Species that are considered high risk have a well-documented history of invasiveness in at least one location globally, and a high or medium climate match to the contiguous United States.
The Threespine Stickleback (Gasterosteus aculeatus) is native to most inland coastal waters above 30°N. It is used as a research model and is occasionally commercially fished. The species has a marine and a freshwater/brackish form. This ERSS is only for the freshwater/brackish form. The history of invasiveness for Gasterosteus aculeatus is high. Records of introductions and establishment were found and records of detrimental impacts were available. The main impacts result from the fish’s aggressive nature in its foraging for food, its ability to hybridize with both native sticklebacks and local, genetically distinct subspecies, and introductions of new parasites in conjunction with the introductions of G. aculeatus. The climate match was high. The native range of this species is in the United States and the highest match centers around the native range but indicates that there are many areas outside the native range that could have suitable climate to support this species. The certainty of assessment is high. The overall risk assessment category is high.
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High Risk
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