Geology topics

Ann E. Gray

Publications and source records attributed to Ann E. Gray.

6 recordsLinked to original sources

USGS2024

Shoreline slope influences movements of larval lampreys over dewatered substrate

Larval lampreys are filter feeders that live for several years burrowed in fine sediments in freshwater streams. Stream side channels and edges, where larval lampreys gather, are vulnerable to natural and human-caused dewatering. Water level reductions can strand and kill thousands of larval lampreys, in part because many remain burrowed until their habitats are exposed, at which point larvae must emerge and attempt to move over dewatered substrate to locate wetted habitat. Dewatering for restoration efforts or seasonal closures of irrigation canals can be done slowly to reduce lamprey strandings, but in some settings, mechanisms are lacking to control the dewatering rate. Phased dewatering, where water level is reduced in stages separated by periods of static water level, could provide options when dewatering rate cannot be tightly controlled. To guide this phased approach, information is needed on the movement capability of larval lampreys. We examined larval lamprey ( Entosphenus tridentatus and Lampetra spp.) movement distance and rate over dewatered substrate at shoreline slopes of 1%, 5%, 10% and 20% in a laboratory setting and modelled results using gamma regression models. Model results suggest both movement distance and movement rate increased with increasing slope and increasing larval length. We used the models to predict minimum distances and rates that 90%, 75% and 50% of medium-sized (75 mm) lampreys would move over dewatered substrates on slopes of 1%–20%. The models predicted that 50% of larvae could move distances of ≥31 cm at rates of ≥0.7 mm/s on a 1% slope and distances of ≥502 cm at rates of ≥8.6 mm/s on a 20% slope. We present an example scenario of how information on larval movement capabilities and shoreline slope could guide phased dewatering events to limit impacts to lampreys.

Aquaculture, Fish and Fisheries↗

USGS2024

Pacific Lamprey responses to stressors: Dewatering and electrofishing

The Pacific Lamprey Conservation Initiative (PLCI) is a collaboration of Tribes, Federal, and State agencies working together to protect and restore Pacific Lamprey ( Entosphenus tridentatus ) and other native lampreys (i.e., Lampetra spp.) in Alaska, Washington, Oregon, California, and Idaho. The U.S. Fish and Wildlife Service hosts and facilitates the PLCI, and the Columbia River Tribes play a large role in setting conservation goals and defining research needs. The PLCI annually solicits proposals for research and restoration activities, which are reviewed and ranked in collaboration with the Bonneville Power Administration (BPA), who annually provides funding to support PLCI priority proposals. This report summarizes two research projects selected through PLCI, and funded under one BPA contract, in support of Pacific Lamprey conservation. The two projects were not topically related apart from a common theme of potential stressors to lampreys and are being reported together because they were combined under one BPA agreement for contracting.

Report↗

USGS2024

Defining sediment handling practices to limit negative impacts to larval lampreys

Sediment manipulation activities such as dredging and restoration efforts (e.g., culvert install/repair) may disturb habitats where larval lampreys live burrowed in stream sediments. Sediment added on top of larval lamprey burrowing areas results in ‘overburden’, which poses risks of mortality from respiratory distress, reduced movement, and crushing injuries or may have sublethal effects such as changes in growth or burrowing activity. To avoid negative outcomes, larvae must be able to vertically migrate through the overburden to reach areas near the new (elevated) sediment-water interface. Current guidance on how to limit negative impacts to lampreys during sediment handling activities is limited by a lack of information on how lampreys respond to overburden. The goal of this study was to evaluate larval lamprey responses to variable overburden depths and exposure durations using two sediment types: fine (<0.250 mm) and sand (0.250 - 0.500 mm). We assessed lamprey (mix of Pacific Lamprey Entosphenus tridentatus and Lampetra spp.) survival and injury and evaluated burrowing performance as an indicator of sublethal impacts of overburden stress. We designed an experimental system using 15-cm diameter plastic tubes partitioned into sections that allowed us to describe the approximate vertical position of larval lampreys within the overburden so we could assess vertical migration ability. The tube sections were stacked in a column and secured using straps. The bottom tube section was 10 cm tall and was attached to a flat, rectangular base plate. This section was filled with sediment and lampreys at the start of a test. The middle tube sections were each 10 cm tall, with the number of sections adapted to the depth of the overburden. The top tube section was 20 cm tall to allow room for 10 cm of water over the surface of the overburden. Sampling involved removing the tubes from a holding tank and quickly separating the sections to locate lampreys and assign their position to the tube section where they were recovered. Our primary objectives for the study were to better understand how depth of overburden and exposure duration affect larval lampreys, but there was no previously published information to inform our selection of test parameters. Thus, we used a two phased approach where Phase 1 was a pre-test to help us refine appropriate treatments for Phase 2. In Phase 1 of the study, we used a constant overburden depth (50 cm) and exposure duration (24 h) to compare four sediment treatments that varied the initial burrowing sediment and the overburden sediment: fine-fine, fine-sand, sand-fine, sand-sand. In all four treatments, most lampreys vertically migrated through the overburden and were recovered in the uppermost tube section 24 h after overburden was added. There were no lamprey mortalities, few injuries, and little evidence of sublethal effects of overburden stress based on burrowing performance tests. Lampreys moved the most in the fine-sand and fine-fine treatments, so they were used for continued testing. In Phase 2 we doubled the overburden depth to 100 cm and tested extended exposure durations (1 to 4 d), and based on those results, added tests of shorter durations (1 to 8 h). Since both treatments used fine sediment for initial borrowing, these tests effectively compared fine and sand sediments as overburden. Overall for Phase 2, there were no lamprey mortalities, little evidence of sublethal effects, and 6.4% of the treatment fish were injured. Most of the injuries were mild abrasions, but some fish had serious damage such as a large gash or nearly complete bisection. We estimate that the serious injuries occurred as tube sections were separated during sampling, but the cause of the minor injuries could not be clearly ascribed to overburden stress or sampling activity. Lampreys moved to the upper sections of the tubes through 100 cm of fine and sand overburden within 1 d. Lamprey position was comparable among the 1-4 d exposures, although position was more variable at 1 d compared to 4 d. Tests of exposures less than 24 h showed that fewer than 40% of lampreys completed vertical migrations to the top of the tube after 4 h, and after 8 h the uppermost tube section contained 33% of lampreys in the sand treatment and 44% of lampreys in the fine treatment. We concluded that the minimum time needed for most lampreys to complete vertical migrations through 100 cm of overburden lies somewhere between 8 and 24 h. Lamprey size influenced recovery position in 4 and 8 h exposures to sand overburden, but not for other tests. The mean size of fish near the bottom of the tubes was significantly larger than the size of fish near the top of the tubes. To our knowledge this was the first formal study to evaluate lamprey responses to overburden. Although our test systems were imperfect simulations of natural conditions, and several questions would benefit from additional research, our findings can inform guidelines on sediment handling practices to limit negative impacts to larval lampreys.

Report↗

USGS2020

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

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.

Oregon↗

USGS2020

Evaluating dewatering approaches to protect larval Pacific lamprey

Executive Summary Larval Pacific lamprey live for several years burrowed in nearshore sediments where they filter feed on detritus and organic matter. Dewatering of larval habitat can occur as a result of flow-management practices, construction projects, or seasonal closures of irrigation diversions. Effective management of dewatering events requires guidance on approaches to protect lamprey, such as dewatering rates and light conditions (day or night) that allow lamprey the best opportunity to relocate water and avoid being stranded. We conducted controlled laboratory experiments comparing five dewatering rates (1, 1.8, 4, 8, and 16 inches per hour [in/h]) and two light conditions (light and dark) to evaluate their effectiveness in protecting larval lamprey. We used a tank with a simulated shoreline at a 10-percent slope filled with river sediment and manipulated the outflow to control the rate of dewatering until water was covering only the sediment in the lowest tank section, at the bottom of the slope. Following dewatering, larvae were classified as either stranded (in or on the substrate outside the watered area) or safe (relocated to the wetted area at the lower end of the tank). All study groups experienced high rates of stranding. The lowest stranding rates were for 1 in/h, in both light (77 percent) and dark (80 percent). Faster dewatering rates generally produced higher percentages of stranded fish, and both the dark and light trials at 16 in/h stranded all larvae. At each of the five dewatering rates, trials conducted in the dark stranded the same or higher proportions of fish than the corresponding trial conducted in the light, so there was no clear advantage to dewatering during dark conditions. The largest contribution to stranding rates for all study groups was the high number of larvae (50–80 percent) that did not initiate movement in response to dewatering and remained in the uppermost tank section where they were stocked at the start of the trials. The proportion of larvae that emerged from the sediment during dewatering trials was approximately 30 percent, and fish that emerged were consistently smaller than those that remained burrowed. Combining all dewatering rates, emergence was 31.3 percent for groups under dark conditions and 30.7 percent for groups under light conditions. We recorded the timing of emergence for 58 larvae and their median time to emerge (after the surface of the sediment in the uppermost tank section was dewatered) was 0.62 hour (h) (range 0–4.5 h). We measured larval movement rates and found that large fish moved faster than small fish. Differences in larval movement rate based on light condition were significant only for large fish, which had a significantly faster rate during light conditions. Larval lamprey moved, over short distances, at rates that exceeded the fastest dewatering rate we tested. The mean movement rates for groups ranged from 19.0 to 44.4 centimeters per minute [cm/min]) and the fastest dewatering rate (16 in/h) is equivalent to less than 1 cm/min. Only the slowest movement rate measured, 6.6 cm/min for one individual lamprey, was slower than the fastest dewatering rate. We also investigated lamprey responses to a series of dewatering and rewatering events. Individual larvae were held in cylinders and exposed to four cycles of dewatering and rewatering using dewatering rates of 1 and 16 in/h and a rewatering rate of 2 in/h. Each dewatering rate was tested under both dark and light conditions. The location of fish, either on the surface of the sediment or burrowed, was recorded after each dewatering event for four rounds. The most common individual fish response for all study groups was to remain burrowed through all four rounds, and there were large differences in response between small and large larvae. Overall for small larvae, combining all groups, 14 of 28 fish emerged, and of those, 8 died and 1 was lethargic. The 1-in/h rate had 7 of the 8 mortalities, split about equally between the dark (3 fish) and light (4 fish) trials. All but one fish that died emerged from the sediment at some point during the four rounds of dewatering. Large larvae predominantly remained burrowed in all four rounds and did not experience any mortality. None of the large fish emerged for more than a single round, and emergence occurred only in the first and second rounds. Larvae emerged more quickly as the number of dewatering events increased. The mean time to emerge after the surface of the sediment in the tube was dewatered, combing all four groups, was 42 minutes (min) in round 1 (14 fish), 16 min in round 2 (5 fish), 11 min in round 3 (3 fish), and 8 minutes in round 4 (3 fish). When all groups and rounds of dewatering were combined, the overall mean time to emerge was 29 min (25 fish) and ranged from 1 min to 2 hours after the surface of the sediment was dewatered. Larvae burrowed deeper during the 1-in/h trials than the 16-in/h trials, and few fish were deeper than about 23 centimeters (cm). Large larvae burrowed deeper than small larvae. Small larvae were most concentrated from 0 to 7.6 cm (83.7 percent), and large fish were concentrated from 15.2 to 22.8 cm (43.3 percent). The second dewatering event resulted in greater mean burrowing depth than the first event, but trends after the second event were less clear. Larval size played a role in lamprey responses to dewatering, having a significant effect on emergence, movement rate, and vertical distribution. The sediment used for laboratory testing or occupied by lamprey in the field appears to affect lamprey response to dewatering and deserves greater attention in future studies. Larvae were more active in the dark, but darkness did not consistently provide better outcomes (e.g., more emergence or reduced stranding) compared to daylight. An improved understanding of the cues that prompt larvae to emerge from the sediment, combined with the ability to manage dewatering rates, would be useful to guide future dewatering events to minimize negative effects to lamprey.

Open-File Report↗

USGS2017

Conservation challenges and research needs for Pacific lamprey in the Columbia River Basin

The Pacific Lamprey Entosphenus tridentatus , an anadromous fish native to the northern Pacific Ocean and bordering freshwater habitats, has recently experienced steep declines in abundance and range contractions along the West Coast of North America. During the early 1990s, Native American tribes recognized the declining numbers of lamprey and championed their importance. In 2012, 26 entities signed a conservation agreement to coordinate and implement restoration and research for Pacific Lamprey. Regional plans have identified numerous threats, monitoring needs, and strategies to conserve and restore Pacific Lamprey during their freshwater life stages. Prime among these are needs to improve lamprey passage, restore freshwater habitats, educate stakeholders, and implement lamprey-specific research and management protocols. Key unknowns include range-wide trends in status, population dynamics, population delineation, limiting factors, and marine influences. We synthesize these key unknowns, with a focus on the freshwater life stages of lamprey in the Columbia River basin.

British Columbia, Idaho, Montana, Nevada, Oregon, ↗