Climate and conspecific density trigger pre-spawning mortality in sockeye salmon ( Oncorhynchus nerka )

Tillotson, Michael D.; Quinn, Thomas P.

doi:10.1016/j.fishres.2016.12.013

Cited by 32 publications

(34 citation statements)

References 54 publications

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“…) to be broadly representative of the conditions that can produce hypoxia in small‐ to medium‐sized watersheds with runoff dominated by rainfall and snowmelt. The mechanisms of hypoxia we describe were parallel to recent similar research conducted in a small southwestern Alaska stream (Tillotson and Quinn ). Our model may not perform as well in small‐ to medium‐sized watersheds in the NPCTR with high percentages of wetland coverage (>30%) and more complicated groundwater dynamics or lake systems contributing significant flow to downstream channels (e.g., see Peterson Creek in Fellman et al.…”

Section: Discussionsupporting

confidence: 74%

“…). Most recently, Tillotson and Quinn () demonstrated that high pre‐spawn mortality rates of sockeye salmon ( Oncorhynchus nerka ) in a small southwestern Alaska creek were strongly correlated with low DO levels caused by dense salmon populations, warm water, and low discharge. To date, most studies touching on this issue provide point estimates or ranges of DO measurements within an individual year.…”

Section: Introductionmentioning

confidence: 99%

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High salmon density and low discharge create periodic hypoxia in coastal rivers

et al. 2017

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Abstract. 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.

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Section: Discussionsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

High salmon density and low discharge create periodic hypoxia in coastal rivers

et al. 2017

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“…Given the large volume of most Willamette River basin tributaries, low flows may not have been sufficient to lead to stranding, substantially affect fish movement to spawning habitats, or result in the types of densities that have been linked to hypoxia in small streams (Sergeant et al. ; Tillotson and Quinn ). Overall, the associations reported here imply direct and indirect effects of temperature on PSM and multiple potential contributing mechanisms related to PHOS that should be examined in future studies.…”

Section: Discussionmentioning

confidence: 99%

“…) and negatively correlated with river discharge (Hyatt et al. ; Tillotson and Quinn ). We also expected that PSM would increase as the percentage of hatchery‐origin fish spawning in the wild increased.…”

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confidence: 99%

Prespawn Mortality of Female Chinook Salmon Increases with Water Temperature and Percent Hatchery Origin

et al. 2018

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High rates of prespawn mortality, when adult salmon die after completing migration but prior to spawning, can lead to population declines and can impede recovery of threatened stocks. In this study, annual prespawn mortality of female Chinook Salmon Oncorhynchus tshawytscha ranged from 1% to 100% over 14 years in seven study reaches located throughout the upper Willamette River basin, Oregon. Prespawn mortality rates were positively correlated with the annual maximum 7‐d average maximum stream temperature and the percentage of spawning fish of hatchery origin. Observed prespawn mortality rates varied considerably, but annual female prespawn rates were consistently >80% where maximum temperatures exceeded 20°C and the composition of spawning fish was >80% hatchery origin. In several spawning tributaries, prespawn mortality rates generally decreased at higher elevations. The proximate cause of prespawn death was not evaluated here, and observed patterns likely reflected additional factors that influence mortality either directly or indirectly, such as handling, dam passage, fishing pressure, instream habitat, energetic budget, fish density, and pathogen loads.

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“…In total, we examined 251,448 fish from Hansen Creek, 61,470 fish from the Pedro Bay ponds, 5,757 fish from A Creek, and 6,510 fish from C Creek. In 2014, the annual abundance of fish at Hansen Creek was three times higher than in any other year, and an unusual, large‐scale pre‐spawning mortality event occurred (Tillotson and Quinn ). The many high‐quality (i.e., ripe) carcasses available for scavenging after being thrown off‐site likely influenced bear consumption of salmon observable to us along the creek, so we excluded this year from our analyses.…”

Section: Methodsmentioning

confidence: 99%

Managing salmon for wildlife: Do fisheries limit salmon consumption by bears in small Alaskan streams?

Lincoln

Hilborn

Wirsing

et al. 2020

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Ecosystem‐based management requires consideration of overlapping resource use between humans and other consumers. Pacific salmon are an important resource for both fisheries and populations of wildlife around the Pacific rim, including coastal brown bears (Ursus arctos); salmon consumption has been positively linked to bear density, body size, and reproductive rate. As a case study within the broader context of human–wildlife competition for food, we used 16–22 yr of empirical data in four different salmon‐bearing systems in southwestern Alaska to explore the relationship between sockeye salmon (Oncorhynchus nerka) availability and consumption by bears. We found a negative relationship between the annual biomass of salmon available to bears and the fraction of biomass consumed per fish, and a saturating relationship between salmon availability and the total annual biomass of salmon consumed by bears. Under modeled scenarios, bear consumption of salmon was predicted to increase only with dramatic (on the order of 50–100%) increases in prey availability. Even such large increases in salmon abundance were estimated to produce relatively modest increases in per capita salmon consumption by bears (2.4–4.8 kg·bear−1·d−1, 15–59% of the estimated daily maximum per capita intake), in part because bears did not consume salmon entirely, especially when salmon were most available. Thus, while bears catching salmon in small streams may be limited by salmon harvest in some years, current management of the systems we studied is sufficient for bear populations to reach maximum salmon consumption every 2–4 yr. Consequently, allocating more salmon for brown bear conservation would unlikely result in an ecologically significant response for bears in these systems, though other ecosystem components might benefit. Our results highlight the need for documenting empirical relationships between prey abundance and consumption, particularly in systems with partial consumption, when evaluating the ecological response of managing prey resources for wildlife populations.

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Climate and conspecific density trigger pre-spawning mortality in sockeye salmon ( Oncorhynchus nerka )

Cited by 32 publications

References 54 publications

High salmon density and low discharge create periodic hypoxia in coastal rivers

High salmon density and low discharge create periodic hypoxia in coastal rivers

Prespawn Mortality of Female Chinook Salmon Increases with Water Temperature and Percent Hatchery Origin

Managing salmon for wildlife: Do fisheries limit salmon consumption by bears in small Alaskan streams?

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