Geology topics

Todd J. Severson

Publications and source records attributed to Todd J. Severson.

At least 19 recordsLinked to original sources

USGS2026

Assessing low-dose copper treatment for dreissenid mussels: Effects on nontarget organisms

Zebra mussels ( Dreissena polymorpha ), an invasive dreissenid mussel, have been established and caused considerable effects in many North American aquatic ecosystems. In response, copper-based pesticides have been used to manage zebra mussel populations. We evaluated the effects of a low-dose (60 µg Cu/L for 10 d) copper-based molluscicide for zebra mussel suppression on nontarget species in Lake Minnetonka (Minnesota, USA). Specifically, we assessed changes in four fish species, a native mussel species, adult zebra mussels, chlorophyll-a concentrations (as a proxy for phytoplankton productivity), the zooplankton community, and the benthic invertebrate community before and after treatment. Chlorophyll- a concentration increased in both the treated and reference bays 1 and 4 d posttreatment. Non-target zooplankton community composition changed in both bays over the course of this study; zooplankton abundance and diversity initially decreased in the treated bay but gradually recovered and was back to pretreatment and reference bay levels after one year. We observed no significant differences in non-target benthic invertebrate abundance or diversity between the treated and reference bays, although abundance and diversity estimates were dynamic and uncertain. Among caged non-target organisms, copper bioaccumulation was higher in both mussel species than in fish, and among fish, was highest in fathead minnow ( Pimephales promelas ). These findings contribute to our understanding of the potential effects of copper-based pesticides on aquatic ecosystems and provide insights for zebra mussel management.

Minnesota↗

USGS2026

Assessing a low-dose copper treatment for dreissenid mussels: Effects on zebra mussel (Dreissena polymorpha) population

We conducted and evaluated a low-dose copper treatment (applied as EarthTec QZ) to suppress zebra mussel ( Dreissena polymorpha Pallas 1771) veliger abundance and settlement in a 66.3 ha bay in Lake Minnetonka (Hennepin County, MN) over a 3-y period. We maintained a mean (standard deviation [SD]) concentration of 83.0 (10.3) µg/L as copper over the 10-d treatment period, much lower than the maximum allowable 1 mg/L as copper. Veliger density was reduced from 6.0 veligers/L before treatment to 0.3 veligers/L following the treatment period. Posttreatment zebra mussel settlement was 1900 times lower in the treated bay compared to an untreated bay days after the treatment despite similar pretreatment veliger densities. Veliger density and settlement remained suppressed nearly 2 y following the treatment. Sampling for adult zebra mussels within the treated bay returned variable results but survival of caged adult zebra mussels indicated ~30% treatment-related mortality. Copper in surface waters returned to near pretreatment concentrations 90 d after treatment. Our study demonstrates that low-dose applications of a copper molluscicide can effectively reduce zebra mussel veliger densities and settlement.

Minnesota↗

USGS2026

Open water control of invasive mussels using benthic mats—Part 1, short-term infusion of carbon dioxide under a mat

This study compared the efficacy of a benthic mat alone with carbon dioxide infusion under a mat for killing Dreissena polymorpha (Pallas, 1771) (zebra mussel). Three sites were selected in Loon Lake, Sleeping Bear Dunes National Lakeshore, Benzie County, Michigan, for replication of reference, benthic mat, and carbon dioxide mat treatments. Within a site, three 4-meter (m) x 4-m plots were delineated for each treatment and a reference. Pretreatment samples were collected to estimate zebra mussel density and macroinvertebrate community composition in reference plots. Zebra mussels (about 360) from outside of the treatment plots were caged and placed in the plots before treatment. Benthic mats (4.25 m x 4.25 m; polyethylene with a vinyl coating) were anchored on the lake bottom with sandbags and weights. Carbon dioxide was infused under a mat of the same material to a maximum of 200 milligrams per liter (mg/L; pH=6.13) every 2–4 hours, for about 12 hours. Benthic and carbon dioxide mats were deployed for 5 days. One day after mat removal, we assessed mortality of resident and sentinel caged zebra mussels and macroinvertebrate community abundance and diversity in each plot. Average pH (as a proxy for carbon dioxide) under the carbon dioxide mats was between 6.38 and 6.80, equivalent to 170.5 and 103.0 mg/L carbon dioxide, respectively. In the posttreatment survey, few zebra mussels were observed in the benthic mat and carbon dioxide treatment plots compared to the reference plots; survival was lowest in the carbon dioxide plots. Mortality of sentinel caged mussels was greater than 80 percent in carbon dioxide treatments compared to mean mortalities of 20.6 percent and 12.7 percent in the benthic mat and reference plots, respectively. Macroinvertebrate community total abundance was lower in both mat treatments compared to reference plots, but diversity was comparable among all treatments. Our study demonstrated that carbon dioxide treatment near 200 mg/L could produce greater than 80-percent mortality of zebra mussels within 5 days. Refinement of the carbon dioxide mat and delivery system could increase spatial coverage of the treatment and broaden its use to other habitats.

Michigan↗

USGS2025

Using bioavailability modeling to refine copper treatments for zebra mussel control and better understanding risks to non-target species

Copper can be toxic to aquatic organisms at high concentrations and has been previously used successfully to control zebra mussels ( Dreissena polymorpha ). Because copper’s toxicity changes with water chemistry, using the same copper concentration in different waterbodies could yield different outcomes. We demonstrate how measuring water chemistry parameters and using the Biotic Ligand Model (BLM) and multiple linear regression (MLR) models can predict a suitable, site-specific copper concentration for management. We exposed zebra mussel adults and non-target organisms to varying concentrations of copper over 10 d in a mobile laboratory. We found that one non-target species, Daphnia magna , had a 50% chance of survival at 9.50 µg Cu/L (i.e., the 50% lethal concentration, LC 50 ), within our BLM-predicted range of 3.38–16.95 µg Cu/L LC 50 values. In the future, managers could make similar predictions and tailor their copper concentrations to their management goals. We also measured zebra mussel larvae mortality at copper concentrations ranging from 0 to 191 µg Cu/L. While those results were inconclusive, we present the results of this work as a foundation for future projects. Our study underscores the importance of developing site-specific copper concentration recommendations and demonstrates the potential utility of the BLM and MLR approaches for informing those recommendations.

Minnesota↗

USGS2025

Carbon dioxide infusion reduces invasive mussel biofouling (quagga mussel; Dreissena rostriformis bugensis) in raw water systems

The efficacy of carbon dioxide (CO 2 ) to reduce biofouling by quagga mussels ( Dreissena rostriformis bugensis ) in raw water systems was investigated. Experiments were conducted in a mobile laboratory located at Bureau of Reclamation Davis Dam Hydropower Facility and supplied with raw water from Lake Mohave, a reservoir of the Colorado River, USA. Incoming water was split between five chambers, each infused with CO 2 at a different rate. Raw reservoir water containing quagga larvae (veligers) was mixed with CO 2 chamber outflows and delivered to tanks containing settlement plates. Two experiments were conducted. Experiment 1 tested continuous infusion at target concentrations of 30, 45, 60, 75, and 100 mg L -1 dCO 2 (dissolved CO 2 ). Experiment 2 evaluated intermittent infusion schedules: 24 h on/off with 50, 75, and 100 mg L -1 dCO 2 and 24 h once/week with 100 mg L -1 dCO 2 . In Experiment 1, the percent settlement decreased with mean CO 2 concentration, ranging from 5.0% to < 0.1% in 28.7 and 92.2 mg L -1 dCO 2 , respectively. In Experiment 2, the efficacy of 24 h on/off at dCO 2 > 72.2 mg L -1 was similar to continuous treatment. The least effective treatment was 24 h once weekly at 95 mg L -1 dCO 2 . These results demonstrate that CO 2 treatment may reduce mussel biofouling in raw water systems.

Arizona, Nevada↗

USGS2024

Carbon dioxide toxicity to zebra mussels (Dreissena polymorpha) is dependent on water chemistry

Carbon dioxide (CO 2 ) is gaining interest as a tool to combat aquatic invasive species, including zebra mussels ( Dreissena polymorpha ). However, the effects of water chemistry on CO 2 efficacy are not well described. We conducted five trials in which we exposed adult zebra mussels to a range of CO 2 in water with adjusted total hardness and specific conductance. We compared dose–responses and found differences in lethal concentration to 50% of organisms (LC50) estimates ranging from 108.3 to 179.3 mg/L CO 2 and lethal concentration to 90% of organisms (LC90) estimates ranging from 163.7 to 216.6 mg/L CO 2 . We modeled LC50 and LC90 estimates with measured water chemistry variables from the trials. We found sodium (Na + ) concentration to have the strongest correlation to changes in the LC50 and specific conductance to have the strongest correlation to changes in the LC90. Our results identify water chemistry as an important factor in considering efficacious CO 2 concentrations for zebra mussel control. Additional research into the physiological responses of zebra mussels exposed to CO 2 may be warranted to further explain mode of action and reported selectivity. Further study could likely develop a robust and relevant model to refine CO 2 applications for a wider range of water chemistries. Environ Toxicol Chem 2024;00:1–8. Published 2024. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Environmental Toxicology and Chemistry↗

USGS2021

Concentration addition and independent action assessments of the binary mixtures of four toxicants on zebra mussel (Dreissena polymorpha) mortality

Researchers most often focus on individual toxicants when identifying effective chemical control agents for aquatic invasive species; however, toxicant mixtures may elicit synergistic effects. Synergistic effects may decrease required concentrations and shorten exposure durations for treatments. We investigated four toxicants (EarthTec QZ, Clam-Trol CT-2, niclosamide, and potassium chloride) that have been considered to control invasive zebra mussels ( Dreissena polymorpha Pallas, 1771). We determined the toxicity of binary mixtures for five different mixture ratios to adult mussels. We compared our observations to predictions made with concentration addition and independent action paradigms, as based on the dose-response relationships of each individual toxicant. We calculated the model deviation ratio for each combination at the LC 50 and LC 90 and identified three possible interactions: synergy, antagonism, and additivity. We found that mixtures of niclosamide and Clam-Trol CT-2 were the most synergistic while mixtures that included potassium chloride were largely additive to antagonistic. The use of synergistic combinations has potential to decrease the overall volume and concentration of individual toxicants required for dreissenid mussel treatments, thereby decreasing cost.

Aquatic Toxicology↗

USGS2021

Avoidance of cold-, cool-, and warm-water fishes to Zequanox® exposure

Zequanox® is a biopesticide registered by the U.S. Environmental Protection Agency (USEPA) and the Canadian Pest Management Regulatory Agency for controlling dreissenid mussels with demonstrated selective toxicity. However, some research has indicated that Zequanox may impact the body condition and survival of some non-target species. We assessed avoidance behaviors of two species of cold-, cool-, and warm-water fishes to Zequanox at the maximum concentration allowed by the USEPA label (100 mg/L as active ingredient). Naïve, juvenile fish (n = 30 per species) were individually observed in a two-flume choice tank through which Zequanox-treated and untreated water simultaneously flowed in an unobstructed arena. Individual fish were observed during an untreated control period (20 min) and two Zequanox-exposure periods (20 min each). Treatment was alternated between arena sides to account for potential side bias in the test subjects. Positional data were collected and tabulated in real time with EthoVision® XT software. Zequanox concentrations and water quality properties (pH, dissolved oxygen, temperature, and specific conductance) were monitored during each trial. Analysis of treatment response was performed using a contrast within linear mixed-effects models. Our results indicate that Brook Trout, Lake Trout, and Bluegill avoided Zequanox-treated water, Yellow Perch were indifferent to Zequanox-treated water, and Lake Sturgeon and Fathead Minnow were attracted to Zequanox-treated water. These results combined with existing species sensitivity literature may help inform resource managers of potential treatment-related risks.

Management of Biological Invasions↗

USGS2021

Use of carbon dioxide to prevent zebra mussel (Dreissena polymorpha) settlement and effects on native mussels (Order Unionoida) and benthic communities

We determined the efficacy of carbon dioxide (CO2) for preventing larval (veliger) settlement of the invasive zebra mussel (Dreissena polymorpha) and compared the response of native juvenile mussels and macroinvertebrate and periphyton communities to hypercapnia. A microcosm system of control (ambient Camb) and CO2 treatments [low PCO2 (Clow)=35,094 µatm, and high PCO2 (Chigh)=66,685 µatm)] was supplied with river water for 11 weeks. We measured zebra mussel settlement, juvenile native mussel (Lampsilis cardium and L. siliquoidea) growth and condition, and macroinvertebrate and periphyton community composition. Zebra mussels settled in all Camb tanks (n=4) from early July through August compared to one mussel in a CO2 treatment tank over the same period. Native mussel growth, tissue condition, and shell condition were reduced in CO2, particularly in the highest treatment. Benthic biomass (excluding zebra mussels) was similar in Camb and Clow but was reduced in Chigh. Macroinvertebrate community composition differed among treatments due to greater abundance of Chironomidae in Clow and Oligochaeata in Chigh. Periphyton abundance and richness increased in both CO2 treatments and was driven by increases in Cyanobacteria, Bacillariophyta and Chlorophyta. Our results indicate that efficacious levels of CO2 (~35,000 µatm PCO2) for reducing biofouling by dreissenids are tolerable to most freshwater benthic taxa. Chronic elevated CO2 infusion (>35,000 µatm PCO2) may reduce native mussel growth and condition and alter benthic invertebrate and periphyton community composition. Further refinement of CO2 application strategies is needed to determine minimal effective dose and duration to prevent dreissenid settlement and minimize effects on nontarget organisms.

Management of Biological Invasions↗

USGS2021

Field evaluation of an improved solid TFM formulation for use in treating small tributary streams

A solid lampricide formulation containing 23% 3-trifluoromethyl-4-nitrophenol (TFM) as the active ingredient was developed in the mid-1980s for use in small tributaries of dendritic streams during routine treatments to kill larval sea lamprey. This TFM bar formulation was designed to use a matrix of commercially prepared surfactants that would dissolve and slowly release their TFM payload over an 8–10-hour period. Although this formulation has proven useful, several matrix surfactants have been discontinued, resulting in the need to reformulate the TFM bar multiple times. Maintaining acceptable performance of the TFM bars while reformulating has been challenging. As a result, an experimental surfactant-free tableted TFM formulation was developed as a potential TFM bar replacement. Release of TFM from the tablet formulation was evaluated in four independent experimental applications made over varied substrates in three small tributaries of the Ford River (Delta County, Michigan). For each tributary, TFM release from tablets was modeled using exponential decay curves and the time required to release 25, 50, 75 and 90% of the TFM tablets was calculated. Differences in water-quality properties were detected using one-way analysis of variance tests, and post-hoc Tukey Honest Significant Difference tests were used to determine which water-quality properties differed among the trials. The influences of water temperature and water velocity on the release of TFM from the tablets has been previously reported; however, in this study substrate type also appeared to be an indicator of TFM release. In this study the performance of the TFM tablets appeared acceptable; however, it may be beneficial to conduct additional investigations to determine storage stability and handling durability as well as to identify potential challenges with mass production.

Report↗

USGS2019

Assessment of uncontained Zequanox applications for zebra mussel control in a Midwestern lake

Zebra mussels ( Dreissena polymorpha ) are invasive bivalves that have perturbed aquatic ecosystems within North America since their introduction in the mid-1980s. Control of zebra mussels has largely been restricted to raw water conveyance systems and associated infrastructures because few control products are registered for application in surface waters. The biopesticide Zequanox was registered in 2014 by the U.S. Environmental Protection Agency for controlling dreissenid mussels (zebra and quagga mussels ( Dreissena rostriformis bugensis ) in surface waters. Previous Zequanox applications in surface waters have used vertical impermeable-membrane barriers to contain treated water. Studies have indicated that uncontained applications may be successful if Zequanox suspensions of the correct viscosity are applied to facilitate the creation of stratified benthic treatment layer. In this study, Zequanox was applied to replicate 0.30-hectare plots within a small inland lake using a custom-engineered, boat-mounted application system to determine if uncontained Zequanox applications could be used to manage zebra mussel populations and to protect native unionid mussels within zebra mussel infested waters. To determine success, the following specific objectives were investigated during, 30 days after, and/or 1 year after Zequanox exposure: (1) evaluate Zequanox concentrations during exposure; (2) monitor water quality during and after exposure; (3) evaluate the mortality of zebra mussels that were caged within treatment zones during the exposures; (4) evaluate the densities of naturally occurring zebra mussels with treatment zones before and after Zequanox exposure; and (5) evaluate the survival, condition, and dreissenid infestation of native mussels in the treatment zones before and after Zequanox exposure. Zequanox rapidly dissipated from the treated plots, resulting in no appreciable treatment-related mortality of zebra mussels and insignificant impacts to water quality. Zequanox exposure-related impacts to native mussels were not observed.

Michigan↗

USGS2018

Exposure-related effects of Zequanox on juvenile lake sturgeon (Acipenser fulvescens) and lake trout (Salvelinus namaycush)

The environmental fate, persistence, and non-target animal impacts of traditional molluscicides for zebra, Dreissena polymorpha , and quagga, D. bugensis , mussel control led to the development of the biomolluscicide Zequanox. Although previous research has demonstrated the specificity of Zequanox, one study indicated sensitivity of salmonids and lake sturgeon, Acipenser fulvescens , following non-label compliant exposures to Zequanox. This study was conducted to evaluate sublethal and lethal impacts of Zequanox exposure on juvenile lake sturgeon and lake trout, Salvelinus namaycush , following applications that were conducted in a manner consistent with the Zequanox product label. Fish were exposed to 50 or 100 mg/L of Zequanox as active ingredient for 8 h and then held for 33 d to evaluate latent impacts. No acute mortality was observed in either species; however, significant latent mortality (P < 0.01, df = 9; 46.2%) was observed in lake trout that were exposed to the highest dose of Zequanox. Statistically significant (P < 0.03, df = 9), but biologically minimal differences were observed in the weight (range 20.17 to 21.49 g) of surviving lake sturgeon at the termination of the 33 d post-exposure observation period. Statistically significant (P < 0.05, df = 9) and biologically considerable differences were observed in the weight (range 6.19 to 9.55 g) of surviving lake trout at the termination of the 33 d post-exposure observation period. Histologic evaluation of lake trout gastrointestinal tracts suggests that the mode of action in lake trout is different from the mode of action that induces zebra and quagga mussel mortality. Further research could determine the sensitivity of other salmonid species to Zequanox and determine if native fish will avoid Zequanox treated water.

Management of Biological Invasions↗

USGS2018

Effects of temperature and exposure duration on four potential rapid-response tools for zebra mussel (Dreissena polymorpha) eradication

Zebra mussels (Dreissena polymorpha) have continued their spread within inland lakes and rivers in North America despite diligent containment and decontamination efforts by natural resource agencies and other stakeholders. Identification of newly infested waterways by early detection surveillance programs allows for rapid response zebra mussel eradication treatments in some situations. Previous eradication treatments have occurred over a broad range of water temperatures which have influenced the efficacy of molluscicides. Natural resource managers will benefit from knowledge regarding the impacts of water temperature and exposure duration on the toxicity of molluscicides to zebra mussels. In particular, temperature specific data are needed to inform the selection of an effective molluscicide and the proper dose that will induce 100% zebra mussel mortality. We evaluated the influences of temperature and exposure duration on the toxicity of two U.S. EPA-registered (EarthTec QZ and Zequanox) and two nonregistered (niclosamide and potassium chloride) molluscicides to zebra mussels at water temperatures of 7, 12, 17, and 22 °C. Our results indicate that treatment options for the eradication of zebra mussels in waters ≤ 12 °C include 336 h or longer treatments with EarthTec QZ and KCl as well as treatments with niclosamide ≥ 24 h in duration. In waters ≥ 17 °C, multiple toxicant and exposure duration combinations are potentially effective for zebra mussel eradication. On-site or in situ zebra mussel bioassays are a useful tool for the evaluation of treatment efficacy.

Management of Biological Invasions↗

USGS2017

Use of alternating and pulsed direct current electrified fields for zebra mussel control

Alternatives to chemicals for controlling dreissenid mussels are desirable for environmental compatibility, but few alternatives exist. Previous studies have evaluated the use of electrified fields for stunning and/or killing planktonic life stages of dreissenid mussels, however, the available literature on the use of electrified fields to control adult dreissenid mussels is limited. We evaluated the effects of sinusoidal alternating current (AC) and 20% duty cycle square-wave pulsed direct current (PDC) exposure on the survival of adult zebra mussels at water temperatures of 10, 15, and 22 °C. Peak voltage gradients of ~ 17 and 30 Vp/cm in the AC and PDC exposures, respectively, were continuously applied for 24, 48, or 72 h. Peak power densities ranged from 77,999 to 107,199 µW/cm 3 in the AC exposures and 245,320 to 313,945 µW/cm 3 in the PDC exposures. The peak dose ranged from 6,739 to 27,298 Joules/cm 3 and 21,306 to 80,941 Joules/cm 3 in the AC and PDC exposures, respectively. The applied power ranged from 16.6 to 68.9 kWh in the AC exposures and from 22.2 to 86.4 kWh in the PDC exposures. Mortality ranged from 2.7 to 92.7% in the AC exposed groups and from 24.0 to 98.7% in PDC exposed groups. Mortality increased with corresponding increases in water temperature and exposure duration, and we observed more zebra mussel mortality in the PDC exposures. Exposures conducted with AC required less of a peak dose (Joules/cm 3 ) but more applied power (kWh) to achieve the same level of adult zebra mussel mortality as corresponding PDC exposures. The results demonstrate that 20% duty cycle square-wave PDC requires less energy than sinusoidal AC to inducing the same level of adult zebra mussel mortality.

Management of Biological Invasions↗

USGS2016

Development of targeted delivery techniques for Zequanox®

The effects of water temperature and concentration on the physical characteristics of Zequanox®, a dead-cell spray-dried powder formulation of Pseudomonas fluorescens (strain CL145A) used for controlling invasive dreissenid mussels (zebra mussel, Dreissena polymorpha, and quagga mussel, Dreissena bugensis), were investigated to determine optimal temperature-specific concentrations and delivery techniques for use during open-water subsurface Zequanox applications. Temperature-controlled laboratory tests evaluated viscosity, settling, stratification, and buoyancy of various concentrations of Zequanox suspension in water to select an optimal target viscosity for Zequanox applications. A two-step linear regression procedure was used to create a temperature-specific Zequanox prediction model from the viscosity data. The prediction model and subsurface application techniques were validated by conducting three independent outdoor pond trials at temperatures of ~9, 14, and 20°C. During these outdoor trials, subsurface applications of Zequanox at concentrations predicted by the model were performed and water samples were collected at varying depths and analyzed via spectroscopy to determine Zequanox concentration and dispersion. Although the predicted Zequanox concentrations and delivery techniques used resulted in successfully maintaining lethal Zequanox concentrations in the bottom 7.5 cm of the water column for the duration of the exposure, a revised prediction model is also provided for more accurately selecting temperature-specific Zequanox concentrations.

Report↗

USGS2016

Efficacy of spray –Dried Pseudomonas fluorescens, strain CL145A (Zequanox®), for controlling Zebra Mussels ( Dreissena polymorpha ) within Lake Minnetonka, MN enclosures

The efficacy of whole water column and subsurface applications of the biopesticide Zequanox®, a commercially prepared spray-dried powder formulation of Pseudomonas fluorescens (strain CL145A), were evaluated for controlling zebra mussels (Dreissena polymorpha) within 27-m2 enclosures in Lake Minnetonka (Deephaven, Minnesota). Five treatments consisting of (1) two whole water column Zequanox applications, (2) two subsurface Zequanox applications, and (3) an untreated control were completed on each of three independent treatment days during September 2014. The two types of samplers used in the study were (1) type 1 samplers, which were custom built multi-plate samplers (wood, perforated aluminum, and tile substrates) that were placed into Robinson’s Bay in June of 2013 to allow for natural colonization by zebra mussels, and (2) type 2 samplers, which consisted of zebra mussels adhering to perforated aluminum trays that were placed into mesh containment bags. One day prior to treatment, three individual samplers of each type were distributed to test enclosures and exposed to a randomly assigned treatment. Sampling to determine the zebra mussel biomass adhering to type 1 samplers and the survival assessments for zebra mussels contained in type 2 samplers were completed ~40 days after exposure. The zebra mussel biomass adhering to type 1 samplers and the survival of zebra mussels contained in type 2 samplers were significantly less in groups treated with the highest Zequanox concentrations and in groups that received whole water column applications than comparable groups treated with lower Zequanox concentrations and subsurface applications. However, standardization of biomass and survival results to the amount of Zequanox applied showed that the lower concentrations and subsurface applications were more cost efficient, with respect to product used, at reducing zebra mussel biomass and for inducing zebra mussel mortality. Although the subsurface application methods and lower treatment concentrations were more cost efficient, biological significance and management goals should be evaluated prior to selecting the application method. Development and refinement of additional application techniques may improve the utility of the subsurface Zequanox applications.

Report↗

USGS2015

Response of Bighead Carp and Silver Carp to repeated water gun operation in an enclosed shallow pond

The Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix are nonnative species that pose a threat to Great Lakes ecosystems should they advance into those areas. Thus, technologies to impede Asian carp movement into the Great Lakes are needed; one potential technology is the seismic water gun. We evaluated the efficacy of a water gun array as a behavioral deterrent to the movement of acoustic-tagged Bighead Carp and Silver Carp in an experimental pond. Behavioral responses were evaluated by using four metrics: (1) fish distance from the water guns ( D ); (2) spatial area of the fish's utilization distribution (UD); (3) persistence velocity ( V p ); and (4) number of times a fish transited the water gun array. For both species, average D increased by 10 m during the firing period relative to the pre-firing period. During the firing period, the spatial area of use within the pond decreased. Carp were located throughout the pond during the pre-firing period but were concentrated in the north end of the pond during the firing period, thus reducing their UDs by roughly 50%. Overall, V p decreased during the firing period relative to the pre-firing period, as fish movement became more tortuous and confined, suggesting that the firing of the guns elicited a change in carp behavior. The water gun array was partially successful at impeding carp movement, but some fish did transit the array. Bighead Carp moved past the guns a total of 78 times during the pre-firing period and 15 times during the firing period; Silver Carp moved past the guns 96 times during the pre-firing period and 13 times during the firing period. Although the water guns did alter carp behavior, causing the fish to move away from the guns, this method was not 100% effective as a passage deterrent.

North American Journal of Fisheries Management↗

USGS2015

Efficacy of Pseudomonas fluorescens (Pf-CL145A) spray dried powder for controlling zebra mussels adhering to test substrates

A mobile bioassay trailer was used to assess the efficacy of Pseudomonas fluorescens ( Pf -CL145A) spray dried powder (SDP) formulation for controlling zebra mussels ( Dreissena polymorpha ) from two midwestern lakes: Lake Carlos (Alexandria, Minnesota) and Shawano Lake (Shawano, Wisconsin). The effects of SDP exposure concentration and exposure duration on zebra mussel survival were evaluated along with the evaluation of a benthic injection application technique to reduce the amount of SDP required to induce zebra mortality. Groups of zebra mussels were collected from each lake and allowed to adhere to test substrates for at least 15 days before exposure to SDP. Two independent trials were completed at each lake: (1) a whole water column (WWC) application trial was used to evaluate the effects of SDP exposure concentration and exposure duration on zebra mussel survival; and (2) a benthic injection (BI) application trial in which the SDP was injected into the test tanks to determine the efficacy of a benthic injection application technique to reduce the amount of SDP required to induced zebra mussel mortality. Three exposure durations (6, 9, and 12 hours) were evaluated in the WWC trials and a 12-hour exposure duration was evaluated in the BI trials. All trials contained zebra mussels which were removed at the completion of each exposure duration, consolidated into wire mesh cages, and held in the lake for approximately 30 days before being assessed for survival. For all trials, treatment was assigned to each test tank according to a randomized block design ( n = 3 test tanks per treatment). The treatment groups included (1) an untreated control group, (2) a group that received an application of 50 milligrams of SDP per liter (mg SDP/L), and (3) a group that received an application of 100 mg SDP/L. During the BI trials, SDP was administered to achieve the desired exposure concentration in the bottom 50 percent (175 L) of the test tank. All exposure concentrations are reported as active ingredient. Approximately 30 days after exposure, zebra mussels were sorted into live and dead, and enumerated. Mean survival of zebra mussels in control treatments exceeded 95 percent. Mean survival of zebra mussels in the Lake Carlos WWC SDP-treated groups ranged from 0.5 to 2.1 percent and when compared at the same exposure duration, no difference was detected in survival between the 50 and 100 milligrams per liter (mg/L) treatment groups. Similarly, mean survival of zebra mussels in the Shawano Lake WWC SDP-treated groups ranged from 2.0 to 12.6 percent and when compared at the same exposure duration, no difference was detected in survival between the 50- and 100-mg/L treatment groups. Mean survival of zebra mussels in the Lake Carlos BI trial SDP-treated groups did not differ ( p = 0.93) and was 18.1 and 18.0 percent in the 50- and 100-mg/L treatment groups, respectively. Mean survival of zebra mussels in the Shawano Lake BI trial SDP-treated groups differed ( p < 0.01) and was 2.9 and 0.9 percent in the 50- and 100-mg/L treatment groups, respectively. Survival of zebra mussels assigned to the SDP-treated groups in the Lake Carlos WWC trial (12-hour exposure duration) differed from the survival of zebra mussels assigned to the SDP-treated groups in the Lake Carlos BI trial; however, after modification of the BI application technique, no difference ( p = 0.22) was detected between the survival of zebra mussel in the Shawano Lake WWC (12-hour exposure duration) and BI trials.

Minnesota, Wisconsin↗