The History of Sea Lamprey Control in Lake Ontario and Updated Estimates of Suppression Targets

Abstract

The Great Lakes Fishery Commission successfully coordinated fishery management and delivered an international program of sea lamprey ( Petromyzon marinus) control and assessment that facilitated the rehabilitation of lake trout ( Salvelinus namaycush) and development of a salmonid fishery in Lake Ontario during 1971 to 1999. During the 1980s and 1990s, the integrated management of sea lampreys (IMSL) strategy optimized control and assessment techniques and refined the stream selection process. The program focused primarily on the juvenile life stage (larval phase) through the application of the selective lampricide 3-trifluoromethyl-4-nitrophenol (TFM) to tributaries of the lake, although the addition of barriers to Lake Ontario tributaries appears to have reduced the reliance on TFM. By 1999, IMSL had eliminated sea lampreys in 20 of the 57 tributaries with historical records of production. Accordingly, the abundance of spawning phase sea lampreys showed a significant downward trend, and substantial declines in marking rates for large lake trout were observed. Targets for control were established through the lake trout rehabilitation plan, fish community objectives, and simulation models incorporating an economic injury level (EIL) approach. The EIL for sea lamprey control is the point in which more treatment is not economically justified. The updated IMSL model developed for Lake Ontario provided a tool to support trade-off analysis to estimate target levels of sea lamprey abundance relative to lake trout harvest. Comparison of model predictions and trends in spawning phase abundance revealed general agreement, but also pointed to inconsistencies that merit further investigation. The EIL of control based on the entire treatment history is 8,100 kg TFM per year, which produces a treatment residual of 4,100 adult sea lampreys. Given recent estimates of transformer production from the Niagara River, the annual contribution from untreated sources is estimated to be in the range of 10,000 to 15,000 adult sea lampreys. The target level (EIL) for adult sea lampreys in Lake Ontario is thus 14,100 to 19,100. Over the past 10 years, Lake Ontario TFM treatments have averaged 4,600 kg per year.