Open Journal of Marine Science, 2012, 2, 157-166
http://dx.doi.org/10.4236/ojms.2012.24019 Published Online October 2012 (http://www.SciRP.org/journal/ojms)
Density, Sex Ratio, Size, Weight, and Recruitment of
Plicopurpura pansa (Gastropoda: Muricidae) in Costa
Chica, Guerrero, México
Rafael Flores-Garza1, Arcadio Valdés González2, Pedro Flores-Rodríguez1,
Sergio García-Ibáñez1, Norma L. Cruz-Ramirez1
1Unidad Académica de Ecología Marina, Universidad Autónoma de Guerrero,
Fraccionamiento las Playas, Acapulco, México
2Facultad de Ciencias Biológicas, Universidad Autónoma de Nuevo León, San Nicolas de los Garza, México
Received May 12, 2012; revised June 26, 2012; accepted July 4, 2012
ABSTRACT
Plicopurpura pansa is a cultural resource with economic importance since ink can be extracted from it to dye clothes.
This snail inhabits the rocky intertidal zone of Mexican Pacific, is found attached to rocks in crevices and holes. The
objective was to analyze the P. pansa population structure in Costa Chica of the State of Guerrero based in density, sex
ratio, size and weight, besides to realize observations on mating and recruitment, for which quarterly sampling was
made during an annual cycle in three beaches. The density was 4.83 snails/m2. Sex ratio ranged from 0.76:1.00 to 1.00:
0.96 (F:M). Average size was 20.91 mm. The best represented sizes in females were from 10.5 to 28.5 mm and in males
13.5 to 28.5 mm. Averaged weight was 1.99 g, females showed a coefficient of variation in weight of 96.53%. Recruit-
ment occurred for the entire year. In December 2006 and September 2007 a larger frequency of recruits was shown. Sex
ratio showed a 1:1 tendency. Snail population was characterized by being small sized and in high densities. Weight
variations in females were found related to their reproductive cycle.
Keywords: Gender; Recruitment; Intertidal; Ink
1. Introduction
Mexican Pacific Coast has large and very important
rocky coast extension s; in the tropics, the ro cky co ast is a
zone with high and very productive biological diversity
[1,2], in this region many mollusks species are known to
be of economic importance: and are being fished, such as
the purple snail, Plicopurpura pansa (Gould, 1853), a
marine gasteropod that belongs to family Muricidae [3].
Plicopurpura pansa has the role of top predator in the
trophic net and is very active. According to Skoglund [3],
purple snail has a distribution that goes from Bahia
Magdalena, Baja California Sur to Colombia including
Coco Islands, Malpelo and Galapagos. This organism
lives in the rocky coasts and it is found attached to rocks,
mainly in cracks and holes, the littoral fringe where it
mostly inhabits is the upper intertidal zone [4].
Besides the ecological role that P. pansa has in the
community, this gastropod represents cultural and eco-
nomic importance given that it shows a gland that se-
cretes a fluid, which in the presence of light and oxygen
forms a purple ink that is used to dye threads and gets the
name of “tyrian purple” [5 ,6]. Threads dyed with this ink
have been used since prehispanic times by the Mexican
indigenes such as Mixtecos and Nahuas to dye clothes
related to social prestige, power and religion [7].
In last century, at the beginnings of the 80’s, a Japa-
nese company hired inexperienced people in harvesting
the ink that the purple snail produces for silk thread col-
oring. By the lack of knowledge and faulty understanding
on the process that these people had over ink harvesting
and cotton thread coloring, this resource was managed
inappropriately. Because of the bad management and the
use of poor techniques for ink harvesting, the abundance
of P. pansa populations were diminished considerably
and the snail population structure size and collapsed,
because larger organisms were seriously affected by the
inappropriate handling by the management that this or-
ganizatio n deployed f or harvesti n g ink.
For the reasons exposed, many people th at were native
collectors for ink and thread dyers by their origins, their
culture and traditions such as the Mexican indigenes,
were displaced. On 1988, in the Official Diary of the
Federation “Diario Oficial de la Federacion” an act was
published to regulate the conservation and proper ex-
C
opyright © 2012 SciRes. OJMS

R. FLORES-GARZA ET AL. 158
ploitation of the purple snail. Currently, P. pansa is con-
sidered as a species under special protection stated on the
statute Mexican Official Statute “Norma Oficial Mexi-
cana NOM-059-SEMARNAT-2010” [8], which deter-
mines species and subspecies of wild terrestrial and aqu-
atic fauna and flora in danger of extinction, threatened,
scarce, and under special protection, and establishes the
specifications for its protection.
Because of the inappropriate management of the pur-
ple snail, its population status was severely affected, this
created biological, ecological, and social problems that
were analyzed from studies like the ones based on analy-
sis of population structure and on reproductive aspects,
among those of Hernández and Acevedo [9], Acevedo et
al. [10], Álvarez [11], León [4], Acevedo et al. [12],
Castillo-Rodríguez and Amezcua-Linares [13], Acevedo
and Escalante [14], Holguín [15], Ramos-Cruz [16],
Reyes [17], Flores [18], Acevedo et al. [19], Enciso et al.
[20], Michel [21], Michel-Morfin et al. [22], Michel-
Morfín et al. [23], Ramírez-Rodríguez and Naegel [24],
García et al. [25] , Michel-Morfin et al. [26].
Our work was carried out in the region of Costa Chica,
on the State Guerrero, where there are not previous
analysis about the of condition P. pansa population; the
objectives was to analyze the population structure cen-
tered on its density, sex ratio, size, weight, besides de-
tailed observations about recruitment and reproductive
seasonality.
2. Methodology
2.1. Study Area
According to Carranza-Edwards et al. [27,28], The State
of Guerrero is located in southeastern Mexico, its coordi-
nates are 16˚18'N to 18˚48'N and 98˚03'W to 102˚12'W.
It adjoins north with the States of Mexico and Morelos,
northwest with Michoacan, northeast with Puebla, east
with Oaxaca and from west to south with the Pacific
Ocean. The coastline is approximately 470 km, located in
the Morphotectonic Un it VIII of the State of Guerrero; it
is a coastal front that according to its regional structure
has a very narrow continental shelf, is parallel to the
Mexico Mesoamerican oceanic trench. It is classified as
continental collision coast, dominated by primary coasts
formed by diastrophic movements, with faults and coasts
of fault scarps. However there are to a lesser extent, se-
condary coasts characterized by wave’s erosion, and
coastal headlands and wave-cut terraces, also higher
secondary coasts formed by marine deposition, same as
barrier and hooks b ea ches.
The weather is warm-subhumid with summer rains
(Aw, wi) an d with five to 10% of winter rain [29].
The territory of the state has seven regions, from
which three are located in the coastal fringe: Costa Chica,
Acapulco, and Costa Grande.
Costa Chica region is located in the southeastern part
of the state, its territory adjoins north with the regions of
La Montaña and Centro, south with the Pacific Ocean,
east with the State of Oaxaca and west with Acapulco.
This study was carried on in the rocky intertidal zone of
three sites in this region: 1) Punta Madonado, located at
the Cuajinicu ilapa municipality on 16˚19'35.49"N,
98˚34'12.65"W. Composed of sedimentary rocks sand-
stone-type from Upper Tertiary period with grayish to-
nalities. Beach of intense waving classified as exposed,
substrate is relatively fragile, it has a great quantity of
holes with variable depths and diameters widely distri-
buted throughout the area; 2) Las Peñitas, Marquelia
municipality, its coordinates are 16˚33'14.4"N,
98˚46'22.0"W. Composed of metamorphic rocks classi-
fied as Gneiss from Jurassic Period with grayish colors
and black strips that weathers in brown and yellow tones.
Beach with soft waving classified as protected. Substrate
hard and resistant to waving action with rough surface
composed of protuberances, great quantity of fissures,
cracks, and holes such as fold-less surfaces; 3) Playa
Ventura, located at Copala municipality its coordinates
are 16˚32'8.3"N, 99˚54'44.6"W. Composed of intrusive
igneous rocks, granodiorite-type from Tertiary Period
forming great compact structure blocks. Beach with in-
tense waving classified as exposed. Substrate hard and
resistant to waving, with great quantity of cracks, fissur es,
and holes distrib uted heterogeneously w ith rough surf ace
(Figure 1). Beaches descriptions were realized according
to geological charts from Instituto Nacional de Estadí-
stica, Geografía e Informática and observations made out
during the present research.
2.2. Field Methodology
Sampling was carried on in upper rocky intertidal zone of
the three sites. Each site was sampled six times, visiting
dates were: September and December 2006, March, June,
Figure 1. Coast of Guerrero, México.

R. FLORES-GARZA ET AL. 159
September, and December 2007. Sampling was realized
during low tide and daylight time. Sampling area size
was 20 m2 for each site, calculated from dispersion grade
of P. pansa through variance/average ratio, as well as
from Morisita’s [30] and Morisita standardized [31] in-
dexes. Later, observed frequencies were adjusted to ne-
gative binomial probability distribution (according to
organism’s dispersion) with 90% confidence level and
30% standard error.
Sampling was systematic. The sample starting point
was selected at random, and then a 30 m length rope was
placed parallel to coastline on the intertidal zone. The
sampling unit was a one square meter frame made of
PVC tube. Two levels were specified for sampling; level
one had its lower limit near to barnacle’s zone or subtidal
zone, and level two had its upper limit near to nerita’s
and litorina’s zone or the most remote to subtidal zone.
Once the starting poin t was selected, a sampling unit was
placed at level one of the selected point. All P. pansa
found within the area of sampling unit were collected and
placed in a labeled plastic bowl or container with sea
water, and protected from direct sunlight for later work
on all the specimens for each site. After the first squared
meter had been checked, the sampling unit was moved
on upwards and immediately placed at level two. When
both levels had been concluded, a 2 m space was left on
the rope, and the next sampling unit was then placed
again at level one. This operation was repeated until
completing the 20 m2.
Once all the collected specimens for all transects were
gathered, the specimens were separated by sex, the sex-
ing of organisms was possible because of male’s copula-
tive organ can be easily observed. In order to it, organ-
isms are taken with the hands and shaken, a minute or so
later, the snails reinitiates its activity when opens and
spread its foot, the right side of the organism is observed
to see if th ere is the pre senc e or abse nce of penis (Figure
2). Once sexing was finished, the specimen was weighed
in grams with a 0.01 resolution digital balance, and the
length measured in mm (from apex tip to the siphonal
channel opening) with a digital Vernier caliper, all the
data for the total number of organisms per sampling unit
was recorded in field sheets for later analysis.
Observations with respect to the reproductive season
were recorded directly by counting the amount of pair
mates on the area copulating in each sampled unit and
registered on the field sheets. After finished sexing, bio-
metrics notations and recording all the observations
within the field sheets, the sampled purple snails were
returned to their original habitat, placing them over hu-
mid rocks in shady places protected from the immediate
direct waving action in order to guarantee their survival.
Through al l of these p rocedur es , n o specimens we r e lost.
(a)
(b)
Figure 2. Snail Plicopurpura pansa. (a) Male; copulative
organ (presence of penis); (b) Female; copulative bursa
(absence of penis).
2.3. Data Analysis
Density was calculated dividing the total number of col-
lected snails by the total of sampled meters (snails/m2).
This operation was made with the total of harvested
snails in all samplings units by total of sampled meters in
all three beaches for all the visits. Density was also cal-
culated per date in which sampling was made, and the
calculus was done based on the total of harvested snails
per date in which each sample was made and total of
sampled area per each visit date.
To know the sexual proportion, a calculus was carried
on which consisted in dividing the total of collected fe-
males by total number of males, the result was expr essed
as females are to males (F:M) ratio. This calculus was
done based on the total of females and males that were
collected in all samplings and the total per each sampled
area in all three beaches, also, calculus based on the total
of collected males and females per each sampling date
and total sampled area per each visit were recorded.
For sex ratio equity test, in each calculus a Chi-square
homogeneity test (p < 0.05) was made [32]. Size struc-
ture analysis (expressed in millimeters) and weight (ex-
pressed in grams) was made, obtaining the descriptive
statistical values as maximum, minimum and average.
Because of the wide variations in weight that P. pansa
showed, weight variation coefficient was also calculated

R. FLORES-GARZA ET AL. 160
[33]. Descriptive statistics were obtained for the total of
examined specimens; this calculus was also made by
separating organisms by sex, and with the analyzed
amount of organisms per sampling date. The best repre-
sented sizes were obtained from frequency distribution
histograms. These histograms were made separately for
females and males and analyzed in the samples set.
Plicopurpura pansa population recruitment analysis
was based on size frequency histograms; this analysis
was carried on by making histograms for each sampling
date, using the total of analyzed specimens without sex
segregation. Those organisms that presented less than
10.5 mm in size were contemplated as recruits because
they were rated as the youngest ag e group. To determine
the reproductive season, direct observations over snail’s
sexual activity was made by counting the mating pairs
that were found copulating in each sampling unit for each
date and place.
3. Results
3.1. Density and Sex Ratio
A total of 1739 organisms of P. pansa were examined,
from which 828 resulted females and 911 males. Esti-
mated density for all sampled units and dates was 4.83
snails/m2 from it 2.30 were females and 2.53 males.
Minimal density was registered in September 2006 with
a value of 3.75 organisms/m2 from which 1.73 was fe-
males and 2.02 males. Maximal density was registered on
December 2007 as 5.78 snails/m2 in which, 2.95 was
females and 2.83 males.
The sex calculated ratio in Costa Chica including the
total of examined snails was 0.90 females per male. The
range of sex ratio was 0.76:1.0 (F:M) to 1.0:0.96 (F:M),
these values were shown in March and December 2007
respectively. Chi-square test (p < 0.05) on the total of
organisms represented in all the samples applied to sex
ratio indicated the existence of statistically significant
differences, but when analyzed per each sampled date did
not present differences in five sampling dates, but statis-
tically significant differences were found in March 2007
(Table 1).
3.2. Size and Weight
About P. pansa overall population size and structure
(Table 2), females presented the largest and the smallest
size. Overall averaged estimated size was 20.91 mm (sd =
Table 1. Total of analyzed specimens, density (organisms/m2), sex ratio (F:M), and results of Chi-square test, in sampling
dates for Plicopurpura pansa population in Costa Chica, Guerrero, México (September 2006 to December 2007).
Date Gender N D Sex ratio Significant difference
Both 1739 4.83
Female 828 2.30 All
Male 911 2.53
0.90:1 YES
Both 225 3.75
Female 104 1.73 Sep. 06
Male 121 2.02
0.85:1 NO
Both 327 5.45
Female 169 2.82 Dec. 06
Male 158 2.63
1:0.93 NO
Both 275 4.58
Female 119 1.98 Mar. 07
Male 156 2.60
0.76:1 YES
Both 249 4.15
Female 111 1.85 Jun. 07
Male 138 2.30
0.80 : 1 NO
Both 316 5.26
Female 148 2.46 Sep. 07
Male 168 2.80
0.88:1 NO
Both 347 5.78
Female 177 2.95 Dec. 07
Male 170 2.83
1:0.96 NO
N = Total of a nalyzed and harvested organisms; D = Density; x 2 P < 0.05 = significant difference according to Chi-square test.

R. FLORES-GARZA ET AL. 161
Table 2. Size and weight of the snail Plicopurpura pansa per sampling dates, on Costa Chica, Guerrero, México (September
2006 to December 2007).
Length (mm) Weight (g)
Dates Gender
AverageMin. Max. s.d. Average Min Max s.d.
V. C.
(%)
Bo 20.9 6.9 45.6 5.6 1.9 0.1 15.2 1.6 80.9
Fe 20.6 6.9 45.6 6.6 2.0 0.1 15.2 1.9 96.5
All
Ma 21.1 7.3 38.3 4.4 1.9 0.1 9.7 1.2 61.7
Bo 20.7 6.9 37.1 6.1 2.0 0.1 8.1 1.6 80.2
Fe 20.5 6.9 37.1 7.4 2.0 0.1 8.1 2.0 96.6
Sep.
06 Ma 20.8 10.1 33.4 4.6 1.9 0.2 7.1 1.2 61.6
Bo 19.1 7.7 39.1 5.9 1.5 0.1 10.6 1.5 96.2
Fe 18.6 8.4 39.1 6.8 1.5 0.1 10.6 1.8 116.4
Dec.
06 Ma 19.7 7.7 36.0 4.6 1.6 0.1 8.2 1.1 70.0
Bo 21.7 7.3 40.4 5.3 2.1 0.10 12.6 1.7 82.8
Fe 22.3 11.2 40.4 6.4 2.3 0.2 12.6 2.2 96.2
Mar.
07 Ma 21.3 7.3 36.2 4.4 2.0 0.1 8.1 1.2 64.5
Bo 22.9 8.6 45.6 4.2 2.3 0.1 15.2 1.5 65.9
Fe 23.4 8.6 45.6 5.0 2.5 0.1 15.2 2.0 77.8
Jun.
07 Ma 22.5 13.3 35.7 3.4 2.2 0.5 7.3 1.1 50.0
Bo 21.0 8.2 43.0 4.9 1.9 0.1 13.7 1.3 67.6
Fe 20.8 8.2 43.0 6.1 2.0 0.1 13.7 1.7 87.8
Sep.
07 Ma 21.1 8.5 30.4 3.5 1.9 0.1 5.0 0.8 41.5
Bo 20.4 8.9 38.4 6.0 1.9 0.1 11.0 1.6 86.9
Fe 19.7 9.2 38.4 6.7 1.8 0.1 11.0 1.8 100.0
Dec.
07 Ma 21.1 8.9 38.3 5.0 2.0 0.2 9.7 1.5 74.2
Min. = Minimum; Max. = Maximum; sd = standard deviation; V. C. = variation coefficient; Bo = Both; Fe = Female; Ma = Males.
5.61) including for all sampling dates.
The analysis for average size per sampling date indi-
cated that the smallest average size was 19.17 mm (sd =
5.91) registered in December 2006 and the largest aver-
age size 22.95 mm (sd = 4.24) recorded in June 2007.
For the female’s group, the smallest size was 6.90 mm
found in September 2006 and the largest size was 45.60
mm found in June 2007. Average estimated size includ-
ing all sampling dates for total of females was 20.69 mm
(sd = 6.68). For the average size analysis per sampling
date on females, the result indicated that the smallest
average was 18.64 mm (sd = 6.89) in December 2006,
and highest average size was 23.46 mm (sd = 5.07) and
registered in June 2007.
According to male’s size structure, the smallest one
was 7.30 mm registered on in March 2007 and the largest
was 38.30 mm found in December 2007.
Average estimated size including all sampling dates
for total of males was 21.12 mm (sd = 4.40). Average
size analysis per sampling date indicated that the smallest
average was 19.73 mm (sd = 4.60) found in December
2006, and the highest average size was 22.55 mm (sd =
3.40) and it was registered in June 2007. Size frequency
distribution histogram results (Figure 3) showed that the
best represented sizes in females occurred between 10.5
and 28.5 mm, since in this size range was shown the
highest abundance. For males, the best represented sizes
were found between 13.5 and 28.5 mm.
In Costa Chica weight average for all P. pansa organ-
isms was 1.99 g (sd = 1.61), ranging from 0.10 to 15.20 g.
Females showed an average of 2.02 g (sd = 1.95) and
males 1.96 g (sd = 1.2 1) .
The weight had greater variability than the length. We
observed a 96.53% coefficient of variation in weight for
females, ranging from 77.82% to 116.4% between the
different sampling dates. In males the coefficient of
variation in weight was 61.73%, ranging from 74.25% to
41.53% (Table 2).
When analyzing per sampling date, on the weight
variation coefficient value in females, it was observed
that it reached its maximum value in December 2006,
followed by December 2007, and September 2006. In
March and June samples, an important reduction of this
coefficient value had occurred (Table 2).

R. FLORES-GARZA ET AL. 162
Figure 3. Histogram of size frequency distri bution for males
and females of Plicopurpura pansa at Costa Chica region,
Guerrero, México (September 2006 to December 2007).
3.3. Recruitment and Reproductive Seasonality
In the mating observations, the highest number of copu-
lating pairs was registered in March 2007. In June 2007
an important quantity of copulating mates was also ob-
served, nevertheless the number was smaller than the
previous sampling date. In other sampling dates, copu-
lating mates were present but the observed quantity was
significantly smaller than the observed for March and
June 2007.
In Costa Chica there swas recruitment of P. pansa dur-
ing the whole year, presenting the highest quantity of
recruits in December 2006 and September 2007 , while in
March and June, presence of organisms with sizes up to
10.5 mm in the rocky in tertidal zone of the analyzed sites
diminished considerably (Figure 4).
4. Discussion
4.1. Density and Sex Ratio
Estimated density of the purple snail P. pansa for Costa
Chica for the present report is higher than that presented
in literature for other places in the Mexican Pacific
Ocean shore. Flores [18] reports the highest density and
it is for Acapulco, Guerrero. Density found in the present
study is very similar to that reported by García et al. [25]
for Guerrero State’s coast. With what was found in the
literature and the reported here, the State of Guerrero is
ranked as the one with the highest densities of P. pansa
for the Mexican Pacific coast.
The high density found for the State of Guerrero is
contradictory to what was reported in by Acevedo et al.
[18] who point out that in Mexican Pacific coast have a
density pattern based in the latitude, where density in-
creases according to the increment in latitude and indi-
cated that “the three states that are located Northwards
(Jalisco, Nayarit, and Sinaloa) are the ones that present
better conditions in terms of density”.
Based on literature reports about density of P. pansa in
Mexican Pacific shores, we believe that it is not possi-
ble to define a density distribution pattern based on the
latitude only.
On sex ratio considering all the analyzed data during
the six sampling dates, in Costa Chica there are signifi-
cant differences in the amount of females with respect to
males, nevertheless, when separated analysis for each of
the sampling dates were conducted, the result was that
for most of the time female-male proportion did not show
statistically significant differences, which clearly indi-
cated that in Costa Chica at the State of Guerrero, the
tendency is towards an equal proportion of female to
male (1.0:1.0).
Michel [21] analyzed sex ratio in different beaches of
Mexican Pacific and found that this proportion has a
tendency towards the unit (1.0:1.0), this behavior is
similar to what was found in our work; however Acevedo
et al. [19] report that males are more abundant than fe-
males, and that this happens throughout Mexican Pacific
coasts. Reports realized by other studies indicate a higher
quantity of males, such as Holguín [15] where males
double females, on the contrary Michel [21] determined
for Baja California Sur a male per each 1.85 females.
Although most literature reports are about 1.0:1.0 sex
ratio in P. pansa.

R. FLORES-GARZA ET AL. 163
Figure 4. Size frequency histogram for different sampling dates of Plicopurpura pansa population in Costa Chica Region,
Guerrero, Mexico.

R. FLORES-GARZA ET AL. 164
4.2. Size and Weight
Few records in literature where size analysis is included
mention to have found sizes smaller th an 10 mm. In most
of the reports the minimum registered sizes are higher
than 15 mm. In the present study sizes of 10.5 mm or
smaller represented a considerable proportion of the total
sampled specimens and formed the first age group,
therefore considered as recruits.
According to size comparison among males and fe-
males, the larger ones were females. In literature, studies
that analyze this aspect report that females are bigger
than males.
Most specimens of purple snail in Costa Chica were
found congregated in a size interval from 10.5 to 28.5
mm. In studies like those made by Hernández and
Acevedo [9], Acevedo et al. [10], León [4], Acevedo et al.
[12], Acevedo and Escalante [14], and Enciso et al. [20]
reported that most of the organisms on which size was
analyzed were larger than 20 mm. The amount of snails
smaller than 20 mm registered in Costa Chica, was ap-
proximately half of the total quantity of analyzed speci-
mens; best represented sizes belonged to small sized
specimens, which indicated that snail population at Costa
Chica was characterized by presenting small sizes and
high densities. The literature reported tendency for the
Mexican Pacific shores, where that female registered
individual larger sizes, in agreement with what was seen
in this study.
With the data reported by Flores [18] for Acapulco,
Guerrero and in this report, it can be considered that the
state has favorable environmental conditions for the ex-
istence of high densities and small sizes of P. pansa,
which differs from that reported by Michel-Morfín et al.
[23], who mention that larger average and individual
sizes are found towards South of Mexico and this could
be owed to the snail’s affinity for tropical environment.
Michel-Morfín et al. [26] report larger average size than
that reported in other studies at a beach of Jalisco. It is
considered that one of the most important factors that
influence the differences among reported results in lite-
rature, and what was found in this work, may have its
base on the variations of the collecting methodology em-
ployed by each researcher.
Purple snail’s weight data was the most variable. Fe-
males varied more than males, weight coefficient of vari-
ation in females exceeded 100%. It was observed that the
smaller weight variation for females was registered in
March and June, while weight variation s for males in the
same dates were nil.
4.3. Recruitment and Reproductive Seasonality
At Costa Chica P. pansa recruitment occurred through
the whole year, registering its maximum value in De-
cember 2006 and September 2007. In March and June
the quantity of registered recruits was very low. Accord-
ing to the recruitment observed in the present work, it is
in agreement with that observed by Michel-Morfín [21]
for Playa Cuastecomate, Jalisco, where they reported
recruitment practically during the entire year (from July
1993 to May 1994). On the other hand, Álvarez [11]
mentions that recruits appearance in Michoacán was in
August, besides that there are extra-seasonal recruitments.
Enciso et al. [20] observed recruitment over most of the
year, starting in August and observed a larger quan tity of
recruits in December. Other studies observed recruitment
just only in some months of the year, such as Hernandez
and Aceved o et al. [10] which reported it in July, August,
and September. Acevedo et al. [12] point out the exis-
tence of recruitment for males in March and June, and
females in May and more evidently in the months of
January and March.
Plicopurpura pansa copulate during the whole year,
but most of such activity was registered during March
2007. Maximum weight coefficient of variation values
for females occurred in September and December 2007,
and minimum values in March and June 2007. Most
copulation activity was observed when the minimum
weight coefficient of variation values occurred for fe-
males, which indicates that most of them in that moment
had empty gonads. This is the reason why minimum
weight variation values were registered, hence, maxi-
mum coefficient of variation in weight values most be
related to a rise in weight because of energy stored for
gonad maturity.
The wide weight variations in females of the purple
snail in Costa Chica are related to the reprod uctive cycle,
from the above mentioned it can be concluded that most
of the sexually mature female population are activate for
copulation during March and June, which is the period
were smaller weight variations are recorded. About this,
Ehrhardt [34] mentions that there can be changes in
weight, as an example when there is a rise in weight dur-
ing spawning season and a sudden lost of it as soon as
spawning products eject have occured. It can then be
perceived that the exponent produced in the length-
weight relationship reflects the dynamic processes re-
lated to feeding and reproduction success.
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