The pros and cons of the invasive freshwater apex predator, European catfish Silurus glanis, and powerful angling technique for its population control

Catfish have spread across Europe and several countries out of this region within the last decades. Basic
knowledge of this apex predator has revealed concerns of invasive behaviour and questions regarding its utilization
as a biomanipulation species. However, a method enabling its regulation to a required level has not yet
been developed. We simulated the impact of angling on the catfish population by method of hook-lines in two
post-mining lakes with a monitored population consisting of tagged individuals and in two reservoirs as reference
sites. Further, the efficiency of hook-lines as a reducing device was examined and the economic aspects
were determined. Catfish population in localities where the species is unwanted or invasive may be efficiently
reduced to a harmless level by hook-lines and angling (depending on the approach of anglers). The most efficient
time of the year seems to be spring to early summer with catch efficiency of 5.4 individuals per 10 baits in one
day. The catch efficiency markedly decreased during the second part of the year and did not exceed 2.8 individuals
per 10 baits in one day. Mean size of catfish had negative impact whereas catfish biomass had positive
impact on the catch efficiency. Trophic status and number of catfish in the locality had no impact on the catch
efficiency. According to model, 11–18 bait-days per 1 ha per season is efficient to decrease catfish population to
10% of the original size. Both angling and hook-lines are very simple, they are financially and time bearable
mechanisms of catfish regulation in any condition. However, catfish play an important role as a biomanipulative
species in many localities. In this case where catfish is beneficial, angling presents a real threat of population
collapse and loss of the biomanipulative effect.