Impacts of climate change and carp pond farming in Austria

The Waldviertel in Lower Austria is the most important carp breeding area in Austria, and a large proportion of the approximately 650 tons of table carp produced annually in Austria come from there. The Waldviertel is a highland area with a low mountain range character, which was originally characterized by long, snowy winters. As a result, the production of table carp took four years. However, in recent decades there has been a significant change in climatic conditions, with corresponding effects on fish farming. The significant increase in temperatures has extended the production period (Fig. 1). This means that carp reach their slaughter weight faster. Often three years are sufficient instead of four. The higher water temperatures in the fall cause problems when it comes to harvesting, as cooler water temperatures are advantageous at this time. However, harvesting cannot be postponed indefinitely into the fall/winter, as the ponds have to be refilled with water in time for spring. This is becoming increasingly difficult due to the reduced precipitation (snow) in winter. Higher water temperatures go hand in hand with lower oxygen levels in the water, especially in the summer months. This is increasingly causing problems, not only for the carp but also for sensitive fish species such as whitefishes (Coregonus), which also have a hard time coping with the high temperature peaks in summer. Blue-green algae blooms occur more frequently into the fall and in deep ponds, stratification occurs with an oxygen-free deep zone. Pond management is therefore faced with a series of challenges that need to be overcome in order to lead a centuries-old form of aquaculture, which has shaped a whole cultural landscape, into the future.