Geneviève M. Nesslage

Gypsy moth response to landscape structure differs from neutral model predictions: implications for invasion monitoring

Simulations of dispersal across computer-generated neutral landscapes have generated testable predictions about the relationship between dispersal success and landscape structure. Models predict a threshold response in dispersal success with increasing habitat fragmentation. A threshold is defined as an abrupt, disproportionate decline in dispersal success at a certain proportion of habitat in the landscape. To identify potential empirical threshold responses in invasion success to landscape structure, we quantified the relationship between progression of the gypsy moth (Lymantria dispar) invasion wavefront across Michigan (1985–1996) and the structure of the Michigan landscape using two indices of invasion success and six landscape metrics. We also examined the effect of scale of analysis and choice of land cover characterization on our results by repeating our analysis at three scales using two different land cover maps. Contrary to simulation model predictions, thresholds in invasion success did not correspond closely with thresholds in landscape structure metrics. Increased variation in invasion success indices at smaller scales of analysis also suggested that invasion success should be studied at larger spatial extents (≥75xa0km2) than would be appropriate for characterizing individual dispersal events. The predictions of individual dispersal models across neutral landscapes may have limited applications for the monitoring and management of vagile species with excellent dispersal capabilities such as the gypsy moth.

Performance of Surplus Production Models with Time-Varying Parameters for Assessing Multispecies Assemblages

Abstract Single-species surplus production models are often used to assess multispecies assemblages in data-poor situations where catch and effort data are insufficient to perform individual species assessments. We examined the performance of single-species surplus production models applied to aggregated multispecies assemblages and explored the incorporation of time-varying parameters to improve model estimates. We simulated the dynamics of three species with different intrinsic growth rates and survey catchabilities over 50xa0years in the presence of fishing and a single fishery-independent survey. Schaefer surplus production models with and without time-varying growth rate and catchability were fitted to simulated data. We then compared the ability of each model to accurately estimate multispecies maximum sustainable yield and terminal year biomass and to accurately reflect overall trends in individual component stocks. All models produced biased estimates, but the accuracy of multispecies assemblage max...

Trends in Relative Abundance and Early Life Survival of Atlantic Menhaden during 1977–2013 from Long-Term Ichthyoplankton Programs

AbstractThe Atlantic Menhaden Brevoortia tyrannus, a commercially important clupeid, supports one of the oldest and largest commercial fisheries on the U.S. East Coast. Despite recent increases in adult biomass, juvenile indices have declined coastwide and have remained particularly low in Chesapeake Bay. In order to understand the underlying causes of this decline, knowledge of larval recruitment is essential. We developed an index of larval abundance by using larval data collected from two large-scale ichthyoplankton sampling programs that occurred from Nova Scotia, Canada, to Cape Hatteras, North Carolina, during 1977–1987 and 1999–2013. Larval abundance data were standardized to a day-0 age by applying an age–length key from a study of larval ingress into Chesapeake Bay; a delta-lognormal model was used to account for spatial and temporal changes in sampling. We found that Atlantic Menhaden larval abundance increased from 1977 to 2013 and was highest in the winter; most individuals were detected at ne...

Quantifying the population response of invasive water hyacinth, Eichhornia crassipes, to biological control and winter weather in Louisiana, USA

Water hyacinth, Eichhornia crassipes, is an invasive, tropical, aquatic plant that has caused significant environmental and economic damage since its establishment in Louisiana, USA, in 1884. Both invasion control programs and freezing temperatures are known to negatively affect water hyacinth populations; however, the combined impact of these factors on water hyacinth population dynamics has not yet been quantified, thereby limiting the ability to isolate the effectiveness of biocontrol and other types of control under variable weather conditions. We built a seasonal logistic population model that included time-varying intrinsic growth and overwinter mortality parameters which were estimated by fitting the model to vegetation survey data. We estimated that annual overwinter mortality rates declined from a peak of 71xa0% in 1977 to the time series low of 11xa0% in the winter of 1992, followed by an average of 28xa0% per year from 1993 to 2013. After accounting for the magnitude and trend of overwinter dieback events, our model predicted that the intrinsic growth rate of the Louisiana water hyacinth population declined by 84xa0% between 1976 and 2013. Despite higher average winter temperatures in recent decades, the population has not rebounded. Our study reveals the dramatic effectiveness of Louisiana’s biological control program to successfully suppress water hyacinth invasion.

Evidence-based economic analysis demonstrates that ecosystem service benefits of water hyacinth management greatly exceed research and control costs

Invasive species management can be a victim of its own success when decades of effective control cause memories of past harm to fade and raise questions of whether programs should continue. Economic analysis can be used to assess the efficiency of investing in invasive species control by comparing ecosystem service benefits to program costs, but only if appropriate data exist. We used a case study of water hyacinth (Eichhornia crassipes (Mart.) Solms), a nuisance floating aquatic plant, in Louisiana to demonstrate how comprehensive record-keeping supports economic analysis. Using long-term data sets, we developed empirical and spatio-temporal simulation models of intermediate complexity to project invasive species growth for control and no-control scenarios. For Louisiana, we estimated that peak plant cover would be 76% higher without the substantial growth rate suppression (84% reduction) that appeared due primarily to biological control agents. Our economic analysis revealed that combined biological and herbicide control programs, monitored over an unusually long time period (1975–2013), generated a benefit-cost ratio of about 34:1 derived from the relatively modest costs of

Spawning locations and larval dispersal of Atlantic Menhaden during 1977–2013

124 million (

Dynamics of early wolf and cougar eradication efforts in Montana: implications for conservation

2013) compared to the

A geostatistical analysis of deer harvest in the Adirondack Park, 1954-1997

4.2 billion (

ratES and Spatial pattErnS of dEClinE in hiStoriCal Cougar and wolf populationS in Montana

2013) in benefits to anglers, waterfowl hunters, boating-dependent businesses, and water treatment facilities over the 38-year analysis period. This work adds to the literature by: (1) providing evidence of the effectiveness of water hyacinth biological control; (2) demonstrating use of parsimonious spatio-temporal models to estimate benefits of invasive species control; and (3) incorporating activity substitution into economic benefit transfer to avoid overstating benefits. Our study suggests that robust and cost-effective economic analysis is enabled by good record keeping and generalizable models that can demonstrate management effectiveness and promote social efficiency of invasive species control.

Bayesian Calibration of Blue Crab (Callinectes sapidus) Abundance Indices Based on Probability Surveys

Spawning locations and larval dispersal of Atlantic Menhaden during 1977–2013 Cara A. Simpson, Hongsheng Bi*, Dong Liang, Michael J. Wilberg, Amy M. Schueller, Geneviève M. Nesslage and Harvey J. Walsh Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, P. O. Box 38, 146 Williams Street, Solomons, MD 20688, USA National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, Beaufort Laboratory, 101 Pivers Island Road, Beaufort, NC 28516, USA National Marine Fisheries Service, Northeast Fisheries Science Center, Oceanography Branch, 28 Tarzwell Drive, Narragansett, RI 02882, USA *Corresponding author: tel: þ1 410 326 7249; fax: þ1 410 326 7318; e-mail: hbi@umces.edu