About forty sturgeons have returned to the middle part of the Ebro, more than fifty years after their extinction in this river. The reproduction of these migratory fish was hampered for many years.
The freshwater fish could not swim freely due to obstacles caused by dams and barrages. Predators also made the survival of the sturgeons difficult.
Return from France
The new specimens come from France and have spent about twenty days at the IRTA aquaculture center in La Ràpita (Montsià). There they could acclimatize before being released.
This release took place on Tivenys beach (Baix Ebre) and attracted a lot of interest. After growing up in the delta on the coast, the sturgeons will swim back up the river to reproduce in fifteen years. Norma Pujol, director of IDECE, emphasized that this is a historic day for the Terres de l’Ebre, the river and the MigratoEbre project.
The 44 European sturgeons arrived in a container on Tivenys beach. They had been transferred to La Ràpita on December 1 from the experimental center of INRAE (National Institute for Environmental and Agricultural Research) in Saint Seurin-sur-Isle (New Aquitaine, France).
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They are a year and a half old and just over eight inches long. In recent days they have become accustomed to the IRTA center. Researchers have applied ultrasound chips for tracking. These chips also use sensors installed in the Ebro River. There have been no sturgeons in the Ebro River since the mid-twentieth century.
The intention is for the sturgeons to remain in the lower Ebro area between Tortosa and Deltebre for about two or three years. Then they will spend some time in the sea, fifty to a hundred meters from the coast. When the breeding phase begins, they will return to the river.
Ecological connectivity must be improved
The ultimate phase of the MigratoEbre project has started two weeks ago. It will be achieved with the construction of a fish passage at the Xerta-Tivenys dam. This ensures the “ecological connectivity of the river” to facilitate the reproduction of migratory species such as sturgeon.
The project coordination team is led by Marc Ordeix. According to him, the current quality of the physico-chemical and biological environment of the Ebro River is good. Only, once the migrating fish arrive at the dam, they face “overpopulation” and are threatened by predators, fishermen and invasive species such as catfish and cormorant.
“They need to be able to swim further upstream to disperse and have a greater chance of reproduction,” said Marc Ordeix, MigratoEbre’s coordinator. “We will increase the number of breeding areas by 10 to 20 times,” he added.
Dependence on water levels
The IDECE director acknowledged that the work will be dependent on weather and river conditions, especially water levels. The fish passage will be about 70 to 80 centimeters deep, so that the sturgeons “have no fear” of swimming through, and will contain elements to reduce the force of the water current. The cost of the project is estimated to be almost one million euros.
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