Research Document 2021/035
Estimating the Mortality of Fishes and Mussels of Conservation Concern Resulting from Bayluscide® Applications within four rivers of the Huron-Erie Corridor
By Smyth, E.R.B., and Drake, D.A.R.
Abstract
Bayluscide, a chemical lampricide, is used by government agencies to assess and control invasive Sea Lamprey (Petromyzon marinus) in the Great Lakes basin. The toxicity of Bayluscide to non-target fishes has been previously investigated. However, the potential mortality of fishes and mussels assessed by COSEWIC or listed under Canada’s Species at Risk Act as Endangered, Threatened, or Special Concern has not been evaluated based on the factors that dictate species responses in the wild. To assess the potential for mortality, the likelihood that fishes and mussels of conservation concern will be exposed to, and experience toxicity-induced mortality from, granular Bayluscide in the Detroit, St. Clair, Thames, and Sydenham rivers in southwestern Ontario were quantitatively estimated. Simulation models were based on: 1) habitat associations that predispose fishes and mussels species to occur in areas targeted for application; 2) population densities susceptible to exposure; and, 3) the toxicity of the compound, based on: i) assumed Bayluscide concentrations in the environment; ii) taxonomic or habitat match with surrogate species; and, iii) four dose-response relationships, using Sea Lamprey LC50 and LC99.9 concentrations as a benchmark (fishes) or a single point estimate (mussels). Population effects were evaluated by combining estimates of Bayluscide-induced mortality with age-structured models of Eastern Sand Darter (Ammocrypta pellucida; SARA Threatened), Northern Madtom (Noturus stigmosus; SARA Endangered), Channel Darter (Percina copelandi; Lake Erie DU, SARA Endangered), and Ichthyomyzon spp. In most cases, simulated applications resulted in no or low mortality of fishes and mussels. However, in some cases (< 5%), mortality of ones to tens of fishes and potentially hundreds of freshwater mussels and Silver Lamprey (Ichthyomyzon unicuspis) or Northern Brook Lamprey (I. fossor) occurred following a single application cycle. Based on a model in which recovery from Bayluscide effects does not occur, the 50–100 year effect of repeated Bayluscide application could reduce abundance by as much as 100% from baseline for some species (Northern Madtom, Ichthyomyzon spp.) or up to 90% for others (Eastern Sand Darter) if populations are small and applications occurred annually but would be less severe if populations are large. Estimated mortality varied with the frequency and size of applications but relationships were non-linear. Several uncertainties were identified including: 1) environmentally relevant concentrations of Bayluscide; 2) species-specific Bayluscide toxicity and appropriateness of surrogates; 3) incidence and effect of avoidance behavior; 4) occurrence, density, and habitat associations based on a limited number of field studies; and, 5) unknown population abundance and trajectory for most species of conservation concern. Results indicate that in some cases, Bayluscide may result in mortality and population effects for species of conservation concern but mortality may be mitigated by several factors associated with the application cycle.
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