Increasing dominance of non-native fishes in the yield of central European streams and rivers

Abstract

Introductions of non-native fishes are among the biggest threats to freshwater ecosystems globally. However, the effects of such introductions on fisheries management and fish yields are understudied. This study is trying to fill this knowledge gap by analyzing relationships between yields of native and non-native fishes with regards to important fisheries management factors, such as fish stocking, fishing effort, and the type or size of the fishery. I analyzed the changes in fish yields in the regions of Prague and central Bohemia from 1986 to 2017. Based on the 32 years of reported data that included 60 million harvested fish weighing 80 tons that were harvested by 250,000 anglers, I conclude that while predominately native fish species were harvested by anglers in the 1980, non-native fish species started dominating in the 21st century. This was true on both small trout streams (1–m wide) and medium-sized cyprinid rivers (5–250 m wide). This dominance is partially explained by the decreasing percentage of native salmonids and cyprinids and by the decreasing or stagnating percentage of native piscivores in the overall fish yield. Conversely, the percentage of non-native salmonids in the overall fish yield was increasing on both streams and rivers. Most importantly though, the percentage of non-native cyprinids – which made 60–80 % of all harvested fish – increased by 16 % over 32 years. Fish yield had a strong positive relationship with fish stocking intensity, a strong negative relationship with angling effort, and strong but mixed relationships with size of the fishery. In conclusion, native fishes are being slowly replaced by non-native fishes in the yield of recreational anglers in central Europe.