Only Survivors Grow – Effects of Predation on Stocked Juvenile Common Carp (Cyprinus carpio Linnaeus, 1758) in a Stagnant Waterbody

This study aims to investigate the suitability of an entirely stocking-based fisheries management strategy to establish a self-sustaining carp population in two water bodies within the Danube catchment east of Vienna. The assessment was generally based on two factors: the effect of predation on juvenile carp`s mortality and potential differences in the growing performance of different age classes. The investigation on predation effects showed, that after one year ~541 of initially 1000 stocked K1 survived in the water body with decreased pressure of predation, while there was no evidence of surviving stocked juveniles in the water body with increased pressure. Regarding the growth-rate, the stocked K1 showed the overall steepest growth curve compared both to the stocked K2 cohort and selected wild populations. After five years the younger stocked cohorts ML was even higher than the older cohorts one at the same age, although the stocked K2 had by far a larger initial TL. Our results showed that predation can massively impact the mortality rate of stocked K1 juveniles and thus the success of fisheries management strategies. Moreover, it demonstrated the benefits of stocking fish in early life stages regarding a best possible adaptation to the given environmental conditions.