Benthic Metabolism in Fluvial Sediments with Larvae of Lampetra sp.

ObjectiveHuman‐induced dewatering of freshwater habitats causes mortality of larval lampreys (family Petromyzontidae). Salvage by electrofishing at dewatering events is assumed to reduce this mortality, but to our knowledge this assumption remains unassessed.MethodsWe estimated mortality of salvaged larval lampreys (Lampetra spp. and Pacific Lamprey Entosphenus tridentatus) within 24 h following collection at field dewatering events in July and October. To assess when salvage may reduce mortality, we compared mortality of salvaged individuals from field dewatering events to mortality of burrowed and emerged individuals in dewatered habitats in the laboratory. Salvage protocols included electrofishing and foot pressure from walking in test enclosures before and after dewatering. Electrofishing after dewatering (“dry shocking”) involves positioning probes on moist sediment to entice burrowed larval lampreys to emerge.ResultDuring the July salvage, air temperature averaged 36°C, bottom water temperature averaged 20°C, and many emerged larval lampreys were dead on the sediment surface. During two October events, air temperatures averaged 18°C and 11°C, bottom water temperatures averaged 12°C and 7°C, and only one dead emerged larval lamprey was observed. Estimated mortality of salvaged larval lampreys was 0.20 (90% credible interval = 0.09–0.37) in July and 0.00 (90% credible interval = 0.00–0.06) and 0.06 (90% credible interval = 0.01–0.18) in October. All larval lampreys that remained burrowed and were excavated from enclosures after salvage were dead in July but alive in October. Logistic regression suggested that mortality declined with increasing larval length. Mortality of salvaged 80‐mm larval lampreys in October was lower than that of 80‐mm individuals emerged for 1 h or burrowed for 8 h at similar water temperatures (8–10°C) in the laboratory.ConclusionIn this study, electrofishing for salvage caused minimal mortality of burrowed and emerged larval lampreys in dewatered habitats. Thus, salvage using electrofishing methods could aid conservation of native lampreys by reducing mortality associated with human‐induced dewatering events, especially when temperatures are elevated.

Section: Introductionmentioning

confidence: 99%

Salvage using electrofishing methods caused minimal mortality of burrowed and emerged larval lampreys in dewatered habitats

Harris

Liedtke

Skalicky

et al. 2023

“…Initial results (410 publications) were reviewed, and those reporting research on Pacific Lamprey or a combination of species that included Pacific Lamprey were included herein (223 publications). 2022; et al 2022) and can play a vital role in ecosystem functioning (Shirakawa et al 2013;Boeker and Geist 2016;Nika et al 2021). Results from Blanchard et al (2023, this special section) and Liedtke et al (2023, this special section) inform the distribution of larval lampreys in freshwater habitats from small (e.g., sediment distribution) to large scales (basin-wide distribution) and highlight effects of stream management decisions on larval lamprey populations.…”

Section: Life History and Population Dynamicsmentioning

confidence: 92%

Bringing partners together: A symposium on native lampreys and the Pacific Lamprey Conservation Initiative

Liedtke,

Harris,

Wang

et al. 2023

“…Laboratory and field studies (Liedtke et al 2015(Liedtke et al , 2020Lampman and Beals 2019;Harris et al 2020Harris et al , 2023 suggest that smaller lampreys, especially age-0 individuals, may be less capable of gaining access to the hyporheic zone and potentially less likely to survive there. Because they are essential to the function of freshwater ecosystems (Shirakawa et al 2013;Boeker and Geist 2016;Nika et al 2021), any larval lampreys inhabiting the hyporheic zone may be vital for systems that experience frequent dewatering.…”

Section: Use Of the Hyporheic Zonementioning

confidence: 99%

Synthesis of larval lamprey responses to dewatering: State of the science, critical uncertainties, and management implications

Liedtke

Harris

Blanchard

et al. 2023

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.