Dissolved oxygen (DO) is essential to the survival of almost all aquatic organisms. Here, we examine the possibility that abundant Pacific salmon (Oncorhynchus spp.) and low streamflow combine to create hypoxic events in coastal rivers. Using high-frequency DO time series from two similar watersheds in southeastern Alaska, we summarize DO regimes and the frequency of hypoxia in relationship to salmon density and stream discharge. We also employ a simulation model that links salmon oxygen respiration to DO dynamics and predicts combinations of salmon abundance, discharge, and water temperature that may result in hypoxia. In the Indian River, where DO was monitored hourly during the ice-free season from 2010 to 2015, DO levels decreased when salmon were present. In 2013, a year with extremely high spawning salmon densities, DO dropped to 1.7 mg/L and 16% saturation, well below lethal limits. In Sawmill Creek, where DO was monitored every six minutes across an upstream–downstream gradient during the 2015 spawning season, DO remained fully saturated upstream of spawning reaches, but declined markedly downstream to 2.9 mg/L and 26% saturation during spawning. Modeled DO dynamics in the Indian River closely tracked field observations. Model sensitivity analysis illustrates that low summertime river discharge is a precursor to salmon-induced oxygen depletion in our study systems. Our results provide compelling evidence that dense salmon populations and low discharge can trigger hypoxia, even in rivers with relatively cold thermal regimes. Although climate change modeling for southeastern Alaska predicts an increase in annual precipitation, snowfall in the winter and rainfall in the summer are likely to decrease, which would in turn decrease summertime discharge in rain- and snow-fed streams and potentially increase the frequency of hypoxia. Our model template can be adapted by resource managers and watershed stakeholders to create real-time predictive models of DO trends for individual streams. While preserving thermally suitable stream habitat for cold-water taxa facing climate change has become a land management priority, managers should also consider that some protected watersheds may still be at risk of increasingly frequent hypoxia due to human impacts such as water diversion and artificially abundant salmon populations caused by hatchery straying.
Many species living in deeper lentic ecosystems exhibit daily movements that cycle through the water column, generally referred to as diel vertical migration (DVM). In this study, we applied bioenergetics modelling to evaluate growth as a hypothesis to explain DVM by bull trout (Salvelinus confluentus) in a thermally stratified reservoir (Ross Lake, WA, USA) during the peak of thermal stratification in July and August. Bioenergetics model parameters were derived from observed vertical distributions of temperature, prey and bull trout. Field sampling confirmed that bull trout prey almost exclusively on recently introduced redside shiner (Richardsonius balteatus). Model predictions revealed that deeper (>25 m) DVMs commonly exhibited by bull trout during peak thermal stratification cannot be explained by maximising growth. Survival, another common explanation for DVM, may have influenced bull trout depth use, but observations suggest there may be additional drivers of DVM. We propose these deeper summertime excursions may be partly explained by an alternative hypothesis: the importance of colder water for gametogenesis. In Ross Lake, reliance of bull trout on warm water prey (redside shiner) for consumption and growth poses a potential trade-off with the need for colder water for gametogenesis.
Resource managers increasingly use habitat suitability map products to inform risk management and policy decisions. Modeling habitat suitability of data-poor species over large areas requires careful attention to assumptions and limitations. Resulting habitat suitability maps can harbor uncertainties from data collection and modeling processes; yet these limitations are not always transparent to resource managers, who increasingly rely on maps for spatial planning and risk assessment purposes. Interpretation of habitat suitability maps can be improved by visually communicating model uncertainty and data foundations. We applied Bayesian networks (BNs) to a small, marine dataset to model the probability of occurrence (PO) of benthic macrofauna. We also used BNs to create maps displaying model parameter uncertainty and data limitations. We developed BN models for three macrofauna species: a marine gastropod, Aystris gausapata, a marine bivalve, Axinopsida serricata, and a marine worm, Sternaspis fossor. We produced three map products from the BN models of each species: (1) a habitat suitability map of the PO projected from regional predictor variables; (2) an uncertainty map, displaying statistical variance of model predictions of occurrence probability; and (3) an experience map, displaying the empirical basis for PO predictions (equivalent sample size). Map results showed occurrence probability to be high and widespread for Ax. serricata, low to moderate and more limited to deeper offshore areas for Ay. gausapata, and low to high in shallow sandy regions and deeper silty regions, respectively, for S. fossor. The uncertainty and experience maps for each species helped identify regions to prioritize for future sampling. Our results are the first to show that BNs can effectively model habitat suitability of benthic macrofauna, and our detailed methods can be applied to a variety of taxa and systems. Visually describing statistical model uncertainty and equivalent sample size in map format improves interpretation of habitat suitability map predictions and supports place-based risk management of marine management.
Habitat selection is a fundamental component of community ecology, population ecology, and evolutionary biology and can be especially important to species with complex annual habitat requirements, such as migratory birds. Resource preferences on the breeding grounds may change during the postfledging period for migrant songbirds, however, the degree to which selection changes, timing of change, and whether all or only a few species alter their resource use is unclear. We compared resource selection for nest sites and resource selection by postfledging juvenile ovenbirds (Seiurus aurocapilla) and Acadian flycatchers (Empidonax virescens) followed with radio telemetry in Missouri mature forest fragments from 2012−2015. We used Bayesian discrete choice modeling to evaluate support for local vegetation characteristics on the probability of selection for nest sites and locations utilized by different ages of postfledging juveniles. Patterns of resource selection variation were species-specific. Resource selection models indicated that Acadian flycatcher habitat selection criteria were similar for nesting and dependent postfledging juveniles and selection criteria diverged when juveniles became independent from adults. After independence, flycatcher resource selection was more associated with understory foliage density. Ovenbirds differed in selection criteria between the nesting and postfledging periods. Fledgling ovenbirds selected areas with higher densities of understory structure compared to nest sites, and the effect of foliage density on selection increased as juveniles aged and gained independence. The differences observed between two sympatric forest nesting species, in both the timing and degree of change in resource selection criteria over the course of the breeding season, illustrates the importance of considering species-specific traits and postfledging requirements when developing conservation efforts, especially when foraging guilds or prey bases differ. We recommend that postfledging habitat selection be considered in future conservation efforts dealing with Neotropical migrants and other forest breeding songbirds.
La historia de las truchas del Pacífico, pertenecientes al género Oncorhynchus, es una historia muy interesante que se basa en la persistencia y diversificación de sus especies debido, en gran parte, al dinamismo propio que existe en su medio ambiente. Desde el oeste de Norteamérica, extendiéndose hasta el este de Asia, las truchas del Pacífico han experimentado la influencia de los avances y retrocesos de glaciares, vulcanismo, condiciones extremas en el caudal de los ríos, al igual que eventos geotectónicos, que han permitido la formación de cordilleras y mesetas. Dichos eventos son los que han determinado el curso actual de los ríos modernos. En el oeste de Norteamérica, entre las especies de trucha del Pacífico se incluyen la trucha degollada (O. clarkii ssp.), la arcoiris (O. mykiss ssp.), la dorada (O. aguabonita ssp.), la trucha gila (O. gilae), la trucha Apache (O. apache) y la trucha dorada Mexicana (O. chrysogaster), además del complejo diverso de truchas de la Sierra Madre Occidental (SMO) en México que aún no son clasificadas taxonómicamente.
Increasing diversity in the fisheries profession, including diversity of members of the American Fisheries Society (AFS), is vital to ensuring the future relevance of fish and their habitats, fisheries, and fisheries professionals in the broader context of society. Any well-informed natural resource professional understands the value of a diverse ecosystem, and savvy investors know that their portfolios must contain diverse investments. Similarly, the fisheries profession will be stronger and more resilient if it better represents the society it serves. The following article by Penaluna et al. suggests nine action areas to enhance diversity and inclusion in AFS. Their suggested actions are timely because developing and implementing strategies to make meaningful progress in increasing diversity throughout the fisheries profession constitutes one of the key aspects of my presidential plan of work. To “move the needle” on diversity, we will need action across all sectors of the profession to open the valves in a pipeline that currently produces only a trickle of diverse candidates for fisheries jobs. Many valves in the talent pipeline require opening: improving current conditions to retain diverse talent, recruitment of diverse candidates to undergraduate university programs, fellowships or other incentives to fund diverse candidates in graduate schools, functional internship programs in all employment sectors of the profession to enhance experiential learning, and realistic job prospects for graduates. AFS is uniquely positioned to assist in this effort because it represents fisheries professionals in education and all employment sectors. Our renewed emphasis on increasing diversity and inclusion in AFS is an opportunity to purposely build an even better professional society that more broadly represents those interested in fish and fisheries as well as fisheries professionals. One of the most important tasks of a leader is to develop the future capacity of an organization, to make it stronger after the leader is gone. As incoming AFS president, I welcome the opportunity and challenge of serving you and building a Society that is even stronger, more diverse, and more resilient than it is today.
In the Pacific Northwest, native salmon and trout are some of the toughest survivors on the block. Over time, these fish have evolved behavioral adaptations to natural disturbances, and they rely on these disturbances to deliver coarse sediment and wood that become complex stream habitat. Powerful disturbances such as wildfire, postfire landslides, and debris flows may be detrimental to fish populations in the short term, but over time, they enrich instream habitats, enhancing long-term fish survival and productivity.
Over the past century, dams, roads, and timber harvest practices have contributed to the decline in the amount and complexity of salmon and trout habitat in the Pacific Northwest. New research indicates that wildfire suppression adjacent to streams also may have inadvertently reduced the quality of aquatic habitat. The accumulation of forest fuels also has set the stage for higher-than-normal fire intensity, and perhaps larger fires that may cause extensive damage to local fish populations. This poses a significant problem for isolated and vulnerable fish populations such as bull trout.
Scientists with the U.S. Forest Service’s Pacific Northwest Research Station and partners modeled the potential effects wildfire on spring Chinook salmon and bull trout habitat in Washington’s Wenatchee River subbasin. Their findings indicate that, in some situations, wildfires or managed wildfires may be a useful management strategy for aquatic habitat restoration.
Research Benefits Society. Forest Service research helps society make choices about water, wildlife, and natural resources. Scientific understanding gained from research transforms the way land managers rise to challenges. For example, the tools and information used daily by managers and policymakers to make cost-effective and environmentally sound fire management decisions are based on research about fire behavior, fire ecology, fuels, and smoke in ecosystems. As a result, citizens are provided ways to secure their homes from fire, are warned when smoke requires them to take precautions, and informed how forests can be managed to reduce fire risk in their communities.
Science-based knowledge and tools are being used to restore our Nations’ forests and protect their ability to provide clean water and air. In doing so, jobs are created, forest products—from lumber for homes to Native American basketry materials—are provided, cities become greener and healthier, wildlife and fish prosper, and humans increase the quality of life for themselves, their children, and grandchildren. Our Nation’s forests provide a bounty of oxygen, water, foods, and wood. Research gives society the means to understand this, appreciate the complexity inherent in forests, and ensure that the values from forests and grasslands are realized today and tomorrow.
Waterways of the USA are protected under the public trust doctrine, placing responsibility on the state to safeguard public resources for the benefit of current and future generations. This responsibility has led to the development of management standards for lands adjacent to streams. In the state of Oregon, policy protection for riparian areas varies by ownership (e.g., federal, state, or private), land use (e.g., forest, agriculture, rural residential, or urban) and stream attributes, creating varying standards for riparian land-management practices along the stream corridor. Here, we compare state and federal riparian landmanagement standards in four major policies that apply to private and public lands in the Oregon Coast Range. We use a standard template to categorize elements of policy protection: (1) the regulatory approach, (2) policy goals, (3) stream attributes, and (4) management standards. All four policies have similar goals for achieving water-quality standards, but differ in their regulatory approach. Plans for agricultural lands rely on outcome-based standards to treat pollution, in contrast with the prescriptive policy approaches for federal, state, and private forest lands, which set specific standards with the intent of preventing pollution. Policies also differ regarding the stream attributes considered when specifying management standards. Across all policies, 25 categories of unique standards are identified. Buffer widths vary from 0 to ~152 m, with no buffer requirements for streams in agricultural areas or small, non-fish-bearing, seasonal streams on private forest land; narrow buffer requirements for small, nonfish- bearing perennial streams on private forest land (3 m); and the widest buffer requirements for fish-bearing streams on federal land (two site-potential tree-heights, up to an estimated 152 m). Results provide insight into how ecosystem concerns are addressed by variable policy approaches in multiownership landscapes, an important consideration to recovery-planning efforts for threatened species.
Water temperature can have a profound influence on development and distribution of aquatic species. Salmon are particularly vulnerable to temperature changes because their reproductive and early development life phases are spent in freshwater river systems where temperature fluctuates widely both daily and seasonally. Flow regulation downstream of dams can also cause temperature regime changes, which in turn may spur local adaptation of early life-history traits. In a common garden laboratory incubation experiment, we exposed spring Chinook salmon (Oncorhynchus tshawytscha) embryos to four temperature regimes: warm stable, cold stable, daily variation and below dam. We found that fry from warmer thermal regimes emerged earlier than those from colder regimes both in terms of calendar date and temperature units and that warmer temperatures caused fry to emerge less developed. There was also a significant effect of family on both emergence timing and development level at emergence. By combining measurements of physiological and behavioural traits at emergence and interpreting them within a reaction norm framework, we can better understand which populations might be more vulnerable to altered thermal regimes.