, Volume 817, Issue 1, pp 41–56 | Cite as

Pathways of unauthorized fish introductions and types of management responses

  • Frank J. Rahel
  • Mark A. Smith


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.


Fish introduction Invasive species Invasion pathways Illegal introduction Unauthorized introductions 



We thank the many fisheries biologists from the Wyoming Game and Fish Department whose field sampling provided data on the sources of fish introductions and subsequent management actions. William Bradshaw, Peter Cavalli, Matthew Hahn, Rob Gipson, Kenneth Kehmeier, Nick Hogberg, Paul Mavrakis, and Craig Amadio provided supplemental information. Mark Kirk, Bryan Maitland, Annika Walters, and three anonymous reviewers provided helpful comments on the manuscript.

Supplementary material

10750_2018_3596_MOESM1_ESM.pdf (473 kb)
Supplementary material 1 (PDF 474 kb)


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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Zoology and Physiology, and Program in EcologyUniversity of WyomingLaramieUSA
  2. 2.Wyoming Game and Fish DepartmentCheyenneUSA

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