Pacific Lamprey Research Articles

Effects of passive integrated transponder (PIT) implantation on Pacific lamprey ammocoetes

BackgroundLittle is known of the larval biology of Pacific lamprey (Entosphenus tridentatus), a species of conservation concern. With miniaturization of passive integrated transponder (PIT) tags, researchers now have the potential to individually mark larval lamprey. However, recent studies with sea lamprey (Petromyzon marinus) ammocoetes indicated that mortality was unacceptably high after surgical implantation of these tags. We examined survival, tag retention, growth, and swimming performance of Pacific lamprey ammocoetes tagged with uniquely coded 8.4-mm PIT tags and controls marked with visible implant elastomer (VIE).ResultsAmmocoetes as small as 71 mm in length were PIT-tagged. Of the 99 PIT-tagged individuals, four died (4%) and two lost their tags (2%) within 2 months of tagging. In this period, controls had 5% mortality and 15% VIE mark loss. Incisions were completely healed within 3 months of tagging, and mean specific growth rate during this period did not significantly differ between treatment groups. Ammocoetes bearing a PIT tag did not exhibit significant reductions in swimming performance relative to controls.ConclusionsWe attribute the success of this tagging effort to changes in tag implantation technique, including use of a lateral incision and no sutures. The ability to individually mark wild larval lamprey will allow research on individual growth rates, environmental effects on growth and metamorphosis, timing and rates of movement, and, ultimately, stage-specific survival.

A Noninvasive Tool to Assess the Distribution of Pacific Lamprey (Entosphenus tridentatus) in the Columbia River Basin.

The Pacific lamprey (Entosphenus tridentatus) is an anadromous fish once abundant throughout coastal basins of western North America that has suffered dramatic declines in the last century due primarily to human activities. Here, we describe the development of an environmental DNA (eDNA) assay to detect Pacific lamprey in the Columbia River basin. The eDNA assay successfully amplified tissue derived DNA of Pacific lamprey collected from 12 locations throughout the Columbia River basin. The assay amplifies DNA from other Entosphenus species found outside of the Columbia River basin, but is species-specific within this basin. As a result, the assay presented here may be useful for detecting Entosphenus spp. in geographic range beyond the Columbia River Basin. The assay did not amplify tissue or synthetically derived DNA of 14 commonly sympatric non-target species, including lampreys of the genus Lampetra, which are morphologically similar to Pacific lamprey in the freshwater larval stage.

Using genetic pedigree reconstruction to estimate effective spawner abundance from redd surveys: an example involving Pacific lamprey (Entosphenus tridentatus)

Redd surveys are a commonly used technique for indexing the abundance of sexually mature fish in streams; however, substantial effort is often required to link redd counts to actual spawner abundance. In this study, we describe how genetic pedigree reconstruction can be used to estimate effective spawner abundance in a stream reach, using Pacific lamprey (Entosphenus tridentatus) as an example. Lamprey embryos were sampled from redds within a 2.5 km reach of the Luckiamute River, Oregon, USA. Embryos were found in only 20 of the 48 redds sampled (suggesting 58% false redds); however, multiple sets of parents were detected in 44% of the true redds. Estimates from pedigree reconstruction suggested that there were 0.48 (95% CI: 0.29–0.88) effective spawners per redd and revealed that individual lamprey contributed gametes to a minimum of between one and six redds, and in one case, spawned in patches that were separated by over 800 m. Our findings demonstrate the utility of pedigree reconstruction techniques for both inferring spawning-ground behaviors and providing useful information for refining lamprey redd survey methodologies.

Inter-Observer Bias in Fish Classification and Enumeration Using Dual-frequency Identification Sonar (DIDSON): A Pacific Lamprey Case Study

Abstract Dual-frequency Identification Sonar (DIDSON) is increasingly used as a fish monitoring and enumeration tool, but many studies do not evaluate potential observer biases. In this project, we assessed inter-observer differences in the identification and enumeration of adult Pacific lamprey (Entosphenus tridentatus) imaged with DIDSON passing a large dam fishway. Six trained viewers independently identified lamprey observation ‘events’ in the same ∼ 12 h of DIDSON data collected at several fishway locations using two sonar orientations. Among-viewer variability in lamprey enumeration was high and viewer agreement on individual lamprey was often low. A total of 274 unique potential Pacific lamprey events was identified, but individual viewers scored only 89–173 events each (mean = 131, CV = 24%) or 32–63% of the total. Viewer identification rates (events/h) varied several-fold at some sites which we attributed primarily to event non-detection rather than species misclassification. Identification diffe...

Application of neural networks to the prediction of a phenotypic trait of pacific lampreys based on single nucleotide polymorphism (SNP) genetic markers

Application of neural networks to the prediction of a phenotypic trait of pacific lampreys based on single nucleotide polymorphism (SNP) genetic markers

Screen Efficiency and Implications for Losses of Lamprey Macrophthalmia at California's Largest Water Diversions

AbstractWe investigated the guidance efficiency of fish screens for the protection of emigrating Pacific Lamprey Entosphenus tridentatus and Western River Lamprey (also known as River Lamprey) Lampetra ayresii in a series of experimental trials. All trials were conducted at the Tracy Fish Collection Facility, located in the Sacramento–San Joaquin River Estuary at the entrance to one of the world's largest surface water diversions. Using 1,200 lamprey macrophthalmia, we tested for the effect of screen type, time of day, and channel water velocity to guide their swimming behavior to avoid entrainment. We found overwhelming evidence for an effect of screen type on efficiency, whereby all lampreys were successfully guided to a holding tank when a vertical traveling screen was used. This was likely due to the small pore size of the screen relative to lamprey sizes. In contrast, the efficiency of louvers, a behavioral screen designed for salmonids, varied by the interaction of time of day and channel velocity. During nighttime, when lamprey typically emigrate, louver guidance efficiency ranged from 21% (95% CI, 14–30%) to 24% (95% CI, 16–34%). These results were applied to estimate the probability for salvage of lamprey macrophthalmia at the Tracy Fish Collection Facility, which includes a two‐stage fish screen design. Between 1957 and 2014, we estimated that 94–96% of the lampreys that were entrained in the export flows were lost and not returned to the delta. However, the probability for fish loss was reduced in 2014 when the secondary louver was replaced with a vertical traveling screen. Our results suggest that lamprey macrophthalmia entrainment into the canals will be eliminated at the Tracy Fish Collection Facility if the primary screen is converted to vertical traveling screen. Surface water diversions may represent a substantial threat to regional metapopulations of anadromous lamprey species worldwide, and screening approaches applied to other fish species such as salmonids may not be protective of lampreys.Received June 7, 2016; accepted August 23, 2016Published online December 20, 2016

Growth and annual survival estimates to examine the ecology of larval lamprey and the implications of ageing error in fitting models.

This study used existing western brook lamprey Lampetra richardsoni age information to fit three different growth models (i.e. von Bertalanffy, Gompertz and logistic) with and without error in age estimates. Among these growth models, there was greater support for the logistic and Gompertz models than the von Bertalanffy model, regardless of ageing error assumptions. The von Bertalanffy model, however, appeared to fit the data well enough to permit survival estimates; using length-based estimators, annual survival varied between 0·64 (95% credibility interval: 0·44-0·79) and 0·81 (0·79-0·83) depending on ageing and growth process error structure. These estimates are applicable to conservation and management of L. richardsoni and other western lampreys (e.g. Pacific lamprey Entosphenus tridentatus) and can potentially be used in the development of life-cycle models for these species. These results also suggest that estimators derived from von Bertalanffy growth models should be interpreted with caution if there is high uncertainty in age estimates.

Free-swimming speeds and behavior in adult Pacific Lamprey, Entosphenus tridentatus

Lampreys are extremely efficient anguilliform swimmers, well–designed for long–distance travel, although they are frequently characterized as poor swimmers when compared to salmonids. We examine free–swimming adult Pacific Lamprey, Entosphenus tridentatus, in a raceway environment to approximate swim speeds and behaviors that may occur in the natural environment. Lampreys (mean Body Length 59.2 ± 3.0 cm, range 50–66 cm BL) traveled upstream at a mean groundspeed of 0.34 ± 0.188 BL/s (n=126, range 0.01–0.79 BL/s). Swimming activity was strongly nocturnal. Observed speeds in the lower range may have been the result of swimming in midwater against faster currents, indirect paths or rest periods. Lampreys generally took advantage of lower near–bottom current velocities by swimming within 6 cm of the bottom, where currents were substantially lower. Equivalent swim speeds, without currents, would be 0.49 ± 0.190 BL/s (range 0.17–0.96 BL/s). These speeds are in the high range of daily travel rates encountered in tagging studies of both Pacific Lamprey and Atlantic Sea Lamprey, Petromyzon marinus, but compare well when migration is limited to hours of darkness or tracking was continuous. Such rates suggest that, travelling only at night, lampreys would cover 1,000 km upriver in under four months. It is crucial that managers and designers incorporate the swimming capability, near–bottom association, utilization of boundary flow conditions, and nocturnal behavior of lampreys into their activities if we are to effectively manage in-stream facilities and conserve these key anadromous species.

Network analyses reveal intra‐ and interspecific differences in behaviour when passing a complex migration obstacle

Summary Network theory offers new perspective on movement data by evaluating the relationships between animal movements (links) and detection locations (nodes) in spatially complex systems, including human‐altered landscapes. We applied network analyses to intra‐ and interspecific movement patterns in the migration behaviour and dam passage success of two anadromous fish species, Pacific lamprey Entosphenus tridentatus Gairdner and Chinook salmon Oncorhynchus tshawytscha Walbaum, when moving through a large multifishway hydroelectric project (Bonneville Dam, USA). Network analyses revealed greater variation in movement for Pacific lamprey compared with Chinook salmon. Salmon that passed the dam had networks consisting of more direct passage routes with fewer overall movements compared with lamprey that passed the dam. Lamprey that did not pass the dam exhibited a wide range of behaviours, from approaching only one fishway site to testing all possible passage routes. Accounting for the time spent in the network improved the ability to detect biological differences in network structure for lamprey that did and did not pass the dam. The movement patterns likely resulted from different behavioural responses to complex environmental and internal factors affecting a philopatric species (Chinook salmon) vs. a non‐philopatric species (Pacific lamprey) when moving through an engineered environment designed primarily for salmon. Synthesis and applications. Our case study highlights the potential for network analyses to link questions of basic movement ecology with monitoring of movement and behaviour in human‐altered landscapes. Network analyses can thus serve as a valuable tool for describing movement and behaviour in the face of environmental change and assessing the effectiveness of mitigation efforts at spatially complex obstacles to animal movement.

Do Native Pacific Lamprey and Invasive Sea Lamprey Share an Alarm Cue? Implications for Use of a Natural Repellent to Guide Imperiled Pacific Lamprey into Fishways

AbstractInstream barriers affect anadromous lampreys worldwide by preventing access to spawning habitat, resulting in the decline of several species. Because lampreys rely heavily on olfactory cues to choose movement paths during upstream migration in rivers, the manipulation of these cues may be used to guide individuals into the vicinity of fish passage devices and thereby mitigate the impacts of barriers during migration. However, because experimentation with imperiled species presents significant legal and ethical challenges, use of a surrogate species that exhibits similar responses may prove very useful. Our laboratory study established that (1) the odor derived from dead Pacific Lamprey Entosphenus tridentatus elicits an avoidance response from invasive Sea Lamprey Petromyzon marinus from the Laurentian Great Lakes, and (2) the magnitude of this response does not differ from the conspecific alarm cue present in Sea Lamprey. By presenting the odor on the side of a river channel opposite a lamprey fish passage device, migrating lampreys of conservation concern may be guided to fishways, if the behavioral response to the cue has evolved in these taxa. Due to their availability and well‐studied chemical communication system, Sea Lamprey may prove to be a useful surrogate for identifying and producing chemosensory cues for use in guiding Pacific Lampreys towards fish passage devices and away from intakes and screens.Received December 10, 2015; accepted May 6, 2016 Published online August 31, 2016

Effects of water velocity, turbulence and obstacle length on the swimming capabilities of adult Pacific lamprey

AbstractThe swimming capabilities of adult Pacific lamprey, Entosphenus tridentatus Gairdner, were tested in an experimental vertical‐slot fishway in response to three different fishway features: water velocity (1.2, 1.8 and 2.4 m s−1), the length of the vertical slot (0.33, 0.66, 1.00 m) and during the presence/absence of a turbulence‐intensifying structure that increased turbulence for each respective treatment. Passage success was lowest (52.7%) and attachment rates were highest (92.9%) during the most difficult passage conditions (high velocity, high turbulence, long slot length). Passage success was >83% for all other treatment combinations. Although passage of the vertical‐slot weir was not associated with fish body size, Pacific lamprey with larger dorsal distances (distance between the two dorsal fins) were more likely to pass the vertical‐slot weir. Increased attachment rates and longer attachment times during strenuous passage conditions suggest that endurance capacity may be an important factor limiting the passage of Pacific lamprey at fishway obstacles.

Sample Sizes Needed to Describe Length-Frequency of Small-Bodied Fishes: An Example Using Larval Pacific Lamprey

Abstract The ability to describe the length distribution of a fish population requires sampling an adequate number of individuals, but collecting more fish than needed is inefficient. While fisheries managers have assessed sample size requirements for many sport fishes, these requirements are not routinely described for small-bodied fishes (i.e., maximum length ≤200 mm), particularly larval lampreys. To improve the efficiency of data collection for these fishes, we used resampling analyses to asses sample size requirements for accurately describing length distributions of larval (freshwater-dwelling) Pacific lamprey Entosphenus tridentatus, an anadromous fish native to western North America (total length 60–156 mm). We found that the highest increases in accuracy occurred with sample sizes <50, and that we needed sample sizes of 40 to 130 to describe length frequency with 95% confidence, depending on length interval used for performing length-frequency analyses. From these results, we recommend collecting 100 individuals if using 5-mm length intervals to examine length frequency of larval lamprey. These findings can also be used to estimate the relative accuracy of sample sizes in existing assessments and develop and refine monitoring programs for larval lampreys and other small-bodied fishes.

Mercury concentrations in Pacific lamprey (Entosphenus tridentatus) and sediments in the Columbia River basin.

The accumulation of mercury was investigated in Pacific lamprey and stream sediments in the Columbia River basin. Mercury concentrations in larval lamprey differed significantly among sample locations (p < 0.001) and were correlated with concentrations in sediments (r2 = 0.83). Adult concentrations were highly variable (range, 0.1-9.5 μg/g) and unrelated to holding time after collection. The results suggest that Pacific lamprey in the Columbia River basin may be exposed to mercury levels that have adverse ecological effects. Environ Toxicol Chem 2016;35:2571-2576. © 2016 SETAC.

Pacific Lamprey in Coastal Drainages of California: Occupancy Patterns and Contraction of the Southern Range

AbstractPacific Lamprey Entosphenus tridentatus have been overlooked historically in fish surveys using standard salmonid methods along the Pacific coast of North America. As a result, little is known of even their broader distribution patterns at the drainage level. Over the last 2 decades, the species has shown a northward range contraction of over 900 km, and at this time the southernmost population is the Big Sur River in California. This study evaluates the hypothesis that Pacific Lampreys do not typically utilize relatively small coastal drainages (&lt;100 km2). We examined historical Pacific Lamprey records throughout California and surveyed 349 current sites in 102 coastal drainages along the California coastline and into Baja California. Within their currently occupied range (north of Big Sur), Pacific Lampreys were found in all drainages &gt;100 km2, but in only 3 of 29 drainages &lt;50 km2, and they were absent in all drainages &lt;25 km2. All historical records are from drainages &gt;50 km2, and primarily from larger drainages in southern California. Our results will support greater exploration of the ecological roles of lampreys in coastal streams, where they act as importers of marine nutrients, substrate engineers and filter feeders, as well as providing a rich prey base for many species. This paper also provides resource managers with an understanding of where Pacific Lampreys are likely to be found and where they were probably not a natural component of the fish fauna, allowing prioritization of conservation actions and more effective use of resources.Received December 3, 2015; accepted February 22, 2016 Published online June 15, 2016

Pacific lamprey (Entosphenus tridentatus) ammocoetes exposed to contaminated Portland Harbor sediments: Method development and effects on survival, growth, and behavior.

Many anthropogenic disturbances have contributed to the decline of Pacific lampreys (Entosphenus tridentatus), but potential negative effects of contaminants on lampreys are unclear. Lamprey ammocoetes are the only detritivorous fish in the lower Willamette River, Oregon, USA, and have been observed in Portland Harbor sediments. Their long benthic larval stage places them at risk from the effects of contaminated sediment. The authors developed experimental methods to assess the effects of contaminated sediment on the growth and behavior of field-collected ammocoetes reared in a laboratory. Specifically, they developed methods to assess individual growth and burrowing behavior. Burrowing performance demonstrated high variability among contaminated sediments; however, ammocoetes presented with noncontaminated reference sediment initiated burrowing more rapidly and completed it faster. Ammocoete reemergence from contaminated sediments suggests avoidance of some chemical compounds. The authors conducted long-term exposure experiments on individually held ammocoetes using sediment collected from their native Siletz River, which included the following: contaminated sediments collected from 9 sites within Portland Harbor, 2 uncontaminated reference sediments collected upstream, 1 uncontaminated sediment with characteristics similar to Portland Harbor sediments, and clean sand. They determined that a 24-h depuration period was sufficient to evaluate weight changes and observed no mortality or growth effects in fish exposed to any of the contaminated sediments. However, the effect on burrowing behavior appeared to be a sensitive endpoint, with potentially significant implications for predator avoidance. Environ Toxicol Chem 2016;35:2092-2102. © 2016 SETAC.

River Lamprey (Lampetra ayresii) Outmigrant Upstream of the John Day Dam in the Mid-Columbia River

The anadromous River Lamprey (Lampetra ayresii) is known to occur in North America from Alaska to central California, generally in association with larger estuarine systems (such as the Fraser River in British Columbia, the Sacramento River in California, and the Columbia River in Washington-Oregon; Vladykov and Follett 1958; Weitkamp and others 2015). Its occurrence in the Columbia River basin, however, has not been well documented. Although small numbers of juvenile (feeding phase) River Lamprey have been captured incidentally in the Columbia River Estuary (Bond and others 1983; Weitkamp and others 2012, 2015), there are few records of this species in freshwater (Kostow 2002). The farthest upriver report in the Columbia River basin is a March 1940 record at Bonneville (presumably at Bonneville Dam), 235 river kilometers (rkm) from the Pacific Ocean (Vladykov and Follett 1958). However, adult River Lamprey (117to 324-mm total length; Vladykov and Follett 1958; Bond and others 1983; Wydoski and Whitney 2003; Weitkamp and others 2015) are less noticeable than the larger Pacific Lamprey (Entosphenus tridentatus) (700to 800-mm total length; Clemens and others 2010) and might spawn in deep water in large river systems similar to other lamprey species (Dawson and others 2015). Thus, even when abundant, they are rarely observed in freshwater (Beamish 1980; Beamish and Youson 1987). Furthermore, during its prolonged freshwater larval stage, it is difficult or impossible to distinguish River Lamprey, either morphologically or genetically, from the closely related and widely distributed Western Brook Lamprey (Lampetra richardsoni) (Docker 2009). The nonmigratory, non-trophic adult Western Brook Lamprey (90to 180-mm total length) can be distinguished from adult River Lamprey by morphological and dentition characters (Wydoski and Whitney 2003; Docker 2009). There is a growing conservation concern for lampreys worldwide. Like other species, the River Lamprey is susceptible to various freshwater threats such as dredging and barriers to migration (Maitland and others 2015). The Columbia River Basin is currently fragmented by many mainstem hydropower, navigation, and flood-control dams, as well as numerous additional dams and irrigation diversions in tributary systems. Many of these dams do not provide fish passage and those that do are likely problematic for migratory adult lampreys (Moser and others 2015). Documentation of River Lamprey in the Columbia River basin would help inform management of this highly regulated system, as well as elucidate distribution patterns to aid conservation. A current effort is underway to increase the monitoring of outmigrating juvenile lampreys through the operation of salmonid smolt monitoring systems at mainstem Columbia River dams (Fish Passage Center 2014). Subsamples of juvenile (metamorphosed to outmigrating phase) and larval (unmetamorphosed) lampreys are collected, anesthetized, identified (to species for juvenile lampreys and to genus for larval lampreys), measured, and assessed for body condition. A putative juvenile (recently metamorphosed) River Lamprey was collected at the John Day Dam smolt bypass facility on 28 May 2013 from a sample time frame of 13:00 to 07:00. The fish was 144-mm total length and weighed 3.1 g. Its dentition pattern clearly distinguished it from the relatively more common Pacific Lamprey (Fig. 1). Pacific Lamprey have 3 large cusps on the supra-oral lamina, 4 pairs of lateral teeth, and 1 row of posterior teeth; whereas the River Lamprey has 2 cusps on the supra-oral lamina, 3 pairs of lateral teeth, and no posterior teeth (Wydoski and Whitney 2003). Its caudal pigmentation was likewise consistent with Lampetra spp. (Fig. 2, Fig. 3); lampreys in the Entosphenus genus possess a lighter caudal ridge, whereas the caudal ridge of Lampetra spp. is uniformly dark (Goodman and others GENERAL NOTES

The punctuated seaward migration of Pacific lamprey (Entosphenus tridentatus): environmental cues and implications for streamflow management

We investigated emigration timing of juvenile Pacific lamprey (Entosphenus tridentatus) over a 10-year period in the Sacramento River, California, USA. Emigration was punctuated with 90% of macrophthalmia in daily catches of at least 50 individuals. Macrophthalmia were observed primarily between November and May, with among-year variation in median emigration date over four times that of sympatric anadromous salmon. Our best model associating catch and environmental factors included days from rain event, temperature, and streamflow. We found strong evidence for an association of catch with days from rain events, a surrogate for streamflow, with 93% of emigrants caught during an event and the two subsequent days. Emigration was more likely during nighttime during subdaily sampling after accounting for the effects of factors significantly associated with daily catch. These results emphasize the importance of natural variation in streamflow regimes and provide insight for management practices that would benefit emigrating lampreys, such as synchronizing dam releases with winter and spring storms to reduce migration time, timing diversions to avoid entrainment during emigration windows, and ensuring streamflows are sufficient to reach the ocean, thereby avoiding mass stranding events.

Interpreting Lamprey Attacks on Pacific Cod in the Eastern Bering Sea

AbstractAdult anadromous lampreys attack several species targeted by large‐scale commercial fisheries in the North Pacific Ocean, and the potential negative impact to these host fishes is not well understood. The Arctic Lamprey Lethenteron camtschaticum and Pacific Lamprey Entosphenus tridentatus are anadromous species that feed in the eastern Bering Sea, and lamprey parasitism is evident on Pacific Cod Gadus macrocephalus near the Bering Slope. To examine this parasitic interaction, we first built models using morphological measurements from lamprey oral discs to predict which lamprey species caused the observed wounds on Pacific Cod. We then examined lamprey wounding rates and explored healing patterns related to the severity and location of lamprey wounds. We scanned 8,746 Pacific Cod for lamprey wounds and found that 4.9% of the cod had at least one wound. Lamprey wound morphology was better predicted by an oral disk model built for Pacific Lamprey than by a similar model built for Arctic Lamprey. The occurrence of lamprey wounds that had penetrated muscle tissue but had not completely healed was more prevalent as Pacific Cod length increased. Generalized additive model results indicated that latitude and mean Pacific Cod length were important in predicting lamprey wounding rates at a sampling station. Recently inflicted lamprey wounds that penetrated Pacific Cod muscle tissue were observed four times as often as superficial wounds that did not penetrate muscle tissue, but superficial wounds were twice as likely to reach a completely healed state. No difference was detected in the likelihood of a lamprey wound to reach a completely healed state among different host body regions. While there is a potential for lamprey attacks to negatively affect individual host fish, we emphasize the importance of understanding population dynamics between native lampreys and their hosts, as this could aid in explaining variations in the natural mortality of commercially important fish species in the eastern Bering Sea.

Feeding and Growth of Larval Pacific Lamprey Reared in Captivity

AbstractPacific Lampreys Entosphenus tridentatus are declining in the Columbia River basin as well as in much of their broader range. To mitigate for reductions in abundance, strategies such as hatchery propagation and captive rearing of lamprey larvae are currently being considered. We conducted a series of experiments using captive larval Pacific Lampreys at Eagle Creek National Fish Hatchery to investigate the effect of different food types and different food concentrations on the growth of larvae. In our first experiment, we evaluated the growth of larvae (TL range, 59–145 mm) given four different food types (algae, leaves, yeast–larval fish food, and salmon carcass analogs) and a control group that was not fed. Assimilation of food types was evaluated by tracking unique stable isotope signatures of δ13C and δ15N within larval tissues. Results from experiment 1 indicated that lampreys fed a diet of salmon carcass analog or algae had positive growth (up to 0.16 mm/d and 42% proportional change in length) over approximately 6 months. Isotopic analyses of larval tissues showed unique signatures that matched those of their specific food treatment. Based on the results of experiment 1, we conducted a second experiment to evaluate the growth of larvae fed four different quantities of salmon carcass analog. Results from this experiment indicated larval growth rate increased with increasing rations of food, but positive growth was observed in all feeding treatments. The highest dose of salmon carcass analog resulted in the highest growth (up to 0.15 mm/d and 36% proportional change in length) over 6 months. We successfully reared larval Pacific Lampreys in captivity with minimal mortality and positive growth, which highlights the potential to use captive rearing and propagation as a conservation tool for this ecologically and culturally important species.

Characterization of Adult Pacific Lamprey Swimming Behavior in Relation to Environmental Conditions within Large‐Dam Fishways

AbstractUnderstanding the migration behaviors of adult Pacific Lamprey Entosphenus tridentatus inside fishways is critical to resolving why the species has low passage rates at hydropower dams. We used an acoustic camera to make in situ observations on the swimming behaviors of Pacific Lampreys at two large Columbia River dams (Bonneville and John Day) and to develop inferences regarding potential mechanisms influencing passage within lower fishway sections (entrances, collection channels, transition areas). Pacific Lampreys were primarily free‐swimming in the middle and upper water column at both the high‐velocity entrance (&gt;1 m/s) and the low‐velocity transition area (&lt;1 m/s) of Bonneville Dam. In contrast, Pacific Lampreys in the high‐velocity fishway channel at John Day Dam were more likely to orient to the fishway floor at the entrance and in the collection channel. Pacific Lampreys exhibited no interaction with diffuser grating along the fishway floor at Bonneville Dam and were observed free‐swimming above these structures. Behavior in the Bonneville Dam transition area appeared to be affected by poor attraction flow and the presence of predatory White Sturgeon Acipenser transmontanus. Higher Pacific Lamprey tail‐beat frequencies and lower ground speeds were observed at the fishway entrances of both dams and in the John Day Dam collection channel, indicating that Pacific Lampreys were exerting greater effort to achieve upstream progress under the high water velocities at these locations. High tail‐beat frequencies and low ground speeds support the hypothesis that fishway entrances may act as short‐distance, high‐velocity barriers for Pacific Lampreys, while passage through the lower John Day Dam fishway may be limited by the endurance requirements for passing a long‐distance (~80 m), high‐velocity challenge (collection channel). Similar in situ applications offer the potential for understanding and improving the passage of migratory fish at anthropogenic barriers.