Fisheries Dynamics of Modified Floodplains in Southern Asia

Background

It is generally assumed that hydrological modifications have caused disastrous declines in the inland fish productivity in Bangladesh. There is, however, little real evidence of a decline in fisheries due to such modifications. Previous studies conducted under the Government of Bangladesh's Flood Action Plan have produced either non-significant or contradictory results. The knowledge base on which to determine such impacts is also notoriously poor for these multi-species, multi-gear fisheries in their hydrologically and morphologically complex river environment. Previous studies of the Flood Action Plan have produced empirical results on the impacts and potentials of different management strategies, sometimes on a large scale over widespread areas, but with little real understanding of the biological processes underlying them.

Approach

This project, run collaboratively with the Bangladesh Agricultural University, Mymensingh and the Central Research Institute for Fisheries, Indonesia, focused on two study sites to clearly determine driving forces behind floodplain fisheries.

Data were collected over two years on catch/effort, length frequency, mark-recapture, biological and hyrdrological data within three habitats in one unmodified site on the River Lempuing, South Sumatra, Indonesia and in hydrologically modified and unmodified sites straddling the Pabna Irrigation and Rural Development Project (PIRDP) in north-west Bangladesh. Data were collected for 6 'key' species at each site, selected as representatives of species 'guilds' of carps, catfish, snakeheads, perches and shrimps.

Six additional sub-projects were undertaken to investigate specific key research issues including fish survival in dry-season water-bodies; density dependence of fish natural mortality rates and growth rates; fish migration through flood control sluice gates; co-management of Indonesian river fisheries and utility of visible implant tags for growth studies.

Findings

This research has made significant advances in appropriate resource management strategies for Asian floodplain river capture fisheries, particularly on the use of riverine reserves and waterbody licensing, and the links between property rights and fish behaviour patterns.

It was concluded that fish catches in modified floodplains could be enhanced by increasing recruitment either from internal or external sources. Fish surviving in dry season water-bodies of modified floodplains inside the PIRDP were identified as the main source of recruits, while external recruitment and immigration through sluice gates was thought to maintain biodiversity. Due to their minimal cost to fisheries and high potential benefits for stock conservation and recruitment enhancement, dry season reserves were recommended as the main management tool for floodplain fisheries, accompanied by appropriate sluice gate operations in Bangladesh. However, it was recognised that these reserves may not provide adequate protection for migratory species, for which barrier controls may also be needed.

Fishing practices at each site were largely determined by the accessibility of fishing grounds - restricted in Indonesia by complete licensing, more open in some Bangladesh waters. It was recommended that the license systems should be maintained at both sites, for their socio-economic benefits, but it was also recognised, that neither system provides any conservation incentives.