On re-introducing sturgeons to the river Rhine and the North Sea

Historically, the anadromous European sturgeon (Acipenser sturio) was found in all marine- and major river basins of north-western Europe. Unfortunately, this species, which has roamed the earth for 90 million years, disappeared in about 150 years as a result of overfishing, habitat degradation and loss of longitudinal connectivity in the natal rivers. Today, the European sturgeon is listed by the IUCN as critically endangered and on the brink of extinction. This endangered status calls for urgent conservation action, which, given the highly migratory nature of the species, must be taken at an international level. Currently, the Rhine is considered a key river for the reintroduction of the species, in addition to the Garonne and Dordogne and the Elbe rivers. Climate change scenarios,
the partially intact longitudinal connectivity of the Rhine, and recent international efforts to improve water quality, suggest that the species might be able to return. However, by-catch in the North Sea, introduction of alien sturgeon species (predation, competition) and specific local/regional pressures such as inland shipping and coastal infrastructure may prevent this. Therefore, a feasibility assessment should be carried out before reintroduction can take place to avoid wasting time, money and extremely rare individuals of a critically endangered species. This thesis aimed to assess the feasibility of reintroducing the critically endangered European sturgeon (Acipenser sturio) to the river Rhine and the North Sea. The assessment provides a basis to define the critical boundary conditions for successful reintroduction and can advise whether it is useful to stop or continue the reintroduction effort, and if so what additional conservation measures are needed. Four research question were answered to be able to perform the assessment:
• Is sufficient suitable habitat available for European sturgeon in the North Sea and
the river Rhine?
• What are the potential threats from incidental bycatch in coastal and estuarine areas for successful sturgeon reintroduction and from the currently present alien (non-native) sturgeons?
• What other local and/or regional threats could hinder the sturgeon’s return?
• What are possible strategies considering the potential reintroduction of two nativesturgeon species?
These research questions were answered in four parts, 1) habitats, 2) threats, 3) tracking, and 4) alternatives, ultimately culminating in part 5) the overall reintroduction feasibility assessment as presented in the synthesis