MARINE AND FISHERY SCIENCES 36 (2): 189-195 (2023)

https://doi.org/10.47193/mafis.3622023010502

ABSTRACT. Mangrove clam Pegophysema philippiana Reeve, 1850, is common to mangroves

muddy substrate in Baganga, Davao Oriental, particularly in barangay Kinablangan, Lucod, Saling-

comot and Bobonao. Sampling was done on May 2-7, 2022, during high tide. Mangrove clam

length-weight relationship was calculated using the exponential equation W =aLb. A total of 769

mangrove clams were collected during sampling. The biggest (4.4 ±0.81 cm) and heaviest (43.4 ±

25.3 g) clams were recorded at Bobonao, the smallest was measured at Lucod (3.7 ±0.65 cm), and

the lightest clam was found at Kinablangan (26.8 ±16.28 g). ANOVA detected significant differ-

ences (p <0.05) in length and weight of mangrove clams between sites. Length-weight relationship

of mangrove clam exhibited a strong positive relationship between length and weight; however, dif-

ferent values of slopes were noted. This is very common in bivalves because they are very sensitive

to environmental changes. In general, the length-weight relationship of mangrove clam in Baganga,

Davao Oriental, revealed allometric growth pattern.

Key words: Davao, exploitation, gleaning, invertebrates, mangrove ecosystem.

Relación longitud-peso de la almeja de manglar (Pegophysema philippiana) en diferentes sitios

dentro de Baganga, Provincia Oriental de Davao, Filipinas

RESUMEN. La almeja de manglar Pegophysema philippiana Reeve, 1850, es común en los sus-

tratos fangosos de los manglares en Baganga, Davao Oriental, particularmente en los barangays de

Kinablangan, Lucod, Salingcomot y Bobonao. El muestreo se realizó del 2 al 7 de mayo de 2022,

durante la marea alta. La relación longitud-peso de las almejas de manglar se calculó mediante la

ecuación exponencial W =aLb. Se recolectaron un total de 769 almejas de manglar durante el mues-

treo. Las almejas más grandes (4,4 ±0,81 cm) y más pesadas (43,4 ±25,3 g) se registraron en Bobo-

nao, las más pequeñas se midieron en Lucod (3,7 ±0,65 cm), y las almejas más ligeras se encontra-

ron en Kinablangan (26,8 ±16,28 g). El ANOVA detectó diferencias significativas (p <0,05) en la

longitud y el peso de las almejas de manglar entre los distintos sitios. La relación longitud-peso de

la almeja de manglar exhibió una fuerte relación positiva entre la longitud y el peso; sin embargo,

se observaron diferentes valores de pendientes. Esto es muy común en los bivalvos porque son muy

sensibles a los cambios ambientales. En general, la relación longitud-peso de la almeja de manglar

en Baganga, Davao Oriental, reveló un patrón de crecimiento alométrico.

Palabras clave: Davao, explotación, espigueo, invertebrados, ecosistema de manglar.

189

*Correspondence:

michaeljeriel.bersaldo@g.msuiit.edu.ph

Received: 14 December 2022

Accepted: 12 January 2023

ISSN 2683-7595 (print)

ISSN 2683-7951 (online)

https://ojs.inidep.edu.ar

Journal of the Instituto Nacional de

Investigación y Desarrollo Pesquero

(INIDEP)

This work is licensed under a Creative

Commons Attribution-

NonCommercial-ShareAlike 4.0

International License

Marine and

Fishery Sciences

MAFIS

NOTE

Length-weight relationship of mangrove clam (Pegophysema philippiana) in

different sites within the Baganga, Davao Oriental Province, Philippines

MICHAEL JERIEL I. BERSALDO1, *, MARIA LOURDES DOROTHY G. LACUNA1, EDISON D. MACUSI2and

PEDRO M. AVENIDO3

1Department of Marine Science, College of Science and Mathematics (CSM), Mindanao State University, Iligan Institute of Technology

(MSU-IIT), Andres Bonifacio Avenue, 9200 - Iligan, Philippines. 2Institute of Agriculture and Life Sciences (IALS), Davao Oriental State

University (DOrSU), Mati, Philippines. 3Institute of Fisheries and Marine Sciences, Southern Philippines Agri-business Marine and Aquatic

School of Technology (SPAMAST) 8012 - Malita, Philippines. ORCID Michael Jeriel I. Bersaldo https://orcid.org/0000-0003-1988-649X

Mangrove clam Pegophysema philippiana

Reeve, 1850, is a highly sought bivalve species in

the Philippines because of its flavor and size, and

is considered as a local seafood delicacy in the

region (Primavera et al. 2002). Mangrove clam is

a burrowing bivalve and one of the most valued

invertebrate species in the Davao Region. It is

considered as the main source of proteins, vita-

mins and minerals for the poorest social commu-

nities living on the coast since most of them rely

on artisanal fishery catch (Dejarme et al. 2015).

Due to the large population of the Philippines,

growing coastal settlement drives increasing fish-

ing pressure on certain commodities, and the man-

grove clam is not exempted from this problem

since it is very susceptible for exploitation (Arane-

ta 2016). A study in biology, ecology, genetics,

and early life stages of P. philippiana was already

conducted (Adan 2000; Primavera et al. 2002;

Araneta 2016); however, the study of its morpho-

metric measurement was limited (Sajol-Degamon

and Fernandez-Gamalinda 2021). Hence, only

taxonomic investigation was conducted in the

Davao Region and no morphometric relationship

study was carried out (Lumogdang et al. 2022).

Morphometric measurements of the associa-

tion between length and weight were computed in

the current investigation. In fisheries biology and

population dynamics, the length-weight relation-

ship (LWR) is crucial and many stock assessment

models suggested the use of LWR parameters

(Jamabo et al. 2009). LWR is basic for evaluating

the growth of any edible and economically signif-

icant invertebrate species since it may directly

represent the organism’s general health by pro-

viding an evaluation of its weight in relation to its

length (Aban et al. 2017).

Mangrove clam was reported to be depleted in

Baganga, Davao Oriental according to the

Municipal Agriculturist and observation of glean-

ers during the pre-sampling visit (Bacaltos et al.

2010). Although mangrove clams could still be

harvested in the mangrove areas of Baganga,

Davao Oriental, a need for scientific data is

essential and this paper aims to fill in this gap.

This paper focuses only on the morphometric

relationship (LWR) of P. philippiana in different

barangay1of Baganga, Davao Oriental, as this

municipality is one of the major exporters of

mangrove clams in Davao City (Bangkerohan

and Agdao Public Markets) with reported 1,000

to 3,000 kg of mangrove clam sold every day

(Bacaltos et al. 2010). Thus, the data generated

from the current study provides a first reference

for the study of mangrove clam fishery manage-

ment and ecological monitoring in the area.

Mangrove clam (P. philippiana) was collected

in barangay Kinablangan, Lucod, Salingcomot

and Bobonao, within the Baganga, Davao Orien-

tal province (Figure 1). Field sampling was done

during daytime on May 2-7, 2022, with the assis-

tance of three hired gleaners. Within the man-

grove forest, gleaning was done during high tide

as preferred by the gleaners to facilitate easy

maneuver in the mud at 1 m depth. Using their

toes, they locate the mangrove clam by doing

rhythmic movement, which is termed locally as

hinol-hinol. Shell length was measured using a

Vernier caliper (±0.1 mm), while weight was

obtained using a digital weighing scale (±0.2 g)

in situ. Collected clams were partially drained

before weighing in order to minimize the influ-

ence of water.

Analysis of Variance (ANOVA) was used to

establish the significant difference in length and

weight of mangrove clams (p =0.05). Further,

Tukey test was used to identify significant differ-

ence between study sites. The relationship

between length and weight was also calculated

using the exponential equation W =aLb, where

W stands for weight, a stands for the intercept,

which represents the initial growth coefficient, L

stands for length, and b stands for the slope,

which represents the relative growth rates of the

190 MARINE AND FISHERY SCIENCES 36 (2): 189-195 (2023)

1Barangay is the lowest territorial and political boundary in the Philippines.

variables and provides growth information

(Aban et al. 2017). The value of the slope was

analyzed using the t-test to determine the growth

exhibited by the mangrove clam (López-Rocha

et al. 2018). Growth is isometric when b =3,

allometric when b substantially differs from 3

(positive if b >3 and negative if b <3) (Sajol-

Degamon and Fernandez-Gamalinda 2021). The

analysis was carried out through SPSS 20 and

Microsoft Excel 365.

A total of 769 mangrove clam P. philippiana

specimens were collected in Baganga, Davao

Oriental. Results indicated that Bobonao had

biggest clams with a mean length of 4.4 ±0.81

cm (n =176) followed by Salingcomot with 4.1 ±

0.71 cm (n =120), Kinablangan with 3.8 ±0.67

cm (n =251), and lastly Lucod with 3.7 ±0.7 cm

(n =222). In terms of mean weight, the heaviest

individual was found in Bobonao (43.4 ±25.3 g),

followed by Salingcomot (37 ±20.57 g), Lucod

(29.8 ±17.77 g) and Kinablangan (26.8 ±16.28

g). The Tukey test found that mangrove clams

from Kinablangan and Lucod showed no signifi-

cant difference (p >0.05) in length and weight,

while significant differences were observed when

comparing Bobonao and Salingcomot (p <0.05).

One factor that might affect the size differentia-

tion (length and weight) of clams between study

sites is the magnitude of harvest of the resource

(Elvira and Jumawan 2017). Moreover, compara-

ble results from barangay Lucod and Kinablan-

gan might be due to the accessibility of both areas

in which no gleaning restrictions were instituted

and as a result gleaners could harvest clams freely

and gleaning pressure increased. In addition,

according to the office of Municipal Agriculture,

the majority of the gleaners were from Lucod, so

it is safe to assume that the harvest in Kinablan-

191

BERSALDO ET AL.: LWR OF MANGROVE CLAM IN BAGANGA, DAVA O ORIENTAL

Figure 1. Collection sites (red spots) of mangrove clam in Baganga, Davao Oriental province, Philippines.

Kinablangan

San Victor

Dapnan

San Isidro

Campawan

Mikit

Lambajon

Lucod

Mahanub

Binondo

Batiano

Salingcomot

Bobonao

02 km

126° 30 E'126° 33 E'126° 36 E'126° 39 E'

7° 30 N'

7° 33 N'

7° 36 N'

7° 39 N'

7° 42 N'

120° 0 E'124° 0 E'

4° 0 N'

8° 0 N'12° 0 N'16° 0 N'20° 0 N'

Kinablangan

01 km

Lucod

Salingcomot

Bobonao

01 km

gan and Lucod was comparable compared to

other study site (Sadino 2022 pers. comm.). High

exploitation pressure on resources in mangrove

wetlands of Butuan (Philippines) may be found in

Elvira and Jumawan (2017), where they found

out that exploitation due to gleaning of mud clam

Polymesoda erosa was a contributing factor of its

size variability. So, different sizes observed in

mangrove clam in the current study might also be

influenced by the gleaning activity in different

barangays. In addition, mangrove clam has high

market value in Baganga, Davao Oriental, with

reported values of 2.2-2.7 USD kg-1 (Sunstar

2018), which may drive an increase in gleaning

pressure on some study sites considering there is

no gleaning restrictions to increase their income

(Table 1).

Mangrove clams in this study ranged from 3.7-

4.4 cm shell length and 26.8-43.4 g weight, indi-

cating that mangrove clam population was in

good condition based on its size structure. Clams

reached first sexual maturity at 3 cm shell length

before being harvested (Primavera et al. 2002;

Araneta 2016). Therefore, growth exploitation

was not observed since bigger clams were

gleaned in the area (>3 cm shell length). In con-

sonance, recruitment exploitation was also not

observed since mangrove clam collected across

study sites were smaller compared to the ideal

brood stock size of 5.7-7.3 cm and weights of 60-

125 g since recruitment exploitation only existed

when the brood stock of a certain fishery were

heavily harvested (Adan 2000). Moreover, results

from the present study are comparable to those of

Kilatong and Bruckner (2010) in which mean

length of mangrove clams collected outside the

protected area of Oikull, Airai Strair, Republic of

Paluau, ranged from 4.45-4.75 cm. However, big-

ger mangrove clam also collected in an unprotect-

ed area in Panay, Philippines by Adan (2000)

reported 4.3-5.1 cm mean length and 21-170 g

weights.

Mangrove clam is a commercially important

bivalve collected for consumption and sold to

local markets and restaurants by the local glean-

ers (Yahya et al. 2020). Due to their size, taste,

and supposed aphrodisiac powers, mangrove

clams are sold in other regions to generate more

income to support daily needs of families (Pri-

mavera et al. 2002). Given its economic value

and dependence of gleaners to mangrove clam to

sustain their regular necessities, fishing pressure

might increase as competition among gleaners

arouse during harvest which could influence a

decline in mangrove clam size and stocks.

The result from morphometric analysis showed

that shell length and total weight of mangrove

clam P. philippiana in all study sites had strong

positive relationship, since all values of correla-

tion coefficients (r2) were close to 1.0 (Table 2).

Thus, shell length and total weight of mangrove

clam P. philippiana were closely related to each

other and could be used to estimate total weight

based on shell length. Values of the slope from

different study sites varied and no isometric

growth was observed. In Kinablangan, a positive

allometric growth pattern (b =3.052) was

observed indicating that the weight of mangrove

192 MARINE AND FISHERY SCIENCES 36 (2): 189-195 (2023)

Table 1. Mean (±SD) length (cm) and weight (g) of mangrove clams (Pegophysema philippiana) collected in different areas of

Baganga, Davao Oriental. Different superscript denotes significant different using ANOVA (p <0.05).

Kinablangan Lucod Salingcomot Bobonao

(n =251) (n =222) (n =120) (n =176)

Mean length 3.8 ±0.65b 3.7 ±0.7b 4.1 ±0.71ab 4.4 ±0.81a

Mean weight 26.8 ±16.28b 29.8 ±17.77b 37.0 ±20.57ab 43.4 ±25.3a

clam increases superiorly compared to its shell

length. This growth pattern could be influenced

by the existing aquaculture pond in the area

which increased organic materials beneficial to

clams nourishment (Lebata 2001; Sarà et al.

2009). On the other side, negative allometric

growth patterns were observed in Lucod (b =

2.811), Salingcomot (b =2.749) and Bobonao (b

=2.913) suggesting that the rate of shell length

increase was higher compared to weight increase.

This negative growth pattern may be driven by

multiple factors such as fluctuating environmen-

tal parameters and the consequent mangrove clam

physiology (Thomas 2013; Singh 2017). The

analysis of the slope was also done to establish

significant difference between the b values and

isometric values (3) using t-test and the result

showed significant difference in all study sites (p

<0.05).

The result of the analysis conforms to the study

of Aban et al. (2017) in which the growth of

organisms proceeds with different factor differing

from the measurement of the length. It was also

noted that the slopes of the paired morphometric

parameters were greater or lesser than 3.0, mean-

ing that the increase in shell length was not pro-

portional to the weight gained of mangrove clam

P. philippiana. Different findings for length and

weight relationship in the selected study sites

maybe influence by ecological or physiological

factors (Ramesha et al. 2009; Malathi and

Thippeswamy 2011) though it was a limitation in

the study. As clams were particularly sensitive to

environmental changes, further studies compar-

ing its state and heterogeneity in different loca-

tions will be needed.

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BERSALDO ET AL.: LWR OF MANGROVE CLAM IN BAGANGA, DAVA O ORIENTAL

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