Pacific Lamprey Research Articles

Predicting larval metamorphosis of Pacific lamprey Entosphenus tridentatus through measurements of length and mass.

The utility of length and mass measurements to predict the larval metamorphosis of Pacific lamprey Entosphenus tridentatus was evaluated. During 2004-2008, larval E. tridentatus were collected from Cedar Creek (Washington, USA) in either the spring or autumn, measured for total length and total mass, reared in captivity and monitored for metamorphosis. The minimum total length, total mass and condition factor of larvae that were observed to go through metamorphosis were 102 mm, 2.0 g and 1.52, respectively. Logistic models indicated that total length and condition factor in both spring and autumn were the most significant variables for predicting metamorphosis of Pacific lamprey during the subsequent summer. Mass in the autumn also appeared important to predict whether metamorphosis occurred in the subsequent summer. Collectively, all models using specific minimums of total length, total mass or condition factor of larvae as criteria for them to metamorphose were sometimes (5 of 14 cases) able to predict the percentage of larvae that would metamorphose but rarely (1 of 12 cases) able to predict which individual larvae would metamorphose. Similar to other anadromous species of lampreys, the size and condition of larval E. tridentatus have utility for predicting metamorphic fate.

Pacific Lamprey drag force modeling to optimize fishway design

Typically, fish passage design is informed by a critical velocity model whereby fish are assumed to fail passage if the water velocity is higher than the critical swim speed, an assumption that may not be met when locomoting fish are partially submerged. We applied a drag force model (DFM) approach for use in design of Pacific Lamprey (Entosphenus tridentatus) Passage Structures (LPS) where lamprey may be partially or fully submerged. Our investigation assessed the dead-drag forces at four levels of static submergence: fully submerged (120 mm), equally submerged (40 mm), partially submerged (15 mm), and skin-flow (5 mm) for a Pacific Lamprey physical model by varying simulated LPS slope and discharge conditions. We then used the results to establish drag force thresholds corresponding to the known critical velocity thresholds of Pacific Lamprey to predict passage success under partial and full submergence conditions. Consideration of drag force in fish passage could be used to improve or create species-specific design recommendations for fishways, or to inform the design of barriers to prevent invasive species passage. The results suggest consideration of drag force in addition to velocity is beneficial to predict Pacific Lamprey passage success under partial submergence conditions.

Factors affecting the fate of Pacific lamprey carcasses and resource transport to riparian and stream macrohabitats

Abstract Anadromous fish transport marine‐derived nutrients to freshwaters during spawning migrations with potential implications for stream food webs. While many studies have explored the role of marine‐derived nutrients instream ecosystems (particularly via Pacific salmonids [Oncorhynchus spp.]), relatively few have examined the spatial distribution and patchiness of non‐salmonid fish carcasses or rates of transport to the riparian zone. We radio‐tagged and released 144 mature Pacific lamprey (Entosphenus tridentatus) prior to spawning and tracked the fate of post‐spawn carcasses in two inland Columbia River basin streams to characterise spatial distribution of carcasses and marine‐derived nutrient deposition. We found that 27 and 40% of lamprey that could be assigned a fate were moved into the riparian zone adjacent to stream segments exhibiting higher velocity conditions with larger substrates. Conversely, lamprey with instream fates were associated with depositional microhabitats and woody debris dams. Estimated carcass loading rates varied by more than an order of magnitude among habitats. These patterns probably reflect a combination of processes influencing the likelihood of carcass removal (e.g. by predators or scavengers, or stranding) and factors affecting the distribution of carcasses remaining within the stream. Our results demonstrate substantial transport of lamprey carcasses across the stream‐riparian ecotone and a non‐random distribution of carcasses within streams, patterns which probably influence how resources enter stream and riparian food webs. More broadly, the results suggest local and landscape‐scale hydrogeomorphic factors, along with species‐specific traits and phenology, affect the distribution and potential roles of fish carrion in stream food webs.

Natural Recolonization by Pacific Lampreys in a Southern California Coastal Drainage: Implications for Their Biology and Conservation

AbstractThe historical range of anadromous Pacific Lamprey Entosphenus tridentatus includes coastal drainages from Alaska south to northern Baja California. However, there has been a widespread loss of distribution inland due to the construction of dams that form impassable barriers as well as a loss of Pacific Lampreys from some historically occupied drainages in the south. These losses have prompted the consideration of suitable approaches to reestablishing Pacific Lamprey populations through either active intervention or natural processes. While Pacific Lampreys apparently do not home to natal streams, they are thought to use cues that are related to such factors as flow patterns or the presence of ammocoete (larval lamprey) pheromones in offshore river plumes to identify suitable rivers for spawning and rearing. In this report, we present documentation of natural recolonization of the San Luis Obispo drainage by Pacific Lampreys on the central California coast, located 130 km south of the nearest freshwater population of Pacific Lampreys and with no existing ammocoete population. We also review recent observations of adult Pacific Lampreys in other southern rivers, recolonization of the Carmel River following dam removal, and indications that Pacific Lampreys are still using oceanic habitat off southern California. The results of our investigation demonstrate that Pacific Lampreys are fully capable of returning to an isolated drainage from which they have been extirpated and then rapidly reestablishing a viable population of ammocoetes, contradicting the hypothesis that they are dependent on existing ammocoete pheromones or adult sex pheromones to attract adults. These results indicate the importance of proactive management for Pacific Lampreys in drainages within their historical range, even if they are not currently present. The results also demonstrate that recolonization does not necessarily require active reintroduction efforts. Rather, conservation efforts should focus on identifying factors that may have led to the loss of Pacific Lamprey and removing potential impediments in order to facilitate natural recolonization.

Rapid Migration and High Survival of Adult Pacific Lampreys in Reservoirs

AbstractDams and reservoirs present diverse hazards for riverine fishes, including slowed migration, reduced or blocked access to essential habitats, and direct and delayed mortality risks. Many of these hazards are evident for Pacific Lamprey Entosphenus tridentatus in the heavily dammed Columbia River basin, where the species’ distribution and abundance has sharply declined. In a 3‐year study, we used acoustic telemetry to investigate behavior and apparent survival of 784 adult Pacific Lampreys in Columbia River reservoirs and turbulent dam tailraces, two environments where previous monitoring efforts have been somewhat ineffectual. We released Pacific Lampreys upstream and downstream from Bonneville Dam to test whether Pacific Lamprey passage at one dam negatively affected upstream dam and reservoir passage metrics (i.e., delayed effects on migration rate or reach passage success) and whether upstream‐released groups migrated further than their downstream‐released counterparts. Overall, results showed that Pacific Lampreys migrated very rapidly (median rates = 50–62 km/d) in reservoir reaches and slowly (1–3 km/d) in reaches with tailraces or fishways. Pacific Lampreys also had much higher passage success in reservoir reaches (reach × year estimates = 0.93–0.99) than in reaches with tailraces or fishways (most estimates = 0.58–0.82). We found little statistical evidence for negative delayed effects of dam passage. Pacific Lampreys released in the Bonneville forebay were far more likely to pass upstream dams (~26–57%) than were those released in the Bonneville tailrace (~20–36%). We conclude that tailraces and fishways constrained the upstream distribution of adult Pacific Lampreys, that reservoirs were not associated with high mortality during active upstream migration, and that translocation past individual dams can increase the upstream migration distance of individuals and population distribution. Areas of continuing uncertainty include behavior and survival during overwintering (i.e., prespawn holding) and the potential delayed effects of tailrace and fishway passage on Pacific Lamprey fitness.

An experimental study to evaluate predation threats on two native larval lampreys in the Columbia River Basin, USA

AbstractExperimental predation studies were conducted to evaluate and compare the predation threats of 10 species of native and non‐native fishes on larvae of Pacific Lamprey, Entosphenus tridentatus, and Western Brook Lamprey, Lampetra richardsoni. The relative predatory threats were examined over four sets of binary factors, including the following: (a) short (2‐day) or long (7‐day) duration, (b) presence/absence of fine sediment, (c) live or dead larvae and (d) species of lampreys. Our short‐term results showed a positive correlation with the sizes of predator fishes and consumed lamprey larvae. Also, most predator fishes had a significantly higher propensity to prey on lamprey larvae when sediment was absent. Conversely, this demonstrated the importance of sediment in protecting lamprey larvae from predation. Based on the predatory behaviour for live and dead larvae, predator fishes were classified into four groups using principal component analysis. Predation rates of larvae in sediment by piscivorous predators including Northern Pikeminnow Ptychocheilus oregonensis and Smallmouth Bass Micropterus dolomieu were lower and showed no differences even when the study duration was extended. In contrast, predation rates by benthic predators including White Sturgeon Acipenser transmontanus and Common Carp Cyprinus carpio, increased when we extended the study duration. This suggests that when given longer duration, benthic predators are more adept at consuming larvae within the sediment. These results provide important context for assessing the potential threat of predation on lampreys in streams, which is a key knowledge gap for lampreys.

Landlocked Pacific Lamprey Entosphenus tridentatus in the Middle Fork Willamette River, Oregon

Pacific Lamprey Entosphenus tridentatus is an anadromous fish native to the west coast of North America and the Pacific coast of Asia. In the 1950s, construction of dams on the Middle Fork Willamette River blocked upstream migration of adult Pacific Lamprey which resulted in their extirpation from otherwise suitable habitats. We report evidence of landlocked Pacific Lamprey surviving for >40 years after the construction of two high-head flood control dams (Dexter and Lookout Point) in the Middle Fork Willamette River 355.0 and 360.3 km upstream of the Pacific Ocean, respectively. In 2001, six putative Pacific Lamprey (two juveniles and four larvae) were captured using an electro shocker during a stream survey, 21.7 km upstream of Lookout Point Dam (the uppermost of these dams) and were entered into the Smithsonian National Museum of Natural History’s Division of Fishes collection. We re-examined these specimens, and their morphometric measurements and dentition are consistent with Pacific Lamprey. Additional evidence supports the existence of a landlocked population of Pacific Lamprey that resided upstream of these two impassable dams for approximately five generations. To our knowledge, this is the first report of Pacific Lamprey surviving for multiple generations upstream of impassable impoundments. However, no Pacific Lamprey have been detected in recent targeted surveys, indicating that this population has since been extirpated or exists in very low numbers.

Climate change vulnerability assessment for Pacific Lamprey in rivers of the Western United States

Pacific Lamprey (Entosphenus tridentatus) are a native anadromous species that, like salmon, historically returned to spawn in large numbers in watersheds along the west coast of the United States (U.S.). Lamprey play a vital role in river ecosystems and are one of the oldest vertebrates that have persisted over time likely influencing the evolution of many aquatic species. Pacific Lamprey have declined in abundance and are restricted in distribution throughout Washington, Oregon, Idaho and California. A key uncertainty influencing Pacific Lamprey status is the impact of climate change. We modified the NatureServe Climate Change Vulnerability Index (CCVI) to accommodate climate predictions from the International Panel on Climate Change. Using downscaled information, we characterized changes in 15 rivers occupied by Pacific Lamprey in the western U.S. We evaluated this risk under Representative Concentration Pathways (RCP) 4.5 and 8.5 for two time periods (mid-century 2040–2069 and end-century 2070–2099). The CCVI scores generally increased when going from RCP 4.5 to RCP 8.5 in three Global Climate Models for both mid-century and end-century, which our analyses forecasts degraded stream temperature and hydrologic conditions under increasing greenhouse gas emissions. The geographically assessed results suggest that climate change impacts to Pacific Lamprey vulnerability are magnified in highly altered rivers. If we continue to observe greenhouse gas emission levels associated with the RCP 8.5, Pacific Lamprey will be at greater risk to climate change impacts. In order to mitigate the risk from climate change toward the end of the century, additional actions will need to be prioritized to rapidly reduce the impact of these threats such as increasing flow, creating backwater habitat, restoring riparian vegetation and reducing stream disturbances. The findings revealed the patterns of vulnerability for Pacific Lamprey across their U.S. range are informative for prioritizing river restoration actions when paired with regional implementation plans.

Aннотированный список рыбообразных и рыб водоемов и водотоков бассейна верхнего Иртыша Восточного Казахстана с комментариями по их таксономии и зоогеографии

Приводится список рыбообразных и рыб, обитающих в водоемах и водотоках бассейна Верхнего Иртыша. Список содержит 43 вида, относящихся к 7 отрядам, 10 семействам и 30 родам. Включены все зарегистрированные на настоящий момент виды, валидность которых была пересмотрена в соответствующих систематических ревизиях. Три вида таймень Hucho taimen Pallas, 1773, нельма Stenodus leucichtys nelma Pallas, 1773, сибирский осетр Acipenser baerii Brandt, 1869 внесены в Красную Книгу Республики Казахстан. В бассейне Верхнего Иртыша к редким ценным видам, нуждающимся в сохранении генофонда из-за возможности его утраты, кроме уже внесенных в Красную Книгу Республики Казахстан можно отнести еще ряд видов: минога тихоокеанская Lethenteron camtschaticum Tilesius, 1811, стерлядь Acipenser ruthenus Linnaeus, 1758 маркакольский ленок Brachymystax savinovi Mitrofanov 1959.

Evaluation of effluent waste water from salmonid culture as a potential food and water supply for culturing larval Pacific lamprey Entosphenus tridentatus

The Pacific lamprey is an iconic native fish of great importance to the ecosystem and indigenous cultures in the U.S. Pacific Northwest. Pacific lamprey populations have declined in abundance from historic levels, and conservation aquaculture has been proposed as a technique to restore these populations. The present research focused on expanding the culture methods for larval lamprey. The larvae filter feed and cohabitate with juvenile salmonids in the wild, therefore the effluent water from rearing salmonids may be a viable source of water and food for culturing lamprey. This approach could be a sustainable method for raising lamprey at existing salmonid hatcheries. A nine week trial investigated the effects of rearing in effluent water from salmonid culture on the growth, survival, proximate composition, and fatty acid profile of larval lamprey. This trial also explored the potential of this rearing strategy to improve the water quality by removing nutrients from the effluent. The trial included three treatments testing the use of the effluent from steelhead trout (Oncorhynchus mykiss), a conventional lamprey diet (control diet), or both combined as a means for rearing lamprey. A fourth treatment where lamprey were excluded served as a water quality control to test the effect of lamprey presence on effluent quality. Lamprey survival was not affected by treatment. Lamprey reared solely on the effluent waste matched the survival and growth of fish fed the conventional diet. Lamprey fed the combination treatment grew faster than the conventional diet fed fish. Whole body lipid levels were elevated in lamprey from the combination treatment relative to the conventional diet fed lamprey. Crude protein in the whole bodies of effluent fed lamprey was low compared to fish from either of the treatments where the conventional diet was fed. Lamprey offered the effluent nutrients were high in saturated fats relative to the control fed fish, which reflected the lipid profile of this diet. However, lamprey from the combination treatment were lower in long chain polyunsaturated fatty acids relative to the control or the effluent treatment lamprey. There was no measureable improvement in water quality due to the presence of lamprey, though lamprey were able to sequester approximately 1.3% of the effluent dry matter as lamprey biomass. Overall, it appears the larval stage of lamprey can be effectively reared on salmonid effluent, and this method provides superior growth when used in combination with a conventional lamprey diet.

How Small Can We Go? Evaluating Survival, Tag Retention, and Growth of Juvenile Chinook Salmon Implanted with a New Acoustic Microtag

AbstractRecently, an acoustic microtag, called the Eel–Lamprey Acoustic Tag (ELAT), was developed for use in juvenile American Eel Anguilla rostrata and Pacific Lamprey Entosphenus tridentatus. The ELAT (12.0 × 2.0 mm; 0.088 g in air) has the potential to be used to study other small‐bodied fishes. In this pilot study, juvenile Chinook Salmon Oncorhynchus tshawytscha 52–99 mm fork length (FL) were surgically implanted with an ELAT (n = 99) or remained untagged (control; n = 101). Fish were held for 30 d to evaluate survival, tag retention, and growth. Survival did not differ significantly between control (n = 98 or 97.0%) and tagged fish (n = 95 or 95.9%). Logistic regression analysis suggested that survival was influenced by initial FL and tag burden. Mortalities only occurred in tagged fish with initial FLs of ≤65 mm (FL range = 57–65 mm; tag burdens = 3.8–5.9%). However, a tagged fish with an initial FL of 62 mm or an initial tag burden of 4.1% (FL range = 58–64 mm) was predicted to have a 90% chance of survival, and the smallest fish that survived the study was 54 mm FL (1.8 g; tag burden = 4.9%). Tag retention was high (99%), with only one fish expelling an ELAT during the study. Control fish grew slightly larger than the tagged individuals, but differences in final pooled FLs and weight gains were not significant. Our results demonstrate the successful surgical implantation of the ELAT into Chinook Salmon as small as 54 mm FL (1.8 g).

TRAUMATIZATION BY LAMPREYS OF SOCKEYE SALMON ONCORHYNCHUS NERKA (WALBAUM, 1792) IN THE MEYNYPIL’GYN LAKE-RIVER SYSTEM (KORYAK COAST OF CHUKOTKA)

Data on traumatization of sockeye salmon Oncorhynchus nerka spawners in the Meynypil’gyn lake-river system by lampreys are presented on results of observations in 1998– 2018. Features and localization of injuries are described comparing the injuries of males and females and biological parameters of fish with and without the injuries. In the Meynypil’gyn lake-river system, relative to other areas of Russian Far East, the portion of fish with injuries from lampreys is medium for sockeye salmon, and low for pink salmon Oncorhynchus gorbuscha and charr Salvеlinus malma. Judging by size of the wounds, the injuries were caused mostly by arctic lamprey Entosphenus tridentatus. Generally, about 68 % of sockeye spawners were attacked by lampreys during their pre-spawning migrations just before entering the fresh waters, but the percentage (P) depends on length (L) of fish: P = 1.2026 . L + 1.2192 (R2 = 0.879). So, the portion of injured fish increased from 2.7 % for the sockeye producers with length < 500 mm to 31.2 % for those with length 671–680 mm. Mean size and weight of the male and female sockeye spawners with traces of lampreys were statistically significantly higher than these parameters for the fish without injuries. The males injured by lampreys were larger than the males without injures in 18 mm and 295 g, the females — in 5 mm and 80 g, on average. Sockeye females had weaker and less numerous damages, so their portion among the fish with 1 injury was 45.4 %, among the fish with 2 injuries — 42.9 %, among the fish with 3 or more injures — 37.0 %. Besides, mean size of the injured sockeye increased with a number of injures and for the groups with 1, 2, and 3 or more injures it was for females: 604, 608, and 613 mm, for males: 655, 667, and 674 mm, respectively. Such dependencies of alive fish traumatization on their size are caused by higher mortality of small fish after lampreys attacks. There is concluded that arctic lamprey affects significantly on sexual and size composition of sockeye spawners in the Meynypil’gyn lake-river system providing selection of fish with larger size and weight, in particular males.

A Stepwise Approach to Assess the Occupancy State of Larval Lampreys in Streams

Abstract Pacific Lamprey Entosphenus tridentatus is an ecologically and culturally important anadromous species of conservation concern for which fisheries managers use information on occupancy state in streams to assess species status and inform stream management decisions. Here we developed a stepwise approach that incorporates the potential for nondetection and a preselected expected maximum probability of stream occupancy if field crews do not document larval Pacific Lamprey during sampling. Our approach includes seven steps: define the occupancy question; select the maximum acceptable probability of occupancy, if the species is not documented during sampling; define an assumed detection probability for the target organism; calculate required sampling effort; select sampling units; conduct sampling; and interpret sampling results into probabilistic occupancy conclusions. We examined detection probability of our approach for larval lamprey using data from multiple occupied streams in the Pacific Northwest. We illustrated our approach by evaluating Balm Grove Dam as a barrier to Pacific Lamprey migration in Gales Creek, Oregon. Bayesian estimates of detection probability in occupied streams ranged from 0.15 to 0.94, with an overall median of 0.70 (95% credible interval: 0.60–0.79). Assuming detection probability is at least 0.15 (i.e., lowest estimate), 19 reaches are required for the expected maximum probability of occupancy to be not more than 0.05, if the species is not documented through our sampling approach. Although detected downstream, we detected no larvae upstream of Balm Grove Dam; thus, we conclude that the maximum probability of occupancy upstream of Balm Grove Dam was not more than 0.05 at an assumed detection probability of 0.4, suggesting the dam as a barrier to adult migration. We provide an occupancy assessment tool with standardized sampling requirements that incorporates the potential for nondetection and the flexibility to select an expected maximum probability of occupancy if researchers document no larvae, to aid management and restoration in a single stream.

Marine biology of the pacific lamprey Entosphenus tridentatus

Pacific lamprey Entosphenus tridentatus has an anadromous life cycle that begins with larvae that filter-feed in freshwater, followed by transformation into juveniles that migrate to the ocean where they parasitize hosts, and adults that migrate into freshwater to spawn and die. The marine-phase (i.e., juvenile life stage) is important yet poorly understood, and is associated with growth opportunities to achieve maximum body size and recruitment. The four goals of this paper are to: (1) synthesize the literature to identify patterns in the marine biology of Pacific lamprey; (2) develop hypotheses to explain these patterns; (3) identify limiting factors and threats, and (4) identify research needs. We hypothesize that recruitment of adult lamprey to spawning populations is influenced by oceanographic regimes through impacts on host abundance. Three marine factors that may be limiting lamprey abundance include: (1) predation and fisheries bycatch; (2) host availability; and (3) host contaminant loads. Four potential marine-related threats to lamprey include: (1) pollution; (2) climate change; (3) unfavorable oceanographic regimes; and (4) the effects of interactions between climate and regimes. Pacific lamprey is not philopatric and the extent to which host migrations and other factors influence lamprey entry into rivers is unclear. Research is needed to fill information gaps on how, when, why, and where lamprey move, feed, and grow in the ocean. Their widespread distribution, parasitic life history, diverse hosts, and multiple predators suggest that Pacific lamprey is integrated into diverse marine ecosystems.

Occurrence of pathogens in Pacific lamprey (Entosphenus tridentatus)

Pacific lamprey (Entosphenus tridentatus) is a First Food of Native Americans. Declines in lamprey abundance due to dam construction and habitat loss have curtailed traditional harvest opportunities. Artificial propagation is an emerging recovery tool for this imperiled species, and other lamprey species in Finland and Japan. To manage disease risk at prospective lamprey hatcheries, it is critical to understand the pathogens and parasites most likely to affect lamprey and other fish, both in culture and in the wild. We assembled data from regional fish health laboratories to assess pathogen prevalence in Pacific lamprey sampled from various sources (518 adults, 275 larvae, and one juvenile). In adults, Aeromonas salmonicida was identified using standard health screening methods in 0–69% of dead lamprey samples submitted, but no other pathogens were typically observed. All larvae were negative for bacterial and viral infections, and larvae experimentally exposed to A. salmonicida showed no infection or mortality. Conspicuously absent were detailed health assessments for metamorphosed larvae (juveniles). However, external examinations of over 20,000 juveniles captured at dams on the lower Columbia River indicated that they are susceptible to fungal infection in warm water conditions (> 12 °C), which can lead to mortality. To fully evaluate the disease risk associated with lamprey culture, directed research is needed along with standardized health screenings of lamprey at all life stages. Control of A. salmonicida, the etiological agent for furunculosis, will be a top priority for Pacific lamprey use, as this was the only pathogen regularly identified in this species.

Evaluation of environmental DNA surveys for identifying occupancy and spatial distribution of Pacific Lamprey (Entosphenus tridentatus) and Lampetra spp. in a Washington coast watershed

AbstractSurveys of environmental DNA (eDNA) have become an important and multifaceted tool for monitoring and identifying distributions and occupancy of aquatic species. This tool is attractive because it is powerful, easy to apply, and provides an alternative to traditional field survey methods. However, validating eDNA survey methods against traditional field survey methods is warranted prior to their application. We used eDNA and electrofishing to survey 10 sites in 3 tributaries of the Chehalis River, Washington, to infer distribution and occupancy of Entosphenus tridentatus and Lampetra spp. Both methods produced similar detection rates for E. tridentatus, and Lampetra spp. were detected at slightly greater frequency with eDNA in the Black River and Skookumchuck River. Within each of the three tributaries, eDNA concentration was negatively related to sample distance from the Chehalis River mainstem for E. tridentatus but not for Lampetra spp., which indicates E. tridentatus and Lampetra spp. may be distributed differently within tributaries. Application of lamprey eDNA data to a multiscale occupancy model indicated high probability of detecting eDNA in water samples and quantitative PCR (qPCR) assays. Broad distribution and high detection of E. tridentatus and Lampetra spp. suggest robust populations inhabit the Chehalis River basin. Our findings suggest eDNA surveys may be comparable to electrofishing for informing lamprey occupancy and distributions. Such sampling is efficient and cost‐effective and we anticipate that eDNA surveys will become a valuable tool in addressing key research and monitoring needs for conservation and restoration of lampreys in general.

Evidence for the genetic basis and epistatic interactions underlying ocean- and river-maturing ecotypes of Pacific Lamprey (Entosphenus tridentatus) returning to the Klamath River, California.

Surveys of genomic variation have improved our understanding of the relationship between fitness-related phenotypes and their underlying genetic basis. In some cases, single large-effect genes have been found to underlie important traits; however, complex traits are expected to be under polygenic control and elucidation of multiple gene interactions may be required to fully understand the genetic basis of the trait. In this study, we investigated the genetic basis of the ocean- and river-maturing ecotypes in anadromous Pacific lamprey (Entosphenus tridentatus). In Pacific lamprey, the ocean-maturing ecotype is distinguished by advanced maturity of females (e.g., large egg mass) at the onset of freshwater migration relative to immature females of the river-maturing ecotype. We examined a total of 219 adult Pacific lamprey that were collected at-entry to the Klamath River over a 12-month period. Each individual was genotyped at 308 SNPs representing known neutral and adaptive loci and measured at morphological traits, including egg mass as an indicator of ocean- and river-maturing ecotype for females. The two ecotypes did not exhibit genetic structure at 148 neutral loci, indicating that ecotypic diversity exists within a single population. In contrast, we identified the genetic basis of maturation ecotypes in Pacific lamprey as polygenic, involving two unlinked gene regions that have a complex epistatic relationship. Importantly, these gene regions appear to show stronger effects when considered in gene interaction models than if just considered additive, illustrating the importance of considering epistatic effects and gene networks when researching the genetic basis of complex traits in Pacific lamprey and other species.

Erratum to: Transoceanic Migration of Pacific Lamprey, Entosphenus tridentatus

Erratum to: Transoceanic Migration of Pacific Lamprey, Entosphenus tridentatus

Pathogens of Pacific Lamprey Detected Through Routine Fish Health Screenings

Abstract Interest in conservation, management, and captive rearing of Pacific Lamprey Entosphenus tridentatus in the Pacific Northwest has risen in recent years. General and specific information regarding the occurrence of fish pathogens and the risk of Pacific Lamprey as a vector for pathogens to other species is not well understood. Specific efforts to captively rear or artificially propagate Pacific Lamprey at facilities that are used for Pacific salmon Oncorhynchus spp. have increased. We performed fish health surveys on wild-caught larval and adult Pacific Lamprey from locations that were used as lamprey sources for captive research to determine the occurrence of bacteria, viruses, and parasites that may be pathogens. A variety of potential pathogens was detected, most notably Aeromonas hydrophila and Vibrio vulnificus from larval Pacific Lamprey and A. salmonicida from adult lampreys. There was a general lack of pathogenic activity and absence of viral detections from all lampreys. The diversity of bacteria encountered from the larvae in our study could be indicative of the wide diversity of bacteria that is known to be associated with larval lamprey in general. Further efforts to understand pathogenic risk from Pacific Lamprey to salmonid propagation programs are warranted.

Providing refuges for adult Pacific lamprey Entosphenus tridentatus inside fishways

Fishways at hydroelectric dams are unnatural environments that typically present fish with channels of uniform depth, variable water velocity, and lack of cover. Fish retention and overall passage success may be improved by providing rest and sheltering areas inside fishways. We examined adult Pacific lamprey Entosphenus tridentatus use of two specially designed fishway refuges at Bonneville Dam on the Columbia River (northwestern USA). These relatively small boxes (1.1 m × 0.4 m × 0.2 m) provided low-velocity, dark refuge from predation for Pacific lamprey, a largely nocturnal species. Refuge boxes were equipped with antennas to detect entry of lamprey tagged with passive integrated transponder (PIT) tags. We PIT tagged and released 3,247 lamprey, including 599 that were double-tagged with a PIT and a radio transmitter, over three study years (2012–2014). In each year, PIT-tagged lamprey detected at nearby fishway exits had used a refuge: 12% in 2012, 28% in 2013, and 36% in 2014. Median residence time of PIT-tagged lamprey in the refuges for each year was 20.3 h, 16.6 h, and 13.1 h. Lamprey entrance into refuges peaked at 0300–0500 PDT, and they typically exited at around 2000 PDT, suggesting that refuges primarily functioned as shelter from daylight. Probability of refuge use increased with a morphological indicator of sexual maturity (distance between dorsal fins). In the radio-tagged group, refuge users were equally likely to pass Bonneville Dam as non-users. However, refuge users were less likely than non-users to be detected at sites upstream from the dam, perhaps owing to their maturation status or longer mean passage time through our study area (2.0 vs. 0.6 d for non-users). Refuges show promise for improving fish retention in fishways, particularly for nocturnal and/or small-bodied species that seek shelter from light or predation.