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 Understanding animal social networks can aid wildlife conservation
23.06.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht Making Oceans Plastic Free - Project tackles the problem of plastic pollution in the oceans
31.05.2017 | Leibniz-Zentrum für Marine Tropenforschung (ZMT)

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: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

Im Focus: Optoelectronic Inline Measurement – Accurate to the Nanometer

Germany counts high-precision manufacturing processes among its advantages as a location. It’s not just the aerospace and automotive industries that require almost waste-free, high-precision manufacturing to provide an efficient way of testing the shape and orientation tolerances of products. Since current inline measurement technology not yet provides the required accuracy, the Fraunhofer Institute for Laser Technology ILT is collaborating with four renowned industry partners in the INSPIRE project to develop inline sensors with a new accuracy class. Funded by the German Federal Ministry of Education and Research (BMBF), the project is scheduled to run until the end of 2019.

New Manufacturing Technologies for New Products

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

A new technique isolates neuronal activity during memory consolidation

22.06.2017 | Life Sciences

Plant inspiration could lead to flexible electronics

22.06.2017 | Materials Sciences

A rhodium-based catalyst for making organosilicon using less precious metal

22.06.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>