P L A T F O R M A B S T R A C T S (in order of presentation)

Thursday 9:30 AM	Conductivity Limits Survival and Growth of the New Zealand Mud Snail from the Upper Owens River, California David B. Herbst, Michael T. Bogan, and Robert A. Lusardi Sierra Nevada Aquatic Research Laboratory, University of California, Mammoth Lakes, CA 93546 herbst@lifesci.ucsb.edu 1. The New Zealand Mud Snail (NZMS) is an invasive exotic species of aquatic snail that is becoming widespread in inland and coastal waters of the western United States. NZMS densities can exceed 300,000 per square meter, and as such they may consume a large fraction of available algae food resources, competing with and displacing native invertebrates. The range of the NZMS is rapidly expanding in the western United States, but little is understood about the conditions that permit snails to thrive and the types of habitats that are most vulnerable to invasion. 2. Observational studies of the NZMS invasion on the Upper Owens River, California, suggested that the snail may be limited to certain water chemistry conditions, so experimental studies of growth and survival were undertaken to evaluate survival and growth as a function of mineral content of the water. 3. Juvenile snails were collected from the Upper Owens River and reared in dilutions of natural river water adjusted to 10, 50, 100, 200 and 300 µS conductivity. Experiments were also conducted with newborn clones raised in river water dilutions ranging from 25 to 200 µS to examine mortality and growth at this sensitive stage of development. In addition, calcium-free artificial river water was prepared at 200 µS to test for the independent effect of limitation of this mineral ion required for shell-building. 4. Low survival and no growth was found at and below 25 µS and significant graded reductions in growth occurred as river water was diluted from 300 to 50 µS conductivity. Growth was also inhibited in calcium-free artificial water compared to the same conductivity of natural river water, indicating that lack of this mineral impedes development. Even though growth was reduced in calcium-free media, it was lower still in 50 µS river water, suggesting that, even with calcium, dilute water may inhibit growth through osmotic stress and/or imbalance in other ions. 5. These results show that the distribution and productivity of the NZMS may be restricted by ecophysiological constraints. The chemistry of water may confine invasion of the NZMS to conductivities above 25 µS, and produce physiological debilitation over the range 25 to 200 µS that would place snails at an energetic disadvantage in competition for food or space with native benthic organisms. 6. This paradigm provides a framework for predictive modeling of the potential vulnerability of streams and rivers to invasion, a mechanism for understanding where colonization and expansion has occurred, and potential controls on NZMS infestations.
Thursday 9:50 AM	Genetic Diversity Within and Among Worldwide Populations of NZMS Mark F. Dybdahl, Devin Drown, and Alison Fromme School of Biological Sciences, Washington State University, Pullman, WA 99164 dybdahl@wsu.edu The success of exotic species depends on their ability to spread across novel environments. There are two broad mechanistic explanations: evolutionary adaptation to diverse environments by genetically diverse founding populations, or phenotypic plasticity that leads to fitness across a broad range of environments. We used genetic marker studies of worldwide populations of NZMS (Potamopyrgus antipodarum) to determine the genetic diversity of invasive populations, and to determine whether the invasive genotypes are genetically different from NZMS populations in the native range. We confirm previous results using both allozyme and microsatellite genetic markers that most worldwide populations lack genetic diversity, with the exception of Australia. We show that invasive genotypes are genetically distinct from native range genotypes because they arise from only two of the five major groups of NZMS in the native range. Finally, we show that invasive clones, which have spread widely in Europe and North America, have also spread widely in clonally diverse Australian populations. However, neither these invasive genotypes nor any other genotypes have spread widely in the native range. Taken together, these results suggest that invasive genotypes of NZMS may differ from native range genotypes in terms of phenotypic plasticity.
Thursday 10:10 AM	Invasion and Production of New Zealand Mudsnails in the Colorado River, Glen Canyon, AZ Kathrine E. Behn^1 (kbehn@uwyo.edu), Wyatt F. Cross^1 (wcross@uwyo.edu), Robert O. Hall^1 (bhall@uwyo.edu), Emma J. Rosi-Marshall^2 (erosi@luc.edu), and Theodore A. Kennedy^3 (tkennedy@usgs.gov) ^1Zoology & Physiology, University of Wyoming, Laramie, WY 82071; ^2Biology, Loyola University Chicago, Chicago, IL 60626; ^3USGS Grand Canyon Monitoring and Research Center, Flagstaff, AZ 86001 New Zealand mudsnails (Potamopyrgus antipodarum) have invaded many rivers in the Western U.S., yet little is known about their production and capacity to sequester carbon. We examined size-specific growth rates, biomass, and secondary production of mudsnails in the Glen Canyon reach of the Colorado River. We measured in situ growth rates using cages, and compared our estimates with those from other systems. Instantaneous growth rates ranged from 0.001 to 0.023 day^-1, and significantly declined with body size (r^2 = 0.55, p<0.001). Growth rates were ~3 times lower than those measured in warmer Yellowstone rivers, but faster than rates measured in their native habitats in New Zealand. These moderate growth rates are likely due to temperatures (average ~11 deg C) that are warmer than New Zealand and colder than geothermal Yellowstone rivers. Since 1995, biomass of mudsnails in Glen Canyon has increased from 0 to ~15 g m^-2, which represents an increase in production from 0 to ~44 g m^-2 y^-1 (quantified using the instantaneous growth method).  In this tailwater ecosystem, which has stable temperatures throughout the year due to hypolimnetic releases, mudsnails have high production and may sequester a large portion of the potential energy otherwise available for higher trophic levels.
Thursday 10:45 AM	Invertebrate abundance and assemblage changes following invasion of New Zealand Mud Snail in the Green River downstream from Flaming Gorge Dam Eric C. Dinger (dinger@cc.usu.edu) and Mark R. Vinson (aqua@cc.usu.edu) National Aquatic Monitoring Center, Department of Watershed Science, Utah State University, Logan, Utah 84322-5210 The discovery of New Zealand Mud Snails (NZMS, Potamopyrgus antipodarum) in the Green River downstream from Flaming Gorge Dam in September 2001 led to an assessment of the their ecological impacts. Using a long-term benthic macroinvertebrate dataset, 7 years pre- and 6 years post-invasion sampling, we analyzed changes in dominant invertebrate assemblage abundances following NZMS invasion. NZMS densities were highest in eddy habitats (> 1300 individuals per meter squared) and lowest in riffle and run habitats (ca. 70 individuals per meter squared). Across all habitats, mean total invertebrate densities were 26% lower than mean pre-invasion densities. However, densities changes within specific habitat types (eddies, riffles, runs) were muted, with the largest decrease observed in run habitats. Changes in other invertebrate abundances included declining numbers of Ephemeroptera and Diptera in riffle habitats and increasing numbers of Diptera in eddy habitats. Ephemeroptera and Amphipoda abundances were inversely related to NZMS abundances. When NZMS abundances were high, these groups were depressed, suggesting NZMS may be outcompeting these organisms which are important food sources for the blue-ribbon trout fishery. Other observed changes in the study period included increasing diversity of aquatic insects, especially Ephemeroptera. We attribute these changes to the more natural hydrograph operations of Flaming Gorge Dam since 1994, rather than responses to NZMS.
Thursday 11:05 AM	Interactions between invasive and native species: Mechanisms and results of competition between benthic invertebrates Valance E. F. Brenneis (vebrenneis@ucdavis.edu) and Beverly C. Ajie (bcajie@ucdavis.edu) Department of Environmental Science and Policy, University of California, One Shields Avenue, Davis, CA 95616 Understanding the behaviors underlying competitive abilities and the outcomes of species interactions across a range of densities are fundamental questions in ecology. These issues have taken on new importance in the field of invasion biology as competition between native and exotic species may result in species loss and community alteration. We investigated mechanisms influencing competitive effects of two ecologically similar snail species, Physa acuta and the highly invasive New Zealand mudsnail (Potamopyrgus antipodarum, (NZMS), on a native caddisfly, Brachycentrus sp. Using a combination of data from behavioral observations of foraging, measures of resource consumption, and growth, we attempted to describe both the processes by which competition between invertebrate grazers occurs and the resulting effects. Overall, physid snails appear to exert the strongest effects on both other species and on themselves, primarily through high levels of foraging. Intraspecific competition between physids results in reduced per capita algal consumption, reduced uptake of d^15N, and reduced growth at higher conspecific densities. Physids have negative effects on the d^15N uptake of NZMS and mixed effects on NZMS growth that are consistent with the hypothesis that the impacts of physids on NZMS are density dependent. We found little evidence for an effect of intra or interspecific competition on Brachycentrus larvae. Notably, NZMS show no evidence of intraspecific competition. This final result may help explain the ability of NZMS to achieve much higher densities than physid snails, as they show no evidence of intraspecific competition at densities similar to those observed in an invaded stream.
Thursday 11:25 AM	Assessing the Distribution, Density, and Potential Impacts of Potamopyrgus antipodarum on Resident Aquatic Invertebrates in the Lower Mokelumne River, California Katy Washburn^1(katywashburn@hotmail.com), Daniel Kratville^2 (dkratville@dfg.ca.gov), and Joseph Merz^3 (jmerz@ebmud.com) ^1Biology Department, California State University, Sacramento, CA; ^2Pacific Marine Fisheries Commission, California Department of Fish and Game, Sacramento, CA; ^3East Bay Municipal Utility District, Fish and Wildlife Office, Lodi, CA 95240 The recent invasion of the New Zealand mudsnail (Potamopyrgus antipodarum) in the lower Mokelumne River, California, provides a unique opportunity to examine effects of an invasive species on resident macroinvertebrates with pre and post invasion comparisons. We examined potential impacts of the New Zealand mudsnail (NZMS) population on resident macroinvertebrates by assessment of 1) the distribution and density of NZMS and associated resident macroinvertebrate assemblages; 2) relationships between instream environmental parameters (ie. depth, velocity, substrate etc.), NZMS and associated resident macroinvertebrate assemblages; and 3) relationships between NZMS density and resident macroinvertebrate density and diversity over spatial and temporal ranges. We sampled the benthos at 11 sites (gravel bars) along a 10-kilometer stretch of the lower Mokelumne River between July and December 2006 to make spatial comparisons. The 2006 post-invasion data was also compared to pre-invasion data collected between 1996 and 2002 (baseline data). Densities of NZMS and native macroinvertebrate assemblages varied seasonally. NZMS density significantly correlated with season, location, and water depth. NZMS densities were also significantly related to whether or not there was a major flow change within the four weeks prior to each sampling. Macroinvertebrate diversity significantly decreased in four of the six sample sites after the invasion. These statistically significant relationships involving NZMS densities are consistent with previous studies and suggest important management implications.
Thursday 1:00 PM	Detection and Monitoring New Zealand Mudsnail in the Putah South Canal Ken W. Davis (ken@creekman.com) Wildlife Survey & Photo Service, 2443 Fair Oaks Blvd. #209, Sacramento, CA 95825 The Putah South Canal was constructed fifty years ago as part of the Solano Project which provides water for agriculture, industry, several cities in Solano County, and three military installations. The canal is 33 miles long and terminates in a reservoir near Cordelia. In late 2003 New Zealand Mudsnails, P. antipodarum, were found in Putah Creek, approximately four miles above the headgates for the canal. Solano County Water Agency, the managing water authority, wanted to prevent movement of the invasive snail in the canal and prevent the entry of P. antipodarum into other waterways. The canal crosses several small creeks, two known to support annual runs of steelhead, Oncorhynchus mykiss. Protocol for monitoring for P. antipodarum in a cement-lined canal did not exist when the initial population was discovered in Putah Creek. The author developed several survey techniques which have proven effective. Monitoring the canal presents several obstacles including flow regime, limited access in some areas, large amounts of sediment, and a condition in some months when P. antipodarum are covered with copious amounts of detritus. This presentation will focus on the techniques used to monitor the relative density and movement of P. antipodarum in the Putah South Canal.
Thursday 1:20 PM	Probabilities of contamination of New Zealand mudsnails (Potamopyrgus antipodarum) on recreational boat trailers in lakes and estuaries in coastal Oregon Chi-Chang Liu (chi-chang.liu@oregonstate.edu)and Selina Heppell (selina.heppell@oregonstate.edu) Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 97331 The New Zealand mudsnail (NZMS), Potamopyrgus antipodarum, has been recently found in multiple water bodies along the Oregon coast. The leap-frog pattern of invasion suggests that it was facilitated by human vectors of dispersal. Dispersal models to predict invasive species spread often over-estimate or ignore the probability of contamination (Pc), which may be a critical parameter for species that are dispersed through human activity. Of the possible vectors, contamination of boat trailers is one of the most likely mechanisms for secondary dispersal of NZMS spread. We conducted field experiments in NZMS- infested rivers and lakes near the Oregon coast to determine the probability of contamination of NZMS on recreational boat trailers. Our response variable was the presence/absence of NZMS on the trailer immediately after the trailer left the water. Pc of NZMS ranged between 0.05 and 0.35 in our study. We also estimated the abundance of NZMS in the area surrounding the boat ramps, and the percent substrate type on and around the boat ramps. Pc was not tightly correlated with density of NZMS on or around the boat ramps, but was related to the presence of aquatic vegetation and debris attached to the boat trailers. This information may be used in dispersal models, and applied in public education and resource management in order to reduce the spread of this invasive species.
Thursday 1:40 PM	Preventing the Upstream Movement of New Zealand Mudsnails By Treating Surfaces with Copper and Copper-Based Compounds: Preliminary Results Christopher A. Myrick Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, CO 80523-1474 Ph: (970) 491-5657 Fax: (970) 491-5091 Chris.Myrick@colostate.edu New Zealand mudsnails (Potamopyrgus antipodarum) actively disperse in both up- and downstream directions following their introduction to a novel environment. The downstream movements are particularly difficult to control because New Zealand mudsnails can drift in the water column. However, when moving upstream, New Zealand mudsnails crawl over the substrate. This mode of dispersal could allow mudsnails to invade upstream areas through irrigation canals, pipes, and other manmade structures. Anecdotal evidence from a Colorado aquaculture facility suggests that lining these potential invasion routes with copper effectively prevents these upstream movements. In order to test this observation under controlled laboratory conditions, New Zealand mudsnail responses to four copper-based surface treatments (copper sheet, copper mesh, and cupric-oxide based ablative and non-ablative antifouling paints) are being quantified using a digital motion analysis system. Preliminary results from these ongoing experiments, including substrate-related differences in New Zealand mudsnail movement rates, velocities, and distances will be presented. Results from parallel tests on Physid snails will also be presented.
Thursday 2:00 PM	Chemical Control of New Zealand Mud Snail Potamopyrgus Antipodarum in California Water Conveyance Canals Brian Finlayson^1 (bfinlays@ospr.dfg.ca.gov), Joel Trumbo^1(jtrumbo@ospr.dfg.ca.gov), and Dan Waligora^2 (dwaligor@ospr.dfg.ca.gov) ^1California Department of Fish and Game, Pesticide Investigations Unit, 1701 Nimbus Road, Rancho Cordova, CA 95670; ^2California Department of Fish and Game Aquatic Toxicology Laboratory, 9300 Elk Grove-Florin Road, Elk Grove, CA 95624 Laboratory toxicity tests were conducted with several chemicals in order to determine the minimum effective doses (MEDs) required to kill New Zealand mud snails in water conveyance canals. Copper sulfate, the molluscicide product Bayluscide^® (niclosamide) and potassium permanganate were tested using 4- and 8-hour exposure intervals. Bayluscide^® and copper sulfate were found to be very effective with 4- and 8- hour MEDs of 8.2 and 1.9 mg/L (measured as niclosamide) and 11.9 and 6.1 mg/L (measured as copper), respectively. Potassium permanganate was much lower in toxicity with 4- and 8-hour MEDs of 396 and 300 mg/L. Copper sulfate and Bayluscide® were retested with potassium chloride (believed to slow the closure of the operculum). These tests revealed little evidence of the potassium chloride increasing the toxicity of either compound. Control strategies based on laboratory results will be tested under field conditions in the Putah South Canal.
Thursday 2:20 PM	A two-step approach for controlling New Zealand mudsnails (Potamopyrgus antipodarum) in fish hatcheries Jordan Nielson^1 (jnielson@vandals.uidaho.edu), Christine Moffitt^1 (cmoffitt@uidaho.edu), and Barnaby Watten^2 (bwatten@usgs.gov) ^1USGS Cooperative Fish and Wildlife Research Unit, Department of Fish and Wildlife Resources, University of Idaho, Moscow, ID, 83844 -1136, (208) 885-7139; ^2USGS Leetown Science Center, 11649 Leetown Road, Kearneysville,WV 25430 (304) 724-4425 Infestations of New Zealand mudsnails (NZMS) at fish hatcheries limit or restrict the options for stocking hatchery-reared fish because of the risks of spreading snails to uninfested locations Reliable and environmentally friendly methods for removing NZMS from source waters are needed by hatchery managers so as to create an environment for snail–free fish production and/or transportation. We are evaluating a two-step control method for the piped spring water supply of the Hagerman National Fish Hatchery (HNFH) in Idaho (USA) that involves separation of snails from water with a hydrocyclone followed by carbonation treatment of the waste (snail) stream generated. Preliminary tests of the hydrocyclone indicate that complete separation of adult, juvenile, and neonate NZMS is likely possible. Further testing will occur during the summer of 2007. Aquatic mollusk species appear to be intolerant to forced increases in dissolved carbon dioxide concentrations (DC) especially at elevated pressures given its effect on water, blood, and hemolymph pH as well as total dissolved gas pressure. Increases in the latter can induce gas bubble trauma. We have tested NZMS at 100 kPa CO2 at 8°, 15°, and 20° C, as well as atmospheric pressure saturations of CO2 and found that both levels of CO2 tension are effective in killing snails. Probit model derived LT100 values demonstrate mortality rates rise with increasing water temperature. We propose that the combination of hydrocyclone filtration and CO2 treatment of the waste stream will offer a way to provide a safe and economical source of snail free water at infested hatcheries.
Thursday 2:40 PM	Controlling the Translocation of New Zealand Mudsnails in Angling Boots Ken W. Davis (ken@creekman.com) Wildlife Survey & Photo Service, Wildlife Survey & Photo Service, 2443 Fair Oaks Blvd. #209, Sacramento, CA 95825 When New Zealand Mudsnails, Potamopyrgus antipodarum, were discovered in Putah Creek in 2003, the suspected vector were the lace-up boots worn by wading anglers and biologists. During the same period, no accepted treatment to remove P. antipodarum from boots was readily available. Suggested applications included hot water, freezing, chlorine bleach, Formula 409, and grapefruit seed extract. The author’s initial 2004 study of 36 waders in Putah Creek confirmed that P. antipodarum were carried in wading boots. A follow-up study by the California Department of Fish & Game examined the effects of various chemicals on wading gear, the effectiveness of some chemicals on P. antipodarum in laboratory conditions, and the effectiveness of several chemicals on P. antipodarum after the snails were picked up in angling boots in Putah Creek. That work was expanded by the author with a grant from Patagonia and the Wildlife Survey & Photo Service. In November 2005, eighty-seven anglers volunteered to wade a section of Putah Creek that had P. antipodarum densities above 200,000 individuals/sq.m., and allowed their boots to be treated randomly with three chemicals. Troublesome results of the Patagonia study and retesting revealed a potential flaw in the protocol originally used in the DFG field study. This presentation will focus on the history of boot treatments, current research being conducted, and suggestions for additional studies to prevent the translocation of New Zealand mudsnails in angling boots.
Thursday 3:20 PM	Mudsnails Invade the ‘Bu: A Case Study in Institutional Responses to Invasions Miwa Tamanaha (MTamanaha@waterboards.ca.gov) and Jack Topel (JTopel@waterboards.ca.gov) Santa Monica Bay Restoration Commission, CA In May 2006, New Zealand mudsnails, Potamopyrgus antipodarum, were discovered during routine macroinvertebrate monitoring in Malibu Creek, located in the Santa Monica Mountains of Southern California. We describe the initial discovery of P. antipodarum, and agency efforts to determine the extent of and response to the invasion. We also discuss the need to manage the threat invasives pose in a more holistic manner, rather than applying a species-by-species approach. Finally, we present a brief overview of invasive species management actions and discuss some of the challenges to implementation. Agencies were able to coordinate and implement a rational, rapid response to the invasion including (1) a “mudsnail summit” to develop coordination between agencies, (2) a 44-site survey to determine the extent of the invasion, (3) a literature review on mudsnails, and (4) the development of a unified education and outreach effort. It is clear that the ability of agencies to coordinate their actions, efforts, and resources is a key factor in the rapid response to an invasion. Now that P. antipodarum has become established in the Malibu Creek watershed, continued management will require on-going monitoring, education, and research. This episode has made it clear that managing invasives post- establishment is inadequate. The investment of time and resources necessary to implement on-going monitoring, education and control measures on a species-by-species basis is neither effective, nor efficient. Management must begin with stopping potential invasions before they occur, specifically by managing the pathways of introduction. Additionally, recognizing that despite our best efforts invasions will occur, we must make early detection of invasives an integrated part of habitat monitoring and restoration efforts.
Thursday 3:40 PM	Rapid response planning for NZMS – worth its weight in ink? Paul Hemowitz (paul_heimowitz@fws.gov) Aquatic Invasive Species and Research, US Fish and Wildlife Service, Portland, OR Although most aquatic nuisance species (ANS) programs emphasize the value of preventing new introductions, rapid response preparedness is a critical second line of defense. The draft National Management and Control Plan for the New Zealand mudsnail, Potamopyrgus antipodarum, (NZMS) notes that geographic-specific rapid response plans can facilitate quick action, including attempts to eradicate a new population. Some states and regions have developed general ANS rapid response plans that cover a broad range of species and waterbodies, and in fact the draft national NZMS plan endorses state-level rapid response plans. However, a broad-scale approach may not be sufficient to truly expedite NZMS response. This paper describes the development of rapid response plan for zebra mussels in the Columbia River Basin as a potential model for watershed-specific NZMS plans. It examines the advantages and disadvantages of planning for NZMS rapid response at a fine-scale (e.g., a specific tributary stream within a state) vs. a large scale (e.g., a major river that connects multiple states and/or countries). It describes a number of factors that affect whether the plan will prove useful if ever activated. Developing a series of watershed-specific NZMS rapid response plans for un-infested waters of the United States would represent a considerable investment of resources, with the added irony that parallel NZMS prevention programs strive to forever keep such plans on ice. However, that investment must be compared to what would be at stake if inadequate response planning eliminated an opportunity to contain a new invasion.

P O S T E R A B S T R A C T S (in alphabetical order by presenter)

Evolutionary consequences of a rapidly evolving invasive species to the viability of a native threatened species

David C. Richards (drichards@ecoanalysts.com) and Tristan Arrington (tarrington@ecoanalysts.com)

EcoAnalysts Inc., Center for Aquatic Studies, Bozeman, MT 59715 (406) 522-7350

Invasive species coupled with habitat deterioration can have both direct and indirect effects on the evolution and possibly extinction of native species. In the regulated and impaired mid-Snake River ecosystem, the prolific, invasive, New Zealand mudsnail (NZMS) is considered to be the major risk to the viability of the remaining fragmented, genetically-restricted, metapopulation of the threatened Bliss Rapids snail (BRS), a Pliocene relict. Relative to NZMS, BRS is a slow disperser, has a more restrictive niche, and is usually out numbered more than 100 to 1. Their diets often overlap where they co-occur. Reproductively, NZMS appears to be quickly evolving from strictly parthenogenic to sexual, which may be in response to intraspecific competition and native parasites. Thus, NZMS can negatively affect BRS viability via interference and exploitative competition, changes in food resources, and increased parasitism. Adaptation and evolution of BRS may be limited within this changing environment. Because of the strength of the Endangered Species Act, mitigation funds, which otherwise would not be allotted to such a relatively unknown species, are available to conduct detailed viability analyses and risk assessments on BRS that assist management decisions, including the development of NZMS biocontrols.

Distribution of the invasive New Zealand mudsnail (Potamopyrgus antipodarum) in the lower Columbia River and its first recorded occurrence in the diet of juvenile Chinook salmon (Oncorhynchus tshawytscha)

Karen Bersine¹ (Karen.Bersine@noaa.gov), Valance E. F. Brenneis^{2, 3} (vebrenneis@ucdavis.edu), Robyn C. Draheim² (draheim@pdx.edu), A. Michelle Wargo Rub¹ (Michelle.Rub@noaa.gov), and Jen Zamon¹ (Jen.Zamon@noaa.gov)

¹NOAA Fisheries - Point Adams Research Station, PO Box 155, Hammond, OR 97121; ²Portland State University, Aquatic Bioinvasions Research and Policy Institute, Portland, OR 97207; ³Department of Environmental Science, University of California, One Shields Avenue, Davis, CA 95616

Here we report the first occurrence of the non-indigenous New Zealand mudsnail (Potamopyrgus antipodarum, NZMS) in the diet of juvenile Chinook salmon (Oncorhynchus tshawytscha) from the lower Columbia River. Although present in Chinook diets at very low densities, our observations may represent early stages of

food web change due to the establishment of dense populations of an introduced benthic invertebrate. Estuaries play an important role as nurseries for Chinook salmon and other fishes, and although the presence of NZMS has been noted in the Columbia and other Oregon estuaries, there have been no studies addressing the impact of NZMS in these systems. Understanding the impact of this invasive species in estuarine systems requires knowledge of its effect on native benthic invertebrates, benthic resources, and benthic predators. New Zealand mudsnails

constitute a major portion of the benthic invertebrate biomass in several bays of the Columbia River Estuary, co-occurring with native amphipod species important in the diet of juvenile Chinook. Here we describe (1) the distribution of NZMS in the Columbia River Estuary, (2) the occurrence of NZMS in the diet of juvenile Chinook salmon, (3) the timeline of the NZMS invasion, and (4) potential impacts of NZMS on estuarine food webs. We encourage fisheries scientists working with salmon or other benthic-feeding species to be alert to the possibility of encountering NZMS in fish diets. We make recommendations for further research on NZMS interactions with native estuarine food webs.

Predicting the Response of Potamopyrgus Antipodarum to a Mixture of Estrogenic and Androgenic Chemicals

Ben D. Giudice (bdgiudice@ucdavis.edu) and Thomas M. Young (tyoung@ucdavis.edu)

University of California, Davis, CA

Endocrine disrupting chemicals (EDCs) can cause biological effects in organisms at extremely low levels. Effects of mixtures of EDCs can be difficult to predict due to the complex nature of the endocrine system and variations in its structure and function between species. Vitellogenin induction in fish, a common biomarker for exposure and effects of estrogenic EDCs, has been shown to exhibit results consistent with the concept of concentration addition for mixtures of the estrogenic chemicals estradiol, ethynylestradiol, nonylphenol, octylphenol, and bisphenol A. For Potamopyrgus antipodarum, increasing effects on embryo production of these chemicals individually have been documented, but the effects of the chemicals in mixtures have not been rigorously studied. In this experiment, first concentration-response curves will be developed for each chemical individually. Next chemicals will be combined at equipotent concentrations and the mixture will be diluted in series. Each dilution will be used to test for the embryo response. Furthermore, a mixture will be made using one fifth of the median effective concentration (EC₅₀) for each of the five chemicals. Finally, an exploratory experiment will be conducted in which mixtures of estrogenic and androgenic chemicals will be tested to determine the effects of mixtures of these different types of EDCs. The results of this study will help understand how environmental mixtures of EDCs can affect populations of P. antipodarum. Not only could this be an important factor in the spread of populations of this invasive species, it could also lead to better risk assessment of EDCs in general.

Managing the Spread of Aquatic Nuisance Species Through HACCP Planning

Denise A. Walther¹ (denise_walther@fws.gov) and David Britton² (david_britton@fws.gov)

¹Non-native Invasive Species Program, California and Nevada Operations, US Fish and Wildlife Service, Stockton, CA; ²US Fish and Wildlife Service, Division of Fisheries, Region 2, Stockton, CA and University of Texas, Arlington, TX

Hazard Analysis and Critical Control Point (HACCP) planning strategically manages pathways to prevent and remove non-target aquatic nuisance species (ANS) which could be moved through natural resource management activities. The HACCP process is an important tool for agencies and organizations that have the potential to inadvertently move ANS from one watershed to another through their natural resource management activities. Developing an effective HACCP plan entails using a team approach to work through the 5 steps of HACCP planning—1) describe the activity, 2) identify potential hazards, 3) diagram the flow of steps for the activity, 4) analyze the hazards, and 5) complete the HACCP plan to guide actions. The U.S. Fish and Wildlife Service provides training and technical assistance to natural resource managers for creating HACCP plans. Additional resources are available on the internet at http://www.haccp-nrm.org/, including a library of completed plans and HACCP Planning Wizard software.

Assessing the Distribution, Density, and Potential Impacts of Potamopyrgus antipodarum on Resident Aquatic Invertebrates in the Lower Mokelumne River, California

Katy Washburn¹ (katywashburn@hotmail.com), Daniel Kratville² (dkratville@dfg.ca.gov), and Joseph Merz³ (jmerz@ebmud.com)

¹Biology Department, California State University, Sacramento, CA; ²Pacific Marine Fisheries Commission, California Department of Fish and Game, Sacramento, CA;

³East Bay Municipal Utility District, Fish and Wildlife Office, Lodi, CA 95240

The recent invasion of the New Zealand mudsnail (Potamopyrgus antipodarum) in the lower Mokelumne River, California, provides a unique opportunity to examine effects of an invasive species on resident macroinvertebrates with pre and post invasion comparisons. We examined potential impacts of the New Zealand mudsnail (NZMS) population on resident macroinvertebrates by assessment of 1) the distribution and density of NZMS and associated resident macroinvertebrate assemblages; 2) relationships between instream environmental parameters (ie. depth, velocity, substrate etc.), NZMS and associated resident macroinvertebrate assemblages; and 3) relationships between NZMS density and resident macroinvertebrate density and diversity over spatial and temporal ranges. We sampled the benthos at 11 sites (gravel bars) along a 10-kilometer stretch of the lower Mokelumne River between July and December 2006 to make spatial comparisons. The 2006 post-invasion data was also compared to pre-invasion data collected between 1996 and 2002 (baseline data). Densities of NZMS and native macroinvertebrate assemblages varied seasonally. NZMS density significantly correlated with season, location, and water depth. NZMS densities were also significantly related to whether or not there was a major flow change within the four weeks prior to each sampling. Macroinvertebrate diversity significantly decreased in four of the six sample sites after the invasion. These statistically significant relationships involving NZMS densities are consistent with previous studies and suggest important management implications.