- By affecting the ecological, pecuniary and aesthetic productivity of ecosystems, invasive species (IS) increase production and management costs to business, while straining public agencies' budgets with monitoring, enforcement and management efforts. Understanding invasion pathways or vectors, and identifying costs and benefits of alternative management strategies are critical to public and private decision making in agriculture, natural resource and recreation industries. This study develops an integrated spatial framework to measure IS risk and cost-efficiency of alternative IS management strategies. For a given spatial unit, the framework weighs expected damages, based on measured IS risk, against the cost of alternative management strategies, i.e. spatial cost minimization. The study then applied the spatial cost minimization framework to the case of New Zealand mudsnails, Potamopyrgus antipodarum, (NZMS) in the Pacific Northwest (PNW) using data from a variety of sources.
The first stage of the integrated framework is the measurement of NZMS establishment risk, which is estimated as a combination of anthropogenic introduction risk and habitat suitability risk. Since recreational boats are a main vector to disperse NZMS, the normalized boat flows in the PNW states—Idaho, Oregon, and Washington—are used as a proxy for the anthropogenic introduction risk. An environmental niche model then revealed the relationship between environmental features and NZMS presence, i.e. habitat suitability risk. Results suggest that distance, area size, water body concentration, and accessibility are major determinants of PNW recreational boat flows. Environmental characteristics such as elevation, geologic features, precipitation in January, March, and September, as well as the minimum temperature of June, July, and August, and the maximum temperature of June, August, and October are important determinants of PNW's habitat suitability for NZMS.
Potential damages arising from NZMS include anglers' utility loss, which is caused by aquatic habitat degradation due to NZMS invasion, and biofouling influence on hydroelectricity plants, drinking water treatment plants, and boats. Because NZMS economic damages and related management cost are not yet fully identified in the literature, damages and management cost of zebra mussels serve as proxies for those of NZMS. Expected damages are then derived as the product of NZMS establishment risk from the first stage and potential damages noted above. Statewide management cost information is compiled from a phone survey of PNW invasive species field managers. Statewide and local management strategies are prevention, early detection and rapid response and its follow-up (EDRR plus) and ex-post management without EDRR. Local strategies additionally include boater decontamination and fish hatchery prevention efforts.
Finally, the spatial cost minimization problem evaluates expected damages against the cost of each alternative management strategy (statewide and local). Solutions to this minimization problem, i.e. cost-efficient strategies, are derived for individual spatial units in each of the three PNW states. Reflecting uncertainty in the relationship between NZMS impacts and management, the spatial cost minimization is solved under different scenarios: unconstrained,
NZMS damages are a fraction of those of zebra mussels, variation in the effectiveness of statewide and local management strategies, a budget constraint, and targeted NZMS risk level constraint. Results show that statewide prevention, local boater decontamination and fish hatchery prevention are the cost-efficient strategies for managing NZMS in the Pacific Northwest in most cases.