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Long-term and short-term underwater visual censuses using SCUBA, technical Nitrox, and closed circuit rebreathers (CCR) were carried out in Pohnpei, Micronesia, to define spatial and temporal dynamics within a semi-protected multi-species epinephelid (fish) spawning aggregation (FSA) of brown-marbled grouper, Epinephelus fuscoguttatus, camouflage grouper, Epinephelus polyphekadion, and squaretail coralgrouper, Plectropomus areolatus. Results identified species-specific patterns of habitat use, abundance, residency, and dispersal of FSAs. Fish spawning aggregations formed and dispersed monthly within a 21–160-d period after winter solstice within adjacent yet distinct outer reef habitats. The reproductive season coincided with periods of seasonally low sub-surface seawater temperature. Peaks in density varied among species both within the calendar year and relative to the winter solstice. Significant long-term declines in FSA density were observed for all three species, suggesting population-level fishery-induced impacts, similar to those previously reported for E. polyphekadion. Differences in density estimates were also observed between dive gear, with a threefold difference in densities measured by CCR for E. polyphekadion versus SCUBA that suggest a disturbance effect from exhaled SCUBA bubbles for this species. CCR also allowed surveys to be conducted over a larger area in a single dive, thereby improving the potential to gauge actual abundance and density within FSAs. Based on these findings, a combination of long-term and intensive short-term monitoring strategies is recommended to fully characterize trends in seasonal abundance and habitat use for aggregating species at single or multi-species FSA sites. Inherent variations in the timing and distribution of species within FSA make fine-scale temporal management protocols less effective than blanket protective coverage of these species at (e.g., marine protected areas covering FSAs and adjacent migratory corridors) and away from (i.e., temporal sales and catch restrictions) FSA sites.
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1 23
Coral Reefs
Journal of the International Society for
Reef Studies
ISSN 0722-4028
Volume 33
Number 3
Coral Reefs (2014) 33:765-775
DOI 10.1007/s00338-014-1172-z
Spatial, temporal, and environmental
dynamics of a multi-species epinephelid
spawning aggregation in Pohnpei,
K.L.Rhodes, R.S.Nemeth, E.Kadison &
1 23
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Spatial, temporal, and environmental dynamics of a multi-species
epinephelid spawning aggregation in Pohnpei, Micronesia
K. L. Rhodes R. S. Nemeth E. Kadison
E. Joseph
Received: 22 September 2013 / Accepted: 16 May 2014 / Published online: 1 June 2014
ÓSpringer-Verlag Berlin Heidelberg 2014
Abstract Long-term and short-term underwater visual
censuses using SCUBA, technical Nitrox, and closed cir-
cuit rebreathers (CCR) were carried out in Pohnpei, Mi-
cronesia, to define spatial and temporal dynamics within a
semi-protected multi-species epinephelid (fish) spawning
aggregation (FSA) of brown-marbled grouper, Epinephelus
fuscoguttatus, camouflage grouper, Epinephelus polyph-
ekadion, and squaretail coralgrouper, Plectropomus areol-
atus. Results identified species-specific patterns of habitat
use, abundance, residency, and dispersal of FSAs. Fish
spawning aggregations formed and dispersed monthly
within a 21–160-d period after winter solstice within
adjacent yet distinct outer reef habitats. The reproductive
season coincided with periods of seasonally low sub-sur-
face seawater temperature. Peaks in density varied among
species both within the calendar year and relative to the
winter solstice. Significant long-term declines in FSA
density were observed for all three species, suggesting
population-level fishery-induced impacts, similar to those
previously reported for E. polyphekadion. Differences in
density estimates were also observed between dive gear,
with a threefold difference in densities measured by CCR
for E. polyphekadion versus SCUBA that suggest a
disturbance effect from exhaled SCUBA bubbles for this
species. CCR also allowed surveys to be conducted over a
larger area in a single dive, thereby improving the potential
to gauge actual abundance and density within FSAs. Based
on these findings, a combination of long-term and intensive
short-term monitoring strategies is recommended to fully
characterize trends in seasonal abundance and habitat use
for aggregating species at single or multi-species FSA sites.
Inherent variations in the timing and distribution of species
within FSA make fine-scale temporal management proto-
cols less effective than blanket protective coverage of these
species at (e.g., marine protected areas covering FSAs and
adjacent migratory corridors) and away from (i.e., temporal
sales and catch restrictions) FSA sites.
Keywords Epinephelidae Fish spawning aggregations
Pacific Ocean Technical diving Fisheries management
Fish spawning aggregations (FSAs) are relatively common
and often spectacular events that characterize the reproduc-
tive life history of a number of tropical groupers (Epinep-
helidae) (Sadovy de Mitcheson and Colin 2012). In some
locales, FSAs form as part of a much larger multi-species
FSA complex, with some sites used by several species, often
within overlapping reproductive sites and seasons (e.g.,
Heyman and Kjerfve 2008; Rhodes et al. 2013). Often pre-
dictable in time and space, grouper (Epinephelidae) and
other FSAs are frequent targets of fishing, with impacts
ranging from negligible to severe, depending on fishing
pressure, FSA size, and species (Coleman et al. 1996; Sala
et al. 2001; Rhodes et al. 2011; Sadovy de Mitcheson and
Colin 2012). In severe cases of FSA fishing, aggregations
Communicated by Biology Editor Dr. Stephen Swearer
K. L. Rhodes (&)
The University of Hawaii at Hilo, Hilo, HI 96720, USA
R. S. Nemeth E. Kadison
Center for Marine and Environmental Studies, The University of
the Virgin Islands, St. Thomas, USVI 00802-9990, USA
E. Joseph
Conservation Society of Pohnpei, Kolonia, Pohnpei, FM 96941,
Coral Reefs (2014) 33:765–775
DOI 10.1007/s00338-014-1172-z
Author's personal copy
have been removed entirely (e.g., Aguilar-Perera 2006;
Manghubai et al. 2011), have become sexually skewed, or
have suffered declines in fecundity sufficient enough to
hinder population persistence (Levitan and McGovern 2005;
Sadovy and Domeier 2005). In such cases, if it occurs,
reproductive populations may require years to decades to be
restored (Nemeth 2005; Hamilton et al. 2011). Because of
their predictability and resultant vulnerability to overfishing,
managers have in recent years focused on FSA protection
through monitoring and management, including spawning
site protection and catch or sales closures during reproduc-
tive periods, as examples (Russell et al. 2012), however these
have met with mixed success (Nemeth et al. 2006; Mang-
hubai et al. 2011; Rhodes et al. 2011).
Throughout much of the Indo-Pacific, brown-marbled
grouper (Epinephelus fuscoguttatus), camouflage grouper
(Epinephelus polyphekadion), and squaretail coralgrouper
(Plectropomus areolatus) often co-aggregate (as paired or
combined species) and spawn in multi-species FSAs (e.g.,
Johannes et al. 1999; Rhodes and Sadovy 2002). The
marbled grouper, Plectropomus punctatus, replaces P.
areolatus in the western Indian Ocean (Robinson et al.
2008). FSA formation and spawning for these species is
generally seasonal and tied to specific lunar periods.
This species complex is one of the most common among
Indo-Pacific multi-species FSAs and is one of the most
favored among fisheries (Sadovy 2005). Within their
respective ranges, these species are targeted both at and
away from FSA sites for commercial and subsistence use,
including by the southeast Asian live reef food fish trade
(Sadovy et al. 2003). In some areas, the vulnerability of FSA
to continued fishing has resulted in various types of moni-
toring to examine population status and abundance trends,
including underwater visual census (UVC; e.g., Rhodes et al.
2012). However, detecting changes in population status
through UVC is both challenging and time-consuming, since
FSAs are known to be highly dynamic in time and space and
temporally variable across regions (e.g., Colin 1992; Rhodes
and Sadovy 2002). Moreover, monitoring often requires
high resource inputs to detect and verify fishery-induced
change over longer time spans (Colin 2012). Thus, deter-
mining how, when, and where to monitor is challenging.
The Kehpara Marine Sanctuary (KMS) in Pohnpei,
Micronesia, provided an ideal location to examine the
challenges of monitoring and managing multi-species FSA
sites. The monitoring program at the KMS has focused on
the P. areolatus,E. polyphekadion, and E. fuscoguttatus
FSA complex for 13 yr, which are among the largest
recorded in the region (Rhodes and Sadovy 2002). Baseline
data on their reproductive seasonality and distribution has
been reported separately for each of these species (Rhodes
and Sadovy 2002; Rhodes et al. 2012,2013). Herein, we
present a unique series of data to illustrate short- to long-
term changes in the number and distribution of these spe-
cies on a daily, monthly, and annual basis. Seasonal FSA
density is presented against both the Gregorian calendar
and winter solstice and in relation to sub-surface water
temperatures. Annual density estimates are shown to
highlight changes in the reproductive population within the
FSA sites over the 13-yr monitoring period. These com-
bined estimates demonstrate how changes to monitoring
regimes (i.e., selected times, gears, locations) can affect the
interpretation of population trends and impact management
decisions. We discuss the findings in relation to develop-
ment of monitoring regimes and regional FSA management
improvement. Herein, reproductive seasonality refers to the
seasonal duration of aggregation formation. Actual
spawning times have only been shown for E. polypheka-
dion at the study site (Rhodes and Sadovy 2002) and no
direct observations of spawning have been made. Some
details of monthly aggregation formation, in terms of
individual(s) monthly arrival and dispersal times within the
reproductive season, are discussed herein, or in prior work
detailing these events (i.e., Rhodes and Sadovy 2002;
Rhodes and Tupper 2008; Rhodes et al. 2012).
Establishing reproductive seasonality, density,
and temperature at the FSA
The spatial and temporal patterns of abundance and density
of E. fuscoguttatus,E. polyphekadion, and P. areolatus
were examined at a multi-species grouper FSA site within
the KMS (N06°48.15, E158°06.71), Pohnpei, Micronesia
(Fig. 1). To examine long-term trends in density and the
effectiveness of the KMS in maintaining FSA reproductive
populations, we used a 13-yr UVC dataset compiled by the
Conservation Society of Pohnpei (CSP). To identify the
reproductive seasonality and lunar timing of aggregation
formation for each species, UVC on open-circuit (OC) air
(SCUBA) was first conducted semi-monthly before new
and full moons for 16 consecutive months (2001–2002),
followed by focused surveys around the full moon from
January 2003 through May 2004. Due to budget con-
straints, UVC was then reduced to full moon periods in
March and April (2005–2013). To identify periods of peak
density relative to the winter solstice (as days after winter
solstice, ‘‘DAWS’’), data from 2001 to 2004 were used,
since counts in these years were made both monthly
throughout the year or seasonally, allowing an unbiased
representation of actual density peaks.
The placement of four fixed transects by CSP in 2001
followed an extensive examination of FSA boundaries.
Based on these initial assessments, the depth and location
766 Coral Reefs (2014) 33:765–775
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of the four transects were placed in a manner to cover both
the FSA core (area of highest density) and staging areas
(areas of lower density; see Nemeth 2012 for FSA area
sub-divisions). All fixed belt transects were 110 m long
(360 ft) with transect width and depth determined by the
spatial characteristics of each species’ aggregation
(Table 1). A total of five dives were made on OC SCUBA
by CSP, one dive along each of the transects at 30 m (all
species) and two dives with different depth ranges along
the 15 m transect for P. areolatus (Table 1). One transect
was placed at 30 m depth within each of the E.
polyphekadion and E. fuscoguttatus FSAs, while two at 15
and 30 m were placed in the P. areolatus FSA. Analyses of
long-term changes in FSA density included all monitoring
years (2001–2013). As total FSA area was only surveyed in
2001, transect density (and not abundance) is presented
herein from fixed transect UVC using OC air SCUBA.
To examine temperature profiles relative to the repro-
ductive season, water temperatures were taken hourly from
December 21, 2009 to February 18, 2010, using an Onset
HOBO Water Temp Pro 2.0
(Onset Computer Corp.,
Cape Cod, MA, USA) moored on the reef flat at the upper
edge of the P. areolatus aggregation.
Daily FSA habitat partitioning, abundance and density
Assessment of FSA habitat and abundance use was initi-
ated in March 2010 by conducting timed drift dives on OC
air along the 30-m-deep contour, while towing a surface
float mounted with a Garmin 76
GPS (Garmin Interna-
tional, Inc., Olathe, Kansas, USA). However, dramatic
changes in current speed along the wall during the UVC in
March 2010 prevented accurate mapping across the FSA
site. Based on these initial constraints, it was determined
that accurate assessments of daily abundance, density, and
habitat use by these species at this site required prolonged
diver surveys. As a result, a series of dives using technical
Nitrox (32 % bottom mix and 50 % decompression mix;
OC Nitrox) and closed circuit rebreathers (CCR; Megal-
, Innerspace Systems Corp, Centralia, Washington,
USA) were made between March 8, 2011 and March 19,
2011, (i.e., 11 days before full moon, DBFM, to full
moon). Logistic constraints prevented diving on 12 (7
DBFM) and 20 March (1 day after full moon, DAFM),
while one of two datasheets was lost during boarding on 18
March (1 DBFM). Data for 18 March reported herein
represent a projected value, based on the abundance ratios
(wall: slope) recorded for the species from combined pre-
vious dives.
In 2011, dives were conducted along a single 1,500-m
transect at 30-m depth that encompassed the entire length
of the FSA for all three species. The transect, which started
Fig. 1 Map of Pohnpei, Federated States of Micronesia (FSM)
showing the location of the Kehpara Marine Sanctuary (polygon),
Kitti Municipality, where the multi-species grouper spawning aggre-
gation occurs. Municipal boundaries are designated by bars
Table 1 UVC regimen for Epinephelus fuscoguttatus (Ef), Epinephelus polyphekadion (Ep), and Plectropomus areolatus (Pa) based on peak
timing of abundance and depth distributions
Species Lunar timing (DBFM) Transect depth (m) Depth range (m) Dive # Transect size Survey area (m
Ef 5 30 21–43 1 110 930.5 3,355
Ep 4 30 21–43 3 110 930.5 3,355
Pa 5 15 \15 2 110 915.2 1,672
4 15 15–30 4 110 915.2 1,672
3 30 30–43 5 110 924.4 2,684
Total survey area for P. areolatus is 6,028 m
. DBFM =days before full moon
Coral Reefs (2014) 33:765–775 767
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600 m north of the most seaward point of the reef and
continued 900 m to the south of this promontory, was
divided into thirty 50-m segments using 20-cm-diameter
sub-surface polystyrene buoys tethered to the reef wall.
During technical dive counts, divers maintained a position
in the water column approximately 5 m from the wall and
reef substrate below to minimize interference with fish
behavior and improve fish detection potential. Diver 1
counted fish from the transect line up along the reef wall,
while Diver 2 counted fish from the transect line down
along with reef wall and slope. Both divers recorded all fish
observed within their respective views within each 50-m
segment. Visibility for all dives was [30 m, allowing
divers to conduct counts ca. 20 m out from each side of
transect and estimate densities and abundances within each
Changes in inter-annual species-specific densities were
tested using an analysis of variance (a=0.05) for a simple
linear regression following Shapiro–Wilk’s testing for
normality (Sigmaplot Version 12, San Jose, CA, USA).
Finally, the relationship between body length, area, and
density, respectively, was tested using a Pearson’s Product
Moment Correlation (a=0.05).
Reproductive seasonality (OC Air), density,
and temperature
Based on 2001–2013 UVC monitoring, each species
aggregated and dispersed monthly over a 3- to 5-month
reproductive season (Fig. 2a), with highest density over
two consecutive months. Peak density varied among spe-
cies. The reproductive season for P. areolatus was shown
to occur from late January (first arrival =26 DAWS) to
mid-May (last departure =143 DAWS) with peak density
from 91 to 120 DAWS (39.5 % of all density; Fig. 2b). E.
fuscoguttatus aggregated within a 5-month reproductive
season that began in January (first arrival =25 DAWS)
and ended in May (last departure =141 DAWS). For E.
fuscoguttatus, peak density was 91-120 DAWS, when
49.7 % of all density was observed. For both E. fusco-
guttatus and P. areolatus, peak density occurred in April.
In contrast, the E. polyphekadion reproductive season las-
ted ca. 80 d overall, beginning in February (first arri-
val =53 DAWS) and ending in April (last
departure =131 DAWS). E. polyphekadion typically
aggregates (and disperses) over only two consecutive
months in a given year. In contrast to the other two species,
E. polyphekadion density peaked 61–90 DAWS, when
56 % of all density was recorded, which coincided with
March (Fig. 2a). For all species, all individuals disperse
monthly within the reproductive season following pre-
sumed spawning on or around full moon (but see Rhodes
and Tupper 2008).
Water temperature at the site (2009 only) ranged from
28.6 ±0.1 (21–160 DAWS) to 30.0 ±0.1 °C (241–270
DAWS; Fig. 2a). The reproductive season for all three
species coincided with seasonal low water temperatures
(28.6 ±0.1 and 29.0 ±0.1 °C), with minor variations in
monthly temperatures during the respective peaks for the
three species.
Long-term FSA density trends
Between 2001 and 2013, significant declines in fish density
were noted within all three FSAs (Fig. 3). For both E. fu-
scoguttatus (Fig. 3a) and E. polyphekadion (Fig. 3b),
densities were 75 % lower in 2013 than 2001; however, the
significance of the decline was weak [power (1 -b)=80]
for both species (E. fuscoguttatus: adj. R
0.05 (1),1,12
=6.79, p\0.01; 1 -b=0.63; E. polyph-
ekadion: adj. R
=0.413; F
=9.44, p\0.05;
1-b=0.75). For P. areolatus, a 69 % decline in density
was observed between 2001 and 2013 (adj. R
=2.88, p\0.01; Fig. 3c). For P. areolatus,
density declines were also noted among transects within
the FSA, with fish density in the shallow transect (B15 m)
trending to zero by 2013 (Fig. 4). Density within the 13-yr
monitoring period was highest for all three species in either
2004 or 2005 before long-term declines were initiated.
March abundance patterns (CCR and OC Nitrox)
UVC of the KMS-based multi-species grouper FSA in
March 2010 and 2011 revealed inter-annual and inter-
specific variability in aggregation build-up and peak
abundance values (Fig. 5). At the start of surveys, E. fu-
scoguttatus was already present in large numbers, 6 and 11
DBFM in 2010 and 2011, respectively (Fig. 5). Highest
abundance of E. fuscoguttatus in 2010 (n=1,019) and
2011 (n=1,671) occurred 1 DBFM and on full moon,
respectively. E. fuscoguttatus departed the FSA in 2010
with only 16 fish remaining 1 DAFM; however, in 2011,
fish were still present in large numbers the day of full moon
(Fig. 5).
E. polyphekadion was largely absent from the FSA site
in March until 3 DBFM in 2010 and 4 DBFM in 2011. In
2010, E. polyphekadion abundance increased over a 25-h
period from 20 (1,400 h) to 680 fish (1,215 h) before
peaking at 1,854 fish 3 h later (1,515 h). Similarly, in 2011,
numbers increased sixfold from 479 (4 DBFM) to 2,985
fish over a 48-h period (Fig. 5). In 2010, 77 E. polyph-
ekadion remained 1 DBFM, with 0 fish 0 DAFM, whereas
in 2011, 1,250 fish were still present on the day of full
768 Coral Reefs (2014) 33:765–775
Author's personal copy
moon. Similar variability was also identified for P. areol-
atus (Fig. 5). Peak abundance for P. areolatus in 2011
occurred 4 DBFM (83 DAWS), when 3,046 fish were
A comparison of gear types (OC air and CCR) showed
species-specific differences in the magnitude of grouper
density estimates. Densities between CCR and OC air (5
DBFM) on fixed transects were roughly similar for E. fu-
scoguttatus between the two methods, although still 1.3
times higher on CCR (OC air =43 fish 1,000 m
CCR =55.6 fish 1,000 m
). In contrast, for E. polyph-
ekadion, densities (4 DBFM) were ca. three times higher
on CCR (53.2 fish 1,000 m
) than on OC air (18.8 fish
1,000 m
), possibly in relation to disturbance caused by the
bubbles from open air systems. For P. areolatus, compar-
isons were not possible, since OC air counts occurred over
2 d on OC air versus 1 d on CCR. Counts on CCR also did
not incorporate shallow water (reef flat) areas.
FSA area, habitat partitioning, and fish density
UVC monitoring in 2011 identified distinct species-specific
spatial area usage, distribution, and habitat partitioning
(Table 2). The P. areolatus FSA was largest in area, with a
distribution of ca. 700 m predominantly south of the
promontory inflection and extending from ca. 15 to ca.
50-m depth, and included the reef flat, wall, and slope. The
E. fuscoguttatus FSA occupied a smaller area horizontally,
with a distribution of ca. 600 m along the reef to the north
of the promontory inflection, and from 25 to 70 m depth,
while the E. polyphekadion FSA was smallest and extended
along ca. 250 m of reef horizontally and from ca. 25 to at
least 60 m depth. Both E. fuscoguttatus and E. polyph-
ekadion FSAs included only wall and slope habitats. Only
minor overlap was observed between adjacent FSAs
(Fig. 6), where E. polyphekadion overlapped ca. 200 m at
its northern boundary with E. fuscoguttatus and over ca.
100 m with the P. areolatus to the south.
Core areas, defined as areas with the highest density,
were confined to the center portions of each FSA (Fig. 6).
Based on 2011 CCR data, fish densities within each FSA
were negatively correlated with fish size, both within the
core (r
=0.149, p[0.05) and within each FSA
=0.165, p[0.05). Conversely, body length was
positively correlated to both FSA (r
p[0.05) and core area (r
=0.171, p[0.05).
Daily changes in FSA habitat use and abundance
Technical dives in 2011 found several hundred E. fusco-
guttatus and P. areolatus present at the FSA site when
surveys began, with species distributed in non-overlapping
areas (Fig. 6a). During subsequent surveys, only minor
spatial changes occurred within these two FSAs; however,
abundance increased daily until the presumed spawning
and dispersal. For the E. fuscoguttatus FSA, increases in
abundance occurred mostly from 8 to 5 DBFM (Figs. 5b,
6c–e). For the P. areolatus FSA, only a slight variation in
Density (# Fish 1000m-2)
Mean (SE) Density
(# Fish 1000m-2)
Fig. 2 Mean (±SE) density
counts (2001–2013) of
Epinephelus fuscoguttatus (gray
bars), Epinephelus
polyphekadion (white bars), and
Plectropomus areolatus (black
bars) during athe calendar year
and bdays after winter solstice
(DAWS; 30-d intervals).
Seasonal FSA formation
coincided with seasonal lows in
sub-surface (12-m depth) mean
monthly ±standard deviation
(SD) water temperature (°C)
(December 21, 2009 to February
18, 2010). Density peaks for all
three species approximate the
period from mid-March to mid-
Coral Reefs (2014) 33:765–775 769
Author's personal copy
Mean (SE) Density (# Fish 1000 m-2)
Fig. 3 Mean ±standard error
(SE) density counts for
aEpinephelus fuscoguttatus,
bEpinephelus polyphekadion,
and cPlectropomus areolatus
recorded during Conservation
Society of Pohnpei monitoring
(2001–2013). Linear regression
analyses identified significant
declines for all three species.
Regression lines are bounded by
95 % confidence (dashed line)
and prediction (solid line) bands
Mean (SE) Density (# Fish 1000 m-2)
Fig. 4 Mean (±SE) density
counts for P. areolatus
(2001–2013) by monitoring
depth along fixed transects at
the KMS. All declines were
significant (a=0.05), with
densities on the shallow-water
transect at or approaching zero
in recent years (2008–2013).
Monitoring depths:
[30 m =triangles;
15–30 m =open circles;
\15 m =closed circles
770 Coral Reefs (2014) 33:765–775
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the FSA core location was noted as it shifted northward as
presumed spawning approached (Fig. 6a–g). P. areolatus
abundance peaked 4 DBFM (Figs. 5b, 6h), and by the day
of full moon, almost all individuals had departed (Figs. 5b,
6i). Among the three species, E. polyphekadion showed the
most dramatic spatial patterns as abundance increased
100-fold over the 5-d period leading up to full moon
(Figs. 5b, 6d–h). From 5 to 3 DBFM, E. polyphekadion
were distributed along 600 m as fish moved from the south
into the FSA core area of ca. 250 m. By full moon
(Fig. 6i), E. polyphekadion were only observed within the
core and along a 100-m section of reef.
Spatio-temporal FSA dynamics
This study provided a unique spatial and temporal assess-
ment of a multi-species FSA site in Pohnpei and highlighted
the benefits of both consistent long-term UVC monitoring
and intensive short-term surveys. These surveys achieved
three important outcomes by (1) demonstrating the utility of
technical dive monitoring to conduct fine-scale spatial
mapping of FSA distribution, density, and abundance; (2)
confirming the highly synchronized, yet variable, aggrega-
tion formation among key commercial species; and (3)
documenting long-term and significant declines of the three
epinephelid FSAs, all while encompassed within a marine
protected area and regulated at the market by a partial sea-
sonal sales ban (1 March to 30 April).
Distinct habitat partitioning was observed among the
three co-aggregating groupers, particularly during the seven-
day period around the full moon (6–0 DBFM). Spatial use by
groupers at multi-species FSA sites has been reported for
only a few locations (Colin and Clavijo 1988; Johannes et al.
1999; Heyman and Kjerfve 2008; Robinson et al. 2008;
Hamilton et al. 2012). In Palau, the distribution of this same
suite of groupers was mapped in detail at two FSA sites
located within two reef passes (channels), which differed in
size and location (see Fig. 2.6 in Nemeth 2012). In the larger,
wider, and deeper channel, groupers were spatially segre-
gated across different depths and habitats, and showed
minimal overlap, similar to the KMS FSA site. In the nar-
rower of the channels, however, the P. areolatus FSA
overlapped considerably with both E. polyphekadion and E.
fuscoguttatus FSAs, similar to that reported from a FSA site
in the Seychelles where both E. polyphekadion and E. fu-
scoguttatus overlap within a 7,700 m
reef area (Robinson
et al. 2008). Although such studies are few, these early results
suggest that preferred habitats exist within FSA sites, par-
ticularly those that may be space limited and that certain fine-
scale physical and oceanographic conditions are required for
FSA formation and persistence, particularly within core
areas (e.g., Molloy et al. 2012).
In Pohnpei, P. areolatus, E. polyphekadion, and E. fu-
scoguttatus each displayed distinctive patterns of aggre-
gation formation, including the duration of the reproductive
Fig. 5 Temporal abundance of
Epinephelus polyphekadion
(squares), Epinephelus
fuscoguttatus (circles), and
Plectropomus areolatus
(triangles) at the Kehpara
Marine Sanctuary relative to the
number of days before full
moon (DBFM) using adrift
diving techniques on OC air
SCUBA (2010) and bCCR and
OC Nitrox technical diving
(2011) techniques
Coral Reefs (2014) 33:765–775 771
Author's personal copy
season(s), residency times during each lunar spawning
period, and timing of arrival, aggregation formation, and
departure from the KMS. Similar to other regional FSAs
(e.g., Johannes et al. 1999; Hamilton et al. 2012), repro-
ductive seasons were longest for P. areolatus (ca. 120 d)
and E. fuscoguttatus (ca. 120 d), and shortest for E. po-
lyphekadion (ca. 80 d). Within each monthly lunar cycle,
maximum residency time at the FSA site was [12 d for E.
fuscoguttatus, 11 d for P. areolatus, and 7 d for E. po-
lyphekadion prior to dispersal from the site. For E. fusco-
guttatus and E. polyphekadion, residency times in Pohnpei
were most similar to those reported earlier by Robinson
et al. (2008) for the Seychelles. In contrast, using acoustic
telemetry Bijoux et al. (2013) reported average residency
times from 6 to 23 d for E. fuscoguttatus and 8 to 14 d for
E. polyphekadion, with longer durations associated with
the first aggregation period of the reproductive season.
These findings confirm prior reports of regional variation in
reproductive seasonality and residency times among this
trio of aggregating groupers (e.g., Johannes et al. 1999;
Rhodes and Sadovy 2002) and support the need for con-
tinued research to understand the dynamics of these species
and examine changes that might be linked to fisheries and
environmental impacts, such as climate change.
Methodological comparisons
This current study highlighted the strengths and weak-
nesses of different survey methods. While CCR produced
higher (and possibly more accurate) estimates than
SCUBA, the inherent cost and the logistical difficulties
associated with CCR in developing country settings pre-
sents a barrier to its use. This is particularly true where
local monitoring teams are solely responsible for con-
ducting UVC, and capacity and funding are limited. In
these environments, it is evident from the current study that
OC air SCUBA can still provide essential data for man-
agement decision-making. However, the study also showed
the benefits of CCR in deepwater settings, particularly
where multi-species FSAs form over an extensive stretch of
reef that requires extended dive times. Specifically, CCR
estimates of E. polyphekadion were three times higher than
on SCUBA, while differences in density estimates for E.
fuscoguttatus, although 1.3 times higher on CCR, were
minor. CCR also allowed surveys over a larger area, with
greater estimation of total population density. These dif-
ferences demonstrate the impact of SCUBA exhaust on the
behavior of some species. Regardless of the methodology,
results clearly demonstrate the need for multi-day moni-
toring to identify actual peaks in abundance (and density),
and to reduce the potential for errors, particularly given the
high variability that occurs seasonally, daily, and hourly
within FSAs. Whenever possible, a combination of
Table 2 FSA parameters for E. fuscoguttatus (Ef), E. polyphekadion (Ep), and [Plectropomus areolatus (Pa)] within the Kehpara Marine Sanctuary
Species Max. length
(cm TL)
range (m)
distance (m)
FSA total FSA core Avg. # of fish (max #) Avg. density (max density)
Distance from
Distance (m)
Total area Core Total FSA
(#/100 m
(#/100 m
Ef 79
25–70 45 0–600 N 600 27,000 5–7 100 4,500 1,567 (1,671) 840 (1,075) 5.8 (6.2) 18.7 (23.9)
Ep 55
20–50 30 200 N–50 S 300 9,000 9–11 100 3,000 1,184 (2,985) 759 (1,743) 13.2 (33.3) 25.3 (58.1)
Pa 67
15–50 35 150 N–550 S 700 24,500 13–15 100 3,500 1,972 (3,046) 669 (1,100) 8.0 (12.4) 19.1 (31.4)
These areas were used to calculate the average density of groupers within total FSA and core areas for March 2011
Rhodes et al. (2012)
Rhodes, fishery-dependent sample, KMS FSA 1999
Purchased fish, Pohnpei market, 2006. N =north, S =south
772 Coral Reefs (2014) 33:765–775
Author's personal copy
techniques should be employed; however, the methods
used should conform to informational and management
needs. Estimates of long-term change in abundance were
hindered in the current study by a failure to re-examine
FSA areas on an annual (or monthly) basis. Thus, moni-
toring programs are advised to incorporate total FSA area
estimates annually (or monthly), particularly where total
abundance counts are reliant on FSA area sub-sampling.
No data for coralgrouper
Number of fish
Numbered Bouys
fm2 dbfm
3 dbfm
6 dbfm 5 dbfm 4 dbfm
9 dbfm 8 dbfm10 dbfm
0.3 0.60.15
(a) (b) (c)
Fig. 6 Daily changes in abundance of Epinephelus fuscoguttatus
(green), Epinephelus polyphekadion (pink), and Plectropomus areol-
atus (blue) beginning 10 days before full moon (DBFM) to full moon
from CCR monitoring. No data were taken 7 DBFM, and P. areolatus
data were absent from counts 2 DBFM. Abundance circles for
individual species are offset to show buoy (yellow circles) placement
along the seaward edge of the reef. The white arrow represents the
promontory inflection point
Coral Reefs (2014) 33:765–775 773
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Fishery impacts and management
Long-term monitoring revealed significant declines in FSA
density that appeared to be initiated in 2004 or 2005, which
coincided with a relaxation of regular patrols by enforce-
ment agencies at the KMS. Prior to the abandonment of
continuous enforcement efforts at the site, FSAs had shown
overall improvements (2001–2005); however, those were
quickly erased when relaxation of vigilant monitoring and
enforcement occurred, as shown elsewhere (e.g., Claro
et al. 2009; Mangubhai et al. 2011). Although the current
study cannot directly link fishing impacts to the observed
long-term declines at KMS, short-term population-level
fishery impacts have previously been identified for E. po-
lyphekadion (Rhodes et al. 2011). For E. polyphekadion,
comparative changes in the linear extent of the FSA were
also noted between earlier surveys (1998–1999) and the
current study (2011). Specifically, Rhodes and Sadovy
(2002) first reported a horizontal distribution of 500 m for
E. polyphekadion; however, CCR surveys in 2011 found
the FSA to be limited to 250–300 m. Depth distribution
over this monitoring period was consistent. Finally,
unpublished findings from E. polyphekadion acoustic tag-
ging showed individuals arriving at the FSA site 6.6 ±0.5
DBFM (mean ±SE) and departing on the full moon or 1
DAFM, which roughly coincides with the seven-day resi-
dency time documented during CCR UVC in 2011. Inter-
estingly, in 1998 and 1999 residency times of 10–12 d
were reported for E. polyphekadion at KMS (Rhodes and
Sadovy 2002) when heavy FSA fishing pressure was first
observed (Rhodes et al. 2011). The combined observations
indicate fishery-induced changes in reproductive behavior
for this species. While suggestive evidence of fishery
impacts is less for the other two aggregating species,
densities of P. areolatus within the uppermost transect,
where fish are most accessible to nighttime spearfishing,
have declined to nil (Fig. 4). These combined findings
suggest FSA fishing may be at least partly contributing to
the noted declines.
The value of UVC data taken from long-term and
intensive monitoring assessments is clearly useful in
guiding monitoring programs and management. For multi-
species FSAs like those within the KMS, greater moni-
toring efforts are required to understand the temporal and
spatial complexities among aggregating species, including
the vulnerability and area usage of reproductively active
fish outside FSAs (Rhodes and Tupper 2008; Nemeth
2012). For example, at Gladden Spit, Belize, groupers were
identified as aggregating between December and April,
while snappers (Lutjanidae) tend to use the site primarily
from April to September (Heyman and Kjerfve 2008). In
the Cayman Islands, multi-species FSAs formed at the
same general location and within the same period;
however, actual spawning times varied among species
relative to the lunar cycle (Whaylen et al. 2004). For a
number of species examined to date, specific reproductive
migratory corridors and staging areas also provide fishing
opportunities and are deserving of investigation and man-
agement consideration when establishing area protection
(e.g., Nemeth et al. 2007; Starr et al. 2007; Rhodes et al.
Findings from this and past studies provide clear evi-
dence for the need of effective management that protects
reproductively active grouper at and away from FSA sites
due to their high inherent vulnerability to overfishing
(Coleman et al. 1996; Beets and Friedlander 1998; Man-
gubhai et al. 2011; Rhodes et al. 2011). In Pohnpei, sig-
nificant declines in the densities of each of the three
aggregating grouper species and population-level changes
to E. polyphekadion size, age, and fecundity have been
identified (Rhodes et al. 2011). These impacts demonstrate
that current management in Pohnpei, which includes both
area protection at the FSA site and a seasonal sales ban
during part of the reproductive season are insufficient.
Given the apparent decline of these species, additional
management tools, such as species-specific catch and sales
bans that match known reproductive season are warranted,
along with stronger enforcement of existing area provi-
sions. Based on current trends, a failure to improve mon-
itoring, enforcement, and management will likely lead to
the imminent demise of these multi-species FSAs, which
were once considered the largest in the region.
Acknowledgments Funding for the research (March 2010–2011)
and technical diving equipment was provided by a NOAA Saltonstall-
Kennedy Kennedy Grant (NA09NMF4270068) and the Lana Vento
Charitable Trust to RN. Funding for CSP was provided by the US
Department of Interior. RN and EK were partially supported by the
Virgin Islands Experimental Program to Stimulate Competitive
Research (VI-EPSCoR #NSF-814417). This is contribution # 97 to
the University of the Virgin Islands’ Center for Marine and Envi-
ronmental Studies. Thanks to M Viti, K Ainslie, W Hawley, S Mal-
akai and D Mathias for technical dive support. Logistic support was
provided by Pohnpei State Department of Lands and Natural
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... However, due to the dynamic nature of SAs, both in space and in time, and the often difficult field conditions where they occur, the assessment of aggregations by UVC methods typically involves logistic and design challenges regarding accuracy/precision, temporal and geolocation elements. Such constraints are evident from studies on these, as well as other, grouper species over the last few decades (e.g., Hamilton and Matawai, 2006;Hamilton et al., 2011;Heppell et al., 2012;Sadovy de Mitcheson and Colin, 2012;Rhodes et al., 2014;Nanami et al., 2017). For example, often the SA is too large, includes inaccessible depths, or the fish are too numerous and moving too quickly for UVC surveys to cover the entire aggregation area or to count all fish. ...
... Over 30 published studies have considered aspects of the spawning aggregations of these species with researchers using varying methods to assess their spatial and temporal dynamics. To date, most studies of the trio comprised surveys that sub-sampled the aggregation area rather than covered the entire aggregation site; none considered both density and total abundance in the same study (e.g., Johannes et al., 1999;Rhodes and Sadovy, 2002;Hamilton and Matawai, 2006;Robinson et al., 2008;Golbuu and Friedlander, 2011;Hamilton et al., 2011Hamilton et al., , 2012Rhodes et al., 2013Rhodes et al., , 2014Hughes et al., 2020). In these studies, the areas sub-sampled were usually where fish were most highly concentrated, usually referred to as 'core' areas, with boundary areas and one or more depth ranges sometimes also included. ...
... For example, variation in the day leading up to a particular moon phase when fish numbers peak, and in the actual time of spawning (which is usually brief), may result in a biased assessment of temporal change if only a single day is surveyed because peak days vary unpredictably between months, between species and among years (Colin et al., 2013). However, due to logistical constraints (e.g., limiting times/areas surveyed), many studies conduct surveys on assumed peak days, whether it be 1 or 2 days in key lunar months, effectively sub-sampling by time (e.g., Golbuu and Friedlander, 2011;Hamilton et al., 2011;Rhodes et al., 2014;Hughes et al., 2020). Other studies may cover a greater number of days, three or more, in each aggregation period, but even these could miss the peak day if timing of peak periods varies substantially (Rhodes and Sadovy, 2002;Hamilton et al., 2012;Bijoux et al., 2013;Rhodes et al., 2014). ...
Full-text available
Groupers (Family Epinephelidae) are valuable and vulnerable reef-associated fishes. Medium to large-sized Indo-Pacific genera, such as Epinephelus and Plectropomus, are important in local/international trade, and are particularly susceptible to overfishing due to their economic value, longevity, late maturation and, for some species, aggregation-spawning. Three species, Plectropomus areolatus, Epinephelus polyphekadion, Epinephelus fuscoguttatus, are threatened (IUCN Red List) and, when exploited on their aggregations, typically undergo declines unless managed. To effectively assess spawning aggregation status and identify changes over time following fishing or management, a robust sampling protocol is essential. This was developed and tested at a protected, but previously depleted, spawning site shared by these three species in Palau, western Pacific. Underwater visual census (UVC) tracked changes in fish abundance (numbers) across their aggregation site between 2009 and 2019. Census data on abundance and density were complemented by additional technologies to generate a more complete picture of this aggregation site and the three species, including stationary cameras to monitor fish with divers absent, stereo-video to measure fish lengths, and oceanographic instruments to measure variability in currents and water temperature. Results show that protection outcomes depend on biology and on active enforcement and that UVC survey design must adequately address temporal/spatial variability to effectively document changes in fish abundance. Over the decade-long study, P. areolatus, the fastest-maturing species, showed a near fourfold increase in peak annual abundance (increasing from annual peak numbers of c.450 to 1,800 fish), followed by a more modest increase in E. polyphekadion (increase from c.500 to at least 600 fish and a twofold density increase) and relative stability in the slowest maturing, longest-lived species, E. fuscoguttatus (stable between approximately 300 and 450 fish). The study highlighted need for caution when fish density is used as a proxy for abundance in studies when entire aggregations cannot be surveyed, because the two measures may not be correlated at higher abundances. The results clearly show the need for robust sampling design and that effective protection contributes to recovery of depleted spawning aggregations.
... Throughout the central and western Pacific coral reef communities are becoming increasingly devoid of once-common fish species important to ecosystem maintenance, e.g., Green humphead parrotfish (Bolbometopon muricatum) and iconic species that contribute to local economies through eco-tourism, e.g., Humphead wrasse (Cheilinus undulatus) (e.g., Hensley and Sherwood, 1993;Dalzell et al., 1996;Houk et al., 2012). Perhaps more troubling is the demise throughout the region of fish spawning aggregations for some of the main target species of coastal commercial fisheries (e.g., Rhodes et al., 2014a). The causes for these impacts are typically broad and often interconnected, and include natural, economic and anthropogenic effects, such as under-valued target species (e.g., Rhodes et al., 2011a), human population increase, common (open) access or proximity to fishing grounds (e.g., Kaunda-Arara et al., 2003), fishing (Jennings and Polunin, 1997;DeMartini et al., 2008), commercialization (e.g., Brewer et al., 2009), sedimentation from terrestrial activities (e.g., Edinger et al., 1998;Victor et al., 2006), destruction of nursery habits (e.g., nearshore corals, seagrass beds and mangroves) (e.g., , targeting of spawning aggregations (e.g., Sadovy de Mitcheson et al., 2008;Rhodes et al., 2011b) and extreme weather events and climate change (Knowlton and Jackson, 2008). ...
... In Pohnpei, Rhodes et al. (2014b) used socio-economic and market data to show that Pohnpei's inshore fishery is well above biocapcity (i.e. consumption is outstripping production), while Rhodes et al. (2014a) show year-over-year declines in spawning aggregations of some of the most important target species. Thus, there are clear indications throughout much of the FSM of a troubling trend in fisheries that will undoubtedly impact future socio-economic and food security. ...
... In 2015, catch volumes increased from February to July relative to other K.L. Rhodes et al. Fisheries Research 204 (2018) 156-164 months, which coincides with the peak spawning season identified for all coral reef fish species examined in Pohnpei to date (Rhodes et al., 2014aTaylor et al., 2014). ...
In Pohnpei, Micronesia, a 10-year (2006–2015) follow-up market survey was conducted to provide the basis for a comparative assessment of the status of the commercial inshore fishery, to inform management and to identify the most relevant management options. Within this timeframe, marketed coral reef fish volumes declined by 50 mt (ca. 20%), the use of unsustainable fishing methods (nighttime spearfishing and small-mesh gillnets) increased from 75.5% to 81.9%, and catch-per-unit-effort decreased from 3.4 ± 0.1 to 3.2 ± 0.4 kg h⁻¹ fisher¹. Simultaneously, the economic return as price per unit effort was nearly halved for all gear types. Trip volumes increased, however, this was paralleled by a rise in the average number of fishers per trip, particularly for nighttime spearfishing. Effort shifted from inner to outer reef areas and further away from high fisher density communities. At the family level, increases in the percentage of lower tropic level catch were observed, with herbivores and planktivores increasing in frequency in catch more than other trophic level fishes. The only weight increase among top carnivores was for epinephelids, however this was accompanied by a greater contribution by juveniles for the most commonly targeted grouper, Camouflage grouper, Epinephelus polyphekadion. Among fish families, eight epinephelids were absent in catch in 2015 compared to 2006, with additional species observed in speared catch in 2015 that were absent in 2006. To reverse continuing declines and prevent the potential for fisheries collapse, government needs to institute rights-based management, ban the use of nighttime spearfishing and small-mesh gillnets, and improve existing enforcement within marine protected areas and markets.
... Previous research has examined the life histories of both E. polyphekadion and P. areolatus, including age-based reproductive life history (Hughes, 2017;Rhodes et al., 2011Rhodes et al., , 2013, spawning seasonality (e.g. Hamilton et al., 2012;Hughes et al., 2020;Rhodes & Sadovy, 2002), and the spatial and temporal dynamics of FSA formation (Hamilton et al., 2012;Hughes, 2017;Hughes et al., 2020;Rhodes et al., 2013Rhodes et al., , 2014Rhodes & Sadovy, 2002). Based on the available data, both E. polyphekadion and P. areolatus are functionally gonochoristic species with the potential for sexual transition (Hughes, 2017;Rhodes et al., 2011Rhodes et al., , 2013. ...
... Pohnpei (Rhodes et al., 2014). In other regional locales, however, temperature profiles during reproductive periods vary. ...
... In spite of overall declines, a few private landowners and communities have made some progress towards conserving resources in localized areas. , few of which are known to form FSA. For those that do, FSA form from January to May, with peaks during March and April (Rhodes et al., 2014), including for E. polyphekadion and P. areolatus (Table 2). Owing to the lengthy spawning season, the ban allowed FSA fishing in non-ban periods of FSA formation, resulting in a market glut in groupers, massive spoilage and continued declines in FSA abundance. ...
1. Camouflage grouper, Epinephelus polyphekadion (Bleeker, 1849), and squaretail coralgrouper, Plectropomus areolatus (Rüppell, 1830), are commercially important medium-bodied groupers that aggregate at specific sites and times to spawn and are highly vulnerable to fishing during these events. Populations of both species are in decline globally, such that management specifically targeting these species is warranted. 2. A 12-month fish market survey in Chuuk, Federated States of Micronesia, provided an opportunity to examine age-based reproductive life history of these two groupers and assess whether current management acts to conserve them. Life history characteristics of both E. polyphekadion and P. areolatus include a functionally gonochoristic sexual pattern and rapid growth particularly during early life history. 3. P. areolatus demonstrated early maturity (2.8 years) and a relatively brief lifespan (10 years), while delayed maturity (4.5 years) and higher longevity (25 years) was shown for E. polyphekadion. The spawning seasons for E. polyphekadion and P. areolatus were 2 and 3 months, respectively, which fall entirely within the January–April grouper sales, catch, and export ban period for Chuuk. Marketed catch included 22% E. polyphekadion and 15% P. areolatus juveniles, suggesting that size limits may aid in the conservation of these species. 4. Findings from this and recent grouper life history studies suggest that the current 4-month ban in Chuuk be applied only to grouper species known to reproduce during these months to minimize economic impacts to fishers and market owners, and prevent shifts in fishing pressure to more vulnerable species, such as those with low population turnover times, slow growth, or late maturity. Size limits for catch, sale and export are also warranted as an additional management option.
... Globally, there are numerous examples of decreases in spawning populations due to excessive targeting and catch at FSAs [9,[10][11][12][13][14]. Heavy fishing on the FSAs of some species, such as the Critically Endangered (CR) Nassau grouper (Epinephelus striatus) [15], has led to several aggregations becoming economically extinct, with other historical aggregations fully extirpated [10,[16][17]. ...
... Globally, there are numerous examples of decreases in spawning populations due to excessive targeting and catch at FSAs [9,[10][11][12][13][14]. Heavy fishing on the FSAs of some species, such as the Critically Endangered (CR) Nassau grouper (Epinephelus striatus) [15], has led to several aggregations becoming economically extinct, with other historical aggregations fully extirpated [10,[16][17]. Globally, these declines have come from a combination of small-scale, large-scale and subsistence fishing [13,[18][19][20][21][22][23], including the Southeast-Asia live reef food fish trade that target FSAs throughout the Indo-Pacific [17]. ...
... In the Central and Western Pacific, three grouper species [brown-marbled grouper, Epinephelus fuscoguttatus (Forsskål, 1775); camouflage grouper, E. polyphekadion (Bleeker, 1849); squaretail coralgrouper, Plectropomus areolatus (Rüppell, 1830)] commonly form multi-species FSAs that overlap temporally during at least a portion of their respective spawning seasons and in areas proximate to each other [13,[18][19][24][25]. The timing and location of most FSAs is common knowledge among fishers who have traditionally depended on them for subsistence and, more recently, small-scale commercial interests, including for domestic export [23,[26][27]. ...
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Globally, groupers (Epinephelidae) that form fish spawning aggregations (FSAs) are highly vulnerable to overfishing and often require site-specific approaches to management. Over 5-years (2009–2013), we conducted underwater visual censuses (UVC) at a well-known spawning site at Njari Island, Gizo, Western Province, Solomon Islands, that supports aggregations of squaretail coralgrouper (Plectropomus areolatus), camouflage grouper (Epinephelus polyphekadion) and brown-marbled grouper (E. fuscoguttatus). Findings show that while there were species-specific variations in the duration and timing of the spawning season, aggregation densities peaked from March to June, representing the main spawning season for all three species. For P. areolatus, gonad analysis from samples taken from 2008 to 2011 confirmed reproductive activity in support of density trends observed through UVC. Over the 5-year UVC monitoring period, FSA densities declined for P. areolatus and E. polyphekadion. Conversely, following the first year of monitoring, E. fuscoguttatus densities increased. These inter-specific differences may reflect variable responses to fishing as shown elsewhere, or for example, differences in recruitment success. In response to known declines in FSAs of these species, in 2018 the Solomon Islands government placed a nationwide ban on these species’ harvest and sale between October and January. As this study shows, this ban does not encompass the peak aggregation period at Njari and will offer limited protection to other FSAs of these species that are known to vary in reproductive seasonality across the Solomon Islands. A more biologically meaningful and practical management strategy would be to implement a nationwide ban on the harvest and sale of these groupers each month between full and new moons when these FSAs form consistently throughout the country. Since effective management of FSAs typically requires a combined approach, spatial management that protects both spawning sites and reproductive migratory corridors is warranted.
... Fish spawning aggregations (FSA) represent critical life history phases for a number of coral reef fishes [1] and serve as biological hotspots that provide food and nutrients to marine organisms across a wide trophic spectrum [2][3][4][5][6][7]. In many locales, FSA are multi-species and may be comprised of 100s or 1000s of individuals [8][9][10], thus representing a rapid and substantial increase in biomass and nutrient flow within areas used as spawning sites. Since FSA are spatially and temporally predictable, they are highly attractive to both fishers who can extract high catch volumes over brief time periods [11][12][13] and to marine organisms that gain from the elevated food and nutrients available during these events [14]. ...
... Similar to the use of MPAs for sharks, the results of small-scale MPAs for FSA have been mixed. In Pohnpei, Micronesia, year-over-year declines in fish density have continued inside a small-scale MPA meant to protect spawning grouper [10]. In contrast, improvements in fish density have been shown for MPA-protected FSA in Papua New Guinea [46]. ...
... Within the state, there are currently 16 small-scale no-take marine reserves ranging in coverage from 0.34 km 2 to 41.4 km 2 (mean = 7.4 km 2 ; median = 2.1 km 2 ); however, most are poorly enforced [10,60], including the Kehpara Marine Sanctuary (KMS) (Fig 1). The KMS was established in 1999 to protect seasonal spawning aggregations of camouflage grouper, Epinephelus polyphekadion (Bleeker 1849; VU A2bd), brown-marbled grouper, Epinephelus fuscoguttatus (Forsskål 1775; VU A2bd+4bd), and squaretail coralgrouper, Plectropomus areolatus (Rüppell 1830; VU A2bd) ( ...
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Fish spawning aggregations (FSA) act as biological hotspots that concentrate food and nutrients across a broad trophic spectrum. In Pohnpei (Federated States of Micronesia), 20 female grey reef sharks (Carcharhinus amblyrhynchos) were acoustically tagged at two multi-species grouper (Epinephelidae) FSA to examine the likelihood that these mesopredators utilize FSA as a seasonal food source. Both FSA sites are within small-scale MPAs, thus providing a secondary opportunity to examine their conservation potential during these ephemeral events. Shark movement and residency was gauged against known spatial and temporal grouper reproductive patterns using an array of 15 and 50 acoustic receivers at Ant Atoll and Pohnpei (Island), respectively. Activity space was investigated using Kernel Density estimates of individual sharks, and residency indices (RI) were analyzed based on daily and monthly occurrence at the array. Three distinct residency patterns were identified: transient, semi-transient, or resident (Daily RI <0.40, >0.40 to 0.80, or >0.80, respectively). Generalized linear mixed models (GLMMs) were used to identify biological and environmental factors influencing shark activity space, including month, temperature, shark size, spawning month, and residency pattern. Findings revealed significant changes in average monthly residency indices and kernel densities during spawning months in support of an opportunistic foraging strategy around FSA. Monthly residency was higher during spawning months among semi-resident and transient sharks, while average monthly activity space was concentrated around FSA. Best-fit models for the GLMM indicated that activity spaces were most influenced by month and grouper spawning month. Seven of 20 sharks demonstrated inter-island movement and wide variations in individual movement and spatial requirements were shown. The concentration of sharks and groupers at unprotected FSA sites increases their vulnerability to fishing and supports the need for combined area and non-area management measures to effectively protect these species.
... In many aggregationforming grouper species, including Epinephelus polyphekadion (the camouflage grouper), individuals make extensive seasonal migrations to form large spawning aggregations at specific locations (Colin, Shapiro, & Weiler, 1987;Nemeth, 2005;Nemeth, Blondeau, Herzlieb, & Kadison, 2007;Rhodes, McIlwain, Joseph, & Nemeth, 2012;Sadovy, Rosario, & Román, 1994). The camouflage grouper is a gonochoristic species (Rhodes, Taylor, & McIlwain, 2011) that inhabits coral reefs (Heemstra & Randall, 1993) and forms large (100-1000s of individuals) transient FSAs at specific times and places (Rhodes, Nemeth, Kadison, & Joseph, 2014;Rhodes & Sadovy, 2002b, 2002aRobinson, Aumeeruddy, Jörgensen, & Öhman, 2008). Within their distributional range, the timing of camouflage grouper FSAs varies with respect to their lunar and seasonal periodicity, with spawning typically occurring at either a new or a full moon (Rhodes & Sadovy, 2002b). ...
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Passive acoustic monitoring (PAM) is a non‐invasive technique that uses hydrophones to monitor populations and ecosystem dynamics. Although many applications of PAM have been developed in recent years, it has never been used to identify a calling marine species. The south pass of Fakarava Atoll, French Polynesia, hosts spawning events of many reef fish species, including the camouflage grouper Epinephelus polyphekadion, with a spawning aggregation abundance exceeding 17 000 individuals during the full moons of June and July. The current study aimed to use PAM to distinguish camouflage grouper sounds among the vocal activities of all fish recorded during the aggregation periods. Audio recordings analysis resulted in the identification of 29 sound types, some of which showed diel and lunar patterns. Temporal analysis of these sounds in relation to spawning activities allowed the identification of camouflage grouper calls. These calls can be described as a single pulse or a series of ‘boom(s)’ with a pulse duration of ~44 ms and a low dominant frequency of 103 ± 31 Hz. Video recordings show that the camouflage grouper produces the ‘booms’ to initialize spawner ascent and to promote synchronous gamete release into the water column. The study highlights for the first time that PAM can be used to identify the previously unknown sound of a fish species. Moreover, we can use it to understand the phenology of some biological activities for improving the resolution of fish biodiversity assessments.
... Research on the MCEs of Pohnpei State is sparse, with the little conducted mostly confined to shallower depths (<30 m) (e.g., Rhodes et al. 2005Rhodes et al. , 2008Rhodes et al. , 2014aGolbuu et al. 2008;Muir and Wallace 2016). Muir and Wallace (2016) reported low-light, "deepwater" scleractinian coral assemblages in the shallow (10-20 m depth) lagoon of southwest Pohnpei. ...
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The mesophotic coral ecosystems (MCEs) of the Senyavin Islands (Pohnpei Island, and neighboring atolls Ant and Pakin) in the Federated States of Micronesia have received little research attention until recent years. These vibrant, environmentally dynamic ecosystems harbor a reservoir of biodiversity, with species and interactions new to science. Depths of ≥90 m have up to 20 °C annual variance. A strong El Niño event in 2016 resulted in a bloom-forming cyanobacteria smothering the upper MCEs of Pohnpei (25–65 m). Conditions persisted into 2017 with extensive coral bleaching and reef degradation with associated smothering by bloom-forming cyanobacteria and algae in the shallows. The initial bloom signature of 2016 at depth may, therefore, serve as a projected indicator of shallow reef health. Of the 160 reef-building scleractinian corals reported, 28 spanned the full depth range (0–45 m). Differences in irradiance due to geomorphology, as well as reef health, determined the depth transition between two primary benthic groups: photosynthetic scleractinians and filter-feeding azooxanthellate gorgonians, 60 m on low-relief atoll reefs and 45 m at high-relief walls and degraded reefs. Of the 109 gorgonian corals reported, 19 spanned the full depth range (0–140 m) with 70 morphospecies specific to lower mesophotic depths. Similarly, fish assemblages partitioned between shallow and mesophotic depths, characterized by herbivores and planktivores, respectively. Continuously growing marine resource exploitation and terrestrial runoff are heavily influencing reef health. The MCEs of Pohnpei are, thus, unique, yet vulnerable to the exacerbating stresses of man.
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Here we describe massive spawning aggregations and seasonal changes in the large-scale distribution of the Patagonian grouper Acanthistius patachonicus in the Southwest Atlantic based on three sources of information: (a) data from bottom trawl research surveys covering the distributional range of the species within the Argentine continental shelf; (b) folk ecological knowledge gathered from experienced captains of the Argentine industrial trawl fisheries; and (c) sampling of an artisanal trap fishery targeting the Patagonian grouper in a specific location off the coast of Buenos Aires Province. The trawl surveys showed a general pattern of aggregation of Patagonian grouper towards the coast during the reproductive period (September-December). Captains described massive aggregations of the species at specific near-shore locations, where trawl catches of up to 15 t in a single haul were registered during the reproductive season. At a local scale, the artisanal trap fishery described operates exclusively during the reproductive period, targeting near-shore aggregations with a high proportion of individuals releasing gametes onboard. These three sources of information provide evidence of the existence of massive transient spawning aggregations of Patagonian grouper in the Argentine shelf. This is the first report of a reef fish spawning aggregation in the southern region of the Southwest Atlantic. Anecdotal information gathered in this study points to the depletion of many of the aggregations targeted during the 1980s and 1990s by the industrial fleet. At the same time, the spawning aggregation site off Buenos Aires Province has been productive for the last 34 years, being exploited exclusively by traps. The Patagonian grouper is classified as Data Deficient by the International Union for Conservation of Nature, which highlights the need for further research to determine its stock status. Mapping its current spawning aggregations should be a priority to inform the design of a targeted monitoring program and management plan for this species.
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Historically unfished, high-density spawning aggregations are vanishingly uncommon. Behavioural observations from such aggregations are rare, and may be sometimes novel and unexpected. Given the weight of evidence required to document spawning aggregations, how can we best report rare and unusual behavioural variations in spawning populations? Based on two years of in-water observations of a high-density spawning aggregation of the squaretail grouper in the Lakshadweep Archipelago, we described a previously unreported male alternative reproductive tactic (ART) and an inverse size assortment with large males courting several small females that shoaled mid-water ( In critiquing our manuscript, it has been suggested that our observations, methodologies and interpretation are inadequate, flawed, and do not fit within currently accepted theory ( While offering a detailed counter of the main methodological and theoretical criticisms we question how best to document and interpret novel behaviours in poorly known systems. Reporting novelty itself can hardly be the basis of criticism. Our report relied on direct in-water observations, conducted at peak densities over two spawning years. The critique ignores this, choosing instead to focus on a supplementary video which was not the basis of our conclusions. Like other researchers working on this species, we did not directly observe mating, but report courtship as a well-established proxy used across mating systems studies. Apart from these methodological concerns, the authors suggest that there is no theoretical support for our observations. However, sexual selection theory provides well-established frameworks showing that, at very high mating densities, a variety of tactics can emerge, that often vary considerably between populations and locations. In our original paper, we use this broader theory of sexual selection together with detailed behavioural data to propose plausible evolutionary explanations that bear testing in these novel, high-density systems. We agree with the authors that novel observations should be scrutinised carefully as they can challenge our current understanding of the range of behaviours populations display and serve as a springboard for theoretical advancement. Given their rarity, these observations should be evaluated against the rigour of their documentation and the transparency of their reporting. In this context, we hope our carefully documented observations serve as a useful addition to the fascinating and complex natural history of species like the squaretail grouper.
Technical Report
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This is a lay-summary of a larger report and subsequent book chapter (Rowley et al. 2019), for the local communities and governmental agencies of Pohnpei, Federated States of Micronesia. The research presented is a summary of what has been conducted by the University of Hawai'i at Manoa and collaborators since 2014 on the mesophotic coral ecosystems (MCEs) and shallow coral reefs of the Senyavin Islands (Pohnpei Island, and neighbouring atolls Ant and Pakin) in the Federated States of Micronesia (FSM). Annual expeditions have revealed that MCEs are biodiverse, dynamic environments that harbour new species to science (>25 spp.), have species-specific depth distributions, and display remarkable resilience to daily and seasonal fluctuations in temperature. At depths of ≥90 m the annual variability in temperature was up to 20ºC. The strong El Niño event in 2016 and into 2017, extensive coral bleaching occurred on the shallow reefs, with bloom-forming cyanobacteria and algae smothering the reefs. We discovered that reef health could be determined by the depth transition between scleractinians and gorgonians, further revealing areas for conservation management. Reef health is also heavily influenced by the continuously growing marine resource exploitation and terrestrial runoff. Furthermore, the growing $36 million international fishing industry and its associated consequences are contributing to the decline in health of the Pohnpei marine environment. The lush reefs of previous times, therefore, are being replaced by barren reefs, smothered by invasive algae, filamentous cyanobacteria on Pohnpei island, or crustose coralline algae at the atolls. Resource management strategies developed by Pacific Island cultures over hundreds of generations face significant challenges in the modern world. Suggested recommendations may mitigate such challenges. Nonetheless, ocean temperatures have fluctuated over the millennia, a single stressor that reefs may well have the capacity to recover from in our current climate, but the addition of multiple stressors such as eutrophication, local and international fishing exploitation compromise coral reef resilience. In summary, it is essential that both the local communities and the government act now if the reefs of the Senyavin Islands are to recover and survive.
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Many species of groupers form spawning aggregations, dramatic events where 100s to 1000s of individuals gather annually at specific locations for reproduction. Spawning aggregations are often targeted by local fishermen, making them extremely vulnerable to over fishing. The Red Hind Bank Marine Conservation District located in St. Thomas, United States Virgin Islands, was closed seasonally in 1990 and closed permanently in 1999 to protect an important red hind Epinephelus guttatus spawning site. This study provides some of the first information on the population response of a spawning aggregation located within a marine protected area. Tag-and-release fishing and fish transects were used to evaluate population characteristics and habitat utilization patterns of a red hind spawning aggregation between 1999 and 2004. Compared with studies conducted before the permanent closure, the average size of red hind increased mostly during the seasonal closure period (10 cm over 12 yr), but the maximum total length of male red hind increased by nearly 7 cm following permanent closure. Average density and biomass of spawning red hind increased by over 60 % following permanent closure whereas maximum spawning density more than doubled. Information from tag returns indicated that red hind departed the protected area following spawning and migrated 6 to 33 km to a ca. 500 km2 area. Protection of the spawning aggregation site may have also contributed to an overall increase in the size of red hind caught in the commercial fishery, thus increasing the value of the grouper fishery for local fishermen.
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The protection of grouper spawning aggregations is a global conservation issue: populations of many grouper species are threatened with collapse due to exploitation of this critical life history behaviour by fisheries. Effective protection of spawning aggregations requires information on spawning site fidelity, residence time and timing of arrivals at, and departures from, the site. To estimate these parameters at a spawning aggregation site at Farquhar Atoll, southern Seychelles, 12 brown-marbled groupers Epinephelus fuscoguttatus and 20 camouflage groupers E. poly phe ka dion were tagged with acoustic transmitters, and their presence and absence was monitored by an array of acoustic receivers positioned at the site over 2 spawning seasons (2010/2011 and 2011/2012). Spawning aggregations formed during 3 consecutive spawning months each season and overlapped spatially and temporally in the 2 species. Intra- and inter-season site fidelity was high, with 91.7% of tagged E. fuscoguttatus and 89.5% of tagged E. polyphekadion detected at the site 1 yr after tagging. The majority (2010/2011: 82.4%, 2011/2012: 80.0%) of fish detected in a spawning season visited the site during at least 2 spawning months. Residence time at the fish spawning aggregation site was influenced by sex (E. fuscoguttatus only) and spawning month (both species). Distinct periodicity in lunar timing of arrivals and departures was observed in both species. This study highlights the spatio-temporal scales involved during spawning aggregations of 2 long-lived, slow-growing coral reef fishes, which need to be considered for their effective management.
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This chapter explores the fishery and biological implications of exploiting aggregating marine fishes, their general importance to subsistence, commercial, and recreational fisheries and the possible consequences of losing them. We synthesize and examine empirical data from a wide range of taxa to determine whether, when and why fish spawning aggregations need to be targets of management. We examine the socioeconomic importance, costs and benefits of exploiting reef fish aggregations for both extractive and non-extractive (e.g. tourism and reproductive output) purposes. We provide recommendations and guidance for future research, education, management and conservation planning for aggregating species.
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Squaretail coralgrouper (Plectropomus areolatus) were captured and tagged at a fish spawning aggregation (FSA) site with conventional and acoustic tags to assess their vulnerability to fishing and spatial dynamics during reproductive periods. Males outnumbered females in catch and, on average, were larger than females. Findings revealed a high vulnerability to fishing, particularly during reproductive periods, and most fish were recaptured within the 5-month spawning season and within 10-12 km of the aggregation site. Individual and sex-specific variability in movement to, and residency times at, the FSA site indicates that individual monthly spawning aggregations represent subsets of the total reproductive population. Some individuals appeared to move along a common migratory corridor to reach the FSA site. Sex-specific behavioral differences, particularly longer residency times, appear to increase the vulnerability of reproductively active males to fishing, particularly within a FSA, which could reduce reproductive output. Both fishery-dependent and fishery-independent data indicate that only males were present within the first month of aggregation. The combined results indicate that reproductively active P. areolatus are highly vulnerable to fishing and that FSAs and migratory corridors of reproductively active fish should be incorporated into marine protected areas. The capture of P. areolatus during reproductive periods should be restricted as part of a comprehensive management strategy.
This chapter examines the needs and tools for managing reef fish spawning aggregations. We present a global overview of the management of aggregations, and explore management options. We evaluate conventional fishery management and marine protected area options in relation to aggregation conservation, and examine examples of management successes and failures. Most management to date has been reactive, and there remains an overwhelming need for proactive management of aggregations. Long-term monitoring, appropriate fishery policy and extensive fisher and community consultation and outreach are key elements in instituting effective and adaptive management of spawning aggregations.
The scientific study and monitoring of spawning aggregations requires field and laboratory work using a wide variety of physical and biological methods; but field work, no matter the technological tools available, will remain of fundamental importance in studying aggregations particularly for future comparison. Methods are becoming increasingly standardized allowing for meaningful comparison between sites, times and species. Methods can be fishery-dependent (gathering data from captured fishes) or -independent (observational, instrumental physical, interview data) within the subject areas of aggregation (1) discovery, (2) composition, (3) dynamics, (4) life history parameters and (5) physical parameters. Methods for each are summarized with selected subjects explored in more detail. Particularly problematic areas for data gathering have been fishery-independent determination of numbers and/or sizes of fishes and their distribution within aggregations and the larger environment. GPS based methods of mapping aggregation location, extent and fish density provide discrete snapshots of an aggregation, allowing visualization of dynamics over days to years and are repeatable any time in the future by others. Digital imaging (still and video) allows documentation previously impossible. Acoustic tagging, particularly alongside conventional tagging, allows delineating spatial and temporal aspects of aggregations. Hydroacoustic surveys are promising, but require validation of data on species present, fish numbers and their sizes. Aggregation sites should be instrumented to record physical data (e.g. temperature, currents, light) ideally year round, rather than just during aggregation, to allow comparison of aggregation periods with the entire year, and non-aggregation sites also evaluated for comparison Detailed bathymetric mapping of sites is important and feasible and allows visualization of geomorphology in relation to aggregations.
Most reef fishes have bipartite life histories, separate pelagic-oceanic (egg/larvae) and benthic (juvenile/adult) periods. The several-week pelagic period has early planktonic (egg, yolk sac and preflexion larva) and later nektonic components (post-flexion larva to settlement); the plankton-nekton transition timing is variable. For aggregating species, larvae are weak swimmers early in life, but late stages are often strong swimmers able to perhaps influence their settlement locations. No obvious differences were found between larval stages of aggregating and non-aggregating species and both types of spawning are found within single families, and even within a species. There are no egg types, morphologies, feeding strategies or special structures exclusive to aggregating species. Initial dispersal is determined by location and time of spawning. Pelagic eggs are buoyant, keeping them in near-surface waters and away from benthic predators. The larvae go through a series of stages (egg, yolk sac larvae, pre- and post-flexion larvae, pelagic juvenile), becoming larger and more capable over time. Critical periods occur and can cause major mortality of a cohort. Ocean conditions during the early egg and yolk sac stage are critical to survival followed by initiation of feeding as a second critical event. During pelagic life larvae must survive in open water, find appropriate food as larvae and avoid predators. Cohorts from aggregations can recruit as a large pulse, but other fishes may also have such pulses. The mass spawnings of reef invertebrates, such as stony corals, are generally not comparable to those of fishes, while crustaceans (spiny lobsters, marine crabs, terrestrial crabs) have some similarities. There is a need for fisheries oceanography research on aggregation spawning, as well as more work on laboratory culture. The question of potential maternal benefits to larvae needs careful attention.
This chapter examines the needs and tools for managing reef fish spawning aggregations. We present a global overview of the management of aggregations, and explore management options. We evaluate conventional fishery management and marine protected area options in relation to aggregation conservation, and examine examples of management successes and failures. Most management to date has been reactive, and there remains an overwhelming need for proactive management of aggregations. Long-term monitoring, appropriate fishery policy and extensive fisher and community consultation and outreach are key elements in instituting effective and adaptive management of spawning aggregations.