Spatial and Ontogenetic Variability of Sea Lamprey Diets in Lake Superior

Invasive sea lamprey (Petromyzon marinus) remain an important source of fish mortality in the Laurentian Great Lakes, yet assessing their impact is hindered by lack of quantitative diet information. We examined nitrogen and carbon stable isotope ratios (δ¹⁵N and δ¹³C) of sea lamprey and host species in six ecoregions of Lake Superior, mainly in 2002–2004. Data implied that most sea lamprey fed primarily on upper trophic level species, including forms of lake trout (Salvelinus namaycush). However, in Ontario waters, particularly semi-enclosed Black Bay, sea lamprey relied heavily on lower trophic levels, such as coregonines (Coregonus spp.) and suckers (Catostomus spp.). Sea lamprey δ¹⁵N and δ¹³C generally increased with sea lamprey size, implying dependence on higher trophic levels later in life. Most parasitic sea lamprey that we captured were attached to either lean lake trout (35% of observed attachments), lake whitefish (Coregonus clupeaformis; 25%), or cisco (C. artedii; 25%); the latter sea lamprey were typically < 15 g. Survey- and fishery-dependent wounding rate data compiled from 1986–2005 suggest that lean and siscowet lake trout were selectively parasitized by sea lamprey, which is consistent with our stable isotope data. Our results largely support the notion that lake trout are the principal host species in Lake Superior. However, stable isotope evidence that sea lamprey feed at lower trophic levels in some regions argues for comprehensive monitoring of sea lamprey impacts throughout the fish community in systems that sea lamprey have invaded.     

Estimating wounding of lake trout by sea lamprey in the upper Great Lakes: Allowing for changing size-specific patterns

A primary fishery concern in the Laurentian Great Lakes is mitigating the persistent negative impact of parasitic sea lamprey (Petromyzon marinus) on native lake trout (Salvelinus namaycush). Wounds observed on surviving lake trout are commonly used by managers to assess damages associated with sea lamprey predation. We estimated the relationship between wounding rates and lake trout size, and how this varied spatially and temporally. We built upon previously published work by fitting wound rates as a logistic function of lake trout size. By using longer time series and data from three Great Lakes, our analysis harnessed substantially more contrast in host populations than previous work, and we also employed software advances for nonlinear mixed-effect models. Candidate models allowed logistic function parameters to be constant or to vary spatially, temporally, or both. Temporal effects were modeled as random walk processes. We also considered models that assumed either Poisson or negative binomial distributions for the number of wounds per fish at a given length. Models that allowed for both spatial and temporal effects in the shaping parameters and assumed a negative binomial wound distribution resulted in the best fit as indicated by Akaike's Information Criterion. Wounding rate estimates from models selected for each lake in this analysis are contrasted with those of wounding rate models currently used as components of lake trout population assessments. Although model fit was improved substantially, differences in wounding rates estimates are modest and estimates follow very similar temporal trends. However, as time series of wound data continue to grow, models that incorporate temporal variability in parameter estimation are expected to be increasingly favored. This research provides managers with an updated tool to obtain more reliable estimates of sea lamprey wounding.     

Variability in sea lamprey fatty acid profiles indicates a range of host species utilization in Lake Michigan

Despite being a “top predator”/parasite in the Great Lakes, knowledge of sea lamprey feeding ecology remains hindered by methodological constraints. Particularly, our knowledge of sea lamprey dietary habits is likely biased as it relies primarily on wounding rates of commercially and recreationally caught fish. Biochemical methods provide a means to extract diet information from sea lamprey themselves, and therefore provide a more objective assessment of sea lamprey feeding ecology. Of particular interest is the use of fatty acid profiles to qualitatively describe foraging patterns of sea lamprey. Adult sea lamprey were captured throughout the Lake Michigan basin during spring spawning migrations into rivers, and muscle tissues were analyzed for fatty acid profiles. Exploratory multivariate analyses were used to investigate variation in fatty acid profiles among captured individuals and to compare these to profiles of potential host species. In general, we noted a large variability in fatty acid profiles suggesting a broad spectrum of host species targeted by sea lamprey. Comparing sea lamprey fatty acid profiles with published data on host species, we concluded that sea lamprey feed on a wide variety of host species.     

Evaluating the growth potential of sea lampreys (Petromyzon marinus) feeding on siscowet lake trout (Salvelinus namaycush) in Lake Superior

Differences in the preferred thermal habitat of Lake Superior lake trout morphotypes create alternative growth scenarios for parasitic sea lamprey (Petromyzon marinus) attached to lake trout hosts. Siscowet lake trout (Salvelinus namaycush) inhabit deep, consistently cold water (4-6 °C) and are more abundant than lean lake trout (Salvelinus namaycush) which occupy temperatures between 8 and 12 °C during summer thermal stratification. Using bioenergetics models we contrasted the growth potential of sea lampreys attached to siscowet and lean lake trout to determine how host temperature influences the growth and ultimate size of adult sea lamprey. Sea lampreys simulated under the thermal regime of siscowets are capable of reaching sizes within the range of adult sea lamprey sizes observed in Lake Superior tributaries. High lamprey wounding rates on siscowets suggest siscowets are important lamprey hosts. In addition, siscowets have higher survival rates from lamprey attacks than those observed for lean lake trout which raises the prospect that siscowets serve as a buffer to predation on more commercially desirable hosts such as lean lake trout, and could serve to subsidize lamprey growth.     

Effectiveness of Using Backpack Electrofishing Gear for Collecting Sea Lamprey (Petromyzon marinus) Larvae in Great Lakes Tributaries

The effects of water depth, larval density, stream conductance, temperature, lamprey length, and larval escapement were examined to determine the efficiency of sampling sea lamprey (Petromyzon marinus) larvae using direct current (DC) backpack electrofishing gear. A higher proportion of larvae of all sizes were collected per unit sampling effort when sample sites were shallower, contained fewer larvae, or were in streams of lower specific conductance (P < 0.001). Temperature did not affect the efficiency of sampling lamprey larvae in this study. The investigation of the effect of larval escapement on observed catch was inconclusive. Similar length distributions were found between lamprey larvae collected using electrofishing gear and those collected using either a suction dredge or collected during a lampricide treatment. These results have implications for the development of a sampling protocol that uses a single-pass electrofishing technique to estimate the overall abundance of sea lamprey larvae in a stream. This estimate is critical to determining the number of larvae with the potential to metamorphose as parasitic lamprey the following year, and consequently, the prioritization of streams for lampricide treatment.     

Movement of Sea Lamprey in the Lake Champlain Basin

Sea lamprey (Petromyzon marinus) are a nuisance aquatic species in the Great Lakes and Lake Champlain that have devastated native fish populations and hampered the restoration of sport fisheries. This study examined inter-basin movement of sea lamprey in Lake Champlain to identify tributaries that contribute parasitic-phase sea lamprey and provide information for prioritizing those tributaries for sea lamprey control. A total of 4,125 recently metamorphosed sea lamprey was captured in tributaries to Lake Champlain and marked using coded wire tags between the fall of 2001 and winter 2003. These sea lamprey migrated to the lake to prey on salmonids and other fishes and returned to tributaries to spawn about 12–18 months after migration. We recaptured 6 tagged sea lamprey from the lake from spring 2002 through winter 2004, and 35 from tributaries in spring 2003 and 2004. We noted no apparent trends in movement among basins. Sea lamprey were collected at distances up to 64 km from their natal tributaries. Tributary contributions of parasites were significantly different from expectations in the 2002 parasitic-phase cohort (χ² = 9.668, p < 0.011, 3 df), suggesting differential survival rates among out-migrating transformers from different tributaries. Estimates of the lake-wide out-migrating transformer population for the 2002 and 2003 parasitic-phase cohorts were 269,139 ± 55,610 (SD) and 111,807 ± 23,511 (SD). Results from this study suggest that sea lamprey movement is not inhibited by causeways dividing sub-basins, but movement among sub-basins is somewhat constrained. This indicates that management efforts to control sea lamprey should continue to treat the lake as a single system.     

Consistent individual differences in sea lamprey (Petromyzon marinus) behaviour: Implications for control via trapping

We tested if consistent individual differences (CIDs) in the behaviour of sea lamprey (Petromyzon marinus) from the Laurentian Great Lakes could influence their vulnerability to trapping. The sea lamprey is invasive in the Upper Laurentian Great Lakes and the target of a binational control program. Trapping could be used for control if trapping efficiency is unbiased and effective. Our test involved comparing the behaviour of sea lamprey collected in the field from a trap (n = 42) at a barrier and electrofished (n = 9) downstream of the barrier. We quantified each individual's latency to exit an enclosure (a measure of exploration), proportion of time spent moving (a measure of general activity), and change in activity in response to a putative predator cue (a measure of boldness). CIDs were detected for each behaviour measured (intraclass correlations: 0.3–0.5). CIDs in behaviour also differed between trapped individuals and those collected downstream using electrofishing, irrespective of size, sex, and maturity status. Trapped individuals decreased their activity in response to a putative predator cue, while individuals collected using electrofishing increased their activity in response to the cue. Trapped individuals also tended to spend a greater proportion of time moving than individuals sampled downstream of the trap. However, the two samples of lamprey did not differ significantly in time taken to exit an enclosure. The behavioural differences between sea lamprey sampled from a trap and those sampled downstream of the trap suggest that CIDs in behaviour can influence an individual's vulnerability to trapping.     

Observations on Twinning in the Sea Lamprey (Petromyzon Marinus) in the Laboratory

Forty-five sets of separate, normal twins were produced from four portions of the eggs from one female sea lamprey (Petromyzon marinus) each fertilized by a different male. The percentage of twinning in the different groups of embryos ranged from 1.0 to 1.7. Although the development of some of the twins was slightly slower than average, that of most was within the normal range for sea lamprey embryos. The twins were smaller than non-twins, and one twin was usually smaller than the other. Although the discovery of Siamese twins in fish is not uncommon, separate, normal twins have seldom been reported.     

A life cycle approach to modeling sea lamprey population dynamics in the Lake Champlain basin to evaluate alternative control strategies

Sea lamprey (Petromyzon marinus) is a nuisance species in the Laurentian Great Lakes and Lake Champlain that has devastated native fish populations and hampered sport fisheries development. We developed a modified stage-based life history matrix for sea lamprey to analyze the effects of various management efforts to suppress sea lamprey population growth in Lake Champlain. These efforts targeted different life stages of the sea lamprey life cycle. A beta distribution was used to distribute stochastic larval populations among twenty sea lamprey-bearing tributaries and five deltas to Lake Champlain, from which sea lamprey that survive through larval metamorphosis were then pooled into a lake-wide parasitic-phase population. Parasitic-phase survival to the spawning stage was evaluated based on proximity to the natal tributary and on the size of the resident larval population in each tributary. Potential control strategies were modeled at egg to emergence, larval, and spawning stages to reduce vital rates at each stage, with the goal of suppressing parasitic-phase production. Simulations indicate that control of the larval stage was essential to achieving this goal, and with supplemental effort to reduce the vital rates at early life stages and at the spawning stage, the parasitic-phase population can be further suppressed. Sensitivity simulations indicate that the life history model was sensitive to egg deposition rate, abundance of parasitic-phase sea lamprey from unknown, uncontrolled sources, and the method in which parasitic-phase sea lamprey select tributaries for spawning. Results from this model can guide management agencies to optimize future management programs.     

Warmer waters increase the larval sea lamprey's (Petromyzon marinus) tolerance to the lampricide 3-trifluoromethyl-4-nitrophenol (TFM)

Invasive sea lampreys (Petromyzon marinus) in the Great Lakes are controlled by applying the pesticide (lampricide) 3-trifluoromethyl-4-nitrophenol (TFM) to waters infested with larval lamprey. However, treatment effectiveness can be undermined by “residual” larval sea lamprey that survive TFM exposure, and subsequently complete metamorphosis into parasitic juvenile sea lamprey that prey on culturally and economically important fishes. We investigated how season and temperature influenced the TFM tolerance of larval sea lamprey. Acute toxicity tests on lamprey collected from the Au Sable River, Michigan, revealed that the 12-h LC₅₀ and LC_99.9 were 2.0- to 2.5-fold greater in late spring and summer, than in early spring and fall. Subsequent toxicity tests indicated that greater TFM tolerance in summer was due to warmer temperatures, based on an almost 2-fold greater 12-h LC₅₀ and LC_99.9 in warm (24 °C) compared to cool (6 °C) water. Variations in energy stores (glycogen, lipid, protein) or condition did not appear to affect TFM sensitivity. We conclude that higher water temperature is the primary factor driving the larval sea lamprey's greater tolerance to TFM during the summer, possibly due to an increase in their capacity to detoxify TFM. Considering seasonal variations in temperature may be prudent when selecting and treating sea lamprey infested streams with TFM to minimize treatment residuals. In the longer term, increases in average and peak water temperatures due to climate change could result in greater TFM requirements and costs due to the greater tolerance of larval sea lamprey to TFM at warmer temperatures.     

Factors affecting recruitment dynamics of Great Lakes sea lamprey (Petromyzon marinus) populations

Knowledge of stock–recruitment dynamics is as important for control of pest species such as the sea lamprey (Petromyzon marinus) as it is for sustainable harvest management of exploited fish species. A better understanding of spatial and temporal variation in recruitment of pest populations may inform managers on where and when to effectively apply different control methods. Sea lamprey stock–recruitment data combined from streams across the Great Lakes basin into a Ricker stock–recruitment model indicated both compensation (density-dependent survival) and a large amount of density-independent recruitment variation. We evaluated the use of a mixed-effects model to look at common year effects and stream-level variables that could affect productivity and growing season length, with the objective of identifying factors that may explain this density-independent variation in recruitment. After selecting the “best model”, we tested factors that might affect recruitment variation, using a Great Lakes dataset comprising 97 stream–years. Lake Superior tributaries, streams with larger numbers of lamprey competitors, and streams regularly requiring lampricide treatment showed significantly higher recruitment. Alkalinity and thermal regulation did not affect the observed recruitment pattern among streams. In four long-term study streams we observed significant variation among streams, tested as a fixed effect, but no evidence suggested a common pattern of variation among years. Differences in recruitment among streams were consistent with evidence of quality of spawning and larval habitat among streams. Our findings suggest that management models should account for differences in recruitment dynamics among sea lamprey-producing streams, but not common year effects.     

Seasonal Patterns in Growth,Blood Consumption,and Effects on Hosts by Parasitic-Phase Sea Lampreys in the Great Lakes: An Individual-Based Model Approach

An individual-based model (IBM) was developed for sea lamprey (Petromyzon marinus) populations in the Laurentian Great Lakes. The IBM was then calibrated to observed growth, by season, for sea lampreys in northern Lake Huron under two different water temperature regimes: a regime experienced by Seneca-strain lake trout (Salvelinus namaycush) and a regime experienced by Marquettestrain lake trout. Modeling results indicated that seasonal blood consumption under the Seneca regime was very similar to that under the Marquette regime. Simulated mortality of lake trout directly due to blood removal by sea lampreys occurred at nearly twice the rate during August and September under the Marquette regime than under the Seneca regime. However, cumulative sea lamprey-induced mortality on lake trout over the entire duration of the sea lamprey's parasitic phase was only 7% higher for the Marquette regime compared with the Seneca regime. Thus, these modeling results indicated that the strain composition of the host (lake trout) population was not important in determining total number of lake trout deaths or total blood consumption attributable to the sea lamprey population, given the sea lamprey growth pattern. Regardless of water temperature regime, both blood consumption rate by sea lampreys and rate of sea lamprey-induced mortality on lake trout peaked in late October. Elevated blood consumption in late October appeared to be unrelated to changes in water temperature. The IBM approach should prove useful in optimizing control of sea lampreys in the Laurentian Great Lakes.     

The behavioural response of migratory sea lamprey (Petromyzon marinus) to potential damage-released larval and migratory chemical alarm cues

We investigated the presence of damage-released alarm cues and the reactions they may cause in landlocked migratory sea lamprey (Petromyzon marinus) using semi-natural laboratory conditions during the day. In two separate experiments, migratory sea lampreys were exposed to stimuli prepared from the skinless carcasses and skin tissue of larval sea lamprey and from the skin tissue and muscle tissue of migratory sea lamprey. Migratory female sea lamprey swam significantly longer after being exposed to the stimulus prepared from the skinless carcass of larval sea lamprey. No significant changes were seen in the behaviour of the migratory female lamprey in response to larval skin extract or in the behaviour of male sea lamprey to any experimental extract in the larval extract experiment. In the second experiment that utilised migratory lamprey stimuli, neither male and nor female migratory sea lamprey showed a significant difference in their behavioural response among different treatments and controls. Our findings indicate that adult female sea lamprey respond strongly to damage-released alarm cues from larval sea lamprey; hence, the latter holds promise for sea lamprey behavioural manipulations for control purposes during the day. Further research is needed to examine responses to damage-released alarm cues at night, when migratory sea lampreys are more active.     

Evaluation of sea lamprey-associated mortality sources on a generalized lake sturgeon population in the Great Lakes

Lake sturgeon populations in the Laurentian Great Lakes experience two age-specific mortality sources influenced by the sea lamprey Petromyzon marinus control program: lampricide (TFM) exposure-induced mortality on age-0 fish and sea lamprey predation on sub-adults (ages 7–24). We used a generic age-structured population model to show that although lampricide-induced mortality on age-0 lake sturgeon can limit attainable population abundance, sea lamprey predation on sub-adult lake sturgeon may have a greater influence. Under base conditions, adult lake sturgeon populations increased by 5.7% in the absence of TFM toxicity if there was no change in predation; whereas, a 13% increase in predation removed this effect, and a doubling of sea lamprey predation led to a 32% decrease in adult lake sturgeon. Our estimates of lake sturgeon abundance were highly dependent on the values of life history and mortality parameters, but the relative impacts of ceasing TFM treatment and increasing predation were robust given a status quo level of predation. The status quo predation was based on sea lamprey wounding on lake sturgeon, and improvements in this information would help better define tradeoffs between the mortality sources for specific systems. Reduction or elimination of TFM toxicity on larval lake sturgeon, while maintaining TFM toxicity on larval sea lamprey, can promote lake sturgeon restoration and minimize negative impacts on other fish community members.     

GUIDING OUT‐MIGRATING JUVENILE SEA LAMPREY (PETROMYZON MARINUS) WITH PULSED DIRECT CURRENT

Non‐physical stimuli can deter or guide fish without affecting water flow or navigation and therefore have been investigated to improve fish passage at anthropogenic barriers and to control movement of invasive fish. Upstream fish migration can be blocked or guided without physical structure by electrifying the water, but directional downstream fish guidance with electricity has received little attention. We tested two non‐uniform pulsed direct current electric systems, each having different electrode orientations (vertical versus horizontal), to determine their ability to guide out‐migrating juvenile sea lamprey (Petromyzon marinus) and rainbow trout (Oncorhynchus mykiss). Both systems guided significantly more juvenile sea lamprey to a specific location in our experimental raceway when activated than when deactivated, but guidance efficiency decreased at the highest water velocities tested. At the electric field setting that effectively guided sea lamprey, rainbow trout were guided by the vertical electrode system, but most were blocked by the horizontal electrode system. Additional research should characterize the response of other species to non‐uniform fields of pulsed DC and develop electrode configurations that guide fish over a range of water velocity. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Development and Evaluation of a New Predictive Model for Metamorphosis of Great Lakes Larval Sea Lamprey (Petromyzon marinus) Populations

Accurate forecasts of the number of larval sea lamprey (Petromyzon marinus) within a stream that will enter into metamorphosis are critical to currently used methods for allocating lampricide treatments among streams in the Great Lakes basin. To improve our ability to predict metamorphosis we used a mark-recapture technique, involving the marking of individual larval lamprey with sequentially coded wire tags, to combine information regarding individual and stream level parameters collected in year t, with direct observations of metamorphic outcome of lamprey recaptured in year t+1. We used these data to fit predictive models of metamorphosis. The best model demonstrated excellent predictive capabilities and highlighted the importance of weight, age, larval density, stream temperature and geographic location in determining when individual lamprey are likely to transform. While this model was informative, it required data whose measures are not practical to obtain routinely during the larval sea lamprey assessment program. A second model, limited to data inputs that can be easily obtained, was developed and included length of larvae the fall prior to metamorphosis, stream latitude and longitude, drainage area, average larval density in type-2 habitat, and stream lamprey production category (a measure of the regularity with which treatments are required). This model accurately predicted metamorphosis 20% more often than current models of metamorphosis; however, we recommend further validation on an independent set of streams before adoption by the Great Lakes Fishery Commission for ranking streams.     

In Situ Determination of the Annual Thermal Habitat Use by Lake Trout (Salvelinus namaycush) in Lake Huron

Records of the temperatures occupied by 33 lake trout (Salvelinus namaycush) at large in Lake Huron were obtained for up to 14 months per fish, at 75-minute intervals, from surgically implanted archival temperature tags. The dataset covered nearly three years, from October 1998 to June 2001, and included 160,000 observations. The objectives of the tagging were to obtain temperature data to refine bioenergetics models of sea lamprey (Petromyzon marinus) predation on lake trout, and compare the temperatures occupied by strains of lake trout stocked in Lake Huron. The seasonal, thermal-use profiles of lake trout followed the general warming and cooling pattern of Lake Huron. During periods when the zone of surface water mixing extended below the depth range occupied by lake trout, variability among individual fish and strains was low and followed surface temperature. However, during the period of summer stratification, the average temperatures occupied varied substantially among individual fish and strains. Strains originating from the upper Great Lakes (Lake Superior and Lewis Lake, WY) occupied similar temperatures. Between June and mid August, upper Great Lakes lake trout typically occupied water several degrees warmer than that occupied by lake trout of Finger Lakes, New York origin. Most of the lake trout occupied summer temperatures lower than the preferred temperatures suggested by laboratory studies. In October, all strains occupied water as warm or warmer than that occupied in summer, which may partially explain the higher lethality of sea lamprey attacks during October.     

Subsidies from anadromous sea lamprey (Petromyzon marinus) carcasses function as a reciprocal nutrient exchange between marine and freshwaters

Nutrient and energy flows across ecosystem boundaries subsidize recipient communities and influence bottom‐up processes in food webs. Migratory fish such as anadromous sea lamprey provide a pulse of marine‐derived nutrients and energy to Atlantic coastal streams in spring when organisms would otherwise be subject to limiting resources. We conducted sea lamprey carcass addition experiments to characterize the role of subsidies on producer and consumer trophic pathways by manipulating subsidy quantity and light exposure. We demonstrated that producer and decomposer productivity is constrained by nutrients during spring; however, these limitations were reduced in producers as light limitations intensified through riparian shading. We observed no significant effects of increasing carcass subsidies on producer and decomposer biomass. Our results suggest that high densities of carcass subsidies may stimulate primary productivity; however, these effects are mediated by the degree of riparian shading, which demonstrated a onefold to fourfold difference in biomass accrual. In addition, sea lamprey carcass nutrients were captured by larval conspecifics. Stable isotopes analysis demonstrated that adult sea lamprey carcass tissue was relatively enriched in ¹⁵N and ¹³C isotopes compared with larvae. We observed significant enrichment in the ¹³C isotope among larvae sampled after 2 and 4 weeks of exposure to adult carcass nutrients. Our work suggests that a portion of sea lamprey subsidies serve as a reciprocal exchange between freshwaters and the ocean. We highlight that this cross‐ecosystem linkage is likely influenced by subsidy quantity from donor systems and is mediated by environmental characteristics affecting the recipient system.     

Survey of Siscowet Lake Trout at Their Maximum Depth in Lake Superior

The siscowet Salvelinus namaycush is a deepwater morphotype of lake trout in Lake Superior. As part of a standardized lake-wide survey in 2006 to assess siscowet populations, bottom-set, multi-mesh gill nets were fished at 36.6 m depth intervals from near shore areas to the deepest waters in south-central Lake Superior. Siscowet length distributions, diet compositions, and sea lamprey wounding rates were compared for three depth zones: shallow (< 200 m), deep (200–394 m), and deepest (395–399 m). There were 39 siscowets collected in proximity to Lake Superior's greatest recorded depth of 405 m. To our knowledge, this is the greatest depth that fish have been collected in the Great Lakes. Higher proportions of siscowets ≤ 500 mm were caught in the shallow zone compared to deeper zones. Deepwater sculpins were the dominant prey for small siscowets (< 600 mm) across all depth zones. The diet of large siscowets (≥ 600 mm) among all depth zones comprised mostly of coregonines and burbot Lota lota. Terrestrial insects were observed in the diet of siscowets in all depth zones, indicating migration to the surface. Type A sea lamprey wounding rates were higher for large (≥ 600 mm) than small siscowets among all depth zones. The highest wounding rate was observed on large siscowets in the deep zone. Recent work indicates that siscowets are the most abundant lake trout form and this research indicates that siscowets use the maximum depths of Lake Superior.     

Assessing Assessment: Can the Expected Effects of the St. Marys River Sea Lamprey Control Strategy Be Detected?

In 1997 the Great Lakes Fishery Commission approved a 5-year (1998 to 2002) control strategy to reduce sea lamprey (Petromyzon marinus) production in the St. Marys River, the primary source of parasitic sea lampreys in northern Lake Huron. An assessment plan was developed to measure the success of the control strategy and decide on subsequent control efforts. The expected effects of the St. Marys River control strategy are described, the assessments in place to measure these effects are outlined, and the ability of these assessments to detect the expected effects are quantified. Several expected changes were predicted to be detectable: abundance of parasitic-phase sea lampreys and annual mortality of lake trout (Salvelinus namaycush) by 2001, abundance of spawning-phase sea lampreys by 2002, and relative return rates of lake trout and sea lamprey wounding rates on lake trout by 2005. Designing an effective assessment program to quantify the consequences of fishery management actions is a critical, but often overlooked ingredient of sound fisheries management.