Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Fisheries forecasting in the Niger inner delta

27.03.2002


The hydrological regime of the inner delta of the River Niger, situated in Mali, is subject to strong annual and indeed intra-annual variability. This delta ecosystem has a characteristic feature, a three-phase cycle. The first, a period of flood, starts in July marking the beginning of the cycle; then, after several months of rising water-levels, the flood recedes, between November and January; finally, a period of low water prevails between March and June.



The river’s various fish species are adapted to this cycle of alternating conditions. Feeding, growth and mortality depend on that rhythm. The flood scatters the fish away from the river bed and brings abundant food. It provides refuge areas, environments where reproduction can take place undisturbed. Growth then proceeds until the waters are in recession, a period of high natural mortality. Fishing effort has to follow the rhythm set by the succession of flood and recession. Most campaigns are concentrated in the period of flood retreat which heralds the return of fish into the fluvial zone and their unavoidable movement through the channels fishermen know well – and when their capturability is highest. Activity diminishes and the season ends with the onset of the next flood, when again the fish are dispersed into flooded areas.

Fishing activity is therefore dependent on the hydrological seasons. Two measurable hydrological parameters can express these: rainfall and river discharge. IRD scientists have sought to determine the extent to which these two variables can provide the basis for a model for predicting annual capturable fish stocks. The team focused first on defining which of the indicators was most pertinent, secondly on finding the number of years’ worth of data necessary for obtaining a reliable forecast.


No significant relationship was found between fishing and rainfall.1 This established, the investigation turned to the other parameter, the Niger river discharge. It appeared to correlate well with the volume of catches, which increased in proportion to the flood intensity. Two hydrological stations in Mali have been recording discharge rates since the beginning of the XXth century: Mopti, in the middle zone of the delta, and Koulikoro, upstream of it. Both these stations supply the necessary data, but Koulikoro’s site further upstream is more convenient. The Niger’s bed there is narrower and discharges are greater, rendering small changes easier to detect and record with finer accuracy. The flood peak occurs in September at that point, one month earlier than at Mopti. The Koulikoro station can hence also provide data sooner and potential catch estimates can be calculated earlier.

An important finding is that only two years of data are required for a reliable prediction to be made. An underlying biological factor is that 70% of the fish caught in the inner delta are less than a year old indicating that they arrived with the last flood, or with the previous one at the earliest.

The model in the end is extremely simple and involves just two easily recorded variables: the average discharge between July and September of the year in course and the same parameter between July and December of the previous year. So constructed it can predict the catches from September, 2 months before the start of the fishing season which runs from November to May. It can also bring into relief the immediate impact of any unusually smaller-scale flood. An intensive catch rate in one fishing season reduces the fish to a population composed mainly of juveniles (less than a year old). If a flood is not strong enough to allow renewal, the following season’s stocks will be depleted and the catches poorer.

This new forecasting model has proved to be extremely useful for giving warnings of insufficiency or overabundance of fish resources without the need for complex modelling systems. Its predictions could be published in the newsletter of the Fisheries observatory and distributed regularly throughout the region. With further development, the model could in the future help define –and hence predict- the places over the delta where fish are most abundant. It could then become an important tool in overall fisheries management.

1 Probably owing to exhaustion of the groundwater sources; any rainfall would be taken up in replenishing the water table rather than in increasing water volume in the River Niger.

Marie-Lise Sabrie | alphagalileo

More articles from Ecology, The Environment and Conservation:

nachricht Scientists team up on study to save endangered African penguins
16.11.2017 | Florida Atlantic University

nachricht Climate change: Urban trees are growing faster worldwide
13.11.2017 | Technische Universität München

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Frictional Heat Powers Hydrothermal Activity on Enceladus

Computer simulation shows how the icy moon heats water in a porous rock core

Heat from the friction of rocks caused by tidal forces could be the “engine” for the hydrothermal activity on Saturn's moon Enceladus. This presupposes that...

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Water cooling for the Earth's crust

23.11.2017 | Earth Sciences

Nano-watch has steady hands

23.11.2017 | Physics and Astronomy

Batteries with better performance and improved safety

23.11.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>