Potential Effects of Forthcoming Climate Change and Biological Introductions on the Restoration of the European Sturgeon

Abstract

The restoration of threatened species is taking place in a changing global environment, creating additional problems for stakeholders and decision-makers to face. Here, the potential influences on the restoration measures developed for the European sturgeon (Acipenser sturio L., 1758) of both climate change and, to a lesser extent, biological introductions are assessed and discussed. Both evaluations were based on intensive literature searches and species distribution models. Most of the former European sturgeon distribution range was calculated as being strongly affected by global warming, especially in basins along its southern margin. Five basins where re-introductions are envisaged were projected to remain highly suitable for the species under climate change assumptions. In addition, some large French basins appeared to be suitable for other sturgeon species that share many ecological similarities with A. sturio. 45.1 Introduction In the context of the changing global environment, the restoration of threatened species is a complex process involving interdisciplinary and multi-scale analysis as well as long-term perspectives. On the one hand, recent climate change has P. Williot et al. (eds.), Biology and Conservation of the European Sturgeon Acipenser sturio L. 1758, DOI 10.1007/978-3-642-20611-5_45, # Springer-Verlag Berlin Heidelberg 2011 593 been demonstrated to have significant effects on both plant and animal species (Parmesan and Yohe 2003; Walther et al. 2002). Consequently, the future distribu-tion of various organisms was assessed using different temperature rise scenarios for the coming decades, e.g., trees (Thuiller 2003), amphibians (Araujo et al. 2006), and freshwater fishes (Buisson et al. 2008). When European diadromous fishes were assessed in their turn, they appeared particularly sensitive to climatic disruption in the surrounding environment (Lassalle et al. 2009). It has been calculated that in the near future, a large proportion of the hydrographic basins where a species is or was known to occur will decrease in favourability or become totally unsuitable for the given species. Even with the wide spectrum of uncertainties inherent in modelling species distribution, these results could be useful to stakeholders and decision-makers to enable them to take more informed management measures. They should be regarded as the first step in a decision-making process combining information on local habitat quality and on the social perception of restoration efforts (Lassalle et al. 2010). On the other hand, current and future global change could raise some other questions on the restoration of threatened species. One major issue concerns the potential interactions with allochthonous species that could proliferate in the niches left vacant by the autochthonous endangered taxa or compete with the remaining weakened populations, leading in some cases to competitive exclusion (Bohn et al. 2008). Most of the time, non-native fish species were introduced accidentally, or intentionally through recreational and commercial activities such as aquaculture and pet fish industries. Nevertheless, they can also colonize new places that become suitable following human-induced environmental modifications. This latter case is illustrated when species extend their range dozens of kilometres, mainly northward, due to current global warming (Thomas and Lennon 1999). In this context, several anadromous and non-anadromous sturgeon species coexist with the Euro-pean sturgeon (Acipenser sturio L., 1758) in the Eastern part of its distribution range (Holcik et al. 1989). Many of these species are currently farmed in Western European countries, e.g., A. baerii in France, Huso huso in Italy or even A. guelden-staedtii in Belgium and Netherlands (Williot et al. 2009). In 1999, farmed specimens of A. baerii accidentally escaped into the Gironde system, survived and have occasionally been recaptured by fishermen (Maury-Brachet et al. 2008). Similarly, A. gueldenstaedtii individuals, originally limited to the Ponto-Caspian region, were regularly caught along the shores of the North and Baltic seas after escapes in the Oder estuary (Gessner et al. 1999; Arndt et al. 2002). No introduction of sturgeon in Europe was followed by the installation of a functional population in the foreign environment. Nevertheless, these examples suggest that there is a high risk of potentially interactive species being introduced into the area where practical measures are being undertaken to restore European sturgeon. Such introductions could expose the protected species to competition for habitat and food resources, and to new parasites and diseases, and could reduce its reproductive success because of interbreeding and the subsequent production of fertile or unfer-tile hybrids. It has not yet been proven that there have been deleterious effects on 594 G. Lassalle et al.