Mortality Of Trout Research Articles

Asymmetric impact of piscivorous birds on size-structured fish populations

Fish are frequently considered the top predator in freshwater food web models despite evidence that predatory birds can impact fish populations. In this study, we quantified bird predation rates on experimental populations of rainbow trout ( Oncorhynchus mykiss (Walbaum, 1792)) created by stocking nine small lakes in British Columbia, Canada. Combining estimates of fish mortality with estimated bird predation rates allowed us to partition fish mortality into that due to birds versus cannibalism. Our results indicated that bird predators had significant impacts on age-1 trout populations, but little impact on age-0 trout. Common loons ( Gavia immer Brunnich, 1764) were the principle predator among eight predatory bird species present, apparently consuming nearly 50% of all stocked age-1 trout and explaining almost 50% of variation in mortality rates. Age-1 trout mortality did not differ significantly from zero in lakes without loons. Birds consumed a small proportion of age-0 trout, and estimated consumption explained none of the variation in age-0 trout mortality among lakes. We conclude that birds affect fish populations by asymmetric predation on different age (size) classes and can be important top predators that should not be ignored when characterizing freshwater food webs in lakes.

In vivo correlates of infectious salmon anemia virus pathogenesis in fish

The phenotypic correlates of pathogenicity for Infectious salmon anemia virus (ISAV) in salmonid fishes have not been thoroughly studied to date. In this study, a comparison was made of 13 different strains of ISAV, isolated from different geographical regions between 1997 and 2004, for their infectivity in three fish species [Atlantic salmon (Salmo salar), coho salmon (Oncorhynchus kisutch) and rainbow trout (Oncorhynchus mykiss)]. When the different virus isolates were used at an approximate inoculum dose of 10(6) TCID(50) in 0.2 ml per fish, it was found that the most virulent strains had an acute mortality phase in Atlantic salmon that started at 10-13 days post-inoculation and lasted for 9-15 days with a cumulative mortality of >/=90 %. These highly pathogenic strains also caused low mortality in rainbow trout, albeit later in infection. Viruses with a more delayed or protracted mortality phase resulting in cumulative mortalities of 50-89 % in Atlantic salmon were considered to be of intermediate pathogenicity and isolates with cumulative mortalities of </=49 % were considered to be of low pathogenicity. On this basis, three of the ISAV isolates showed a high-, eight an intermediate- and two a low-pathogenicity phenotype in Atlantic salmon. Coho salmon were resistant to all ISAV isolates. These results confirmed that there is variation in pathogenicity among ISAV strains for Atlantic salmon and rainbow trout, and that other salmonid species such as coho salmon can carry highly pathogenic strains of ISAV without showing signs of disease. The identified pathogenicity phenotypes may aid in the identification of molecular markers of ISAV virulence.

Spatial and Temporal Occurrence of the Salmonid Parasite Ceratomyxa shasta in the Oregon–California Klamath River Basin

AbstractThe parasite Ceratomyxa shasta has been implicated as a significant source of salmonid mortality in the lower Klamath River, California (i.e., below Iron Gate dam). A study of the prevalence of C. shasta and its geographic and temporal distribution throughout the Klamath River basin was conducted to determine when and where juvenile salmonids encounter lethal parasite doses. Susceptible rainbow trout Oncorhynchus mykiss were exposed to C. shasta 3–4 d at seven locations in the Klamath River between Beaver Creek and Keno Reservoir in April, June, July, September, and November 2003. Individuals from a Klamath River strain of fall Chinook salmon O. tshawytscha were held in three locations in the upper Klamath River in April, June, and July. In June 2004, rainbow trout were exposed to the parasite for 4 d at 18 locations from Klamath Lake to the mouth of the Klamath River, including several major spawning tributaries; one exposure occurred in the lower Klamath River. Rainbow trout mortality due to infection for groups exposed in the upper Klamath River was lower (&lt;8.0%) and delayed (mean time to death, 40–110 d) in comparison with that in groups exposed in the lower Klamath River (&gt;98%; mean time to death, 33–36 d). Experimental fall Chinook salmon did not become infected in the upper Klamath River, but infection was detected in Chinook salmon exposed in the lower Klamath River, nearly 50% of these succumbing to infection. These dramatic differences in mortality between the upper and lower Klamath River could not be explained by differences in water temperatures during exposure and are probably a result of differences in infectious dose. Lack of infection in groups exposed in tributaries supports the hypothesis that the parasite life cycle and the invertebrate host are largely confined to the main‐stem Klamath River.

Rhabdovirus carpio as a causative agent of disease in rainbow trout (Oncorhynchus mykiss - Walbaum)

High mortality of 1-year old rainbow trout occurred on a fish farm in the spring season, with clinical symptoms typical for acute septicemia. Histological examination revealed inflammatory changes and necrosis of the internal organs. The causative agent was isolated on RTG-2 and EPC cell lines and identified by serum neutralisation, enzyme-linked immunosorbent assay (ELISA) and immunofluorescence (IFAT) as Rhabdovirus carpio. Experimental infection using the virus isolated from rainbow trout caused disease in carp fry, as well. This is the first case of disease of rainbow trout caused by Rhabdovirus carpio, and the first reported isolation of Rhabdovirus carpio from rainbow trout in Serbia. Also, this is the first successful infection of carp with Rhabdovirus carpio isolated from rainbow trout.

Causes of mortality of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) smolts in a restored river and its estuary

AbstractDuring October 2000 to August 2002, the River Skjern Nature Project was implemented by removing dykes and re‐meandering 20.5 km of the lower canalized river. As a consequence the length of the river stretch increased to 23 km. A lake of 250 ha developed in the river valley 5 km upstream from the river mouth because of subsiding soils caused by reclamation and drainage since the 1960s. Using radiotelemetry, the mortality of wild Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) smolts in the River Skjern and its estuary was investigated prior to and after the implementation of the project. Altogether, 77 Atlantic salmon and 66 brown trout smolts were caught, tagged and released in the river upstream of the restoration project during the spring of 2000 and 2002. The in‐river smolt mortality was more than double in 2002 for both Atlantic salmon and brown trout compared with 2000. This was primarily due to bird predation in 2002 which was not observed in 2000. The in‐river bird predation in 2002 was mediated by the new lake, which quickly became an important bird rest area. Estuarine mortality mainly caused by cormorants (Phalacrocorax carbo sinensis) differed significantly between species, but was high for both Atlantic salmon (39%) and brown trout (12%) in both years of investigation. The aggregated smolt mortality in the river and in the estuary (48%) may threaten an indigenous self‐sustaining Atlantic salmon population in the River Skjern. When planning river restoration projects, caution should be used, especially where permanently flooded floodplains (lakes) develop due to subsiding soil. In situations where rivers pass directly through newly developed lakes, migratory species such as Atlantic salmon and brown trout may be severely affected due to increased exposure to predation from predatory fish and birds. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Genetic stability within the Norwegian subtype of salmonid alphavirus (family Togaviridae)

Salmonid alphavirus (SAV) (family Togaviridae) causes mortality in Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss W.) in Norway, France, UK, and Ireland. At least three subtypes of SAV exist: SPDV in UK/Ireland, SDV in France/UK, and the recently reported Norwegian salmonid alphavirus (NSAV) in western Norway. During 2003 and 2004, disease caused by NSAV was reported for the first time in northern Norway, more than 800 km away from the enzootic area in western Norway. The present study has investigated the phylogenetic relationships among 20 NSAV isolates, based on a 1221-nt-long segment covering part of the capsid gene, E3, and part of the E2 gene, collected over a period of eight years. The results revealed genetic homogeneity among NSAV isolates, including those from northern Norway. The SDV or SPDV subtypes were not found in diseased Norwegian fish. A substitution rate of 1.70 (+/-1.03) x 10(-4) nt subst/site/year was obtained for the NSAV subtype by maximum likelihood analysis. The second aim of this study was to clarify whether NSAV changes genotypically in cell culture by culturing a NSAV isolate through 20 passages in CHSE-214 cells. Sequencing of almost the entire genome (11530 nt) after 20 passages revealed four nucleotide substitutions, all resulting in amino acid substitutions. One of these substitutions, serine to proline in E2 position 206, was also found to have occurred in field isolates.

Development and evaluation of portable PIT tag detection units: PITpacks

Portable passive integrated transponder (PIT) technology has been used by biologists to study fish behavior non-invasively. However, the method's efficacy has not been evaluated rigorously. To address this, we evaluated the design and field application of three portable backpack PIT tag units (PITpacks) over three years in Abernathy Creek, Longview, WA. Specifically, we assessed options for PITpack design and construction, PIT tag loss and mortality in steelhead trout following the implantation of 23 mm PIT tags, field efficiency of PITpack surveys and the effect of approaching PITpacks on steelhead trout behavior. Our results indicate that antennas constructed of 14 gauge ribbon cable operated consistently when held at a 45° angle to the water surface. Design modifications reduced equipment weight and made PITpacks easier to use. Read range of optimized PITpacks approached 90 cm off the antenna plane when the antenna and tag were submerged in water. Mortality was higher in 23 mm PIT tagged (1.8%) than in non-PIT tagged (0.5%) fish maintained in the same raceways. Tag loss was estimated to be 7.2%, peaked 4 weeks after implantation, and continued at a lesser rate throughout the 4-month study. Instream use of PITpacks resulted in a consistent survey efficiency of 38% in three separate trials. In addition, behavioral observations of tagged fish revealed minimal disturbance to fish approached by PITpacks. Results show that PITpacks can be applied in small streams to study individual fish behavior with only one collection and handling event (for tagging) and minor further disruption.

Formalin treatment to reduce mortality associated with Saprolegnia parasitica in rainbow trout, Oncorhynchus mykiss

Formalin has been used to treat fish egg fungal infections, but its ability to reduce mortality in fish with fungal infections has not been clearly demonstrated. An experimental infection was induced with abrasion, exposure, and temperature stress to evaluate the ability of formalin to reduce mortalities in rainbow trout ( Oncorhynchus mykiss) infected with Saprolegnia parasitica (ATCC 22284). The trout were anesthetized and abraded with a controlled abrasion technique. Temperature stress was performed concurrently with the fungal exposure by moving the trout from an acclimation temperature (15 ± 2 °C) to a higher exposure temperature (22 ± 2 °C) as they were immersed in an exposure tank inoculated with S. parasitica for 4 h. After the exposure, the fish were randomly distributed into 16 experimental tanks (3 fish/tank). Four treatment doses (0, 50, 100, and 150 ppm formalin solution) were evaluated. Fish were given three treatments of 1 h duration: on day 1, 1 h after the fungal exposure, and then the morning of days 3 and 5. The infection rate was 100% for all of the four trials in the study. The average percent mortality from the four trials was 67 (0 ppm), 35 (50 ppm), 29 (100 ppm), and 40 (150 ppm). Statistical analysis of the percent mortality at days 5 and 19 showed that the 50-, 100-, and 150-ppm doses were all significantly different from the 0-ppm dose on both days.

Mass-Marking Rainbow Trout and Brown Trout Fingerlings with Oxytetracycline

ABSTRACT We immersed fingerling rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) in a 500-mg/L solution of oxytetracycline (OTC) for 6 h to determine marking efficacy. The technique marked 100% and 92% of rainbow trout and brown trout otoliths, respectively. In a blind test using known marked and unmarked otoliths, one reader correctly identified 99% of rainbow trout and 95% of brown trout otoliths as either marked or unmarked. Reading errors for rainbow trout (1 out of 78) and brown trout (8 out of 167) were of omission. Mortality of OTC-marked trout was less than 3.5% and statistically similar to control groups. Thirty-five thousand fingerling brown trout stocked into two Tennessee tail waters were treated on the hatchery truck with 500 mg/L OTC and all of the fish in a subsample (n = 95) that was held for 30 d were marked. When fish were recaptured up to 14 months post-stocking, OTC marks were subsequently detected on all brown trout otoliths known be treated (n = 23). We concluded that OTC immersion is an effective technique for mass marking fingerling rainbow trout and brown trout during short-term stocking evaluations.

Stream acidification and mortality of brook trout (Salvelinus fontinalis) in response to timber harvest in Catskill Mountain watersheds, New York, USA

Effects of clear-cut and timber-stand improvement (TSI) harvests on water chemistry and mortality of caged brook trout (Salvelinus fontinalis) were evaluated in a study of three Catskill Mountain streams, 1994–2000. Harvests removed 73% of tree basal area (BA) from a clearcut subbasin, 5% BA from a TSI subbasin, and 14% BA at a site below the confluence of both streams. A fourth nonharvested site served as a control. Water quality and trout mortality were affected only in the clearcut stream. Acidity and concentrations of nitrate and inorganic monomeric aluminum (Alim) increased sharply during high flows after the first growing season (fall 1997). Acid–Alim episodes were severe during this period and decreased steadily in magnitude and duration thereafter. All trout at this site died within 7 days during spring 1998 and 85% died during spring 1999. Only background mortality was observed in other years at this site and at the other three sites during all tests. The absence of mortality in TSI watersheds indicates that limited harvests should not harm brook trout populations in acid-sensitive streams. Effects of tree harvests on fish communities are of concern, however, because many stream-dwelling species are more sensitive to acidified waters than brook trout.

Survival of brown trout during spring flood in DOC-rich streams in northern Sweden: the effect of present acid deposition and modelled pre-industrial water quality

Mortality and physiological responses in brown trout ( Salmo trutta) were studied during spring snow melt in six streams in northern Sweden that differed in concentrations of dissolved organic carbon (DOC) and pH declines. Data from these streams were used to create an empirical model for predicting fish responses (mortality and physiological disturbances) in DOC-rich streams using readily accessible water chemistry parameters. The results suggest that fish in these systems can tolerate higher acidity and inorganic aluminium levels than fish in low DOC streams. But even with the relatively low contemporary deposition load, anthropogenic deposition can cause fish mortality in the most acid-sensitive surface waters in northern Sweden during spring flood. However, the results suggests that it is only in streams with high levels of organically complexed aluminium in combination with a natural pH decline to below 5.0 during the spring where current sulphur deposition can cause irreversible damage to brown trout in the region. This study support earlier studies suggesting that DOC has an ameliorating effect on physiological disturbances in humic waters but the study also shows that surviving fish recover physiologically when the water quality returns to less toxic conditions following a toxic high flow period. The physiological response under natural, pre-industrial conditions was also estimated.

Effects of treated sewage effluent on immune function in rainbow trout ( Oncorhynchus mykiss)

In this study, the immune reactions of rainbow trout ( Oncorhynchus mykiss) were examined, after exposure to 10, 30 and 70% of tertiary-treated municipal sewage effluent for 27 days. Exposures were conducted concurrently with and without an immune challenge using intraperitoneal injections of inactivated Aeromonas salmonicida salmonicida. Due to the time required to prepare and analyse samples, fish sampling was conducted over two consecutive days. There was no trout mortality for any of the experimental treatments. The exposure to effluent increased in vitro lymphocyte proliferation, decreased circulating lymphocytes and increased degrading erythrocytes in peripheral blood samples. Circulating lymphocytes were only decreased in the sham-injected, but not in the A. salmonicida-injected group. In addition to effluent effects, circulating lymphocytes and lymphocyte proliferation were decreased on day 2 of sampling as compared to day 1. Concentration-dependent degradation of erythrocytes was only observed on day 2 of sampling. Capture and removal of trout on day 1 of sampling presumably caused low-level stress that affected some results on day 2. Oxidative burst, phagocytosis, lysozyme, leucocyte populations other than lymphocytes and A. salmonicida-specific IgM production were not affected by exposure to effluent, and of these parameters, only oxidative burst and total leucocytes showed sampling day effects. From these results it can be observed, that with the exception of oxidative burst, those variables affected by effluent exposure were also significantly changed by the low-level sampling stress imposed by staggered sampling. Elevated liver mixed-function oxygenase activity as measured by 7-ethoxyresorufin- O-deethylase activity, and increased bile polycyclic aromatic hydrocarbon (PAH) metabolites were observed in response to sewage effluent exposure. As both PAHs and stress are known immune suppressors, it is difficult to conclude whether or not changes in immune parameters due to effluent exposure were caused by the direct action of chemicals, or were due to a general stress response.

The significance of water ionic strength on aluminium toxicity in brown trout ( Salmo trutta L.)

The toxicity of aluminium to fish is related to interactions between aluminium and the gill surface. We investigated the possible effect of water ionic strength on this interaction. The mortality of brown trout ( Salmo trutta L.) exposed to three different degrees of Al polymerisation was compared in water with increased ionic strength (mean 7.31 × 10 −4 M) after additions of the base cations Ca 2+, Mg 2+, Na + or K +, and in water with no such addition (mean ionic strength 5.58 × 10 −4 M). Only a very slight ameliorating effect of increased ionic strength was observed, while the degree of Al polymerisation was of major importance in fish mortality. In addition, it was observed that smaller fish survived the Al exposures for a longer time than larger fish. We hypothesise that this is because larger fish are more susceptible to hypoxia than smaller fish.

Effect of Hook Type on Mortality, Trauma, and Capture Efficiency of Wild Stream Trout Caught by Angling with Spinners

AbstractThis study assessed short‐term (48‐h) hooking mortality, eye damage, jaw injury, and capture efficiency of three species of wild stream trout caught on size‐1 Mepps spinners having barbed or barbless treble or single hooks. The mortality of rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, and brook trout Salvelinus fontinalis was low (&lt;4%). Hook types did not differ significantly in causing mortality or severe eye damage of rainbow trout or brown trout. Severe eye damage was evident on about 10% of the trout landed (range = 2% to 13%, depending on species). Jaw injuries were found on about 6% of the catch. Barbed hooks hooked and held more trout than barbless hooks and treble hooks hooked and held more trout than single hooks. Barbless single hooks were quicker to remove than the other hook types, but the difference was insufficient to reduce mortality. Our results do not indicate a biological advantage with the use of single‐ or barbless‐hook spinners when caught wild stream trout will be released.

An Inhibitor of Bacterial Quorum Sensing Reduces Mortalities Caused by Vibriosis in Rainbow Trout (Oncorhynchus mykiss, Walbaum)

The fish pathogen Vibrio anguillarum produces quorum sensing signal molecules, N-acyl homoserine lactones (AHLs), which in several Gram-negative human and plant pathogenic bacteria regulate virulence factors. Expression of these factors can be blocked using specific quorum-sensing inhibitors (QSIs). The purpose of this study was to investigate the effect of a QSI, furanone C-30, on mortality of rainbow trout during challenge with V. anguillarum. Addition of 0.01 or 0.1 microM furanone C-30 to rainbow trout infected by cohabitation caused a significant reduction in accumulated mortality from 80-100% in challenge controls to 4-40% in treated groups. Furanone C-30 had no effect in an immersion challenge system, probably due to a very high water exchange and a rapid dilution of furanone C-30. Growth and survival of V. anguillarum were not affected by the concentrations of furanone C-30 used in the challenge experiments, thus avoiding selection for resistance. To elucidate the mechanism of disease control by furanone C-30, we determined its effect on the bacterial proteome, motility, and respiration. No effects were seen of furanone C-30 in any of these experiments. Although no cytotoxic effect on HeLa cells were observed, exposure to 1 microM (or higher) concentrations of furanone C-30 had detrimental effects on the rainbow trout. Our results indicate that QSIs can be used in non-antibiotic based control of fish diseases. However, they also underline the need for development of novel, less toxic QSI compounds and the need for understanding the exact mechanism(s) of action.

Density-dependent mortality is mediated by foraging activity for prey fish in whole-lake experiments.

Whereas the effects of density-dependent growth and survival on population dynamics are well-known, mechanisms that give rise to density dependence in animal populations are not well understood. We tested the hypothesis that the trade-off between growth and mortality rates is mediated by foraging activity and habitat use. Thus, if depletion of food by prey is density-dependent, and leads to greater foraging activity and risky habitat use, then visibility and encounter rates with predators must also increase. We tested this hypothesis by experimentally manipulating the density of young rainbow trout (Oncorhynchus mykiss) at risk of cannibalism, in a replicated single-factor experiment using eight small lakes, during an entire growing season. We found no evidence for density-dependent depletion of daphnid food in the nearshore refuge where most age-0 trout resided. Nonetheless, the proportion of time spent moving by individual age-0 trout, the proportion of individuals continuously active, and use of deeper habitats was greater in high density populations than in low density populations. Differences in food abundance among lakes had no effect on measures of activity or habitat use. Mortality of age-0 trout over the growing season was higher in high density populations, and in lakes with lower daphnid food abundance. Therefore, population-level mortality of age-0 trout is linked to greater activity and use of risky habitats by individuals at high densities. We suspect that food resources were depleted at small spatial and temporal scales not detected by our plankton sampling in the high density treatment, because food-dependent activity and habitat use by age-0 trout occurs in our lakes when food abundance is experimentally manipulated (Biro, Post & Parkinson, in press).

The effects of ultraviolet‐b radiation on the toxicity of fire‐fighting chemicals

The interactive effects of ultraviolet (UV) and fire-retardant chemicals were evaluated by exposing rainbow trout (Oncorhyncus mykiss) juveniles and tadpoles of southern leopard frogs (Rana sphenocephala) to six fire-retardant formulations with and without sodium ferrocyanide (yellow prussiate of soda [YPS]) and to YPS alone under three simulated UV light treatments. Yellow prussiate of soda is used as a corrosion inhibitor in some of the fire-retardant chemical formulations. The underwater UV intensities measured were about 2 to 10% of surface irradiance measured in various aquatic habitats and were within tolerance limits for the species tested. Mortality of trout and tadpoles exposed to Fire-Trol GTS-R, Fire-Trol 300-F, Fire-Trol LCA-R, and Fire-Trol LCA-F was significantly increased in the presence of UV radiation when YPS was present in the formulation. The boreal toad (Bufo boreas), listed as endangered by the state of Colorado (USA), and southern leopard frog were similar in their sensitivity to these chemicals. Photoenhancement of fire-retardant chemicals can occur in a range of aquatic habitats and may be of concern even when optical clarity of water is low; however, other habitat characteristics can also reduce fire retardant toxicity.

Isolation and Identification of the Infectious Haematopoietic Necrosis Virus (IHNV)-like Agent from Farmed Rainbow Trout (Oncorhynchus mykiss) from Iran

Summary The isolation of viral causative agent of fry trout mortality syndrome in farmed rainbow trout in Iran was discussed. Four hundred twenty samples were collected from six provinces for virological, serological and electron microscopic examinations from October 2001 till May 2002. No cytopathic effect (CPE) was observed in the cell cultures except for EPC and BF-2 cells in which signs of CPE appeared one day postinoculation during the second and third passages of two brooder ovarian fluids. Electron microscopic examination revealed the viral particles measured 67-73×128-182nm in the pelleted materials from the CPE positive in BF-2 and EPC cell lines. Indirect immunoflurecence antibody test were positive for some of smears obtained from kidney tissues of the larvae, the samples of ovarian fluids that showed CPE on EPC and BF-2 cell lines as well as CPE positive cell cultures. Using ELISA eight of all sera samples tested were positive with optical density ranged 0.316-2.268 compared to 0.06 for negative controls.

Characterizing Aquatic Health Using Salmonid Mortality, Physiology, and Biomass Estimates in Streams with Elevated Concentrations of Arsenic, Cadmium, Copper, Lead, and Zinc in the Boulder River Watershed, Montana

Abandoned tailings and mine adits are located throughout the Boulder River watershed in Montana. In this watershed, all species of fish are absent from some tributary reaches near mine sources; however, populations of brook trout Salvelinus fontitalis, rainbow trout Oncorhynchus mykiss, and cut-throat trout O. clarki are found further downstream. Multiple methods must be used to investigate the effects of metals released by past mining activity because the effects on aquatic life may range in severity, depending on the proximity of mine sources. Therefore, we used three types of effects—those on fish population levels (as measured by survival), those on biomass and density, and those at the level of the individual (as measured by increases in metallothionein, products of lipid peroxidation, and increases in concentrations of tissue metals)—to assess the aquatic health of the Boulder River watershed. Elevated concentrations of Cd, Cu, and Zn in the water column were associated with increased mortality of trout at sites located near mine waste sources. The hypertrophy (swelling), degeneration (dying), and necrosis of epithelial cells observed in the gills support our conclusion that the cause of death was related to metals in the water column. At a site further downstream (lower Cataract Creek), we observed impaired health of resident trout, as well as effects on biomass and density (measured as decreases in the kilograms of trout per hectare and the number per 300 m) and effects at the individual level, including increases in metallothionein, products of lipid peroxidation, and tissue concentrations of metals.

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.