Characterizing Risk

The Aquatic Nuisance Species Task Force (ANSTF) and National Invasive Species Council (NISC) identified air transportation as a pathway for invasive species introduction and spread (2014). Seaplanes, which broadly include flying boats, amphibious planes, and float planes, have also been identified as a vector in the spread of high-risk invasive species. Seaplane transportation was directly correlated to the spread of Elodea sp. from high traffic seaplane bases to remote waterbodies in Alaska (Schwoerer 2017). Despite this key example, it is challenging to quantify the role of seaplanes as an AIS vector because of a variety of dynamic factors. This seaplane pathway risk assessment framework is meant to characterize various factors that contribute to the risk of seaplanes serving as a spread vector of AIS. The risk assessment identifies and characterizes risk, rather than assigning a quantitative value of seaplane pathway compared to other pathways.

 

Risk Assessments and Frameworks

A risk assessment is a systematic approach to assess the scale and likelihood of arrival, establishment, spread, and impact of nonnative species (Robertson et al. 2021, Venette et al. 2021). Risk assessments analyze, identify, and estimate the dimension, characteristics, and type of risk (Commission for Environmental Cooperation 2009). There are three categories of risk assessments—approaches that target lists of potential species, species-focused approaches, and pathway-focused approaches (Lonsdale 2011). Risk assessments inform prediction, a process to forecast the likelihood and consequence of an invasion, and pathway analysis, a process to evaluate how invasive species might be introduced (Venette et al. 2021). Venette et al. (2021) emphasized pathway analyses and subsequent regulation of those pathways as frontline in the prevention of biological invasions (Hulme 2009) and cost-effective approaches (Leung et al. 2002, Keller et al. 2007, Essl et al. 2015; Tidbury et al. 2016). The discipline of risk assessment is an important area of analysis to identify strategies for managing potential threats. Invasive species risk assessment and horizon scans have been successfully used to develop watch lists, prioritize funding and management activities.

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Species risk assessments differ from pathway risk assessments in a variety of ways. Species assessments examine multiple predictors of species risk, such as climate suitability and history of invasiveness. Further, species assessments may include specific possible pathways for the introduction of a specific species. Pathway assessments examine the various ways that multiple species may be moving globally or regionally under intentional and unintentional scenarios. Further, pathway assessments may consider the likely taxa that may be introduced and spread by way of specific pathways.

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Multiple efforts have described the pathways that can result in the introduction of species from one area to another (e.g., Hulme et al. 2008, Hulme 2009). The 18th Subsidiary Body on Scientific, Technical, and Technological Advice to the Convention on Biological Diversity documented six principal pathways of nonindigenous species introduction, including transport stowaway, which refers to the movement of live organisms attached to transporting vessels and associated equipment and media (Convention on Biological Diversity 2014). This pathway most closely describes the role seaplanes may play in AIS transport and introduction. Many pathway frameworks suggest describing pathways as mechanisms of commodity, vector and dispersal (see Hulme et al. 2008, Convention on Biological Diversity 2014, Faulkner et al. 2020). The specific pathway of transport stowaway indicates a transportation mechanism where invasive species are unintentionally moved. Many different transportation pathways can provide hitchhiking opportunities including aviation, international shipping and land transport. A recent analysis of high impact species pathways and their economic cost indicates that the transport stowaway pathway represented the primary mechanism and greatest cost globally compared to other pathways (Turbelin et al. 2022).  Measures that may be taken to address transport stowaway pathways on a global landscape could include strengthening institutional legal frameworks and improving quality assurance of border inspections.

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Horizon scans and species-specific risk assessments have been used to evaluate risk for species establishment in new areas. An improved understanding of the relative risk that various pathways and the associated vectors can pose will assist managers in decision making to adequately address possible invasive species introduction and spread. For example, there has been considerable effort to mitigate the risk that trailered watercraft pose in the secondary spread of dreissenid mussels and other aquatic invasive species (AIS) throughout North America. This effort has relied on states and provinces to conduct prevention programs, enact legislative provisions, and engage industry partners in innovation.

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It is critical to consider strategies that minimize spread regionally (Paini et al. 2010), where established species could spread shorter distances and between states based on seaplane traffic and activities.