Native Lamprey Research Articles

Stream and river flows mediate adult lamprey spawning migrations: Considerations for management

AbstractOrganisms have adapted to dynamic river flows as part of the natural flow regime. However, climate change and humans' use of fresh water are associated with decreases in the quality and quantity of surface waters. In addition, river impoundments and water withdrawals for human use regulate and dampen the dynamism of flow in many rivers. These changes to the natural flow regime can impact the spawning migrations of lampreys (Petromyzontiformes). Here, our goal is to review the ecology of lamprey spawning migrations associated with river flows, with considerations for controlling invasive sea lamprey (Petromyzon marinus) and conserving native lampreys (including native, anadromous sea lamprey). We identify five common themes: (1) natural flow regimes provide a competitive edge to native fishes over non‐native fishes; (2) high flows (up to a threshold) attract adult lamprey and large streams attract large numbers of lamprey; (3) larval lamprey pheromones attract adult lampreys; (4) behavioral responses by adult lamprey to flow (including localized hydraulics) can inform dam passage and trapping methods; and (5) changes to rivers induced by climate change have been implicated in changing the phenology of run timing and spawning location. Controlling invasive sea lamprey and conserving native lampreys can be done with pheromones and flow management. Pheromones may be of more use under focused management efforts to control invasive sea lamprey, whereas flow management can provide a foundation for conservation of native lampreys.

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

Impact statementA symposium at the 2023 American Fisheries Society meeting highlighted collaborations among biologists, policymakers, and Native American tribes addressing conservation for native lampreys. We present key findings from the symposium and related research and an example of grassroots effort to protect and restore Pacific Lamprey.

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

AbstractObjectiveHuman‐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 and 11°C, bottom water temperatures averaged 12 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.

Incidence of lamprey marks on Lake Sturgeon ( Acipenser fulvescens Rafinesque, 1817) in the St. Clair – Detroit River System: Implications for Sea Lamprey ( Petromyzon marinus Linnaeus, 1758) effects

Laurentian Great Lakes Lake Sturgeon (Acipenser fulvescens) are hosts to lamprey species, including native Silver Lamprey (Ichthyomyzon unicuspis) and invasive Sea Lamprey (Petromyzon marinus). Silver Lamprey coevolved with Lake Sturgeon and cause negligible mortality, but Sea Lamprey can negatively affect Lake Sturgeon populations. Sea Lamprey abundance in Lake Erie has been above targets set by resource managers, with the St. Clair – Detroit River System (SCDRS) suspected as a source of Sea Lamprey production into Lake Erie. This study summarizes lamprey marking on Lake Sturgeon captured during agency assessment surveys in the SCDRS since 1996 and provides insight on the potential for Sea Lamprey to negatively affect Lake Sturgeon in the SCDRS. Lamprey marks (any lamprey species) were noted on 48.2% of Lake Sturgeon (2.5 marks/fish) and 3.3% of Lake Sturgeon assumed to be susceptible to mortality by Sea Lamprey (<760 mm TL; 0.06 marks/fish). Silver Lamprey were the only lamprey species found attached to Lake Sturgeon and there was no difference between oral disc diameters of Silver Lamprey and marks measured on Lake Sturgeon in Lake St. Clair and the lower St. Clair River (p = .45). Based on logistic regression, probability of at least one lamprey mark increased with Lake Sturgeon total length and was highest in Lake St. Clair. The probability of observing at least one lamprey mark on a 760 mm Lake Sturgeon was 8.1% or less for each sampling location in the SCDRS aside from Lake St. Clair (28.1%). Results suggest that parasitism of Lake Sturgeon by Sea Lamprey in the SCDRS is rare, particularly for Lake Sturgeon <760 mm TL. Low incidence of lamprey marks on Lake Sturgeon assumed to be susceptible to mortality from Sea Lamprey parasitism and zero occurrence of Sea Lamprey being observed attached to a Lake Sturgeon suggest Sea Lamprey at their current abundance likely have little effect on the Lake Sturgeon population in the SCDRS. Caution should be taken when using mark size to assign marks to lamprey species as there is substantial overlap among species oral disc diameters, potentially inflating the perceived impact of Sea Lamprey on Lake Sturgeon in areas with native lampreys.

Dispelling misperceptions of native lampreys (Entosphenus and Lampetra spp.) in the Pacific northwest (USA)

AbstractNative lampreys continue to be misunderstood by some citizens in the Pacific Northwest (PNW; USA). This misunderstanding is caused by persistent misperceptions reinforced in media and exacerbated by a long‐running (mid‐1900s to present) and pervasive outreach campaign on the control of the invasive sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes, Lake Champlain and the Finger Lakes of New York. The use of outreach to encourage conservation of native lampreys in the PNW has been comparatively recent. Along with other native non‐salmonid fishes, lampreys were perceived by Euro‐American settlers as “undesirable”, “coarse” or “trash” fish that parasitized desirable trouts and salmon (Oncorhynchus spp.) and competed with them for environmental resources. These concerns have been magnified by the seemingly physical and ecological similarities between native and invasive sea lampreys. To dispel the misperceptions of native lampreys, we recommend a multi‐prong approach that: sharpens the specificity of outreach materials on sea lamprey control; develops outreach media that distinguishes invasive and native lampreys, includes recognition of the multiple ecosystem benefits that native lampreys offer, and includes hands‐on, place‐based learning led by or in collaboration with local tribes that can provide cultural context, and employs a broad outreach campaign to facilitate conservation of native lampreys.

Changes in native lamprey populations in the Great Lakes since the onset of sea lamprey (Petromyzon marinus) control

The control of invasive sea lamprey in the Great Lakes basin has been highly successful, but has deleteriously affected native lamprey species. American brook, northern brook, silver and chestnut lampreys are all susceptible to lampricide treatments. Incidental catch from surveys that targeted sea lamprey were used to determine changes in distributions and catch rates of these native species within the Great Lakes basin since the onset of the sea lamprey control program. Over 2.4 million native lampreys were collected during sea lamprey control operations between 1947 and 2018. Native lampreys were no longer captured from many treated and untreated streams. Silver lamprey and northern brook lamprey distributions were reduced most substantially. These species were no longer found in about three quarters of the number of streams in which they were historically present. The number of streams inhabited by chestnut lamprey has diminished by half. American brook lamprey were still present in the majority of streams previously occupied. Catch rates declined in northern brook lamprey and Ichthyomyzon larvae in some Great Lakes basins, but changes in collection gear and methods made comparisons difficult. Trap and weir data show drastic declines in silver lamprey and chestnut lamprey. Streams that have not been treated with lampricide have suffered similar or greater declines in both the number of streams occupied and catch rates for all four species when compared to untreated streams. Therefore reductions in native lamprey populations were likely due to a number of environmental changes, and not exclusively from lampricide treatments.

River Network and Reach‐Scale Controls on Habitat for Lamprey Larvae in the Umpqua River Basin, Oregon

AbstractThis study developed a spatially explicit framework to support the conservation of Western Brook Lamprey Lampetra richardsoni and Pacific Lamprey Entosphenus tridentatus in the Umpqua River basin, Oregon. This framework identified locations within the river network likely to support “potential burrowing habitat” for lamprey larvae based on geomorphic conditions and evaluated the overlap of potential burrowing habitat with water temperatures suitable for the nonnative, piscivorous Smallmouth Bass Micropterus dolomieu. The study also documented reach‐scale factors that create heterogeneity in potential burrowing habitat to guide on‐the‐ground habitat restoration. Based on criteria for mean annual suspended sediment loads and channel slope, 18% of the Umpqua River network was classified as potential burrowing habitat. Existing mean August water temperatures of ≥20°C were suitable for Smallmouth Bass for 32% of the potential burrowing habitat. This percentage increased to 41% of the potential burrowing habitat using projected mean August water temperatures for year 2040, suggesting that water temperatures in the future will facilitate upstream expansion of Smallmouth Bass into the potential burrowing habitat. At finer spatial scales, potential burrowing habitat was influenced by channel features, such as large wood, pools, and local channel slope and width. These results provide an initial template for identifying locations in river networks likely to have potential burrowing habitat, considering the overlap between threats and lamprey habitats, and planning conservation actions to support native lampreys.

High predation of native sea lamprey during spawning migration

Sea lamprey (Petromyzon marinus) is a unique jawless vertebrate among the most primitive of all living vertebrates. This migratory fish is endangered in much of its native area due to dams, overfishing, pollution, and habitat loss. An introduced predator, the European catfish (Silurus glanis), is now widespread in Western and Southern European freshwaters, adding a new threat for sea lamprey migrating into freshwater to spawn. Here, we use a new prototype predation tag coupled with RFID telemetry on 49 individuals from one of the largest sea lamprey European populations (Southwestern France) to quantify the risk of predation for adult sea lampreys during its spawning migration in rivers with large populations of European catfish. We found that at least 80% of tagged sea lampreys (39 among 49) were preyed upon within one month, and that 50% of the released lampreys were rapidly consumed on average 8 days after tagging. This very high predation rate suggests that the European catfish represents a supplementary serious threat of extirpation for the native sea lamprey population we studied. This threat is likely to happen throughout most of the native lamprey distribution area, as the European catfish is becoming established almost everywhere the sea lamprey is.

Molecular and evolutionary perspectives of the renin-angiotensin system from lamprey

The recent advance and revision on the renin-angiotensin system in lamprey were summarized and we emphasized that presence of two types of angiotensins (Angs) in lamprey. Due to the parasitic nature on fish blood, teleost-type Angs were produced in their buccal gland and secreted into the lamphredin to evade the host immunorejection. A native lamprey angiotensinogen (AGT) was identified in genome and it retains serine-protease inhibitor activity for thrombin that regulates the blood coagulation pathway. The native lamprey angiotensin II (Lp-Ang II) is hypotensive instead of hypertensive, suggesting a functional divergence on cardiovascular regulation from the main vertebrate groups. The renin gene was absent from the lamprey genome so far, and the mutation on the renin-recognition site on lamprey AGT suggested that other proteases may have replaced the role of renin. Lp-Ang II was shown to bind to AT1 receptor and internalized, but the downstream signaling was still unknown. Molecular and phylogenetic evidence on invertebrate ACE-like proteins indicated that they were not homologous to those in vertebrates and could be acting on other native peptides. Although it was generally believed that the RAS was a well-conserved hormone system in vertebrates and invertebrates, revision by molecular data indicated that invertebrates lack homologous RAS components while lamprey possess an almost complete RAS. This suggests that the hormone cascade system was first evolved around cyclostome emergence and invertebrates could have taken up the RAS components from vertebrates through horizontal gene transfer.

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.

Neuropeptide Y family receptors Y1 and Y2 from sea lamprey, Petromyzon marinus

The vertebrate gene family for neuropeptide Y (NPY) receptors expanded by duplication of the chromosome carrying the ancestral Y1–Y2–Y5 gene triplet. After loss of some duplicates, the ancestral jawed vertebrate had seven receptor subtypes forming the Y1 (including Y1, Y4, Y6, Y8), Y2 (including Y2, Y7) and Y5 (only Y5) subfamilies. Lampreys are considered to have experienced the same chromosome duplications as gnathostomes and should also be expected to have multiple receptor genes. However, previously only a Y4-like and a Y5 receptor have been cloned and characterized. Here we report the cloning and characterization of two additional receptors from the sea lamprey Petromyzon marinus. Sequence phylogeny alone could not with certainty assign their identity, but based on synteny comparisons of P. marinus and the Arctic lamprey, Lethenteron camtschaticum, with jawed vertebrates, the two receptors most likely are Y1 and Y2. Both receptors were expressed in human HEK293 cells and inositol phosphate assays were performed to determine the response to the three native lamprey peptides NPY, PYY and PMY. The three peptides have similar potencies in the nanomolar range for Y1. No obvious response to the three peptides was detected for Y2. Synteny analysis supports identification of the previously cloned receptor as Y4. No additional NPY receptor genes could be identified in the presently available lamprey genome assemblies. Thus, four NPY-family receptors have been identified in lampreys, orthologs of the same subtypes as in humans (Y1, Y2, Y4 and Y5), whereas many other vertebrate lineages have retained additional ancestral subtypes.

A spatial age-structured model for describing sea lamprey (Petromyzon marinus) population dynamics

The control of invasive sea lampreys (Petromyzon marinus) presents large-scale management challenges in the Laurentian Great Lakes. No modeling approach has been developed that describes spatial dynamics of lamprey populations. We developed and validated a spatial and age-structured model and applied it to a sea lamprey population in a large river in the Great Lakes basin. We considered 75 discrete spatial areas, included a stock–recruitment function, spatial recruitment patterns, natural mortality, chemical treatment mortality, and larval metamorphosis. Recruitment was variable, and an upstream shift in recruitment location was observed over time. From 1993 to 2011, recruitment, larval abundance, and the abundance of metamorphosing individuals decreased by 80%, 84%, and 86%, respectively. The model successfully identified areas of high larval abundance and showed that areas of low larval density contribute significantly to the population. Estimated treatment mortality was less than expected but had a large population-level impact. The results and general approach of this work have applications for sea lamprey control throughout the Great Lakes and for the restoration and conservation of native lamprey species globally.

The presence of teleost-type angiotensin components in lamprey buccal gland suggests a role in endocrine mimicry

Previous characterization of a native lamprey angiotensin II (LpAng II) that possesses a different sequence and function than teleost-type angiotensin II (Ang II) has raised a question as to the role of teleost-type angiotensin peptides in lampreys. In this study, teleost-type angiotensin like-peptides were identified in the buccal gland of lampreys by immunoassays and immunohistochemistry. The possible sources of angiotensin like-peptides were investigated in lampreys by manipulating their choice of host and food. Ang II immunoreactivity (irAng II) was detected in the buccal gland and plasma of feeding phase sea lampreys exposed to Atlantic cod, but was mostly absent in fasting lamprey. Qualitatively, the HPLC profiles of irAng II observed in the plasma, when present, were highly similar to those in buccal gland, implying that the buccal gland could be a source of plasma Ang II. Japanese lampreys force-fed with dogfish blood had significantly elevated concentrations of irAng II in their buccal glands when compared to unfed individuals, suggesting that feeding stimuli may have enhanced buccal gland activity. Teleost-type Ang II-containing proteins, other than angiotensinogen, are present in the buccal gland as trypsinization generated Ang II in vitro, and the HPLC profile of these irAng II was highly comparable to those naturally present in the buccal gland. [Asn1, Val5, Thr9]-Ang I that was identified in the buccal gland of Japanese lampreys has the same amino acid sequence to those previously isolated from the incubation of plasma and kidney extract, providing an alternative explanation for the previous isolation of teleost-type Ang I in lampreys. irAng I and irAng II were localized in the granule-like structures in the apical region of the secretory epithelia, suggesting that these peptides may be active components of lamphredin. The teleost-type angiotensin peptides in the buccal gland secretion suggested that these host-specific peptides could be part of the endocrine mimicry strategy used by lampreys to evade host immune responses and reduce immune-rejection.

Characterization of a native angiotensin from an anciently diverged serine protease inhibitor in lamprey

Angiotensinogen belongs to family A serine protease inhibitors (SERPIN family) and we have cloned and characterized SERPIN genes in two lamprey species, which possess all the properties of angiotensinogen. The putative angiotensinogens in lampreys can be considered as an evolutionary link between SERPIN and other angiotensinogen according to the phylogenetic analyses. The inferred sea lamprey angiotensinogen gene was expressed abundantly in liver and to a lesser extent in other tissues. The predicted lamprey angiotensin I (Ang I) sequence was unique and different from the teleost-type Ang I identified previously by the incubation of lamprey plasma with its kidney extract. Therefore, we characterized and compared the biochemical and physiological properties of this native lamprey Ang II (LpAng II) (EEDYDERPYMQPF) with teleost-type Ang II (NRVYVHPF). Using a newly developed RIA for LpAng II, plasma levels in Japanese lamprey were measured (157.4 ± 35.2 fmol/ml, n=6), but teleost-type Ang II was undetectable. In conscious cannulated lamprey, LpAng II at 100 pmol/kg elicited a transient vasodepressor effect. At doses higher than 300 pmol/kg, a biphasic cardiovascular response with an initial vasodepressor effect followed by a transient rebound vasopressor effect was observed in a dose-dependent manner. However, teleost-type Ang II was not vasoactive up to 1 nmol/kg. In Japanese eel, LpAng II injection up to 3 nmol/kg did not alter the cardiovascular parameters. Our results suggested that the renin-angiotensin system first appeared in cyclostomes, and LpAng II could be important for the regulation of cardiovascular dynamics in lampreys because of its potent and acute vasoactive effect.

Predation on Native Lamprey Species by Nonnative Brown Trout in Hokkaido, Japan

In June 2006, we found Predation on native lamprey species by a large, nonnative brown trout (600 mm in fork length) in a small stream in Hokkaido, Japan. The trout ate 15 adult lampreys and one unidenti-fied fish. Brown trout may cause decline of endangered native lamprey species.

In Situ D-periodic Molecular Structure of Type II Collagen

Collagens are essential components of extracellular matrices in multicellular animals. Fibrillar type II collagen is the most prominent component of articular cartilage and other cartilage-like tissues such as notochord. Its in situ macromolecular and packing structures have not been fully characterized, but an understanding of these attributes may help reveal mechanisms of tissue assembly and degradation (as in osteo- and rheumatoid arthritis). In some tissues such as lamprey notochord, the collagen fibrillar organization is naturally crystalline and may be studied by x-ray diffraction. We used diffraction data from native and derivative notochord tissue samples to solve the axial, D-periodic structure of type II collagen via multiple isomorphous replacement. The electron density maps and heavy atom data revealed the conformation of the nonhelical telopeptides and the overall D-periodic structure of collagen type II in native tissues, data that were further supported by structure prediction and transmission electron microscopy. These results help to explain the observed differences in collagen type I and type II fibrillar architecture and indicate the collagen type II cross-link organization, which is crucial for fibrillogenesis. Transmission electron microscopy data show the close relationship between lamprey and mammalian collagen fibrils, even though the respective larger scale tissue architecture differs.

Capture and collection of lampreys: the state of the science

The need for native lamprey conservation, improved lamprey fishery management, and better assessment of non-indigenous lamprey control measures has resulted in increased effort to survey lamprey populations and assess their status. Depending on the study objectives and target species/life stage, collection methods vary dramatically. We therefore provide a comprehensive review of sampling considerations and techniques used to capture, collect, handle, and enumerate both juvenile and adult lamprey life stages. Surveys for lamprey are often constrained by the lack of basic biological information, such as reliable characters for field identification of larvae (ammocoetes), migratory timing of anadromous forms, and spawning/nest building behavior of adults. However, there are a number of studies that have documented habitat preferences of the relatively sedentary ammocoetes. Consequently, existing sampling protocols have focused on the development of stratified sampling that targets optimal ammocoete habitat. In addition to this approach, we discuss methods and gear that can be used to survey migratory life stages, lamprey nests, and difficult-to-sample, deepwater ammocoete habitats.

HPLC and ELISA analyses of larval bile acids from Pacific and western brook lampreys

Comparative studies were performed on two native lamprey species, Pacific lamprey ( Lampetra tridentata) and western brook lamprey ( Lampetra richardsoni) from the Pacific coast along with sea lamprey ( Petromyzon marinus) from the Great Lakes, to investigate their bile acid production and release. HPLC and ELISA analyses of the gall bladders and liver extract revealed that the major bile acid compound from Pacific and western brook larval lampreys was petromyzonol sulfate (PZS), previously identified as a migratory pheromone in larval sea lamprey. An ELISA for PZS has been developed in a working range of 20 pg–10 ng per well. The tissue concentrations of PZS in gall bladder were 127.40, 145.86, and 276.96 μg/g body mass in sea lamprey, Pacific lamprey, and western brook lamprey, respectively. Releasing rates for PZS in the three species were measured using ELISA to find that western brook and sea lamprey released PZS 20 times higher than Pacific lamprey did. Further studies are required to determine whether PZS is a chemical cue in Pacific and western brook lampreys.

Sea Lamprey Control in Lake Champlain

In 1990, the United States Fish and Wildlife Service (USFWS) and state agencies initiated an 8-year experimental sea lamprey ( Petromyzon marinus) control program on Lake Champlain to reduce parasitic phase sea lamprey and increase sport fish survival and growth. Twenty-four 3-trifluoromethyl-4-nitrophenol (TFM) treatments were conducted on 13 tributary systems, and nine Bayluscide treatments were conducted on five deltas. Most tributaries received two rounds of treatment, 4 years apart. Trap catches of spawning-phase sea lamprey in three monitored tributaries declined by 80–90% from 1989 to 1997, but nest counts were reduced by only 57% during the same period. Sixteen of 24 TFM treatments reduced ammocoetes to less than 10% of pre-treatment levels. Eight of nine Bayluscide treatments resulted in mean ammocoete mortality rates over 85% in caged test animals. Nontarget effects were noted among amphibians, mollusks, macroinvertebrates, native lamprey, and other fishes, and were higher for Bayluscide treatments than TFM. Recovery of delta taxa occurred within 4 years after treatment. Wounding rates on lake trout and Atlantic salmon were reduced in the Main Lake basin. Catches-per-unit-effort (CPUE) and estimated angler catch of lake trout increased. A moderate (25%), statistically significant increase in survival of 3–4 yr lake trout was noted. Returns of Atlantic salmon (Salmo salar) to tributaries increased significantly after treatment, and there was an estimated 3-fold increase in returns to the Main Lake sport fishery. Angler catches of brown ( Salmo trutta) and rainbow trout ( Oncorhynchus mykiss) were higher in 1997 than in 1990. Economic analysis of the program indicated a 3.5:1 economic benefit: cost ratio. Results indicate that the experimental control program was successful, and provide justification for continuing sea lamprey control on Lake Champlain.

Possible Applications of Pheromones in an Integrated Sea Lamprey Management Program

A group of research scientists and fishery managers met during the Sea Lamprey International Symposium II to discuss how recent progress understanding sea lamprey ( Petromyzon marinus) pheromone systems might contribute to an integrated management program. Summarized here are those discussions about how pheromone cues might be used and what steps should be taken to develop them as new tools in Great Lakes sea lamprey management. It is now evident that larval sea lampreys release a migratory pheromone that guides maturing adults into streams, and that mature sea lampreys use sex pheromones to affect locomotion and distribution of conspecific individuals on spawning grounds. Synthetic and purified pheromones have potential to enhance trap efficiencies, divert spawning migrations to streams with favorable management characteristics, and disrupt spawning behavior. Populations of native lamprey species might be established in strategic locations to provide migratory pheromone attraction. Pheromone production in spawning-phase males could be enhanced to bait traps and lure females, or to provide sterilized males with a competitive advantage in mating. Assays for analysis of the migratory pheromone could estimate the size of spawning runs and detect larval populations in streams. Pheromone strategies that integrate and enhance existing management techniques are likely to be the most beneficial. For example, the low density of adult sea lampreys in the St. Marys River makes it a good candidate for use of pheromones to enhance the current strategy of sterile-male release and trapping. Variation in recruitment and changes in growth and mortality could affect success of pheromone strategies that reduce reproduction. Continued support for basic research into developing and understanding pheromones and the new technologies associated with them is recommended.