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 Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF

nachricht Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.

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: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Research finds new molecular structures in boron-based nanoclusters

13.07.2018 | Materials Sciences

Algae Have Land Genes

13.07.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>