Is current floodplain management a cause for concern for fish and bird conservation in Bangladesh's largest wetland?

Abstract

1. Worldwide, water regulatory structures have impacts on aquatic ecological connectivity. This study determined the effects of current sluice management on the fish community in the Baral River, a major connection to the largest wetland (Chalan Beel) in Bangladesh. It also examines wider problems for biodiversity conservation (particularly waterbirds) in that wetland, which has shrunk to 30% of its former dry-season size in 50 years. 2. During the flood period, the peak breeding time for native floodplain fishes, sluices were in undershot operation (open by 16-60% of water depth). During this time, fish abundance and species richness were 229% and 155% higher respectively at sites upstream of the sluices, despite similar habitat upstream and downstream. Outside this period, when sluices were fully open, abundance and species richness were similar upstream and downstream. 3. Fish samples were dominated by fry, which are susceptible to damage by sluices. Twenty (41.7%) of 48 fish species captured in this study are classed as threatened in Bangladesh and their abundance was significantly lower downstream of the sluices. Two alien species, Aristichthys nobilis and Hypophthalmichthys molitrix, were recorded, probably escapees from local aquaculture activities.4. Twenty-five species of wetland birds were recorded in the Chalan Beel. From interviews, 64% of these species appear to have decreased in the last 20 years, together with 11 more species that may have become locally extinct over this period. This suggests that widespread ecological disruption is occurring. 5. Improved water management (e.g. gate opening height and duration) or modification (e.g. fish pass) of the Baral sluices is needed, to meet biodiversity and fisheries needs, rather than just for flood control and crop production. Improved hydrological and ecological connectivity and habitat protection are needed, as are a cessation of destructive fishing and seasonal fish ranching practices that currently provide synergistic pressures.

Fish Diversity in the Andharmanik River Sanctuary in Bangladesh

“…Considering the rich fish biodiversity and threats to the biodiversity of the Andharmanik River, a sustainable biodiversity conservation action plan needs to be formulated and implemented. Improved hydrological and ecological connectivity and habitat protection, as well as elimination of all destructive fishing gears, are urgently needed to conserve biodiversity Rahman, 2015;Galib et al, 2018). Some destructive gears have been extremely harmful for juvenile fish, which include set-bag-nets (Behundi jal, Pona jal and Badha jal), beach seine nets (Ber jal, Moshari jal and Char Ghera jal) and small-meshed monofilament net (Current jal).…”

Municipal wastewater can result in a dramatic decline in freshwater fishes: a lesson from a developing country

“…The lift nets were hauled five times at each sampling site and the total fishing duration was about one hour. The cast nets were hauled 15 times at each sampling site and the fishing duration was about 1.5 h. The combination of these fishing gears was effective in sampling fishes of a wide range of species and sizes from different depth strata (Galib et al, 2018). All the fishing gears were operated over the same time on every sampling date to standardize the sampling effort.…”

“…Although lower numbers of individuals and species were observed in downstream sites in 2016 this difference was comparatively smaller from July to September than in other months. This might be due to the rise in water level associated with heavy rains during the rainy season (Galib et al, 2016(Galib et al, , 2018 that may reduce the level of unfavourable physicochemical properties of water through pollutant dilution (Kumar and Reddy, 2009). When the water level began to recede, the impact of wastewater pollution on fish abundance and species richness became much more apparent.…”

Thermal and asphyxia exposure risk to freshwater fish in feral‐pig‐damaged tropical wetlands

“…Duration and frequency of coastal floodplain connection with primary rivers is an essential element in successful fish production (Bennett & Kozak, ; Galib et al ., ; Górski et al ., ; Hurd et al ., ). However, many months after river flow ceases, floodplain wetlands disconnect from primary rivers and progressively become smaller and shallower (Pusey & Arthington, ), many drying completely (Datry et al .…”