Impacts of hydraulic engineering on the dynamics and production potential of floodplain fish populations in Bangladesh

Abstract

The present paper examines the impact of hydraulic engineering on fish production potential in Bangladesh by comparing the population dynamics of six species sampled from floodplains inside and outside the Pabna Irrigation and Rural Development Project (PIRDP) during 1995 and 1996. All the sampled populations were dominated by a single cohort for most of the year. Recruitment occurred both inside and outside the flood control scheme, coinciding with floodplain inundation. The growth of all the six species was rapid and strongly seasonal, and all species reached sexual maturity by the end of their first year. With only one exception, growth rates, condition and fecundity were either significantly higher inside the scheme, or not significantly different between the two sampling locations. Differences in growth performance were explained by fish density. No significant differences between sampling locations were detected in the length at maturity (Lm~o), spawning period or instantaneous total mortality rate (Z). Estimates of 2 were very high for all six species ranging from Z = 3.2 year-' to Z = 4.7 year-', equivalent to only 4% and 1% survival yea.-', respectively. It was concluded that the production potential of individual fish is at least as high inside as outside the PIRDP and that the 38-51% lower yields per unit area recorded inside the scheme reflect its partial inaccessibility to migrant species. K E Y w o R D s : Bangladesh, floodplain, hydraulic engineering, river fisheries. cover * 30% of the total land area of the country, and with increasing demand for greater Medicine, 8 Princes Gardens, London SW7 INA, UK (e-rnail: a.halls@ic.ac.uk). 0 1999 Blackwell Science Ltd 261 262 A.S. HALLS ETAL.agricultural output and economic stability, more schemes are planned for the fkture (Rahman, Huq, Haider & Jansen 1994).Against this backdrop, fish provide more than 80% of the total animal protein consumed in the country and the second most important export commodity after jute. Fishing also provides livelihoods and supplementary incomes for millions of people in Bangladesh (Rahman et al. 1994). Manipulating water levels within FCDI schemes to optimize agricultural output has the potential to significantly modify the extent, duration and timing of floodplain inundation, the principal driving force responsible for the productivity of floodplain fisheries (Junk, Bayley & Sparks 1989).The impact of FCDI schemes on fish productivity (measured as catch per unit area, CPUA) in Bangladesh has been previously examined as part of the World Bank/ODA-funded Flood Action Plan Project 17 (Flood Action Plan 17 1995), based largely upon the comparisons of catch rates inside and outside FCDI schemes throughout the country, but little attempt was made to gain an understanding of the biological processes underlying these figures. Firm conclusions on the impacts of FCDI schemes were prevented by non-significant or contradictory results, and the effects of breached embankments and partially functioning schemes (Halls 1998).The present pa...

Growth parameters estimates for a small fish of the Pantanal, Brazil: Moenkhausia dichroura (Characiformes; Characidae)

“…Therefore, this indicates that the pequira growth reduction is related to the decrease in temperature. In fact, under controlled experiment conditions, it is observed that the decrease in temperature can delay the growth of the fish (Lorenzen, 1996;Halls et al, 1999). The Moekhausia dichroura growth curve indicated that the recruitment -the entrance of a new cohort in the population -would occur in the middle of October, but there is no available information about the species reproduction.…”

Size at Sexual Maturity of the Female Pool Barb, Puntius sophore (Cyprinidae) in the Old Brahmaputra River, North Eastern Bangladesh

“…For example, Halls et al (1999) reported that the size at sexual maturity of female P. sophore in the Pabna Irrigation and Rural Development Project (PIRDP), Talimnagar Sluicegate, Pabna, Bangladesh was 6.1 cm TL. However, in a later study, Halls (2005) reported the size at sexual maturity of female P. sophore in the Lohajang river, Tangail, Bangladesh was 4.5 cm TL.…”

Multiple-use management in a large irrigation system: an assessment of technical constraints to integrating aquaculture within irrigation canals

“…It is evident that the extensive hydraulic engineering works associated with large-scale irrigation development have had a profound negative impact on many river ecosystems, which is reflected in a dramatic loss of biodiversity (Halls et al, 1999;Tomislav and Mitrofanov, 1998). Where this has resulted in loss of important subsistence fisheries, the impact of this change has generally been felt disproportionately by poor people.…”