Amy M. Schueller

Sensitivity of Lake Sturgeon Population Dynamics and Genetics to Demographic Parameters

Abstract Uncertainty in population parameters can make managing fisheries difficult, especially for long-lived species such as lake sturgeon Acipenser fulvescens. Models can be used to explore population parameter uncertainty and how uncertainty affects demographic and genetic population outputs through the use of sensitivity analyses. The objective of this study was to determine which lake sturgeon population parameters have the greatest influence on demographic characteristics, including rates of extinction and percentage of populations increasing from their initial size, and population genetic characteristics, including percentage of unique alleles retained and average inbreeding coefficient. An individual-based modeling approach that represented demographic and genetic processes was used to achieve this objective. Individual lake sturgeon were tracked throughout the modeling process with unique identifiers, allowing for the determination of the degree of inbreeding and the number of unique alleles ret...

Minimum viable population size for lake sturgeon (Acipenser fulvescens) using an individual-based model of demographics and genetics

Population viability analysis is a useful tool to explore the relationship between extinction risk and population size, but often does not include genetic factors. Our objectives were to determine minimum viable population size (MVP) for lake sturgeon (Acipenser fulvescens) and examine how inbreeding depression may affect MVP. Our individual-based model incorporated inbreeding depression in two ways: individuals with inbreeding coefficients above a threshold experi- enced inbreeding depression (threshold), and individuals experienced inbreeding depression at a rate related to their in- breeding coefficient (gradual). Three mechanisms relating inbreeding to fitness were explored (young-of-the-year (YOY) viability, post-YOY viability, number of progeny). The criterion we used to determine MVP was a 5% chance of extinc- tion over 250 years. The estimated MVP without inbreeding effects was 80 individuals. For some scenarios incorporating inbreeding, MVP did not change, but for others, MVP was substantially higher, reaching values up to 1800. Results dem- onstrate that extinction risk and MVP can be influenced by both demographic stochasticity and inbreeding depression. This research should inform management by determining MVP and how inbreeding, which is expected to accrue in rem- nant populations because of generations of low abundance, may affect MVP.

Invasive lionfish reduce native fish abundance on a regional scale

Invasive lionfish pose an unprecedented threat to biodiversity and fisheries throughout Atlantic waters off of the southeastern United States, the Caribbean, and the Gulf of Mexico. Here, we employ a spatially replicated Before-After-Control-Impact analysis with temporal pairing to quantify for the first time the impact of the lionfish invasion on native fish abundance across a broad regional scale and over the entire duration of the lionfish invasion (1990–2014). Our results suggest that 1) lionfish-impacted areas off of the southeastern United States are most prevalent off-shore near the continental shelf-break but are also common near-shore and 2) in impacted areas, lionfish have reduced tomtate (a native forage fish) abundance by 45% since the invasion began. Tomtate served as a model native fish species in our analysis, and as such, it is likely that the lionfish invasion has had similar impacts on other species, some of which may be of economic importance. Barring the development of a control strategy that reverses the lionfish invasion, the abundance of lionfish in the Atlantic, Caribbean, and Gulf of Mexico will likely remain at or above current levels. Consequently, the effect of lionfish on native fish abundance will likely continue for the foreseeable future.

Effect of Changes in Dissolved Oxygen Concentrations on the Spatial Dynamics of the Gulf Menhaden Fishery in the Northern Gulf of Mexico

Abstract Declines in dissolved oxygen (DO) concentrations in aquatic environments can lead to conditions of hypoxia (DO ≤ 2 mg/L), which can directly and indirectly affect aquatic organisms. Direct effects include changes in growth and mortality; indirect effects include changes in distribution, movement, and interactions with other species. For mobile species, such as the pelagic filter-feeding Gulf Menhaden Brevoortia patronus, indirect effects are more prevalent than direct effects. The northern Gulf of Mexico experiences one of the largest areas of seasonal hypoxia in the world; this area overlaps spatially and temporally with the Gulf Menhaden commercial purse-seine fishery, which is among the largest fisheries by weight in the United States. Harvest records from the Gulf Menhaden fishery in 2006–2009 and fine-scale spatial and temporal predictions from a physical—biogeochemical model were used with spatially varying regression models to examine the effects of bottom DO concentration, spatial location, depth, week, and year on four response variables: probability of fishing, total Gulf Menhaden catch, total fishery effort, and CPUE. We found nearshore shifts in the probability of fishing as DO concentration declined, and we detected a general westward shift in all response variables. We also found increases in CPUE as DO concentration declined in the Louisiana Bight, an area that experiences chronic, severe hypoxia. The overall effects of environmental conditions on fishing response variables appeared to be moderate. Nevertheless, movement of either Gulf Menhaden or the purse-seine fishery in response to environmental conditions could potentially affect the susceptibility of Gulf Menhaden to harvest and could therefore influence assessment of the stock and associated stock status indicators.

Inbreeding and Allele Retention for Lake Sturgeon Populations under Different Supplementation Strategies

Abstract Lake sturgeon Acipenser fulvescens once were abundant throughout the Great Lakes basin but have been reduced to less than 1% of historical levels because of habitat degradation and overexploitation. Current management plans suggest stocking as a tool to increase abundance, but stocking also has genetic implications. The objectives of this study were to determine the supplementation level that would maintain long-term population persistence with the smallest genetic impact and to determine whether different supplementation strategies would be required for different starting conditions. An individual-based model that incorporated demographics and genetics was used to explore scenarios that included three initial population sizes, two different supplementation time frames, varying sex ratios, variance in family size, and different percentages of the adult population contributing progeny for supplementation. As expected, all supplementation scenarios reduced extinction risk, increased population size...

Modeling the Sustainability of Walleye Populations in Northern Wisconsin Lakes

Abstract Population sustainability of walleyes Sander vitreus in the face of angling and spearing fisheries has been a concern of fishery managers in northern Wisconsin since off-reservation tribal fishing rights were affirmed by federal court decisions. We evaluated sustainability of walleye populations across a range of densities that were subjected to various exploitation rates and allocations of angling and spearing harvest (the fisheries differ in size selectivity). We developed an age-structured population model for estimating extinction risk and time to extinction for a hypothetical walleye population at a specified exploitation rate, fishery allocation, and initial density. The model was parameterized from data obtained during surveys of walleye populations in northern Wisconsin lakes. Simulations covered a range of annual exploitation rates that included the currently accepted rate of 35% and a range of population densities that are presently included in regression models relating walleye abundan...

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...

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

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