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At least 739 records · Page 41Linked to original sources
USGS2017

An integral projection model with YY-males and application to evaluating grass carp control

Invasive fish species disrupt ecosystems and cause economic damage. Several methods have been discussed to control populations of invasive fish including the release of YY-males. YY-males are fish that have 2 male chromosomes compared to a XY-male. When YY-males mate, they only produce male (XY) offspring. This decreases the female proportion of the population and can, in theory, eradicate local populations by biasing the sex-ratio. YY-males have been used as a population control tool for brook trout in montane streams and lakes in Idaho, USA. The YY-male control method has been discussed for grass carp in Lake Erie, North America. We developed and presented an integral projection model for grass carp to model the use of YY-males as a control method for populations in this lake. Using only the YY-male control method, we found that high levels of YY-males would need to be release annually to control the species. Specifically, these levels were the same order of magnitude as the baseline adult population (e.g., 1000 YY-males needed to be released annual for 20 years to control a baseline adult population of 2500 grass carp). These levels may not be reasonable or obtainable for fisheries managers given the impacts of YY-males on aquatic vegetation and other constraints of natural resource management.

Ecological Modelling↗
USGS2016

Spatially explicit control of invasive species using a reaction-diffusion model

Invasive species, which can be responsible for severe economic and environmental damages, must often be managed over a wide area with limited resources, and the optimal allocation of effort in space and time can be challenging. If the spatial range of the invasive species is large, control actions might be applied only on some parcels of land, for example because of property type, accessibility, or limited human resources. Selecting the locations for control is critical and can significantly impact management efficiency. To help make decisions concerning the spatial allocation of control actions, we propose a simulation based approach, where the spatial distribution of the invader is approximated by a reaction–diffusion model. We extend the classic Fisher equation to incorporate the effect of control both in the diffusion and local growth of the invader. The modified reaction–diffusion model that we propose accounts for the effect of control, not only on the controlled locations, but on neighboring locations, which are based on the theoretical speed of the invasion front. Based on simulated examples, we show the superiority of our model compared to the state-of-the-art approach. We illustrate the use of this model for the management of Burmese pythons in the Everglades (Florida, USA). Thanks to the generality of the modified reaction–diffusion model, this framework is potentially suitable for a wide class of management problems and provides a tool for managers to predict the effects of different management strategies.

Ecological Modelling↗
USGS2015

On formally integrating science and policy: walking the walk

The contribution of science to the development and implementation of policy is typically neither direct nor transparent. In 1995, the U.S. Fish and Wildlife Service (FWS) made a decision that was unprecedented in natural resource management, turning to an unused and unproven decision process to carry out trust responsibilities mandated by an international treaty. The decision process was adopted for the establishment of annual sport hunting regulations for the most economically important duck population in North America, the 6 to 11 million mallards Anas platyrhynchos breeding in the mid-continent region of north-central United States and central Canada. The key idea underlying the adopted decision process was to formally embed within it a scientific process designed to reduce uncertainty (learn) and thus make better decisions in the future. The scientific process entails use of models to develop predictions of competing hypotheses about system response to the selected action at each decision point. These prediction not only are used to select the optimal management action, but also are compared with the subsequent estimates of system state variables, providing evidence for modifying degrees of confidence in, and hence relative influence of, these models at the next decision point. Science and learning in one step are formally and directly incorporated into the next decision, contrasting with the usual ad hoc and indirect use of scientific results in policy development and decision-making. Application of this approach over the last 20 years has led to a substantial reduction in uncertainty, as well as to an increase in transparency and defensibility of annual decisions and a decrease in the contentiousness of the decision process. As resource managers are faced with increased uncertainty associated with various components of global change, this approach provides a roadmap for the future scientific management of natural resources.

Journal of Applied Ecology↗
USGS2014

Site fidelity and condition metrics suggest sequential habitat use by early juvenile snook

The common snook Centropomus undecimalis is an estuarine-dependent fish that relies on landward wetlands as nursery habitat. Despite its economic importance, portions of the snook's early life history are poorly understood. We compared habitat use of young-of-the-year (YOY) snook in 2 geomorphic mesohabitats (tidal pond and tidal creek) along an estuarine gradient (upstream vs. downstream) within a single wetland during fall recruitment. We used abundance, length, condition indices, and stable isotopes to assess ontogenetic mesohabitat use and site fidelity. We found that (1) YOY snook were more abundant within the upstream creek and ponds; (2) the smallest snook were found only in ponds; (3) snook from ponds had lower condition (Fulton's K and hepatosomatic index); (4) snook began moving from ponds to the creek at ~40 mm standard length; and (5) snook from the 2 mesohabitats were isotopically distinct, indicating high site fidelity at rather small spatial scales. Collectively, these data identified sequential use of mesohabitats, wherein seaward-spawned YOY snook moved landward and recruited to pond habitats, where they dedicated energy to growth (as length) before making an ontogenetic habitat shift to the creek. Once in the creek, YOY snook condition improved as they approached maturity and started the downstream return towards seaward locations. The wetland network that was previously viewed as generalized nursery habitat instead consists of mesohabitats that support different life stages in sequence. This represents ontogenetic habitat complementation, in which lower availability of a required mesohabitat type may limit the entire wetland's contribution to the adult population.

Marine Ecology Progress Series↗
USGS2021

Tradeoffs in habitat value to maximize natural resource benefits from coastal restoration in a rapidly eroding wetland: Is monitoring land area sufficient?

Louisiana contains nearly 40% of estuarine herbaceous wetlands in the contiguous United States, supporting valuable ecosystem services and providing significant economic benefits to the state and the entire United States. However, coastal Louisiana is a hotspot for rapid land loss from factors including hurricanes, land use change, and high subsidence rates contributing to high relative sea-level rise. The Coastal Protection and Restoration Authority (CPRA) was established after major hurricanes in 2005 to coordinate coastal restoration in Louisiana and develop the Louisiana Coastal Master Plan. The LA Coastal Master Plan uses numerical modeling of multiple scenarios to select a suite of restoration projects based on maximum land area created and flood reduction (as proxies for ecosystem value). Using potential value to aquatic, terrestrial, and social resources, our work compared habitat value of shallow open water areas to emergent wetland. While potential resource benefits varied by emergent wetland salinity type and emergent wetland versus water, they were similar, suggesting that restoration planning based primarily on wetland land area may not achieve the maximum possible ecosystem benefits. After nearly 20 years of integrated restoration planning in coastal Louisiana, a reassessment of restoration planning decision drivers may be beneficial to ensure maximum benefits from coastal restoration. As a result of the Deepwater Horizon oil spill, settlement funds will be a major support to coastal restoration in Louisiana for many years. Assessing potential habitat value to multiple natural and social resources in Louisiana has potential to maximize synergy with large northern Gulf of Mexico restoration programs.

Louisiana↗
USGS2020

Carrying capacity of a population diffusing in a heterogeneous environment

The carrying capacity of the environment for a population is one of the key concepts in ecology and it is incorporated in the growth term of reaction-diffusion equations describing populations in space. Analysis of reaction-diffusion models of populations in heterogeneous space have shown that, when the maximum growth rate and carrying capacity in a logistic growth function vary in space, conditions exist for which the total population size at equilibrium (i) exceeds the total population that which would occur in the absence of diffusion and (ii) exceeds that which would occur if the system were homogeneous and the total carrying capacity, computed as the integral over the local carrying capacities, was the same in the heterogeneous and homogeneous cases. We review here work over the past few years that has explained these apparently counter-intuitive results in terms of the way input of energy or another limiting resource (e.g., a nutrient) varies across the system. We report on both mathematical analysis and laboratory experiments confirming that total population size in a heterogeneous system with diffusion can exceed that in the system without diffusion. We further report, however, that when the resource of the population in question is explicitly modeled as a coupled variable, as in a reaction-diffusion chemostat model rather than a model with logistic growth, the total population in the heterogeneous system with diffusion cannot exceed the total population size in the corresponding homogeneous system in which the total carrying capacities are the same.

Mathematics and Computers in Modern Science - Acou↗
USGS2023

Connecting dryland fine-fuel assessments to wildfire exposure and natural resource values at risk

Background Wildland fire in arid and semi-arid (dryland) regions can intensify when climatic, biophysical, and land-use factors increase fuel load and continuity. To inform wildland fire management under these conditions, we developed high-resolution (10-m) estimates of fine fuel across the Altar Valley in southern Arizona, USA, which spans dryland, grass-dominated ecosystems that are administered by multiple land managers and owners. We coupled field measurements at the end of the 2021 growing season with Sentinel-2 satellite imagery and vegetation indices acquired during and after the growing season to develop predictions of fine fuel across the entire valley. We then assessed how climate, soil, vegetation, and land-use factors influenced the amount and distribution of fine fuels. We connected fine fuels to fire management points, past ignition history, and socio-economic vulnerability to evaluate wildfire exposure and assessed how fuel related to habitat of the endangered masked bobwhite quail ( Colinus virginianus ridgwayi ). Results The high amount of fine fuel (400–3600 kg/ha; mean = 1392 kg/ha) predicted by our remote sensing model ( R 2 = 0.63) for 2021 compared to previous years in the valley was stimulated by near-record high growing season precipitation that was 177% of the 1990–2020 mean. Fine fuel increased across the valley if it was contained within the wildlife refuge boundary and had lower temperature and vapor pressure deficit, higher soil organic content, and abundant annual plants and an invasive perennial grass ( R 2 = 0.24). The index of potential exposure to wildfire showed a clustering of high exposure centered around roads and low-density housing development distant from fire management points and extending into the upper elevations flanking the valley. Within the Buenos Aires National Wildlife Refuge, fine fuel increased with habitat suitability for the masked bobwhite quail within and adjacent to core habitat areas, representing a natural resource value at risk, accompanied with higher overall mean fine fuel (1672 kg/ha) in relation to 2015 (1347 kg/ha) and 2020 (1363 kg/ha) means. Conclusions By connecting high-resolution estimates of fine fuel to climatic, biophysical and land-use factors, wildfire exposure, and a natural resource value at risk, we provide a pro-active and adaptive framework for fire risk management within highly variable and rapidly changing dryland landscapes.

Arizona↗
USGS1988

Assessment of the role of bottomland hardwoods in sediment and erosion control

Drainage and clearing of bottomland hardwoods have long been recognized by the U.S. Environmental Protection Agency (EPA) and the U.S. Fish and Wildlife Service (Service) as important impacts of Federal water projects in the lower Mississippi River Valley. More recently, the water quality impacts of such projects (e.g., increases in sediments, nutrients, and pesticides) have also become of concern. In 1984, in an effort to better define problems concerning wetland losses and water degradation, EPA initiated a cooperative project with the Western Energy and Land Use Team (now the National Ecology Research Center) of the Service. Three phases of the project were identified: 1. To collect existing literature and data; 2. To select, develop, and test the utility of methods to quantify the relationships between land use, cover types, soils, hydrology, and water quality (as represented by sediment); and 3. To apply selected methodologies to several sites within the Yazoo Basin of Mississippi to determine the, potential effectiveness of various management alternatives to reduce sediment yield, increase sediment deposition, and improve water quality. Methods development focused on linking a simulation of water and sediment movement to a computerized geographic information system. We had several objectives for the resulting model. We desired that it should: 1. Estimate the importance of bottomland and hardwoods as a cover type that performs the functions of erosion and sediment control, 2. Simulate effects of proportions of ' various cover types and their specific spatial configurations, 3. Be applicable to moderately large spatial areas with minimal site-specific calibration, 4. Simulate spatial patterns of sediment loss-gain over time, and 5. Represent both sediment detachment and transport. While it was recognized that impacts and management alternatives could be sorted roughly into landscape measures and channel measures, the decision was made to focus study efforts mainly on landscape measures. Landscape measures include altered drainage and flooding patterns, altered cover types (e.g., conversion of bottomland hardwoods to agricultural crops, reforestation of cropland to bottomland hardwoods, and creation of riparian buffer strips), altered cropping and tillage patterns, altered routing of water, and creation of buffer strips along wetlands and channel margins. Channel measures include vegetative bank stabilization, grade control structures, and regulation of channel water volume and velocity. During the first year of the study, EPA decided not to fund the third phase of the project. This required considerable rescoping of the project with the result that application of the sediment mobilization, routing, and deposition models to various management alternatives and portions of the Yazoo Basin was somewhat restricted. We believe, however, that this report will provide a good understanding of the various modes of sediment mobilization, transport, and deposition within the Yazoo Basin, as well as of the role of bottomland hardwoods. The model developed in this study could be applied to a variety of management or mitigation alternatives prior to implementation to determine their relative effectiveness. Policy, political, and socio-economic consequences of any proposed management/mitigation practice, however, must ultimately be taken into consideration by those charged with management of water resources within the Yazoo Basin before any practice is implemented. This study makes no effort to judge the feasibility of management alternatives in this regard.

Report↗
USGS2019

Invasive buffelgrass detection using high-resolution satellite and UAV imagery on Google Earth Engine

Methods to detect and monitor the spread of invasive grasses are critical to avoid ecosystem transformations and large economic costs. The rapid spread of non‐native buffelgrass (Pennisetum ciliare) has intensified fire risk and is replacing fire intolerant native vegetation in the Sonoran Desert of the southwestern US. Coarse‐resolution satellite imagery has had limited success in detecting small patches of buffelgrass, whereas ground‐based and aerial survey methods are often cost prohibitive. To improve detection, we trained 2 m resolution DigitalGlobe WorldView‐2 satellite imagery with 12 cm resolution unmanned aerial vehicle (UAV) imagery and classified buffelgrass on Google Earth Engine, a cloud computing platform, using Random Forest (RF) models in Saguaro National Park, Arizona, USA. Our classification models had an average overall accuracy of 93% and producer's accuracies of 94–96% for buffelgrass, although user's accuracies were low. We detected a 2.92 km 2 area of buffelgrass in the eastern Rincon Mountain District (1.07% of the total area) and a 0.46 km 2 area (0.46% of the total area) in the western Tucson Mountain District of Saguaro National Park. Buffelgrass cover was significantly greater in the Sonoran Paloverde‐Mixed Cacti Desert Scrub vegetation type, on poorly developed Entisols and Inceptisol soils and on south‐facing topographic aspects compared to other areas. Our results demonstrate that high‐resolution imagery improve on previous attempts to detect and classify buffelgrass and indicate potential areas where the invasive grass might spread. The methods demonstrated in this study could be employed by land managers as a low‐cost strategy to identify priority areas for control efforts and continued monitoring.

Arizona↗
USGS2016

Mapping technological and biophysical capacities of watersheds to regulate floods

Flood regulation is a widely valued and studied service provided by watersheds. Flood regulation benefits people directly by decreasing the socio-economic costs of flooding and indirectly by its positive impacts on cultural (e.g., fishing) and provisioning (e.g., water supply) ecosystem services. Like other regulating ecosystem services (e.g., pollination, water purification), flood regulation is often enhanced or replaced by technology, but the relative efficacy of natural versus technological features in controlling floods has scarcely been examined. In an effort to assess flood regulation capacity for selected urban watersheds in the southeastern United States, we: (1) used long-term flood records to assess relative influence of technological and biophysical indicators on flood magnitude and duration, (2) compared the widely used runoff curve number (RCN) approach for assessing the biophysical capacity to regulate floods to an alternative approach that acknowledges land cover and soil properties separately, and (3) mapped technological and biophysical flood regulation capacities based on indicator importance-values derived for flood magnitude and duration. We found that watersheds with high biophysical (via the alternative approach) and technological capacities lengthened the duration and lowered the peak of floods. We found the RCN approach yielded results opposite that expected, possibly because it confounds soil and land cover processes, particularly in urban landscapes, while our alternative approach coherently separates these processes. Mapping biophysical (via the alternative approach) and technological capacities revealed great differences among watersheds. Our study improves on previous mapping of flood regulation by (1) incorporating technological capacity, (2) providing high spatial resolution (i.e., 10-m pixel) maps of watershed capacities, and (3) deriving importance-values for selected landscape indicators. By accounting for technology that enhances or replaces natural flood regulation, our approach enables watershed managers to make more informed choices in their flood-control investments.

Ecological Indicators↗
USGS2015

Proposed best modeling practices for assessing the effects of ecosystem restoration on fish

Large-scale aquatic ecosystem restoration is increasing and is often controversial because of the economic costs involved, with the focus of the controversies gravitating to the modeling of fish responses. We present a scheme for best practices in selecting, implementing, interpreting, and reporting of fish modeling designed to assess the effects of restoration actions on fish populations and aquatic food webs. Previous best practice schemes that tended to be more general are summarized, and they form the foundation for our scheme that is specifically tailored for fish and restoration. We then present a 31-step scheme, with supporting text and narrative for each step, which goes from understanding how the results will be used through post-auditing to ensure the approach is used effectively in subsequent applications. We also describe 13 concepts that need to be considered in parallel to these best practice steps. Examples of these concepts include: life cycles and strategies; variability and uncertainty; nonequilibrium theory; biological, temporal, and spatial scaling; explicit versus implicit representation of processes; and model validation. These concepts are often not considered or not explicitly stated and casual treatment of them leads to mis-communication and mis-understandings, which in turn, often underlie the resulting controversies. We illustrate a subset of these steps, and their associated concepts, using the three case studies of Glen Canyon Dam on the Colorado River, the wetlands of coastal Louisiana, and the Everglades. Use of our proposed scheme will require investment of additional time and effort (and dollars) to be done effectively. We argue that such an investment is well worth it and will more than pay back in the long run in effective and efficient restoration actions and likely avoided controversies and legal proceedings.

Ecological Modelling↗
USGS2021

Demographic risk assessment for a harvested species threatened by climate change: Polar bears in the Chukchi Sea

Climate change threatens global biodiversity. Many species vulnerable to climate change are important to humans for nutritional, cultural, and economic reasons. Polar bears Ursus maritimus are threatened by sea-ice loss and represent a subsistence resource for Indigenous people. We applied a novel population modeling-management framework that is based on species life history and accounts for habitat loss to evaluate subsistence harvest for the Chukchi Sea (CS) polar bear subpopulation. Harvest strategies followed a state-dependent approach under which new data were used to update the harvest on a predetermined management interval. We found that a harvest strategy with a starting total harvest rate of 2.7% (˜85 bears/yr at current abundance), a 2:1 male-to-female ratio, and a 10-yr management interval would likely maintain subpopulation abundance above maximum net productivity level for the next 35 yr (approximately three polar bear generations), our primary criterion for sustainability. Plausible bounds on starting total harvest rate were 1.7–3.9%, where the range reflects uncertainty due to sampling variation, environmental variation, model selection, and differing levels of risk tolerance. The risk of undesired demographic outcomes (e.g., overharvest) was positively related to harvest rate, management interval, and projected declines in environmental carrying capacity; and negatively related to precision in population data. Results reflect several lines of evidence that the CS subpopulation has been productive in recent years, although it is uncertain how long this will last as sea-ice loss continues. Our methods provide a template for balancing trade-offs among protection, use, research investment, and other factors. Demographic risk assessment and state-dependent management will become increasingly important for harvested species, like polar bears, that exhibit spatiotemporal variation in their response to climate change.

Chukchi Sea↗
USGS2023

Marginal value analysis reveals shifting importance of migration habitat for waterfowl under a changing climate

Migratory waterfowl are an important resource for consumptive and non-consumptive users alike and provide tremendous economic value in North America. These birds rely on a complex matrix of public and private land for forage and roosting during migration and wintering periods, and substantial conservation effort focuses on increasing the amount and quality of target habitat. Yet, the value of habitat is a function not only of a site's resources but also of its geographic position and weather. To quantify this value, we used a continental-scale energetics-based model of daily dabbling duck movement to assess the marginal value of lands across the contiguous United States during the non-breeding period (September to May). We examined effects of eliminating each habitat node (32 × 32 km) in both a particularly cold and a particularly warm winter, asking which nodes had the largest effect on survival. The marginal value of habitat nodes for migrating dabbling ducks was a function of forage and roosting habitat but, more importantly, of geography (especially latitude and region). Irrespective of weather, nodes in the Southeast, central East Coast, and California made the largest positive contributions to survival. Conversely, nodes in the Midwest, Northeast, Florida, and the Pacific Northwest had consistent negative effects. Effects (positive and negative) of more northerly nodes occurred in late fall or early spring when climate was often severe and was most variable. Importance and effects of many nodes varied considerably between a cold and a warm winter. Much of the Midwest and central Great Plains benefited duck survival in a warm winter, and projected future warming may improve the value of lands in these regions, including many National Wildlife Refuges, for migrating dabbling ducks. Our results highlight the geographic variability in habitat value, as well as shifts that may occur in these values due to climate change.

Ecology and Evolution↗
USGS2022

Numbers and presence of guarding dogs affect wolf and leopard predation on livestock in northeastern Iran

Livestock predation can pose socio-economic impacts on rural livelihoods and is the main cause of retaliatory killings of carnivores in many countries. Therefore, appropriate interventions to reduce livestock predation, lower conflict and promote coexistence are needed. Livestock guarding dogs have been traditionally used to reduce predation, yet details regarding the use of dogs, especially the number of dogs per herd effectively required, are rarely studied. In this study, we assessed how the number and presence of guarding dogs in a herd can reduce livestock losses to leopard and wolf in corrals at night and on grazing grounds in day-time. Using systematic interview surveys (2016-2019), we documented sheep/goat losses per attack (predation rates) from 139 shepherds across 32 villages around Golestan National Park, Iran. We analysed the effects of the number of dogs, presence of dogs, presence of shepherds, seasons, corral quality, livestock number, dog size, distance to villages and distance to reserve on predation rates using generalized linear models. For the leopard model, dog presence significantly decreased ( β = –1.80, 95% confidence interval –2.61 to –0.81) predation rates during day-time to 1.41 individuals per attack. For wolf attacks in corrals at night, predation rates significantly decreased ( β = –0.29, –0.54 to –0.04) with increasing dog numbers. Also, shepherd presence ( β = –0.56, –1.10 to –0.10) and herd size (β = –0.36, –0.60 to –0.12) significantly reduced predation rates. In the wolf day-time model, shepherd presence significantly decreased ( β = –0.93, –1.74 to –0.10) predation rates. Our study suggests that (1) using dogs can reduce, but not eliminate, predation by leopards during day-time; (2) with every additional dog, predation rates by wolves in corrals at night are likely to decrease on average by 25.2%; and (3) the presence of shepherds in corrals at night and during day-time can reduce predation rates.

Azizabad No-Hunting Area, Golestan National Park↗
USGS2024

Simulating past and future fire impacts on Mediterranean ecosystems

Worldwide, large wildfires are becoming increasingly common, leading to economic damages and threatening ecosystems and human health. Under future climate change, more frequent fire disturbance may push ecosystems into non-forested alternative stable states. Fire-prone ecosystems such as those in the Mediterranean Basin are expected to be particularly vulnerable, but the position of tipping points is unclear. We compare long-term palaeoecological data from Sardinia with output from a process-based dynamic vegetation model to investigate the mechanisms controlling the complex interactions between fire, climate, and vegetation in the past and the future. Our results show that past vegetation changes from Erica -shrublands to mixed evergreen-broadleaved Quercus ilex -dominated forests were driven by a climate-induced fire regime shift. By simulating vegetation dynamics under varying fire regimes, we could reproduce Holocene vegetation trajectories and mechanistically identify tipping points. Without an immediate reduction of greenhouse gas emissions, we simulate future expansion of fire-prone Mediterranean maquis and increasing fire occurrence. Similarly, high anthropogenic ignition frequencies and plantations of non-native, highly flammable trees could induce a shift to fire-adapted Erica shrublands. However, our simulations indicate that if global warming can be kept below 2°C, Quercus ilex forests will be able to persist and effectively reduce fire occurrences and impacts, making them a valuable restoration target in Mediterranean ecosystems. Synthesis . By combining long-term records of ecosystem change with a dynamic vegetation model, we show that past climate-driven fire regime shifts were the main driver of vegetation change, creating alternative stable states that persisted over centuries. Projected future climate change exceeding Holocene variability leads to pronounced vegetation changes and increased fire risks in our simulations, requiring new fire management strategies to maintain current ecosystem services.

Journal of Ecology↗
USGS2012

Allowable levels of take for the trade in Nearctic songbirds

The take of Nearctic songbirds for the caged-bird trade is an important cultural and economic activity in Mexico, but its sustainability has been questioned. We relied on the theta-logistic population model to explore options for setting allowable levels of take for 11 species of passerines that were subject to legal take in Mexico in 2010. Because estimates of population size necessary for making periodic adjustments to levels of take are not routinely available, we examined the conditions under which a constant level of take might contribute to population depletion (i.e., a population below its level of maximum net productivity). The chance of depleting a population is highest when levels of take are based on population sizes that happen to be much lower or higher than the level of maximum net productivity, when environmental variation is relatively high and serially correlated, and when the interval between estimation of population size is relatively long (≥5 years). To estimate demographic rates of songbirds involved in the Mexican trade we relied on published information and allometric relationships to develop probability distributions for key rates, and then sampled from those distributions to characterize the uncertainty in potential levels of take. Estimates of the intrinsic rate of growth (r) were highly variable, but median estimates were consistent with those expected for relatively short-lived, highly fecund species. Allowing for the possibility of nonlinear density dependence generally resulted in allowable levels of take that were lower than would have been the case under an assumption of linearity. Levels of take authorized by the Mexican government in 2010 for the 11 species we examined were small in comparison to relatively conservative allowable levels of take (i.e., those intended to achieve 50% of maximum sustainable yield). However, the actual levels of take in Mexico are unknown and almost certainly exceed the authorized take. Also, the take of Nearctic songbirds in other Latin American and Caribbean countries ultimately must be considered in assessing population-level impacts.

Ecological Applications↗
USGS2021

The Chesapeake Bay program modeling system: Overview and recommendations for future development

The Chesapeake Bay is the largest, most productive, and most biologically diverse estuary in the continental United States providing crucial habitat and natural resources for culturally and economically important species. Pressures from human population growth and associated development and agricultural intensification have led to excessive nutrient and sediment inputs entering the Bay, negatively affecting the health of the Bay ecosystem and the economic services it provides. The Chesapeake Bay Program (CBP) is a unique program formally created in 1983 as a multi-stakeholder partnership to guide and foster restoration of the Chesapeake Bay and its watershed. Since its inception, the CBP Partnership has been developing, updating, and applying a complex linked modeling system of watershed, airshed, and estuary models as a planning tool to inform strategic management decisions and Bay restoration efforts. This paper provides a description of the 2017 CBP Modeling System and the higher trophic level models developed by the NOAA Chesapeake Bay Office, along with specific recommendations that emerged from a 2018 workshop designed to inform future model development. Recommendations highlight the need for simulation of watershed inputs, conditions, processes, and practices at higher resolution to provide improved information to guide local nutrient and sediment management plans. More explicit and extensive modeling of connectivity between watershed landforms and estuary sub-areas, estuarine hydrodynamics, watershed and estuarine water quality, the estuarine-watershed socioecological system, and living resources will be important to broaden and improve characterization of responses to targeted nutrient and sediment load reductions. Finally, the value and importance of maintaining effective collaborations among jurisdictional managers, scientists, modelers, support staff, and stakeholder communities is emphasized. An open collaborative and transparent process has been a key element of successes to date and is vitally important as the CBP Partnership moves forward with modeling system improvements that help stakeholders evolve new knowledge, improve management strategies, and better communicate outcomes.

Chesapeake Bay estuary and watershed↗
USGS2015

Flow management and fish density regulate salmonid recruitment and adult size in tailwaters across western North America

Rainbow and brown trout have been intentionally introduced into tailwaters downriver of dams globally and provide billions of dollars in economic benefits. At the same time, recruitment and maximum length of trout populations in tailwaters often fluctuate erratically, which negatively affects the value of fisheries. Large recruitment events may increase dispersal downriver where other fish species may be a priority (e.g., endangered species). There is an urgent need to understand the drivers of trout population dynamics in tailwaters, in particular the role of flow management. Here, we evaluate how flow, fish density, and other physical factors of the river influence recruitment and mean adult length in tailwaters across western North America using data from 29 dams spanning 1-19 years. Rainbow trout recruitment was negatively correlated with high annual, summer, and spring flow and dam latitude, and positively correlated with high winter flow, sub-adult brown trout catch, and reservoir storage capacity. Brown trout recruitment was negatively correlated with high water velocity and daily fluctuations in flow (i.e., hydropeaking) and positively correlated with adult rainbow trout catch. Among these many drivers, rainbow trout recruitment was primarily correlated with high winter flow combined with low spring flow, whereas brown trout recruitment was most related to high water velocity. The mean lengths of adult rainbow and brown trout were influenced by similar flow and catch metrics. Length in both species was positively correlated with high annual flow but declined in tailwaters with high daily fluctuations in flow, high catch rates of conspecifics, and when large cohorts recruited to adult size. Whereas brown trout did not respond to the proportion of water allocated between seasons, rainbow trout length increased in rivers that released more water during winter than in spring. Rainbow trout length was primarily related to high catch rates of conspecifics, whereas brown trout length was mainly related to large cohorts recruiting to the adult size class. Species-specific responses to flow management are likely attributable to differences in seasonal timing of key life history events such as spawning, egg hatching, and fry emergence.

Ecological Applications↗