A Self-Reproducing Population of Common Carp Cyprinus carpio at 59°16'N in Sweden

In this brief report, we report on the occurrence of young-of-the-year common carp, as well as older juveniles, in a golf course irrigation pond in Stockholm County, Sweden (59°16′40.4″N 18°28′0.6″E). This documents a case of natural reproduction of the regularly stocked non-native carp in Swedish waters, near the northern limit for the stocking operations. Stocking of common carp in Sweden is generally conducted under assumptions that reproduction is not possible due to low spring-time water temperatures not meeting the reproductive requirements of common carp. Our observation suggests that risks for ecological impacts through the establishment of self-reproducing populations of common carp can be higher than previously assumed. We recommend that this observation is considered when deciding on permits for future carp stocking in Sweden.