POPULATION ASSESSMENT OF THE CONCH STROMBUS GALEATUS
(GASTROPODA, STROMBIDAE) IN PACIFIC PANAMA
ROBERTO CIPRIANI,1,2 HECTOR M. GUZMAN,1* ANGEL J. VEGA3 AND MELINA LOPEZ4
1Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Panama;
2Departamento de Estudios Ambientales, Universidad Simo?n Bolivar, A.P. 89000, Caracas 1080,
Venezuela; 3Departamento de Biolog??a Marina y Limnolog??a, Escuela de Biolog??a, Universidad de
Panama?-Sede Veraguas, Apartado 0923-00173, Panama?; 4Department of Chemistry, Geosciences and
Environmental Science, Tarleton State University, Box T-0540, Stephenville, Texas 76402
ABSTRACT Populations ofStrombus galeatus Swainson 1823 have been severely over?shed in Paci?c Panama. In this study, we
assessed the status of the S. galeatus population in Las Perlas and Coiba Archipelagos. Average densities per site were dismal:
0.45 ? 3.8 indha?1 and 6.0 ? 18 indha?1 in Las Perlas and Coiba, respectively. In Las Perlas, low densities occurred on the
southwest coast of Del Rey, the south coast of Chaperas, and Bolan?os, whereas intermediate densities were found on the eastern
coast of Saboga. In Coiba, high relative densities occurred only on the west coast of Coiba Island and at the north and south of
Bah??a Damas. Environmental variability and depth did not explain the differences found between densities nor the low
abundances in the archipelagos. Shell length of S. galeatus from Coiba ranged from 91.0?213.3 mm (156 ? 22.2 mm). We ?tted a
von Bertalanffy growth model to juvenile data using the following parameters: LN ? 315 mm, K ? 0.029 mo?1, and to ? 0.5 mo.
The model suggests that 27?28 mo are required (on average) before the outer lip begins to form. Two years after the enactment of
Decree No. 159 in September 2004, which banned the Strombus ?sheries in Panama for ?ve years, the conch populations in Las
Perlas and Coiba have not recovered. The Las Perlas population is recruitment limited and we recommend that a program of law
enforcement and monitoring should be implemented immediately to protect this species, conducive to increase spawning and
settlement in nursery grounds.
KEY WORDS: conch, Strombus galeatus, over?shing, Las Perlas, Coiba, Panama
INTRODUCTION
The giant conch, Strombus galeatus Swainson 1823 inhabits
the coastal waters of the Eastern Paci?c, ranging from the Gulf
of California to Ecuador, the Galapagos Islands, and Peru
(Keen 1958, Arroyo-Mora 2003). The giant conch, S. galeatus,
is popularly known in Panama, Costa Rica, and Nicargaua as
cambute and inMexico as caracol burro and the Cortez conch. It
lives on sandy bottoms with rocks (Arroyo-Mora 2003) and
adjacent to mangrove areas (Gonza?lez 1997) from the low tide
mark to 15 m deep, but it has been found as deep as 30 m. S.
galeatus feeds primarily on macroalgae and is preyed upon by
octopi, rays (Myliobatidae), trigger?sh (Balistidae), and snap-
pers (Lutjanidae). It spends part of the time partially buried in
the sand, but it also is capable of moving long distances (on the
scale of km; Arroyo-Mora 2003) over the course of months.
During the early months of the year, S. galeatus forms large
aggregations in shallow waters where mating and oviposition
takes place. Females lay egg masses directly on the sand and on
dead shells (Arroyo-Mora 1998, Arroyo-Mora 2003).
Strombus galeatus, Melongena patula Broderip & Sowerby
1829, Pleuroploca princeps Sowerby 1825, and Malea ringens
Swainson 1822 are all gastropod species important for sub-
sistence and small commercial ?sheries on the Paci?c coast of
Panama. The largest conch production in Panama comes from
San Blas and Bocas del Toro on the Caribbean coast (Martans
1997). There, and throughout the Caribbean Sea, the exploita-
tion pressure on S. gigas and S. costatus has been driven by the
high demand for their meat and their increasing market values
(Tew?k 1997).
Coiba and Las Perlas Archipelagos in Paci?c Panama were
designated as protected areas in 2004 and 2007, respectively.
These designations prohibit the use of particular ?shing meth-
ods and guarantee the regulation of ?sheries using the best
scienti?c evidence available. However, very little is known
about the biology, ecology, and distribution of S. galeatus in
Paci?c Panama. No formal studies on the giant conch in Las
Perlas have ever been conducted, and only one report is
available in the literature for Coiba (Vega & Pe?rez 2003),
although anecdotal information is available from local people.
Fishermen from the Ensenada community on Las Perlas have
informally reported their catches for the past 4 y. Their reports
show an average catch of nonspeci?ed gastropods of about 949
kg per year, with harvest peaks in September and November.
Panama?s Marine Authority has also recorded national totals
annually, and according to these records, catches of conch have
been declining rapidly. In 1998, the annual catch was 116 metric
tons, declined in 1999 to 17 metric tons, and collapsed in 2000
and 2001 when only 1 metric ton was reported. Pinpointing the
source of conch decline is impossible, however, as the data from
Panama?s Marine Authority comes from catch values pooled
from both Paci?c and Caribbean conch species. Decree No. 159
by the Government of Panama, which went into effect in
September 2004, established a 5-y ?shing ban for all species of
Strombus in Panama. It was enacted because S. costatus and S.
gigas were overexploited throughout the Caribbean, but it was
not based on any speci?c knowledge about the potential
over?shing of S. galeatus in the Paci?c.
In this study, we assessed the status of the S. galeatus
population in Las Perlas and Coiba Archipelagos, quanti?ed
this species? abundance and density, and documented its geo-
graphical distribution in these regions. We also ?t a growth*Corresponding author. E-mail: guzmanh@si.edu
Journal of Shell?sh Research, Vol. 27, No. 4, 889?896, 2008.
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model to juvenile and subadult conchs from Coiba to estimate
their age at maturity. Finally, we suggested candidate areas in
both archipelagos for population monitoring. Further studies
on the ecology and growth of this species will certainly improve
the management plans necessary for the rational exploitation
and protection of the giant conch resource in the years to come.
MATERIALS AND METHODS
Study Areas
The Las Perlas Archipelago lies in the Gulf of Panama 60 km
southeast of Panama City. It consists of approximately 255
islands with ca. 318,460 km of coastline (Campbell 2005). The
largest island, Del Rey, (822#54.64$ N, 7854#20.16$ W), sits
approximately 38 km southwest of the mainland. The Las
Perlas Archipelago, which is enclosed in a marine special
management zone, is Panama?s most important ?shing
area (Villalaz & Go?mez 1997). This zone covers a core area of
1688 km2, as well as two small satellite areas, Roca Trollope
and Isla Galera, that are located to the southeast. Upwelling,
produced by northerly winds, occurs along the Gulf of Panama
between January and April and strongly affects the water
temperature and salinity of the region (Glynn & Stewart 1973).
Coiba National Park, located in the Gulf of Chiriqu??,
contains 30 islands and islets and has a surface area of ca.
270,125 ha. The largest island is Coiba (728#00.72$ N,
8146#53.27$ W), which lies approximately 24 km southwest
of the mainland. The upwelling that occurs in the Gulf of
Panama does not seem to strongly affect Coiba National Park,
but every 4 y both archipelagos experience El Nin?o Southern
Oscillation (McNiven 2003, D?Croz & O?Dea 2007) which has
severely affected coral reef ecosystems and related ?sheries in
1982/83 and slightly in 1997/98.
Both archipelagos contain rich and biodiverse coastal
and shallow water ecosystems, ranging from sandy bottoms
and rocky shores to mangroves, seagrasses, and coral reefs
(Guzman et al. 2004, 2008).
Sampling Design
We selected the sampling localities of our study using the
ArcGIS V9.1 software (Environmental System Research Insti-
tute) with LANSAT-7 ETM satellite images (2000) and topo-
graphic maps (1:50,000) following the methodology described
in Guzman and Guevara (2002) and Guzman and Tew?k
(2004). Irregular polygons of ca. 2 3 2 km arbitrarily posi-
tioned one adjacent to another delimited our sampling sites.
They covered the waters surrounding each archipelago (sensu
Guzman et al. 2004, Cipriani et al. in review).
In Las Perlas, we randomly selected 68 out of the 108
available polygons (108 sites ? 28,891 ha; 68 sites ? 63%)
and in Coiba, 35 out of 84 polygons (84 sites ? 29,326 ha; 35
sites ? 42%). We designated an imaginary boundary at ;10 m
deep to divide each sampling site into two depth levels, although
depth ranges varied according to local geomorphology. In each
of the two depth levels, we randomly selected three bottom
transects of 6 3 100 m (totaling 6 per site), which covered a
surface area of 3600 m2 per site. Gauged depths varied from
1.50?18.3 m in Las Perlas and from 1.20?14.0 m in Coiba.
Depth levels were considered separate treatments, as depth
differences between levels were still signi?cant in 40% of
transects after corresponding tidal amplitudes of 4.85 m (Las
Perlas) and 5.67 m (Coiba) were added to the gauged data.
Scuba divers conducted visual surveys between June 2 and
July 11, 2006 in Las Perlas and between October 6, 2006 and
February 1, 2007 in Coiba.
Substrates
Substrate characterization followed Cipriani et al. (in
review), which describes substrates by considering the presence
of rocks (R); hard carbonate substrates (H); coral communities
(C); seagrasses (G); algae (A); sand (S); and mud (M), and their
combinations. Using this nomenclature, for example, category
SA described any transect dominated by sand and algae and
CH any transect with abundant corals and hard carbonate
substrates. Substrates differ between the archipelagos, but both
have a large proportion of substrates categorized as S (48%
of transects in Las Perlas and 57% in Coiba) (Ben?eld 2005,
Cipriani et al. in review). Such substrates are known to be pre-
ferred by conchs (Arroyo-Mora 1998, 2003).
Densities
We estimated the abundances of S. galeatus by directly
counting the number of living individuals found in each
transect. Densities per transect were estimated by dividing the
abundance per transect by 600m2 and scaling it to hectares (ha).
The overall mean density of each sampling site was obtained
by averaging the density of all six transects. Transect densities
from neighboring polygons were used to interpolate conch
densities in polygon areas that were not surveyed (i.e., for 40 of
the polygons at Las Perlas and 49 in Coiba). All averaged values
and their corresponding standard deviations are reported as
mean ? s.d.
We used a chi-square (c2) test based on permutations
implemented in Microsoft Visual Basic (2005) (PER test) to
compare the frequency of conchs per substrate and the pro-
portion of substrates in Coiba Archipelago, but not in Las
Perlas due to small sample size. We used signi?cant differences
between these parameters to pinpoint habitat preferences in
conchs. Differences in densities were tested by depth level using
statistical analyses based on resampling tests (RES test) (Manly
1997) and implemented in Microsoft Visual Basic (2005). For
these tests, we used 5000 iterations and set signi?cance at a ?
0.05. We used Bonferroni?s method to calculate and correct
con?dence intervals (CIs), which allowed for multiple compar-
isons, such that aBonf. ? ac?1, where c was the number of
groups to be simultaneously compared. Results are reported as
mean ? CI.
Information shared by ?shermen from Las Perlas about the
distribution of sites in which adult conchs were abundant was
geo-referenced and compared with the distribution of conch
densities resulting from our survey.
Biometrics and Juvenile Growth
Because densities of S. galeatus in Las Perlas and Coiba were
very low, we performed a growth analysis on 88 tagged conchs
from Coiba Archipelago that were followed between 1999 and
2000 (data partially analyzed in Vega & Pe?rez 2003). These data
consist of 510 values of S. galeatus shell length (i.e., distance
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from the apex to the siphon opening) collected over the course
of 9 mo (April through January, excluding December) and
measured to the nearest millimeter. The modes of the age
groups of juveniles and subadults (following Arroyo-Mora
1998) identi?ed on the shell length frequency histograms were
assumed to be representative of S. galeatus age groups in Coiba
Archipelago and were used to ?t a von Bertalanffy growth
model (Hilborn & Walters 1992, Essington et al. 2001). In the
Caribbean queen conch (S. gigas), shell length is a relatively
good predictor of relative age only before sexual maturity. After
that, the thickness of the recently formed outer lip becomes
the best proxy of relative age (e.g., Appeldoorn 1988). In Vega
and Perez?s 2003 data set, the thickness of the outer lip of
S. galeatus was measured to the nearest millimeter in a subset
of 40. Here, the relation between lip thickness and shell length
in these individuals of S. galeatus was compared with that in
191 individuals of S. gigas collected in the similarly exploited
area of Los Roques Archipelago, Venezuela (data from
Cipriani & Posada 2003) as both species are closely related
(Latiolais 2003).
RESULTS
Densities
We found S. galeatus in only 7 of the 408 transects (24.5 ha)
surveyed in Las Perlas, and only 11 individuals were observed
(1?3, 1.6 ? 0.8 per inhabited transect). Substrates in these
transects included 5 of the 20 categories present in the archi-
pelago (substrate category, abundance of S. galeatus): H, 2; SH,
1; SA, 2; A, 3; and S, 3. No robust statistical inferences about
the association of conchs with different substrates could be
obtained because the number of conchs was too low.
We found living conchs in only 32 of the 210 transects
surveyed (12.6 ha) in Coiba, and the total conch abundance was
70 (1?10, 2.1 ? 1.8 per inhabited transect). Relative abundances
varied according to the substrate category assigned to transects.
Conchs were found in 8 of 15 categories of substrates present
in Coiba (proportion of transects in that category, abundance
of S. galeatus): RC 1, C 15, SH 1, SRA 2, SC 4, SCA 1, SA 6,
and S 30). The corresponding relative abundances found in
these substrate categories were statistically different from those
expected at random (PER test, c2 ? 32.9, d.f. ? 7, P < 0.0001).
The highest proportion of individuals was found in transects
with substrate category S, but conchs were more abundant than
expected in substrates SRA and SA.
The density in transects with living conchs in Las Perlas
varied considerably, ranging from 16.7?50 ind. ha?1 and
averaging 26.2 ? 13.1 indha?1. Density in all four surveyed
sites with conchs ranged from 2.8 and 13.9 indha?1 and
averaged 7.6 ? 4.7 indha?1 per site.
In Coiba, the densities in transects with living conchs were
greater than those recorded in Las Perlas, varying from 16.7?
167 indha?1 and averaging 35.4 ? 30.6 indha?1. Density in all 16
surveyed sites with conchs ranged from 2.8?38.9 indha?1 and
averaged 12.2 ? 11.1 indha?1 per site.
In Las Perlas, abundances were too low to make any
statistical inference about the distribution of density by depth
level per transect, and in Coiba, statistical differences were not
found (average ?CI) (shallow level 38.0 ? 10.2; deep level 32.2 ?
16.0; RES test, NS).
Average densities per sampling site (considering all sites in
each archipelago, even those not sampled) were low for both
archipelagos. In Las Perlas, the estimated density was 0.45 ?
3.8 indha?1, and in Coiba, 6.0 ? 18 indha?1. Estimates of
population sizes based on these values are ;13,000 conchs
in Las Perlas and ;176,000 conchs in Coiba. Because visual
surveys are not the best method to account for recruits and
small juveniles, these values are probably underestimates.
In both archipelagos, we categorized sites as having low
(1?16 indha?1), intermediate (17?32 indha?1), and high relative
densities (33?48 indha?1) of conchs. In Las Perlas, 104 of 108
sites (27,801 ha, 96% of the total area surveyed in this
archipelago) had no conchs, whereas 3 sites (815 ha, 3%) had
relative low densities and 1 site (275 ha, 1%) had an interme-
diate density of S. galeatus. Low densities occurred on the
southwest coast of Del Rey, the south coast of Chaperas, and
Bolan?os Island. An intermediate density was found only on the
eastern coast of Saboga (Fig. 1A).
Fishermen reported usually collecting adult S. galeatus in
several areas around Las Perlas Archipelago, mostly on Galera
Island, on the coast and shoals located south and southeast of
Del Rey, in several localities around San Jose, and in shoals
located west of PedroGonzalez (Fig. 1B). Other collecting areas
extend to the north of the archipelago and include the islands of
Mina, Bayoneta, Casaya, Mogogo, Chapera, Contadora, and
Pacheca (Fig. 1B). Few of these shoals pointed out by ?sher-
men, relatively far from land, were not surveyed in our study.
In Coiba, conchs were absent in 47 of 84 sites (16,502 ha,
56%). In 27 sites (8541 ha, 29%) density was relatively low, in
7 sites (2816 ha, 10%) density was intermediate, and in 3 sites
(1467 ha, 5%) density was relatively high (Fig. 2). High densities
were found on the west coast of Coiba Island, north of Bah??a
Damas (Punta Damasi), and on the southern extreme of the
same bay (Fig. 2).
Biometrics and Juvenile Growth
Shell length of S. galeatus from Coiba ranged from 91.0?
213.3 mm (156 ? 22.2 mm). We pooled shell length values by
month (from April to November 1999, and January 2000) and
used their frequency distributions to identify 17 shell length
modes that allegedly represented different age groups (Fig. 3).
Following the recruitment that occurred in November, we
used 10 modes belonging to juveniles and subadults (with
shells# 175 mm in shell length) to ?t a von Bertalanffy growth
model of the form:
L?t? ? L?  1  eK?tto?
 
? 315  1  e0:029?t0:5?
 
; (1)
where L(t) is shell length at time t, LN ? 315 mm is the hypo-
thetical maximum length that shells can attain, K ? 0.029 y?1, is
the rate of growth, and to ? 0.5 is the time at which growth
described by a convex curve starts (Fig. 4).
In smaller S. galeatus, lip thickness remains approximately
constant as shell length increases. When the shell reaches ap-
proximately 170mm in length, the lip starts to thicken (values at
bottom of Figure 5). In conchs larger than 170mm, lip thickness
varies from 5 mm to more than 27 mm (values at center of
Figure 5). When we compared shell length and lip thickness, to
relate age of two exploited Strombus congeners with similar
growth (Arroyo-Mora 1998), for 40 S. galeatus individuals from
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Coiba (data used in Vega & Pe?rez 2003) (shell length ? 111?213
mm, 172 ? 26 mm; lip thickness ? 0.5?27 mm, 10.1 ? 10.3 mm)
with those of 191 individuals ofS. gigas fromLosRoquesArchi-
pelago, Venezuela (Cipriani & Posada 2003) (shell length ?
165?215mm, 202 ? 11.3mm; lip thickness?1?34mm, 17.6 ? 9.5
mm), we found that the shape of the relationship between these
two variables was similar in both species (Fig. 5).
DISCUSSION
In this extensive survey, we assessed the population status,
abundance, density, and distribution of S. galeatus in Las Perlas
and Coiba Archipelagos in Paci?c Panama. The abundance
of the giant conch in both archipelagos was very low: In our
surveys, we found only 11 living individuals in Las Perlas and
70 in Coiba.
Densities per transect in Las Perlas varied, averaging
26.2 ? 13.1 indha?1 in the 7 transects that contained living
conchs. In the 32 transects from Coiba in which conchs were
found, densities were one order of magnitude higher, 35.4 ? 30.6
indha?1, but these values are still low when compared with
those reported for transects from Laguna de San Miguel,
Reserva Natural Absoluta de Cabo Blanco, in Costa Rica
(500 indha?1) between 1993 and 1997 (Arroyo-Mora 1998,
2003).
Estimations of population sizes obtained from average
site densities ? 0.45 ? 3.8 indha?1 in Las Perlas and 6.0 ?
18 indha?1 in Coiba?also were extremely low: approximately
13,000 conchs in Las Perlas and 176,000 in Coiba. In Las Perlas,
this population size barely surpasses the lowest production of
conch of Panama (Caribbean and Paci?c) in 1999: 11,300 shells
Figure 1. Maps of LasPerlas Archipelago showing the distribution of conch
S. galeatus. (A) Map from survey showing the distribution of low (orange)
and medium (yellow) relative densities (indha?1) of conchs in the region. (B)
Map made with information from ?shermen showing distribution of adult
conchs. Insert shows relative position of the archipelago in Paci?c Panama.
Red indicates areaswith no conchs. Sampling sites are labeledwith numbers.
The large polygon and circles represent the limits of the protected areas.
Figure 2. Map of Coiba Archipelago showing the distribution [low
(orange), medium (yellow), and high (green) relative densities (indha?1)]
of the conch S. galeatus. Red indicates areas with no conchs. Sampling
sites are labeled with numbers. The large polygon represents the limits of
the national park.
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Figs. 1,2 live 4/C
or 17 tons at 1.5 kg per adult conch (Arroyo-Mora 2003),
according to the Panama?s Marine Authority. These average
densities and population sizes of S. galeatus in Paci?c Panama
are low compared with those of exploited populations of
S. gigas in the Caribbean. For example, in Cayo Cochinos,
Honduras, the overall density of queen conch was 14.6 ? 36
indha?1 (Tew?k et al. 1998). In Los Roques Archipelago
National Park, Venezuela, the actual population of S. gigas
had average densities of 17.5 indha?1 (Schweizer & Posada
2006) and population size (considering only subadults and
adults) was estimated to be 1,278,415 (Schweizer & Posada
2006, Cipriani & Antczak in review). These values suggest that
S. galeatus is under strong harvesting pressure in Paci?c
Figure 4. Von Bertalanffy growth model (small white circles) ?t to shell
length modes (white squares) of juvenile and subadults of S. galeatus.
Small gray squares represent adults (data from Vega & Pe?rez 2003.
Model parameters: LN$ 315 mm, K$ 0.029 y
?1, to$ 0.5.
Figure 5. Relationship between shell length and lip thickness of the Paci?c
giant conch, S. galeatus (black squares, this study) and the Caribbean
queen conch, S. gigas (gray crosses) (data from Cipriani & Posada 2003).
Figure 3. Size frequency histograms of S. galeatus shell length of
from April 1999 to January 2000 in Coiba Archipelago. Large white
squares represent juveniles and subadults. These modes were used to ?t the
Von Bertalanffy growth model. Small gray squares on bars represent
adults.
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Panama, assuming that unexploited populations for both
species were similar.
The effects of over?shing were most clearly seen in Las
Perlas Archipelago. Overall, 96% of the sites in Las Perlas were
devoid of conchs (Fig. 1, Fig. 2). As the distribution of ?shing
grounds of adult conchs reported by ?shermen in Las Perlas was
mostly covered in our survey (Figs. 1A, B), we could extrapolate
that the ?shermen?s catch of 949 kg of giant conchmeat per year
(4.8 tons of living animal), approximately 2791 shells (at 1.7 kg
per adult conch; sensu Arroyo-Mora 2003), represented ;22%
of the standing population size. We found the population of
S. galeatus in Las Perlas to be dangerously reduced, and under
these conditions, even a 22% catch might lead to the regional
collapse of its population in few years. For example, low
densities are known to hinder or even prevent reproduction in
some species. This process, also known as the Allee effect, seems
to play an important role in the dynamics of S. gigas in the
Bahamas. There, queen conchs seem unable to ?nd a mate at
densities lower than 56 ind ha?1 (Stoner & Ray-Culp 2000).
The conch population in Coiba Archipelago, even if larger
than that in Las Perlas, is also very reduced compared with
Costa Rica; 56% of all sites in Coiba had no conchs, and the
west coast of Coiba Island and the northern and southern
extremes of Bah??a Damas were the only localities with the
highest relative densities of conch in Paci?c Panama (Fig. 2).
Historical evidence also suggests that conchs in Coiba have
been under ?shing pressure for at least a decade. The maximum
and average shell length values for conchs collected in Coiba
Archipelago National Park between 1999 and 2000 (91.0?213.3
mm, 156 ? 22.2 mm) were smaller, respectively, than those
found in conchs from Reserva Absoluta Natural Cabo Blanco,
Costa Rica between 1993 and 1997 (87.0 mm to 293.5 mm,
average 183 mm) (Arroyo-Mora 2003; Arroyo-Mora & Mena
1998).
The giant conch also has been exploited or depleted in
Nicaragua (Gonza?lez 1997, Anonymous 2006), Costa Rica
(Arroyo-Mora 2003), and the Gulf of California (Saenz-Arroyo
et al. 2005). In Mexico in 2004, the price of 1 kg of its meat was
US$4.6 (Anonymous 2004). In Costa Rica between 1993 and
1997, the average number of conchs surveyed by divers was 4?8
conchs hour?1 in localities in which S. galeatus was exploited,
such as Lagarto and San Juanillo in Guanastes. In Reserva
Natural Cabo Blanco, the rate obtained during the same period
of time was 14?40 conchs hour?1 (Arroyo-Mora 1998) or 500
indha?1 (Arroyo-Mora & Mena 1998, Arroyo-Mora 2003),
considerably high for a previously exploited population under
protection because 1963.
Environmental variability did not explain the differences
between conch densities in Las Perlas and Coiba archipelagos
or the low abundances. The substrate composition was quali-
tatively different between them (Cipriani et al. in review), but
this variability was minimal when considering only those
substrates in which S. galeatus was more likely to be found.
The substrates in which we found living conchs in Las Perlas (H,
SH, SA, A and S occurred in 141 transects (8.5 ha), and those in
Coiba (RC, C, SH, SRA, SC, SCA, SA, and S) in 154 transects
(9.2 ha) (Cipriani et al. in review). These results do not differ
from those previously reported for S. galeatus in Coiba, where
juveniles were found buried in sand, close to corals, and on
substrates with algae, whereas adults crawled on sandy bottoms
(Vega & Pe?rez 2003), or from those reported in Laguna de San
Miguel, Costa Rica, where individuals were found living on
sand and rocks (Arroyo-Mora 1998).
Variation in the distribution of conchs with depth did not
explain our results either. Previous literature on the vertical
distribution of S. galeatus in Costa Rica and Coiba indicated
that small conchs live in shallow water (from 0.5?4 m deep) and
large conchs live in deeper waters (Arroyo-Mora 1998, Arroyo-
Mora 2003, Vega & Pe?rez 2003). However, our survey in Coiba
Archipelago did not reveal any statistical difference between
conch densities at different depth levels (estimated in those
transects that contained living conchs).
The distribution of length data on the monthly histograms
suggests that every year juveniles recruited to the conch
population of Coiba Archipelago at least twice (Fig. 3). The
?rst recruitment occurred during themonths of April, May, and
June, and the second started in November and continued at
least until January. Results of a similar analysis in Costa Rica
using tagged giant conchs suggested that recruitment in Cabo
Blanco occurred over the course of several months, indicating
that reproduction was constant throughout the year (Arroyo-
Mora&Mena 1998). In a study from two decades ago,Weil and
Laughlin (1984) reported that S. gigas in Los Roques Archi-
pelago, Venezuela, reproduced throughout the year, with a
peak in intensity between April and November.
We ?tted a Von Bertalanffy model to the modes of shell
lengths of juveniles and subadults, considering the limitations
of the model itself (Roff 1980, Hilborn & Walters 1992, Day &
Taylor 1997) and those of using it on conchs (Appeldoorn 1990,
Appeldoorn 1992, Glazer & Berg 1992) (Figs. 3 & 4). Particu-
larly in S. gigas, the Von Bertalanffy model seems to describe
shell growth in juveniles reasonably well, until the outer lip
begins to form and thicken (Appeldoorn 1988, Appeldoorn
1990). The lip thickness of the giant conch changes slowly
whereas the shell grows, but after maturity the shell stops
growing and the outer lip becomes thicker (Fig. 5). Thus, using a
Von Bertalanffy model based on shell length categories, to
describe growth for the conch?s entire life span results in
biological interpretations that are misleading (Appeldoorn
1990). This model is not recommended for application to adult
conchs for another reason: in old S. gigas specimens, erosion by
epibionts and borers reduces the shell?s length, completely
obliterating the age structure signal of the shell length modes.
We assumed that S. galeatus suffers a similar process, as
epibionts and signs of erosion are common on adult shells
(Arroyo-Mora 1998, 2003).
As growth in different isolated groups of conchs of the same
stock can be heterogeneous (Glazer & Berg 1992), in this study
we used the growth model to determine a rough estimate of the
amount of time (in months) S. galeatus juveniles from Coiba
must grow before the outer lip develops and thicken. According
to Arroyo-Mora (1998), in S. galeatus this occurs at shell
lengths of 170 mm. In our data, the outer lip began to thicken
at a shell length interval including this value, 170?175 mm (Fig.
5). The Von Bertalanffy model suggested that a conch would
need 27?28 mo (on average) to begin forming its outer lip, or
2.3?2.4 y. Strombus gigas requires longer times to reach
maturity than S. galeatus: 3.19?3.22 y in La Parguera, PR
(Appeldoorn 1992) and 3.5?4.0 y in the Florida Keys (Glazer &
Berg 1992).
Notice that the value of LN ? 315 mm is larger than any
available S. galeatus shell length. To our knowledge, the
CIPRIANI ET AL.894
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maximum shell length reported in the region is 293.5 mm
(Arroyo-Mora 2003). As we only worked with juvenile and
subadult conchs, LN ? 315 mm should be interpreted as the
maximum hypothetical size the giant conchwould attain if it did
not mature and invest its energy in reproduction (Appeldoorn
1990).
A positive value of to ? 0.5 was indicative of the existence of
a very early in?exion point in the growth curve (Appeldoorn
1990). The average rate of growth in shells from 110?120 mm
long was 8.21 mm month?1 in Vega and Pe?rez?s (2003) study,
but in our model the same interval of sizes showed a smaller
average rate of 5.91 mm month?1. This difference also suggests
that the actual growth curve of S. galeatus possesses an early
in?exion point. However, our sample size was too small to study
it further. Indeed, the results obtained from the Von Bertalanffy
model should be considered preliminary rather than de?nitive,
as more data and work are necessary to understand the growth
of this species in this region.
Future studies of the growth of the giant conch must include
a complete record of paired values of shell length and lip
thickness to study growth in juveniles and subadults and in
adults, respectively. Different models for males and females also
should be considered. In addition, to identify the adequate shell
biometrics to regulate harvesting, it is necessary ?rst to establish
a precise relationship between shell morphology and sexual
maturity. Strombus galeatus is considered to be sexually mature
when it reaches 170 mm in length and begins to grow its shell?s
outer lip (Arroyo-Mora 1998, Arroyo-Mora & Mena 1998,
Arroyo-Mora 2003). We know that S. gigas is mature only
when its lip is completely formed and its thickness reaches 5 mm
(Egan 1985, Appeldoorn 1988, Glazer & Berg 1992, but see
Avila-Poveda & Baqueiro-Ca?rdenas 2006). However, the
appearance of a thin shell lip is considered a poor criterion
for sexual maturity and a lip of 13.5 mm or greater is
recommended to protect stocks under heavy ?shing pressure
(Avila-Poveda & Baqueiro-Ca?rdenas 2006). The differences
between these two closely related species (Latiolais 2003) and
the little knowledge we have about the biology and ecology of
S. galeatus warrant a closer and better look at the gonadal
development and the reproductive cycle of the giant conch.
Two years after the enactment of Decree No. 159 in
September 2004, which banned the Strombus ?sheries in
Panama for ?ve years, the populations of S. galeatus in Las
Perlas and Coiba Archipelagos have not recovered. On the
contrary, the giant conch population from Las Perlas seems to
be in critical condition or near collapse. Inasmuch as Decree
No. 159 is a sensible measure taken at the right time, its
enforcement is fundamental to achieving its goal: the recovery
of the conch resources in Panama.
The Las Perlas giant conch population is in such meager
condition that we recommend that a program of monitoring
begin at once. The progress of the population can be evaluated
and potentially restored by transplanting adults to increase
spawning stocks into nursery grounds (sensu Glazer & Delgado
2003). The areas in the archipelago that should be monitored
immediately are those in which conchs are still alive; the
southwest coast of Del Rey, the south coast of Chaperas,
Bolan?os Island, and the eastern coast of Saboga. Strombus
galeatus stocks can be successfully restored under protected
areas (Arroyo-Mora &Mena 1998, Arroyo-Mora 2003) and the
suggested creation of a marine reserves network within the ar-
chipelagomay contribute to increase nursery grounds (Guzman
et al. in rev.). For instance, a Costa Rican small reserve (18 km2
marine area) has reached over 500 indha?1 in almost 45 y of
protection (see Arroyo-Mora & Mena 1998). Education, train-
ing, and involvement of local ?shermen in the management and
restoration efforts of the giant conch in Las Perlas and Coiba
Archipelagos are actions that should be considered without
delay, as the experience and knowledge of local peoples about
the resource will undoubtedly be helpful in designing future
programs for conserving and harvesting of S. galeatus in Paci?c
Panama.
ACKNOWLEDGMENTS
The authors thank C. Guevara, A. Lam, C. Vega, C.
Pimiento, and F. Torres for providing invaluable assistance in
the ?eld and to all the ?shermen who kindly provided infor-
mation about the distribution of conchs in Las Perlas. The
Government of Panama provided permits to work in the area.
This research was partially sponsored by the International
Community Foundation, the Smithsonian Tropical Research
Institute, the United Nations Foundation?Global Conserva-
tion Fund, the UNESCO, Conservation International, the
Universidad Simon Bolivar, and DEFRA?s Darwin Initiative
Fund (UK).
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