1.1 BACKGROUND TO THE STUDY
Inland capture fisheries in whole world including African rivers deliver food security and income for rural households and also serve as a valuable source of protein and important micro-nutrients. Nevertheless, inland fisheries are becoming increasingly threatened by riverine development projects (Bell, 1991). Construction of cross-river obstacles such as dams, weirs, roads, etc. as means for rapid development in response to increasing population and demand for agriculture products, hydropower generation or urbanization, are major threats to the long term sustainability of inland capture fisheries as any changes in migration, reproduction and biodiversity of aquatic populations has the potential to decrease capture fisheries productivity. Appropriate mitigation measures to alleviate possible impacts from such migration barrier are therefore necessary. According to Abernathy et al (1991), fish ways (fish passage) have been constructed worldwide and have proved to help mitigate many fisheries globally. Nevertheless, in order to assure the effectiveness of the fish ways, it is important that fish passage design criteria are established for local species and conditions of the specific region, and not adopted from studies conducted elsewhere. Fish passage systems may provide a means to mitigate the barrier effect of dams on migrating fish species. Even though design criteria were initially developed for the fish fauna of temperate regions, they are widely used in tropical rivers with relative success (Brett et al, 1998).
A fish passage concept has been developed for a hydroelectric power project on the Niger River in the absence of suitable fish passage design criteria. The design of a fish passage, the effectiveness of which is closely linked to the water velocities and flow patterns, should take into account the behaviour of the target species. Thus the water velocities in the passage must be compatible with their swimming capacity and behaviour. A large water level difference between pools, excessive aeration or turbulence, large eddies or low flow velocities can act as a barrier for fish. In addition to hydraulic factors, fish are sensitive to other environmental parameters (level of dissolved oxygen, temperature, noise, light, odour, etc.), which can have a deterrent effect. Downstream fish passage technologies are much less advanced than those for upstream passage. Obviously, this is partly due to the fact that efforts towards reestablishing free movement for migrating fish began with the construction of upstream fish passage facilities and that downstream migration problems have only more recently been taken into consideration. Second, the development of effective facilities for downstream migration is much more difficult and complex. Research continues to improve downstream passage, especially at large obstacles where satisfactory solutions were scarce (EPRI 1994). Design for fish passage can either be a low flow or high flow.
Design low flow for fish passage is the mean daily average stream flow that is exceeded 95% of the time during periods when migrating fish are normally present at the site. This is determined by summarizing the previous 25 years of mean daily stream flows occurring during the fish passage season, or by an appropriate artificial stream flow duration methodology if stream flow records are not available (Clay, 1995). Shorter data sets of stream flow records may be useable if they encompass a broad range of flow conditions. The fish passage design low flow is the lowest stream flow for which migrants are expected to be present, migrating, and dependent on the proposed facility for safe passage. Design high flow for fish passage is the mean daily average stream flow that is exceeded 5% of the time during periods when migrating fish are normally present at the site.
This is determined by summarizing the previous 25 years of mean daily stream flows occurring during the fish passage season, or by an appropriate artificial stream flow duration methodology if stream flow records are not available. Shorter data sets of stream flow records may be used if they encompass a broad range of flow conditions. The fish passage design high flow is the highest stream flow for which migrants are expected to be present, migrating, and dependent on the proposed facility for safe passage (Clay, 1995). However, this study is examining the application of fish passage design principles to enhance sustainability of inland fishery resources in the west Africans waters considering Niger River as the case study.
1.2 STATEMENT OF THE PROBLEM
Any form of conduit, channel, lift, other device or structure which facilitates the free passage of migrating fish over, through or around any dam or other obstruction, whether natural or man-made, in either an upstream or a downstream direction can be considered as fish passage which the application can enhance the sustainability of the inland fisheries resources. In the past the provision of fish passes has usually only been concerned with the upstream migration of the diadromous (sea to freshwater cycle) migratory salmonid species. In recent years interest has widened to include the potadromous (within fresh water) coarse fish species, and other diadromous species such as eels and shad. This study seeks to encourage the consideration of fish passes for the all species. Recently there has been an upsurge in the use of existing, and sometimes new, obstructions for the purposes of electricity generation by hydropower. It is essential in such projects that account is taken of fish passage needs both in the upstream and downstream directions.
1.3 OBJECTIVES OF THE STUDY
The following are the objectives of this study:
1. To examine the various design of fish passage that is applicable in West African waters.
2. To examine the applicability of fish passage design principles to enhance inland fisheries resources in West African waters.
3. To identify the factors limiting the application of fish passage design principles in West African waters.
1.4 RESEARCH QUESTIONS
1. What are the various designs of fish passage that is applicable in West African waters?
2. What is the applicability of fish passage design principles to enhance inland fisheries resources in West African waters?
3. What are the factors limiting the application of fish passage design principles in West African waters?
1.5 SIGNIFICANCE OF THE STUDY
The following are the significance of this study:
1. Outcome of this study will be useful in developing a better fish passage that can enhance the sustainability of the inland fisheries resources especially in West African waters.
2. This research will be a contribution to the body of literature in the area of the effect of personality trait on student’s academic performance, thereby constituting the empirical literature for future research in the subject area
1.6 SCOPE/LIMITATIONS OF THE STUDY
This study will cover various approaches to fish passage design with respect to West African waters especially the Niger River which shall be focused upon in this study.
LIMITATION OF STUDY
Financial constraint– Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).
Time constraint– The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.
Abernathy, C.S., D.A. Neitzel, and E.W. Lusty. 2009. Velocity Measurements at Six Fish Screening Facilities in the Yakima Basin, Washington, Summer 2008. Annual report to the Bonneville Power Administration.
Bell. M. C. 1991. Fisheries handbook of engineering requirements and biological criteria. Fish Passage and Development Evaluation Program, U.S. Army Corps of Engineers, Portland.
Brett, J.R., Hollands, M., and Alderdice, D.F. 1998. “The effect of temperature on the cruising speed of young sockeye and coho salmon” Fisheries Research Board of Canada, Journal 15(4): pp 587-605.
Clay, C. H. 1995. Design of Fishways and Other Fish Facilities. Boca Raton, Florida: CRC Press.