Forecasting suppression of invasive Sea Lamprey in Lake Superior: data and code for Bayesian forecast model

Resource managers frequently are tasked with mitigating or reversing
adverse effects of invasive species through management policies and
actions.  In Lake Superior, of the Laurentian Great Lakes,
invasive sea lamprey populations are suppressed to protect valuable fish
stocks.  However, the relationship between choice of long-term
control strategy and the future chance of achieving the suppression target
is unclear. Using a 60+ year time-series of suppression effort and
monitoring data from 50 assessment sites located on Lake Superior
tributaries, we developed a Bayesian state-space model to forecast the
probability of suppressing lamprey below the suppression target. With
annual application of lampricide (i.e., lamprey-specific pesticide) at
historical mean levels, we forecasted a 15% chance of achieving the Lake
Superior sea lamprey suppression target in 2040. Increasing lampricide
effort and/or supplementing lampricide control with age-1 recruitment
reduction increased suppression chance.  Annual application of
the maximum historical lampricide effort resulted in a 50% predicted
chance of achieving the target, annual application of the mean historic
lampricide effort plus a 40% reduction in recruitment resulted in a 54%
chance, and the maximum amount of effort considered (maximum historic
lampricide and 60% reduction in recruitment) resulted in a 94% chance.
Policy implications. We developed a simulation model from a robust,
long-term monitoring dataset that improves understanding of why long-term
sea lamprey suppression objectives have been difficult to achieve in Lake
Superior.  Furthermore, the model provides a means to gauge
efficacy of sea lamprey control policy and action scenarios based on
forecasted chance of achieving the suppression target. Creating processes
for iteratively refining our forecasting model with stakeholder and
technical-expert input and integration with a decision analysis framework
could strengthen the link between ecological knowledge obtained from
long-term monitoring and invasive sea lamprey management.