Measuring the Mangroves: Morphometric Insights into Panganiban’s Mangrove Crabs | InformativeBD

Recie B. Bonaos, from the institute of Philippine  and Minerva I. Morales, from the institute of Philippines. wrote a Research Article about, Measuring the Mangroves: Morphometric Insights into Panganiban’s Mangrove Crabs. Entitled, Morphometrics relationship of the Mangrove crab from the Mangrove Swamp. This research paper published by the International Journal of Biosciences | IJB. an open access scholarly research journal on Biosciences. under the affiliation of the International Network For Natural Sciences| INNSpub. an open access multidisciplinary research journal publisher.

Abstract

Mangrove crab is a commercially important commodity in Catanduanes. But little is known in the study of morphometrics and its relationship. This study investigates some aspects of biology, particularly on sex ratio, morphometrics (Carapace Length, Carapace Width, and Body), and its relationships. Samples were gathered during the full moon last January 16 to 26, 2019, during both low and high tide using lift-net at the estuary part of Panganiban, Catanduanes. A total of 53 crabs were collected, of which 48.83% were male and 52.17% were females. The sex ratio of females to males was 1:1.12 and not significantly different from the hypothetical distribution of 1:1. Results revealed that a female crab seems to have a smaller carapace width compared to males. Bodyweight favored the male mangrove crabs with a mean bodyweight of 132.89g compared to females (113.23 g). A positive correlation was observed between carapace length- carapace width and carapace width – body weight in both sexes (R2= 0.8). Both sexes showed negative allometric growth on CL-CW and CW – BW with b<3. It showed that carapace length grows faster than carapace width and body weight increases faster than carapace width. Hence, harvesting of this resource should be minimized to the sizes of >8cm to allow continuous breeding and recruitment thus ensuring the sustainability of this resource. A follow-up study is needed in some areas to determine the status of mangrove crab covering a different period that will serve as a continuation of the study for the whole year-round.

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Introduction

Mangrove crab (MC) locally known as “alimango” or “kinis” is an important fishing commodity in the Philippines and Indo-Pacific Region. Mangrove crab belongs to the family Portunidae of the class Crustacea plays a vital role in the ecological balance and income generation (Keenan, 1999). Mangrove crab includes four different species; S. serrata, S. tranquebarica, S. olivacea, and S. paramamosain (Keenan et al., 1998). The mangrove crab is a relatively large crab with a smooth carapace that can grow more than 3kg (Kaliola et al., 1993). The color varies from dark brown to mottled green, depending on the dominating habitat. Located on each side of the carapace are nine similar-sized spines and the hind legs are flattened to aid the animal in swimming (Kaliola et al., 1993). In nature, male mangrove crabs are normally larger than female mangrove crabs (Keenan, 1999).

They are crabs that live among mangroves and may belong to many different species and even families. They are ecologically significant in many ways. They keep much of the energy within the forest by burying and consuming leaf litter. Along with burrowing in the ground, at high tide, and in the face of predators these crustaceans can climb trees to protect themselves (Makowski and Finkl, 2012). Mangrove crabs are euryhaline animals and can tolerate a wide range of salinities, ranging between 1 and 42 ppt (Davenport & Wong, 1987).

In the Philippines, the farming of mangrove crab has been progressing rapidly due to a promising market and profitability. With the availability of mud crab juveniles from the wild throughout the year and the recent development in hatchery technology, there is a strong indication that the production of mud crabs on a commercial scale could be a lucrative industry.

Their size, high meat yield, delicate flavor, and ease of capture mean that almost everywhere they occur mangrove crabs are highly sought-after as a quality food item. Their sedentary habits, accessible habitat, and relative ease of capture also, however, make them susceptible to overexploitation (Brown, 2013). The current price of mangrove crabs in the local market is relatively higher than fish and mollusks and is projected to increase in the world market. This increasing trend in the domestic and export market is expected to step up the demand for crab seeds. In the Philippines, the technology of mangrove crab growout culture is already being transferred to resourcepoor fisher folks for adoption as an alternative livelihood. However, buying competition among big and small crab farmers is foreseen to be disadvantageous to small farmers. There is a need to hasten the development and transfer of technology on mangrove crab breeding and hatchery to stabilize the supply and price of crab seeds. Mangrove crabs are known for their major importance in the Philippines, particularly in Catanduanes Island. But little is known on the study of morphometrics and its relationship with mangrove crabs on Catanduanes. According to Bagenal (1978), a study of the length-weight relationship in aquatic animals has a wide application in delineating the growth patterns during their developmental pathways. In population studies, the morphometric analysis provides a powerful complement to genetic and environmental stock identification approaches (Cadrin, 2000) and lengthweight relationships allow the conversion of growthin-length equations to growth-in-weight for use in a stock assessment model (Moutopolos & Stergiou, 2002). Information about individual body weightlength/width relationships in populations is important for estimating the population size of stock, specifically for its exploitation. The lengthwidth/weight relationships are regarded as more suitable for evaluating crustacean populations (Atar & Sector, 2003; Gorce et al., 2006; Sangun et al., 2009). Thus, this study input some essential information on the sex ratio, morphometrics, and its relationships particularly in carapace width, carapace length, and body weight.

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Source : Morphometrics relationship of the Mangrove crab from the Mangrove Swamp of Panganiban,Catanduanes Philippines