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Map of Prince William Sound, and the adjacent Copper River Alaska. Triangles indicate the location of wild salmon stocks included in our analyses, circles show towns, and the asterisk shows where the Exxon Valdez ran aground in 1989.
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The Exxon Valdez oil spill occurred in March 1989 in Prince William Sound, Alaska, and was one of the worst environmental disasters on record in the United States. Despite long-term data collection over the nearly three decades since the spill, tremendous uncertainty remains as to how significantly the spill affected fishery resources. Pacific herr...
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Citations
... Even early studies on oil spills found that laboratory experiments often failed to predict real-world outcomes, and that effects on fish populations and fisheries were often the hardest component of coastal ecosystems on which to quantify impacts of offshore oil spills (Teal and Howarth 1984). Salmon and groundfish displayed only muted responses to the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska (Ward et al. 2017;Shelton et al. 2018). While the herring population collapsed several years after the spill and has not rebounded, the cause of the persistent low herring abundance remains unclear; several mechanisms have been proposed and are likely acting in concert (Trochta and Branch 2021). ...
The Deepwater Horizon disaster released 4.9 million barrels of oil into the Gulf of Mexico. Despite clear evidence of exposure and toxicity, there has been little evidence of population-level declines of most nearshore fish and invertebrate populations. Several hypotheses have been proposed to explain this paradox. Two possibilities include a fishing moratorium following the spill and reductions in predation pressure following predator die-offs. We tested both using mass-balance food web models to quantify direct and indirect population sensitivity to perturbations in fishing pressure and bird and dolphin mortality. In doing so, we developed a new method allowing us to quantify responses of one functional group to changes in fishing pressure across all fished groups. We inferred support for a compensatory mechanism, either release from fishing or predation, when populations modeled without any oil-induced mortality displayed large increases to negative perturbations in fishing or predation. We found the fishing moratorium to be the most likely potential mitigating mechanism, especially for penaeid shrimp, menhaden, and blue crabs. Dolphin mortality may explain the stability of small sciaenids. Increased seabird mortality did not lead to major changes in any functional group we examined. The consideration of indirect trophic pathways within the food web model produced a wide range of plausible population responses, especially responses to increases in predator mortality. Broadly, this work shows that oil spills are one driver of population dynamics within a broader socioecological system, and understanding oil spill impacts on populations requires consideration of this complexity.
... One of the three no-effect publications focused explicitly on potential juvenile competition in nearshore habitats during early marine residence (Sturdevant et al., 2011), while the other two focused on adult hatchery Chinook salmon production (Ohlberger et al., 2018;Nelson et al., 2019). Most other publications examined correlations between hatchery chum salmon and pink salmon and the productivity and growth wild adult salmon in the ocean (e.g., Cunningham et al., 2018;Frost et al., 2020;Ward et al., 2017). ...
Hatcheries have long produced salmonids for fisheries and mitigation, though their widespread use is increasingly controversial because of potential impacts to wild salmonids. We conducted a global literature search of peer-reviewed publications (1970–2021) evaluating how hatchery salmonids affected wild salmonids, developed a publicly available database, and synthesized results. Two hundred six publications met our search criteria, with 83% reporting adverse/minimally adverse effects on wild salmonids. Adverse genetic effects on diversity were most common, followed by effects on productivity and abundance via ecological and genetic processes. Few publications (3%) reported beneficial hatchery effects on wild salmonids, nearly all from intensive recovery programs used to bolster highly depleted wild populations. Our review suggests hatcheries commonly have adverse impacts on wild salmonids in freshwater and marine environments. Future research on less studied effects—such as epigenetics—could improve knowledge and management of the full extent of hatchery impacts.
... However, as the director of Fisheries Research of Alaska Department of Fish and Game said to the Board of Fish, "correlation is not causation" (Medred, 2021). Recent research is documenting how interactions between the two variables are more complicated because of several confounding factors (Ward et al., 2017). Oke et al. (2020) found hatchery production alone accounted for only a small amount of the total variance in the declines of adult salmon size; however, hatchery Pink Salmon abundance was the only variable negatively related to salmon body size in Chinook, Chum, Sockeye, and Coho Salmon. ...
We present a collaboratively developed social-ecological model of the Kenai River Fishery. We developed the model through iterative interviews with stakeholders throughout the Kenai Peninsula using a novel participatory Fuzzy Cognitive Mapping process grounded in Ostrom's social-ecological systems framework. Individual social-ecological models, developed one-on-one with stakeholders, were combined into a single aggregated model representing the system's structure and function. We validated this aggregated model through subsequent interviews with stakeholders and focused literature reviews. The result is a model that can: 1) illustrate the breadth and interconnectedness of the Kenai River Fishery's social-ecological system; 2) be used to facilitate discussions around management of the fishery; and 3) be used to explore the components and interactions that move the system toward or away from sustainability. Using the model, we identify how the nature of salmon (migratory) and their habitat (large and unpredictable) leads to uncertainty about effective management strategies. This uncertainty, in addition to a large and diverse set of resource users, creates conflicting management goals that ultimately limit the governance system in making decisions that might increase the sustainability of the fishery. 3
... Oil components such as Polycyclic Aromatic Hydrocarbons (PAHs) particularly affect early life stages of fish at the individual level through malformations, for example, cardiovascular function (Marris et al., 2020) or development (Sørhus et al., 2015). Moreover, some evidence suggests a reduced abundance of fish larvae proceeding the Deepwater Horizon oil-spill (Rooker et al., 2013), but few studies have reported effects at the population level (Fodrie et al., 2014;Ward et al., 2017). This apparent paradox can have many possible explanations, including biological processes, such as a dampening of effects by density-dependent survival (Ohlberger & Langangen, 2015). ...
Mass mortality events are ubiquitous in nature and can be caused by, for example, diseases, extreme weather and human perturbations such as contamination. Despite being prevalent and rising globally, how mass mortality in early life causes population-level effects such as reduced total population biomass, is not fully explored. In particular for fish, mass mortality affecting early life may be dampened by compensatory density-dependent processes. However, due to large variations in year-class strength, potentially caused by density-independent variability in survival, the impact at the population level may be high in certain years. We quantify population-level impacts at two levels of mass mortality (50% and 99% additional mortality) during early life across 40 fish species using age-structured population dynamics models. The findings from these species-specific models are further supported by an analysis of detailed stock-specific models for three of the species. We find that population impacts are highly variable between years and species. Short-lived species that exhibit a low degree of compensatory density dependence and high interannual variation in survival experience the strongest impacts at the population level. These quantitative and general relationships allow predicting the range of potential impacts of mass mortality events on species based on their life history. This is critical considering that the frequency and severity of mass mortality events are increasing worldwide.
... For example, in the Bering Sea, migration of herring to spawning grounds is highly correlated with ice melt, as herring likely use thermoclines to orientate themselves (Tojo et al. 2007). Ward et al. (2017) showed that herring productivity is negatively correlated with freshwater discharge in the Prince William Sound region. Although they proposed that freshwater impacts to lower trophic level productivity could be the root cause, our results suggest another potential impact earlier in the life history, as changes in spawn timing (as well as the phenology of the annual productivity cycle) could result in match−mismatch situations for larval herring post-hatch. ...
Shifts in spawning phenology may impact the early life stages of small pelagic fishes,
affecting their first-year survival and recruitment. In Prince William Sound, Pacific herring is a key
forage species that once supported commercial and subsistence fisheries for many decades, but
collapsed in 1993 and has yet to recover. Starting in 1980, spawn timing shifted earlier by approximately
2−4 wk over a 27 yr period, then abruptly shifted later by approximately 3 wk over the next
7 yr. We quantified the influence of 15 environmental and population-level covariates on these spawn
timing shifts using generalized linear models. Earlier spawn timing was associated with higher
biomass in the eastern sound and older mean age in the western sound. Across the entire sound, earlier
spawning was associated with weaker downwelling, weaker meridional winds, and the positive
phase of the Pacific-North American teleconnection pattern, which is characterized by warmer
North Pacific waters. These results are a critical first step towards assessing how changes in spawning
phenology impact first-year survival of herring offspring and potentially contribute to persistent
poor recruitment that has inhibited the recovery of the Prince William Sound population.
... Even early studies on oil spills found that laboratory experiments often failed to predict real-world outcomes, and that effects on fish populations and fisheries were often the hardest component of coastal ecosystems on which to quantify impacts of offshore oil spills (Teal and Howarth 1984). Salmon and groundfish displayed only muted responses to the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska (Ward et al. 2017;Shelton et al. 2018). While the herring population collapsed several years after the spill and has not rebounded, the cause of the persistent low herring abundance remains unclear; several mechanisms have been proposed and are likely acting in concert (Trochta and Branch 2021). ...
The Deepwater Horizon disaster released 4.9 million barrels of oil into the Gulf of Mexico. Despite clear evidence of exposure and toxicity, there has been little evidence of population-level declines of most nearshore fish and invertebrate populations. Several hypotheses have been proposed to explain this paradox. Two possibilities include a fishing moratorium following the spill and reductions in predation pressure following predator die-offs. We tested both using mass-balance food web models to quantify direct and indirect population sensitivity to perturbations in fishing pressure and bird and dolphin mortality. In doing so, we developed a new method allowing us to quantify responses of one functional group to changes in fishing pressure across all fished groups. We inferred support for a compensatory mechanism, either release from fishing or predation, when the magnitude of modeled population increases following perturbations in fishing or predation far exceeded observations. We found the fishing moratorium to be the most likely potential mitigating mechanism, especially for penaeid shrimp, menhaden, and blue crabs. Dolphin mortality may explain the stability of small sciaenids. Increased seabird mortality did not lead to major changes in any functional group we examined. The consideration of indirect trophic pathways within the food web model produced a wide range of plausible population responses, especially responses to increases in predator mortality. Broadly, this work shows that oil spills are one driver of population dynamics within a broader socioecological system, and understanding oil spill impacts on populations requires consideration of this complexity.
... Freshwater drivers have variable ecological effects across species; for instance, high river discharge has been linked to higher densities of chum salmon (O. keta) (Kohan et al. 2013), but negatively affects recruitment of Pacific herring (Clupea pallasii) populations (Ward et al. 2017, Grimaldo et al. 2020. Glacial melt also contributes large quantities of silt to the nearshore, which provides substrate beneficial for some species of flatfishes (Abookire and Norcross 1998). ...
Coastal ecosystems in Alaska are undergoing rapid change due to warming and glacier recession. We used a natural gradient of glacierized to non-glacierized watersheds (0–60% glacier coverage) in two regions along the Gulf of Alaska—Kachemak Bay and Lynn Canal—to evaluate relationships between local environmental conditions and estuarine fish communities. Multivariate analyses of fish community data collected from five sites per region in 2019 showed that region accounted for the most variation in community composition, suggesting that local effects of watershed type were masked by regional-scale variables. Seasonal shifts in community composition were driven largely by the influx of juvenile Pacific salmon ( Oncorhynchus spp.) in late spring. Spatiotemporal differences among fish communities were partly explained by salinity and temperature, which accounted for 19.5% of the variation in community composition. We used a multi-year dataset from Lynn Canal (2014–2019) to examine patterns of mean length for two dominant species. Generalized additive mixed models indicated that Pacific staghorn sculpin ( Leptocottus armatus ) mean length varied along site-specific seasonal gradients, increasing gradually through the summer in the least glacially influenced sites and increasing rapidly to an asymptote of ~ 150 mm in the most glacially influenced sites. Starry flounder ( Platichthys stellatus ) mean length was more strongly related to environmental conditions, increasing with temperature and turbidity. Together, our findings suggest that community compositions of estuarine fishes show greater variation at the regional scale than the watershed scale, but species-specific variation in size distributions may indicate differences in habitat quality across watershed types within regions.
... While large abundances of pink salmon have previously been linked to declines in the growth and survival of other salmon species in the North Pacific Ocean, in particular sockeye salmon (Cline et al., 2019;Connors et al., 2020;Pyper & Peterman, 1999;Ruggerone & Connors, 2015;Ruggerone & Nielsen, 2004;Ward et al., 2017), competition from other Pacific salmon on the productivity of wild pink salmon has been studied much less, possibly because pink salmon are the most abundant salmonid. Our results suggest a nonlinear effect of sockeye and chum salmon abundance, indicating a potential threshold abundance above which competitors reduce the survival of wild pink salmon. ...
... It should also be noted that the Exxon Valdez oil spill in PWS occurred in 1989 during the NE Pacific regime shift. However, previous work found no evidence for a link between wild pink salmon productivity and the Exxon Valdez oil spill in PWS (Ward et al., 2017). Our finding that pink salmon productivity is linked to regional-scale temperature conditions is also in line with previous studies (Mueter et al., 2002;Springer & van Vliet, 2014). ...
Pacific salmon (Oncorhynchus spp.) are exposed to increased environmental change and multiple human stressors. To anticipate future impacts of global change and to improve sustainable resource management, it is critical to understand how wild salmon populations respond to stressors associated with human-caused changes such as climate warming and ocean acidification, as well as competition in the ocean, which is intensified by the large-scale production and release of hatchery reared salmon. Pink salmon (O. gorbuscha) are a keystone species in the North Pacific Ocean and support highly valuable commercial fisheries. We investigated the joint effects of changes in ocean conditions and salmon abundances on the productivity of wild pink salmon. Our analysis focused on Prince William Sound in Alaska, because the region accounts for ~50% of the global production of hatchery pink salmon with local hatcheries releasing 600–700 million pink salmon fry annually. Using 60 years of data on wild pink salmon abundances, hatchery releases, and ecological conditions in the ocean, we find evidence that hatchery pink salmon releases negatively affect wild pink salmon productivity, likely through competition between wild and hatchery juveniles in nearshore marine habitats. We find no evidence for effects of ocean acidification on pink salmon productivity. However, a change in the leading mode of North Pacific climate in 1988/89 weakened the temperature-productivity relationship and altered the strength of intraspecific density dependence. Therefore, our results suggest non-stationary (i.e. time-varying) and interactive effects of ocean climate and competition on pink salmon productivity. Our findings further highlight the need for salmon management to consider potential adverse effects of large-scale hatchery production within the context of ocean change.
... Neither bottom-up nor top-down control alone has conclusively explained the depression of these stocks, although both of these mechanisms are likely involved along with non-trophic factors Pearson et al., 2012;NMFS 2014). For example, in Prince William Sound, freshwater runoff and density-dependence (Ward et al., 2017), pathogens (Marty et al., 2003), the 1989 Exxon Valdez oil spill (Thorne and Thomas 2008;Incardona et al., 2015), and increased predation by recovering humpback whales Straley et al., 2018) may all have been contributing factors. In any case, the importance of herring to aboriginal and commercial fisheries and the depression of many stocks in the Gulf of Alaska underscore the acute need for improved knowledge of the trophic interactions linking this potentially key forage fish to its numerous predators. ...
Pacific herring (Clupea pallasii) is a schooling planktivorous fish consumed by numerous fish, seabirds, and marine mammals. This paper aimed to determine whether Pacific herring serves as a key forage fish (i.e. strongly supports predator populations) in the southeastern Gulf of Alaska. All analyses were conducted using mass- and energy-balanced ecosystem models constructed in Ecopath with Ecosim. Supportive Role to Fishery (SURF) index values were computed using predator diets and food web structure encoded in static ecosystem models. Ecosystem impacts of herring stock depletion and collapse were evaluated using quantitative criteria (thresholds) applied to dynamic ecosystem simulations. SURF index values from mass-balanced models lay below the threshold required to designate herring as a key forage fish. However, values from an energy-balanced model supported the key status of herring. Dynamic ecosystem simulations in mass- and energy-balanced models revealed strong negative effects of herring depletion on several predators. In most energy-balanced models, simulation results designated herring as a key forage fish despite indications of functional redundancy in the forage fish guild. Impacts of herring depletion on predators were stronger and more numerous in energy-balanced models, suggesting that the high energy content of herring enhances its importance to predators. Simulation results also demonstrated positive impacts of herring depletion on two zooplankton groups due to release from predation pressure. The status of Pacific herring as a key forage fish apparently depends on its energy content relative to other forage fish. Nevertheless, the results of this study support precautionary, ecosystem-based management of Pacific herring fisheries.
... There is uncertainty as to the causes of the initial population collapse and subsequent lack of recovery, with hypotheses including poor nutrition (Pearson et al. 1999(Pearson et al. , 2012, infectious disease (Rice and Carls 2007;Hulson et al. 2008), and the combined effects of the 1989 Exxon Valdez oil spill and overexploitation by the fishery (Thorne and Thomas 2008). Continued low population size and poor recruitment have been attributed to repeating disease cycles from multiple pathogens (Rice and Carls 2007), shifts in environmental conditions in the Gulf of Alaska (Pearson et al. 2012;Ward et al. 2017), humpback whale (Megaptera novaeangliae) predation (Pearson et al. 2012), competition with hatchery-released pink salmon (Oncorhynchus gorbuscha) (Deriso et al. 2008;Pearson et al. 2012), and cardiac abnormalities resulting from trace exposure to lingering oil (Incardona et al. 2015). Since the collapse, no recruitment events have come close to the magnitude of the 1980, 1981, 1984, and 1988 birth years (Muradian et al. 2017), and there have only been two cohorts of moderate size (1999, 2016 birth years) in the past 30 years ( Fig. 1B; J. Trochta, University of Washington, personal communication, 23 December 2019), creating uncertainty as to which conditions are required for recovery. ...
The location and timing of spawning play a critical role in pelagic fish survival during early life stages and can affect subsequent recruitment. Spawning patterns of Pacific herring (Clupea pallasii) were examined in Prince William Sound (1973-2019) where the population has failed to recover since its collapse in 1993. Abrupt shifts in spawn distribution preceded the rapid increase in population size in the 1980s and later its collapse by one and two years, respectively. Following the population collapse, spawning contracted away from historical regions towards southeastern areas of the Sound, and the proportion of occupied spawning areas declined from 65% to <9%. Spatial differences in spawn timing variation were also apparent, as the median spawn date shifted earlier by 26 days in eastern and 15 days in western areas of Prince William Sound between 1980 and 2006, and then shifted later by 25 (eastern) and 19 (western) days over a 7-year period. Effects of contracted spawning areas and timing shifts on first-year survival and recruitment are uncertain and require future investigation.
