COS 52-6 ship-borne non-indigenous species diminish ecosystem services of the Great Lakes: a structured expert judgment study

John D Rothlisberger, David M Lodge, David Finnoff, Roger M Cooke

Research output: Contribution to conferencePaperpeer-review


We performed a structured expert judgment (EJ) study on the ecological and economic impacts of ship-borne nonindigenous species (NIS) in the Laurentian Great Lakes (GL). We used EJ because uncertainty is large about the impact of NIS, especially in the context of other interacting factors that affect ecosystem services (e.g., climate and land use change, pollution, management activities, economic market fluctuations). Empirical studies that control for other factors to isolate NIS effects are almost always conducted at small spatio-temporal scales, with no clear approach available for scaling effects up to levels relevant for guiding policy and management decisions. In other disciplines, EJ has been used for broad-scale risk and impact assessment when substantial scientific uncertainty exists, especially when uncertainty bears on decision-making. In the context of on-going policy debates about the net value of oceanic shipping into the GL, we use EJ to contribute to the quantification of the net costs of NIS on ecosystem goods and services. Since the opening of the St. Lawrence Seaway in 1959, 70% of the NIS newly discovered in the GL (57 spp.) have been introduced via transoceanic shipping. We elicited ten North American GL experts regarding ecosystem services affected by NIS in several economic sectors: commercial and recreational fishing, raw water usage, and wildlife watching. A calibration method assessed each expert’s ability to characterize uncertainty.
Experts differed significantly in calibration performance, and experts' opinions indicated substantial uncertainty about impacts. To generate aggregate impact assessments, with uncertainty bounds, we combined experts' judgments based on calibration performance. Aggregate results indicated that NIS-associated reductions in commercial fishing range from 11% (L.Erie) to 338% (L.Ontario); (mean reduction for other 3 lakes = 36%). Experts estimated overall losses to recreational fishing at 18%. For 2006, US losses were estimated at $11M for commercial fisheries and $600M for recreational fisheries. Average annual NIS-related expenses for raw water users were estimated at $66K per facility. Wildlife watching impacts were negligible (<1%). All impacts are expected to grow into the future, at most doubling during our 20yr time horizon. Our study used a novel application of EJ to provide the first comprehensive and bounded estimates of ship-borne NIS impacts in the GL. These results will be available to compare with estimates from other sources on the costs to replace oceanic shipping in the GL with other transportation modes or otherwise reduce the probability of introduction of NIS from ships.
Original languageEnglish
Publication statusPublished - 6 Aug 2008
Event93rd ESA Annual Meeting - Milwaukee, United States
Duration: 1 Aug 20089 Aug 2008


Conference93rd ESA Annual Meeting
Country/TerritoryUnited States


  • COS 52-6
  • ship-borne
  • non-indigenous species
  • ecosystem services
  • Great Lakes
  • judgement study


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