Sea Lamprey Abundance Research Articles

Lake Superior fish community and fisheries, 2001–2022: An era of stability

Lake Superior is the least anthropogenically impacted of the Laurentian Great Lakes ecosystems, yet dramatic changes to the fish community are evident. Previous published works chronicled those changes and the efforts to rehabilitate the fish community through the year 2000. Here, we review through the year 2022, where post-rehabilitation stability was driven by lean lake trout (Salvelinus namaycush namaycush) as the most abundant piscivore in nearshore waters, siscowet lake trout (Salvelinus namaycush siscowet) as the most abundant piscivore in offshore waters, and a healthy, intact assemblage of native prey species, which created ecological redundancies and helped stabilize the food web. Stocking of non-native salmonines was reduced 74%, and populations of Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) were maintained through natural reproduction. Despite reduced stocking, yield from recreational fisheries was stable. Likewise, developments in population modeling led to evaluations and refinement of management strategies that helped create stability for lake trout, lake whitefish (Coregonus clupeaformis), and cisco (Coregonus artedi) fisheries. With lake trout rehabilitation achieved, focus shifted toward rehabilitation of native brook trout (Salvelinus fontinalis), lake sturgeon (Acipenser fulvescens), and walleye (Sander vitreus). Despite continued control efforts, sea lamprey (Petromyzon marinus) abundance increased considerably, and estimates of fish killed by lampreys averaged 2.65 million kg annually. Environmental changes have benefited sea lampreys and fostered thermal habitats more suitable to non-native organisms, posing new challenges for managers and researchers. Nevertheless, the post-rehabilitation stability in the contemporary fish community will help provide resilience to future perturbations in the ecosystem.

Estimation of lake-scale stock-recruitment models for Great Lakes sea lampreys

Understanding recruitment dynamics is an essential part of effective fisheries management, whether the focus is on conservation, harvest policy development, or invasive species control. We developed a model that estimates lake-wide Ricker stock-recruitment relations for invasive sea lampreys (Petromyzon marinus) in each of the five Laurentian Great Lakes to inform future control efforts. We fit adult-to-adult models, taking advantage of a long time series of lake-wide, adult, sea lamprey abundance estimates. We incorporated proportional contributions at age for the stock as well as additional explanatory variables sea lamprey weight, as a surrogate for fecundity, and lampricide quantity applied, as a surrogate for anthropogenic mortality, to explain residual recruitment variability. The best model incorporated equal cohort contributions from the adult stock (that matured 5, 6, and 7 years prior to recruitment), a single productivity parameter (α) common to all five lakes, lake-specific carrying capacity parameters (βj), and coefficients for sea lamprey weight and lampricide quantity applied. The precision of the estimated Ricker parameters compared favorably to those estimated by adult-to-larva models, a promising development in the pursuit of sea lamprey recruitment prediction. The model should be useful to fisheries managers in the Great Lakes wishing to consider various recruitment overfishing strategies in the control of invasive sea lampreys, reaffirming that even models built on a single life stage can inform our understanding of ecological interactions and explorative management scenarios.

Setting and tracking suppression targets for sea lampreys in the Great Lakes

In response to invasive species, the course of action taken by management agencies often evolves over a range of options from a do-nothing approach to suppression to complete eradication. As a case study of suppression targets, we explore the history of approaches used by the Great Lakes Fishery Commission in response to the invasion of the Laurentian Great Lakes by sea lampreys (Petromyzon marinus). With the early realization that eradication was not possible using available techniques, focus shifted to suppression of sea lampreys to support fish community objectives for the lakes. As a surrogate for damage to the fishery, a suppression target was defined for the maximum acceptable marking rate, indicated by the average number of sea lamprey wounds observed on every 100 large lake trout (Salvelinus namaycush) surveyed. Historic marking rates were used to delineate time periods of acceptable sea lamprey predation levels as an approximate measure of sea lamprey-induced mortality. A second target, independent of lake trout population status, was based on the average sea lamprey abundance estimated during the specified time periods. These intuitive targets have served as suppression benchmarks for the Sea Lamprey Control Program in the Great Lakes, allowing decision makers to gauge progress towards targets, refine control strategies and prioritize geographic areas for increased control effort. Here we document the development and subsequent changes to targets, summarize the methods used to implement these changes, and provide considerations for the future.

Targeted lampricide treatment strategies for sea lamprey suppression in the Great Lakes: 2008–2018

The invasive sea lamprey, Petromyzon marinus, continues to be a persistent threat to the Great Lakes fishery. Beginning in 2008, the Great Lakes Fishery Commission’s resources for controlling sea lamprey were increased and directed toward maintaining sea lamprey populations at or below target levels utilizing experimental lampricide treatment strategies. The Commission’s Sea Lamprey Control Program executed five targeted treatment strategies in the Great Lakes from 2008 to 2018. These strategies focused on killing large numbers of sea lamprey larvae prior to metamorphosis. Strategies included consecutive lampricide stream treatments (streams treated twice within three years), comprehensive treatment of specific geographic regions, and increased treatment effort toward the most productive sea lamprey streams. Determining the effect of individual strategies proved challenging and results were mixed; yet, the additional treatment effort expended in the upper Great Lakes appears to have contributed to overall declines in the index of adult sea lamprey abundance. The complete effect this additional treatment effort has on sea lamprey populations may be revealed through future assessments.

A seasonal electric barrier blocks invasive adult sea lamprey (Petromyzon marinus) and reduces production of larvae

Sea lamprey (Petromyzon marinus) control is achieved in the Laurentian Great Lakes by applying lamprey-specific pesticides (lampricides) to habitats containing larval sea lamprey. Lampricide treatments cost less and are more effective in watersheds where dams block adult sea lamprey migration and limit larval distribution relative to watersheds with no barriers to migration. However, dams impound water and can block movement of valued fishes, outcomes that are untenable for some stakeholders. Here, a seasonal and non-physical barrier of pulsed direct electrical current was tested to block adult sea lamprey while also monitoring the movement and mortality of non-target fish species. The electric barrier was operated in the Black Mallard River, a tributary to northern Lake Huron, March through August 2016–2018. The electric field blocked adult sea lamprey; 1056 adult sea lamprey were captured downstream of the electric field and two were captured upstream of the electric barrier over the three-year study. In 2018, larval sea lamprey abundance upstream of the barrier was about 50% less than historical averages, and genetic analysis found that roughly 98% of larvae upstream of the barrier were spawned in years prior to barrier installation. When the barrier was electrified, non-target fish species were blocked, and a small percentage (<3%) were killed. This study demonstrated that a seasonally deployed electric barrier can reduce the abundanceoflarval sea lamprey upstream without impounding water, but effects on the movements and survival of other fish species remain a concern.

A case history of sea lamprey (Petromyzon marinus) abundance and control in Lake Huron: 2000–2019

Beginning with the first lampricide treatments of Lake Huron streams in 1960, applying lampricides and maintaining barriers to migration in Lake Huron tributaries continue to be the primary methods of controlling sea lampreys (Petromyzon marinus). In years leading up to the new millennium, sea lamprey abundance in Lake Huron remained at high levels, yet well below the pre-control adult abundance estimate of 700,000 adults. Two decades later, a variety of sea lamprey control strategies have been developed and employed to further reduce sea lamprey abundance in Lake Huron. In recent years, record low numbers have been achieved and continue to be at or near target levels for sea lamprey abundance. The St. Marys River continues to be one of the largest producers of sea lampreys to Lake Huron and additional actions have been taken to address this challenge. Controlling larval abundance in the St. Marys River along with increasing lampricide treatments throughout the basin and focusing on the largest sea lamprey producing streams have contributed to the decline in sea lamprey abundance. Lake trout (Salvelinus namaycush) restoration efforts along with increased sea lamprey control has facilitated natural reproduction and increase in wild stocks across the basin. The fish community objective for sea lampreys in Lake Huron has not been entirely met and efforts to achieve this objective are ongoing.

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.

Understanding sea lamprey abundances in the Great Lakes prior to broad implementation of sea lamprey control

Control of invasive sea lamprey in the Great Lakes with a selective pesticide (lampricide) that targeted larval sea lamprey began in the late 1950's and continues to be one of the main methods for control. Although the Great Lakes Fishery Commission, which was formed with the mandate of controlling sea lamprey, often expresses the success of the sea lamprey control program in terms of percent reduction from lake-wide pre-lampricide control adult sea lamprey abundances, there remains a large amount of uncertainty surrounding these estimates. In this study, we gathered historical data on adult sea lamprey captures from trapping efforts from the mid-1950's through the late 1970's to better understand pre-control abundance. We used this information to estimate lake-wide population abundances of adult sea lamprey using a weighted linear regression that includes environmental and lampricide treatment predictor variables. We varied trapping efficiency for early trapping data to evaluate the uncertainty in abundance estimates. Pre-control adult sea lamprey abundances in all lakes were much greater than current population sizes, but estimates were quite sensitive to trapping efficiency. In Lake Superior, declines in abundance aligned with increases in control efforts, but in other lakes, declines were occurring prior to the onset of lampricide application, perhaps because of a loss of prey. We suggest that previous estimates of pre-control adult sea lamprey abundance may have been underestimated unless trapping efficiency was greater than what is currently achieved in the basin.

Quantifying Great Lakes sea lamprey populations using an index of adults

Effective control of aquatic invasive species requires knowledge of the population throughout the infested area. Lake-wide assessments of invasive sea lampreys (Petromyzon marinus) are used to assess their status in the Laurentian Great Lakes, informing fisheries managers and decision makers in the sea lamprey control program. Initially these assessments focused on an estimate of absolute abundance, but later switched to an estimate of relative abundance as an index. In this paper, we describe the recently developed index of sea lamprey abundance and the reasons for its use. Rather than trying to estimate spawning run sizes of all Great Lakes tributaries, the index instead estimates run sizes of a small subset of index streams. Streams chosen for the index had large spawning runs and a history of trapping operations that consistently yielded mark-recapture estimates. This change enabled the sea lamprey control program to abandon a previously used regression model that predicted run size on streams with no sea lamprey traps. Further research is needed to determine how strongly correlated the index is with actual patterns in the lake-wide population of adult sea lampreys.

What can commercial fishery data in the Great Lakes reveal about juvenile sea lamprey (Petromyzon marinus) ecology and management?

The Laurentian Great Lakes of North America support a large and profitable freshwater fishery, but one continuously beset by parasitism from the invasive sea lamprey (Petromyzon marinus). Despite being the life stage that inflicts damage to the fishery, therefore necessitating a bi-national control program, our knowledge of juvenile sea lamprey ecology is poor and their response to control efforts are not assessed. Incidental capture of juvenile sea lamprey by commercial fishers is one means to collect data on this enigmatic life stage, and in Lake Huron such data have been collated since 1967. Here, we explore incidental captures of juvenile sea lamprey and their hosts from northern Lake Huron between 1987 and 2017 (n = 33,246 observations) to address four objectives. Firstly, we document collection efforts by fishers to provide historical context to the dataset. Secondly, we pose and test a series of questions related to fishery encounter, host selection, growth, distribution, and sex ratio to highlight how these types of data can be informative regarding juvenile sea lamprey ecology. Results presented here could be used to develop biological hypotheses to be addressed in future work. Thirdly, we directly assessed whether juvenile sea lamprey capture data could be useful in corroborating trends observed in adult sea lamprey abundance and wounding, as well as in identifying abundance and wounding hotspots. Lastly, we summarize research and outreach efforts that have benefited from the capture of juvenile sea lamprey in recent years.

Investigating apparent misalignment of predator-prey dynamics: Great Lakes lake trout and sea lampreys

Interpreting ecological dynamics is challenging when observed patterns are not aligned with presumed models. Investigating possible sources of uncertainty is critical to understand the underlying system and ultimately inform management decisions. In this study, we used simulation to investigate the hypothesis that observed inconsistencies in Great Lakes lake trout (Salvelinus namaycush) and sea lamprey (Petromyzon marinus) predator-prey dynamics were caused by measurement error in the abundance and predation metrics. When lake trout abundances increase and sea lamprey abundances decrease, predation rates are expected to decline (and vice versa). Occasionally predation rates do not change as expected, leading to an inconsistency in expected predator-prey dynamics. We used a Type II functional response model to align lake trout relative abundance, adult sea lamprey abundance, and sea lamprey marking rates of lake trout in each Great Lake. Then we added measurement error to each of the simulated metrics to see how it contributed to observed inconsistencies in the marking rates. The simulated inconsistency rate was far less than the observed inconsistency rate in Lakes Superior and Erie, indicating that measurement error was not primarily responsible for the misalignment of metrics, contrary to our hypothesis. Rather than ignoring these inconsistencies as unfortunate consequences of imperfect assessments, we recommend that future inconsistencies be scrutinized for possible mechanistic explanations. We suspect that predator-prey dynamics are being influenced by spatially structured within-lake components and the presence of alternative hosts, neither of which were accounted for in the functional response model we used.

Using simulation to understand annual sea lamprey marking rates on lake trout

Sea lampreys attack fish, killing some and leaving marks on others. Great Lakes fishery managers rely on observed marking rates to assess the success of the sea lamprey control program and estimate sea lamprey-induced mortality of lake trout. Because marking rates are only observed on survivors of sea lamprey attacks, they may not provide a reliable index of actual attack or mortality rates. To investigate the effect of survivor bias, we developed a simulation model representing a single season (June–December) of sea lamprey attacks. Simulated attack rates varied with month and lake trout size; simulated pierce and lethality rates varied with month alone. Surveyed marking rates were represented by simulated survivors in October; true rates were calculated from all simulated lake trout (dead and alive) in December. Simulation results were subsetted to include only those within the range of marking rates actually observed in the Great Lakes. Type A (piercing) marking rates were a good index of the sea lamprey attack rate and the sea lamprey-induced mortality rate if annual lethality rates were relatively constant. Type B (non-piercing) marking rates were a good index of the sea lamprey attack rate and the sea lamprey-induced mortality rate if annual pierce rates were relatively constant. Due to the uncertainty surrounding the pierce and lethality rates, we recommend that sea lamprey abundance information be incorporated in existing lake trout statistical catch-at-age models via a functional response component relating sea lamprey feeding to lake trout abundance, if possible.

Where you trap matters: Implications for integrated sea lamprey management

Barriers and pesticides have been used in streams to control sea lamprey in the Laurentian Great Lakes for nearly 70 years. Considerable effort has been spent to develop additional control measures, but much less effort has gone toward identifying how or where additional control measures might be cost-effectively integrated into the sea lamprey control program. We use a management strategy evaluation model in Lake Michigan to identify the stream types that would be most suitable for deploying traps to remove adults prior to spawning and estimate the likely impact on adult sea lamprey abundance in subsequent years under several trapping scenarios relative to status quo abundance. The greatest reduction in lake-wide adult sea lamprey abundance predicted by the model resulted when removing adult sea lampreys from streams that are difficult for control program personnel to treat with lampricide because lampricide applications would be required less frequently. Additionally, targeting streams which experience regular sea lamprey recruitment and streams with low adult sea lamprey density should result in reduced lake-wide abundance if trapping costs are relatively low or removal is high. Our results provide direction on where to trap and why, and indicate that trapping may be a valuable part of an integrated sea lamprey control approach advancing the goals of the Great Lakes Fishery Commission.

Implications of the sea lamprey control program for lake sturgeon conservation and rehabilitation efforts

Lake sturgeon, a species of conservation concern, can be affected by sea lamprey control activities in the Great Lakes basin. Specifically, age-0 lake sturgeon are sensitive to the pesticides used to kill larval stage sea lampreys; and, as tributary spawners, barriers that restrict access to habitat for adult sea lampreys can also restrict access to spawning lake sturgeon habitat. Conversely, lake sturgeon are also potentially prey for juvenile sea lampreys, so they benefit from control measures that reduce sea lamprey abundance. Over the past 20 years research has defined conditions under which treatments to control sea lampreys, such as high tributary alkalinity levels, are of highest risk for age-0 lake sturgeon mortality. Adult lake sturgeon are likely to survive a sea lamprey attack, and adult wounding rates vary through time and space across the Great Lakes basin and in Lake Champlain. Juvenile lake sturgeon are at higher risk of mortality from a sea lamprey attack, yet rarely display wounds. There are mitigation measures, including treating tributaries later in the year, capturing and holding age-0 lake sturgeon prior to treatment in high-risk tributaries, maximizing the time between treatments, and providing passage for spawning lake sturgeon above sea lamprey barriers that can minimize risks to lake sturgeon populations. As such, we believe that there remains room for both a robust sea lamprey control program moving forward in concert with lake sturgeon rehabilitation across the Great Lakes basin.

Analysis of sea lamprey environmental DNA during lampricide treatment in a tributary of Lake Ontario

Sea lamprey (Petromyzon marinus) is a species of invasive parasitic fish in the Great Lakes region of North America. Accurate estimates of larval lamprey populations in lake tributaries are necessary for making control decisions regarding treatment of lake tributaries with 3-trifluoromethyl-4-nitrophenol (TFM), a piscicide toxic to lamprey larvae. Analysis of environmental DNA (eDNA) isolated from water samples is a recent innovation under consideration for sea lamprey biomonitoring. eDNA analysis was performed before and at three time points after TFM treatment in a tributary of Lake Ontario (Ninemile Creek) to assess presence of invasive sea lamprey. Lamprey DNA was detected in four out of four sample locations before TFM treatment and three of four locations 72 hours following treatment. No lamprey DNA was detected in any of the locations 4 months or 12 months after TFM treatment of the creek. These results are consistent with known effectiveness of TFM treatment and provide evidence for the potential of eDNA analysis as a tool for monitoring decline of larval sea lamprey abundance due to TFM treatments.

Evaluation of a Sterile‐Male Release Technique: A Case Study of Invasive Sea Lamprey Control in a Tributary of the Laurentian Great Lakes

AbstractInvasive species can have detrimental impacts on native species and ecosystem services for humans. A technique that involves sterilization and release of males into wild populations of the same species can be useful in the control of invasive or pest species. A sterile‐male release technique (SMRT) was used on a novel vertebrate system, the invasive Sea Lamprey Petromyzon marinus in the Great Lakes, in an attempt to control population size. Sea Lamprey populations in the Great Lakes have been suppressed since the 1950s by (1) pesticide applications to kill larvae in streams and (2) barriers to block upstream spawning migrations. Here, we present a literature review and meta‐analysis of the SMRT by using a case study from the St. Marys River, where the SMRT was applied as an experimental method of Sea Lamprey control from 1991 to 2011. Observations obtained from the St. Marys River during and after SMRT application were used to evaluate whether the SMRT was effective at suppressing reproduction. Males were successfully sterilized and exhibited normal mating behaviors. The survival of embryos in nests was lower during the years when the SMRT was applied (32%) than during the post‐SMRT period (67%). The overall distribution of embryo viability in the river shifted after the SMRT was applied. During the SMRT application period, the observed ratios of sterile males to normal (fertile) males on nests were significantly different than expected, possibly due to an underestimation of adult Sea Lamprey abundance in the St. Marys River. Even at lower sterile male : normal male ratios, the number of viable embryos produced would have declined, but the level of reproductive suppression required to overcome recruitment variability was unclear. We discuss the effectiveness of the SMRT as it pertains to the Sea Lamprey, and we highlight difficulties in data interpretation and provide future direction for similar control programs.Received December 1, 2015; accepted June 16, 2016 Published online August 31, 2016

Telemetry narrows the search for sea lamprey spawning locations in the St. Clair-Detroit River System

Abstract Adult sea lamprey (Petromyzon marinus) abundance in Lake Erie has remained above targets set by fishery managers since 2005, possibly due to increased recruitment in the St. Clair-Detroit River System (SCDRS). Sea lamprey recruitment in the SCDRS poses an enormous challenge to sea lamprey control and assessment in Lake Erie because the SCDRS contains no dams to facilitate capture and discharge is at least an order of magnitude larger in the SCDRS than most other sea lamprey-producing tributaries in the Great Lakes. As a first step toward understanding population size, spatial distribution, and spawning habitat of adult sea lampreys in the SCDRS, we used acoustic telemetry to determine where sea lampreys ceased migration (due to spawning, death, or both) among major regions of the SCDRS. All tagged sea lampreys released in the lower Detroit River (N = 27) moved upstream through the Detroit River and entered Lake St. Clair. After entering Lake St. Clair, sea lampreys entered the St. Clair River (N = 22), Thames River (N = 1), or were not detected again (N = 4). Many sea lampreys (10 of 27) were last observed moving downstream (“fallback”) but we were unable to determine if those movements occurred before or after spawning, or while sea lampreys were dead or alive. Regardless of whether estimates of locations where sea lampreys ceased migration were based on the most upstream region occupied or final region occupied, most sea lampreys ceased migration in the St. Clair River or Lake St. Clair. Results suggest that spawning and rearing in the St. Clair River could be an important determinant of sea lamprey recruitment in the SCDRS and may direct future assessment and control activities in that system.

MANAGEMENT STRATEGY EVALUATION OF PHEROMONE‐BAITED TRAPPING TECHNIQUES TO IMPROVE MANAGEMENT OF INVASIVE SEA LAMPREY

AbstractWe applied a management strategy evaluation (MSE) model to examine the potential cost‐effectiveness of using pheromone‐baited trapping along with conventional lampricide treatment to manage invasive sea lamprey. Four pheromone‐baited trapping strategies were modeled: (1) stream activation wherein pheromone was applied to existing traps to achieve 10−12 mol/L in‐stream concentration, (2) stream activation plus two additional traps downstream with pheromone applied at 2.5 mg/hr (reverse‐intercept approach), (3) trap activation wherein pheromone was applied at 10 mg/hr to existing traps, and (4) trap activation and reverse‐intercept approach. Each new strategy was applied, with remaining funds applied to conventional lampricide control. Simulating deployment of these hybrid strategies on fourteen Lake Michigan streams resulted in increases of 17 and 11% (strategies 1 and 2) and decreases of 4 and 7% (strategies 3 and 4) of the lakewide mean abundance of adult sea lamprey relative to status quo. MSE revealed performance targets for trap efficacy to guide additional research because results indicate that combining lampricides and high efficacy trapping technologies can reduce sea lamprey abundance on average without increasing control costs.

Re-examination of sea lamprey control policies for the St. Marys River: completion of an adaptive management cycle

The St. Marys River (SMR) historically has been a major producer of sea lampreys (Petromyzon marinus) in the Laurentian Great Lakes. In the early 2000s, a decision analysis (DA) project was conducted to evaluate sea lamprey control policies for the SMR; this project suggested that an integrated policy of trapping, sterile male releases, and Bayluscide treatment was the most cost-effective policy. Further, it concluded that formal assessment of larval sea lamprey abundance and distribution in the SMR would be valuable for future evaluation of control strategies. We updated this earlier analysis, adding information from annual larval assessments conducted since 1999 and evaluating additional control policies. Bayluscide treatments continued to be critical for sea lamprey control, but high recruitment compensation minimized the effectiveness of trapping and sterile male release under current feasible ranges. Because Bayluscide control is costly, development of strategies to enhance trapping success remains a priority. This study illustrates benefits of an adaptive management cycle, wherein models inform decisions, are updated based on learning achieved from those decisions, and ultimately inform future decisions.

Factors Influencing Capture of Invasive Sea Lamprey in Traps Baited With a Synthesized Sex Pheromone Component.

The sea lamprey, Petromyzon marinus, is emerging as a model organism for understanding how pheromones can be used for manipulating vertebrate behavior in an integrated pest management program. In a previous study, a synthetic sex pheromone component 7α,12α, 24-trihydroxy-5α-cholan-3-one 24-sulfate (3kPZS) was applied to sea lamprey traps in eight streams at a final in-stream concentration of 10(-12) M. Application of 3kPZS increased sea lamprey catch, but where and when 3kPZS had the greatest impact was not determined. Here, by applying 3kPZS to additional streams, we determined that overall increases in yearly exploitation rate (proportion of sea lampreys that were marked, released, and subsequently recaptured) were highest (20-40%) in wide streams (~40 m) with low adult sea lamprey abundance (<1000). Wide streams with low adult abundance may be representative of low-attraction systems for adult sea lamprey and, in the absence of other attractants (larval odor, sex pheromone), sea lamprey may have been more responsive to a partial sex pheromone blend emitted from traps. Furthermore, we found that the largest and most consistent responses to 3kPZS were during nights early in the trapping season, when water temperatures were increasing. This may have occurred because, during periods of increasing water temperatures, sea lamprey become more active and males at large may not have begun to release sex pheromone. In general, our results are consistent with those for pheromones of invertebrates, which are most effective when pest density is low and when pheromone competition is low.