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Fishing in the dark-local knowledge, night spearﬁshing and spawning
aggregations in the Western Solomon Islands
, M. Giningele
, S. Aswani
, J.L. Ecochard
The Nature Conservancy, Indo Paciﬁc Resource Center, 51 Edmondstone, South Brisbane, QLD 4101, Australia
Dunde Community, Munda, Western Province, Solomon Islands
Department of Anthropology and Interdepartmental Graduate Program in Marine Science, University of California, Santa Barbara, CA 93106-3210, USA
Technology and Information Systems, The Nature Conservancy, Arlington, VA, USA
Received 30 May 2011
Received in revised form 21 November 2011
Accepted 26 November 2011
Available online 19 December 2011
Fish spawning aggregation
Local ecological knowledge
Marine protected area
Within the marine conservation community there is considerable interest in combining local knowledge
and science to achieve management objectives. Yet there remain few studies which have examined the
merits and caveats of local knowledge, or shown how combining both knowledge systems has resulted in
better management outcomes. This study outlines collaborative efforts to conserve ﬁsh spawning aggre-
gations (FSAs) in Roviana Lagoon, Western Solomon Islands. Baseline information on FSAs was obtained
through local knowledge and spearﬁshing creel surveys. This information provided the starting point for
establishing a 2-year community-based underwater monitoring program at the largest known FSA in
Roviana Lagoon, where the brown-marbled grouper (Epinephelus fuscoguttatus), camouﬂage grouper
(Epinephelus polyphekadion) and squaretail coralgrouper (Plectropomus areolatus) co-aggregate. This par-
ticipatory research shows that local knowledge on FSAs is utilised to maximise returns from ﬁshing, with
spearﬁshermen targeting aggregations at night during the lunar periods when abundances peak. Because
of its shallow distribution P. areolatus is the most vulnerable of the three groupers to nighttime spearf-
ishing, with two ﬁshermen capable of removing 15–30% of the total spawning biomass in two nights.
Underwater monitoring demonstrates that while ﬁshermen provided accurate information on many
aspects of FSAs, their knowledge on spawning seasons was inaccurate for the FSA reported on here. Peak
aggregations occurred from December to April each year, which differs from the traditionally recognised
grouper season of October to January. A combination of local knowledge and science was used to develop
appropriate management measures for this FSA, with the aggregation declared a community-based mar-
ine protected area (MPA) in 2006.
Ó2011 Elsevier Ltd. All rights reserved.
Within the marine conservation community there is consider-
able interest in understanding how local knowledge of ﬁshers
can be utilised to advance both management and conservation
agendas (e.g. Drew, 2005; Johannes and Neis, 2007). Fishers can
provide important information on such things as inter-annual, sea-
sonal, lunar, diel, tide- and habitat-related differences in species
distributions and abundance, as well as providing a historical per-
spective on the state of ﬁsheries (Johannes et al., 2000). To date
marine scientists and conservation practitioners have incorporated
ﬁshers’ local knowledge into research programs, ﬁsheries assess-
ments, species evaluations and conservation planning processes
(e.g. Sadovy and Cheung, 2003; Aswani and Hamilton, 2004; Dulvy
and Polunin, 2004; Saénz-Arroyo et al., 2005; Silvano et al., 2006;
Aswani et al., 2007; Almany et al., 2010; Game et al., 2011; Taylor
et al., 2011). One of the most widely applied uses of ﬁshers local
knowledge is in the research and conservation of ﬁsh spawning
aggregations (FSAs) (Hamilton et al., 2012). In many locations, ﬁsh-
ers have known of FSAs for generations, or have experienced sea-
sonal gluts in landings subsequently identiﬁed as FSAs (Johannes,
1978; Colin et al., 2003). In recognition of this, and because of
the practical difﬁculties of discovering FSAs that typically form at
highly localised areas for brief periods of time, scientists that study
FSAs have often drawn on local knowledge in the initial stages of
their research (e.g. Johannes et al., 1999; Robinson et al., 2008;
Sadovy de Mitcheson et al., 2008).
Three large-bodied aggregating reef ﬁshes that have received
considerable attention in the past decade are the brown-marbled
grouper (Epinephelus fuscoguttatus), camouﬂage grouper (Epinephe-
lus polyphekadion) and squaretail coralgrouper (Plectropomus
areolatus). In the Indo-Paciﬁc these three groupers frequently
co-aggregate to spawn at predictable sites and times around the
0006-3207/$ - see front matter Ó2011 Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +61 7 3214 6913; fax: +61 7 3214 6999.
E-mail address: email@example.com (R.J. Hamilton).
Biological Conservation 145 (2012) 246–257
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/biocon
Author's personal copy
new or full moon (e.g. Johannes et al., 1999; Rhodes and Sadovy,
2002; Pet et al., 2005; Hamilton et al., 2011). These groupers make
up important components of many small-scale commercial ﬁsher-
ies in the Paciﬁc (e.g. Rhodes and Tupper, 2007) and they are three
of the most economically valuable species in the Southeast Asia-
based live reef food ﬁsh trade (LRFFT) (Sadovy et al., 2003). As a re-
sult of their predictable aggregating behaviour, all are highly sus-
ceptible to overexploitation, with E. fuscoguttatus and E.
polyphekadion listed as near threatened (Cornish, 2004; Russell
et al., 2006, respectively) and P. areolatus listed as vulnerable (Thi-
erry et al., 2008) in the 2008 IUCN Red List.
Globally there are numerous examples of where targeted ﬁsh-
ing of FSAs has resulted in aggregation decline or loss (e.g. Sadovy
and Domeier, 2005; Hamilton and Matawai, 2006; Rhodes et al.,
2011), which has negative implications for local ﬁsheries and the
communities that depend on them (Sadovy and Domeier, 2005).
Fisheries managers and conservation practitioners are increasingly
recognising that FSAs need protection, with marine protected areas
(MPAs) and closed seasons being the most commonly imple-
mented conservation measures (e.g. Beets and Friedlander, 1999;
Sadovy de Mitcheson et al., 2008; Rhodes et al., 2011). In some in-
stances management measures for FSAs have been designed solely
on local knowledge (e.g. Hamilton et al., 2012). In other cases, long-
term underwater monitoring has helped to establish a more com-
plete picture of FSAs than local knowledge alone, while building lo-
cal capacity and support for management (e.g. Hamilton et al.,
The multi-species FSA reported on in this paper is the largest
known grouper aggregation in Roviana Lagoon, Western Solomon
Islands. A Roviana spearﬁsherman discovered this FSA in 1995,
and between 1995 and 2006 it was exploited by nighttime spear-
ﬁshermen. By 2004 Roviana spearﬁshermen perceived catches at
this FSA to be in steep decline, and when a non-government organi-
sation (NGO) raised community awareness on the importance of
conserving FSAs, the customary owners of this FSA agreed to estab-
lish a science-based, community-led underwater monitoring pro-
gram at the aggregation site (Hamilton and Kama, 2004). The
purpose of this monitoring was to obtain scientiﬁc information on
aggregation seasons and status, with a view that this information
could be utilised to develop appropriate community-based man-
agement strategies for the FSA. Feedback on the scientiﬁc ﬁndings
resulted in the FSA being declared a no-take community-based
MPA in June 2006. While compliance with this MPA has generally
been good, a limited amount of poaching by nighttime spearﬁsher-
men has occurred since 2006. The aims of this paper are to (1)
establish the temporal and spatial trends of E. fuscoguttatus,E.
polyphekadion and P. areolatus at this site, (2) determine if small-
scale commercial nighttime spear ﬁsheries pose a signiﬁcant threat
to spawning aggregations of E. fuscoguttatus,E. polyphekadion and P.
areolatus, and (3) evaluate whether or not local knowledge needs to
be independently validated before being used as the basis for
2.1. Environmental setting
The current study was conducted in Roviana Lagoon, Western
Solomon Islands (Fig. 1) in the Solomon Sea, which forms the most
eastern part of the Coral Triangle (Veron et al., 2009). Roviana La-
goon is a body of shallow water approximately 50 km long en-
closed between the New Georgia mainland and a series of
uplifted coral reef islands lying 2–3 km offshore. In Roviana ﬁshing
practices are strongly inﬂuenced by local knowledge of the lagoon
environment. Knowledge of the tides, lunar stages and seasons in-
form ﬁshers when, where and for what they should ﬁsh (e.g. Ham-
ilton and Walter, 1999; Aswani and Hamilton, 2004; Aswani and
Vaccaro, 2008). October to the end of January is widely known as
the ‘pazara’ season, when groupers such as E. fuscoguttatus,E.
polyphekadion,P. areolatus and the white-streaked grouper (Epi-
nephelus ongus) are said to aggregate at a minimum of 14 FSAs in
Roviana Lagoon, in the 10 days leading up to and including the
new moon (Hamilton and Kama, 2004). In Roviana Lagoon spawn-
ing aggregations are targeted by subsistence and small-scale com-
mercial ﬁsheries, and in several cases it appears that FSAs have
been ﬁshed almost to the point of extirpation (Hamilton and Kama,
2.2. Site description
The studied FSA is located on a seaward facing reef promontory
within the western region of Roviana Lagoon (Fig. 1). In order to
protect this FSA from further exploitation by outside entities, the
exact location is not shown. The reef ﬂat of the promontory is
3 m deep, with the reef slope dropping steeply to below 200 m.
Aggregations of all three species overlap over a linear reef distance
of ca. 300 m and between depths of 3–50 m (Fig. 2). P. areolatus are
most abundant between depths of 3–15 m, whereas E. fuscogutta-
tus and E. polyphekadion are most abundant in the middle section
of the FSA between depths of 5–50 m (Fig. 2).
This FSA is predominantly ﬁshed by nighttime spearﬁshermen
although daytime spearﬁshing occasionally occurs here. Hook
and line ﬁshing is not practiced. Nighttime spearﬁshermen free
dive with the aid of ﬁns, mask, snorkel, a rubber powered spear
and an underwater ﬂashlight with a maximum 4-h battery life.
Spearﬁshermen prefer to ﬁsh this site at night, as this method pro-
duces higher catch rates than daytime spearﬁshing (authors, per-
sonal observations), a pattern that is common in many parts of
the Paciﬁc (Gillett and Moy, 2006). Local spearﬁshermen reported
that in the ﬁrst 2 years that they exploited this site (1995–1996)
the maximum catch of two spearﬁshermen exceeded 200 P. areol-
atus a night (Hamilton and Kama, 2004). Fishermen noted declines
in maximum catches from 1997 onwards, and in 2001 the maxi-
mum catch of two spearﬁshermen was 71 P. areolatus in a night
(see Table 3). Commercial spearﬁshermen sell their catches at ﬁsh-
eries centres in the Munda Township (Fig. 1). In 2004 approxi-
mately ten spearﬁshermen were known to periodically ﬁsh this
2.3. Creel survey
Between the 23rd of January 2001 and the 20th of April 2001
one of the authors (MG) led 41 nighttime spearﬁshing trips over
all of the outer reefs shown in Fig. 1. Twenty-seven percent
(n= 11) of these ﬁshing trips occurred at the FSA site and 73%
(n= 30) occurred on outer reefs 1–12 km from the FSA. After each
ﬁshing trip MG recorded the date, ﬁsher name(s), location, time
spent travelling and ﬁshing, species caught and their frequency
and weight. In some instances species were clumped at the genus
level. Fish names were recorded in Roviana and translated to scien-
tiﬁc names by the senior author, who participated in several of
these ﬁshing trips. On two occasions in 2005 and one occasion in
2010 one of the authors (MG) documented additional information
on three nighttime spearﬁshing trips at the FSA that he did not par-
ticipate in. He did this through informal discussions with the
spearﬁshermen who led these trips, and by recording the total
weights of gutted P. areolatus that were purchased from these ﬁsh-
ermen at local ﬁsheries centres in Munda. Since 2005 and 2010
data represent gutted catches, these total weights were raised by
a factor of 1.15 to represent the ungutted condition (Grandcourt,
2005). Catch per unit effort (CPUE) for the 2005 and 2010 trips
R.J. Hamilton et al. / Biological Conservation 145 (2012) 246–257 247
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were estimated by assigning 4 h of effort to each spearﬁshermen,
based on the authors knowledge of the maximum battery life of
the underwater ﬂashlights used in Roviana Lagoon.
2.4. Community-based underwater monitoring program
In March 2004 four Roviana spearﬁshermen who exploited FSAs
(free diving) and were also experienced SCUBA divers received
training in monitoring spawning aggregations (Rhodes, 2004). Fol-
lowing this training community approval was sought and given to
establish a 2 year community-based monitoring program at the
FSA reported on here (Hamilton and Kama, 2004). A monitoring
team and protocols were established, and over the next 2 years
the senior author provided scientiﬁc advice, mentoring, logistical
and ﬁeld support to Roviana community monitors.
To determine the seasonality with which aggregations form a
250 m by 10 m wide (2500 m
), 20 m deep belt transect was placed
at the FSA in April 2004, and a second 200 m by 10 m wide
), 10 m deep belt transect placed at the FSA in March
2005 (Fig. 2). The upper and lower boundaries of transects were
marked by inserting 1 m long re-bar stakes into the reef at 10 m
(horizontal) intervals, and white PVC pipe sleeves were placed over
each re-bar stake to increase visibility. The two transects covered
12% of the total FSA area, exceeding the 10% minimum area that
is recommended in order to ensure sufﬁcient precision (Pet et al.,
2006). A HOBO
data logger (Water Temp Pro H2O-001, Onset,
Southern MA, USA) was placed at the start of the deep transect
(20 m) in October 2004 and recorded water temperatures hourly
until it was recovered in June 2006.
Transects were monitored by underwater visual census (UVC)
in the early afternoon on 100 days between the 19th April 2004
and the 12th June 2006 (Table 1). Initially monitoring occurred
once a month on the new moon. The decision to monitor on the
new moon was based on local knowledge and UVC surveys con-
ducted at this site in March 2004, which showed peak FSAs abun-
dances persisted several days after the new moon had passed. It
was expected that sampling on the new moon would provide a
‘snapshot’ of the peak aggregation density. We became aware of
full moon P. areolatus aggregations in October 2004 and began reg-
ular full moon monitoring in March 2005.
To verify that new moon monitoring conformed to periods of
peak density and abundance, intensive (daily) UVC surveys were
conducted just before and just after the new moon in February
and March 2005 (6 and 5 days respectively) and February 2006
(7 days). To better understand daily aggregating patterns intensive
surveys were also conducted over all lunar phases between March
and April 2006. One of the authors (MG) led all 100 UVC surveys,
accompanied by another trained monitor. During monitoring, di-
vers swam side-by-side along the midpoint of a transect, maintain-
ing a position several metres above the aggregated ﬁsh. Monitors
recorded the total number of each of the three species sighted
within transect boundaries.
2.5. Calculation of FSA area
In order to estimate maximum FSA abundances the total aggre-
gation area was estimated in March 2005 and 2006. In both years
we placed permanent markers at the aggregation boundaries
where densities declined rapidly and neared non-reproductive val-
Fig. 1. The lagoon and reef habitat at the western end of Roviana Lagoon. The location of the provincial centre Munda is shown.
248 R.J. Hamilton et al. / Biological Conservation 145 (2012) 246–257
Author's personal copy
ues (Pet et al., 2006). Float lines were then attached to each marker
and sent to the surface, and a handheld GPS was used to mark
aggregation boundaries from the surface (Rhodes and Sadovy,
2002). The start and ends of both transects were marked using
the same method. In June 2006 we made a 3-D bathymetric map
of the FSA using a low cost bathymetric mapping method (Fig. 2).
The method converts echosound data collected in sparse geometry
over the reef by a Lowrance brand ﬁshﬁnder (LCX-15 MT, Lowrance
Electronics Inc., Oklahoma, USA) into a three dimensional map
suitable for analysis with ARCGIS 9 (ESRI
California, USA) soft-
ware (see Zurk et al., 2006; Heyman et al., 2007 for details). We cal-
culated total FSA area in 2005 and 2006 by importing GPS points
onto the bathymetric map using ArcView. We subdivided the total
FSA area into a shallow (high density P. areolatus) stratum (3–
15 m) and a deep (low density P. areolatus) stratum (15.1–50 m)
(Fig. 2). Estimates of total population size per month were calcu-
lated by extrapolating mean transects counts for each depth stra-
tum using the formula: No. ﬁsh in transect total aggregation
stratum area/transect area. Total estimates are the sum of the esti-
mated abundances in the shallow and deep stratum (Nemeth,
2.6. Statistical analysis
The mean weights of P. areolatus speared outside of the FSA and
at the FSA, and the mean CPUE of P. areolatus and Epinephelus spp.
speared outside of the FSA (all lunar periods) and at the FSA during
the second lunar quarter (the period when FSAs peak) were com-
pared using Mann–Whitney rank sum tests as data were nonpara-
metric. Mann–Whitney rank sum tests were also used to compare
the mean densities of P. areolatus on new and full moons. Wilcoxon
Signed rank tests were used to compare mean densities of E. fusco-
guttatus,E. polyphekadion and P. areolatus on shallow and deep
transects as these data were paired and nonparametric. All statis-
tical tests were conducted in SigmaStat 3.5 (Systat Software, San
Jose, California, USA).
Fig. 2. Bathymetric map of the FSA. The red line represents the midpoint of the shallow 200 m long transect and green line represents the midpoint of the deep 250 m long
transect. The green area shows the shallow (3–15 m) stratum and the purple area shows the deep (15.1–50 m) stratum of the FSA. The yellow dashed line shows the region
where the highest densities of E. fuscoguttatus and E. polyphekadion are found.
The number of days that transects were surveyed during new moon, 1st 1/4, full
moon and 2nd 1/4 in the months of April 2004–June 2006.
Date New moon 1st 1/4 Full moon 2nd 1/4
April 2004 1 0 0 0
May 2004 1 0 0 0
June 2004 1 0 0 0
July 2004 1 0 0 0
August 2004 1 0 0 0
September 2004 1 0 0 0
October 2004 1 0 1 0
November 2004 1 0 0 0
December 2004 1 0 0 0
January 2005 1 0 0 0
February 2005 3 0 1 3
March 2005 4 0 1 1
April 2005 1 0 1 0
May 2005 1 0 1 0
June 2005 1 0 1 0
July 2005 1 0 1 0
August 2005 1 0 1 0
September 2005 1 0 1 0
October 2005 1 0 1 0
November 2005 1 0 1 1
December 2005 1 0 1 1
January 2006 2 0 1 2
February 2006 2 0 1 3
March 2006 6 0 3 6
April 2006 7 6 7 7
May 2006 1 0 1 0
June 2006 0 0 1 0
Total 44 6 26 24
R.J. Hamilton et al. / Biological Conservation 145 (2012) 246–257 249
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3.1. Creel survey
The weight (kg) and proportion of total catch (%) of different
species captured in the 2001 creel survey are presented in Table 2.
Serranids made up 23.6% of the nighttime catch, with P. areolatus
representing 76% of the total serranid catch. A detailed breakdown
of the P. areolatus and Epinephelus spp. creel data is presented in
Table 3. Seventy-nine percentage of P. areolatus caught (244/308)
[representing 87% (295.9 kg/345.3 kg) of the P. areolatus catch by
weight] were taken at the FSA over ﬁve nights in January and
March 2001 (12% of total sample days). All of these large catches
were made during the second lunar quarter, with the highest
catches by number, weight and CPUE made 1 day before the new
moon in January and March 2001 (Table 3). The mean CPUE of P.
areolatus obtained from the FSA during the second lunar quarter
was signiﬁcantly greater than the mean CPUE of P. areolatus ob-
tained on reefs outside of the FSA (all lunar periods) (9.107 kg/ﬁsh-
er/h ± SE 2.59 kg (n= 6 trips) and 0.318 kg/ﬁsher/h ± SE 0.07 kg
(n= 30 trips), respectively; P< 0.001). The mean weight of P. areol-
atus speared from within the FSA was signiﬁcantly greater than
outside the FSA (1.253 kg (SE = 0.06 kg) and 0.827 kg (SE = 0.10 kg),
respectively; P= 0.032).
E. fuscoguttatus and E. polyphekadion also aggregate at this FSA
in large numbers from December to April during the second lunar
quarter (see below), however the mean CPUE of Epinephelus spp.
captured on reefs outside of the FSA (all lunar periods) and at the
FSA (during the second lunar quarter) [0.51 kg/ﬁsher/h ± SE
0.18 kg (n= 30 trips) and 0.68 kg/ﬁsher/h ± SE 0.28 kg (n= 6 trips),
respectively] were not signiﬁcantly different at
The total weights and CPUE for P. areolatus captured at the FSA
during the second lunar quarter in December 2005 and April 2010
were very similar to the maximum weights and CPUE obtained at
the FSA in the 2001 creel survey (Table 3).
3.2. UVC surveys
3.2.1. Inter-annual and lunar seasonality
At the FSA E. fuscoguttatus aggregated on the new moon 4 or
5 months annually between December and April. The E. polypheka-
dion reproductive season was briefer, with aggregations forming
on the new moon in March 2005 and February and March 2006.
In contrast, P. areolatus aggregations formed throughout the year
on both new and full moons (Fig. 3). On the shallow transect signif-
icantly higher densities of P. areolatus were sighted on the new
moons (P= 0.004), but on the deep transect the mean densities of
P. areolatus sighted on new and full moons were not signiﬁcantly
= 0.05. The largest new moon aggregations of P. areol-
atus coincided with periods when E. fuscoguttatus and E. polypheka-
dion aggregations peaked.
3.2.2. Inﬂuence of depth on species distributions
On the new moon E. fuscoguttatus densities were higher in deep
water (P= 0.014), whereas E. polyphekadion densities did not differ
signiﬁcantly between depths at
= 0.05. On both the new and full
moon the densities of P. areolatus were signiﬁcantly higher in shal-
low water (P< 0.001 and P= 0.008 respectively).
3.2.3. Daily aggregation patterns
Intensive daily monitoring that was conducted on 39 days be-
tween 14th March and 30th April 2006 allowed a close examina-
tion of the build-up of FSAs (Fig. 4). In March 2006 E.
fuscoguttatus began to arrive at the FSA 6 days prior to the new
moon, with peak densities occurring 1–4 days prior to the new
moon. In the same month E. polyphekadion began to aggregate at
least 7 days prior to the new moon, with peak densities 1–3 days
Weight (kg) and proportion of total catch (%) of different species caught in the night
time creel survey conducted between the 23rd of January and 20th April 2001. Data is
summed across 41 separate spearﬁshing trips during this period. Eleven trips targeted
the ﬁsh spawning aggregation (FSA) and 30 trips targeted outer reefs outside the FSA
but within 12 km of the FSA (see Section 2.3).
Species kg %
Acanthurus lineatus 14.8 0.77
Acanthurus nigricauda 97.8 5.06
Acanthurus spp. (not listed above) 151.4 7.84
Ctenochaetus striatus 1.2 0.06
Naso lituratus 101.7 5.27
Naso spp. (not listed above) 107.8 5.58
Balistoides viridescens 7.8 0.40
Pseudobalistes ﬂavimarginatus 31.7 1.64
Caranx spp. 9.8 0.51
Chelonia mydas 40.6 2.10
Eretmochelys imbricata 20.7 1.07
Diodon hystrix 6.1 0.32
Platax teira 1.8 0.09
Plectorhinchus spp. 18.2 0.94
Myripristis spp. 1.3 0.07
Sargocentron spp. 1.9 0.10
Cheilinus undulatus 23.8 1.23
Lethrinus erythracanthus 8.1 0.42
Lethrinus hypselopterus 16.9 0.87
Lethrinus spp. (not listed above) 29.6 1.53
Monotaxis grandoculis 10.6 0.55
Lutjanus gibbis 6.7 0.35
Lutjanus rivulatus 4.5 0.23
Lutjanus spp. (not listed above) 25.3 1.31
Macolor macularis 16.9 0.87
Parupeneus spp. 24.1 1.25
Gymnothorax spp. 2.5 0.13
Ostracion cubicus 9.1 0.47
Panulirus penicillatus 14.1 0.73
Panulirus vesicolor 10 0.52
Bolbometopon muricatum 512.1 26.51
Scarus spp. 110.2 5.71
Sepia spp. 10.5 0.54
Epinephelus spp. 110.6 5.73
Plectropomus areolatus 345.3 17.88
Siganus lineatus 0.4 0.02
Siganus puellus 10.8 0.56
Sphyraena barracuda 14.8 0.77
Total 1931.5 100.00
250 R.J. Hamilton et al. / Biological Conservation 145 (2012) 246–257
Author's personal copy
prior to the new moon. For these two species no clear aggregating
pattern was obvious in April 2006, as by then the spawning season
for that year had ended. In March 2006 P. areolatus were already
aggregated on the full moon, with peak densities sighted 1–5 days
prior to the new moon. In April 2006 the P. areolatus aggregation
was smaller and the pattern of FSA formation differed somewhat,
with P. areolatus beginning to aggregate just after the full moon,
and peak densities occurring 1–6 days prior to the new moon.
Additional intensive surveys that were conducted around the
new moon period in February and March 2005 and February
2006 reveal that the lunar day on which FSAs begin to decline after
presumed spawning can vary, with FSAs declining on the new
moon or 1 or 2 days after new moon (Fig. 5).
The onset of the E. fuscoguttatus reproductive season began
shortly after sea temperatures had begun to rise from their annual
lows, with peak spawning months occurring during periods of
maximum sea temperatures (Fig. 3). E. polyphekadion FSAs also oc-
curred during periods when sea temperatures were near their
maximum. Mean monthly sea temperatures had no clear associa-
tion on the formation of P. areolatus FSAs (Fig. 3). There was no cor-
relation between daily water temperatures and the pattern of
monthly aggregation formation for E. fuscoguttatus,E. polyphekadi-
on or P. areolatus (Fig. 4).
3.3. Aggregation areas and total population size estimates
In March 2005 the total FSA area was 36,503 m
tum = 8698 m
, deep stratum = 27,805 m
). In March 2006 FSAs oc-
curred over a slightly larger horizontal reef area, and as such, the
total FSA was 38,462 m
(shallow stratum = 9157 m
, deep stra-
tum = 29,269 m
). Estimates of the total number of E. fuscoguttatus,
E. polyphekadion and P. areolatus present at the FSA on the new
moon from March 2005 to May 2006 are presented in Table 4.
4.1. Aggregation seasons
Between 100 and 700 E. fuscoguttatus aggregated at the study
site in the week leading up to the new moon during the months
of December–April, and 200–300 E. polyphekadion aggregated in
the week leading up to the new moon in the months of February
Detailed breakdown of the 2001 creel data presented in Table 2 for P. areolatus and Epinephelus spp. Data for several P. areolatus catches that were made at the FSA in 2005 and
2010 is also shown.
Date Location Lunar stage No. ﬁshers Effort (h) Plectropomus areolatus Epinephelus fuscoguttatus
Weight (kg) No. CPUE (kg/h
) Weight (kg) No. CPUE (kg/h
23.1.01 FSA 2nd 1/4 2 5 84 70 16.80 1.2 1 0.24
24.1.01 Outside 2nd 1/4 2 6 0 0 0 0 0 0
26.01.01 FSA New moon 2 9 0.8 1 0.09 2 2 0.33
30.1.01 Outside New moon 1 2.5 2.4 5 0.96 0 0 0
31.01.01 Outside New moon 1 3 3.1 4 1.03 0 0 0
2.2.01 Outside 1st 1/4 1 3.5 0 0 0 0.5 1 0.14
3.2.01 Outside 1st 1/4 1 2.5 1.3 5 0.52 1.6 1 0.64
18.2.01 Outside 2nd 1/4 2 4 4.1 5 1.03 5.2 1 1.3
21.2.01 Outside 2nd 1/4 2 8 0.2 1 0.03 3.2 3 0.4
3.3.01 Outside New moon 2 6.5 0 0 0 0.6 1 0.09
4.3.01 FSA 1st 1/4 2 6 2.9 4 0.48 4.5 1 0.75
5.3.01 Outside 1st 1/4 2 6 1.7 3 0.28 3.7 3 0.63
6.3.01 Outside 1st 1/4 1 4 0 0 0 0 0 0
8.3.01 Outside 1st 1/4 2 6 0 0 0 2 2 0.33
11.3.01 Outside Full moon 2 5.5 3.2 3 0.58 2.5 3 0.45
12.3.01 Outside Full moon 2 8 3.1 2 0.39 4.9 3 0.39
13.3.01 FSA Full moon 1 4 1.5 2 0.38 6.1 1 1.53
14.3.01 Outside Full moon 2 6 1.5 2 0.25 1.7 2 0.28
15.3.01 Outside Full moon 2 6.5 3.8 3 0.58 1.8 1 0.28
16.3.01 Outside 2nd 1/4 2 6 0.5 1 0.08 21.5 6 3.58
17.3.01 Outside 2nd 1/4 1 3 0 0 0 0 0 0
18.3.01 Outside 2nd 1/4 2 4 0 0 0 0.7 1 0.18
19.3.01 FSA 2nd 1/4 2 4 4 3 1.00 4 1 1
21.3.01 FSA 2nd 1/4 2 6 26.8 18 4.47 0 0 0
22.3.01 FSA 2nd 1/4 2 5.5 29.2 24 5.31 8.5 3 1.55
22.3.01 Outside 2nd 1/4 2 6.5 0 0 0 0 0 0
23.3.01 FSA 2nd 1/4 2 5.5 70.6 61 12.84 0 0 0
24.03.01 FSA 2nd 1/4 2 6 85.3 71 14.22 7.6 4 1.27
25.03.01 Outside New moon 1 3 0 0 0 1.3 1 0.43
26.03.01 FSA New moon 2 6 1.4 2 0.23 9.5 5 1.58
29.3.01 Outside New moon 1 2.5 0 0 0 0 0 0
30.3.01 Outside New moon 1 3 0 0 0 11.4 4 3.8
31.3.01 Outside New moon 1 3 1.9 1 0.63 1.2 1 0.4
1.4.01 FSA New moon 2 5.5 2.4 3 0.44 0 0 0
7.4.01 Outside 1st 1/4 2 6 3.4 5 0.57 0 0 0
8.4.01 Outside Full moon 1 3 3.2 5 1.07 0 0 0
11.4.01 Outside Full moon 1 2.5 1.7 1 0.68 3.1 3 1.24
12.4.01 Outside Full moon 1 2.5 1.3 3 0.53 0.3 1 0.23
18.4.01 Outside 2nd 1/4 1 3 0 0 0 0 0 0
19.4.01 Outside 2nd 1/4 1 3 0 0 0 0 0 0
20.4.01 Outside 2nd 1/4 2 7.5 0 0 0 0 0 0
26.12.05 FSA 2nd 1/4 2 8 74.5 ? 9.3 ?
28.12.05 FSA 2nd 1/4 2 8 87.1 ? 10.9 ?
9.4.10 FSA 2nd 1/4 2 8 72.5 ? 9.1 ?
R.J. Hamilton et al. / Biological Conservation 145 (2012) 246–257 251
Author's personal copy
and March. Clearly deﬁned spawning seasons of 2–5 months have
been reported for E. fuscoguttatus and E. polyphekadion in various
other geographies (e.g. Johannes et al., 1999; Rhodes and Sadovy,
2002; Robinson et al., 2008). In Roviana Lagoon P. areolatus aggre-
gated on new and full moon in every month of the year, with abun-
dances ranging from 100 to 1000 individuals. Densities of P.
areolatus in shallow water were signiﬁcantly higher on new moons.
P. areolatus has also been shown to form new moon FSAs through-
out the year in Papua New Guinea and Palau (Johannes et al., 1999;
Hamilton et al., 2011), however neither of these studies conducted
full moon monitoring. In Komodo National Park, Indonesia, P. areol-
atus aggregations occur on the full moon between September and
Fig. 3. Mean densities (±1 SE) of Epinephelus fuscoguttatus,Epinephelus polyphekadion and Plectropomus areolatus on the deep (20 m) and shallow (10 m) transects on the new
and full moons between April 2004 and June 2006. Mean monthly seawater temperature (±1 SE) is shown from October 2004–June 2006. Note that monitoring on the shallow
transect commenced in March 2005 and y-axis scale differs between panels for presentation clarity.
252 R.J. Hamilton et al. / Biological Conservation 145 (2012) 246–257
Author's personal copy
February, with occasional new moon aggregations forming be-
tween April and July (Pet et al., 2005).
We believe that in most instances the full moon aggregations
observed in our study represent the beginning of a prolonged per-
iod of FSA build up, with spawning occurring around the new
moon. The daily monitoring conducted in March and April 2006
provides evidence of this, with small full moon aggregations build-
ing rapidly approximately a week prior to the new moon. Similar
patterns have also been observed for this species in Palau (Johan-
nes et al., 1999), and this pattern was recently validated for P.
areolatus in Manus Province, Papua New Guinea, where 416 P.
areolatus were captured, sexed and released over 16 days of contin-
uous ﬁshing at a FSA between the 29th of April (full moon) and the
14th of May 2010 (new moon). None of the captured P. areolatus
had developed oocytes or ripe sperm until the second lunar quarter
(Almany and Hamilton, unpublished data).
However, our above interpretation is complicated by the fact
that in October 2004 and October and November 2005 full moon
aggregations of P. areolatus were larger than the new moon aggre-
gations. Hence, we cannot rule out the possibility that full moon
spawning occurs in some months of the year, which in turn sug-
gests that two different populations of P. areolatus may be using
the same spawning site, with one population larger than the other.
Two alternative explanations for the large full moon aggregations
is that in some months ﬁshing pressure may have greatly reduced
the size of the P. areolatus aggregation by the time new moon mon-
itoring occurred, or that in these months peak aggregations had be-
gan to decline by the time new moon monitoring took place.
In Melanesia, FSAs of E. fuscoguttatus,E. polyphekadion and P.
areolatus disperse around the new moon; however, the speciﬁc lu-
nar day on which aggregations disperse can vary slightly both
within and between nearby FSAs of the same species (Johannes,
1989; Hamilton et al., 2011). The intensive UVC surveys that were
conducted in February and March 2005 and February 2006 indicate
that our new moon sampling protocols captured the peak spawn-
ing periods, with peak densities of all three species persisting until
at least the new moon in these months. However in March 2006
peak aggregations of E. fuscoguttatus,E. polyphekadion and P. areol-
atus only persisted until 1 day prior to the new moon. The observed
inter-monthly and inter-annual variability in when FSAs peak and
subsequently disperse highlights the inherent difﬁculty in sam-
pling peak aggregations representatively between successive
months and years. While this variability did not inhibit our ability
to determine aggregation seasons, it shows that in at least 1 month
of this study the new moon UVC survey occurred after peak densi-
ties of all three species had began to decline.
Fig. 4. The daily aggregation trends of Epinephelus fuscoguttatus,Epinephelus polyphekadion and Plectropomus areolatus (±1 SE) on deep (20 m) and shallow (10 m) transects in
relation to new and full moons between the 14th March and 30th April 2006. Mean daily seawater temperature is shown. Note that y-axis scale differs between panels for
R.J. Hamilton et al. / Biological Conservation 145 (2012) 246–257 253
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Changing water temperatures have been linked to the onset and
cessation of the spawning season for aggregating groupers and
snappers in both Australia and the Caribbean (Colin, 1992; Samoi-
lys, 1997; Heyman et al., 2005). In Roviana Lagoon only E. fusco-
guttatus showed a possible correlation between temperature and
the onset of the annual spawning season, with UVC monitoring re-
sults showing that E. fuscoguttatus initiates spawning aggregation
formation 1 or 2 months after water temperatures have began to
rise from their annual lows, with peak aggregations occurring dur-
ing periods of maximum sea temperatures (30 °C). This correla-
tion contrasts with recent ﬁndings in Pohnpei, where E.
fuscoguttatus forms spawning aggregations during periods of sea-
sonally low water temperatures (28.5 °C) (Kevin Rhodes, pers.
comm.). In Roviana Lagoon none of the three grouper species stud-
ied showed any correlation between daily water temperatures and
the pattern of monthly aggregation formation. From the Roviana
and Pohnpei data, it appears that if temperature acts to stimulate
reproductive activity, it alone is not likely the overriding environ-
mental factor. Additional temperature data from other regional
spawning sites for these species may help clarify what role, if
any, temperature plays in reproduction.
4.2. Vulnerability of FSAs to spearﬁshing
Of the three groupers studied, P. areolatus is the most vulnera-
ble to nighttime spearﬁshing during aggregation periods. Night-
time spearﬁshermen that targeted the FSA during the second
lunar quarter obtained P. areolatus at a CPUE 29 times higher than
CPUE obtained outside the FSA. Likewise, P. areolatus captured at
the FSA were signiﬁcantly larger than those captured outside.
The nighttime spearﬁshing trips that were conducted at the FSA
in December 2005 are insightful since they occurred during a per-
iod when UVC monitoring took place. Over two nights in December
2005 (5 and 3 days prior to the new moon) two spearﬁshermen
captured 161.6 kg of P. areolatus from the FSA, which represents
approximately 129 ﬁsh, based on the mean weight of P. areolatus
(1.253 kg) captured at the FSA in the 2001 creel survey. A UVC sur-
vey conducted in that same month provides an estimate of 299 P.
areolatus at the FSA on the new moon (i.e., 72 h after the last
spearﬁshing trip). If we account for the ﬁsh removed from this site
prior to UVC monitoring, and assume that the peak FSA persisted
until the new moon in December 2005, then we can estimate that
over two nights two spearﬁshermen removed 30% (129/429) of the
P. areolatus FSA in 16 h or less. A more conservative estimate is ob-
tained if we assume that the peak P. areolatus FSA only persisted
until a day prior to the new moon in December 2005. Intensive sur-
veys show that on average densities of P. areolatus sighted the day
after peak aggregation periods are 50% lower than the previous
day. Thus we can estimate that in peak periods 858 P. areolatus
were present at the site and over two nights two spearﬁshermen
removed approximately 15% (129/858) of the P. areolatus FSA.
Other studies have shown similar vulnerabilities of the species to
hook and line ﬁshing. Speciﬁcally, Wilson et al. (2010) used UVC
and CPUE surveys to estimate that 20–25 hook and line ﬁshers in
Raja Ampat, Indonesia, removed more than two-thirds of a large
P. areolatus aggregation in 6 days.
E. fuscoguttatus and E. polyphekadion also aggregate in shallow
and deep water at the FSA during the second lunar quarter be-
tween December–April, however CPUE for Epinephelus spp. at the
FSA were not signiﬁcantly different from CPUE on reefs 1–12 km
away from the FSA. The dominance of P. areolatus in FSA catches
is attributable to four factors. Firstly, some Roviana spearﬁshermen
prefer not to spear large aggregated serranids such as E. fuscogutt-
atus, as they have to spend considerable time ﬁlleting this species
before sale, whereas P. areolatus is purchased whole at ﬁsheries
centres in Munda. Secondly, P. areolatus is an intermediate size that
is easy for spearﬁshermen to catch and handle, whereas spearing
the considerably larger E. fuscoguttatus risks gear damage or loss.
Thirdly, P. areolatus is relatively inactive at night and consequently
easier to spear than E. polyphekadion and E. fuscoguttatus, which are
more active and often ﬂee from divers (Hamilton et al., 2005). Fi-
-3 -2 -1 0 1 2 3
-3 -2 -1 0 1 2 3
-3 -2 -1 0 1 2 3
Per 1000 m2
3 days before and after the new moon. New moon = 0
-3 -2 -1 0 1 2 3
Fig. 5. Mean densities (±1 SE) of Epinephelus fuscoguttatus,Epinephelus polyphekadion and Plectropomus areolatus on the deep (20 m) transect before, during and after new
moon in February and March 2005 and 2006.
254 R.J. Hamilton et al. / Biological Conservation 145 (2012) 246–257
Author's personal copy
nally, as revealed in the UVC data reported here, P. areolatus is the
most abundant species in shallow water and thus search time is
4.3. Local knowledge of FSAs
This study shows how local knowledge on FSAs is utilised to
maximise capture success, with Roviana spearﬁshermen predomi-
nating targeting the FSA during the second lunar quarter, when
numbers of P. areolatus are at their maximum in shallow water.
In Roviana Lagoon spearﬁshermen provided detailed information
on the locations of FSAs, species composition, the lunar stages
when FSAs disperse, depth distributions of aggregated ﬁsh and
their behaviours (Hamilton and Kama, 2004). This level of detail
is not surprising, as ﬁshers from the Western Solomon Islands
are renowned for having highly detailed local knowledge (e.g.
Hviding, 1996; Johannes, 1989; Hamilton and Walter, 1999; Asw-
ani and Vaccaro, 2008).
Nevertheless, local knowledge of the October to January pazara
spawning season was incorrect for the FSA reported on here, with
UVC data demonstrating that aggregations of E. fuscoguttatus and E.
polyphekadion occurred from December to April. Furthermore, P.
areolatus aggregations of variable size occurred in virtually every
month of the year, and often from full to new moons, information
that was absent from the Roviana local knowledge base. We do not
know why local knowledge on the pazara season did not prove to
be correct in this instance. One possible explanation is that the
FSA reported on here has a different spawning season from other
well known FSAs in central and eastern Roviana Lagoon that have
been exploited for generations (Hamilton and Kama, 2004), and
Roviana ﬁshermen may have simply assumed that this recently
discovered FSA had the same spawning seasons.
This ﬁnding highlights that while local knowledge can be of
great value, it will often only provide part of the picture and at
times may be inconsistent with scientiﬁc ﬁndings (e.g. Daw
et al., 2011; Ruddle and Davis, 2011). As a result, local knowledge
should be independently validated before it is used as the basis for
management or conservation (Usher, 2000), especially when it re-
lates to the management of vulnerable species and critical habitats.
Indeed, when we held the initial meeting with local leaders in
Roviana that claim ownership of the FSA reported on here, they ex-
pressed interest in placing a closed season at this FSA from Octo-
ber–January based on their traditional knowledge of the Roviana
pazara season (Hamilton and Kama, 2004). However, when UVC
data were presented back to local leaders they realised that a
closed season from October to January would offer limited protec-
tion to E. fuscoguttatus and E. polyphekadion, and very little protec-
tion to P. areolatus. Consequently they declared this FSA as a year-
round no-take MPA in 2006.
4.4. Success and challenges of running a community-based monitoring
In Roviana Lagoon the decision to train local spearﬁshermen in
monitoring was pivotal to both the success of the UVC program
and the conservation of this FSA. With sufﬁcient training and men-
toring, spearﬁshermen who had limited formal education became
competent FSA monitors, due to their acute underwater observa-
tional skills. As their awareness on the importance of maintaining
FSAs grew they advocated for this FSA to be protected, and since
monitoring ceased in 2006 have not returned to ﬁsh at the FSA. De-
spite these beneﬁts, monitoring is expensive and it is unrealistic to
think that communities (or even provincial ﬁsheries departments)
in Melanesia could fund ongoing FSA monitoring programs. The di-
rect cost of running the Roviana FSA monitoring program for
2 years was USD $25,000. This included salaries for FSA monitors,
boat hire, SCUBA equipment and insurance. This amount does
not include the indirect costs of having the senior author support
this program. We suggest that in the short to medium term, FSA
monitoring programs should be co-funded by environmental NGOs
and national government agencies until a long-term sustainable
funding solution is achieved.
4.5. Current status of the FSA
Low levels of nighttime spearﬁshing (2–6 incidents a year) have
continued to occur at the FSA since it was declared a community-
based MPA in 2006 (MG personal observations). Incidents of
poaching at the FSA appear to relate to three factors. Firstly, multi-
ple communities claim customary rights to ﬁsh this FSA, making
consensus on management difﬁcult. Secondly, the FSA is situated
some distance from communities, which means poachers are unli-
kely to be seen and thirdly, local leaders and provincial ﬁsheries
ofﬁcers have limited capacity to enforce the closure. Despite some
poaching, respect for this closure is generally good, and anecdotal
observations of the FSA indicate no changes in the abundances of E.
fuscoguttatus and E. polyphekadion and only slight reductions in the
abundances of P. areolatus since 2006 (MG personal observations).
The limited creel data that we have from 2010 supports Giningele’s
observations, with the total weight and CPUE of P. areolatus landed
on a single night in April 2010 being similar to the highest total
weight and CPUE of P. areolatus landed on single nights in 2001
In this paper we have shown how local knowledge and marine
science can be utilised in combination to conserve critical life
stages of vulnerable species. Speciﬁcally we were interested in
the conservation of E. fuscoguttatus,E. polyphekadion and P. areola-
tus FSAs in Roviana Lagoon. By documenting local knowledge of
FSAs and conducting a spearﬁshing creel survey we obtained base-
line information on the locations, species composition, seasons,
status and threats to grouper FSAs in Roviana Lagoon. To further
advance our understanding of FSAs a 2-year long community-
based monitoring program was established at the largest known
FSA in Roviana Lagoon.
The results of this cooperative NGO-community study shows
that P. areolatus is extremely vulnerable to nighttime spearﬁshing,
due to long residency times at FSAs, high densities in shallow
Total population estimates of E. fuscoguttatus,E. polyphekadion and P. areolatus at the FSA on the new moon between the months of March 2005 and May 2006.
E. fuscoguttatus 606 112 56 0 0 0 6 41 0 228 655 704 507 0 6
E. polyphekadion 199 18 35 0 0 0 0 0 0 0 23 299 275 6 0
P. areolatus 604 283 445 353 299 34 64 199 102 299 1089 1039 576 367 234
Total No. groupers 1409 413 536 353 299 34 70 240 102 527 1767 2042 1358 373 240
R.J. Hamilton et al. / Biological Conservation 145 (2012) 246–257 255
Author's personal copy
water and the ease with which it can be approached at night.
Clearly FSAs of P. areolatus need to be protected from nighttime
spearﬁshing wherever it is practiced. Conversely, the depth distri-
butions and diver avoidance behaviour of deeper-dwelling E. fusco-
guttatus and E. polyphekadion at FSAs offers them a greater degree
of protection from free diving spearﬁshers. However both E.
polyphekadion, and to a lesser extent E. fuscoguttatus, are highly
susceptible to hook and line ﬁsheries (Rhodes and Sadovy, 2002;
Rhodes et al., 2011), and are therefore also deserving of protection.
In Roviana Lagoon the monitoring program served as an effec-
tive vehicle for building community support for managing the
FSA, and it also provided an independent validation of local knowl-
edge on grouper spawning seasons. Results of the monitoring
study showed that while local knowledge can be highly detailed,
like all knowledge systems, it is not infallible (Johannes et al.,
2000), with science-based underwater monitoring building a more
complete picture of FSA seasons than local knowledge alone.
Clearly, local knowledge is most useful in management and conser-
vation if it is carefully collected, evaluated and validated, and the
cultural sensitivities and conﬁdentiality of local knowledge is re-
spected (Ruddle et al., 1992; Usher, 2000; Daw, 2008; Hamilton
et al., 2012).
In this study it was local knowledge and the scientiﬁc results of
the community-based monitoring program that led to the develop-
ment of appropriate management measures for this FSA, with the
aggregation declared a year-round community-based MPA in
2006. Finally, while we cannot prove that the conservation efforts
reported on here have assisted in the FSA remaining healthy, one
thing is clear; this site is one of the largest known multi-species
FSAs in Melanesia, and its ongoing preservation is critical for the
long-term health of grouper ﬁsheries in Roviana Lagoon.
First and foremost we would like to thank W. Kama for assisting
with the local knowledge survey and FSA monitoring. We also
thank S. Baso, G. Gadepeta and S. Kari for assisting with FSA mon-
itoring. We are grateful to the Munda area communities who al-
lowed us to work on their reefs. We thank N. Peterson for
producing Fig. 1, and G. Almany and K. Ruddle for improving an
earlier version of this manuscript. Funding for this project was pro-
vided by Oak Foundation, The David and Lucile Packard Foundation
and The John D. and Catherine T. MacArthur Foundation.
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