Effects of dewatering on behavior, distribution, and abundance of larval lampreys

Abstract

Anthropogenic dewatering of aquatic habitats can cause stranding and mortality of burrowed larval lampreys; however, the effects of dewatering have not been quantified. We assessed: (a) changes in spatial distribution, abundance, and emergence of larvae dewatered at Leaburg Reservoir (OR); (b) emergence and mortality of larvae dewatered in a laboratory; and (c) bias, precision, and interpretation of field results by simulation and modeling of laboratory results. In the field, we examined the distribution, abundance (by N-mixture model), and density of larvae by electrofishing at randomly selected sites before dewatering and after refill, and assessed the emergence rate by observation and excavation during dewatering. Due to dewatering in the field, about 42% of larvae emerged and spatial distribution changed toward sites dewatered less than 20 hours. Estimated average density decreased from 10.8 larvae/m 2 before dewatering to 2.3 larvae/m 2 after refilling, suggesting that abundance declined by 79%; simulation suggested this decline ranged 71-84% (interquartile range). In the laboratory, we examined the emergence and mortality rates of larvae dewatered 0-48 hrs. The emergence rate in the laboratory was similar to that in the field. Mortality rate increased with hours dewatered and was higher for emerged than burrowed larvae. Laboratory estimates of mortality rate predicted a 61% decline in abundance if only burrowed larvae survived and a 54% decline if both burrowed and emerged larvae survived. Abundance declines in the field could be from mortality (e.g., desiccation, predation) and relocation to watered habitat. Our results indicate dewatering can substantially affect spatial distribution and abundance of larval lampreys in freshwater ecosystems.

Reducing River Flows to Control a Parasitic Salmonid Disease in the Klamath River: Simulations Question the Efficacy of Desiccation as a Management Tool

“…The segment of the Klamath River that would be most impacted by desiccation is also home to Pacific Lamprey Entosphenus tridentatus , the endemic Klamath Lamprey Entosphenus similis , Rocky Mountain ridged mussel Gonidea angulate , western pearlshell mussel Margaritifera falcata , and other freshwater mussels Anodonta spp., all of which are species of management conservation concern (Goodman and Reid 2012; Davis et al 2013). Like salmonids, these other species may be highly susceptible to the unintended impacts of river desiccation, such as reduced mobility, stranding, or increased predation risk in shallower depths (Maitland et al 2015; Nogueira et al 2019; Harris et al 2020). As such, the negative, indirect effects of river drawdown on the Klamath River aquatic community would likely be widespread and significant and warrant additional research and careful consideration by river managers.…”

Extreme low‐flow effects on riverine fauna: A perspective on methodological assessments

“…Furthermore, few studies have directly compared faunal responses to ELFs detected from field‐based assessments with controlled experiments. Harris et al (2020) represents a rare exception, reporting comparable emergence rates of lamprey species ( Entosphenus tridentatus and Lampetra richardsoni ) in response to ELF events observed under both field and laboratory conditions. However, the authors did report some discrepancies in measured body size versus survival relationship during an ELF and attributed this to factors including avian predation in the field that was not possible to account for in the controlled experiment.…”

“…Medium -Ecological stressors not directly attributed to ELFs can confound scientific findings (Harris et al, 2020). Structured sampling designs (e.g.…”

“…Nevertheless, there remain a limited number of studies that have employed a dual approach. Notable exceptions include Harris et al (2020) (see Section 4.1). Avery‐Gomm et al (2014) supplemented field‐based measurements highlighting declines in Nooksack dace ( Rhinichthys cataractae ) abundances with evidence from an experimental setup highlighting the effects of ELFs on their growth rates.…”

“…However, such findings are often based on localised ecohydrological data rather than information spanning catchments or larger spatial scales. Furthermore, few studies have directly compared faunal responses to ELFs detected from field-based assessments with controlled experiments Harris et al (2020). represents a rare exception, reporting comparable emergence rates of lamprey species (Entosphenus tridentatus and Lampetra richardsoni) in response to ELF events observed under both field and laboratory conditions.…”