Geology topics

Samuel G. Roy

Publications and source records attributed to Samuel G. Roy.

5 recordsLinked to original sources

USGS2025

anadrofish: Anadromous fish population responses to dams

Diadromous fishes world-wide experienced precipitous declines during the 19th and 20th centuries due to a combination of overfishing, pollution, and freshwater habitat loss through construction of dams (Limburg & Waldman, 2009). Following wide-spread fishing closures and large-scale remediation of many historical pollution sources, dams in coastal rivers remain as the largest tractable impediment to population recovery for many of these species (Waldman & Quinn, 2022). In some cases, dams reduce access to as much as 95% of freshwater and rearing habitat (Hall et al., 2011). These effects are especially pronounced for species that rely on long-distance migrations to spawning and rearing habitat upstream of barriers such as various alosines (herrings; e.g., American shad Alosa sapidissima , alewife A. pseudoharengus , and blueback herring A. aestivalis (Noonan et al., 2012)) and salmonines (trout and salmon; e.g., Salmo spp. (Parrish et al., 1998) and Oncorhynchus spp. (Quiñones et al., 2015). Traditional stock assessment tools such as per-recruit analyses often fail to capture management complexities related to diadromous life histories such as fish passage at dams, and integrated assessment models can be difficult to parameterize for data-poor species such as herrings (Atlantic States Marine Fisheries Commission, 2024). This has resulted in the development of species- and system-specific approaches to fisheries stock assessment and management strategy evaluation (Barber et al., 2018; Nieland et al., 2015; Roy et al., 2018; Stich et al., 2019). We created the anadrofish package (Stich, Hardesty, et al., 2025) for R (R Core Team, 2025) to provide a generalized approach that also allows broader application to novel species, systems, and scenarios.

Journal of Open Source Software↗

USGS2021

What have we lost? Modeling dam impacts on American shad populations through their native range

American shad ( Alosa sapidissima ) are native to the east coast of North America from the St. Johns River, Florida, to the St. Lawrence River region in Canada. Since the 1800s, dams have reduced access to spawning habitat. To assess the impact of dams, we estimated the historically accessed spawning habitat in coastal rivers (485,618 river segments with 21,113 current dams) based on (i) width, (ii) distance from seawater, and (iii) slope (to exclude natural barriers to migration) combined with local knowledge. Estimated habitat available prior to dam construction (2,752 km 2 ) was 41% greater than current fully accessible habitat (1,639 km 2 ). River-specific population models were developed using habitat estimates and latitudinally appropriate life history parameters (e.g., size at age, maturity, iteroparity). Estimated coast-wide annual production potential was 69.1 million spawners compared with a dammed scenario (41.8 million spawners). Even with optimistic fish passage performance assumed for all dams (even if passage is completely absent), the dam-imposed deficit was alleviated by fewer than 3 million spawners. We estimate that in rivers modeled without dams, 98,000 metric tons of marine sourced biomass and nutrients were annually delivered, 60% of which was retained through carcasses, gametes and metabolic waste. Damming is estimated to have reduced this by more than one third. Based on our results, dams represent a significant and acute constraint to the population and, with other human impacts, reduce the fishery potential and ecological services attributed to the species.

Frontiers in Marine Science↗

USGS2020

Coordinated river infrastructure decisions improve net social-ecological benefits

We explore the social, ecological, economic, and technical dimensions of sustainable river infrastructure development and the potential benefits of coordinating decisions such as dam removal and stream crossing improvement. Dam removal is common practice for restoring river habitat connectivity and ecosystem health. However, stream crossings such as culverts are often 15 times more abundant than dams and may pose similar ecological impacts. Using multi-objective optimization for a model system of 6100 dams and culverts in Maine, USA, we demonstrate substantial benefit-cost improvements provided by coordinating habitat connectivity decisions. Benefit-cost efficiency improves by two orders of magnitude when coordinating more decisions across wider areas, but this approach may cause inequitable resource distribution. Culvert upgrades improve roadway safety and habitat connectivity, creating cost-effective opportunities for coordinating and cost-sharing projects between conservationists and safety managers. Benefit-cost trends indicate significant overlaps in habitat and safety goals, encouraging flexible stakeholder collaborations and cost-sharing strategies.

Maine↗

USGS2019

Managing dams for energy and fish tradeoffs: What does a win-win solution take?

Management activities to restore endangered fish species, such as dam removals, fishway installations, and periodic turbine shutdowns, usually decrease hydropower generation capacities at dams. Quantitative analysis of the tradeoffs between energy production and fish population recovery related to dam decision-making is still lacking. In this study, an integrated hydropower generation and age-structured fish population model was developed using a system dynamics modeling method to assess basin-scale energy-fish tradeoffs under eight dam management scenarios. This model ran across 150 years on a daily time step, applied to five hydroelectric dams located in the main stem of the Penobscot River, Maine. We used alewife ( Alosa pseudoharengus ) to be representative of the local diadromous fish populations to link projected hydropower production with theoretical influences on migratory fish populations on the model river system. Our results show that while the five dams can produce around 427 GWh/year of energy, without fishway installations they would contribute to a 90% reduction in the alewife spawner abundance. The effectiveness of fishway installations is largely influenced by the size of reopened habitat areas and the actual passage rate of the fishways. Homing to natal habitat has an insignificant effect on the growth of the simulated spawner abundance. Operating turbine shutdowns during alewives' peak downstream migration periods, in addition to other dam management strategies, can effectively increase the spawner abundance by 480–550% while also preserving 65% of the hydropower generation capacity. These data demonstrate that in a river system where active hydropower dams operate, a combination of dam management strategies at the basin scale can best balance the tradeoff between energy production and the potential for migratory fish population recovery.

Maine↗

USGS2018

A multiscale approach to balance trade-offs among dam infrastructure, river restoration, and cost

Aging infrastructure and growing interests in river restoration have led to a substantial rise in dam removals in the U.S. However, the decision to remove a dam involves many complex trade-offs. The benefits of dam removal for hazard reduction and ecological restoration are potentially offset by the loss of hydroelectricity production, water supply, and other important services. We use a multi-objective approach to examine a wide array of trade-offs and synergies involved with strategic dam removal at three spatial scales in New England. We find that increasing the scale of decision-making improves the efficiency of trade-offs among ecosystem services, river safety, and economic costs resulting from dam removal, but this may lead to heterogeneous and less equitable local-scale outcomes. Our model may help facilitate multilateral funding, policy, and stakeholder agreements by analyzing the trade-offs of coordinated dam decisions, including net benefit alternatives to dam removal, at scales that satisfy these agreements.

New England↗