Passage and freshwater habitat requirements of anadromous lampreys: Considerations for conservation and control

Abstract

Understanding the relationship between a species and its habitats is important for both conservation of imperiled species and control of invasive species. For migratory species, we hypothesize that maintaining connectivity between segregated habitats is more important than improving the quality of each habitat. In the case of anadromous lampreys of conservation concern, we posit that restoring passage routes between spawning, rearing and feeding habitats will result in higher larval abundance upstream from barriers than efforts to improve quality of these freshwater habitats. To explore this hypothesis, we reviewed conservation actions for native anadromous lampreys in freshwater and found that: i) improving passage between habitats results in immediate and quantifiable increases in larval abundance, ii) anadromous lampreys are capable of existing in suboptimal habitats, and iii) small reservoirs of production drive rapid expansion when anadromous lampreys are released from passage constraints. Hence, maintaining habitat connectivity is clearly crucial for conservation of anadromous lampreys. There are fewer examples of improvements to freshwater habitat that increased larval lamprey abundance, perhaps because lampreys are rarely the focus of these efforts. However, habitat limitations such as stream de-watering, chemical pollution, and scour occur and will likely be exacerbated by climate change. Documenting habitat actions that reverse these problems may provide evidence for the merits of lamprey-specific habitat improvement. Our observations are relevant to sea lamprey control in the Great Lakes because barriers and chemical treatment are key instruments of population regulation, and can be strategically deployed to limit production.