Two decades have passed since the initiation of the National Oceanic and Atmospheric Administration’s research program aimed at advancing the understanding of estuary and ocean ecology of U.S. West ...Coast Pacific salmon (Oncorhynchus spp.). In this review and prospectus, we summarize key findings from this program and describe a plan for transitioning it to better support Ecosystem-Based Management (EBM). While we focus on salmon research, our approach applies to research design generally. Our path forward involves increasing understanding of ecosystem processes to improve the dependability of scenario testing under novel conditions. Over the past two decades, we developed a conceptual model for how climate, predators, prey, fisheries, and human activities influence salmon. Knowledge gaps we identified from our conceptual model include limited understanding of salmon distributions, behavior, maturation dynamics, and population dynamics, and salmon interactions with predators, competitors, and prey during winter. We consider emerging risks and vulnerabilities facing salmon and propose analysis frameworks for evaluating them. Increased predator populations, coupled with climate change, pose increasing threats to West Coast salmon and will require new strategies and actions to mitigate their negative impacts. We propose research to support the development of decision-support tools to evaluate tradeoffs associated with alternative management strategies and to inform an adaptive ecosystem management system to improve the resilience of salmon populations and salmon-dependent fisheries.
Hatchery programmes for supplementing depleted populations of fish are undergoing a worldwide expansion and have provoked concern about their ramifications for populations of wild fish. In ...particular, Pacific salmon are artificially propagated in enormous numbers in order to compensate for numerous human insults to their populations, yet the ecological impacts of this massive hatchery effort are poorly understood. Here we test the hypothesis that massive numbers of hatchery-raised chinook salmon reduce the marine survival of wild Snake River spring chinook, a threatened species in the USA. Based on a unique 25-year time-series, we demonstrated a strong, negative relationship between the survival of chinook salmon and the number of hatchery fish released, particularly during years of poor ocean conditions. Our results suggest that hatchery programmes that produce increasingly higher numbers of fish may hinder the recovery of depleted wild populations.
Columbia River plume fronts Morgan, Cheryl A.; De Robertis, Alex; Zabel, Richard W.
Marine ecology. Progress series,
09/2005, Letnik:
299
Journal Article
Recenzirano
Odprti dostop
Well-defined fronts develop at the leading edge of the Columbia River (USA) plume. Convergent flow at these frontal boundaries may concentrate zooplanktonic organisms, which may in turn increase ...local prey availability to planktivorous fishes. In May 2001 and 2002, we compared the density, biomass and community structure of planktonic and neustonic zooplankton among plume fronts, low-salinity plume waters, and within the more saline, coastal marine waters. Fronts were characterized by distinct color discontinuities and high wave energy and were usually accompanied by foam and flotsam. The surface manifestation of the fronts was narrow and formed a thin lens of warm, low-salinity water overlying colder and more saline shelf waters. Overall, neither zooplankton nor neuston densities were higher in frontal regions. However, some zooplankton taxa were more abundant at fronts, and plankton biomass was 4 to 47 times higher in the frontal regions than in the neighboring plume and more oceanic shelf waters. The zooplankton community in the front habitat was distinct, particularly in the near-surface neuston, and was comprised of more surface-oriented organisms compared to the adjacent ocean and plume waters. We conclude that convergence zones at frontal regions at the leading edge of the Columbia River plume concentrate organisms that, either through active swimming or positive buoyancy, are maintained near the surface. Time scales of these fronts are much shorter than generation times in these organisms and therefore we believe that the observed changes in biomass and community composition in the front habitat are due to physical concentrating mechanisms and not toin situgrowth. Increased zooplankton biomass at plume fronts may provide a unique and valuable food resource for planktivorous fishes, including juvenile salmonids as they transition from freshwater to the ocean environment.
•Timing data are difficult to analyze because conditions vary during the observation period.•We demonstrated methods to analyze “time-to-event” data under time-varying conditions.•We applied ...parametric models to the time for migrating salmonids to successfully pass a barrier.•The model captured pronounced diel behavior and the effects of time-varying covariates.
Timing phenomena are integral to many ecological processes but are difficult to analyze due to the unique nature of timing data and because environmental conditions and behavior can vary during the observation period. We demonstrated methods, based on parametric hazard-rate modeling, to analyze “time-to-event” data under time-varying conditions. We developed routines in R to apply parametric models, based on the exponential, Weibull, and modified Weibull distributions, to time-to-event data. We applied the models to data on the time for migrating adult salmonids to successfully pass a hydroelectric dam. The model captured pronounced diel behavior and the effects of time-varying covariates river flow, spill, and water temperature on passage times. The methods we demonstrated have potential application to a broad range of ecological questions.
Conservation biologists often ignore density dependence because at‐risk populations are typically small relative to historical levels. However, if populations are reduced as a result of impacts that ...lower carrying capacity, then density‐dependent mortality may exist at low population abundances. Here, we explore this issue in threatened populations of juvenile chinook salmon (Oncorhynchus tshawytscha). We followed the fate of more than 50 000 juvenile chinook in the Snake River Basin, USA to test the hypothesis that their survival was inversely associated with juvenile density. We also tested the hypotheses that non‐indigenous brook trout and habitat quality affect the presence or strength of density dependence. Our results indicate that juvenile chinook suffer density‐dependent mortality and the strength of density dependence was greater in streams in which brook trout were absent. We were unable to detect an effect of habitat quality on the strength of density dependence. Historical impacts of humans have greatly reduced population sizes of salmon, and the density dependence we report may stem from a shortage of nutrients normally derived from decomposing salmon carcasses. Cohorts of juvenile salmon may experience density‐dependent mortality at population sizes far below historical levels and recovery of imperiled populations may be much slower than currently expected.
For species of conservation concern, an essential part of the recovery planning process is identifying discrete population units and their location with respect to one another. A common feature among ...geographically proximate populations is that the number of organisms tends to covary through time as a consequence of similar responses to exogenous influences. In turn, high covariation among populations can threaten the persistence of the larger metapopulation. Historically, explorations of the covariance in population size of species with many (>10) time series have been computationally difficult. Here, we illustrate how dynamic factor analysis (DFA) can be used to characterize diversity among time series of population abundances and the degree to which all populations can be represented by a few common signals. Our application focuses on anadromous Chinook salmon (Oncorhynchus tshawytscha), a species listed under the US Endangered Species Act, that is impacted by a variety of natural and anthropogenic factors. Specifically, we fit DFA models to 24 time series of population abundance and used model selection to identify the minimum number of latent variables that explained the most temporal variation after accounting for the effects of environmental covariates. We found support for grouping the time series according to 5 common latent variables. The top model included two covariates: the Pacific Decadal Oscillation in spring and summer. The assignment of populations to the latent variables matched the currently established population structure at a broad spatial scale. At a finer scale, there was more population grouping complexity. Some relatively distant populations were grouped together, and some relatively close populations – considered to be more aligned with each other – were more associated with populations further away. These coarse‐ and fine‐grained examinations of spatial structure are important because they reveal different structural patterns not evident in other analyses.
Considerable interest and recent attention have been paid to the importance of intraspecies diversity and the ability of species to be resilient to perturbations much as diverse financial investment portfolios do. However, there is not as much attention paid to the mechanisms behind this. In our manuscript, we attempt to characterize intraspecies diversity through the analysis of empirical data sets of population abundance from a temporal and spatial perspective. We employ and illustrate an application of state‐space modeling, dynamic factor analysis, which is gaining some attention in the ecological literature.
To aid the recovery of a species, understanding the extent to which populations are connected is useful for targeting conservation efforts. Pacific hake within waters of Puget Sound, Washington ...State, USA, and Georgia Strait, British Columbia, Canada are listed as a species of concern under the U.S. Endangered Species Act due to dramatic declines in the Puget Sound population. To assess the role of dispersal in the recovery of Pacific hake, we sought to quantify patterns of connectivity between populations in Puget Sound and Georgia Strait. Using natural chemical markers from otoliths of fish sampled from these two populations, we linked natal signatures of fish to signatures of individuals from known spawning grounds. Results indicated that 82 % of individuals collected from Puget Sound (
n
= 78) were estimated to have originated there, while 40 and 92 % of the individuals collected from two cohorts within Georgia Strait (
n
= 9 and 24, respectively) had originated from Puget Sound. A trend of “population abandonment” of fish from Puget Sound suggests that recovery of this Pacific hake population will depend on local management practices.
Behavioral heterogeneity among individuals is a universal feature of natural populations. Most diffusion-based models of animal dispersal, however, implicitly assume homogeneous movement parameters ...within a population. Recent attempts to consider the effect of heterogeneous populations on dispersal distributions have been somewhat limited by the high number of parameters required to subdivide a population into several groups. A solution to this problem is to characterize the value of a movement parameter as continously distributed within a population. We present several cases in which this method is useful and tractable, applying the framework both to spatial distribution data and closely related first passage times. The resulting models allow ecologists to identify the extent to which the variability in dispersal distributions can be attributed to population-level heterogeneity as opposed to intrinsic randomness. We apply the formulation to two very different cases of dispersal: resident organisms in a stream (freshwater chub Nocomis leptocephalus) and migrating organisms (juvenile salmonids Oncorhynchus spp.). In both cases, the application of heterogeneity-explicit models provides insights into the behavioral mechanisms of movement.
In recent years, returns of adult sockeye salmon Oncorhynchus nerka to the Columbia River Basin have reached numbers not observed since the 1950s. To understand factors related to these increased ...returns, we first looked for changes in freshwater production and survival of juvenile migrants. We then evaluated productivity changes by estimating smolt‐to‐adult return rates (SAR) for juvenile migration years 1985–2010. We found SAR varied between 0.2 and 23.5%, with the highest values coinciding with recent large adult returns. However, the largest adult return, in 2012, resulted not from increased survival, but from increased smolt production. We evaluated 19 different variables that could influence SARs, representing different facets of freshwater and ocean conditions. We used model selection criteria based on small‐sample corrected AIC to evaluate the relative performance of all two‐ and three‐variable models. The model with April upwelling, Pacific Northwest Index (PNI) in the migration year, and PNI in the year before migration had 10 times the AICc weight as the second‐best‐supported model, and R² = 0.82. The variables of April ocean upwelling and PNI in the migration year had high weights of 0.996 and 0.927, respectively, indicating they were by far the best of the candidate variables to explain variations in SAR. While our analyses were primarily correlative and limited by the type and amount of data currently available, changes in ocean conditions in the northern California Current system, as captured by April upwelling and PNI, appeared to play a large role in the variability of SAR.
Considerable research has highlighted the important role of anadromous salmon in importing marine-derived nutrients to freshwater and riparian ecosystems. These subsidies are thought to support ...diverse food webs and increase the growth and survival of juvenile salmon during their freshwater residency. Quite recently, however, salmon smolts have been identified as important exporters of nutrients from freshwater ecosystems. Using a mass-balance approach, we examined the phosphorus-transport dynamics by spring/summer Chinook salmon (Oncorhynchus tshawytscha) in the Snake River basin and estimated that net phosphorus transport into the basin over the past 40 years was <2% of historical levels. Furthermore, a nonlinear relationship existed between nutrient import by adults and subsequent export by smolts, such that smolts exported proportionally more phosphorus as spawner abundance decreased. In 12% of years, smolts exported more than adults imported, resulting in a net loss of phosphorus from the ecosystem. This loss of marine subsidies may have caused a state shift in the productivity of the freshwater ecosystem, resulting in strong density-dependent survival observed in juvenile salmon. These results suggest that conserving this threatened stock of salmon requires the need to explicitly address the important role of marine-derived nutrients and energy in sustaining salmon populations.
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