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David A. Boughton

Publications and source records attributed to David A. Boughton.

8 recordsLinked to original sources
USGS2023

Vulnerability to climate change of managed stocks in the California Current large marine ecosystem

Introduction: Understanding how abundance, productivity and distribution of individual species may respond to climate change is a critical first step towards anticipating alterations in marine ecosystem structure and function, as well as developing strategies to adapt to the full range of potential changes. Methods: This study applies the NOAA (National Oceanic and Atmospheric Administration) Fisheries Climate Vulnerability Assessment method to 64 federally-managed species in the California Current Large Marine Ecosystem to assess their vulnerability to climate change, where vulnerability is a function of a species’ exposure to environmental change and its biological sensitivity to a set of environmental conditions, which includes components of its resiliency and adaptive capacity to respond to these new conditions. Results: Overall, two-thirds of the species were judged to have Moderate or greater vulnerability to climate change, and only one species was anticipated to have a positive response. Species classified as Highly or Very Highly vulnerable share one or more characteristics including: 1) having complex life histories that utilize a wide range of freshwater and marine habitats; 2) having habitat specialization, particularly for areas that are likely to experience increased hypoxia; 3) having long lifespans and low population growth rates; and/or 4) being of high commercial value combined with impacts from non-climate stressors such as anthropogenic habitat degradation. Species with Low or Moderate vulnerability are either habitat generalists, occupy deep-water habitats or are highly mobile and likely to shift their ranges. Discussion: As climate-related changes intensify, this work provides key information for both scientists and managers as they address the long-term sustainability of fisheries in the region. This information can inform near-term advice for prioritizing species-level data collection and research on climate impacts, help managers to determine when and where a precautionary approach might be warranted, in harvest or other management decisions, and help identify habitats or life history stages that might be especially effective to protect or restore.

California, Oregon, Washington↗
USGS2021

Capacity of two Sierra Nevada rivers for reintroduction of anadromous salmonids: Insights from a high-resolution view

Historically, anadromous steelhead Oncorhynchus mykiss and spring-run Chinook Salmon O. tshawytscha used high-elevation rivers in the Sierra Nevada of California but were extirpated in the 20th century by construction of impassable dams. Plans to reintroduce the fish by opening migratory passage across the dams and reservoirs can only succeed if upstream habitats have the capacity to support viable populations of each species. To estimate capacity in the Tuolumne and Merced rivers of the central Sierra Nevada, we used a high-resolution approach based on remote sensing and dynamic habitat modeling. Our results suggested that for both species in both systems, sediment grain sizes would support widespread spawning and the water temperatures, depths, and velocities would generate ample capacity for fry and juveniles. However, the unregulated Merced River was consistently too warm for adult Chinook Salmon to hold in the dry season prior to spawning, while the regulated Tuolumne River maintained a cooler, more stable thermal regime with a capacity for thousands of holding adults. In our high-resolution approach, we also discovered several specific physical controls on life history expression, including thermal constraints on the timing of spawning, hydraulic prompts for downstream migration of fry, divergence of the hydraulic niches of steelhead and Chinook Salmon, and a key but uncertain role for thermal tolerance in adult Chinook Salmon. Our results suggested that steelhead reintroduction could succeed in either system and Chinook Salmon could succeed in the Tuolumne River if passage strategies account for large numbers of migrant fry and juveniles driven downstream by winter storms and snowmelt. The Merced River appeared too warm for adult Chinook Salmon, which raises questions about the current limited understanding of thermal tolerance in holding adults. Our study shows how a high-resolution approach can provide valuable insights on specific limiting factors that must be addressed for reintroduction to succeed.

California↗
USGS2019

Climate vulnerability assessment for Pacific salmon and steelhead in the California Current Large Marine Ecosystem

Major ecological realignments are already occurring in response to climate change. To be successful, conservation strategies now need to account for geographical patterns in traits sensitive to climate change, as well as climate threats to species-level diversity. As part of an effort to provide such information, we conducted a climate vulnerability assessment that included all Pacific salmon and steelhead (Oncorhynchus spp.) listed under the U.S. Endangered Species Act. Using an expert-based scoring system, we ranked 20 attributes for the 28 listed units, and 5 additional units. Attributes captured biological sensitivity, or the strength of linkages between each listing unit and the present climate; climate exposure, or the magnitude of projected change in local environmental conditions; and adaptive capacity, or the ability to modify phenotypes to cope with new climatic conditions. Each listing unit was then assigned one of four vulnerability categories.

California↗
USGS2018

River response to large‐dam removal in a Mediterranean hydroclimatic setting: Carmel River, California, USA

Dam removal provides a valuable opportunity to measure the fluvial response to changes in both sediment supply and the processes that shape channel morphology. We present the first study of river response to the removal of a large (32‐m‐high) dam in a Mediterranean hydroclimatic setting, on the Carmel River, coastal California, USA. This before‐after/control‐impact study measured changes in channel topography, grain size, and salmonid spawning habitat throughout dam removal and subsequent major floods. During dam removal, the river course was rerouted in order to leave most of the impounded sediment sequestered in the former reservoir and thus prevent major channel and floodplain aggradation downstream. However, a substantial sediment pulse occurred in response to base‐level fall, knickpoint migration, and channel avulsion through sediment in the former reservoir above the newly rerouted channel. The sediment pulse advanced ~3.5 km in the first wet season after dam removal, resulting in decreased riverbed grain size downstream of the dam site. In the second wet season after dam removal, high flows (including a 30‐year flood and two 10‐year floods) transported sediment >30 km downstream, filling pools and reducing cross‐channel relief. Deposition of gravel in the second wet season after dam removal enhanced salmonid spawning habitat downstream of the dam site. We infer that in dam removals where most reservoir sediment remains impounded and where high flows follow soon after dam removal, flow sequencing becomes a more important driver of geomorphic and fish‐habitat change than the dam removal alone.

California↗
USGS2015

Seasonal weather patterns drive population vital rates and persistence in a stream fish

Climate change affects seasonal weather patterns, but little is known about the relative importance of seasonal weather patterns on animal population vital rates. Even when such information exists, data are typically only available from intensive fieldwork (e.g., mark–recapture studies) at a limited spatial extent. Here, we investigated effects of seasonal air temperature and precipitation (fall, winter, and spring) on survival and recruitment of brook trout ( Salvelinus fontinalis ) at a broad spatial scale using a novel stage‐structured population model. The data were a 15‐year record of brook trout abundance from 72 sites distributed across a 170‐km‐long mountain range in Shenandoah National Park, Virginia, USA. Population vital rates responded differently to weather and site‐specific conditions. Specifically, young‐of‐year survival was most strongly affected by spring temperature, adult survival by elevation and per‐capita recruitment by winter precipitation. Low fall precipitation and high winter precipitation, the latter of which is predicted to increase under climate change for the study region, had the strongest negative effects on trout populations. Simulations show that trout abundance could be greatly reduced under constant high winter precipitation, consistent with the expected effects of gravel‐scouring flows on eggs and newly hatched individuals. However, high‐elevation sites would be less vulnerable to local extinction because they supported higher adult survival. Furthermore, the majority of brook trout populations are projected to persist if high winter precipitation occurs only intermittently (≤3 of 5 years) due to density‐dependent recruitment. Variable drivers of vital rates should be commonly found in animal populations characterized by ontogenetic changes in habitat, and such stage‐structured effects may increase population persistence to changing climate by not affecting all life stages simultaneously. Yet, our results also demonstrate that weather patterns during seemingly less consequential seasons (e.g., winter precipitation) can have major impacts on animal population dynamics.

Virginia↗
USGS2007

Viability criteria for steelhead of the south-central and southern California coast

Recovery planning for threatened and endangered steelhead requires measurable, objective criteria for determining an acceptably low risk of extinction. Here we propose viability criteria for two levels of biological organization: individual populations, and groups of populations within the SouthCentral/Southern California Coast Steelhead Recovery Planning Domain. For populations, we adapt criteria commonly used by the IUCN (The World Conservation Union) for identifying at-risk species. For groups of populations we implement a diversity-based “representation and redundancy rule,” in which diversity includes both life-history diversity and biogeographic groupings of populations. The resulting criteria have the potential for straightforward assessment of the risks posed by evolutionary, demographic, environmental, and catastrophic factors; and are designed to use data that are readily collected. However, our prescriptive approach led to one criterion whose threshold could not yet be specified due to inadequate data, and others in which the simplicity of the criteria may render them inefficient for populations with stable run sizes or stable life-history polymorphisms. Both of these problems could likely be solved by directed programs of research and monitoring aimed at developing more efficient (but equally risk-averse) “performance-based criteria.” Of particular utility would be data on the natural fluctuations of populations, research into the stabilizing influence of life-history polymorphisms, and research on the implications of drought, wildfires, and fluvial sediment regimes. Research on estuarine habitat could also yield useful information on the generality and reliability of its role as nursery habitat. Currently, risk assessment at the population level is not possible due to data deficiency, highlighting the need to implement a comprehensive effort to monitor run sizes, anadromous fractions, spawner densities and perhaps marine survival. Assessment at the group level indicates a priority for securing inland populations in the southern Coast Ranges and Transverse Ranges, and a need to maintain not just the fluvial-anadromous life-history form, but also lagoon-anadromous and freshwater-resident forms in each population.

Report↗