Forecasting the Impacts of Silver and Bighead Carp on the Lake Erie Food Web

Nonindigenous bigheaded carps (Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix; hereafter, “Asian carps” [AC]) threaten to invade and disrupt food webs and fisheries in the Laurentian Great Lakes through their high consumption of plankton. To quantify the potential effects of AC on the food web in Lake Erie, we developed an Ecopath with Ecosim (EwE) food web model and simulated four AC diet composition scenarios (high, low, and no detritus and low detritus with Walleye Sander vitreus and Yellow Perch Perca flavescens larvae) and two nutrient load scenarios (the 1999 baseline load and 2× the baseline [HP]). We quantified the uncertainty of the potential AC effects by coupling the EwE model with estimates of parameter uncertainty in AC production, consumption, and predator diets obtained using structured expert judgment. Our model projected mean ± SD AC equilibrium biomass ranging from 52 ± 34 to 104 ± 75 kg/ha under the different scenarios. Relative to baseline simulations without AC, AC invasion under all detrital diet scenarios decreased the biomass of most fish and zooplankton groups. The effects of AC in the HP scenario were similar to those in the detrital diet scenarios except that the biomasses of most Walleye and Yellow Perch groups were greater under HP because these fishes were buffered from competition with AC by increased productivity at lower trophic levels. Asian carp predation on Walleye and Yellow Perch larvae caused biomass declines among all Walleye and Yellow Perch groups. Large food web impacts of AC occurred in only 2% of the simulations, where AC biomass exceeded 200 kg/ha, resulting in biomass declines of zooplankton and planktivorous fish near the levels observed in the Illinois River. Our findings suggest that AC would affect Lake Erie's food web by competing with other planktivorous fishes and by providing additional prey for piscivores. Our methods provide a novel approach for including uncertainty into forecasts of invasive species' impacts on aquatic food webs. Received December 6, 2014; accepted July 15, 201

Offense and defense in landscape-level invasion control

Biological invasions are multi-stage processes comprising chance demographic events, species interactions, and dispersal. Despite this complexity, simple models can increase understanding of the invasion process. We model the spread of aquatic invasive species through a network of lakes to evaluate the effectiveness of two intervention strategies. The first, which we call offense, contains the invader at sources; the second, which we call defense, protects uninvaded destinations. Deterministic models reveal the effects of these intervention strategies on spread rates. Practical applications involve finite collections of uninvaded lakes, however, and we therefore also present a stochastic model to describe how these strategies affect expected times to important invasion milestones. When the goal is to reduce overall spread rates, both approaches agree that offense is better early in invasions, but that defense is better after 1/2 the lakes are invaded. When the goal is to protect areas of high conservation value, however, defensive site protection always provides lower per site introduction rates. Although we focus on lakes, our results are quite general, and could be applied to any discrete habitat patches including, for example, fragmented terrestrial habitats

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

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

Future declines of the binational Laurentian Great Lakes fisheries : the importance of environmental and cultural change

It is increasingly clear that future long-term environmental challenges (eg climate change) are being driven by economic and cultural choices, as well as by physical and biological mechanisms. We looked at the extent to which these apply to potential future changes in fisheries in the Laurentian Great Lakes. These fisheries rank among the most valuable freshwater fisheries in the world, but have declined markedly in recent decades. To investigate how these fisheries might develop in the future, we elicited projections from experts in fisheries and related fields. Experts provided assessments on variables relating to US and Canadian commercial (pounds landed) and sport (participation and expenditures) fisheries for the years 2006 and 2025. We measured each expert's ability to quantify their uncertainty, producing performance-weighted combinations of expert estimates. All experts expected commercial fisheries to decline from 2006 to 2025, with greater declines in the US (25%) than in Canada (9%). Expectations for sport fishing differed more between lakes and less between countries, with median expected declines ranging from 1% to 13%. Experts attributed expected declines primarily to changes in economic market demands and shifts in societal interests. Increased attention to social and economic trends could aid Laurentian Great Lakes fishery policy and management

Ship-borne nonindigenous species diminish Great Lakes ecosystem services

We used structured expert judgment and economic analysis to quantify annual impacts on ecosystem services in the Great Lakes, North America of nonindigenous aquatic species introduced by ocean-going ships. For the US waters, median damages aggregated across multiple ecosystem services were $138 million per year, and there is a 5$800 million annually. Plausible scenarios of future damages in the US waters alone were similar in magnitude to the binational benefits of ocean-going shipping in the Great Lakes, suggesting more serious consideration is warranted for policy options to reduce the risk of future invasions via the St. Lawrence Seaway. © 2012 The Author(s)

Using Structured Expert Judgment to Assess Invasive Species Prevention: Asian Carp and the MississippiGreat Lakes Hydrologic Connection

Recently, authors have theorized that invasive species prevention is more cost-effective than control in protecting ecosystem services. However, quantification of the effectiveness of prevention is rare because experiments at field scales are expensive or infeasible. We therefore used structured expert judgment to quantify the efficacy of 17 proposed strategies to prevent Asian carp invasion of the Laurentian Great Lakes via the hydrologic connection between the Mississippi and Great Lakes watersheds. Performance-weighted expert estimates indicated that hydrologic separation would prevent 99% (95,100; median, 5th and 95th percentiles) of Asian carp access, while electric and acoustic-bubble-strobe barriers would prevent 92% (85,95) and 92% (75,95), respectively. For all other strategies, estimated effectiveness was lower, with greater uncertainty. When potential invasions by other taxa are considered, the effectiveness of hydrologic separation increases relative to strategies that are effective primarily for fishes. These results could help guide invasive species management in many waterways globally

Using Structured Expert Judgment to Assess Invasive Species Prevention: Asian Carp and the MississippiGreat Lakes Hydrologic Connection

Recently, authors have theorized that invasive species prevention is more cost-effective than control in protecting ecosystem services. However, quantification of the effectiveness of prevention is rare because experiments at field scales are expensive or infeasible. We therefore used structured expert judgment to quantify the efficacy of 17 proposed strategies to prevent Asian carp invasion of the Laurentian Great Lakes via the hydrologic connection between the Mississippi and Great Lakes watersheds. Performance-weighted expert estimates indicated that hydrologic separation would prevent 99% (95,100; median, 5th and 95th percentiles) of Asian carp access, while electric and acoustic-bubble-strobe barriers would prevent 92% (85,95) and 92% (75,95), respectively. For all other strategies, estimated effectiveness was lower, with greater uncertainty. When potential invasions by other taxa are considered, the effectiveness of hydrologic separation increases relative to strategies that are effective primarily for fishes. These results could help guide invasive species management in many waterways globally