LAUSR

Unauthorized introductions are an ongoing problem for fisheries managers. To understand reasons for the continued spread of nonnative fish species, the pathways of nonnative fish introductions were analyzed from 1961 to 2017 in Wyoming, USA. Unauthorized introductions are those that occurred without oversight of a management agency. The largest source of unauthorized introductions was the deliberate, illegal release of fish by the public at 46% of the 215 introduction events. The next largest source was colonization of new water bodies after initial establishment at 29%. Inadvertent (accidental) stockings (8%) and unknown sources (17%) were the other pathways documented. Management responses consisted of attempts at complete eradication (9%), population reduction (10%), or containment (3%) although in the majority of introductions (79%) no action was taken. The introductions involved 49 taxa but three sport fish constituted 26.5% of all events: brook trout Salvelinus fontinalis, walleye Sander vitreus, and yellow perch Perca flavescens. The prevalence of illegal introductions and the difficulty of eradicating introduced species indicate the continuing need for public education and enforcement efforts. The high frequency whereby species colonize new waterbodies indicates that fish introductions, even those authorized by management agencies, must consider the high probability that species will expand into unintended waterways.