Structured expert judgment to forecast species invasions: Bighead and silver carp in Lake Erie

Background/Question/Methods

Identifying which nonindigenous species will become invasive, and forecasting their damages is difficult and presents a significant problem for natural resource management. Often, the data or resources necessary for ecological risk assessment are incomplete or absent, leaving environmental decision-makers ill-equipped to effectively manage valuable natural resources. Structured expert judgment (SEJ) is a mathematical and performance-based method of eliciting, weighting and aggregating expert judgments. A mathematical approach was used to combine the expert responses using a linear opinion pool, or a weighted arithmetic mean of the distributions provided by experts. We used SEJ to forecast the impact of nonindigenous Asian carp in Lake Erie, where it is believed not to be established. Experts quantified Asian carp biomass, production, consumption as well as the impact to other recreational and commercial Great Lakes fishes if Asian carp were established.

Results/Conclusions

According to experts, Asian carp can establish in Lake Erie with the potential to achieve biomass levels that are similar to other Lake Erie taxa. Peak biomass (represented in metric-tons/km²) for both bighead and silver carp ranged from 1.56 to 25.9 and equilibrium biomass was lower and ranged from 0.39 to 12.18. However, the impact of Asian carp on recreational and commercial fishes is estimated to be small and potentially positive. Biomass estimates for walleye, a top predator and priority recreational species in Lake Erie, ranged from 0.87-2.21, which encompassed the 2011 (1.42 metric-tons/km²) and the long term (1990-2011) average (1.396 metric-tons/km²) for this species. In contrast, yellow perch, the top commercially fished species in Lake Erie, biomass was predicted to increase relative to both its 2011 (1.00 metric-tons/km²) and long term average (0.789 metric-tons/km²) realizations. SEJ can be used to quantify key uncertainties of invasion biology and also provide an important decision support tool when the necessary information to inform natural resource management and policy is not available or when the information required for decision-making is sparse or debated.