| Abstract |
Dewatering of fine sediments in rivers and streams can kill many thousands of larval lampreys (Order Petromyzontiformes) burrowed in these habitats. The larval life stage for lampreys lasts 3- 10 years, and because larvae often aggregate in large numbers, negative impacts from dewatering could potentially deplete local populations and affect multiple year classes. Larval lampreys have not traditionally been considered during in-stream projects, but recent efforts to increase awareness of lamprey habitats have resulted in guidance on dewatering approaches to limit impacts to lampreys. Salvage efforts to rescue and relocate lampreys aim to mitigate losses, but a lack of understanding of lamprey responses limits optimization of dewatering and salvage procedures. We summarize the state of the science for nine factors that influence larval lamprey (Entosphenus and Lampetra spp.) responses to dewatering, including: burrowing depth, the prevalence and timing of emergence, movements, survival, and the influence of slope, dewatering rate, light, and lamprey size. Research suggests that shoreline slope influences movement capability; hot and sunny conditions increase the risk of mortality; salvage activities cause minimal direct mortality; and smaller larvae are especially vulnerable to negative impacts from dewatering because they are more likely to emerge and are less capable of movement. Critical uncertainties associated with dewatering include cues that drive emergence, influence of sediment composition and stratigraphy, vertical distribution of larvae in natural settings, use of the hyporheic zone, the scale of predation losses, and the effectiveness and impacts of salvage activities. Balancing investments in salvage efforts and lamprey exclusion efforts (e.g., screening) and developing field survey approaches to evaluate use of the hyporheic zone by lampreys are identified management implications and research needs. Addressing the critical uncertainties discussed here and providing updated, science-based guidance on dewatering and salvage practices are suggested management actions to support lamprey conservation. |