6

IR

22

1/4/07

2740

920

9.2

363

18

1,542

17

ML

23

1/23/07

0120

1,005

11.2

345

41

13,496

13

ML

24

1/30/07

1881

980

11.3

550

81

17,136

10

ML

25

1/30/07

1882

809

5.9

230

62

6,889

19

PI

26

1/30/07

1883

816

6.5

273

37

6,544

7

PI

27

2/5/07

1884

929

9.0

356

95

47,968

13

ML

28

2/5/07

1885

1,107

15.6

31

94

7,514

5

ML

29

2/5/07

1886

1,099

16.7

210

9

3,313

5

ML

30

2/5/07

1887

1,041

13.7

3

100

625

4

ML

31

2/5/07

1888

1,044

13.9

550

93

68,432

8

ML

32

4/1/07

1889

998

13.7

304

80

46,925

10

IR

33

4/23/07

0027

766

5.6

281

33

1,540

11

ML

34

4/23/07

1890

1,110

16.8

478

91

23,054

11

ML

35

4/23/07

1891

1,120

14.2

499

85

27,469

20

ML

36

4/23/07

1892

855

6.6

335

61

4,269

11

ML

37

4/23/07

1893

850

38

4/23/07

1894

1,100

39

4/23/07

1895

40

4/23/07

1896

41

4/23/07

1897

6.5

146

72

4,130

10

PI

15.5

262

92

21,608

15

ML

749

5.1

499

29

5,319

6

ML

792

6.3

159

45

3,733

12

IR

846

6.7

281

19

2,226

9

ML


350

Environ Biol Fish (2011) 90:343–360

Table 1 (continued)
Fish
No.

Release
Date

Tag
Code

Fork Length
(mm)

42

5/4/07

1898

791

43

5/4/07

1899

803

44

6/4/07

1900

750

Mean

953

Weight
(kg)

Days at
Liberty

% Days

Detected

Total
Detects

5.3

179

57

4,179

15

PI

5.1

124

1

2

1

ML

113

86

15,455

8

PI

271

50.3

9,826

9.3

NR
10.6

Despite an increase in activity each fall, a singular
movement pattern or direction of travel was not
observed and red drum which were previously associated in the same schools dispersed widely. Nine fish
were never detected leaving ML during this time.
Sixteen fish, while also residing primarily in ML,
undertook a combined 86 round trip excursions through
Haulover Canal into the IRL proper and back from July
through October of 2006 and 2007 (Fig. 4). Movement
of some individuals was pronounced; fish no. 34 made
17 ML-IRL proper round trips between September and

October 2007; fish no. 13 performed eight round trips
from July–October 2006 and an additional 15 from
July–October 2007. Three of the four red drum which
permanently exited the array via the IRL proper (nos.
16, 21, and 40) also did so at this time. While only two
stations (I1-2) were established in the IRL proper
during the first year of the study, the mean duration of
stay for fish visiting this area (± 1 S.D.) was only 4.7
(± 11.1) days suggesting that most remained nearby
and did not undertake long distance movements to
other ocean inlets. This assumption was reinforced
following installation of six additional IRL stations
(I3-8) in August 2007 which confirmed that most fish
leaving ML via Haulover Canal ranged widely
throughout the expanded array but remained within
the northern IRL proper before returning to ML. There
was little evidence that red drum gathered at a discrete
location in the IRL proper (as suggested by fishing
guides to occur near Station I4; Table 2) but
individuals which remained in the estuary throughout
fall often returned to locations they frequented prior to
the start of the spawning season, indicating some
degree of philopatric behavior (Fig. 5).
Seven red drum were observed emigrating to the
open Atlantic Ocean via Ponce Inlet and were not
detected again, all of which did so in either September
2006 (n=1) or September–October 2007 (n=6). An
additional two fish (nos. 27 and 41) moved to Ponce

Stations

Visited

Last Known
Location

Inlet in September 2007 but returned to southern ML
after 3 and 32 days, respectively. Movements out of
ML via Ponce Inlet were often rapid. Fish no. 42, for
example, swam 39 km from Haulover to Ponce Inlet
in 18.4 h (2.1 km·hr−1; Fig. 5). Excursions from ML
to either the IRL proper or Ponce Inlet occurred
equally across all lunar phases (G-Test, Gadj =3.1,
3 df, p=0.41). Unexpectedly, fish which left the array
via Ponce Inlet averaged only 832 (± 67) mm FL,
significantly smaller than those which remained
within the estuary throughout the study (one-way
ANOVA, F=7.3, df=33, p<0.01). Sizes of fish which
remained wholly within ML (1,004±107 mm FL) vs.
those which also utilized the IRL proper (976±
119 mm FL) did not differ.
Angler recaptures independently supported the notion that many red drum were long term estuarine
residents. Eighteen of 44 tagged red drum (41%) were
reported recaptured by local anglers as of July 2010
(with one fish recaptured twice) with returns 8 to 1,465 d
after release (mean=433 d). Local fishing guides
informally reported at least seven additional recaptures
of our fish near original tagging sites but without
supporting information. Except for one fish recaptured
at Ponce Inlet, all tag returns were from ML. Most
notably, three fish at liberty in excess of 3 years (red

drum nos. 2, 7, and 28) were recaptured at the exact
location they were originally tagged. Nine recaptured
fish were detected moving within the array soon after
angler release indicating they were not post-release
mortalities. One expired acoustic tag (ID unreadable)
was reported as found near a roadside pond 8 km to the
east of (and not connected to) the IRL proper. This fish
was likely poached with remains discarded at this site.
Diel movement patterns
Diel variability in activity was also readily discernable. Red drum were detected more during the night


Environ Biol Fish (2011) 90:343–360

351

Fig. 2 Scatterplot depicting timing and location of detections and angler recaptures of all 44 adult red drum between May 2006 to
September 2008. Angler recaptures after termination of acoustic tracking (September 2008) are not shown


352

Environ Biol Fish (2011) 90:343–360

Fig. 3 a Mean number (± 1 SE) of receiver stations visited by tagged red drum during each month of the study. Dashed lines delineate the
July–October spawning season in east-central Florida; b associated water temperature and salinity during the study timeline

and morning crepuscular period and less during the day
and evening crepuscular period (G-Test, Gadj =15,401,
3 df, p<0.001) with peak detections occurring from

05:00–09:00 and fewest detections from 14:00–18:00
(Fig. 6). Further, results from a Fourier analysis using
4,096 continuous h (171 day) of detection data from
nine schooling red drum revealed a strong cyclical
activity pattern around Station M10 with a periodicity
of 23.95 h (Fig. 7). Neither weekly cycles (possibly
resulting from elevated angling-induced behavioral
changes on weekends) nor monthly (i.e., lunar) cycles
were apparent.

Discussion
This study serves as the first behavioral assessment of
adult red drum using autonomous acoustic telemetry
anywhere within the species range and has allowed
resolution of seasonal movement patterns with detail
unobtainable using traditional mark-recapture or short
duration manual tracking efforts. While the large area
of interest and relatively wide receiver spacing
prohibited strict quantification of home range size,
our findings clearly demonstrated that mature red
drum in Mosquito Lagoon exhibited strong site