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Grayling survival expectancy and climate change illustrated by the status of the population of the Lower Ain river

Henri PERSAT1*, Jean-Paul Mallet2, Charlotte Robichon3, Benjamin Alric4 and Hervé Capra5
  • 1 Société Française d'Ichtyologie, France
  • 2 Other, France
  • 3 Other, France
  • 4 UMR5023 Laboratoire d'Ecologie des Hydrosystemes Naturels Anthropises (LEHNA), France
  • 5 National Research Institute of Science and Technology for Environment and Agriculture (IRSTEA), France

Like all the other salmonid species, graylings (genus Thymallus) require rather low temperatures to survive, usually less than 23°C in high quality waters. However, in contrast to many other salmonid genera, grayling usually require rather fast flowing waters throughout their life cycle. This is especially the case of the European grayling (T. thymallus), which rarely enters standing waters, and only in some large cold lakes of Northern Europe or the Alpine range. Its nominal habitat is medium to large sized rivers with a significant slope ( > 1 ‰) and a minimum discharge higher than 1 m3/s (Mallet et al. 2000). Unfortunately this kind of rivers is quite suitable for hydropower development and more than half of its historical distribution in the European river network has been inundated under large dam reservoirs. Nowadays, its longitudinal distribution in rivers is often fragmented in some small populations upstream of reservoirs, i.e. in the trout (Salmo trutta) zone, and downstream in the barbel (Barbus barbus) zone (Persat 1996). Both situations are worrying in the context of climate change, mainly because of a diminution of water supply and then a drop of water velocities especially in the upstream sections, and an increase in water temperatures in the downstream sections, both affecting the growth rate of the fish (Mallet et al. 1999). The Ain river system illustrates both of these situations with contrasting responses (Dolédec et al. 2017). The size of the fish drives its survival expectancy, the juveniles being the most exposed because of their higher requirements with respect to temperatures and water velocities, and their higher exposure to predation. One important statment is that the growth can be drastically reduced or even stopped during too hot summers (fig. 1), and oogenesis, starting in mid-July in European grayling (Jankovic 1961), as well, making females sterile for the next spring. For about three decades, an adaptive management scheme (the Early Warning Cell) has been developed to overcome temporary critical conditions in the downstream section in summer by optimizing reservoir releases according to a weekly multi-partner committee meeting supported by Electricité De France (EDF), the dam concession company, and the Rhône-Méditerranée-Corse Water Agency, and driven by the state departmental service DDT-01. The main decisional criteria are the daily amplitudes and extreme values of both temperature and oxygen in three locations monitored by EDF permanent probes and the local joint municipal authority SR3A ) (Robichon 2018). For each parameter, two thresholds, one for an alert and one for an emergency, have been selected to drive water releases for either buffering the amplitudes of physical-chemical variations or flushing the benthic algae in excès (fig. 2). This allows maintenance of a significant population in the Lower Ain River despite the rather extreme conditions (temperatures often exceeding 23 °C and sometime 25 °C), demonstrating an unexpected resilience in that population. It is mainly based on a peculiar survival behaviour of the adults, which seek out standing water habitats in some margins of the main channel that are fed by cold underground supplies. This behaviour is nevertheless risky and a source of mortality if maintained too long. Knowing the climate forecast for the near future, we cannot ascertain that this population, like many others, will survive for a long time. Long-term conservation of this gene pool would then require translocation of the population towards more suitable catchments with colder temperatures, but it would no more be the "Ain Grayling".

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Acknowledgements

Over time, many people, services and companies participated physically, intellectually or financially to the monitoring of the Ain grayling population dynamics by the UMR CNRS 5023 Université Lyon 1 (CSP-ONEMA-AFB, EDF, SBVA-SR3A, Agence de l'Eau RMC, Angling Federation and angler societies...) and we are grateful for all these long supports. We are very pleased to address special thanks to the AUPRA angler society team without which almost no fishing campaigns would have been possible.

References

Dolédec S., Mermillod-Blondin F., Simon L., Alric B., Persat H., Robin J., Creuzé des Chatelliers M., Dole-Olivier M.-J., Marmonier P., Blémus J., Vienney A., 2017: Dynamique, fonctionnement et biodiversité des communautés aquatiques face aux pressions anthropiques sur la vallée de l'Ain. ZABR Technical Report for EDF and RMC Water Agency, UMR CNRS 5023 LEHNA, Université Lyon 1, 123 p + Annexes. Jankovic, D. 1960. Sistematika i ekologija lipljena (Thymallus thymallus L.) u Jugoslaviji, Vol. 7. Bioloski Institut, Beograd: 145 pp. Mallet J.P., Lamouroux N., Sagnes P., Persat H., 2000 : Habitat preferences of European grayling in a medium size stream, the Ain river, France. J. Fish Biol. , 56, 1312-1326. Mallet J.P., Charles S., Persat H., Auger P., 1999 : Growth modelling in accordance with daily water temperature in European Grayling (Thymallus thymallus L.). Can. J. Fish. Aquat. Sci. 56: 994–1000. Persat, H., 1996. Threatened populations and conservation of the European grayling, Thymallus thymallus L., 1758. In Kirchhofer, A. & Hefti, D. (Eds.), Conservation of endangered freshwater fish in Europe, Birkhäuser Verlag Basel, Switzerland : 233-247. Robichon C., 2018 : Rapport de cellule d'alerte, septembre 2018 – Bilan du suivi écologique de la basse rivière d'Ain. SR3A Ambérieux en Bugey, 49 p. + Annexes.

Keywords: Ain River, grayling survival, Climate Change, dams, Temperatures, Oxygene, discharge, Water Quality

Conference: XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.

Presentation Type: Oral

Topic: GRAYLING (GENUS THYMALLUS): EVOLUTION, SYSTEMATICS, MANAGEMENT AND CONSERVATION

Citation: PERSAT H, Mallet J, Robichon C, Alric B and Capra H (2019). Grayling survival expectancy and climate change illustrated by the status of the population of the Lower Ain river. Front. Mar. Sci. Conference Abstract: XVI European Congress of Ichthyology. doi: 10.3389/conf.fmars.2019.07.00069

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Received: 19 Jun 2019; Published Online: 14 Aug 2019.

* Correspondence: Mx. Henri PERSAT, Société Française d'Ichtyologie, Paris, France, grayling@laposte.net