The Atlantic salmon advances in the Bidasoa and goes up the river to the Txokoto dam in Elizondo

 

The Atlantic salmon advances in the Bidasoa and goes up the river to the Txokoto dam in Elizondo

The obstacle elimination strategy has allowed this progress, which has not been observed for at least 30 years

From a total of 19 copies of radio-marked Atlantic salmon, 11 have reached points on the Bidasoa River located upstream from the San Tiburcio dam in Doneztebe / Santestaban, and three of them have arrived in Elizondo in recent days, from that two have managed to pass the Txokoto dam in the town center.

This data has been verified through the radio-monitoring program developed by the Department of Rural Development and the Environment, through the staff of the public company Environmental Management of Navarra / Nafarroako Ingurumen Kudeaketa (GAN-NIK) and the Environment Guard , within the LIFE IREKIBAI project. In the middle of the ski lift and thanks to suitable flow conditions, it was possible to verify its presence already detected last year in the upper part of the river basin. According to the technicians, the obstacle elimination strategy in the river has allowed this progress, which was not observed at this point for at least 30 years.

The increase in the area used by salmon was detected already in 2018, when three specimens (of 28 in total) arrived upstream from the great San Tiburcio dam and one of them to the Oharriz dam, in Irurita, 5 kilometers away from Elizondo. This year, the ski lift season has confirmed the data, reversing the trend of the last decades, in which the construction of numerous obstacles in the form of dams and azudes in the middle and lower section of the Bidasoa for the use of water force it motivated that the salmon could not reach the upper part of the basin as they did before.

This year, adequate flows for migration and the current situation of the basin have allowed a good number of specimens to reach the high end. Despite this exceptional fact, the Oharriz dam remains a major obstacle to such migration, and several other specimens are at the foot of the dam and have not yet managed to overcome it.

The Government of Navarra, together with the Cantabrian Hydrographic Confederation, began working more than 15 years ago to reverse the fragmentation of the Bidasoa River, eliminating some disused dams and improving the permeability of those in use. Currently, the Government of Navarra, through its public company GAN-NIK, together with the Provincial Council of Gipuzkoa, participates in the LIFE IREKIBAI project “Open rivers: Improving connectivity and habitats in the rivers shared by Navarra and Gipuzkoa” , which has allowed the elimination in the Bidasoa account of dams such as Endarlatsa, Bera or Ituren, to which we must add those demolished by other initiatives in Arraioz and Elgorriaga.

Benefits for salmon and other species

All these efforts made in the Bidasoa basin have allowed a slow but sustained improvement of the salmon population, since in the last 10 years it has remained above 400 copies. Today there are 409 salmon that have been traced, a figure that could increase, since the season is not over. In addition, the permeabilization work has allowed a greater number of salmon to reach the middle and upper part of the basin, so that they can spawn in better fry and conditions more appropriate for the development of the fry.

Until a few years ago, given the large number of obstacles that a specimen had to overcome to reach Bertiz’s height, the Reparacea bridge (Bertiz) was the furthest place from the mouth where a few salmon came more or less regular. It should be noted that, in addition to salmon, all its accompanying species such as trout, inmate, eel, tarpon or lampreys, among others, are also benefiting from permeation work on the river.

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