Fisheries Resources of a Floodplain of the North-western Region of Bangladesh with Reference to its Environmental Aspects

Abstract

A study was conducted on fish biodiversity, environmental features, about fishers and fishing practices of the Roktodaha beel, a floodplain of north-western region of Bangladesh. A complete environmental cycle of the floodplain i.e. from inundation phase up-to dry phase was considered for the study. A total of 46 species of fishes and prawns were identified out of which 8 were exotic species. Perches (27.69%) were the most dominant groups followed by cat fishes (20.99%), prawns (18.62%), minnows (17.84%), eels (05.87%), murrels (02.25%), gouramies (01.55%) and carps (00.98%). Five top dominant species were Chanda nama, Pseudotropius atherinoides, Macrobrachium sp., Puntius ticto, Parambasis ranga and five least available species were Labeo kalbasu, Oreochromis mossambicus, Clarias batrachus, Notopterus notopterus and Pangasius hypophthalmus. Resident fish species were highly dominant (63.04%) followed by migratory (17.39%), exotic (17.39%) and riverine (2.17%) species which is an indication of lowering trend of fish species biodiversity. Fish biodiversity from different viewpoints viz., trophic niches, trophic levels, habitat preference, seasonal variation in abundance etc. were analyzed. Special attention was given on brush-vegetation park (katha) fishing. In katha Pesudotropius atherinoides was the most dominant in number (39 .19%) followed by Wall ago attu ( 14.67%) which is an impact of the sanctuary established by the Department of Fisheries, Govt. of Bangladesh. Average Shanon diversity (H1) index was 3.33 which can be mentioned as a moderately rich biodiversity ecosystem. At least 16 fish species were documented as recently disappeared from this bee! out of which 43.75% were migratory, 18.75% were riverine. Flood control structure, climate change impact viz., shrinking flood pulse, indiscriminate fishing practice etc. were found to be responsible for possible lowering of fish biodiversity. Almost all physico-chemical parameters except NH3-N2 were found to be more or less suitable for fish fauna. Rainfall had a wide range (0-768mm), the highest was in June, 2007, no rainfall was recorded in November, 2007-February, 2008. Water was more transparent in the rainy season. Water temperature showed negative correlation (r=-0.38) with dissolved oxygen. The average total hardness was found as 103.91±21.23 mgr1 Soil properties were also found to be suitable for agricultural crops. Average organic carbon was 2.257±0.3 I% which indicates good productivity of the floodplain. A total of 50 genera of plankton were identified out of which 34 were of phytoplankton and 16 genera zooplankton. Monthly quantitative abundance of phytoplankton varied from 23±2/ml (July, 07) to 56±20 (October, 07). Among phytoplankton Myxophyceae (30.84%±8.5) was the most dominant group followed by Chlorophyceae (28.82%±7.6), Bacillariophyceac (22.92%±6.4), protozoans (11.15%±6.1) and desmids (6.27%±5.5). Monthly average abundance of zooplankton varied from 466±90/1 (July, 07) to 610±46/1 (October, 07). Among zooplankton, Copepoda (26.38%±2.27) was the most dominant group followed by Rotifera (25.68%±3.8), Cladocera (24.91 %±6.1) and nauplius larvae (23.03%±4.5). Phytoplankton and zooplankton population showed a strong and positive correlation (r-0.67). Several plankers viz., Melosira, Ceratium, Anabaena, Anacystis obtained from the floodplain indicate its eutrophic nature. A total of 20 varieties of gear were observed for fishing. Among them katha fishing and ber/badhai jal were found to be extremely harmful for fishes. Intensive and repeated katha fishing were found to be harmful for fish biodiversity. Most fish and prawn species were caught in the nets (97.83%) followed by FAD (91.30%), traps (58.70%), wounding gear (26.09%) and others (15.52%). Considering numerical abundance nets were also the most dominant gear (44.15%) followed by FAD (42.32%), traps (9.71%), wounding gear (3.05%) and other methods (0.77%). Demographic and socio-economic variables of the fishers were studied, 31-40 years were found to be the highest (27.27%) age group. I 0.42% fishermen were illiterate, 25.00% could sign only, 60.42% were primary level, 6.25% were secondary and no fisherman was above SSC level. Most of their houses were kacha (72.92% ), semi-pucca were I 0.42%, about 16.66% houses were earthen. 54.17% fishermen possessed less than 5 decimal land. Full-time fishermen were 42.86%, part-time 24.49% and subsistence 32.65%. Various stakeholders involved only exploited benefits from the limited resource of the floodplain without any input or nourishment, a holistic approach is needed with special attention to conserve its pristine environment for the proper management and sustainable development of the floodplain.