Fish and Aquatic Conservation


Ecological Risk Screening Summaries (ERSS)

What are Ecological Risk Screening Summaries and Why Are They Important?

Introduced Species

A plant or animal species that has been transported by human activities, either intentionally or unintentionally, into a new region.

Invasive Species

An introduced species that causes, or is likely to cause, economic or environmental harm or harm to human, animal, or plant health in the new area of introduction.

Invasive species cause incredible harm to the environment and cost billions of dollars to state and federal governments and private industry. Although many species introductions happen each year, only some will cause harm and become invasive.

An Ecological Risk Screening Summary, or Risk Summary, provides a rapid evaluation of a species’ potential invasiveness. These evaluations give us, as well as our natural resource stakeholders and the public, a quick way to determine which species are most likely (high risk) and least likely (low risk) to cause damage if they spread outside of their natural range, and which ones have insufficient information to make such a determination (uncertain risk).

Because we need to assess many species quickly, the standards set forth in the Standard Operating Procedures manual allow Risk Summaries to be prepared by a broad range of biologists, ecologists, and invasive species specialists trained in conducting literature searches and evaluating data according to the Standard Operating Procedures. Risk Summaries should not be considered as a substitute for in-depth risk assessment methods that rely on species-specific expertise. We encourage our stakeholders and the public to carefully consider what type of risk assessment best meets their needs.

We evaluate risk based on similarity of climate and history of invasiveness.

Our Risk Summaries use similarity of climate and history of invasiveness to determine risk because research has shown that these two factors are predictive of invasion risk across a wide range of plants and animals. Other biological factors (predation, lack of prey, lack of habitat, etc.) could limit the ability of a species to become invasive. For some species, risk of introduction already may be limited by regulations that prohibit importation or trade, or by non-regulatory risk management options. Risk Summaries do not factor risk management options, which may reduce risk, into the risk category.

We use our Risk Assessment Mapping Program to compare air temperature and precipitation patterns within a species’ known range with climates across the United States. The result is a map showing how the local climate in the United States compares to the climate where the species is distributed and an overall climate score for the United States. While the climate score in the Risk Summary is classified as a high, medium, or low climate match for the contiguous United States, those interested in the climate match for a specific local area can view the map in the Risk Summary to determine a local climate match.

There are limitations to the climate match, such as:

We also look at where the species has been introduced in other parts of the world outside of its native range and whether it became established and caused harm. We call this the species’ history of invasiveness. There is a compelling body of evidence that invasion history is among the most useful variables to predict whether nonnative species introduced into new ecosystems may become invasive.

Finally, we look at how certain we are that the information used for the climate match and history of invasiveness is scientifically credible, reliable, and sufficiently documented to be used for the intended purpose. You can review all of our supporting documentation for more details on how each risk category is determined and how we establish certainty. 

What are the risk categories?

High risk: 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. While a high-risk species may not be an invasive risk to every locality in the United States, great caution is needed when trading or acquiring high-risk species, particularly in parts of the United States where environmental conditions in the wildlife have been identified as suitable for their survival. Please consider choosing an alternative species from the low risk category for pets and other uses, rather than a high-risk species. If new species are being considered for trade, then we do not recommend high-risk species.

Low risk: Species that are considered low risk present a minimal risk of invasiveness because the climate where they are established is sufficiently different from the United States climate AND there is no evidence of invasiveness globally.

Uncertain risk: Species that are considered uncertain risk need a more in-depth assessment beyond the Risk Summary to better define the species’ risk to U.S. environments. This additional information will help inform decisions on where, when, and how the species may be used to minimize risks of them becoming invasive.

Our process results in many species being classified as uncertain risk because strong evidence is required to place them in either the high-risk or low-risk categories. As a precaution, results are weighted toward an uncertain risk categorization when our rapid screening process results in conflicting signals about level of risk based on climate match and history of invasiveness, and may warrant additional evaluation. If a species is not yet in trade and is uncertain risk, we do not recommend its utilization without conducting or consulting a more in-depth assessment.

Risk Summaries are used to inform the public and help prevent future harm from invasive species.

Risk Summaries are publicly available to governments, industry, and other stakeholders as a readily available source of information to aid in making informed decisions about developing watch lists, and trading, transporting, or possessing a particular species. Uses include:

Certain species that have a high or uncertain overall risk may warrant additional detailed evaluations to determine if a proposal for listing as injurious wildlife is appropriate. The Service does not list species based solely on the Risk Summary. More detailed reviews are completed on species being evaluated for a proposed injurious wildlife listing. Read more about  Injurious Wildlife Listing Criteria.

Risk Summaries are updated as new information becomes available.

Since Risk Summaries are prepared relatively rapidly, it is possible some information is unavailable or missed. Because new information could change the Risk Summary results, we periodically update Risk Summaries. Please check the Risk Summary website regularly to obtain the most current versions.

You can help improve our Risk Screenings. If you have information that could help improve the accuracy of our assessments please contact us at preventinvasives@fws.gov.


Ecological Risk Screening Summary Reports

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