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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 (Lm50), spawning period or instantaneous total mortality rate (Z). Estimates of Z were very high for all six species ranging from Z = 3.2 year?1 to Z = 4.7 year?1, equivalent to only 4% and 1% survival year?1, 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. 相似文献
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Abstract The sources of fish recruitment in the hydrologically modified, impounded Pabna Irrigation and Rural Development Project (PIRDP) flood control and irrigation scheme in NW Bangladesh were investigated. Catches at sluice gates were analysed to determine the migratory behaviour of fish. Fish attempted to migrate through the undershot sluice gates when they were opened, both with and against the currents, and both in and out of the PIRDP. Many fish were caught by the fishermen at such locations, but it is argued that some fish were probably able to enter the PIRDP from outside. One to two percentage of fish survived the dry season at the PIRDP, mostly in the deeper, perennial water bodies, both in rivers and lakes, and both inside and outside the flood control scheme. Fewer species survived inside the scheme, and the numbers of species remaining declined as the dry season progressed. It was shown in companion papers that fish production inside the PIRDP was lower than outside in both 1995 and 1996 even though the growth and reproductive potential of individual fish were at least as good inside as outside. The apparently negative impact of the PIRDP was explained by the reduced accessibility of the scheme to some migrant fish, as reflected by the inside/outside species compositions. It was concluded that fish catches within the PIRDP are sustained mainly from recruits produced by residing annual populations, while the biodiversity of the stocks was augmented by limited recruitment of fish migrating through the sluice gates from external sources. Two management approaches were proposed for increasing recruitment to the impounded PIRDP fishery as cheap alternatives to fish stocking: the use of dry season reserves to protect the residing spawning stocks; and the management of flood control sluice gates to maximise recruitment from external sources. 相似文献
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In tropical fisheries where ageing fish is often difficult, tagging programmes offer an important means to estimate growth parameters and mortality rates. The majority of tags are large and attached externally via a puncture in the muscle. These characteristics may cause significant biological effects which bias parameter estimates. Visible implant (VI) tags offer a more benign means to individually mark fish. The utility of VI tags for marking five species of tropical river fish was examined. The results indicate that the tag and tagging operation had no influence on either growth or mortality, although tag retention was poor compared with other studies. For three of the five species, the only suitable tagging location was highly inconspicuous and therefore inappropriate for tagging programmes that rely upon fishermen to return tagged fish. Alternative tagging locations may improve retention rates and the visibility of the tag. 相似文献
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