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Assessment of Aquatic Faunal Diversity in the Ratargul Swamp Forest at Sylhet in Bangladesh

M. S. Islam*
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail-1902, Bangladesh

M. A. Islam
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail-1902, Bangladesh

N. A. Sweety
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail-1902, Bangladesh

M. A. R. Hossain
Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh2202, Bangladesh

M. H. Kabir
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail-1902, Bangladesh

Abstract/ Executive Summary:

The study was conducted to asses the aquatic faunal diversity in the Ratargul Swamp Forest during the period from November 2014 to October 2015. For the systematic study of aquatic fauna, the quadrate method along with transect was used where 4 transects were selected in the swamp forest each with 5 stations based on topography and vegetation. A total of 24 species of aquatic fauna belonging to 18 families were identified during the period, which were crustaceans (7), molluscs (4), fishes (12) and annelid (1). Among them, fishes were the most dominant and abundant groups. The crustaceans, molluscs, fishes and annelid were shown different pattern of density and diversity within the Transects. The density of individuals in Ratargul Swamp Forest varied from station to station within a range of 8 to 40 Indm^-2. The lowest Simpson’s Index of Diversity was 2.76 in T-4, which was situated in the transitional area between forested land and relatively deep lake within the forest. Leptocarpus potamiscus, Nandus nandus, and Pila globosa were the dominant shrimp, fish and mollusc species in the T-4, respectively. The highest Simpson’s Index of Diversity was 3.89 in T-3, which was situated along the bank of a small channel within the forest. Nematopalaemon tenuipes, Puntius ticto, and Pila globosa were the dominant shrimp, fish and mollusc species in T-3, respectively.

Keywords: Aquatic fauna, Biodiversity, Swamp forest

Location: Ratargul Swamp Forest

Start Date: 00-11-2014

End Date: 00-10-2015

Program Area: Conservation and Biodiversity

Commodity: Aquatic animal

Objectives:

The objective of the study were i). to identify the species of aquatic fauna based on morphometric characteristics, and ii). to estimate aquatic faunal diversity of Ratargul Swamp Forest.

Methodology:

Study area Ratargul Swamp Forest is located at about 45Km in the North-West of Sylhet town on the bank of the river Goyain. The river Goyain is originated from the hilly areas of Meghalaya and falls into the Surma River. Ratargul Swamp Forest is on the south-east bank of Goyain river. Administrative location of the swamp is under the upazilla of Goainghat in Sylhet district. The administrative beat office is situated at latitude 25°00.025´N and longitude 91°58.180´E (Choudhury et al., 2004). The total area of the forest is 3325.61 acre (BFD, 2013). It has unique floral and faunal composition than other forested areas of Bangladesh. Sample collection Collection of aquatic species was done in daytime from 20th to 22th December 2014. For a systematic study of aquatic fauna, the quadrate method along with transect was used. Four transects (T-1, T-2, T-3 and T-4) were selected in the swamp forest each with five station. The length of each transect was fixed at 100m long. Transect-1 was situated behind the forest office and run from west to east direction along the bank of a small channel. At this point, the transect crosses some bushes of Clinogyne dichotoma (1.5-2.0m) as under story vegetation and Pongamia pinnata (12-13m) and Barringtonia acutangula (8-9m) as over story vegetation. In T-1, Pongamia pinnata was the predominant tree species. Transect-2 started from west direction and run towards east direction. Transect-2 was situated on the northward side in relation to the T-1. It was a grass field with shallow water area. The height of the grass was about 0.5-1.0m. Transect-3 started from north and run towards south direction along the bank of a small channel and it was situated on northward side in relation to the T-2. Transect-3 crosses a dense stand of Clinogyne dichotoma (1.5-2.0m). Rosa involucrata (1.0-1.5m), Barrintonia acutangula (7-9m) and Pongamia pinnata (12-13m) were also found in the way of the transect. Transect-4 started from a low land in east and run towards west along the bank of a lake. It is mainly a transitional area between forested land and relatively deep lake. Pongamia pinnata (12-14m) was the predominant tree species in this transect. It was situated on southward side in relation to the T-3. Five stations (St) were selected randomly in eact transect. In Transect-1, water depth not more than 50cm. In Transect-2, the water depth (45-30cm) decreased gradually from St-1 to St-5. In Transect-3, the water depth of all five stations was not exceeded 45cm. In Transect-4, St-1 and St-2 were situated on lowland with a water depth of 35cm, where St-3, St-4 and St-5 were situated on the bank of a lake with a depth not more than 50cm. Sample analysis To measure species density within a given area, a 0.25×0.25 m quadrate were taken for the sampling of aquatic fauna and all the specimens within this area, both on the surface to the bottom were collected for further identification and measurement. Density was calculated for each sampling station using the formula, Density: d = # Species ⁄ Area sampled and species diversity for each station was calculated using Simpson’s Index of Diversity: D = 1 ⁄ ∑ΙΙ2, where ∑ΙΙ2 = ∑ (ni ⁄ N)2, N = total number of individuals, ni = number of individuals in “i”th species (Islam et al., 2003). Collected samples were preserved with 8% formalin in plastic jar. The identification of species and their taxonomic classification were followed i) Freshwater Fishes of Bangladesh (Rahman, 2005); ii) Inland Fishes of India and Adjacent Countries (Talwar and Jhingran, 1992); iii) Encyclopedia of Flora and Fauna of Bangladesh: Molluscs (V.17), Asiatic Society, Bangladesh; iv) Commercial and Medicinal Important Molluscs of Sundarbans, India (Dey, 2008); v) Encyclopedia of Flora and Fauna of Bangladesh: Arthropoda: Crustacea (V. 18, Part-II), Asiatic Society, Bangladesh; vi) FAO Species Catalogue: V. 1. Shrimps and Prawns of the world (Holthuis, 1980); vii) The Caridean Shrimps of the Albatross Philippine Expedition, (Fenner et al., 1993) and viii) FAO species identification guide for fishery purposes (Carpenter and Niem, 1998). Some renowned websites such as Fish Base (www.fishbase.org), Encyclopedia of life (www.eol.org), ITIS report (www.itis.gov) and The IUCN Red List of Threatened Species (www.iucnredlist.org) were also followed for recent classification and relevant taxonomic information of species. Preserved specimens were identified in laboratory. For identification of fish species fin-formula was used. The fin-formula is constructed with the letters D for dorsal; D1, D2 if two dorsals are present, P1 for pectoral, P2 for pelvic, A for anal and C for caudal fins. Roman figures indicate true and hard spines, arabic figures indicate soft rays. To differentiate the spines from the rays or branched from the unbranched rays the formula is used as follows: D. VII-IX/12 - 15 = Dorsal fin composed of 7-9 spines, 12-15 soft rays. D. 3/8 = Dorsal fin composed of 3 unbranched and eight branched rays. A. 2-3/8-10 = Anal fin composed of 2 or 3 unbranched and 8-10 branched rays. P1. I/10-12 = Pectoral fin composed of one spine and 10-12 soft rays. P2. 1/5 = Pelvic fin composed of one unbranched and five branched rays.
D1. X; D2. I/10-12 = First dorsal fin composed of 10 spines and second dorsal fin composed of one spine and 10-12 soft rays (Rahman, 2005).

Source of Information: J. Environ. Sci. & Natural Resources, 9(2): 51-64, 2016 ISSN 1999-7361

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1.

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Achievement/Findings:

The present study shows that highest diversity occurs in the habitat bearing a dense stand of Clinogyne dichotoma (locally called murta) at the small channel in the middle of the forest, which provides undisturbed shelter for aquatic fauna. It indicates that a greater number of successful species were present in this habitat. The present study also shows that the lowest diversity occurs in the habitat situated in the transitional area between forested land and relatively deep lake, where there was a very little amount of small vegetation to provide shelter for aquatic fauna. It indicates that the environment was quite stressful with relatively few ecological niches and only a few organisms were really well adapted to that environment. Because of being a transitional zone this habitat faces human disterbance.

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