Synchrony of Pacific Lamprey Populations Across a Broad Geographic Range

Understanding factors that drive Pacific Lamprey Entosphenus tridentatus abundance is essential to interpreting perceived population declines or taking meaningful conservation measures. We compared seven datasets from Oregon, Washington, and Alaska, U.S.A., British Columbia, Canada, and the western Pacific Ocean near Kamchatka, Russia to compare and contrast trends in adult abundance across a broad geographic range. Indices of adult abundance from nearly all of these locations had a high degree of synchrony, suggesting that conditions in the marine environment exert a strong influence on abundance and largely mask local effects of freshwater residence in adult returns. However, the two southernmost datasets showed a departure from this general trend, suggesting that other processes may influence population dynamics in these systems. We use these data to propose a series of mechanisms behind population trends of Pacific Lamprey and the potential for limiting factors to shift between marine and freshwater environments.