SUPERVISOR: Gertrud HAIDVOGL

PROJECT ASSIGNED TO: Nikolaus TÖCHTERLE

Freshwater ecosystems are home to an overproportioned share of the world's biodiversity (Darwall et al. 2018). This biodiversity is under severe threat, with extinction rates and population declines exceeding those of terrestrial or marine systems by far (Dudgeon et al. 2006). The Danube is the most international river of the world, touching ten and draining even nineteen European countries on its way to the Black Sea (Sommerwerk et al. 2009). The Danube’s role as energy source for hydropower production and as transport route for navigation, as well as the development of human settlements in its floodplains have led to the implementation of a wide range of river regulations since the middle of the 19th century including the construction of dams and channelization of the Danube mainstem (Jungwirth et al. 2014). Hydro-morphological interventions like these heavily alter the habitat availability for aquatic organisms including fish, either by habitat degradation or ecosystem fragmentation (Belletti et al. 2020). Longitudinal migration barriers as well as the lateral decoupling of main channel and floodplains can hinder fishes from fulfilling their life cycle due to the impaired access to suitable spawning grounds (Grill et al. 2019).

While in historical context the Austrian Danube provided high natural yields which were sold on the Viennese fish markets, nowadays recreational angling has fully replaced commercial fishing. Along with this transition, the introduction of hatchery-reared fish to the wild (stocking) became the main tool of fishery managers to enhance harvest by rod and reel despite reduced natural stocks. The efficiency of different stocking practices and the implications for the ecosystem are nowadays controversially discussed (Radinger et al. 2023). 

The first part of this PhD-project aims to provide scientific input to that discussion by analyzing the connection of stocking and harvest based on records provided by fishery managers. The study area is comprised of 45 fishing beats between the hydropower plant Altenwörth and the Slovakian border, 33 contain a part of the Danube mainstem. Other occurring waterbody types are tributaries, oxbows and ponds (Figure 1 left). The investigated time frame includes the past 60 years, in this period three hydropower plants (HPP) have been constructed in the study area (Figure 1 right). The main stocked and harvested fish species are pike, pikeperch, catfish, eel, trout, carp, tench and grass carp. 

Figure 1 Schematic depiction of a fishing beat (left) and the study area (right); S = stocking, H = harvest.

 

First, stocking and harvest will be investigated treating fishing beats as independent from each other to identify spatial, temporal and typological patterns. Second, the chance of migration of stocked fish and their harvest in another beat will be included. If neighboring beats show a statistically significant stronger dependence than non-neighboring beats, longitudinal and lateral connectivity will be investigated based on the available stocking and harvest data using the meta-ecosystem concept (Loreau et al. 2003) as framework.

Following working steps in this PhD-project include a survey conducted via a questionnaire among the fishing community of the study area to evaluate catch-related and non-catch related demands and motives. Further, ecological data like fish stock assessments will be used to intersect results obtained before. The findings on the one hand will contribute to the scientific knowledge on ecological and social aspects of the human-nature interaction recreational angling, on the other hand they will function as a sustainable guideline for decision makers which supports the conservation and restoration of the Danube system and its biodiversity.

References

Darwall, W., Bremerich, V., De Wever, A., Dell, A. I., Freyhof, J., Gessner, M. O., ... & Weyl, O. (2018). The Alliance for Freshwater Life: A global call to unite efforts for freshwater biodiversity science and conservation. Aquatic Conservation: Marine and Freshwater Ecosystems, 28(4), 1015-1022.

Dudgeon, D., Arthington, A. H., Gessner, M. O., Kawabata, Z. I., Knowler, D. J., Lévêque, C. & Sullivan, C. A. (2006). Freshwater biodiversity: importance, threats, status, and conservation challenges. Biological reviews, 81(2), 163-182.

Sommerwerk, N., Hein, T., Schneider-Jakoby, M., Baumgartner, C., Ostojić, A., Siber, R., Bloesch, J., Paunović, M., Tockner, K. (2009). The Danube river basin. Rivers of Europe, 59-112.

Jungwirth, M., Haidvogl, G., Hohensinner, S., Waidbacher, H., & Zauner, G. (2014): Österreichs Donau. Landschaft – Fisch – Geschichte. Institut für Hydrobiologie und Gewässermanagement, BOKU Wien, 420 S.

Belletti, B., Garcia de Leaniz, C., Jones, J., Bizzi, S., Börger, L., Segura, G., ... & Zalewski, M. (2020). More than one million barriers fragment Europe’s rivers. Nature, 588(7838), 436-441.

Grill, G., Lehner, B., Thieme, M., Geenen, B., Tickner, D., Antonelli, F., ... & Zarfl, C. (2019). Mapping the world’s free-flowing rivers. Nature, 569(7755), 215-221.

Radinger, J., Matern, S., Klefoth, T., Wolter, C., Feldhege, F., Monk, C. T., & Arlinghaus, R. (2023). Ecosystem-based management outperforms species-focused stocking for enhancing fish populations. Science, 379(6635), 946-951.

Loreau, M., Mouquet, N., & Holt, R. D. (2003). Meta‐ecosystems: a theoretical framework for a spatial ecosystem ecology. Ecology Letters, 6(8), 673-679.