Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The European eel - To migrate or not to migrate in freshwaters?

15.12.2008
The European eel’s biology and ecology never cease to amaze us. At the elver stage, certain individuals swim up estuaries to grow in rivers, whereas others spend their entire life cycle at sea. In Bordeaux, researchers have looked into the origin of this divergence in migratory behaviour. What if it was only a question of energy reserves and feeding behaviour?

Over-fishing, pollution, river development, global climate changes, etc. are threatening a large number of migratory fish. Among the endangered species, one can cite the European eel whose numbers have been divided by 10 over the two last decades. To save the species, the priority is better management of the populations subjected to the pressures of the environment.

However, this first assumes better knowledge of the species’ biology and ecology. The exercise is complex, because the European eel’s life cycle is still not fully understood. The species has long been considered a migratory fish that reproduces at sea and grows in rivers. Yet studies conducted over the last 10 years have shown that certain individuals do not spend their growth period in freshwaters. Migratory divergences may exist at the elver stage. At Bordeaux and Saint-Pée-sur-Nivelle, in doctoral work co-supervised by Cemagref and the INRA, Sarah Bureau du Colombier has been studying the source of these different migratory patterns in European eel elvers.

Sorting migrant fish and sedentary fish
What morphological characteristics differentiate a sedentary elver from a migratory elver in the natural environment? Today the response is “none”. To sort individuals by their propensity to migrate, the young doctoral student chose to concentrate on behavioral studies. To swim up the estuaries, the migratory elvers use the current from the ebb tide. Since light inhibits migration, they prefer to move in darkness, therefore especially at night. By reproducing the two main stimuli of migration in experimental conditions, it was possible to distinguish highly mobile individuals (with a strong propensity to migrate) from more passive individuals, buried in the gravel (with a weak propensity to migrate). The hundreds of elvers tracked during this study were captured upon entering the estuary or in the middle of the Adour estuary.
A question of an individual energy threshold
When they swim up the Adour estuary, the young elvers stop feeding more or less totally. This is a true obstacle course which requires good energy reserves upon entering the mouth of the estuary and then rapidly resuming feeding once the river has been reached. To verify these hypotheses, the young scientist compared the energy state of the two categories of elver as well as their capacity to resume feeding. In the estuary environment, elvers with a strong propensity to migrate seemed better equipped, in terms of energy stores, to conquer the freshwater environment and pursue their growth. Upon entering the estuary, the differences are not significant. This result points towards the existence of an individual energy threshold determining whether the individual will pursue its migration. In addition, the results have also underscored the greater energy expenditures and slower and/or lower resumption of feeding in sedentary elvers.

All of these data were then used to feed an estuarial migration model that will eventually be used to simulate the migratory behaviour of elvers according to different parameters, some of which are related to global climate changes.

Contacts:
Sarah Bureau du Colombier (Cemagref, Bordeaux : +33 (0)5 57 89 27 14 - sarah.bureau-du-colombier@cemagref.fr), Patrick Lambert (Cemagref, Bordeaux : +33 (0)5 57 89 08 09 - patrick.lambert@cemagref.fr)

Agnès Bardonnet, bardonne@st-pee.inra.fr (INRA, Saint-Pée-sur-Nivelle)

A complex life cycle

The European eel reproduces near the North American coast in the Sargasso Sea. The young larvae, called leptocephalus, cross the Atlantic Ocean on the ocean currents. Near the European and North African coasts, they metamorphose into elvers (young yellow eels). These individuals then settle in coastal zones or in estuaries, or swim up rivers. After they have metamorphosed into silver eels, the adults embark on their migration and reproduction in the Sargasso Sea.

Marie Signoret | alfa
Further information:
http://www.cemagref.fr/Informations/Presse/IM.htm

More articles from Ecology, The Environment and Conservation:

nachricht How does the loss of species alter ecosystems?
18.05.2017 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig

nachricht Excess diesel emissions bring global health & environmental impacts
16.05.2017 | International Institute for Applied Systems Analysis (IIASA)

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: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>